Winter thermal behaviour

The Health Sector has a large glazed area facing the North that collects direct solar radiation in winter. The hourly sunlight projection on the wall of the North corridor entering through a window of the Health Sector, is shown in Fig. 4 for a winter day. The projection was calculated through the



software LuzSol [5], developed at Universidade Federal de Sao Carlos, Brasil. The openings are 2m width and 1m high. Because solar radiation reaches the half bottom of the wall most of the day, a dark colour painting is Fig. 4. Sunlight projection on a North wall recommended to increase the absorbed solar energy in of a window in the Health Sector (winter). winter.

Подпись: (b)(a)

Fig. 5. Hourly thermal behaviour of the Health Sector in typical winter day. (a) North and central thermal

zones; (b) South thermal zones.

The hourly thermal behaviour of the Health Sector is shown in Figs. 5 (a) and (b) for the North, central and South thermal zones. For a mean outdoor temperature of 10.7°C, the North corridor reaches a mean temperature of 15°C, with a maximum of 19 °C at 14PM (solar hour). The mean temperatures of the central offices are around 13°C, requiring small conventional air heaters to reach the comfort zone. The thermal swings are 8°C in the North corridor and 6°C in the offices. All zones facing South will require auxiliary heating (Fig. 5b). Only in clear sky days, when the solar irradiance reaches 10.6MJ/m2, the offices will not require auxiliary heating (Fig. 6a). A possibility to heat the central offices would be the use of the North corridor as a sunspace from which the hot air could be introduced by natural convection into the offices through little openings in the wall, that should be mechanically closed during the night.

This strategy was evaluated by the simulation of the building in a clear sky day. Two openings were considered in each office, one at floor level and the other at 2m height, near the ceiling. The openings sizes were 0.75m x 1m, that is, a 1% of the office wall area. When the vents are open (Figure 6b), the air temperature of the corridor and the offices are 1 °C lower and 1°C higher, respectively, than in Fig. 6a. Because the temperature in the corridor is still high, extract fans could be added to remove the air of the corridor and blow it within the doctors offices.

(a) (b)

Fig. 7 Hourly outdoor temperature, solar irradiance on horizontal surface (W/m2) and hourly temperature of
the thermal zones in the Development Sector for a winter day. a) Original design, b) an additional roof


In those days when the solar radiation approaches the monthly daily average value (7.93 MJ/m2), it will be necessary auxiliary heating because the direct solar gains are not sufficient to reach the thermal comfort. For any solar radiation value, southern rooms always require auxiliary heating.

The Development Sector needs auxiliary heating during the winter, because the solar heat gain is mostly collected only on East windows (the West windows are shaded by the surrounding buildings). Figure 7a shows the hourly thermal behaviour of this Sector: when the mean outdoor temperature is 10.7 °С, the mean indoor air temperatures are around 11.7 °C with thermal swings of 5°C. Between 10:00AM and 16:00PM, the outdoor air temperature is higher than indoors, and the maximum temperature is reached at 14:00PM. The office of the social assistant is the warmest

local because it is small and it collects direct solar gain, whereas the more cold local is the storeroom, that does not have direct solar gain. To reduce the auxiliary heat load in winter, two options were tested: an increase of the solar collection through clerestories in the roof, and a lowering of the thermal losses through the roof. The simulation of the first option, that is, the addition of glazed areas facing North in the roof showed no significant increase of the indoor air temperatures. The second tested option was the addition of a tight air chamber in the roof (with ventilation in summer), between the metal sheet and the thermal insulation. The results are shown in Figure 7b: in this case, with an outdoor mean temperature of 10.7°C, the indoor mean temperature is around 12.7 °С. Also it was observed that diurnal temperatures of several rooms increased behind the outdoor temperature. A greater indoor thermal amplitude is not a problem since the thermal behaviour of the building was significantly improved during the occupation hours. For example, the daily thermal amplitude of the classrooms is 9 °С, but during the occupancy period (8 AM to 20PM) it is around 5°C and the mean temperature is 15°C.