How energy efficient is the EEBC ? Evaluation based on a simulated office building

In this paper, we analyze the recently introduced "Energy Efficient Building Code (EEBC) for Commercial Buildings in Sri Lanka" for its applicability to Sri Lankan office buildings. The focus is on the building envelope and air conditioning requirements of the EEBC and their effect on energy saving. In order to this, we develop a "typical" multi-story office building designed as per the EEBC and simulate its energy and thermal comfort performances using a parametric energy simulation software. The results reveal that the application EEBC to Sri Lankan commercial buildings will actually increase energy consumption over the present scenario. Based on our analysis we recommend a set of improvements to the EEBC in terms of building envelope and set-point temperature requirements. Introduction Sri Lankan architects pay little attention to the energy efficiency aspects of commercial buildings in the present context. Compounding the problem is the lack of detailed guidelines / standards applicable to the Sri Lankan conditions. The recent introduction of an "Energy Efficient Building Code (EEBC) for Commercial Buildings in Sri Lanka" (EEBC, 2000) by the Government of Sri Lanka through the Ceylon Electricity Board (CEB), therefore augurs well for the "Demand Side Management" (DSM) efforts in the country. The EEBC was introduced by the Government of Sri Lanka in September 2000 for a trial period of three years. During this period, the performance of the EEBC will be monitored and changes, if any, to improve the code may be suggested by energy users. Although compliance with the code is voluntary at present, it may be made compulsory at the end of the review period. At this point, the scope of EEBC may be enlarged to cover other types of buildings as well. In this study, we simulate the air conditioning load and thermal comfort effects of the EEBC on a "typical" multi­ storey office building in Colombo to test the efficiency of the code. The "typical" building is specified in terms of wall, roof and window types; window: floor area ratio; floor-to-ceiling height; activity and occupancy level; usage of equipment, etc. Air conditioning (thermostat setting) and the building envelope standards (in terms of the Overall Thermal Transfer Value OTTV) of the code are analyzed in detail. Based on our results, we suggest some improvements to the code.


Introduction
Sri Lankan architects pay little attention to the energy efficiency aspects of commercial buildings in the present context.Compounding the problem is the lack of detailed guidelines / standards applicable to the Sri Lankan conditions.The recent introduction of an "Energy Efficient Building Code (EEBC) for Commercial Buildings in Sri Lanka" (EEBC, 2000) by the Government of Sri Lanka through the Ceylon Electricity Board (CEB), therefore augurs well for the "Demand Side Management" (DSM) efforts in the country.
The EEBC was introduced by the Government of Sri Lanka in September 2000 for a trial period of three years.During this period, the performance of the EEBC will be monitored and changes, if any, to improve the code may be suggested by energy users.Although compliance with the code is voluntary at present, it may be made compulsory at the end of the review period.At this point, the scope of EEBC may be enlarged to cover other types of buildings as well.
In this study, we simulate the air conditioning load and thermal comfort effects of the EEBC on a "typical" multi storey office building in Colombo to test the efficiency of the code.The "typical" building is specified in terms of wall, roof and window types; window: floor area ratio; floor-to-ceiling height; activity and occupancy level; usage of equipment, etc.Air conditioning (thermostat setting) and the building envelope standards (in terms of the Overall Thermal Transfer Value -OTTV) of the code are analyzed in detail.Based on our results, we suggest some improvements to the code.

Background
The main type of fuel used in Sri Lanka are bio-mass (including fuel wood, agro-waste), oil (petroleum, crude based) and electricity.However, sustained economic growth and a proliferation of rural electrification programs in recent years have led to a rapid increase in electricity demand in particular.Of this, the electric energy demand by the building sector is considerable.
During the recent past, the demand for electricity rose by 9.5% per annum.In 1999, the electricity demand during daytime was 864.5 MW while the nighttime demand was 1291 MW.Presently, electricity demand growth rate varies between 8 -10% per annum.It is forecasted that the Sri Lankan electricity demand will quadruple in the next 15years (CEB, 1996).In 1999, the installed capacity of hydroelectric power plants were 1143 MW and that of thermal plants were 545 MW.However, most of the economically viable hydro-electric potential has already been utilized.Moreover, periodic droughts and the changing climatic patterns (cf.Emmanuel, 1999) reduce the reliability of hydro-electric generation.This had led to severe brown outs in 1996 and 2001/2002.In this context, the last few years have seen the country gradually shifting towards thermal power generation.It is estimated that by 2014, 82% of the total electricity demand will be met by thermal power generation (Shrestha and Shrestha 1997).At the same time, the authorities are finding it very difficult to construct thermal power plants in the face of rising opposition from the citizenry on economic and ecological grounds.
Additionally, thermal electricity generation is a highly expensive process, one which the cash-strapped local utility authority (the Ceylon Electricity Board -CEB) can ill-afford: in 1996, the utility company spent about US$ 1,500 per kVA of thermal power generation (CEB 1996).Thus, economic and political factors make energy conservation an attractive option to the utility company.In this paper, we concentrate on the "Ventilation and Air Conditioning" and the "Building Envelope" aspects of the EEBC.The section below describes the standards stipulated by the EEBC in this regard.

Ventilation & Air Conditioning
Calculation Procedures: Cooling system design loads for the purpose of sizing systems and equipment are to be determined in accordance with the procedures described in the latest edition of the ASHRAE Handbook or other equivalent publications.
Indoor Design Conditions: The indoor conditions of an air-conditioned space to be designed for a dry bulb temperature of 24°C ± 1 °C and relative humidity of 55% ± 5%.The recommended dry bulb temperature is described as the "Set Point Temperature" in the discussions that follow.
Outdoor Design Conditions: Dry bulb temperature of 32°C and wet bulb temperature of 27°C.

Building Envelope
Solar heat gain through building envelope constitutes a substantial share of the cooling load in a building that will have to be eventually removed by the air-conditioning system at the expense of energy and utility bills.

Method
In this paper we evaluate the cooling load and thermal comfort performance of a typical" office building located in the city of Colombo and designed according to the "Ventilation & Air Conditioning" and the "Building Envelope" requirements of the EEBC.We design the "typical" building according to the EEBC and compare fts performance with a building of comparable complexity but designed with a superior (OTTV = 45 W/m 2 ) and an The hourly variations in internal loads are assumed to be distributed on the basis of the following time inferior (OTTV = 135 W/m 2 ) building envelope as well as a higher indoor set-point temperature (27°C).Based on the comparisons, a set of guidelines to improve the efficacy of the EEBC are suggested.
In order to define a "typical" office building in Colombo, we carried out a survey of contemporary multi-storey office buildings in the city, whose results are presented in Table 1 below.

Results & Analysis
In this section, we present the results obtained from computer simulation runs in terms of cooling load and thermal comfort.Cooling load figures (in kWh) are shown for the period of 07:00 -20:00 hrs.per day.It is assumed that the air-conditioning system will not be run during the rest of the day.The thermal comfort conditions are plotted for the same time period and are indicated in terms of the Operative Temperature (°C).As can be expected, a lower set-point temperature leads to higher cooling loads and therefore higher energy consumption for space conditioning.It is also clear from the above that lower OTTV lead to lower cooling load.A

Building Envelope Requirements
The fact that building envelope conditions could be made more thermally conducive in the Sri Lankan context without compromising thermal comfort suggests that the EEBC specifications in terms of OTTV need to be reviewed.
The analysis presented above suggest that reducing the OTTV value to 45 W/m 2 will lead to a minimum of 11% reduction in cooling load.But the question is, can such reductions be possible in the Sri Lankan context?Our preliminary analysis leads us to answer the question in the affirmative.
The primary determinants of OTTV are, wall type, window type, window area, window orientation and window overhangs.Among these, window area and orientation exert a disproportionate influence on OTTV than the others.By reducing the window area, locating windows predominantly in the north/south walls only, and shading the windows, the OTTV can be significantly reduced.Additionally, better window type (i.e.insulating glass or double glazing) and higher thermal mass in walls could play a role, albeit a small one, in reducing the OTTV.Taking the "typical" building described in Table 1 as an example, Table 4 shows the range of possible OTTV variations in the Sri Lankan context.The OTTV values in each row is calculated keeping all other parameters same as the "typical" building indicated in Table 1.Current thermal comfort practice in the region usually follows the more frequently used temperate climate thermal comfort standards.However, there is evidence that outdoor climate heavily influences human thermal comfort indoors, particularly in the tropics.In fact, the strongest evidence for adaptation to the outside conditions or acclimatization related to thermal comfort has come from the hot-humid areas.These studies seem to indicate that thermal comfort of those living in a hothumid environment has closer ties to their previous climatic experiences.To paraphrase Prins (1992), people in the hot-humid zone seems to put their minds and bodies to adapt to heat.Humphreys (1981), having analyzed over 50 thermal comfort studies utilizing over 250,000 subjects, found strong correlation between the reported comfort temperatures of these studies and the outdoor temperatures under which they were conducted.Auliciems in particular found the following linear relationship suggesting that the preferred temperature of human beings is directly related to outdoor conditions:

Auliciems (1983) and
T n = 63.7 + 0.31 (T 0 -32) (°F), where T n is thermal neutrality temperature and T 0 is the outdoor monthly average air temperature.
Considering the fact that outdoor conditions in Sri Lanka typically remain at about 32°C during the hot months, the above equation would imply that a thermal neutrality temperature of 27.6°C may be acceptable here.
It therefore seems reasonable to suggest that the setpoint temperature in the EEBC be raised up to 27°C.Up to 20% cooling energy savings may be realized by such an action.

Conclusion
The main findings of the present study may be summarized as follows: 1. Maintaining of the upper limit of OTTV to 90 W/ m z (as suggested in EEBC) is more energy consuming.
2. Reducing a building's OTTV through architectural means is practically possible without incurring much expenditure.
3. Approximately 20% of air conditioning energy use could be saved by increasing the set point temperature from 24°C -27°C.
Based on these findings we recommend that the upper limit of a commercial building's OTTV be reduced from 90 W/m 2 to 45 W/m 2 .Further reductions may be possible with a more secure economic future.It is also recommended that the set point temperature be increased to 27°C.
The existing commercial buildings also could be required to adjust themselves to suit the code and the standards for existing buildings could be relaxed and easily achievable.
This exercise has been carried out for three different OTTVs and their respective cooling loads.The "real" relationship of these two would be seen clearly if this experiment were conducted for a uch wider range of OTTV.Furthermore, a study on energy consumption throughout the year need to be conducted to gather the true picture of a building's energy consumption pattern.Other aspects not considered here, such as window angles, surface texture, surface color, overhang type and angle, consideration of adjoining buildings...etc.and their effect on OTTV also need to be analyzed.The present study is merely a first attempt at providing a framework for further analysis of the EEBC with a view to improve the energy efficiency of Sri Lankan buildings.More designers and engineers are encouraged to build on this platform to create a truly energy efficient building code that will actually save energy and provide vital economic and ecological benefit to the country.
percentages in parenthesis indicate the fraction of load assumed to be in actual use.The analysis is carried out in a typical middle floor (6 th simplified into the three occupied volumes and a ceiling floor).The comparisons are made using a parametric volume.All calculations and findings discussed hereafter energy simulation software (DEROB -LTH).For are of this "typical floor."computer modeling purposes the 'typical" building has been values, maintaining the same height and internal conditions (except the set-point temperature) and by changing the other factors like window area, materials of building envelope, orientation, dimensions and window overhangs.The other variable is the internal set-point temperature setting, the three models have been put under temperatures of 24°C (which is stipulated in EEBC) and 27°C for cooling load calculations.

Figure 1
Figure1shows the thermal comfort comparisons of the three OTTV values considered.Figure2indicates the same but for the two set point temperatures.

combination of lower OTTV and higher set-point temperature would enable our 'typical" building to consume approximately 28% less energy than a building that fulfills the EEBC reccmmertdatjons. IrresrjectJvedttebuM^ in set-point temperature will lead to approximately 18 -21 % reduction in the cooling energy requirements of a "typical" commercial building in Cdcmrx).Atthesametime,aninciease in set-point temperature will lead to an operative temperature rise of approximately 2.5°C, irrespective of the butcfing envelope conditions. In an already stressful climate such as that of Colombo, such an increase in OT may not be tolerated by all. On the other hand, manipulating the building envelope conditions provide greater opportunity for energy saving than the mere increase in set-point temperature. While up to 11 % saving in cooling load is possible with an OTTV reaticticnfrom 90 to 45 W/m 2 , no discernible drop in thermal comfort (OT differences < 0.5°C is detected; see also Figure 2). At the same time an increase in OTTV from 90 to 135 W/m 2 lead to greater increase in OT (07 -1.3°C). Thus, building envelope manipulation could not only result in signiftcarrt energy savings, they would do so with little or no noticeable drop in thermal discomfort. Figure 2: OT Comparisons across set point temperatures
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