e-ISSN: 2550-1461 https://ijeisr.net
THERMAL PERFORMANCE INVESTIGATION OF SINGLE-STOREY TERRACE HOUSE IN TROPICAL CLIMATE
Fahanim Abdul Rashid1 Mahanim Abdullah Sadali2
Nur Hidayah Rosman3
1Department of Civil Engineering, Politeknik Port Dickson, Malaysia (E-mel: [email protected])
2Department of Civil Engineering, Politeknik Port Dickson, Malaysia (E-mel: [email protected])
3Department of Civil Engineering, Politeknik Port Dickson, Malaysia (E-mel:[email protected])
Abstract: This paper investigates the building thermal performance of terrace house in tropical climate. An experimental study of residents’ thermal comfort in a naturally ventilated intermediate single-storey terrace house was carried out at Taman Seremban 3, Negeri Sembilan. An intermediate single-storey terrace house was chosen as a case study and indoor thermal condition measurements were recorded for 72 hours. The indoor ambient temperature and air speed were measured using on-site monitoring equipment to evaluate the thermal performance of this house. A questionnaire survey was also conducted involving all occupants to determine their thermal comfort perception of the same case study house. The aim of this study is to analyse the indoor thermal condition of an intermediate single-storey terrace house in order to improve building design to climatically adapt to the local climate. The results showed that this house is thermally uncomfortable and the indoor thermal condition was between 2.70C to 5.90C higher than the suggested temperatures stipulated in ASHRAE Standard 55.
Keywords: Thermal Comfort, Building Thermal Performance, Terrace House
1. INTRODUCTION
In recent years in Malaysia, the residential building industry has recently experienced exceptional growth to meet consumer demand but without much focus on the improvement of building thermal comfort. Thermal comfort was described by ASHRAE (2020) as “condition of mind which express satisfaction with the thermal environment and is assessed by subjective evaluation”. Overheated and poor thermal comfort in residential buildings lead to unhealthy thermal environment and affect occupants’ wellbeing and quality of life. According to a previous survey, people spend over 80% of their lives indoors (Wei et al., 2007). Indoor environment for residential buildings should provide healthy, comfortable and safe condition as much as possible. Previous studies have shown that occupants who are satisfied with their thermal environment will increase their productivity by 15% (Kim et al., 2007). According to Fanger (1972), a person who live in comfortable thermal condition, can achieve his maximum potential of intellectual performance and perception.
However, earlier surveys also reported that the number of occupants who installed air- conditioning in their homes had increased tremendously (Sadafi et.al., 2011; Kubota et.al., 2009). Poor thermal comfort forced the occupants to look at air-conditioning as an alternative and a quick solution in order to improve the indoor thermal condition and achieve thermal comfort (Kubota et.al., 2009). Findings revealed that 40% of energy use in buildings are mostly for cooling, lighting, heating and electrical equipment (Chan et.al., 2009; Saidur et.al., 2007).
Due to continuous trends of rising air conditioning usage, Malaysia’s energy consumption is anticipated to climb steadily. Residential buildings’ electricity consumption increased dramatically from 1.28 billion kWh in 1978 to 24.73 billion kWh in 2012 (Malaysia Energy Comission, 2012). Therefore, this study analyses the indoor thermal condition of an intermediate single storey terrace house in Seremban 3, Negeri Sembilan to identify the sources of thermal discomfort.
Malaysian Climatic Condition
Malaysia has a tropical climate, which is described as warm and humid climate. It is located within 20 30’ North latitude and 1120 30’ East longitude. The climatic elements categorized as high relative humidity, excessive rainfall and plenty of sunshine. It is also monsoonal in nature with distinctively dry and wet seasons. The average daily maximum temperature is 340C and average daily minimum temperature is 230C (Al-Tamimi et.al.,2011). The annual mean temperature is 26.40C and the annual relative humidity ranges between 75% and 86%. The average rainfall distribution over the country is recorded from 2500 mm to 3500 mm.
On average, Malaysia receives high solar radiation approximately 400 MJ/m2 to 600 MJ/m2 every month. Malaysia experienced the highest solar intensity during the Northeast monsoon while the lowest solar intensity during the Southwest monsoon. The combination of high global radiation with inconsistent and low wind speeds resulted in many houses getting overheated internally, especially from February to June.
Terrace House
Since 1960’s, terrace houses in Malaysia have been constructed ubiquitously due to the consistently large demand for housing. This significant housing demand was caused by rapid urbanization where people moved from the rural areas to the cities. The most prevalent type of housing typology in Malaysia is the terrace house, which made up 41.4% of the Malaysian existing housing stock in 2014 (NAPIC, 2014). It is also known as the ‘row house’ which is formed in rows and with fire-proof party walls (Ju et.al., 2010). Typically, it is repetitively and monotonously built on rectangular lots with distinct boundaries, with a deep plan and narrow frontage (Hashim et.al.,2008).
Despite vast numbers of terrace houses in Malaysia, the typical characteristics of terrace houses remained the same for the past few decades. Previous studies revealed that many terrace houses in Malaysia have not been constructed in accordance with the local climate and do not meet the requirements for thermally comfortable indoor environments (Ju et.al., 2010; Sadafi et.al., 2008). Numerous Malaysian terrace houses suffer from overheating due to excessive solar radiation penetrations in tropical climate, contributing to the poor indoor thermal condition. Solar radiation is indeed the main source of heat gain in terrace houses, since their large roofs are exposed to the sun throughout the day. Furthermore, additional heat is transferred to external walls and window panels by through conduction, convection and radiation (Aun et.al., 2009). Unfortunately, the terrace house overheats as a result of this
excessive solar energy absorption, which makes the occupants uncomfortable (Sadafi et.al., 2011).
The indoor thermal condition of these houses need to be more thermally comfortable and habitable because the occupants spend a large amount of time at their home. Regardless of the prevailing ambient condition, the human body must be kept in thermally comfortable zone (Schaudienst et.al., 2017; Wei et.al., 2010). A standard thermal environmental conditions for human occupancy has been established by ASHRAE (ASHRAE Standard 55) which is determined by various factors including air temperatures, humidity, air velocity, metabolic rate and clothing. This study focuses on environmental factors which are air temperature, relative humidity and air speed as parameter controls for the intermediate terrace house typology.
2. RESEARCH METHODOLOGY
This study’s primary research approach was a field experiment which was conducted in Taman Seremban 3, Negeri Sembilan. This field study was carried out for 72 hours at a selected single storey intermediate terrace house. The HOBO U12 data loggers and HOBO T-DCI-F900-S-O air speed sensor were used to measure the indoor temperature, air speed and relative humidity.
In order to record the indoor temperature and relative humidity, a HOBO data logger was installed in the living area. At the same location, a second data logger was installed with a HOBO air speed sensor in order to record indoor air speed. For 72 hours, the data loggers were programmed to record datai every minute.
A questionnaire survey was also conducted involving all nine occupants of the selected case study house to determine their thermal comfort perception. This questionnaire survey bases its representation of the comfort preferences of the occupants on the ASHRAE thermal sensation seven-point scale.
Figure 1: Floor Plan of Case Study House
An intermediate single storey terrace house in Seremban 3, Negeri Sembilan was selected as the case study for this research. It is located in a large housing development. The floor area of this house is 105 m2. Figure 1 represents the floor plan layout of this house, which includes four bedrooms, a living room, a dining area, two bathrooms and a kitchen. The entire house has natural ventilation. It was constructed with a reinforced concrete structure, 200 mm thick of party wall, cement brick walls and a reinforced concrete floor slab. The roof was built with cement roof tiles on the galvanized iron roof structure. Figure 2 illustrates the front
elevation of the case study house. The front elevation of the house was designed with 3 panel sliding door and 2 panel aluminium casement windows.
Figure 2: Front Elevation of Case Study House
3. RESULTS AND DISCUSSION
Figure 3 illustrates the results of measuring the indoor temperature of the house for 72 hours.
The highest indoor temperature measured throughout these 72 hours of observation is 31.400C.
Within every 24-hour cycle, the indoor temperature of the house rises gradually after 10 am and reaches its highest levels between 3 pm and 4 pm in the afternoon. On the other hand, the lowest indoor temperatures of this house were recorded from 8 am to 9 am with respective readings of 29.410C, 28.90C and 28.20C in each 24-hour period. However, most of the measured indoor temperatures were higher than the ASHRAE Standard 55 comfort level. This poor condition was observed mostly in the afternoons until late evenings when this house experienced overheating. This is due to the fact that the building fabric has a large thermal mass capacity which stores heat gained during the day which was then re-radiated into the internal rooms until late evening. As a result, thermally comfortable temperatures were not observed at this house.
Figure 3: Indoor Temperature
Figure 4 shows the indoor air speed of the house which varies from 0.05 m/s to 0.36 m/s and peaks in the afternoon of each 24-hour cycle. The indoor air speed tends to be lower as compared to the outdoors. In accordance with ASHRAE Standard 55, the average air speed
in this house is 0.18 m/s which is below the range of recommended air speed. In this instance, the inadequate indoor air speed is caused by the long deep plan design of this house, obstructions by internal walls and insufficient fenestrations, which limit cross ventilation for air movement and air exchange rate. This condition caused the house to overheat during the daytime due to poor ventilation and negligible indoor air movement.
Figure 4: Indoor Air Speed
Figure 5 indicates the relative humidity distribution in the house over the 72 hours observation period. The graph demonstrates that the relative humidity fluctuates within the range from 65.5% to 81.8%. The highest relative humidity for this house is 81.8%, which occurred between 7 am and 8 am. It is evident that when the indoor temperature dropped to the lowest point, the relative humidity rose dramatically. It also indicated that the combination of temperature and relative humidity were above the comfort zone as specified by ASHRAE Standard 55. This condition happens most likely due to the porosity of the building envelope.
Figure 5: Indoor Relative Humidity
In addition to the indoor environmental monitoring, a questionnaire survey was also conducted and Figure 6 illustrates the results of the occupants’ thermal sensation. It shows that the majority of the occupants voted ‘slightly warm’ sensation and ‘warm’ sensation. According to ASHRAE Standard 55, at least 80% of occupants’ vote have to be within the central range of 0 (neutral), 1 (slightly warm) and 2 (warm) of the thermal sensation seven-point scale. In this case five (5) out of eight (8) occupants or 62.5% of occupants responded either ‘neutral’
or ‘slightly warm’. As a result, this case study house is perceived as thermally uncomfortable.
Figure 6: Thermal Sensation Vote
These results demonstrate that the poor thermal performance of the house caused the occupants to experience uncomfortable and overheated throughout the day. The poor thermal performance of the house is mainly because its heavyweight construction (cement bricks wall and reinforced concrete floor slab) which absorb and store a lot of heat energy from direct solar penetration during the day and release heat into the house throughout the night (figure 7). In addition, limited diurnal range in tropical climate will keep the house stay warm and uncomfortable, since heavyweight thermal mass is not beneficial where there is a small difference between day and night outdoor temperatures. As a result, it is crucial to take into account the type of construction system and local climate adaptation strategies, in order to maintain comfortable indoor thermal condition, reduce the overall heat load and ensure that the occupants achieve thermal comfort in their surroundings.
Figure 7: Thermal Mass To Absorb Heat During The Day And Release By The Night Source: (Reardon et.al., 2013)
According to Fanger (1972), variations of air temperature have greater influence on comfort condition in comparison with higher air velocity. Nevertheless, air movement will help to dissipate and discharge stale and warm indoor air. The indoor air speed can be increased by opening windows and doors throughout the 24-hour cycle leaving the high level glass louvers unobstructed. This could also improve dissipation of heat by stack effect through the high level glass louvers and increase the air change rate (Kim et.al., 2007). Installing large openings on all external walls will also aid in increasing the air change rate per hour and not obstruct air flow whenever opened.
Alternatively, installing a layer of insulation underneath the existing cement tile roof and on the external walls will reduce gained heat transfer into the house from the heavy building
envelope construction. The researchers also could incorporate architectural features to this house without making significant changes to the existing house by utilising building performance modelling and simulation software such as the Integrated Environmental Solution (IES-ve).
4. CONCLUSION
This paper presents analysis on thermal condition of the case study for 72 hours through on- site field measurements. According to recorded results, none of the indoor thermal condition parameters were in compliance with the ASHRAE Standard 55. The study found that the average temperature, average air speed and average relative humidity were out of the ASHRAE comfort range. This is reflected by the thermal comfort perception of the occupants who felt discomfort and overheating. All in all, comfortable indoor temperatures must be maintained in order to provide a comfortable thermal condition for the occupants of the house. Therefore, the researchers proposed the incorporation of climatic design approaches with consideration of the local climatic condition, the understanding of heat transfer, thermodynamics and thermal comfort perception.
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