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The principle scheme of air flow, temperature and heat flux meter sensors arrangement in the roof construction, where: T15-Thermocouple on the interior surface of the roof coating; T16-Thermocouple in the middle of the ventilated air gap; T17-Thermocouple on the external surface of the breather membrane; T18-Thermocouple between the polyethylene film and chipboard; T19-Thermocouple on the interior surface of the chipboard; T20-Thermocouple inside the cell for measuring the internal temperature; TReg01-Digital temperature sensor inside the cell to measure and maintain the temperature; HF01-Heat flux meter on the interior surface of the chipboard; HF02-Heat flux meter on the interior surface of the chipboard; AFR01-Air flow sensor in the ventilated air gap of the roof
Source publication
Exterior and interior air temperatures are commonly used for calculating the rated thermal parameters of the roofs. However, the values of heat flows of the lightweight ventilated roofs are determined by the difference between the temperatures of premises and the ventilated air gap of the roof rather than by the difference between exterior and inte...
Citations
... the intensity of radiation heat exchange with the environment in external surfaces of the ventilated and non-ventilated envelopes depends on the values of solar radiation absorption coefficient α and emission ε of these surfaces (synnefa et al. 2006shi, Zhang 2011). the intensity of convective heat exchange between the boundary surfaces of the ventilated air gap and air flowing in the gap depends on the air flow speed (Banionis et al. 2011;Monstvilas et al. 2005). Moreover, emission of the boundary surfaces of the ventilated air gap determines the intensity of radiation heat exchange between these surfaces (roels, deurinck 2011). ...
The article presents the solution of heat balance equation system, describing heat exchange processes in ventilated envelopes, which was applied to derive formulas for the calculation of temperatures in the ventilated layers of the envelopes. The accurateness of the formulas was assessed by experimental research and analysis of the calculation results. During the process of heat exchange balance equation solution, the equations were simplified by introducing the following restriction into the derived formulas: they may only be applied for the ventilated envelopes with steel or similar coatings as their external layers, i.e. coatings having small heat capacity and minor difference between the external and internal surface temperatures. The derived formulas enable the calculation of the temperatures of the ventilated envelopes in the distance which does not exceed a half of the ventilated air gap length measuring from the air entrance into the gap. However, this restriction does not impede the estimation of the average thermal indicators of the ventilated envelopes.
... Multiple combinations of performance parameters and adopted constructional designs may lead to substantial differences in thermal energy efficiency of heating surface and thus increase cost of the entire system. Furthermore, thermal analysis of the horizontal surface is often time dependent since the external climate temperature, wind speed, solar radiation vary with time (Banionis et al. 2011(Banionis et al. , 2012Tabares-Velasco, Srebric 2012). That is why an efficient and economically viable surface heating system for open space design requires carrying out numerous comparative analyses. ...
This paper presents studies on thermal energy efficiency of heating surface at an open space according to structural solutions and climatic conditions. Numerical simulation research was conducted to assess three different types of heating surfaces at an open space over chosen period of time in real weather conditions. Performance parameters such as surface temperature, supply temperature and efficiency of heating surface relative to constructional designs and model of control strategy used were analysed. The number, thickness and type of material layers beneath ground level were modified. The distance between heating pipes and their diameters were kept constant. The carried out analyses show that the used solutions can lead to significant differences in the performance and consequently in the energy efficiency of the heating system for open spaces.
... Therefore, a part of short wave solar radiation does not pass inside the building even through glazed enclosures . Heat exchange at external surfaces of enclosures proceeds as thermal convection and long wave thermal radiation (ASHRAE 2009; Banionis et al. 2011; LST EN ISO 6946 2008). Surface thermal transmittance of external surfaces of enclosures h se is calculated according to Eq. (2). ...
Correct evaluation of solar heat gains through fenestration into the rooms has a great impact on energy demand calculations for buildings. This article presents an hourly energy demand calculation method for heating and cooling, which considers the fact that the solar radiation flow passed through the transparent fenestration into the rooms is not adequate to the thermal energy flow. This method considers that the thermal energy flow in the rooms transformed from solar thermal radiation depends on the short-wave thermal radiation absorption coefficient of internal surfaces of the rooms. The value of short-wave thermal radiation absorption coefficient forms a considerable impact on the flow of thermal energy gains in the room. The presented method differs from others on that score that it considers additionally physical lows, according to which the solar short-wave thermal radiation energy admitted into the room is converted into the thermal energy. This hourly method enables precise calculating the hourly mean of indoor temperature and energy demand for heating and cooling of the buildings during the day.
The multilayer reflective insulation is relatively new product on a construction market, used as efficient insulation and continuously improved. The thermal resistance of this product has to be determined according to the standard EN 16012+A1 [1], which not defines product's sample installation procedure into a hot box and indicates only rough requirement for emissivity values of surfaces of a tested sample and of adhesive tape for fixing the thermocouples must be similar, but it does not specify allowed differences and its effect on the accuracy of the measurement result. These standard's shortcomings do not ensure reliable and comparable results of the thermal resistance of multilayer thermal insulation. Therefore, a study was conducted and the method for installation and fixing of these products into hot box using frame was created. The influence of the frame on the measured thermal resistance was evaluated as a linear thermal bridge. The research of the influence of the difference between emissivity values of the sample and adhesive tape surfaces on the measured thermal resistance was performed using a calibration standard with known R-value. The research results showed that the linear thermal bridge value of frame was increasing with the increment of emissivity value of adhesive tape. Significant difference between sample and adhesive tape emissivity values can create more than 20% relative difference between both measured and calculated R-values from the known real R-value of the calibration standard. In order to avoid more than 3% relative errors, the limits of difference between emissivity values were set.
In many EU countries, the normative requirements for thermal characteristics of roofs are associated only with rating the heat losses through the roofs during the heating period. The problem of overheated premises under the light-weight ventilated roofs, covered with steel sheets, arises in the summer time. During this period of the year, because of the intensive solar radiation and high air temperature, the steel roof coatings heat up during the day and cause additional heat inflows to the premises. One of the most effective means to reduce the additional radiative heat flow from the interior surfaces of the roof coating into the attic is to install radiant barriers with low emissivity coefficient into the roof construction. The experimental research has shown that having heat reflective coatings with low emissivity coefficient (ε = 0.09) installed on the exterior surface of the thermal insulation layer of the ventilated roofs with steel coatings, the heat flow from the roof coating through the roof construction into the interior premises can be reduced on the daily average of 23–25% in the summer time.
