Thermal Comfort Evaluation of HDB flats

Transcription

1 Thermal Comfort Evaluation of HDB flats Objective Measurements For this study, empirical data on the thermal comfort parameters (i.e. room space temperature, velocity and relative humidity) was collected for the computation of the PMV and PPD thermal comfort index for the three flat types. The study shows that wind ventilation has a great effect on the interior comfort condition. This is evident from the diurnal variations of PMV values. Majority of the daily empirical indoor temperatures and humidity obtained inside the flat units do not comply with the comfort requirements defined in the ASHRAE Standards, yet the PMV scale variability of the interior condition stills falls within the comfort ranges of PMV +1.0 for large proportionate of the time. This is primarily due to the influence of the wind-induced ventilation, which helps to relieve the oppressive indoor condition. It is due to the effect of the air flow speed that the value of PMV decreases to the comfort ranges. On the other hand, the impact of wind can be so strong that it brings undesirable coldness into the unit. This is primarily reflected in the maisonette (door opened condition), which pushes the PMV to the extreme limit and PPD to the highest. This represents the more extreme situation. However, nonetheless, ventilation is still a promising tool to cool the interior housing in our hot, humid climate, which always poses the difficulties in achieving a thermally comfortable environment indoors. Hence, cooling is much needed during daytime to counter the radiant heat form the searing heat of the sun. Conversely, the average maximum relative humidity occurs during the midnight hours. Cooling is needed during these hours to counter the high RH in the air, which is not conducive for comfortable sleep. Subjective Measurements The main objectives of this part of the study are to investigate the occupants perception of the degree of comfort in HDB flats and to examine the adaptive behavior of the residents on the usage of available climatic controls in modifying the indoor thermal environment. Questionnaire surveys on thermal comfort were carried out in four housing estates between June and September The assessment of the thermal environment in HDB flat was based on the occupants votes on thermal sensation (ASHRAE scale /Ts) and comfort perception (Bedford scale/tc). One further five-point scale specifically addressing perceptions of occupants on air movement sensation (wind sensation) was also used. In naturally ventilated buildings, when air

2 temperature and humidity of indoor air is almost impossible to be modified, it is believed that only higher wind speed can create higher thermal comfort satisfaction. The main objective is to highlight the variations in the comfort perception of the occupants using the ASHRAE and the Bedford scale and attempt to link them to the adaptive behaviour of the residents. The survey also collected data about the resident s personal adjustment (clothing, drink etc), and assessed their behavior in modifying the indoor thermal environment through the use of air-conditioning, fan and windows. The purpose of this collection is to find out the occupant s preference to create more comfortable thermal environment through the day inside their tropical residences. A comparison of both direct and indirect assessments of comfort reveals that the indirect methodology registered thermal responses over a broader range on the ASHRAE scale than using the direct assessment (Bedford scale). The relatively high percentage acceptability (i.e. 82.6%) suggests that the occupants are generally satisfied (i.e. feel comfortable) with their thermal environment even if their TS votes are outside the central three categories of neutral comfort zone. This finding is also supported by the low correlation in the linear regression of TS against TC, and the analysis showing the cross tabulation of the ASHRAE thermal sensation and Bedford comfort sensation. Findings show evidence that occupants are naturally acclimatized to the local hot and humid climate conditions. In terms of the use of climatic control to modify the indoor environment, it is found that the opening of windows and usage of fans are high in both the afternoon and evening. The high usage of air-conditioning for night hours is observed though satisfactory results from the direct measure of subjective responses on percentage thermal acceptability of environment show no justification for such high level of usage. Finally, these findings can also be useful for the future planning of high-rise housings in Singapore. The results indicate that the differences in the thermal comfort perceptions between flat types and floor levels are minimal (less than 10% in most cases). However, the strong correlation between the thermal comfort perception and wind sensation reveals that more critical considerations should be given to the layout and window opening area of the building design, which can create the preferred higher air movement (wind) and thus increase the thermal comfort of the residents.

3 % observation Thermal comfort acceptability on different flat types Mean ASHRAE (ashrae and Bedford scale) 3-room : room : 0.68 mais : 0.34 Mean Bedford 3 rm (Ts) 3 rm (Tc) 4 rm (Ts) 4 rm (Tc) Mais (Ts) Mais (Tc) (-3,-2) (-1,0,+1) (+2,+3) vote scale Wind Sensation votes for different flat types % Observations Wind Sensation Mean Wind Sensation 3-room : room 4-room Masionette Figure Error! No text of specified style in document..1 a-b Thermal comfort and wind sensation for different flat types

4 Thermal comfort (TC) Comparison of TS vs TC y = x R 2 = Thermal sensation (TS) Figure Error! No text of specified style in document..2 Regression of Thermal Sensation (TS) against Thermal Comfort (TC) Go out Aircon Frequency of Adaptive Behavior in Thermal Comfort Adaptive actions Fan Window Drink Clothing Bath Percentage (%) Always Most likely Often Seldom Very unlikely Figure Error! No text of specified style in document..3 Adaptive Behavior in thermal comfort perception

5 Profile of PMV in a 3-room unit over time (door opened) a.m PMV living room bedroom 2 bedroom 1 kitchen Figure Error! No text of specified style in document..4 Diurnal variation of PMV (3 room, doors open) Profile of PPD in a 3-room unit over time (door opened) PPD a.m living room bedroom 2 bedroom 1 kitchen

6 Figure Error! No text of specified style in document..5 Diurnal variation of PPD (3 room, doors open)