Embedding Passive Intelligence in Educational Buildings in Warm Summer Humid Continental Climates: A case study in Minneapolis

Abstract

The application of passive intelligence in buildings has been gaining attention widely the past decade; however, it becomes more significant in challenging environments. In warm summer humid continental climates, it can be challenging to maintain a cool indoor environment in a hot summer, and at the same time have a warm environment indoors during the extremely cold winter. In this paper, an emphasis will be done on applying passive intelligence in extreme climates; the focus will be kept on the buildings' envelope. A representative case study of an educational building in Minneapolis was selected. The main part of the school building stock in Minneapolis was built before the energy regulations, so most of the buildings need comprehensive refurbishment to achieve the performance required by laws that are in force. This study aimed at identifying passive design features through extensive virtual studies done on an energy modelling program that can be incorporated in warm summer humid continental climates to make them energy efficient. The strategies targeted had the goal of reducing the large heating loads in winter and the cooling loads in summer. To accomplish the reduction in heating loads, an analysis was performed comparing between the existing building envelope and an improved one conforming to the recent building energy codes in Minnesota. The total effect of insulating the building envelope can be seen in a reduction of the energy use intensity of about 51%. Moreover, improving the building's air tightness resulted in a further improvement of nearly 19%. To tackle the cooling loads, an emphasis was held on the use of high thermal mass and natural ventilation strategies in summer. Applying high thermal mass and night flushing resulted in a 9.5% decrease in the EUI, all through the reduction of cooling loads. Finally, it can be concluded that an accurate climatic and case study analysis to select the appropriate union of the different passive strategies, can have a significant effect on the reduction of energy consumption.

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477 ZEMCH 2021 International Conference | 26-28 October | Dubai | UAE
Embedding Passive Intelligence in Educational
Buildings in Warm Summer Humid Continental
Climates: A case study in Minneapolis
Boshra Akhozheya, Sawsan Dagher, Hamza Elsayed Ahmed Mohamed and Hamza Slimani5
Boshra Akhozheya 1*, Sawsan Dagher 2, Hamza Elsayed Ahmed Mohamed 3,4, Hamza Slimani5
1 Department of Building & Architectural Engineering, Polytechnic University of Milan, Milan, Italy;
boshrakhaled.akhozheya@mail.polimi.it
2 Department of Electromechanical Engineering, Abu Dhabi Polytechnic, Abu Dhabi, UAE;
sawsan.dagher@adpoly.ac.ae
3 UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University
of South Africa, Pretoria, South Africa; hamza@aims.ac.za
4 Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation of South
Africa, SomersetWest, Western Cape 7129, South Africa.
5 Department of Physics, University of El Oued, Fac. Exact Sciences, 39000 El Oued, Algeria;
slimani_hamza@yahoo.fr
* Correspondence: boshrakhaled.akhozheya@mail.polimi.it
Abstract: The application of passive intelligence in buildings has been gaining attention widely the
past decade; however, it becomes more significant in challenging environments. In warm summer
humid continental climates, it can be challenging to maintain a cool indoor environment in a hot
summer, and at the same time have a warm environment indoors during the extremely cold winter.
In this paper, an emphasis will be done on applying passive intelligence in extreme climates; the
focus will be kept on the buildings’ envelope. A representative case study of an educational building
in Minneapolis was selected. The main part of the school building stock in Minneapolis was built
before the energy regulations, so most of the buildings need comprehensive refurbishment to
achieve the performance required by laws that are in force. This study aimed at identifying passive
design features through extensive virtual studies done on an energy modelling program that can be
incorporated in warm summer humid continental climates to make them energy efficient. The
strategies targeted had the goal of reducing the large heating loads in winter and the cooling loads
in summer. To accomplish the reduction in heating loads, an analysis was performed comparing
between the existing building envelope and an improved one conforming to the recent building
energy codes in Minnesota. The total effect of insulating the building envelope can be seen in a
reduction of the energy use intensity of about 51%. Moreover, improving the building’s air tightness
resulted in a further improvement of nearly 19%. To tackle the cooling loads, an emphasis was held
on the use of high thermal mass and natural ventilation strategies in summer. Applying high
thermal mass and night flushing resulted in a 9.5% decrease in the EUI, all through the reduction of
cooling loads. Finally, it can be concluded that an accurate climatic and case study analysis to select
the appropriate union of the different passive strategies, can have a significant effect on the
reduction of energy consumption.
Keywords: Passive design; Insulation; Natural Ventilation; Energy; Sustainability; Warm Climates;
Cold Climates; Heating Loads; Cooling Loads; Energy Use Intensity
1. Introduction
Building envelopes represent both a physical barrier between inside and out, and a great means
to showcase architecture in terms of character, impression, and sustainability. With latest
development in technology, buildings are presenting themselves more and more as a canvas to put
the idea of passive sustainable design into practice [1]. Passive intelligent buildings date back to as

AKHOZHEYA ET AL. 478
early as 1980s [2] if not before, almost certainly one of the most widespread definitions of intelligence
in building can be that of Clements-Croome’s [3] where he suggests: ‘An intelligent building is a
dynamic and responsive architecture that provides every occupant with productive, cost-effective
and environmentally approved conditions through a continuous interaction among its basic
elements: places (fabric; structure; facilities); process (automation; control; systems); people (services;
users) and management (maintenance; performance) and the interrelation between them’.
However, the application of passive intelligence becomes more significant in challenging
environments. In warm summer humid continental climates, it can be challenging to maintain a cool
indoor environment in a very hot summer, and at the same time have a warm environment indoors
during the extremely cold winter. In this paper, an emphasis will be done on applying passive
intelligence in extreme climates; the focus will be kept on the buildings’ envelope, understanding the
effect of insulation and air tightness on the construction elements, and natural ventilation strategies
the on reducing the cooling and heating loads.
It can be argued that, across the globe, warm days are becoming warmer and more frequent,
while we are experiencing fewer cold days. Over the past decade, daily record temperatures have
struck twice as often as record lows across the continental United States, up from a near 1:1 ratio in
the 1950s. Heat waves are becoming more widespread, and extreme heatwaves are more frequent in
the U.S [4]. Although warmer winters will reduce the need for heating, modeling suggests that total
U.S. energy use will increase in a warmer future due to cooling needs [4]. Therefore, will this change
the focus of designers trying to heat the buildings, to a more focus on trying to cool the building? In
this research, a focus was casted on educational buildings in Minneapolis, to study applying passive
strategies to reduce cooling and heating needs in a warm summer humid continental climate.
In the largest school district in Minnesota, Minneapolis 58 schools are found with 72 buildings
that all need major renovations because their function has changed so significantly since they were
built[5]. The University of Minnesota has more than 850 buildings, and nearly 25 percent of them are
more than 70 years old. Similarly, many of Minnesota’s private colleges are old, some are over 150
years old [6]. Many of those older facilities are struggling to serve the technological and thermal
comfort needs of the students and teachers. Multiple renovation projects are part of a $77 million 2015
capital request to the state, which also includes a $55 million request for Higher Education Asset
Preservation and Renovation funds [7]. Building new schools in Minneapolis would cost a combined
$41.1 million, $22.1 million to replace Northport and $19 million for Lakeview. The renovation cost
for Northport, which opened in 1956, will be $21.8 million; for Lakeview, dating to 1964, it will be
$10.9 million [8]. Consequently, needless to say, finding uncostly passive intelligent solutions to
renovate the buildings becomes an urgent issue in Minneapolis’s educational sector.
2. Methodology
2.1. Climate and design data analysis
In the first step, a study of the climate analysis of Minneapolis, Minnesota was done using the
EPW (Energy Plus Weather) data file of a typical meteorological year (TMY) in excel. Excel was used
to analyze the EPW data in terms of average daily and monthly dry bulb temperatures, relative
humidity, cooling and heating degree hours, and wind speed and direction.
Then, an analysis of the design data and internal gains considered was done taking into account
the CIBSE guides[9], and a typical school calendar in Minnesota. The usage schedules and diversity
factors throughout the days were inferred. Following that, ASHRAE’s psychometric chart was used
to determine the passive strategies required in Minneapolis to reach the thermal comfort, the two
most significant strategies for summer and winter where analyzed.
2.2. Case study selection and construction detailing
The school building selected is characterized by a U shape, with an internal courtyard, typical
of the school building built at that time, shown in Figure 1. It is composed of four floors in which
classrooms, playrooms and laboratories are located. For the energetic analysis, we have considered

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just half of the building, so an L shaped structure, since both sides are symmetrical. In the years when
the school building was built, in the 80’s, the implementation of energy codes was not as widespread
as today. The main entrance is facing west, however most of the classrooms are facing south and
north.
The case study model was modeled using Revit software. A scenario of a typical construction
used in school buildings in the 80’s in Minneapolis, was used as the base case to compare the
improved scenario with. Description of Analyzed building scenarios as follows:
1. The existing case scenario, where the building has inappropriate insulation and is considered
loose, since it has been built before any energy standards were applied in building regulations. In1
terms of natural ventilation, it highly depends on the occupants’ usage of the building and it does
not seem to be regulated mechanically or in a strategic manner.
2. The improved case scenario was analyzed based on the recent construction methods and
energy codes and can be considered airtight [10]. The strategies include insulation of the existing
building, air tightness of openings, and incorporating natural ventilation strategies. Table 1 shows
improved case construction detail of a wall.
Table 1. Improved case construction detail of a wall
2.3. Energy analysis
In the following steps, the Integrated Environmental Solutions Virtual Environment (IESVE)
software was used for the energy analysis of the case study model of a school building in Minneapolis.
The energy analysis was done focusing first on the effect of two passive strategies within the
envelope, the first one includes applying insulation to construction elements within the building
envelope to attempt to reach the optimum indoor comfort temperature during winter and summer.
The insulation specifications were improved according to the recent Minnesota Building Energy
Codes, effective since 2018 until now[10]. Specifically, chapter 1323.0402 of the commercial energy
code section C402, building envelope requirements [11]. The second strategy focuses on achieving
Wall
Inside
Thickness (m)
1
10 mm polymer render
0.010
2
bedding component
0.010
3
light weight block
0.100
4
air cavity
0.050
5
light weight block
0.100
6
Kingspan thermal
insulation
0.045
7
plaster
0.013
Outside
Figure 1. a) Case study of a typical school building in Minneapolis b) West facing main entrance

AKHOZHEYA ET AL. 480
comfort during summer, by applying different strategies of ventilation and studying which one
allows the building to reach the highest number of comfort hours. As shown in Table 2.
Table 2. Existing and improved case scenario of thermal resistances
Building envelope element
Existing
Improved
Wall U -value (W/m2.C)
0.60
0.17
Roof U -value (W/m2.C)
0.35
0.13
Glazing U -value (W/m2.C)
5.52
1.25
Air tightness (ACH)
1.3
0.25
3. Results and Discussions
3.1. Climate Minneapolis
The climate of Minneapolis is classified as hot-summer humid continental without dry season,
has a hotter all-time record high temperature of 42 °C. Humid continental climate is a
major climate type of the Köppen classification that exhibits large seasonal temperature contrasts
with hot summers and cold winters. It is found between 30° and 60° N in central and eastern North
America and Asia in the major zone of conflict between polar and tropical air masses [12].
Figure 2 depicts the hourly dry bulb temperatures throughout the year in Minneapolis. It can be
noted that most of the months are considered cold and fall below the comfort level (20- 26 C). January,
February, March, November and December have freezing temperatures falling below 0 C. Maximum
temperatures can be spotted during summer months, June, July and August. The maximum
temperature reached is around 38 C during July, while the minimum is around -28 C in December.
Rain is the most common form of precipitation during the summer months, while snow, sleet,
freezing rain, and occasionally rain occur during the winter [13]. The average of the humidity is
ranging between 60% and 70% along the years, with a high fluctuation of the temperature in the
months. In Minnesota, the relative humidity is highest during August and January, while a steep
decrease in the relative humidity can be seen in May.
Figure 2. Dry bulb temperature average daily and monthly and relative humidity
The maximum average temperature can be seen during the month of July, while the minimum
average can be seen during January and December. Furthermore, Figure 3 compares between the
heating and cooling degree hours, it can be noted that the number of heating degree hours is much
larger than the cooling degree hours. Therefore, in the analyzed climate the heating needs are much
higher than the cooling needs, a focus on reducing heating and cooling needs will be done, by
utilizing passive strategies.

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In order to examine the applicability of utilizing natural ventilation as a passive strategy, a study
of the available wind source speed and direction was done. First, analyzing the wind direction from
the EPW wind data. In Figure 4, the concentric circles represent the percentage of the wind that blows
in each direction. As it is possible to notice, the wind blows in all the direction with an irregular trend.
The peak is august with the 24% of the time the wind being oriented towards the south. The average
wind direction along the year is prominent in the northwest and southeast directions. In the following
figure and table, the cumulative frequency is represented as a function of the wind speed. It can be
seen that for most of the months the greatest frequency lies between an interval between 3.5 and 6.5
m/s. Higher velocities can be spotted in December, while lower velocities can be spotted in mid-
summer months. A study of the climate surrounding the building under investigation is necessary to
determine appropriate passive strategies.
Figure 4. a) Wind direction b) Cumulative frequency of the wind speed along the year
3.2. Design data internal gains analysis
Studying the internal gains depends highly on the building’s use. In the following tables, 3 and
4, the thermal templates data assumed for the building is presented. The sensible and latent gains
coming from each different source has been decided according to the CIBSE guides, in particular:
CIBSE Guide A: Table 6.2 ‘Benchmark allowances for internal heat gains in typical buildings and
Table 6.3, and ASHRAE Fundamentals handbook (2001)[14]. The users’ schedules in a 24-hour
working day can be seen in Figure 5 for both a classroom and a laboratory, in addition to the diversity
factors in terms of the different heat gains during the day. The main difference between the two rooms
lies in the laboratory equipment increased heat gains which will require higher cooling loads during
summer. The study of the internal gains allowed a more accurate understanding of the space’s
requirements in terms of heating and cooling along the different seasons.
Figure 3. Cooling and Heating degree hours

AKHOZHEYA ET AL. 482
Table 3. Internal heat gains
Room Types
Internal Heat Gains
m2/person
People Peak
(W/person)
Lighting Peak (W/m2)
Equipment (W/m2)
Latent
Sensible
Sensible
Sensible
Classroom1
1.5
60
80
12
10
Lab
1.5
60
80
8
43.32
1The sensible and latent heat emission were taken from Table 6.2 in CIBSE Guide A, as 53 and 40 W/m2
respectively.
2 The sensible loads for the computer lab were taken from 2001 ASHRAE Fundamentals Handbook (SI), Table 8
Recommended Heat Gain from Typical Computer Equipment.
Table 4. Room conditions for school working hours
Room Conditions
Heating
Cooling
Profile
Setpoint(C)
Profile
Setpoint (C)
All rooms
8:30 am -17:30 pm
20
8:30 am -17:30 pm
26
Figure 5. Usage and diversity factors of a) a Classroom and b) a Laboratory
3.3 Analysis of Passive Strategies
3.3.1. Site Context
Minneapolis is the most-populous city in the US state of Minnesota. As of 2019, Minneapolis has
an estimated population of 429,606. The school district in Minneapolis is located in a suburban area
not too far from the city center, the buildings surrounding the district are low rise buildings reaching
up to 4 stories. Therefore, the assumed context of the school is semi exposed which is also in line with
the real case of the school in Milan.

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3.3.2. Analysis of passive strategies based on ASHRAE standards.
Considering the psychrometric chart below the zones highlighted and numbered are explaining
the passive strategies to be used according to season, Number 1 shows all the area with temperatures
falling below 8 C need direct solar gains to reduce heating. On the other hand, Number 2 shows
mostly summer months in Minneapolis which will need sun shading. Points lying in zone 3 require
insulation to increase indoor temperatures and reach comfort. Points lying in zone 4, rely on natural
ventilation and when combined with high thermal mass, points lying in zone 5 which have high
temperatures can use night flushing. In this study a focus is done on the actual effect of insulation
and natural ventilation strategies and thermal mass to reduce cooling loads, as shown in Figure 6.
Figure 6. Psychometric chart analysis of hourly temperatures in Minneapolis
3.4. Retrofitting Analysis: Insulation and Air Tightness
The selected classrooms and laboratory, shown in Figure 7a, were analyzed in terms of Gains
and losses. This was done to spot the issues within the building envelope and study the suitable
passive strategies to be implemented. As it can be seen from the results of the distinct rooms analyzed
in Figure 7b, most of the heat losses are due to external conduction, therefore a focus on external
building envelope elements should be done to reduce the heating needs, since the heating degree
hours are higher than the cooling degree hours in Minneapolis. In addition, the building’s infiltration
rate was reduced to simulate an airtight building compared to the existing loose one, the effect of air
tightness on reducing heating loads was analyzed.

AKHOZHEYA ET AL. 484
Figure 7. a) Floor plan and selected rooms to be analyzed, b) Analysis of heat gains and losses within
the rooms located on the south for room 42 and lab 35.
As depicted in Figure 8 in the improved case, the conduction gains were reduced significantly
compared to the existing case in all classrooms and the lab. The reduction in conduction gains was
highest in room 56 facing east, because it has the highest surface area of glazing. From the analysis
below, a priority should be given to insulating windows due to their high effect on the conduction
losses in winter. Classrooms 42 and 35 are both south facing therefore, they have high conduction
losses in winter due to the high solar transmittance.
Figure 8. Reduction of conduction losses in the improved case scenario when insulating the building.
The improved case was analyzed per building element, the contribution of the building envelope
elements was studied in order to prioritize the retrofitting options. The contribution can be critically

485 ZEMCH 2021 International Conference | 26-28 October | Dubai | UAE
analyzed in terms of its effect on the heating and cooling loads and the energy use intensity (EUI).
The effect can be explained by the existing case envelope’s heat transmission properties and the
surface area of each of the building envelope elements. An Ideal heating and cooling system was
inserted to maintain an inside air temperature between 20 C and 26 C for heating and cooling
respectively, and the heating and cooling loads were studied for each change.
The results in Figure 9 have shown the most significant effect by retrofitting the Windows, first
by replacing the single glazed windows by a double-glazed window with a U-value of 1.2 W/m2C.
Furthermore, Improving the airtightness of windows lead to a reduction in the infiltration and an
improvement in the heating loads specifically. The contribution of insulating windows was around
30% reduction of energy use intensity, this can be explained by the very high transmittance of the
existing case in comparison to the improved case and the high surface area of windows. Improving
the air tightness contributed to around 38% reduction in energy use intensity, specifically heating
loads, since the warm air will be maintained inside the room with an increased tightness of the
envelope.
Retrofitting the roof had the second most significant contribution resulting in a decrease of 17%
of energy use intensity. Which leads to the conclusion that improving old attics in educational
buildings can have a great impact on the energy savings of the building. Although walls have a big
surface area, the contribution was 15% savings, a little less than that of the roof’s, mainly due to the
fact that the roof’s sloped surface is highly exposed to the sun most of the day, while the walls surface
area is partially shaded by the courtyard and has a large surface area of the walls along the north
direction. The total EUI reduction due to insulation accounted for around 51%, and improving the
infiltration reduced the EUI by 19%. The analysis of heat gains and losses was beneficial to determine
the main deficiencies which need to be focused on and treated to reduce the EUI as much as possible,
particularly during winter.
Figure 9. a) Cumulative energy use intensity savings (kWh/m2/year) b) the contribution of each of the
improvements of building elements on the total savings
3.5. Thermal Mass and Ventilation
To reduce the cooling needs in summer and reach the indoor thermal comfort, a study was done
comparing medium thermal mass and high thermal mass effect on storing heat. Moreover, the
analysis extended to compare the effect of having natural ventilation during the day, or at night, and
weather cross ventilation will help in reducing the cooling loads.
The effect of applying high thermal mass can be seen in Figure 10a in terms of dampening of
temperatures, delays in peak temperatures during summer, and adjustment of temperatures within
the comfort range. In terms of cooling hours and indoor temperatures, switching from a medium
thermal mass to a high thermal mass did not have a big effect; a reduction of around 1% of cooling
hours in mid-summer months can be observed in Figure 10b.

AKHOZHEYA ET AL. 486
High thermal mass has been combined and compared with natural ventilation during the day,
night flushing, and cross ventilation. Results in Figure 10a, have shown that opening windows during
the night at 50% angle and a threshold of 24 C, to provide free cooling during the summer, reduced
the temperatures during the night releasing the heat, which was stored during the day, towards the
outside of the building.
The percentage of cooling hours utilizing the different passive ventilation techniques and
thermal mass has shown similar results. The analysis was done on all summer months to investigate
the suitable strategies for each month and evaluate the most efficient strategy. The results in Figure
10b have shown, that during mid-summer months, where the focus is mainly on reducing cooling
loads, a decrease in cooling needs is observed when using high thermal mass and night flushing,
providing free cooling for the building during the day when releasing the accumulated heat and
allowing the cool night air to ventilate through the building. On the other hand, in May and
September, when it was noticed that sometimes temperatures at night are higher than temperatures
during the day, and cooling loads are not that high, night flushing was not the most efficient. Instead
opening windows during the day was more beneficial to reduce the cooling hours. The cooling hours
shown in Figure 10b was between 9% and 7% for mid-summer months when using night flushing,
while in May and September, utilizing natural ventilation had the best effect on reducing cooling
hours achieving only 6% and 3% respectively.
The effect of natural ventilation and night flushing can also be seen in terms of indoor
temperatures in Figure 10c, where the indoor temperatures decreased in mid-summer months but
increased in May and September when incorporating night flushing.
Finally, as depicted in Figure 11a, the strategy that achieved the highest number of neutral hours
in Minneapolis during the year, achieving temperatures lying between 20 and 26 C, is the High
thermal mass with Night flushing Ventilation scenario. During months where lower cooling loads
are experienced such as May and September, Natural Ventilation during the day works best. When
we have higher cooling loads, in June, July, and August, night flushing is more effective with high
thermal mass to remove the heat acquired during the day and cool the building. Utilizing the high
thermal mass and night flushing passive technique resulted in a large decrease in the cooling hours
across all months. The savings were mainly in terms of cooling loads, shown in Figure 11b, allowing
passive cooling during night resulted in a decrease of the total energy use intensity by about 9.5%,
while the cooling loads were reduced by almost 50%. Key benefits in terms of passive cooling
efficiency were realized when analyzing and comparing multiple natural ventilation techniques.

487 ZEMCH 2021 International Conference | 26-28 October | Dubai | UAE
Figure 10. a) effect of high thermal mass and the different ventilation strategies on indoor
temperatures. b) Comparison between cooling hours using different thermal mass and ventilation
scenarios c) The effect of using different thermal mass and ventilation scenarios on indoor
temperatures.
Figure 11. a) Percentage of neutral hours achieved when utilizing the different ventilation strategies.
b) Cooling Load saving after applying night flushing in mid-summer months
4. Conclusion
To conclude, a study was done on an educational building in Minnesota, Minneapolis
embedding passive intelligent strategies. An emphasis was kept on the buildings’ envelope,
understanding the effect of insulation, air tightness, and natural ventilation strategies on reducing
the cooling and heating loads. A representative case study of a school building in Minneapolis was
selected. The main part of the school building stock in Minneapolis was built before the energy
regulations, so most of the buildings require comprehensive refurbishment to achieve the
performance required by laws that are in force. This study identified passive design features through
extensive virtual studies done on IESVE, that can be incorporated in warm summer humid
continental climates to make them energy efficient. The strategies targeted accomplished a reduction
in heating loads, by improving the building envelope, so it conforms to the recent building energy

AKHOZHEYA ET AL. 488
codes in Minnesota. The total effect of insulating the building envelope can be seen in a reduction of
the energy use intensity of about 51%. The largest effect was achieved by insulating the glazing
elements, having a 38% contribution to the total reduction of the EUI. Moreover, improving the
building’s air tightness resulted in a further improvement of nearly 19%. Moreover, the cooling loads
can be tackled by utilizing high thermal mass and natural ventilation strategies in summer. The
analysis results have shown that applying high thermal mass and night flushing resulted in a 9.5%
decrease in the EUI, all through the reduction of cooling loads. Finally, it can be concluded that if
passive intelligence was embedded within the envelope at an early stage through applying the latest
construction methods, conforming to most recent energy standards, and utilizing climatic resources
strategically, a significant reduction of energy consumption can be achieved.
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© 2021 by the authors. Submitted for possible open access publication under the terms
and conditions of the Creative Commons Attribution (CC BY) license
(http://creativecommons.org/licenses/by/4.0/).