3.1. Experimental Analysis
Summer thermal comfort measurements were conducted during a period of high thermal load in late June and early July (3 days) 2012. Measurement data were recorded at 10 min time intervals. During the third day of the study, i.e., 01.07., a sports competition was held in the hall. On the first and second day of measurements, the hall was not used.
Detailed measurement conditions of the sports hall in summer are presented in
Table 2. As already mentioned, due to the proximity of meteorological station Kraków Balice, data on outdoor air temperature, as well as humidity and wind speed values, not included in the table, were obtained from the IMGW Institute of Meteorology and Water Management during the study days.
The location of the measuring device on the mezzanine floor was dictated by the safety of the meter and the possibilities resulting from the way the facility is used. The location of the sensors could not interfere with the schedule of the sports activities taking place. It was verified that the difference in height between the level of the hall floor in Słomniki, where the classes occurred, and the location of the device could have some small effect (±0.5 °C) on the final results of the analyses. However, this was the only possibility to conduct measurements during the normal operation of this facility.
The calculated values of environmental parameters and comfort indices are summarized in
Table 3.
The resulting mean PMV was several times greater than the highest acceptable thermal comfort index of +0.5, confirming the intense overheating of the room. The mean value of the predicted percentage of unsatisfied PPD exceeded 90%.
The average calculated indoor air temperature during the study period was 25.1 °C. The highest measured temperature was 27.9 °C. The average value of the radiant temperature of the surrounding surfaces was 25.8 °C, and the average operative temperature was 25.3 °C.
Polish formal requirements for thermal conditions inside buildings [
36] (Section IV, Chapter 4, §134) provide a design temperature, used in the design of gymnasiums, of 16 °C. However, there are no explicit guidelines for the range of thermal comfort of athletes. It is obvious that intense physical exertion (from 300 W/person upward) is more beneficial at lower air temperature [
37], but this issue is not clearly defined. According to the CIBSE Guide [
38], for sports activities in a multi-purpose hall, the optimal operative temperature may be between 12 and 18 °C depending on the type of activity. In turn, the authors Trianti-Stourna et al. [
39] came to the conclusion that desirable indoor conditions for sports hall facilities are temperature between 18 and 20 °C. The available sources lack consistency and unambiguously specified categories of sports, metabolic values, and corresponding thermal comfort temperature. The analysis of indoor conditions for the assumed level of metabolism and insulation of clothing made it possible to establish a range of indoor thermal comfort using the algorithm formulated by Fanger. It was finally assumed that indoor air temperature in the hall, which is comfortable for active users of the hall in summer, is within the range of 14–18 °C. From the obtained measurement results, it should be concluded that the range of comfortable temperature in the hall was exceeded to a considerable degree.
The results of measurements clearly show that large energy gains related, among others, to placing transparent partitions mainly on the southern side (which are in accordance with the assumptions of passive construction) and gains from people and devices, while extremely desirable in winter, constitute a significant heat load for the building in summer. In the literature, researchers often refer to shading devices as an effective way to reduce overheating. However, the study shows that in the case of the analyzed hall, the shading used in the building is insufficient to maintain thermal comfort in the summer. Using the DesignBuilder simulation program, it was checked whether changing the parameters and dimensions of the applied shading could reduce the discomfort during high thermal load.
3.2. Simulation Variants and Results
Rooms overheated in summer pose considerable economic and operational problems. Sunshades are one of the simplest possible architectural and construction solutions to rationalize energy use and reduce discomfort in summer. However, the effectiveness of the used and widely advertised protection against excessive solar radiation depends on many factors related to, among others, the location, size, and technical characteristics of the shading device. Therefore, looking for solutions to reduce the discomfort in the sports facility in Słomniki, the effects of sun shading, which have actually been applied and modified on the southern façade, were examined. However, the type of glazing was not changed.
Simulations were performed for the following versions:
Variant 1: Overhangs brise-soleils were used (
Figure 5b) with an overhang of 1 m, and shading roller blinds located on the inner side of the window, assuming the following output parameters:
- ∘
Solar energy transmittance of the blind—0.05;
- ∘
Solar energy reflectance of the blind—0.35.
Variant 2: no brise-soleils; shading roller blinds located on the external side of the window, with the parameters as above.
Variant 3: Overhangs with a range of 2 m, shading roller blinds placed on the inner side of the window, with the same parameters as above.
Variant 4: Overhangs with a reach of 1 m, shading roller blinds located on the internal side of the window, with the following parameters:
- ∘
Solar energy transmittance of the window shade- 0.1;
- ∘
Solar energy reflection of the window shade- 0.5.
Variant 5: Overhangs with an overhang of 1 m, shading roller blinds located on the external side of the window and parameters:
- ∘
Solar energy transmittance of the window shade—0.00;
- ∘
Solar energy reflection of the window shade—0.35.
The simulations were carried out for a period of a month from 15 June 2012 to 15 July 2012 due to the occurrence of the highest outdoor temperatures during this period. The adopted period of analysis, which is much shorter in relation to the entire summer season, allows for more precise observation of internal conditions on charts and a more precise assessment of the impact of individual modifications. It should be added that although the simulation period includes the summer break, the school hall is often used in the afternoon or evening hours (7–10 p.m.) by people from outside the school who rent it. On Sundays, it is not uncommon for sports competitions to take place, which involves a high thermal load on the hall at that time.
The analyses initially maintained the assumptions used to validate the model, consistent with the actual use of the facility at that time (
Section 2.3). It was determined that the blinds are closed between 9 a.m. and 3 p.m., every day of the week except Saturdays. Windows are tilted at the weekend as assumed for validation (
Table 3). From Monday to Thursday, the north windows are opened from 7 to 9 a.m. and 7 to 10 p.m., and on the south side from 7 to 10 p.m.
In the simulations for the use of sunshades, mechanical ventilation is turned off (as it was during the study). In this way, during periods of high outdoor air temperatures, an attempt is made to limit the influx of warm air into the hall while reducing the energy expenditure to drive the ventilation.
Because of the assumed weekly cycle of use of the hall and for the sake of clarity of the results, the following diagrams show only the selected weekly period 29.06–5.07 with high values of the indoor air temperature. However, the statistical measurements in the tables are given for the whole month period of simulation.
The distribution of solar gains for the selected week is shown in
Figure 8. The highest daily solar gains can be observed in variant 2, in which the external brise-soleils were removed. On Saturday 30.06, when the window blinds were not closed as per the schedule of hall use (according to the observations made during the study), there was a significant increase in the total solar gains to about 18 kW—(red circle in
Figure 8) compared to the other days, during which the highest value per day was 11 kW.
As expected, the lowest values of gains can be observed in variant 5, where, apart from the brise-soleils, impermeable sun blinds located on the external side of the window were used. In the morning hours (7–9 a.m.) and in the afternoon (after 3 p.m.), when the roller blinds are not closed, the lowest gains are observed in variant 3, where the outreach of the brise-soleils was increased to 2 m. In
Figure 8, it can be seen that there is a difference in gain of 1.3–6.4 kW between the period when the internal blinds are used, i.e., 9 a.m.–3 p.m. (Sunday–Friday), and the hours when they are not used.
Analyzing the entire monthly period (
Table 4), it can be concluded that variant 2, without the external breakers applied, is associated with the highest solar gains, 2607.7 kWh. Variant 5, in which a “double” external cover was applied (breakers + impermeable blinds on the external side), comes out most favorably from the point of view of protection against excessive solar gains in summer but only between 9 a.m. and 3 p.m. Outside these hours, the least amount of energy, amounting to 1868.2 kWh, can be seen in variant 3. In the variant with breakers with an overhang of 2 m, the total monthly gains are 28.4% lower compared to variant 2. Variant 5, on the other hand, has energy gains that are 23.1% less than model 2. Focusing only on external breakers, variant 1 (1 m overhang breakers) provides 6.8% more total gains than variant 3 (2 m overhang breakers). This difference is, therefore, completely disproportionate to the cost of this cover and its impact on the aesthetic value of the façade.
Small differences in heat gains from lighting result from the fact that the hall was used mostly in the evening hours (7–10 p.m.) and only then illuminated by artificial light. The hours of closing the roller blinds assumed in the model, based on the information obtained, are independent of people being in the facility. They are operated by a technical employee who is present in the hall. So, between 9 a.m. and 3 p.m., even though the internal blinds are used, the lighting is not switched on (except on Sunday).
Considering the sum of internal gains for the whole month (
Table 4), in the hall building equipped with roller blinds and brise-soleils with a 2 m overhang, its value is 2304.0 kWh. The highest total gains from radiation, lighting, and people are 3027.8 kWh and are obviously related to the situation when no blinds were installed.
The arithmetic mean values of indoor air temperature are similar for all five simulation variants (
Table 5). The difference between variant 2, where the indoor air temperature is highest (23.2 °C), and variant 5, where the indoor temperature is lowest (22.6 °C), is only 0.6 °C. Averaged over the monthly simulation period, the radiant temperature is in the range of 22.8–23.5 °C, and the difference between the adopted modifications is 0.7 °C.
In
Figure 9, it is possible to observe the distribution of air temperature in the hall for the selected week and analyzed variants of window shading.
Figure 9 additionally added the upper limit of optimal operative temperature for cooling season equal 26 °C, in accordance with PN-EN ISO 7730: 2006 [
26], for low activities of users up to 70 W/m
2. As the graph shows, the disproportion between the thermal comfort limit temperatures, depending on the users’ metabolic rate, can be as high as 8 °C. It can be seen that microclimatic conditions, which are a considerable discomfort for athletes, may still be comfortable for inactive users.
The differences of 0.0–1.2 °C depend on the hourly interval and the day of the week and the related thermal loads of the building. The red dashed graph (variant 5) is characterized by the lowest values of internal temperature in relation to the remaining options. The greatest disproportion in values occurs between 1 p.m. and 3 p.m. due to the use of shading at that time.
The variability and irregularity in the way the hall is used have a decisive influence on the course of the internal temperature. An additional comparison of changes of indoor temperature and solar gains (
Figure 10 and
Figure 11) for the initial variant 1, in which the presence of people was not taken into account, explains the reason for these discrepancies. From Sunday to Monday, between 9 a.m. and 3 p.m., the blinds are closed, so the solar gains are then only 3 kW. On Saturday, the interior shades are not used, hence the significant jump to a value of 8.5 kW in the baseline variant and up to 18 kW in the case of variant 2, without brise-soleils,
Figure 8.
The significant rise of temperature on 01.07. at 3 p.m. is connected with the assumed tilting of windows on the southern side at that time and the gains from the inflow of warm air from outside (
Figure 12). On the other hand, the decrease in temperature inside the hall on 03.07. at about 7 p.m. is connected with the inflow of cooler outside air.
It should be added that the shading simulations use the window opening schedule assumed from the research, which is independent of the outside temperature. Airing in the morning and evening hours is a constant activity, not related to the presence of people. Analyses show that for hot summer days, natural ventilation should be avoided. Opening windows when outdoor temperatures are higher than indoor temperatures results in significant deterioration of indoor thermal conditions. Therefore, the following analyses present simulation variants in which the scheduled window opening is made dependent on the outdoor conditions. If the outdoor air temperature Tout is higher than the indoor air temperature Tint (Tout > Tint), the windows will be closed.
The adopted variants of shading the windows of the building were analyzed according to the criterion of the number of hours with the internal air temperature in the range of 14–18 °C and the temperature above the thermal comfort limit of the athlete. In each considered case, the number of hours with the air temperature above the thermal comfort limit of the athlete (18 °C) is absolutely dominant in relation to all hours in a month (95.8–98.8%).
Only 1.2–4.2% of all 744 h falls within the comfortable temperature range of 14–18 °C. Only the fifth variant, with the use of brise-soleils and impermeable blinds located on the outside, is slightly more favorable. In this case, the number of hours with air temperature within the thermal comfort range is higher by 3% than in the worst case, i.e., variant 1. Changing the parameters of the roller blinds in variant 4 increased the number of hours within the thermal comfort range almost two-fold, in comparison with the basic variant 1, but those effects are still insignificant and practically imperceptible for the user.
The distribution of PMV values for the selected weekly simulation balance is presented in
Figure 13. The graph for three selected days has been additionally enlarged for a more detailed analysis of the adopted variants.
The lowest values of PMV are found for variant 5 (dashed red graph), the highest for variant 2 (gray graph). The difference in PMV values for the extreme variants is about 0.2. The use of brise-soleils and the location of the blinds on the outside, and the complete reduction in solar transmittance proved to be the most effective. As with temperature, modifying the characteristics of the blinds in variant 4 did not significantly increase the number of hours of thermal comfort.
The number of hours for which conditions fall within the thermal comfort range for variant 2 and variant 1 is the same, at only 4 h. Only the number of hours with PMV > 2.0 (
Table 6) differs slightly for each variant. Even in the most favorable option, i.e., variant 5, in which the number of hours falling within the range −0.5 < PMV < +0.5 is the highest (24 h), it constitutes only 3.2% of all 744 h in a month. Therefore, it can be concluded that in the best variant, only one day in a month is fully comfortable, and during the other days, the users experience strong discomfort due to overheating of the building.
In view of the results obtained and the clear discomfort for all sunshade variants used, additional simulations were performed. The irrational schedule of closing the roller blinds, independent of the conditions assumed on the basis of the interview, raised significant doubts. Therefore, in subsequent analyses, the way of using the roller blinds was made dependent on the values of the indoor temperature and the intensity of solar radiation. The following variants were adopted:
Variant 1: assumptions as in point 3.2, roller blinds closed 9 a.m.–3 p.m. (except Saturdays)—this option has been included here only in order to be able to compare the applied modifications with the actual use of the facility;
Variant 2—blinds closed when indoor air temperature > 18 °C;
Variant 3—blinds closed when indoor air temperature > 21 °C;
Variant 4—blinds closed when solar radiation intensity > 100 W/m2;
Variant 5—blinds closed when solar radiation intensity >200 W/m2.
The solar radiation intensity values considered in the analysis were determined based on data from the Institute of Meteorology and Water Management IMGW and literature. In summer, the typical range of variation in the intensity of radiation on the horizontal plane is from 100 to 800 W/m
2 [
40]. The range of values 100–400 W/m
2 was analyzed, and the corresponding hours during the summer analysis period were examined. It was found that the protection against excessive gains makes sense only from the early morning hours, so in the detailed simulations, the threshold values of 100 W/m
2 (already present at around 4 a.m.) and 200 W/m
2 (around 6 a.m.) were kept.
The distribution of the indoor air temperature for the chosen week is presented in
Figure 14. Generally, it should be stated that making the shading control dependent on the ambient conditions did not obtain the expected significant improvement of the conditions in the hall. Individual variants also differ little from each other. The momentary differences in the obtained results are very small and amount to a maximum of 0.7 °C.
The variant, in which closing the blinds was conditioned by the maximum value of solar radiation intensity equal to 200 W/m
2, is the least favorable for the analyzed summer period and generates the highest temperatures in the hall (orange graph
Figure 14). Two out of the five applied variants practically overlay in weekly distribution. The yellow graph (irradiance > 100 W/m
2) and the gray dashed graph (t
a > 21 °C) do not show significant mutual differences in the course of the temperature in the hall but are more favorable in relation to the initial variant. The blue graph, reflecting the actually applied shading schedule from 9 a.m. to 3 p.m., is not, as can be seen in
Figure 13, the best solution for limiting direct radiation. The lowest temperatures are observed in variant 2 (green graph) when the blinds are closed at ta >18 °C. It is worth noting again, however, that the differences in internal temperature values between all the variants are negligible and not perceptible for the hall user.
The analysis of indoor conditions for the assumed variants also concerns the indicator of the predicted mean PMV,
Figure 15. On its basis, it would be necessary to resign from the fixed schedule of closing the indoor blinds (blue figure) and make their use dependent on the indoor air temperature (green figure = upper limit of the athlete’s comfort range).
It is worth noting that none of the adopted variants significantly improves the microclimate conditions inside the hall, and the momentary differences in PMV values in individual cases are so small (max. 0.2) that even the best option will not reduce the thermal discomfort.