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A review of domestic heat pumps
Abstract
Heat pumps are a promising technology for heating (and cooling) domestic buildings that provide exceptionally high efficiencies compared with fossil fuel combustion. There are in the region of a billion heat pumps in use world-wide, but despite their maturity they are a relatively new technology to many regions. This article gives an overview of the state-of-the-art technologies and the practical issues faced when installing and operating them. It focuses on the performance obtained in real-world operation, surveying the published efficiency figures for hundreds of air source and ground source heat pumps (ASHP and GSHP), and presenting a method to relate these to results from recent UK and German field trials. It also covers commercial aspects of the technologies, the typical savings in primary energy usage, carbon dioxide emissions abatement that can be realised, and wider implications of their uptake.
... As BC baseiam-se fundamentalmente num ciclo de Carnot Inverso, isto é, em vez de transformar energia térmica em energia mecânica, faz o oposto, converte a energia mecânica em energia térmica. Deste modo, com base na segunda lei da termodinâmica, mais precisamente o enunciado de Clausius, as BC transferem calor de uma fonte fria para uma fonte quente através de um fluido denominado fluido refrigerante, possibilitando, consequentemente, o arrefecimento e o aquecimento de espaços e produção de águas quentes sanitárias (AQS) (Staffell et al., 2012;Osterman & Stritih, 2021 Apesar de existirem diversos tipos de Bombas de Calor, tais como Ar-Água, Água-Água, Salmoura-Água, Ar-Ar, Água-Ar, Salmoura-Ar, as BC podem ser divididas em duas categorias principais de acordo com a localização do permutador de calor externo, sendo estas as BC aerotérmicas e as BC geotérmicas ( Staffell et al., 2012;Carroll et al., 2020). ...
... As BC baseiam-se fundamentalmente num ciclo de Carnot Inverso, isto é, em vez de transformar energia térmica em energia mecânica, faz o oposto, converte a energia mecânica em energia térmica. Deste modo, com base na segunda lei da termodinâmica, mais precisamente o enunciado de Clausius, as BC transferem calor de uma fonte fria para uma fonte quente através de um fluido denominado fluido refrigerante, possibilitando, consequentemente, o arrefecimento e o aquecimento de espaços e produção de águas quentes sanitárias (AQS) (Staffell et al., 2012;Osterman & Stritih, 2021 Apesar de existirem diversos tipos de Bombas de Calor, tais como Ar-Água, Água-Água, Salmoura-Água, Ar-Ar, Água-Ar, Salmoura-Ar, as BC podem ser divididas em duas categorias principais de acordo com a localização do permutador de calor externo, sendo estas as BC aerotérmicas e as BC geotérmicas ( Staffell et al., 2012;Carroll et al., 2020). ...
... As BC aerotérmicas, são aquelas que utilizam o ar externo como fonte fria ou fonte quente, conforme a operação em curso. As BC aerotérmicas são extremamente populares em muitos países e muito utilizadas devido à sua ampla variedade de aplicações, à sua flexibilidade e ao seu menor custo de investimento (Staffell et al., 2012;Osterman & Stritih, 2021). ...
O presente trabalho aborda a gestão de ativos num ambiente crítico — o Biotério da Faculdade de Ciências da Saúde (FCS) da Universidade da Beira Interior (UBI), Portugal — uma instalação onde as condições ambientais devem ser mantidas ininterruptamente a uma temperatura de 21 ºC e com uma humidade relativa de 50%. A manutenção de tais condições exige uma constante utilização do sistema de Aquecimento, Ventilação e Ar Condicionado (AVAC), sobretudo dos chillers e caldeiras para o arrefecimento e aquecimento, respetivamente. Consequentemente, devido à significativa variação climática ao longo do ano, uma avaria no sistema pode resultar em drásticas consequências para os ativos da instalação e também, para as atividades em curso. Visto que, eventualmente, os chillers e caldeiras deverão ser encaminhados para o abate, o objetivo deste artigo é efetuar uma análise de possíveis alternativas para a substituição de tais equipamentos levando em conta os aspetos económicos e ambientais. Por esta razão, são aqui abordadas as Bombas de Calor (BC), que operam segundo o ciclo de compressão de vapor, pois são equipamentos que satisfazem ambos os aspetos ao promoverem quer o arrefecimento quer o aquecimento do ambiente de modo mais eficiente e sustentável. Deste modo, são discutidas as tecnologias de BC aerotérmicas e geotérmicas e os aspetos de operação intrínsecos às mesmas. Por fim, é realizada uma simulação, em linguagem Python, de ambos os equipamentos, para diversos cenários de aquecimento e arrefecimento do ambiente em questão, com vista a uma análise mais detalhada do tema.
... Similar equations used to quantify the performance of water-source heat pumps have been described in the literature. For example, in 2012, Staffel et al. [30] published an article to provide an overview of the state-of-the-art of heat pump technology in domestic applications. Their focus was on the real-world performance of air and ground-source heat pumps, indicating both commercial and environmental aspects of these systems. ...
... This model can be used when data for more than four operating conditions are available due to the high number of required coefficients. • Model wh03 uses generic coefficients given in Ref. [30]. Model wh02 uses the same equation form as wh03 but fits the coefficients using the GLS method. ...
... However, the coefficients are different and calculated using the GLS or the GRG non-linear methods from the catalogs containing the cooling performance of the investigated heat pumps. Model wc03 is the same as proposed in Ref. [30], while wc04 and wc05 investigate some possible modifications to the original equation, which might reduce the RMSE and whose effectiveness will be discussed in the Results section 5. ...
... The thermal load applied to the model results from the heating demand from the building, ℎ as the thermodynamic law states energy conservation: ℎ = + , knowing the definition of the COP factor. Staffell and al. [3] proposes an empirical relationship between the COP factor and the temperature lift between the hot and cold sources of HPg. Completing the problem by adding a few simple thermal resis- ...
... Such thermal anomalies are supposedly dissipated through seasonal operations of the system. However, inappropriate conditions might result in a multiyear soil temperature shift [2] and durable degradation of HPg efficiency [3]. Specifically, energy geostructure are often installed as dense networks, such as pile groups. ...
... The thermal load applied to the model results from the heating demand from the building, ℎ as the thermodynamic law states energy conservation: ℎ = + , knowing the definition of the COP factor. Staffell and al. [3] proposes an empirical relationship between the COP factor and the temperature lift between the hot and cold sources of HPg. Completing the problem by adding a few simple thermal resis-tive equations and assuming a hot source at 40°C, we can solve the overall equation in order to compute the COP factor depending on the soil temperature. ...
Energy geostructure are a group of technical methods aiming to use the geotechnical structures as heat source exchangers for a geothermal Heat Pump (HPg) [1]. As with any heat pump system, the goal is usually to extract soil energy in order to heat buildings. HPg system efficiency is described by the COP factor (Coefficient of Performance) defined as the ratio between the quantity of useful energy for building heating and consumed electric power . Its value has a great influence on the economic sustainability of geothermal systems. This efficiency is strongly correlated to the temperature lift between the cold and hot sources of HPg. However, while operating, HPg will drain energy from the soil, decreasing soil temperature, increasing the temperature gap, and decreasing the COP factor. Such thermal anomalies are supposedly dissipated through seasonal operations of the system. However, inappropriate conditions might result in a multiyear soil temperature shift [2] and durable degradation of HPg efficiency [3]. Specifically, energy geostructure are often installed as dense networks, such as pile groups. Such proximity might generate thermal interaction and affect the surrounding soil temperature [4, 5]. In the case of an underground water table, seepage might help to dissipate the thermal anomaly [2], but it will also generate stronger and more directional thermal interaction [5, 6]. Based on numerical modeling [5], we were able to predict the COP evolution for a small energy pile. We propose now to use this modeling process to predict the COP evolution of a more realistic geothermal installation. The study case model is based on a housing building constructed in Gonesse France, in 2012 [7]. The model represents a group of 20 energy piles, each 12 m long, used to heat 1000 m² of housing with a peak heating demand of 15,5 kW. The system is supposed to be used at peak power supply for 12 hours out of 24 hours during four consecutive weeks. The final resulting COP is considered an indicator of installation performance. We studied the effects of pile proximity (inter-pile distances from 1.2 m to 6 m) and seepage velocity (from 0 m/day to 2 m/day). We expect to observe a beneficial effect of the water movement as it renews the soil energy around the pile. Also, we expect to observe a negative effect of the pile proximity, as the thermal anomalies will have a cumulative effect on the soil temperature drop. All the numerical modeling is realized with CESAR-LCPC software, which is a FEM software specialized for civil engineering problems [8]. It has the possibility of treating diffusive problems such as thermal problems or hydraulic diffusion in porous media. Also, CESAR-LCPC could be used with a Python script interface, which is useful to describe the needed iterative process and conduct the parametric studies. The numerical modeling processes principally aim to solve the thermal problem in the soil and foundation systems. It takes into account heat transfers from conduction defined by Fourier’s law: ( has the material thermal conductivity), and the heat transfer due to underground water displacement (advection phenomenon) defined has (with the volume thermal capacity and the underground water flow velocity). The seepage velocity field is then computed preliminarily in order to take account of the disturbance effect due to the structure. The thermal load applied to the model results from the heating demand from the building, as the thermodynamic law states energy conservation: , knowing the definition of the COP factor. Staffell and al. [3] proposes an empirical relationship between the COP factor and the temperature lift between the hot and cold sources of HPg. Completing the problem by adding a few simple thermal resistive equations and assuming a hot source at 40°C, we can solve the overall equation in order to compute the COP factor depending on the soil temperature. The results show, as expected, a progressive COP decrease during the 4 weeks as long as soil temperatures decrease. Moreover, in the case of a seepage velocity below 0.2 m/day, the temperature and COP factor tend to decrease without a steady state. Figure 1 summarizes the numerical results, showing the final COP value depending on seepage velocity and interpile distance. It shows that the absence of seepage will have a negative impact on system efficiency as long as the pile proximity. Logically, in a smaller group, a cluster effect will intensely affect soil temperature, while the absence of seepage won’t renew soil energy. We can conclude that in cases of slow seepage (below 0.2 m/day), it is possible to improve system efficiency by opting for more distant piles. Also, for seepage over 0.5 m/day, the distance between piles in the same group will have a limited impact on the heat pump's efficiency. In an extended study, this modeling process has been complemented with summer mode ability and used for longer simulations, allowing the study of a multi-year thermal shift and various seasonal activation patterns (balanced and unbalanced, peak use, etc.).
... Performance efficiency of the HGSHP system and thermal behaviour of the shallow ground depend on a number of factors, which can be broadly classified into four categories: i) site conditions, such as the local climatic conditions, ground temperature variation, and soil saturation/ moisture change [32,51,37,30]; ii) ground characteristics, such as soil thermal conductivity, density, and specific heat capacity, which vary greatly between different soils [41,10,56,47], iii) system configurations and design, such as pipe length, diameter, spacing, buried depth, the thermal load of the building, and integration with other renewable energy sources, such as solar energy, which have considerable effects on the performance of the HGSHP system [6,[17][18][19]27,28,36,52]; and iv) heat pump coefficient of performance or COP, which regulates the thermal load on ground loop systems [55,45,52]. ...
... Along with the soil-atmosphere boundary, processes at the soil-soil boundary such as heat and moisture transfer from the areas adjacent to the site is considered for realistic representation of in-situ conditions. Moreover, the coupling of the ground loops and the heat pump is achieved by the heat pump COP model proposed by Staffell et al. [55]. ...
... By fitting the industry-average data of the heat pump COP and operation temperatures for UK conditions, Staffell et al. [55] proposed an empirical model for predicting the heat pump COP in heating and cooling modes, respectively, which is adopted in the literature [31,52] and this study. The heat pump COP can be obtained by the following equations: ...
Exploitation of shallow ground and its low-grade heat potential is fundamental to designing 5th generation district heating and cooling (DHC) networks. Horizontal ground-source heat pump (HGSHP) systems are a common way to utilize shallow geothermal energy. Realistic estimation and prediction of performance of a HGSHP system and shallow ground thermal behaviour should consider the whole system including building heating and cooling load, heat pump and ground heat exchanger, and the ground. This should be accompanied by realistic atmospheric and ground conditions. In this paper, a three-dimensional coupled thermal–hydraulic model with realistic boundary conditions adopting a whole system approach is presented. Dynamic heat pump coefficient of performance (COP) that depends on seasonal variation of heating/cooling demand and ground conditions are also considered. Model validations are conducted against experimental and analytical results in literatures. The model is applied for evaluating a HGSHP system to support development of a 5th generation DHC network on a potential site in the UK. Several influencing factors, such as ground moisture transfer, building thermal load mode, buried depth of ground loops, and initial ground temperature profile are studied to assess performance efficiency of the HGSHP system and evolution of ground thermal behaviour in response to heat extraction or rejection into the ground. The results show that 5% of the monthly total heat demand of the site could be met by the designed HGSHP system, consisting of 200 U-shaped ground loops buried at the depth of 3 m and pure water as the heat carrier. Overlooking the ground moisture transfer or hyperbolizing the ground saturation would overestimate the load-carrying capacity of the HGSHP system. The HGSHP system is more efficient with a higher heat pump COP under the heating and cooling mode than under the heating-only mode. Predicted performance of the HGSHP system improves with buried depth of the ground loops. The results also show that a 1 ℃ increase in the undisturbed ground temperature could suffice up to 8% of the monthly total heat demand of the site.
... Other barriers were hard to find trustworthy information, system performance reliability and unsuitable home/ location. Staffell, Brett, Brandon, & Hawkes (2012) also evidenced that some of the users reveal that earning money from installation (via saving energy use, especially as a result of Feed-in Tariffs) as well as protection from future energy costs motivated adopting HPs. ...
... Boait, Fan, and Stafford (2011) using a system model show that the heat pump performance in the UK is on average worse than in continental Europe on account of a mismatch between the size of the dwelling and corresponding heat load. For instance, the average HP system installed in Germany can produce an extra 1.2 kW of heat per kW of electricity than a similar system operating in the UK (Staffell et al. 2012). The Energy Saving Trust's trial study suggests that wrongly sized HPs for the properties along with incorrectly set up and operation in sub-optimal modes are some of the reasons for inefficient systems (Roy, Caird, and Potter 2010) Currently, HPs designed for UK's market are for 5kW which is much more than required to meet the need of winter load of a small (60-80 m 2 ) well-insulated home needing 100 W/°C (Staffell et al. 2012). ...
... For instance, the average HP system installed in Germany can produce an extra 1.2 kW of heat per kW of electricity than a similar system operating in the UK (Staffell et al. 2012). The Energy Saving Trust's trial study suggests that wrongly sized HPs for the properties along with incorrectly set up and operation in sub-optimal modes are some of the reasons for inefficient systems (Roy, Caird, and Potter 2010) Currently, HPs designed for UK's market are for 5kW which is much more than required to meet the need of winter load of a small (60-80 m 2 ) well-insulated home needing 100 W/°C (Staffell et al. 2012). ...
Mitigation within the UK’s residential sector will play a crucial role in achieving a net-zero target by 2050, given this sector accounts for 16% of total greenhouse gas emissions. In the residential sector, space and water heating are the predominant sources of energy consumption and greenhouse gas emissions. One key renewable
source for space and water heating is the heat pump, however, their deployment is significantly lower in the UK compared to neighbouring countries, despite a reasonable attempt at sector growth in the recent past.
This review attempts to assess the evidence in relation to the underlying factors responsible for or against transitioning to heat pumps (HPs). Employing evidence synthesis based on peer-reviewed published outputs (n=15), and relevant other outputs from snowballing and grey literature (n=9), this study examines key factors across three broad themes – households’ socio-technical characteristics, built environment attributes and stakeholders’ competing and differing economic and organisational interests – that provide motivations or barriers to scaling up HPs in the UK.
Evidence suggests that saving money, increasing household energy independence and reducing greenhouse gas emissions are the households’ principal positive drivers, whereas higher capital and running costs are the major barriers to adopting heat pumps. The current imbalance in energy taxes and levies (environmental levies for electricity and gas bills are 23% and 2% respectively) weakens the economic
competitiveness of heat pumps in the UK. Convincing evidence suggests that appropriate knowledge and awareness – choices, technical and financial knowledge – help in the adoption of heat pumps which can be achieved through adopting a bottom-up approach like community-based energy plans.
In the context of the built environment, evidence suggests that the heat pump system is often mistargeted, for example, wrongly sized heat pumps are installed and focus on existing smaller homes (social housing) via retrofits. Contrary findings suggest that current HPs’ loads are more suitable for larger and newly built homes. The dominance of the existing housing stock (low stock replacement rates) implies a more nuanced and careful approach should be adopted for this part of the housing system. One of the most important features is to adopt the ‘fabric first approach’, where heating options should be chosen after achieving building efficiency (and in some cases, energy demand reduction) through appropriate retrofitting.
Furthermore, the stakeholders’ competing and differing economic and organisational interests as well as the lack of appropriate skill sets to execute the HPs system are major barriers to upscaling HPs. Existing policies and regulations are not sufficiently aligned to incentivise manufacturers and installers and there is a lack of coherence in policies and regulations. For instance, due to the short-term span of existing programmes, manufacturers and installers are unable to attract and train suitable
skill sets for the next generation of workers. These findings have important policy implications:
• Incentives: enhance financial incentives and make an economic case for HPs on the demand�side among consumers by reducing the imbalance in levies on electricity and gas bills.
• Information: increase demonstrator projects (provides real-world data on all forms of benefits, including energy saving). Adopting a bottom-up approach, particularly involving local governments and community-based organisations. Also, targeting the right segments of households who are potential innovators and early adopters.
• Regulation: targeting the right segments, for example, large homes and new buildings initially and then existing buildings after adequate retrofitting. Also, addressing stakeholders’ concerns such as manufacturers, traders, and
installers in such a way that end-users positively experience the journey of HPs (pre- and post-installations).
... The estimation of the EER of heat pumps and chillers is undertaken using two relationships acquired from the literature [35], which were derived from experimental datasets for air-source heat pumps and water-to-water heat pumps. As the relationships are defined concerning the temperature difference between the supply temperature and source temperature (ΔT), the same relationships are employed in this study for both heating and cooling [35]. ...
... The estimation of the EER of heat pumps and chillers is undertaken using two relationships acquired from the literature [35], which were derived from experimental datasets for air-source heat pumps and water-to-water heat pumps. As the relationships are defined concerning the temperature difference between the supply temperature and source temperature (ΔT), the same relationships are employed in this study for both heating and cooling [35]. For space heating, the supply temperature is assumed to equal 40 • C, and for space cooling equal to 6 • C. The equation is considered valid for 15 ≤ ΔT ≤ 60, and the minimum and maximum values of this relationship are used for smaller or larger ΔT. ...
... In the Networked configuration and Combined case, the heat pump consumption is added to the pumping power. Reported [35] water-towater heat pump EER relationships were used to estimate the heat pumps efficiency in heating or when the lake is used as a source through the district thermal network (EER HPw h,i ). ...
Lake-source thermal district networks can efficiently supply heating and cooling to buildings and thus save
energy and CO2 emissions. However, it remains unclear to which degree they are a sustainable alternative at a
larger geographical scale. An evaluation of the potential of developing technically and economically feasible
lake-source district systems in Europe was performed in this study, with an integrated spatial explicit technoeconomic
assessment that accounts for different boundary conditions, such as electricity price, CO2 price and
climate change. The feasibility of covering building energy demand near lakes was found to be particularly
sensitive to the relationship between capital costs from network design and operational costs from heat pumps,
associated electricity consumption and CO2 emissions. Results suggest a European techno-economic potential of
1.9 TWh/y considering only direct cooling and 11.3 TWh/y if thermal networks supply both direct heating and
cooling by heat pumps. Respective electricity savings are 0.36 TWh/y and 0.78 TWh/y. An estimated 17% of the
cooling demand near European lakes can thus be covered by viable cooling-only lake-source systems. For
combined systems, the viable potential is estimated to be 7% of the total combined heating and cooling demand.
Lake-source district systems are found to be particularly promising for Italy, Germany, Turkey and Switzerland.
The integration of lake-source thermal networks should rarely lead to severe lake water temperature alteration
and therefore not limit the techno-economic potential. The introduced methodology allows for a combined
evaluation of technological, ecological and economic boundary conditions for using lakes as a source for district
heating and cooling. Thereby, a more realistic estimation of their potential implementation becomes possible,
enabling informed energy planning for central or decentral system configurations.
... In 2021, residential space heating accounted for 17% of the final energy consumption in the European Union's group of 27 1 and 11% globally across the International Energy Agency's group of 61 countries, contributing to 8% of total carbon-dioxide (CO 2 ) emissions 2 . Heat pumps (HPs) represent a critical technological shift towards high-efficiency, electrically driven heating systems, offering a sustainable alternative to fossil fuel-based systems [3][4][5] . While previous research has underscored the potential of HPs in reducing buildings' energy consumption and greenhouse gas emissions 6,7 , their effectiveness is contingent upon the system type, operational practices and electricity generation sources [7][8][9] . ...
... indoor air). Depending on where the energy is sourced or released (e.g. in air, ground, or water) several HP types exist 3 . Air-to-air heat pumps (AAHPs; Supplementary Fig. 1) are the predominant type globally 17,18 , meriting focused investigation into their performance and environmental impact. ...
Heat pumps (HPs) have emerged as a key technology for reducing energy use and greenhouse gas emissions. This study evaluates the potential switch to air-to-air HPs (AAHPs) in Toulouse, France, where conventional space heating is split between electric and gas sources. In this context, we find that AAHPs reduce heating energy consumption by 57% to 76%, with electric heating energy consumption decreasing by 6% to 47%, resulting in virtually no local heating-related CO2 emissions. We observe a slight reduction in near-surface air temperature of up to 0.5 °C during cold spells, attributable to a reduction in sensible heat flux, which is unlikely to compromise AAHPs operational efficiency. While Toulouse’s heating energy mix facilitates large energy savings, electric energy consumption may increase in cities where gas or other fossil fuel sources prevail. Furthermore, as AAHPs efficiency varies with internal and external conditions, their impact on the electrical grid is more complex than conventional heating systems. The results underscore the importance of matching heating system transitions with sustainable electricity generation to maximize environmental benefits. The study highlights the intricate balance between technological advancements in heating and their broader environmental and policy implications, offering key insights for urban energy policy and sustainability efforts.
... The ambition to phase out the installation of new natural gas boilers in many countries implies remarkable infrastructural and regulatory changes in the upcoming years [2,3]. Electricity-driven vapour-compression heat pumps are a proven technology [4] associated with a considerably better thermodynamic performance than gas boilers [5]. Although they are widely recognised as a sustainable alternative to conventional heating systems, the share of heat pumps in the market remains low in most countries [6]. ...
... GSHPs require heat collector tubes to be buried underground. Therefore, they are associated with higher installation costs than ASPHs [4]. However, since the temperature of the ground experiences smaller fluctuations throughout a year compared to the ambient air, GSHPs can often be operated more efficiently on average than ASHPs. ...
A detailed methodology is proposed to design and optimise the operation of a ground-source heat pump (GSHP) coupled to a phase-change material (PCM) thermal battery. The objective is to minimise the cost of supplying space heating and hot water to a medium-demand house in the UK during a typical winter day with fluctuating electricity prices. A bespoke 8-kW GSHP is designed and used to optimise the charging schedule of the thermal battery to minimise daily operational costs while meeting the heat demand. If no limit is imposed on the size of the thermal battery, in the best scenario, a 41-kWh thermal battery is required to achieve costs as low as 1.85 £/day. However, large PCM batteries mean high upfront costs and little space restrictions. Therefore, a constraint is imposed on the thermal store capacity to identify the optimal trade-off that can be achieved between PCM battery size and daily power consumption costs. Operational costs strongly depend on the battery size, increasing from 1.85 £/day for a 41-kWh thermal battery to 3.50 £/day for a 6.3-kWh store.
... According to IEA [69], 'Other sources' contains heat pumps, electric boilers, and other sources; Heat Pumps are assumed to make up 1/3 of this total. methodology follows Staffell et al. [70] for Air-to-Air Heat pumps, using 30 degree Celsius as the outlet temperature. See appendix Appendix A.4 for the equations used for the calculations. ...
... The methodology follows Staffell et al. [70] for Air-to-Air Heat pumps, using 30 degree Celsius as the outlet temperature. See Eqs. ...
... Several studies perform sizing of HPs for different objectives [42][43][44] along with numerous heat pump designs that consider the available heat source (such as air, earth, or water) and the way the heat is delivered to the building. (e.g., ducted air, ductless air, hydronic) [45]. ...
To enable net zero sustainable thermal building energy, this study develops an open-source thermal house model to couple solar photovoltaic (PV) and heat pumps (HPs) for grid-connected residential housing. The calculation of both space heating and cooling thermal loads and the selection of HP is accomplished with a validated Python model for air-source heat pumps. The capacity of PV required to supply the HPs is calculated using a System Advisor Model integrated Python model. Self-sufficiency and self-consumption of PV and the energy imported/exported to the grid for a case study are provided, which shows that simulations based on the monthly load profile have a significant reduction of 43% for energy sent to/from the grid compared to the detailed hourly simulation and an increase from 30% to 60% for self-consumption and self-sufficiency. These results show the importance of more granular modeling and also indicate mismatches of PV generation and HP load based on hourly simulation datasets. The back-calculation PV sizing algorithm combined with HP and thermal loads presented in this study exhibited robust performance. The results indicate this approach can be used to accelerate the solar electrification of heating and cooling to offset the use of fossil fuels in northern climates.
... Several studies perform sizing of HPs for different objectives [42][43][44] along with numerous heat pump designs that consider the available heat source (such as air, earth, or water) and the way the heat is delivered to the building. (e.g., ducted air, ductless air, hydronic) [45]. ...
To enable net zero sustainable thermal building energy this study develops an open-source thermal house model to couple solar photovoltaic (PV) and heat pumps (HP) for grid-connected residential housing. The calculation of both space heating and cooling thermal loads and the selection of HP is accomplished with a validated Python model for air-source heat pumps. The capacity of PV required to supply the HPs is calculated using an System Advisor Model integrated Python model. Self-sufficiency and self-consumption of PV and the energy imported/exported to the grid for a case study are provided, which shows that simulations based on the monthly load profile have a significant reduction of 43% for energy sent to/from the grid compared to the detailed hourly simulation and an increase from 30% to 60% for self-consumption and self-sufficiency. These results show the importance of more granular modeling and also indicate mismatches of PV generation and HP load based on hourly simulation datasets. The back-calculation PV sizing algorithm combined with HP and thermal loads presented in this study exhibited robust performance. The results indicate this approach can be used to accelerate the solar electrification of heating and cooling to offset the use of fossil fuels in northern climates.
... A third expert noted: 84 ." This leaves many homeowners and social landlords with an unpleasant choice. ...
Heat pumps are a cornerstone of the government’s decarbonisation agenda in the United Kingdom. The electrification of domestic heating, underwritten by the installation of ground-, air-, and water-source heat pumps is expected to reduce the UK’s greenhouse gas emissions by around 15 – 17%. In late 2020, the Johnson government announced a target of 600,000 heat pump installations per year by 2028. In mid-2023, despite a grant fund of £450m, data revealed the UK was installing 55,000 heat pumps annually, suggesting the government’s goal is unlikely to be met. Consumers of domestic heat pumps in the UK are owner-occupiers, developers, private and social landlords, as well as local councils responsible for social housing (although tenants are the primary beneficiaries in the last three instances).
This report investigates the reasons for this profound gap between government intentions and consumer behaviour. Key actor interviews as well as scrutiny of secondary scientific literature produced data that was interpreted through a systems thinking method of analysis. Systems thinking conceives of outcomes as emergent properties where different aspects and dimensions of the system interact and influence one another. Consequently, this research was interested in identifying relevant negative and positive feedback loops that contribute to the suboptimal uptake of heat pumps. Systems thinking analysis is particularly useful when making policy recommendations since policy interventions are seen as mechanisms necessary to disrupt undesirable feedback loops and, thereby, overcome what are commonly thought of as market failures.
... The effective monthly Coefficient of Performance (COP) as a function of the ambient temperature is assumed according to the values reported by Staffell et al. in their review of domestic heat pumps [235]. ...
Micro gas Turbines are small fuel-flexible units for on-site power and heat generation. The scientific community has often recognised their potential as a technology to address the energy trilemma. However, despite being in the market for over two decades, they have yet to achieve significant market success. The industry and scientific community acknowledge the existence of this problem, but any remedial action so far proved unsuccessful. In fact, the scientific literature does not contain any study tackling this matter holistically and scientifically. This study aims to fill this gap by devising a methodology that could define the problem, identify the root causes, and propose solutions in a scientific manner. The author initially investigated two qualitative methodologies that could lay the foundations for such purpose - traditional process-based Root Cause Analysis and system-based Theory of Constraint - and found the latter to be more suitable. After performing the problem definition through gap analysis and the root cause identification through the Current Reality Tree, the author validated the identified root cause with a study in patent data and innovation trends. Further, the authors developed a numerical tool to measure innovation; the study performed in existing market niches confirmed the conclusion of the Current Reality Trend andmeasured the position of micro gas turbines in the market against competing technologies. Finally, the author defined competitiveness as a combination of an absolute and relative term. This final concept is applied to the methodology above to produce a simple tool. This ultimate tool aims to gauge the current position of technologies in the market and to differentiate feasible and unfeasible technology innovation paths. This study finally suggests some final work which involves implementing the proposed innovation paths and refining the utilised methodologies employing ongoing research resulting from the NextMGT project.
... [6][7][8] Indoor air conditioning accounts for the main part of building energy consumption, 9,10 and air source heat pump (ASHP) shows great advantages in energy saving and is widely used in air conditioning. [11][12][13] Air source heat pump can be divided into air-to-air system, air-to-water system and radiation system with refrigerant as the medium. Air-toair system has the advantages of high efficiency while it also causes discomfort with draught 14 and large temperature gradient. ...
The radiant systems come to the fore due to energy saving potential and good integration. The effect of different forms of cold surfaces on human thermal comfort is focused on its application. A novel natural convection-radiant evaporator for heat pumps was developed and its influence on thermal comfort was investigated. A numerical model of the chamber with the evaporator was established and verified with experimental results. Thermal comfort experiments were conducted in a climate chamber and the influence of its asymmetric and uneven cold radiation on the thermal comfort was investigated. Due to the limitation of PMV in uneven radiation situations, the revised predicted mean vote (RPMV) was proposed to assess the thermal comfort in asymmetric and uneven radiation environments based on experimental results. Based on RPMV, the influence of the surface area and temperature of the evaporator on thermal comfort was numerically analyzed. The results indicate that indoor air temperature and relative humidity, RPMV increase with the increase of plate temperature, but decrease with an increase in plate area. The most favourable indoor thermal comfort environment was obtained at an indoor air temperature of 28°C and relative humidity of 50%, which is 2°C higher than traditional air conditioning system.
... In the context of electrification, electricity-driven air-source heat pumps are a commercially mature technology able to harness ''renewable'' energy taken from the environment. 10 In many countries, the process of energy transition has started: according to the International Energy Agency (IEA), air-source heat pumps are becoming the most common technology in newly built houses in many countries. 11 In Europe, the annual sales of air-source heat pumps have been steadily increasing by more than 10% per year since 2012. ...
... Results strongly depend on the correlations used for describing heat pumps' and chillers' performance, namely c 0 and c 1 in Eq. (4). The values assumed here were obtained by regressing the correlations proposed by Staffell et al. [6] for heat pumps (c 0 = 0.2384 and c 1 = -0.00308) and by Joe and Karava [7] for chillers (c 0 = 0.09913 and c 1 = 0.006571). ...
Seasonal thermal storage systems can reduce the temporal mismatch between renewable energy availability and energy demand. Ice storage systems exhibit a non-linear behaviour in the heat exchange and storage processes, complicating the formulation of optimal design and operation problems. In this work, we propose a mixed-integer quadratically-constrained programming formulation, which minimizes the Levelized Cost of Energy for space heating and cooling, including sizing of a supporting PV array. The optimization was repeated for different storage volumes, finding the system optimal operation in each case –and thereby the optimal system sizing. The heating and cooling demands were computed from an archetypal office building, placed in three reference locations with cold and semi-arid, warm and humid continental, and temperate and humid continental climates. Results show that the optimal PV size decreases with growing ice storage volume, and an ice storage works best in a temperate continental climate, covering up to 47% of the cooling demand with a 250 m ³ storage.
... If heating is electrified via heat pumps, the amount of storage needed for heating demand could be a factor of 3 to 4 lower due to their high coefficient of performance (i.e. 1 unit of electricity is converted to 3 to 4 units of heat). 52 However, this still leaves a requirement for hundreds of TWh electric . A similar analysis could be conducted for energy storage reserves for transport, yielding similar orders of magnitude storage requirement. ...
Storage does not only offer private value to investors, but also public value to society by reducing the cost of decarbonizing power systems. This chapter introduces research into the ‘system value’ of storage and conducts a meta-analysis of how much storage and flexible capacity is needed in power systems to accommodate increasing reliance on variable renewable generation. These findings are generalized to give global implications for how much storage the world’s power systems may need in the coming decades. The chapter then goes on to consider the larger issue of completely eliminating fossil fuels from the power sector. It introduces a simple framework to assess how much storage is required to allow wind and solar power to meet 100% of hourly electricity demand. A worked example tied to www.EnergyStorage.ninja> allows for the individual assessment of future flexibility requirements.
... Several LCA studies (G. Li, 2015;Mattinen et al., 2015;Staffell et al., 2012) confirm the significance of electricity mix for the overall environmental impacts for the climate effects of heat pumps, in contrast to a relatively minor contribution from climate-active refrigerant losses. Two additional studies point out the relevance of using temporal resolved electricity mixes when running heat pumps (Frapin et al., 2022) and (Peters et al., 2022). ...
The globally agreed climate targets require an expansion of renewable energies within the entire supply system. To support this a well-developed set of methods is needed to assess technical, environmental, social, and economic impacts. These methods must cover the entire life cycle and should enable an efficient and target-oriented assessment of energy technologies and systems. The Josef-Ressel (JR) centre LiSA (established 1st January 2022) will address this need. It will develop assessment methods focusing on thermal energy conversion systems embedded in a renewables-rich energy landscape.
... Modern personal vehicles in the United States are projected to last nearly 20 years (Zhu et al., 2021). Electric appliances such as heat pumps may have similar lifetimes (Staffell et al., 2012). An analysis that assumes unchanging marginal emission factors from the electricity grid ignores the possibility of better performance over the lifetime of a new technology than in its first year of operation. ...
Quantitative analyses may aim to provide actionable answers to policy questions and to generate tools or insights for decision-making. Given the deep uncertainties involved in any realistic reckoning of policy questions, this study argues that only the second of these goals is achievable. Here, this argument is illustrated by considering analyses of how the electrification of an activity changes the damage from the air pollution emissions that occur because of that activity. The sources of uncertainty in such an analysis include the long life of the technologies being studied. Consequently, the structure and operation of the electricity grid might change because of the new technology and independent of it. Analysts must make subjective choices about what to include in their analysis and what to exclude. For example, policies modeled in isolation may, in reality, be bundled with other policies; interactions between technologies may be missed if the analysis focuses on only one technology; and certain benefits or costs may be neglected because they lie outside the scope of the analysis and the expertise of the analyst. Quantitative policy analysis must aim to be part of the broader discussions in society that ultimately determine what policies get implemented.
... The empirical model proposed by Staffell et al. [32] is employed to predict the COP of a heat pump. The model was obtained by fitting the temperature difference and the heat pump COP data taken from industrial surveys and field trials: ...
The configurations of ground heat exchangers (GHEs) play a significant role in the efficiency and sustainability of ground-source heat pump (GSHP) systems. However, there is a knowledge gap in understanding the performance differences between the horizontal and vertical GSHP systems in the same project under various heating and cooling demands. In this study, a technical performance comparison between GSHP systems coupled with horizontal ground loops and vertical boreholes under three scenarios of heating-to-cooling ratios (6 : 1, 2.4 : 1, and 1 : 1) was conducted. The simulations were based on a coupled thermal–hydraulic model for unsaturated soils that takes into account realistic ground surface boundary, GHE boundary, and the dynamics of heat pump efficiency. The GHEs were designed based on an experimental site located on the campus of a UK university. Results showed significant differences in the development of fluid temperatures and coefficient of performance (COP) of heat pumps between the horizontal and vertical GSHP systems due to the differences in the soil profiles and temperature boundaries. Both the fluid temperatures and heat pump COPs in the horizontal GSHP system reached a steady annual cycle after 2 years regardless of the heating-to-cooling ratios. For the vertical system, a general downward trend in the fluid temperatures and the COP of the heat pump in the heating mode can be found when a heating-to-cooling ratio was 6 : 1 or 2.4 : 1, while an overall upward trend in the fluid temperatures and the COP of the heat pump in the heating mode can be noted in the case of 1 : 1 heating-to-cooling ratio. Additionally, the heat pump operating in the cooling mode was off most of the time when a heating-to-cooling ratio was 6 : 1 or 2.4 : 1, while a declining trend in the COP of the heat pump in the cooling mode was exhibited in the case of a heating-to-cooling ratio of 1 : 1. The technical comparison reveals that the heating-to-cooling ratios would significantly affect the efficiency and sustainability of both GSHP systems.
... Heat pump cost Fig. 5 shows the cost trends for heat pumps according to the proposed method and the cost correlation published by Staffell, Brett, Brandon and Hawkes (2012). When Staffell's correlation is compared with updated market heat pump costs, it can be seen that the correlation results in lower costs than the actuals. ...
The climate change, volatile geopolitical conditions, energy insecurity, and supply disruptions experienced lately have highlighted the need for a solid strategy to speed up the transition to green energy and reduce dependence on fossil fuels. Developing tools and methods for fast assessment of techno-economic, environmental and socioeconomic aspects of sustainable energy solutions will contribute to this goal. This paper presents results of a case study using an inhouse techno-economic analysis tool developed to provide access to detailed data settings, reflecting the most important technical as well as economic parameters of studied energy technologies. Five different energy solutions for heating and cooling of a specified building in a given geographical position and thereby economic environment have been assessed and compared using the inhouse analysis tool. Based on the proposed techno-economic framework, the energy efficiencies, costs, subsidies and negative CO 2 emissions are estimated and used to identify the critical economic parameters on profitability and policy making recommendations. Using the coal-based heating system as reference case, the comparative study carried out shows the advantages and disadvantages of biomass and natural gas based boilers as well as the geothermal installation. Considering the environmental benefits of the renewable based energy resources, which will become a stronger market driver for every year. The results show that both air-source and ground source heat pumps are currently profitable under current subsidy schemes. The net present value is highly influenced by capital costs and subsidies. In the same way, natural gas prices significantly affect the net present value of gas boilers. As gas prices increase over 43 % of the current level in Poland, heat pumps become more attractive. Replacing a coal-fired boiler with gas will take up to years to pay-off. However, the air source heat pump and ground source heat pump will take longer to pay off, up to 10 years for the air source heat pump and 15 years for the ground source heat pump. The carbon intensity of the ground source heat pump (186 kg CO 2 eq) is lower than the levels of the gas boilers (203 kg CO 2 eq) and the air source heat pump (263 kg CO 2 eq). Ground source heat pump system installation expects to provide a substantial saving of 58 % on CO 2 emissions versus coal-fired systems. Air source heat pump P emits 267 kg CO 2 /kWh/year more than gas boilers, but emissions decrease drastically as the Polish power grid becomes greener in 2030 and 2040.
... The HP is a very efficient technology for heating and cooling purposes, since its efficiency, the COP (Coefficient of Performance), usually varies from 2 to 5 and is particularly high when used to heat a utility or process. The value of the COP is calculated according to (13), considering the efficiency dependence on the temperature difference between the water supply temperature and the ambient air temperature [22]. ...
The Italian Natural Gas (NG) distribution network includes thousands of NG metering and pressure reduction stations, called City Gate Stations (CGS), for injecting gas into low-pressure networks. These plants are mainly based on the isenthalpic throttling of the gas flow to reduce its pressure, which leads to a significant reduction of its temperature by the Joule-Thompson effect. Gas preheating systems that avoid excessive cooling are installed upstream of pressure reduction valves and usually exploit conventional gas boilers. The energy consumption and carbon footprint could be reduced by integrating heat pumps coupled with renewable energy sources for NG preheating to support gas boilers. For this work, an ad-hoc thermodynamic model for estimating the thermal energy demand for pre-heating is developed, exploiting experimental data from a real CGS, and simplified models of heat pumps and renewable systems. This work aims to assess the actual technical and economic feasibility of energy savings through these technologies. Results show the validated model to be sufficiently accurate to estimate the need for gas preheating for these applications. For the considered case study, up to 38%, 32%, or 26% of the total thermal energy can be recovered with a PBT of less than 20 years, 15, and about 13 years, respectively.
... article[11], Staffel et al donnent une approximation du COP en fonction de la différence de température entre le fluide dans le condenseur et dans l'évaporateur. Cette loi a été obtenue empiriquement grâce à une base de données[12] et s'écrit : , en première approximation que la température du fluide dans le condenseur est celle d'un plancher chauffant donc $ " 40° et que la température du fluide dans l'évaporateur correspond à la température du fluide qui entre dans le sol. ...
Depuis quelques décennies, on assiste au développement des géostructures thermiques dont le principe consiste à fixer des tubes échangeurs aux cages des fondations géotechniques. Une pompe à chaleur fait alors circuler de l'eau dans ces tubes afin d'extraire de la chaleur du sol en hiver ou alors de la fraicheur en été. Cependant, ces géostructures sont très fréquemment implantées dans des sols parcourus par des écoulements souterrains qui impactent le champ thermique du sol et donc la performance de la pompe à chaleur. Une étude numérique est alors réalisée pour apprécier l'impact de l'écoulement sur la performance d'une pompe à chaleur reliée à un groupe de pieux géothermiques. Nomenclature Charge thermique, W V Débit de pompage moyen, m 3 .s-1 Vitesse de Darcy, m. s-1 Perméabilité, m.s-1 Cv Capacité thermique, J.K-1 H Charge hydraulique, m T Température, K
... The annual sum of thermal demand divided by the sum of electrical loads results in a seasonal COP of 2.51. This value is derated by a conservative 25% to account for losses due to defrosting, fans, heat exchanger fouling, and backup heating element use [39], resulting in a nominal seasonal performance factor (SPF) of 1.9 and an annual electricity use of 6,652 kWh el for heating. When combined with appliance loads, the total annual electricity demand of the heat pump house is 17,462 kWh el . ...
This study aims to quantify the techno-economic potential of using solar photovoltaics (PV) to support heat pumps (HP) towards the replacement of natural gas heating in a representative North American residence from a house owner’s point of view. For this purpose, simulations are performed on: (1) a residential natural gas-based heating system and grid electricity, (2) a residential natural gas-based heating system with PV to serve the electric load, (3) a residential HP system with grid electricity, and (4) a residential HP+PV system. Detailed
descriptions are provided along with a comprehensive sensitivity analysis for identifying specific boundary conditions that enable lower total life cycle cost. The results show that under typical inflation conditions, the lifecycle cost of natural gas and reversable, air-source heat pumps are nearly identical, however the electricity rate structure makes PV costlier. With higher rates of inflation or lower PV capital costs, PV becomes a hedge
against rising prices and encourages the adoption of HPs by also locking in both electricity and heating cost growth. The real internal rate of return for such prosumer technologies is 20x greater than a long-term certificate of deposit, which demonstrates the additional value PV and HP technologies offer prosumers over comparably secure investment vehicles while making substantive reductions in carbon emissions. Using the large volume of results generated, impacts on energy policy are discussed, including rebates, net-metering, and utility business
models.
... The temperature of the heating floor is considered equal to 40°C. The COP can be estimated empirically through (Staffell et al., 2012) (equation (13)). ...
Development of energy geostructures into cities induces proximity interaction. When placed in a groundwater flow, advection effect will increase heat pump efficiency and avoid multiyear thermal shift. Yet, it also creates a thermal plume that can interact with downstream structures. In order to study these interactions, this article presents an experimental study conducted within the Sense City experimental facility, and a numerical hydraulic-thermal coupled model, developed with the FEM software CESAR-LCPC to extrapolate the experimental results. Both experimental and numerical studies allowed us to understand and estimate thermal interaction within a group of piles. Thermal interactions are strongly directional and aligned with the water flow, effects of multiple piles are cumulative and decrease within the distance. Simulation of heat pump efficiency show the benefits of underground water flow and thermal washing, increasing efficiency coefficient above 4 and erasing thermal cluster effect.
... Electrification of building heat is a practical approach to mitigate emissions from buildings and comply with the Paris Climate Accord ("The Paris Agreement"). Air-source heat pumps (ASHPs) are the electric alternative to fossil fuel-based systems and have proven to be effective in mitigating emissions and reducing energy consumption (Valancius et al. 2019;Staffell et al. 2012). ...
Air-source heat pumps (ASHPs) are energy-efficient alternatives to conventional natural gas heating systems. At very low ambient temperatures, the coefficient of performance (COP) of an ASHP drops drastically with rising refrigerant discharge temperatures at the compressor exit. Two-stage ASHPs have a staged compression process, which improves the COP and reduces discharge temperatures. The current study investigates the performance of a two-stage ASHP used to supply heat to an office building in Saskatoon, considering the effects of frosting on the evaporator. The average annual COP of two-stage ASHP is 2.04, while frosting and defrosting cycles increase energy consumption by 12.5%. The GHG emissions from two-stage ASHP operation are compared with natural gas heating systems indicating that two-stage ASHPs can reduce emission by 8% compared with natural gas heating systems in Saskatoon.
Ferroelectric polymer-based electrocaloric effect may lead to sustainable heat pumps and refrigeration owing to the large electrocaloric-induced entropy changes, flexible, lightweight and zero-global warming potential. Herein, low-k nanodiamonds are served as extrinsic dielectric fillers to fabricate polymeric nanocomposites for electrocaloric refrigeration. As low-k nanofillers are naturally polar-inactive, hence they have been widely applied for consolidate electrical stability in dielectrics. Interestingly, we observe that the nanodiamonds markedly enhances the electrocaloric effect in relaxor ferroelectrics. Compared with their high-k counterparts that have been extensively studied in the field of electrocaloric nanocomposites, the nanodiamonds introduces the highest volumetric electrocaloric enhancement (~23%/vol%). The resulting polymeric nanocomposite exhibits concurrently improved electrocaloric effect (160%), thermal conductivity (175%) and electrical stability (125%), which allow a fluid-solid coupling-based electrocaloric refrigerator to exhibit an improved coefficient of performance from 0.8 to 5.3 (660%) while maintaining high cooling power (over 240 W) at a temperature span of 10 K.
Industrial waste heat is a valuable heat source to provide a decarbonized supply to district heating networks. In particular, sewage water treatment plants are a widely-available source of waste water, which can be used as part of low-temperature district heating networks.
In this paper, we present an assessment framework to estimate the potential from existing heat sources to supply a new district network, in terms of heat supplied consumers (number, location and heat coverage) and plausible network layout.
The case-study application is an evaluation of the waste-water potential in the canton of Zurich. Considering 61 waste-water treatment plants for a total unexploited potential of 607 GWh, we show that 13,077 buildings could be connected to a district heating network originating from such plants. This value represents about 6% of the building stock in the canton of Zurich and 6% of the current estimated heating demand. By considering decentralized water-water heat pumps for each building connected to the network, we find that a 14% electricity saving could be obtained compared to standalone air-water heat pumps.
By clustering substations according to the potential net revenue for the network operator and automating the tracing of the shortest-path network layout, we estimate the pipework length and the related investment costs.
Micro gas turbines are an on-site power and heat generation technology with a small footprint, low gaseous (NOx) and acoustic emissions, low maintenance and high-grade heat. They entered the market at the dawn of the twentieth century; nevertheless, they achieved minimal success and a marginal role in the microgeneration market. Reciprocating internal combustion engines raised considerable barriers hindering their market deployment, and Fuel Cells are also set to compete in this segment.
In this scenario, this work presents an analysis of competitiveness grounded in the Theory of Constraints. To this end, a specific Key Performance Indicator has been produced, which combines technical, economic, and operational factors according to the end-user requirement. This indicator is a function of several penalty factors representing technology and market barriers, which aims to yield a unique insight into the most competitive technology for a given application, accounting for the uncertainty deriving from technical and economic elements.
This novel methodology is applied to a new potential niche market: Power-to-Hydrogen-to-Power for remote applications. The methodology is applied to an independent rural community in South Wales, for which a backup power system is assessed. Four technologies are considered in the analysis: reciprocating engines, fuel cells and two different microturbines layouts.
Finally, this work provides an overview of the possible R&D&I paths necessary to increase the competitiveness of micro gas turbines in certain markets.
This paper presents a new framework which fills the gap between heating technology comparison and home energy management studies by holistically considering all home energy demands. The paper answers what the cost and emissions optimal technology combinations are to meet these demands and how the inclusion of baseload and cooking demands change the technology landscape. Evaluation is completed for hundreds of heating and ancillary system combinations to show their economic and environmental potential, with optimisation using lowest net present cost (NPC) solutions. Analysis is completed for an average UK dwelling, results indicate high capital expenditure (CapEx) electrified systems result in the lowest NPC solutions and lowest emissions, ideally coupled with solar photovoltaics (PV) especially with the increased demand when including baseload demand. When including cooking fuels, Blue Hydrogen has a slight increased potential due to similar cooking efficiencies to electric cooking, but with potentially lower fuel emissions than current grid generated electricity emissions.KeywordsDomesticEnergyLow-CarbonHeatingCooking
Electrifying space heating is essential to reduce climate impacts in the building sector, and heat pumps have emerged as an energy-efficient and increasingly cost-effective solution. However, other clean energy technologies (e.g., rooftop solar) are less likely to be adopted in underserved communities, and thus policies incentivizing their adoption can be regressive. Unlike previously-studied technologies, the effects of heat pumps on energy bills may be positive or negative, and thus inequities in their adoption are context specific. Here we propose a framework for identifying inequities in heat pump adoption and map these inequities across the U.S. We find that households in communities of color and with high percentages of renters are adopting heat pumps at lower rates across the board, but differences are largest in areas where heat pumps are likely to reduce energy bills. Public policies must address these inequities to advance beneficial electrification and energy justice.
Thermal energy storage (TES) is required to allow low-carbon heating to meet the mismatch in supply and demand from renewable generation, yet domestic TES has received low levels of adoption, mainly limited to hot water tanks. Current reviews and studies primarily focus on the comparison of storage materials neglecting the performances at a system level and analysis studies tend to solely look at hot water tanks, missing the key technology developments in thermal storage systems which are under development. Therefore, this paper investigates performance and cost variations of TES from material-level to system-level analysis and assesses impacts of emerging heat storage technologies. By simulating different types of TES materials and varied system integration options, a significant reduction in energy densities and increase in specific costs of TES systems were found compared to the material-level analysis. Direct electrical heating has much greater potential to integrate with TES from its high operating temperature with TES compared to heat pumps or solar thermal which are constrained to lower temperatures. TES properties are simulated in various scenarios in a domestic heating techno-economic framework. It was found that for heat pumps there is economically-limited potential for TES, even if very high energy densities are possible. In addition, the priority for TES coupling with heat pumps is low capital cost, although current high tariff rates due to the energy-crisis do improve economic viability of TES. On the other hand, with direct electrical heating, high energy density is the most valuable parameter for TES, as it allows significant quantity of demand to be shifted to very low-tariff times, in particular for low demand dwellings where negligible amounts of peak electricity could be required for heating.
Installing carbon capture and storage (BECCS) capability at existing biomass-fired combined heat and power (bio-CHP) plants with substantial emissions of biogenic CO2 could achieve significant quantities of the negative CO2 emissions required to meet climate targets. However, it is unclear which CO2 capture technology is optimal for extensive BECCS deployment in bio-CHP plants operating in district heating (DH) systems. This is in part due to inconsistent views regarding the perceived value of high-exergy energy carriers at the plant level and the extended energy system to which it belongs. This work evaluates how a bio-CHP plant in a DH system performs when equipped with CO2 capture systems with inherently different exergy requirements per unit of CO2 captured from the flue gases. The analysis is based upon steady-state process models of the steam cycle of an existing biomass-fired CHP plant as well as two chemical absorption-based CO2 capture technologies that use hot potassium carbonate (HPC) and amine-based (monoethanolamine or MEA) solvents. The models were developed to quantify the plant energy and exergy performances, both at the plant and system levels. In addition, heat recovery from the CO2 capture and conditioning units was considered, as well as the possibility of integrating large-scale heat pumps into the plant or using domestic heat pumps within the local DH system. The results show that the HPC process has more recoverable excess heat (∼0.99 MJ/kgCO2,captured) than the MEA process (0.58 MJ/kgCO2,captured) at temperature levels suitable for district heating, which is consistent with values reported in previous similar comparative studies. However, using energy performance within the plant boundary as a figure of merit is biased in favor of the HPC process. Considering heat and power, the energy efficiency of the bio-CHP plant fitted with HPC and MEA are estimated to be 90% and 76%, respectively. Whereas considering exergy performance within the plant boundary, the analysis emphasizes the significant advantage the amine-based capture process has over the HPC process. Higher exergy efficiency for the CHP plant with the MEA capture process (∼35%) compared to the plant with the HPC process (∼26%) implies a relatively superior ability of the plant to adapt its product output, i.e., heat and power production, and negative-CO2 emissions. Furthermore, advanced amine solvents allow the BECCS plant to capture well beyond 90% of its total CO2 emissions with relatively low increased specific heat demand.
This paper reviews the current status of microgeneration technologies at the domestic scale. Overviews are given for nine such technologies, grouped into three sections: (a) low carbon heating: condensing boilers, biomass boilers and room heaters, air source and ground source heat pumps; (b) renewables: solar photovoltaic panels, flat plate and evacuated tube solar thermal panels and micro-wind; and (c) combined heat and power: Stirling engines, internal combustion engines and fuel cells. Reviews of the construction, operation and performance are given for the leading commercial products of each technology. Wherever possible, data are presented from the field, giving the actual prices paid by customers, efficiencies and energy yields experienced in real-world use, reliability and durability, and the problems faced by users. This information has a UK focus but is generally relevant in the international context. Two issues are found to be prevalent throughout the microgeneration industry. Total installed costs are a premium and vary substantially between technologies, between specific products (e.g. different models of solar panel), and between individual installations. Performance in the field is found in many cases to differ widely from manufacturers’ quotes and laboratory studies, often owing to installation and operational problems. Despite this, microgeneration has demonstrated substantial improvements over conventional generation in terms of fossil fuel consumption, carbon dioxide emissions and energy cost, provided that the appropriate technologies are employed, being installed and operated correctly according to the load requirements of the house and their physical location.
In the UK, gas boilers are the predominant energy source for heating in housing, due primarily to the ready availability of natural gas. The take-up of heat pumps has lagged far behind Europe and North America. However, with the development of standards for low and zero-carbon housing, gas price rises and the depletion of the UK's natural gas reserves, interest in heat pump technology is growing. Heat pumps, particularly air source heat pumps (ASHPs), have the potential to be a direct, low-carbon replacement for gas boiler systems in housing.In this paper, monitored data and simulations were used to assess the performance of an ASHP when retrofitted into a dwelling. This required the development and calibration of a model of an ASHP device and its integration into a whole-building, dynamic simulation tool. The predictions of the whole-building model were compared to field trial data, indicating that it provided a suitable test bed for energy performance assessment. Annual simulations indicated that the ASHP produced 12% less carbon that an equivalent condensing gas boiler system, but was around 10% more expensive to run. However, the proposed UK renewable heat incentive transforms this situation, with income from ASHP heat generation exceeding the fuel costs.
Obstructive sleep apnoea (OSA) is a highly prevalent condition with proven neurocognitive and cardiovascular consequences. OSA patients experience repetitive narrowing or collapse of the pharyngeal airway during sleep. Multiple factors likely underlie the pathophysiology of this condition with considerable inter-individual variation. Important risk factors for OSA include obesity, male gender, and ageing. However, the mechanisms underlying these major risk factors are not well understood. We briefly review the state-of-the-art knowledge regarding OSA pathogenesis in adults and highlight the potential role of genetics in influencing key OSA pathophysiological traits.
Obstructive sleep apnoea/hypopnoea syndrome (OSAHS) is a common condition affecting approximately 2-4% of the middle-aged population. A hereditary component to the condition has long been recognised but its genetic basis has been difficult to elucidate. Progress in determining the genotype of OSAHS is hampered by the lack of a consistent definition of phenotype and the large environmental influences on its expression. "Intermediate phenotypes", such as craniofacial structure, obesity and upper airway control, have been utilised. Multiple gene polymorphisms have been explored in association with the latter, as well as with the sequelae of OSAHS, such as hypertension and increased insulin resistance. To date, two genome-wide scans have identified potential regions that may be of interest in further defining the intermediate phenotypes. The present paper focuses on human studies with an update of the most recent work in the area, including a short discussion on methods of genetic studies.
Interleukin-1 beta (IL1) and tumor necrosis factor alpha (TNF) promote non-rapid eye movement sleep under physiological and inflammatory conditions. Additional cytokines are also likely involved but evidence is insufficient to conclude that they are sleep regulatory substances. Many of the symptoms induced by sleep loss, e.g. sleepiness, fatigue, poor cognition, enhanced sensitivity to pain, can be elicited by injection of exogenous IL1 or TNF. We propose that ATP, released during neurotransmission, acting via purine P2 receptors on glia releases IL1 and TNF. This mechanism may provide the means by which the brain keeps track of prior usage history. IL1 and TNF in turn act on neurons to change their intrinsic properties and thereby change input-output properties (i.e. state shift) of the local network involved. Direct evidence indicates that cortical columns oscillate between states, one of which shares properties with organism sleep. We conclude that sleep is a local use-dependent process influenced by cytokines and their effector molecules such as nitric oxide, prostaglandins and adenosine.
Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Metabolic syndrome is another highly prevalence emerging public health problem that represents a constellation of cardiovascular risk factors. Each single component of the cluster increases the cardiovascular risk, but the combination of factors is much more significant. It has been suggested that the presence of OSAS may increase the risk of developing some metabolic syndrome features. Moreover, OSAS patients are at an increased risk for vascular events, which represent the greatest morbidity and mortality of all associated complications. Although the etiology of OSAS is uncertain, intense local and systemic inflammation is present. A variety of phenomena are implicated in this disease such as modifications in the autonomic nervous system, hypoxemia-reoxygenation cycles, inflammation, and coagulation-fibrinolysis imbalance. OSAS patients also present increased levels of certain biomarkers linked to endocrine-metabolic and cardiovascular alterations among other systemic consequences. All of this indicates that, more than a local abnormality, OSAS should be considered a systemic disease.
Now in its fourth edition, this respected text delivers a comprehensive introduction to the principles and practice of refrigeration. Clear and straightforward, it is designed for students (NVQ/vocational level) and professional HVAC engineers, including those on short or CPD courses. Inexperienced readers are provided with a comprehensive introduction to the fundamentals of the technology. With its concise style yet broad sweep the book covers most of the applications professionals will encounter, enabling them to understand, specify, commission, use and maintain these systems. Many readers will appreciate the clarity with which the book covers the subject without swamping them with detailed technical or product specific information. New material in this edition includes the latest developments in refrigerants and lubricants, together with updated information on compressors, heat exchangers, liquid chillers, electronic expansion valves, controls and cold storage. Topics also covered include efficiency, environmental impact, split systems, retail refrigeration (supermarket systems and cold rooms), industrial systems, fans, air infiltration and noise. Author Information Guy Hundy studied Mechanical Engineering at Leeds University, UK. He started his career in the refrigeration industry with J & E Hall Ltd, Dartford. In 1985 he joined Copeland Europe and in 1998 he was appointed Director, Application Engineering, Copeland Europe. He has authored and co-authored papers and articles on compressors, applications and refrigerant changeover topics. Guy Hundy is a Chartered Engineer and works as a Technical Consultant. He is past - President of the Institute of Refrigeration. * Covers principles, methods and application of refrigeration, air conditioning and heat pumps in a concise volume, without the encumbrance of handbook information found in other volumes * Ideal for students, and professionals in other disciplines, not too theoretical but with sufficient depth to give an understanding of the issues, this book takes the reader from the fundamentals, through to system design, applications, contract specifications and maintenance * Full revision by Guy Hundy with new diagrams and illustrations.
In recent years, heat pumps have emerged as a promising new form of technology with a relatively low environmental impact. Moreover, they have presented householders with an opportunity to reduce their heating bills. Heat pumps can heat a building by "pumping" heat from either the ground or the air outside: an intriguing process which utilizes principles that are somewhat analogous to those employed in the domestic refrigerator. This book describes what a heat pump is, how it works, the different methods of pumping heat, and the importance of an appropriate and well-planned installation. It examines the air, the ground, and water as sources of heat and explains how to make an informed choice; considers the all-important subject of distributing the heat through radiators or through an under-floor system; covers hot water production and delivery to the taps; outlines environmental and financial issues associated with heat pumps; dispels common misconceptions; and presents a number of case studies.
This paper presents the results of a life cycle assessment of domestic heat pumps in the UK in comparison with gas boilers. The study considers air (ASHP), ground (GSHP) and water (WSHP) source heat pumps. The results show that heat pumps have higher environmental impacts than gas boilers due to the use of electricity. On average, the impacts for the ASHP are 82% higher than from the boiler and 73% for the GSHP and WSHP. The exception to this are the global warming, fossil resource depletion and summer smog impacts which are lower for the pumps than the boilers. For example, up to 36% of CO2 eq. can be saved with the WSHP and 6% with the ASHP in comparison with the boiler. Among the heat pumps considered, ASHP have the highest impacts due to lower efficiencies and higher material requirements for the system. The GSHP and WSHP have comparable impacts, with the latter being marginally better. The life cycle impacts of heat pumps may improve if the UK electricity mix is sufficiently decarbonised; however, they will still remain higher than for the gas boiler. Overall, their potential to contribute to the UK climate change targets is limited.
The book is intended for use in two regular semester courses, following which the student should be capable of participating in the design of all types of HVAC systems. The information is intended for use at the undergraduate and beginning graduate levels by students who have some familiarity with thermodynamics, heat transfer, and fluid mechanics. Numerous practice problems are provided. Topics covered include: moist air properties and conditioning processes; comfort and health; heat transmission in building structures; solar radiation; space heat load; the cooling load; complete air-conditioning systems; fluid flow, pumps, and piping design; room air distribution; fans and building air distribution; mass transfer and the measurement of humidity; direct contact transfer processes; extended surface heat exchangers; refrigeration; solar heating and cooling. (LEW)
By 1997 about 90 million heat pumps have been installed worldwide, only less than 5% are located in Europe, historically the cradle of this “thermodynamic heating and cooling process”. The majority of the approximately 4 million installed heat pumps are imported reversible air-to-air systems in southern Europe and only 30% represent the typical European-made heating only electric driven compression systems for space and water heating in buildings in central and northern Europe. The first and second oil crises has been the main cause for a first European heat pump “boom” at the end of the seventies. Consequently the following drop in energy prices negatively influenced the market in some countries. The new renaissance in Europe in the middle of the nineties was initiated by the understanding of sustainable development for a more efficient energy use and the related protection of the environment.
A ground-source heat pump (GSHP) model is formulated and used to estimate the potential of a domestic GSHP as a carbon-saving technology (compared to a conventional gas boiler) with actual thermal data for a dwelling in the UK. The model shows good agreement with current sizing guidelines but shows possible barriers to the carbon-savings (and running cost savings) of GSHPs. This includes an analysis of output temperatures, system sizes and grid CO2 intensity. The model suggests that GSHPs should be aimed towards a new-build market (rather than retrofit) due to the likely reliance on high surface area/low temperature distribution systems. Also, grid CO2 intensity needs to be better understood when estimating the electrical consumption CO2 emissions of GSHPs, both for current and future scenarios.
This study reviews gas engine-driven heat pump (GEHP) systems for residential and industrial applications in terms of energetic and exergetic aspects for the first time to the best of the authors' knowledge. These systems are novel heat pump systems (one of today's promising new technologies). Although the first investigations had been performed at late 1970s, the first merchandized GEHP was produced and introduced in the market in 1985. Gradually, it has become widespread all over the world for various purposes. Main application of GEHPs are for space and water heating/cooling purposes. However, they can be integrated to industrial applications, especially to drying processes. In this study, historical development of GEHP systems was briefly given first. Next, the operation of these systems was described, while studies conducted on them were reviewed and presented in tabulated forms. GEHPs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, an illustrative example was given, while the results obtained were discussed. In addition, a new project on integration of GEHP systems to food drying processes in Turkey initiated by the authors was introduced. It is expected that this comprehensive study will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis and performance of assessment of GEHP systems.
Ground-source or geothermal heat pumps are a highly efficient, renewable energy technology for space heating and cooling. This technology relies on the fact that, at depth, the Earth has a relatively constant temperature, warmer than the air in winter and cooler than the air in summer. A geothermal heat pump can transfer heat stored in the Earth into a building during the winter, and transfer heat out of the building during the summer. Special geologic conditions, such as hot springs, are not needed for successful application of geothermal heat pumps. Ground-source heat pumps (GSHPs) are receiving increasing interest because of their potential to reduce primary energy consumption and thus reduce emissions of greenhouse gases. The technology is well established in North America and parts of Europe, but is at the demonstration stage in the UK. This article provides a detailed literature-based review of ground-source heat pump technology, concentrating on loops, ground systems, and looks more briefly at applications and costs and benefits. It concludes with the prospects for GSHP in the UK. It is concluded that, despite potential environmental problems, geothermal heat pumps pose little if any serious environmental risk when best management practices are applied during the installation, operation, and decommissioning of these systems.
The carbon dioxide (CO2) emissions reduction afforded by a demand-side intervention in the electricity system is typically assessed by means of an assumed grid emissions rate, which measures the CO2 intensity of electricity not used as a result of the intervention. This emissions rate is called the "marginal emissions factor" (MEF). Accurate estimation of MEFs is crucial for performance assessment because their application leads to decisions regarding the relative merits of CO2 reduction strategies. This article contributes to formulating the principles by which MEFs are estimated, highlighting the strengths and weaknesses in existing approaches, and presenting an alternative based on the observed behaviour of power stations. The case of Great Britain is considered, demonstrating an MEF of 0.69Â kgCO2/kWÂ h for 2002-2009, with error bars at +/-10%. This value could reduce to 0.6Â kgCO2/kWÂ h over the next decade under planned changes to the underlying generation mix, and could further reduce to approximately 0.51Â kgCO2/kWÂ h before 2025 if all power stations commissioned pre-1970 are replaced by their modern counterparts. Given that these rates are higher than commonly applied system-average or assumed "long term marginal" emissions rates, it is concluded that maintenance of an improved understanding of MEFs is valuable to better inform policy decisions.
Heat pump systems offer economical alternatives of recovering heat from different sources for use in various industrial, commercial and residential applications. As the cost of energy continues to rise, it becomes imperative to save energy and improve overall energy efficiency. In this light, the heat pump becomes a key component in an energy recovery system with great potential for energy saving. Improving heat pump performance, reliability, and its environmental impact has been an ongoing concern. Recent progresses in heat pump systems have centred upon advanced cycle designs for both heat- and work-actuated systems, improved cycle components (including choice of working fluid), and exploiting utilisation in a wider range of applications. For the heat pump to be an economical proposition, continuous efforts need to be devoted to improving its performance and reliability while discovering novel applications. Some recent research efforts have markedly improved the energy efficiency of heat pump. For example, the incorporation of a heat-driven ejector to the heat pump has improved system efficiency by more than 20%. Additionally, the development of better compressor technology has the potential to reduce energy consumption of heat pump systems by as much as 80%. The evolution of new hybrid systems has also enabled the heat pump to perform efficiently with wider applications. For example, incorporating a desiccant to a heat pump cycle allowed better humidity and temperature controls with achievable COP as high as 6. This review paper provides an update on recent developments in heat pump systems, and is intended to be a “one-stop” archive of known practical heat pump solutions. The paper, broadly divided into three main sections, begins with a review of the various methods of enhancing the performance of heat pumps. This is followed by a review of the major hybrid heat pump systems suitable for application with various heat sources. Lastly, the paper presents novel applications of heat pump systems used in select industries.
During the last decade, a number of studies have been conducted by various investigators in the design, modeling and testing of solar assisted heat pump systems (SAHPSs). This paper reviews the studies conducted on the energy and exergy analysis of SAHPS systems in Turkey and around the world as of the end of December 2004. The studies undertaken on the SAHPS systems are categorized into four groups as follows: (i) SAHPSs for water heating, (ii) SAHPSs with storage (conventional type) for space heating, (iii) SAHPSs with direct expansion for space heating, and (iv) Solar-assisted ground source heat pump greenhouse heating system (SAGSHPGHS). This paper investigates the studies on SAGSHPs, especially ground-source heat pumps, also known geothermal heat pumps, at the Turkish universities in more detail, by giving Turkey's solar energy potential.
After the CFCs and the HCFCs were deemed unfit as working fluids in refrigeration, air conditioning, and heat pump applications, there has been a renaissance for carbon dioxide technology. Heat pumps is one of the application areas where theoretical and experimental investigations are now performed by an increasing number of research institutions and manufacturers. This paper gives an overview of some of the current activities in the CO2 heat pump field. Discussed are the important characteristics of the transcritical CO2 process applied to heat pumps, and also discussed are theoretical and experimental results from several heat pump applications. Provided that calculations and system designs are performed on the premises of the working fluid, and that test plants are constructed and operated to fully exploit the specific characteristics of both the fluid and the transcritical process, the results show that CO2 is an attractive alternative to the synthetic fluids. Competitive products may be launched in the near future.
A computer model has been developed to simulate the performance of a novel thermoelectric heat pump system. The modelling was based on the performance of a small prototype system. Results were obtained for various operating and weather conditions, and these were compared with experimental results obtained for a fabricated prototype system. Reasons for differences between the modelled and test results were analysed, and correction factors were produced to modify the computer model. More accurate modelling results were then obtained. The work provides a basis for analysis and design of the thermoelectric heat pump system.
Chemical heat pumps (CHPs) provide high storage capacity and high heat of reaction as compared to sensible heat generated by absorption. Investigation of material properties and their operation have led to their heat pumps exploitation for commercial and industrial applications. Integration of solar thermal system to the CHPs would assist in expanding the utilization of CHPs and also for many applications in the tropical region. The research done in CHP regarding to status of technology, current applications and their future prospect has been reviewed, with special reference to their utilization with solar thermal energy for cold production and upgrading/storage of heat.
We employ the Schwartz and Smith [Schwartz, E., and J. Smith, 2000, Short-term variations and long-term dynamics in commodity prices, Management Science 46, 893–911.] model to explore the dynamics of the UK gas markets. We discuss in detail the short-term and long-term market prices of risk borne by the market players and how deviations from expected cyclical storage affect the short-term market price of risk. Finally, we illustrate an application of the model by pricing interruptible supply contracts that are currently traded in the UK.
A heat pump water heater (HPWH) operates on an electrically driven vapor-compression cycle and pumps energy from the air in its surroundings to water in a storage tank, thus raising the temperature of the water. HPWHs are a promising technology in both residential and commercial applications due to both improved efficiency and air conditioning benefits.Residential HPWH units have been available for more than 20 years, but have experienced limited success in the marketplace. Commercial-scale HPWHs are also a very promising technology, while their present market share is extremely low.This study dealt with reviewing HPWH systems in terms of energetic and exergetic aspects. In this context, HPWH technology along with its historical development was briefly given first. Next, a comprehensive review of studies conducted on them were classified and presented in tables. HPWHs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, the results obtained were discussed. It is expected that this comprehensive review will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis, performance assessment and applications of various types of HPWH systems.
To assess sleepiness, TNF-α plasma levels, and genomic variance in the TNF-α gene in children with obstructive sleep apnea (OSA).
Children being evaluated for OSA (n = 60) and matched control children (n = 80) were assessed with a modified Epworth Sleepiness Scale questionnaire and underwent a blood draw the morning after nocturnal polysomnography. TNF-α plasma concentrations were assayed using ELISA, and genomic DNA was extracted. Genotyping and allelic frequencies were determined for 4 TNF-α single nucleotide polymorphisms using real-time polymerase chain reaction genotyping assays.
Morning TNF-α levels and Epworth Sleepiness Scale scores were increased in the presence of OSA, but substantial variability was present. Although TNF-α plasma concentrations were globally increased in OSA, most of the variance was attributable to the presence or absence of TNF-α -308G gene polymorphism.
TNF-α levels are increased in a subset of children with OSA, particularly among those harboring the TNF-α -308G single nucleotide polymorphism. Among the latter, significant increases in excessive daytime sleepiness symptoms are also present. The relatively high variability of excessive daytime sleepiness in pediatric OSA may be related to underlying TNF-α gene polymorphisms, particularly -308G.
Obstructive sleep apnoea syndrome (OSAS) is a highly prevalent disorder associated with reduced quality of life and adverse cardiovascular and metabolic sequelae. Recent years have seen an intensification of the research effort to establish the genetic contribution to the development of OSAS and its sequelae. This review explores emerging evidence in this field.
A genetic basis for sleep-disordered breathing has been demonstrated for discrete disorders such as Treacher-Collins and Down syndromes, but the picture is less clear in so-called idiopathic OSAS. A degree of heritability appears likely in some of the intermediate phenotypes that lead to OSAS, particularly craniofacial morphology. However, only sparse and often contradictory evidence exists regarding the role of specific polymorphisms in causing OSAS in the general population. Similarly, investigations of the cardiovascular sequelae of OSAS have in general failed to consistently find single causative genetic mutations. Nonetheless, evidence suggests a role for tumour necrosis factor-α polymorphisms in particular, and large-scale family studies have suggested shared pathogenetic pathways for the development of obesity and OSAS.
As with other common disorders, OSAS is likely to result from multiple gene-gene interactions occurring in a suitable environment. The application of modern genetic investigative techniques, such as genome-wide association studies, may facilitate new discoveries in this field.
Resistant hypertension is always fount to be accompanied with obstructive sleep apnea syndrome (OSAS). Previous studies assumed inflammation participated in OSAS and hypertension. The fact that tumor necrosis factor a (TNF-alpha) was related to OSAS, while neuropeptide Y (NPY) was related to hypertension, was widely reported separately. To investigate the involvement of TNF-alpha and NPY simultaneously in hypertension accompanied with OSAS, 417 subjects who underwent the polymonograph and blood pressure measurement were consecutively selected. Plasma TNF-alpha and NPY levels were determined in normotensive with OSAS (n = 113), hypertensive without OSAS (n = 73), hypertensive with OSAS (n = 134), and those of controls (n = 97), respectively. A significant increase of plasma TNF-alpha and NPY were both observed in hypertensive subjects with or without OSAS, the highest level of TNF-alpha and NPY were in hypertension with the OSAS group. TNK-alpha, NPY, and neck circumference contributed to OSAS and hypertension as risk factors in the logistic regression model. Neck circumference was impacted by apnea/hyponea index, mean diastolic blood pressure, and TNF-alpha level, which was indicated via the multiple linear model. The present study indicated a positive interplay between plasma TNF-alpha, NPY, hypertension, and OSAS in the Han population of Xinjiang. Although there is evidence that inflammation plays a role in the pathophysiology of hypertension and OSAS, clear evidence is still lacking, and raises the dilemma of the hen and the egg. Further studies are needed to clarify the role of inflammation in the pathogenesis of hypertension with OSAS, in which neck size should be considered as a linked independent factor.
Thesis (M.S.)--Catholic University of America. Includes bibliographical references.
The temperature at a certain depth in the ground remains nearly constant throughout the year and the ground capacitance is regarded as a passive means of heating and cooling of buildings. To exploit effectively the heat capacity of the ground, a heat-exchanger system has to be constructed. This is usually an array of buried pipes running along the length of a building, a nearby field or buried vertically into the ground. A circulating medium (water or air) is used in summer to extract heat from the hot environment of the building and dump it to the ground and vice versa in winter. A heat pump may also be coupled to the ground heat exchanger to increase its efficiency. In the literature, several calculation models are found for ground heat exchangers. The main input data are the geometrical characteristics of the system, the thermal characteristics of the ground, the thermal characteristics of the pipe and the undisturbed ground temperature during the operation of the system. During the first stages of the geothermal systems study, one-dimensional models were devised which were replaced by two-dimensional models during the 1990s and three-dimensional systems during recent years. The present models are further refined and can accommodate for any type of grid geometry that may give greater detail of the temperature variation around the pipes and in the ground. Monitoring systems have been set up to test various prototype constructions with satisfactory results.
Tumor necrosis factor-alpha (TNF-alpha) is a potent immunomediator and proinflammatory cytokine that has been implicated in the pathogenesis of a large number of human diseases. The location of its gene within major histocompatibility complex and biological activities has raised the possibility that polymorphisms within this locus may contribute to the pathogenesis of wide range of autoimmune and infectious diseases. For example, a bi-allelic single nucleotide substitution of G (TNFA1 allele) with A (TNFA2 allele) polymorphism at -308 nucleotides upstream from the transcription initiation site in the TNF-alpha promoter is associated with elevated TNF-alpha levels and disease susceptibilities. However, it is still unclear whether TNF-alpha -308 polymorphism plays a part in the disease process, in particular whether it could affect transcription factor binding and in turn influence TNF-alpha transcription and synthesis. Several studies have suggested that TNFA2 allele is significantly linked with the high TNF-alpha-producing autoimmune MHC haplotype HLA-A1, B8, DR3, with elevated serum TNF-alpha levels and a more severe outcome in diseases. This review discusses the genetics of the TNF-alpha -308 polymorphism in selected major diseases and evaluates its common role in health and disease.
Obstructive sleep apnea (OSA) is emerging as a significant disorder in India. Tumor necrosis factor-alpha (TNFalpha) is an important marker of inflammation. Recent data indicate that inflammation may be an important correlate of OSA. The relationships of OSA with TNFalpha levels and TNFalpha gene promoter polymorphism (-308G/A) have not been investigated in obese Asian Indians with OSA.
To look for the correlation if any, between TNFalpha gene promoter polymorphism (-308G/A) in obese Asian Indians with and without OSA and correlation of TNFalpha levels with severity of OSA.
We studied 207 obese (BMI>25kg/m(2)) subjects; 104 with OSA and 103 without OSA. Both groups were matched for age, body mass index (BMI) and percentage body fat (%BF). Measurements included anthropometric and biochemical (fasting blood glucose, lipid profile and serum TNFalpha levels) parameters and TNFalpha gene promoter polymorphism (-308G/A). The frequency of '-308A'allele in TNFalpha gene was significantly higher in obese subjects with OSA (28.8%; 60/208), when compared with obese subjects without OSA (12.6%; 26/206, p=0.001). Serum TNFalpha levels were significantly higher in obese subjects with OSA [(3.6+/-0.8)pg/ml], when compared with obese subjects without OSA [(3.3+/-0.6)pg/ml, p=0.009].
Frequency of TNFalpha (-308A) allele and serum TNFalpha level was significantly higher in obese Asian Indians with OSA.
Population-based epidemiologic studies have uncovered the high prevalence and wide severity spectrum of undiagnosed obstructive sleep apnea, and have consistently found that even mild obstructive sleep apnea is associated with significant morbidity. Evidence from methodologically strong cohort studies indicates that undiagnosed obstructive sleep apnea, with or without symptoms, is independently associated with increased likelihood of hypertension, cardiovascular disease, stroke, daytime sleepiness, motor vehicle accidents, and diminished quality of life. Strategies to decrease the high prevalence and associated morbidity of obstructive sleep apnea are critically needed. The reduction or elimination of risk factors through public health initiatives with clinical support holds promise. Potentially modifiable risk factors considered in this review include overweight and obesity, alcohol, smoking, nasal congestion, and estrogen depletion in menopause. Data suggest that obstructive sleep apnea is associated with all these factors, but at present the only intervention strategy supported with adequate evidence is weight loss. A focus on weight control is especially important given the expanding epidemic of overweight and obesity in the United States. Primary care providers will be central to clinical approaches for addressing the burden and the development of cost-effective case-finding strategies and feasible treatment for mild obstructive sleep apnea warrants high priority.
Inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) may have a direct effect on glucose and lipid metabolism. On the other hand, it is known that IL-6 and TNF-alpha are important pro-inflammatory cytokines in the pathogenesis of atherosclerosis. The goal of present study was to test whether sleep apnea contributes to the previously reported increases of IL-6 and TNF-alpha independent of obesity. Forty-three obese (body mass index, BMI>27 kg/m2) men with newly diagnosed obstructive sleep apnea syndrome (OSAS) (apnea-hypopnea index, AHI> or =5) and age- and BMI-matched 22 obese nonapneic male controls (AHI<5) were enrolled in this study. To confirm the diagnosis, all patients underwent standard polysomnography in the sleep disorders center. Serum samples were taken at 08:00 h in the morning after overnight fasting. Serum IL-6 and TNF-alpha levels were found significantly higher in OSAS patients than in controls (p=0.002, p=0.03). Serum IL-6 and TNF-alpha levels were significantly correlated with AHI in OSAS patients (r=0.03, p=0.046 and r=0.36, p=0.016). There was no significant correlation between serum IL-6, TNF-alpha levels and AHI in controls. Serum IL-6 and TNF-alpha levels were not correlated with BMI both in OSAS patients and controls. In conclusion, circulating IL-6 and TNF-alpha levels in patients with OSAS, as independent of BMI are significantly higher than levels in controls and there is a positive relationship between previously mentioned cytokines' levels and the severity of OSAS. According to these results, the link between cardiovascular morbidity and OSAS may be explained by the coexistence of other cardiovascular risk factors such as circulating IL-6 and TNF-alpha levels.
To investigate the relationship between tumor necrosis factor-alpha (TNF-alpha) gene promoter polymorphism and obstructive sleep apnea-hypopnea syndrome (OSAHS).
The plasma TNF-alpha level of OSAHS group and non-OSAHS group was detected by enzyme-linked immunosorbent assay (ELISA). Eighteen patients with severe OSAHS were treated with continuous positive airway pressure (CPAP) for 1 month, and the serum levels of TNF-alpha was also measured. The genotypes of TNF-alpha gene promoter polymorphism were determined by polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP). The genotypes and allele of the polymorphisms were compared between OSAHS group and non-OSAHS group. The effects of the polymorphisms in OSAHS group on body mass index (BMI), neck circumference (NC), waist/hip rate (WHR), polysomnography (PSG), systolic blood pressure (SBP), diastolic blood pressure (DBP) were analyzed.
The plasma level of TNF-alpha in OSAHS group was higher than the control group [(12.3 +/- 3.62) ng/L and (8.59 +/- 1.62) ng/L, respectively, t = 7.716, P < 0.01]. CPAP significantly decreased the serum levels of TNF-alpha, but its level (10.31 +/- 1.91) ng/L was still higher in the patients than the control group. The frequencies of TNF-alpha AA/AG genotype in OSAHS group (frequencies 31/76, 40.8%) was higher than the control one (frequencies 7/42, 16.7%) (chi(2) = 7.485, P < 0.05). Statistical analysis showed that OSAHS group had a significantly higher TNF-alphaA allele frequency (frequencies 39/152, 25.7%) than that of the control one (frequencies 39/152, 9.5%) (chi(2) = 8.830, P < 0.01). The OSAHS patients with AA/AG genotype had significantly higher serum levels of TNF-alpha, NC, WHR and aphea-hypopnea index [(13.39 +/- 3.71) ng/L, (45.2 +/- 4.2) cm, (0.91 +/- 0.12), and (34.8 +/- 15.6)/h, respectively] than those with GG genotype group [(11.09 +/- 3.54) ng/L, (42.7 +/- 4.9) cm, (0.85 +/- 0.12) and (26.4 +/- 12.3)/h, respectively] (t = 2.725, 2.278, 2.150, 2.609 respectively, P < 0.05 or < 0.01). The L SaO(2) (the lowest SaO(2)) in patients with AA/AG genotype [(78.8 +/- 10.9)%] was significantly lower than that in patients with GG genotype [(83.4 +/- 8.6)%] (t = 2.039, P < 0.05). There was no significant difference in BMI, SBP and DBP.
The presence of the TNF-alphaA allele may be associated with susceptibility to OSAHS, and it maybe an important candidate gene for OSAHS.
Over the last 15 years, an increasing number of electricity industries has replaced vertical integration with markets as the main method of organizing production. Electrical energy is traded in many European and US markets, while the USA also has markets for generating capacity. US generators can reduce the cost of complying with environmental regulations by trading emissions of sulphur dioxide, while Europe has just started a carbon-dioxide emissions-trading scheme. This article discusses the way in which these markets put economic principles into practice. In particular, it shows that several different market designs can provide theoretically equivalent incentives for generators to build capacity, and that emissions trading may have unexpected impacts upon electricity prices. Copyright 2005, Oxford University Press.
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