When analyzing large panel buildings, it is very rare to take into consideration the requirements connected with the overheating effect. The paper presents the results of the annual computational simulations of thermal comfort conducted for one flat of W70 multi-family large panel building. Basing on the simulations the authors analyzed the influence of night cooling on thermal comfort inside the flat. Different simulation steps were taken into consideration: windows with and without shading systems, opened during entire night or just during given periods of time to keep specific thermal conditions

Nowak-Dzieszko, Katarzyna

Rojewska-Warchał, Małgorzata

Portal Czasopism Naukowych (E-Journals)

TECHNICAL TRANSACTIONS
CIVIL ENGINEERING
4-B/2015
CZASOPISMO TECHNICZNE
BUDOWNICTWO
KATARZYNA NOWAK-DZIESZKO, MAŁGORZATA ROJEWSKA-WARCHAŁ*
SYMULATION OF NIGHT COOLING IN A SINGLE 
DWELLING OF A LARGE PANEL BUILDING
SYMULACJA NOCNEGO CHŁODZENIA 
W POJEDYNCZYCH MIESZKANIACH W BUDYNKU 
Z WIELKIEJ PŁYTY
A b s t r a c t
When analyzing large panel buildings, it is very rare to take into consideration the requirements 
connected with the overheating effect. The paper presents the results of the annual computational 
simulations of thermal comfort conducted for one flat of W70 multi-family large panel building. 
Basing on the simulations the authors analyzed the influence of night cooling on thermal 
comfort inside the flat. Different simulation steps were taken into consideration: windows with 
and without shading systems, opened during entire night or just during given periods of time to 
keep specific thermal conditions.
Keywords: large panel building, thermal comfort, PMV (Predicted Mean Vote), balcony 
framings, loggia
S t r e s z c z e n i e 
Podczas analizy budynków wielkopłytowych bardzo rzadko uwzględniane są wymagania 
związane z ich przegrzewaniem. W artykule przedstawiono roczne symulacje komfortu 
cieplnego przeprowadzone dla pojedynczego mieszkania w wielorodzinnym budynku 
wielkopłytowym w systemie W70. Na podstawie symulacji autorzy przeprowadzili analizę 
wpływu nocnego chłodzenia na komfort wewnatrz mieszkania. Analizie poddano rózne 
warianty: okna z systemem zacienień zewnętrznych i wewnetrznych, otwierane w okresach 
nocnych w celu obniżenia temperatury. 
Słowa kluczowe: budynki wielkopłytowe, komfort cieplny, PMV, loggia, balkon
* MSc. Katarzyna Nowak-Dzieszko, MSc. Małgorzata Rojewska-Warchał, Institute of Building 
Materials and Structures, Faculty of Civil Engineering, Cracow University of Technology.
DOI: 10.4467/2353737XCT.15.397.5028
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1. Description of problem
Overheating problems in buildings are very common and seem to be very important from 
occupants’ point of view. Taking into consideration the fact that almost a quarter of Poles 
lives in large system panel buildings the issues related to this subject are very important and 
common. Occupants can control their thermal environment by means of clothing, operable 
windows, fans, heaters, internal and external sun shades.
Unfortunately at the simulation stage it is very difficult to predict the way the individual 
flat will be used. Looking globally at the multi-family building probably each flat should 
be analyzed separately after considering the requirements and expectations of inhabitants 
regarding temperature and humidity conditions. Many analyses were conducted by the 
authors and results were described in [1–4]. All of them under the assumption that all windows 
are closed during the entire day. For those unfavorable conditions there are problems with 
overheating of internal spaces even after using of internal and external shading systems. This 
assumption is however only theoretical as in practice the inhabitants open the windows when 
temperature inside exceeds uncomfortable values. Internal cooling through the windows 
makes sense especially during the night when external temperature is lower than internal. 
From the safety reasons sometimes opening of the windows during the night is impossible, 
especially at the lowest levels.
2. Description of analyzed building
The simulations were conducted for the W70 panel dwelling building, built in 1974. Plan 
area 21.5 m × 13.2 m; usage building area – 2279 m2, 25 m high with 11 levels. Basement 
below the entire building, flat roof. 
The building has natural ventilation and a central heating system with convection heaters. 
A communication area is located in the central part of the building. There are four flats at 
every single level. Exterior walls made of prefabricated panels in the W70 system, insulated 
with 15 cm of styrofoam with plasters at both sides: U = 0.20 [W/m2K]. Triple glazing 
windows: U = 1.1 W/m2K to keep current national requirements (Warunki Techniczne), 
SHGC (solar heat gain coefficient) equal to 0.63. SHGC is a description of windows used 
in United States, refers to the solar energy transmittance of the glass. In Europe the g value 
describes the same parameters of the glazing.
The simulations conducted for the Polish climatic conditions (building located in 
Cracow). The calculations were carried out in Design Builder v.3. The program has been 
specifically developed around Energy Plus, allowing the simulation of the building envelope 
and building interiors.
Analysis based on standard PN-EN ISO 7730, ‘Ergonomics of the thermal environment. 
Analytical determination and interpretation of thermal comfort using calculation of the PMV 
and PPD indices and local thermal comfort criteria’.
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3. Simulation settings
Simulations were conducted for one flat, located at 7th floor with balcony at south elevation 
and windows at west side. The flat was analyzed as one thermal zone, an assumption that 
all internal doors are open was made. The main aim of simulations was to determine the 
temperature and PMV (Predicted Mean Vote) index during the summer months. The period 
of time between 15th May and 15th September was taken into consideration because at this 
time in Poland, there is a risk of overheating.
Fig. 1. Typical zones’ visualization at every building level. Analyzed flat #2
The assumptions to the simulations:
 – Heating system on from September to March (22°C), 7 days a week, 24 hours a day.
 – Occupancy density: flats – about 1 person per 15 m2.
 – Operating schedule: flats – 100% occupancy density between 4 pm and 7 am, 5 days a week; 
at the weekends between 6 pm and 9 am; 50% reduced occupancy between 9 am and 6 pm. 
 – Metabolic activity: factor 1.2 met, winter clothing – clo = 1.0, summer clothing clo = 0,5.
 – Ventilation requirements per Polish national standards PN-83/B–03430, in every flat 
70 m3/hour for kitchen and 50 m3/hour for bathroom.
 – Internal solar shadings (blinds with high reflexivity slats), and external shading panel 
(7 panels – louvre blades).
4. Test results
Six different simulation steps were analyzed and compared with one another.
1. All windows closed. 
2. All windows closed, internal and external shading systems used.
3. Night cooling of the flat between 8p.m. and 6 a.m. without shading systems.
18
4. Night cooling of the flat during the night until the internal temperature drops to 20°C, 
without shading systems.
5. Night cooling of the flat between 8p.m. and 6 a.m. with shading systems.
6. Night cooling of the flat during the night until the internal temperature drops to 20°C, 
without shading systems.
4.1. Influence of shadings
In the first simulation step there is an assumption that all building windows are closed for 
the entire day. It affects the internal temperatures significantly. All simulation results have 
shown that during some days in the analyzed period of time the average interior air temperature 
exceeds 30°C and the PMV factor is even higher than 2. Those microclimate building conditions 
exceed the optimal internal summer temperature of 25°C and recommended value –0.5 < PMV 
< +0.5. In the second step, the internal and external shading systems were used at all windows. 
Those solutions affected the results significantly however did not eliminate the overheating 
temperatures entirely. Figures 3 and 4 present the number of overheating hours in the analyzed 
months. The number of discomfort hours, with the temperature above 25°C in the first simulation 
step is 2549, usage of shading systems reduces this number by about 35% to 1659. 
Fig. 2. Number of overheating hours in different months
Fig. 3. Number of overheating hours, with internal and external shading systems, in different months
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4.2. Influence of night cooling on thermal conditions
Simulation steps #3 through #6 assume night cooling of the flat which, in program, was 
modelled as additional ventilation rate. It represents the cooling of the flats by opened windows 
and was modelled as 5 air ventilation exchanges of the flat volume for a flat with and without 
shading systems. Night cooling itself was also analyzed in two different options. First case when 
the windows are opened between 8 p.m. and 6 a.m. (steps 3 and 5), second option – windows are 
opened until the internal temperature drops to 20°C, then windows are closed (steps 4 and 6).
Table 1 presents comparison of the number of discomfort hours in all analyzed cases. 
T a b l e  1
Number of overheating hours (above 25°C) in different simulation steps.
Simulation step Number of overheating hours Temperatures above 30˚C
Step 1 2549 1144
Step 2 1659 296
Step 3 591 71
Step 4 727 79
Step 5 229 0
Step 6 278 0
Night cooling exerts significant influence on the internal thermal conditions. In all cases 
(3 thru 6), night cooling affected the number of discomfort hours significantly, decrease up 
to 80% can be observed comparing to the assumption when all windows are closed (steps 
1 and 2). Temperatures above 30°C were almost entirely eliminated. 
Using both shading systems and night cooling eliminated temperatures above 30°C 
entirely. From the overheating point of view the most favorable solution is using of night 
cooling together with internal and external shading systems (steps 5 and 6). However in those 
cases low temperatures even below 20°C can be observed. Figures 5 through 7 present the 
number of hours below 25°C and PMV factor in 6th simulation step. Values are even lower 
than –2.0 and temperatures drops down to 15°C. Number of hours below 20°C is 433 and 
those are very unfavorable conditions for inhabitants.
Fig. 4. Number of hours below 25°C in different months
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Fig. 5. Total number of hours below 25°C
Fig. 6. PMV factor in 6th simulation step (night cooling plus internal and external shading systems)
5. Conclusions
The results of the conducted analysis show that the overheating problem occurs in large 
panel buildings. Windows in the prefabricated panel buildings in most cases are poorly 
shaded from solar radiation. Glazing is the source of the excessive heat gains and results in 
the overheating of the dwellings. Using of internal and external shading systems reduces 
the number of discomfort hours however the most significant results are observed when 
internal spaces are cooled by opening the windows during the night. In practice this solution 
is commonly used by inhabitants. Modelling of this process is however complicated 
and difficult as it depends on the way separate flats are used. Cooling of the flats during 
every night would result in too low temperatures which affects the thermal conditions 
unfavorably. Simulations of night cooling by ventilation air exchanges is a simplification 


Symulation of night cooling in a single dwelling of a large panel building

http://www.ejournals.eu/sj/index.php/Cz/article/download/6636/pdf_760

Symulation of night cooling in a single dwelling of a large panel building

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