Lighting profile

5.2.3 Lighting profile

Design guidelines recommended the provision of daylight in a space by employing the term daylight factor which was first proposed in the UK in early 1900s and included in building standards over fifty years ago (Hopkinson, 1963). The CIE overcast sky developed by The Commission Internationale de L‘Éclairage (CIE) which quite well models the completely cloudy skies in temperate climate such as the UK and western Europe are used in many daylight calculations (CISBE, 1999). The daylight factor is used to quantify the amount of diffuse daylight in a space and is measured at the height of working plane. This refers to the ratio of ratio of internal illuminance to unobstructed horizontal illuminance under standard CIE overcast sky conditions (i.e. 100% cloud

cover), expressed as a percentage. A space is said to be dimly lit with a mean daylight factor of less than 2% and between 2 and 5% is considered to be well lit and it will require little or no electric lighting during daytime (BSI, 2008). Meanwhile, it is suggested for dwelling space that the required average daylight factor is 2% for kitchen, 1.5% for living space and 1% for bedroom (BSI, 2008). Minimum daylight factors for these spaces are respectively 0.6, 0.5 and 0.3 determined as an estimation obtained by dividing the average daylight factor by 2.3 (CISBE, 1999). The average daylight factor could either be calculated by the formula given in (CISBE, 1999) or determined by simulation results. The IES<VE> FlucDL tool was used to provide day lighting analysis regarding daylight factor and daylight illuminance results. In such sky condition, the daylight will refer to the diffuse light from a whole overcast sky. The worst case for natural daylight is likely to be a completely cloudy sky in mid-winter and it could be improved under a partly cloudy or clear sky with sunlight. Mid-winter design date as the 21^st December with CIE overcast sky condition was selected for determining values of average daylight factors of different rooms. The mid-day (i.e. 12:00) of 21^st December under CIE overcast sky condition was selected to calculate average daylight illuminance levels on the working plane at 0.85 meters height above the floor level in five different spaces as the lowest illuminance levels as given in Table 5-4. For the design purposes, the working plane is defined at 0.85m above the floor level in industry and domestic buildings or 0.7m in office like a desktop height (CISBE, 1999). These daylight results were in comparison with the recommended maintained illuminance level (Table 1.5 in CIBSE, 2006a) which could be fulfilled either by daylight or artificial lighting or both with dimming option available for electric lighting for the purpose of lighting energy savings.

The comparison of the results in Table 5-4 and the required average daylight factor confirms that the clear glazed fenestrations of the building unit are well lit for their purposes and no artificial lighting is needed during the daytime. Thus, it was supposed that there is no need of artificial lighting in the premise during the daytime in weekends/holidays.

Table 5-4: Daylight illuminance on the 21^stDecember, CIE Overcast sky

Room Average daylight

factor, %

Average daylight illuminance, lux

Recommended maintained illuminance, lux

Living space 3.9 161 150 - 300 (kitchen area);

50 – 300 (lounge)

Bedroom 4 166 100

Hall 1.7 71 100

Bathroom 2.1 88 150

Office 2 83 300

Whilst considering the recommended range for maintained illuminance of the living space (See Table 5-4), an average illuminance level of 161 lux was deems reasonable since the day lighting level will be improved under partly cloudy sky or clear sky with the sun. Higher illuminance level would be preferable for kitchen area which could be fulfilled by the use of electric lighting. Also, the cooking activities was developed in occupancy profile to take place between18:30 and 19:30 daily during this period of time, the daylight maybe still available during summer time but not in winter time thus electric lighting is required. The same argument can be applied with the use of artificial lighting in the office during the occupied period between 21:00 and 23:00 and the bathroom between 7:00 – 7:30 and 20:30 – 21:00. For the bedroom, lighting was switched on for half an hour at night and another half an hour in the morning to ensure illuminance for personal preparation before and after bedtime. During these times, the room was either dark or dim so electric light was an obvious use. As shown in Table 5-4, the illuminance in the hall was below the recommended value thus the electric light might be required during the daytime in the weekend. However, whilst considering the occupation time assumed for the hall and the length of this circulation area, is was reasonable to assume electric light to be off between 8:30 and 17:30.

In order to specify sensible lighting gain as well as power consumption, if the required illuminance level is known, the parameter “installed power density” is employed. The installed power density per 100 lux is the power needed per square metre of floor area to achieve 100 lux of the average maintained illuminance on a horizontal working plane (IES, 2011a). Lighting power consumption in Watts was calculated by a multiple of lighting power density value (W/m² per 100lux), the maintained illuminance (lux) and floor area (m²) as shown in Table 6-5. The 2010 Approved Document part L for new dwelling requires 75% of the fitted luminaires to be low energy that provide luminous efficacy of 45 lumens per watt (lm/W) (DCLG, 2010a). For this requirement to be

applied, taking the living space as an example, to achieve the required illuminance of 200 lux (i.e.200 lumen per m²), the lighting power consumption to illuminate the floor area of 20.43 m² is 90.8 watts.

Meanwhile, a research study conducted by Centre of Energy and the Environment at University of Exeter showed that the installed lighting density of the notional building (as discussed in 2010 Approved Document part L) ranged between 2.2 - 2.4 W/m² per 100 lux. This finding was derived from the graph presented in the study showing the installed density lighting as a function of room geometry.(CEE, 2011). The lighting power consumption for the living space ranged between 90 and 98W. This agreed with previous calculation by using the installed power density of 2.2W/m² per 100 lux and was used to determine lighting power consumption for five rooms in the building unit (See Table 5-5). The hall was considered as the circulation area thus the presence of the building occupant was at low density and random time (see Section 5.2.1). When the day lighting is not available, electric lighting in the hall should be switched on and off in accordance to save energy. An assumption of lighting in use was as half as the occupancy time as stated in the table below.

Table 5-5: Lighting power consumption and usage pattern Room Installed 5.2.4 Heating profile

It is generally accepted in the UK that if the average outdoor air temperature is higher than the “base temperature” at 15.5°C, the building will not need to be heated. (CIBSE, 2006c). Figure 5-2 depicts the outdoor air temperatures over a year from the CIBSE TRY weather file. By using the base temperature reference as threshold value, the

heating period is selected between the months of October and May during which the outdoor air temperature is below 15.5°C.

The comfort range in domestic buildings is designed such that the operative temperatures are between 19 and 25°C (See Appendix A, Section A.4.3.1). In comparison with this criterion, the operative temperatures in the living space (e.g. grey line shown in Figure 5-2) were lower than the recommended level during the months between October and mid-April. This result would be higher as it excluded internal heat gains, thus the heating period might be shorter.

From this observation, the heating period was determined based on room operative temperatures during the time the room was occupied rather than based on generic outdoor temperatures threshold value (e.g. base temperature). This could be explained that the base temperature was a historical convention applied for UK conventional dwelling materials (e.g. concrete blocks or stones). New dwellings with good insulation reduces significant amount of heat loss whilst receiving additional heat gain through effective solar passive design that helps maintaining a warmer indoor conditions.

It is stated that The Fuel and Electricity (Heating) (Control) Order 1974 and The Fuel and Electricity (Heating) (Control) (Amendment) Order 1980 prohibit the use of fuels or electricity to heat premise above 19°C (CIBSE, 2006a). Hence, the room operative temperature was heated up to 19°C by a heating device though the comfort would be enhanced by additional heat sources from solar radiation and internal heat gain. A central heating system with time and thermostat control per room was assumed for the simulation development. This meant that the heating profile was established that the heating system in operation only if the room operative temperature was below 19°C and the occupant was at home. From the energy saving point of view, there was no need for heating during the bedtime so the heating was switched off at 23:00. Timer set was then at between 6:30 to 8:30 and 17:00 to 23:00 during weekdays and 6:30 – 23:00 in the weekend.

Figure 5-2: External air temperature and operative temperatures in main area 5.2.5 Domestic Hot Water consumption

Hot water in residential buildings is used for different purposes such as bath/shower, hand washing, clothes washing and dish washing (by hand or machine). According to English House Condition Survey data of consumed hot water for different usage levels for each appliance, a total average usage is of 49 litres of hot water per person per day.

Where, the average consumption of hot water across all households is 4 litres per person per day for washing machines and 35 litres per person per day for baths and showers.

An additional 10 litres of hot water is used for the cleaning of dishes at the sink and for hand and face washing (BIS, 2005).

Domestic hot water (DHW) consumption profile in litres/hour per person established in the model is of 6.65 litres/ hour per person for the living space during 4 hours occupied and 26.4 litres/ hour per person for shower and hand washing with 1 hours of use in total.