Twenty-five residential buildings were selected evenly over the five provinces of Kuwait (i.e. Capital, Hawalli, Aljahra, Alahamidi and Mobarak Alkabeir). The sizes of the selected buildings ranged from one to three floors with a plot area of 400 m². Whilst it was impossible to cover all residential building types in Kuwait in this study, those buildings selected were considered from the perspective of the following specific criteria:

・ Typical type, size and construction materials.

・ Selected buildings are not older than 10 years and distributed evenly amongst the five provinces of Kuwait.

・ Centralized air-conditioning with similar cooling size.

・ Openings, i.e. windows, doors, etc., are closed completely in selected surveyed building during filed experiments.

・ Buildings were selected based on the location schemes shown in Figure 1.

In this way, a reasonable sample of housing types from the Kuwaiti residential building stock is covered by this investigation.

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The subjective study involved collecting data using questionnaires which were given to each subject to complete simultaneously with collection of the physical measurements in each residential building. The subjective questionnaires and a description of the experimental work procedure had been translated carefully into the Arabic language in order that the occupants could follow and understand. The questionnaire addressed the following areas: 1) background and personal information; 2) current clothing garments; 3) subjective thermal sensation

vote (the Actual Mean Vote, or AMV) based on the ASHRAE-seven point scale and consisting of: (−3) cold, (−2) cool, (−1) slightly cool, (0) neutral, (+1) slightly warm, (+2) warm, and (+3) hot); (iv) humidity sensation, scaled as: (−3) very humid, (−2) humid, (−1) slightly humid, (0) neither humid nor dry, (+1) slightly dry, (+2) dry, and (+3) very dry. (v) Air movements’ sensation scaled as: (−3) very low, (−2) low, (−1) slightly low, (0) neither high nor low, (+1) slightly high, (+2) high, and (+3) very high.

The subjects were required to make only one choice from the scale for each question.

In addition to the subjective data collection, physical measurements were carried out in the 25 air-conditioned residential buildings using a Bruel & Kjaer Indoor Climate Analyser Type 1212. The physical measurements included transducers to measure dry bulb and wet bulb air temperatures, relative humidity, air velocity, and operative temperature. The transducers and data logging system were fitted into a trolley arrangement to collect indoor climatic data at a height of 1.1 m above the floor, as specified by ISO 7730 (2005) [6] for a seated person. This was performed while respondents completed the questionnaires. A period of fifteen minutes was taken prior to the measurements survey to explain and demonstrate the procedure of the field experiments to the subjects in each building. This contributed to allowing the subjects to achieve a steady state thermal balance with their surroundings. The data collection period lasted for 75 minutes in each building. During this period, occupants were asked to sit in the living room, and were limited to light activity movement, such as body parts movements of hands, feet, neck etc. The metabolic rate value used in this study was estimated to be 1.2 met as recommended by ISO-7730 [3] for sedentary activity. Five sets of measurements were taken each at 15-minute intervals.

Indoor Kuwaiti clothing ensembles are different from those of outdoor ensembles in terms of their appearance, thickness and colours. A checklist of Kuwaiti male and female garments shown as photographs and descriptive schemes of ensembles was provided to the occupants at the time of completing the questionnaire survey. A full description of male and female clothing ensembles and clothing insulation values were published in [11] and [12] , and were coded in ISO 9920 [13] . However, the overall average clothing insulation values used in this study were estimated to be between 0.65 - 1.3 clo, with a mean value of 0.9 clo, Table 1.

Table 1 provides a summary of the personal data from the 111 occupants in the survey, together with their clothing insulation values. Data are presented as the mean of the family occupants in each of the 25 households. Indoor climate measurements for the 25 residential buildings are presented in Table 2. Indoor air temperature values ranged between 18.8˚C - 28.7˚C with a mean value of 22.7˚C, and standard deviation of 0.8, whilst recorded indoor relative humidities ranged from 33.2% - 69.7% with a mean value of 43.5% and standard deviation of 1.97, Figure 2(a), Figure 2(b) show these data in histogram forms. Average indoor air movements varied between 0.01 - 0.38 m/s with mean value of 0.13 m/s and standard deviation of 0.03, whilst operative temperatures were in the range 20.2˚C - 27.6˚C, with a mean of 23.71˚C and standard deviation of 0.54, Figure 2(a). Table 2 also provides statistical summaries of thermal environments and thermal indices of occupants, with actual mean votes (AMVs) ranging from −1.2 to +1.5 with a mean of −0.28 and standard deviation of −0.33. Further analysis was conducted to find the indoor neutral temperature and thermal acceptability for the residential buildings, as may be shown in [1] .

The first and most critical step of IAQ investigation for preparing of data analysis and evaluation (step 3) of a building is walkthrough inspections. This method can help to clarify the most critical areas of the house design and may help to develop detailed on-site data collections (step 2).

Measurements of CO₂ concentrations level were carried out at different locations in the occupied zone within each house during occupant’s thermal comfort sensation measures. Three sampling points were selected in the occupied space with point 4 in an outdoor location. These measurements were performed as the respondents completing the thermal comfort questionnaires and during the data collection period. In addition to carbon dioxide concentration CO₂ measurements, air temperature, relative humidity and air velocity were measured at 5 min intervals which lasted for approximately 75 min for each house.

The collected data of IAQ are analyzed, based on the Concentration of carbon dioxide (CO₂) measures. Measured values of thermal comfort parameters are analyzed as in section 2 and tabulated as shown in Table 1, Table 2 and Table 3. In this section, measurements of CO₂ Concentration levels can be considered as an indicator of fresh air required in the space in terms of ventilation rate [5] . Table 4 gives for each house; mean concentrations of (CO₂), minimum, maximum, and standard deviation. The (CO₂) monitoring shows that concentrations vary from house to house and may be changed according to A/C type used, air tightness of enclosed space, window operation etc, and building location. The Concentration levels of (CO₂) were measured using a GE Telaire 7001 CO₂/Temperature Monitor.

The results of indoor CO₂ concentration levels for the surveyed Kuwaiti houses are between 598 ppm, as the lowest value and 1252 ppm as a highest value. However, CO₂ concentration for Zone D (house no. 24) exhibits higher mean concentration levels. The mean values in Zone D ranged between 790 ppm and 1250 ppm, while that in Zone A exhibits lower mean concentration level range ina between 598 ppm and 720 ppm. Meanwhile, the higher and lower CO₂ concentration levels for zone B (house no. 9) are 710 ppm and 935 ppm respectively, while that for zone C are 715 ppm (house no. 7) and 842 ppm (house no. 19) respectively.

Taken as a whole, the mean concentration levels of CO₂ in the buildings located in zone D is 42.6% higher than that in the buildings of zone A. As may be seen from Figure 1, the buildings located in zone A are detached building, which are location is open toward the street from three sides, promoting in leakage and dilution of outdoor air when windows are open. However, buildings located in zone D are attached to other buildings from three sides and open to the street from only one side, which may cause them to be affected less with outdoor fresh air. However, the mean CO₂ concentration level values of all surveyed buildings show that house no. 16 exhibits the highest value equal to 994 ppm, while that for house no. 6 exhibits the lowest value equal to 706 ppm. Thus, air-conditioned residential buildings in Kuwait during summer season are in spite of that, within the criteria limits of 1000 ppm, Table 4. However, air-conditioned residential buildings located as zone of D exhibit higher CO₂ concentration levels, which may require an engineer/architect to consider increasing the ventilation rate through window operation or may be using mechanical ventilation.