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Energy characteristics and savings potential in office buildings
Solar EnergyVol. 52, No. I, pp. 59-66, 1994
0038-092X/94 $6.00 + .00 Copyright © 1993 Pergamon Press Ltd.
Printed in the U.S.A.
E N E R G Y CHARACTERISTICS AND SAVINGS POTENTIAL IN OFFICE BUILDINGS M. SANTAMOURIS,A. ARGIRIOU,E. DASCALAKI,C. BALARAS,and A. GAGLIA Laboratory of Meteorology, Department of Applied Physics, University of Athens, Ippokratous 33, 106 80, Athens, Greece Abstract--The present paper reports the findingsof a monitoring campaign in 186 officebuildingsin Greece. The specific energy consumption of the buildings for heating, cooling, and lighting purposes, as well as the consumption of the officeequipment is reported. The impact of the used systems,techniques,and components is investigated. The potential and the limitations of various energy conservation systems and alternative techniques is assessed. The present study provides useful information for efficientenergy planning, as well as appropriate design and equipment selection, in office buildings.
1. I N T R O D U C T I O N
building engineers in order to choose energy efficient systems and techniques applicable to office buildings.
Residential and commercial buildings consume more than one-third of Europe's primary energy budget. Commercial buildings, and primarily office buildings, are classified among the buildings presenting the highest energy consumption. Typical primary energy values for offices in Northern Europe, [1], fall between 270 and 350 kWh per year and m 2. Energy in office buildings is consumed mainly for heating, cooling, and lighting purposes, while a significant portion is devoted to the consumption of office equipment. Application of energy conservation techniques, as well as use of solar or ambient alternative energy sources in offices, require knowledge of the specific energy characteristics of the buildings. The frequency distribution of the building's final energy con: sumption, the specific energy requirements for each type of use, and the characteristics of the installed systems are amongst the necessary information. In order to assess information on energy consumption and identify the main energy characteristics, as well as the potential for energy conservation in office buildings in Greece, an extensive campaign based on short monitoring techniques has been designed and executed. Detailed data from 186 representative office buildings from around the country have been collected and analyzed. The potential effectiveness of various energy conservation techniques has also been assessed, taking into account the specific limitations for each building. The aim of this paper is to describe the energy consumption characteristics of the office buildings in a representative Southern European country, to provide specific information on the potential for energy conservation, and, finally, to investigate the technical, environmental, and social limitations of the existing technologies for energy conservation. The results of the present study provide the necessary information to energy planners in order to effectively design energy conservation policies. It can also provide useful knowledge to building designers and
2. M E T H O D O L O G Y
Short monitoring of buildings has been performed by a trained panel of engineers using standard reporting forms and an extensive questionnaire addressed to the building occupants. The following information has been collected from each building: 1. General information about the occupants and the building: this include the name, address, legal status, owner, the construction year, the number of stories, the heated surface and volume, and the daily occupation profile. 2. General and specific information about the building envelope: for each side of the building, the orientation, the vicinity with heated or unheated space, and the type of glazing and shading were recorded. A detailed description of each exterior building element, walls, ceiling, and floors was also included. 3. Information about the heating, cooling, and lighting systems. Here, the type, the power, and the operational profile was recorded. The duration of the heating and cooling period, the control type and the set points, as well as the maintenance policy were also noted. 4. Information about the office equipment. The type and the power of the used office equipment was recorded in each building. Also, information about specific appliances like water heaters, refrigerators, fans, and pumps were collected. 5. The energy consumption of the building. The quantity of every type of fuel and the consumed electricity in each building was recorded. The exact data were taken from the monthly electricity and fuel consumption official receipts kept in each building. In parallel with the standard forms, a specific questionnaire was designed in order to collect information 59
60
M. SANTAMOURIS el
about the thermal comfort and the indoor air quality inside the office buildings. The opinion of the occupants regarding the thermal comfort inside the building during the heating and the cooling seasons was separately recorded. The seven steps of the thermal comfort scale proposed in [2] were used. To study the applicability of natural ventilation techniques in high density urban areas and the impact of office equipment to the indoor air quality of the buildings, a specific study has been carried out. This investigation has been executed in 30 buildings located in the central Athens area. Two questionnaires were used for this purpose. The first one dealt with the outdoor and indoor air quality perceived by the visiting staff. The questionnaire and the methodology proposed in [ 3 ] has been used to collect this type of information. The purpose of the second questionnaire was to record the health symptoms of the building occupants to investigate the impact of the used energy options, and more generally of the indoor and outdoor environment, to the occupants' health. For this purpose, the questionnaire and the methodology proposed in [4] for office buildings has been used. A data base has been created using the information recorded from all the buildings. The collected primary data have been analyzed in order to identify the energy characteristics of the office buildings in Greece and then to assess the applicability, potential, and limitations of some important energy conservation techniques and use of high efficiency energy systems. Energy savings calculations are based on the assumption that the building operates inside the standard ASHRAE thermal comfort zones during the heating and cooling period. Also, the visual comfort standards for office buildings are used. 3. ENERGY CONSUMPTION OF OFFICE BUILDINGS
The audited office buildings have been classified in the following five groups based on the utilized energy systems: 1. Group A includes the whole set of buildings. In total, 186 buildings have been audited. 2. Group B includes only the buildings that are equipped with conventional air conditioning systems. In total, 89 buildings or 48% of the total number of buildings were included in this group. 3. Group C includes only the buildings that are equipped with electrical heating systems. In total,
al.
29 buildings or 16% of the total number of buildings were included in this group. 4. Group D includes only the buildings that are equipped with both an electrical heating system and an A / C system. In total, 24 buildings or 13% of the total number of buildings were included in this group. 5. Group E includes only the buildings that are equipped with a combustion fuel based heating system. In total, 153 buildings or 82% of the total number of buildings were included in this group. The characteristics of a sixth group, F, including the "nonAC buildings" have been also analyzed. The annual energy consumption per square meter of building for each one of the above groups as well as for each specific energy use is given in Table I. The mean energy consumption of the office buildings is close to 187 k W h / m 2. The frequency distribution of the annual energy consumption of all the office buildings, is shown in Fig. 1. Accordingly, 39% of the office buildings have an energy consumption lower than 100 k W h / m E, while for 36% of the buildings the energy consumption ranges between 100-200 kWh / m E. The electrical energy consumption for 44% of the office buildings is lower than 50 k W h / m E, while for 24% of the buildings it ranges between 50-100 k W h / m 2. The thermal energy consumption for 45% of the office buildings is lower than 50 k W h / m E, while for 22% of the buildings it ranges between 50-100 k W h / m 2. Over half of the total energy consumption (50.8%) is consumed for heating purposes, while 10.7 and 12.6% are consumed for lighting and cooling purposes, respectively. Also, 25.9% of the total consumption is due to the office equipment and the other electrical equipment in the office buildings. Buildings that are equipped with air conditioning systems (Group B) exhibit a mean annual energy consumption increase of about 226 k W h / m E. In this case the percentage for the heating and cooling of the buildings are 44 and 15.6%, respectively. Similar figures are also obtained for buildings equipped with an electrical heating system (Group C). Buildings equipped with a conventional A / C and an electrical heating system (Group D) exhibit the highest energy consumption, reaching a value equal to 250 k W h / m 2. In this case, heating represents 37.5% of the total energy consumption, while for cooling this corresponds to 17.5%. The total energy consumption of the buildings
Table 1. Energy conservation of the buildings (kWh/m2)
Group A Group B Group C Group D Group E Group F
Lighting
Cooling
Heating
Office equipment
Total
24 25 21 23 22 15
20 36 36 44 15 0
95 99 90 94 101 100
48 66 78 89 50 34
187 226 225 250 188 149
Energy-savingpotential in offices +
(%)
+
100
100
80
80
60
60
40
40
20
20
0
i
i
i
i
170
340
510
680
61
N/V
z~
A/C
ol 0
850
170
340
510
680
850
(W/S.M)
(W/S.M)
Fig. 1. Cumulative distribution of the annual energy consumption in kWh/m 2 for all the monitored office buildings.
Fig. 2. Cumulative distribution of the annual electric consumption in kWh/m 2 for the naturally ventilated and the air conditioned office buildings.
equipped with a combustion heating system (Group E) is close to 188 k W h / m 2. Approximately 27% is consumed by the office and other electrical equipment, while for satisfying the heating, cooling, and lighting requirements of the buildings the consumed energy in each case represents 53.4, 8. l, and 11.9%, respectively. Finally, the total energy consumption of the "'nonAC" buildings, group F, is close to 149 kWh per square meter. Almost 67% of the annual energy is consumed for heating purposes, while almost 10% is the lighting consumption. Also, 23% is used by the office and other electrical equipment.
office building stock in the country. It is found that insulated buildings in Athens present a mean annual energy consumption for heating purposes close to 81 kWh/m 2, while the corresponding consumption of the noninsulated buildings is approximately 23% higher, with a value of 100 k W h / m 2. The cumulative distribution of the annual energy consumption for heating purposes given in Fig. 3 for insulated and noninsulated buildings shows that 80% of the insulated buildings and 70% of the noninsulated buildings present a heating consumption less than 100 k W h / m 2 per year. The type of devices used for lighting determines the corresponding energy consumption of the office buildings. The overall analysis has shown that 155 buildings use fluorescent lighting devices, 19 buildings use both fluorescent and incadescent lights, and 12 buildings use only incadescent lights. However, the specific energy consumed in every building for lighting purposes also depends on other factors, like the percentage of used daylight and the lighting schedule of the building. Therefore, a comparison between the lighting consumption of the various buildings should not be attempted. On the other hand, it is very useful to know
4. A N A L Y S I S O F S P E C I F I C P A R A M E T E R S
The use of conventional cooling systems is a major source of energy consumption. To analyze the impact of air conditioning to the overall energy consumption of the office buildings, a comparison has been performed between the naturally ventilated and the air conditioned buildings. The mean annual energy consumption of the naturally ventilated ( N / V ) buildings is close to 179 k w h / m 2 while the corresponding consumption for the A / C buildings is 226 k W h / m 2. Subsequently, the use of A / C in office buildings increases the annual energy consumption by approximately 4050 k W h / m 2. A comparison of the cumulative distribution of the electrical consumption of the N / V and A / C buildings is shown in Fig. 2. It is calculated that 55% of the naturally ventilated and 43% of the A / C buildings, present a total electrical consumption lower than 50 k W h / m 2. In addition, 80% of the N / V and 67% of the A / C buildings present an electrical consumption lower than 100 k W h / m 2. To examine the impact of thermal insulation on the buildings' energy consumption, a separate analysis has been performed for buildings with and without thermal insulation. Insulation in buildings has been obligatory in Greece since 1979. Insulation levels are determined as a function of the surface-to-volume ratio and the climatological zone. The overall study has been performed in 136 noninsulated and 50 insulated buildings. This sample is almost representative of the
LIGHTING - -
CONSUMPTION
(%) E~.JILDINS
100
J
i
0
10
20
30
40
50
60
K WH/M2
Fig. 3. Cumulative distribution of the annual electric energy consumed for lighting purposes, in kWh/m2.
62
M. SANTAMOURIS el a/.
the distribution of the lighting consumption of the buildings. Figure 3 shows the cumulative distribution of the electrical energy consumption for lighting purposes in all the audited office buildings. Accordingly, 50% of the buildings present a lighting consumption less than 11 k W h / m 2, while for the majority of the buildings (86%) the consumption is less than 20 k W h / m 2. Energy consumption by the office equipment represents an important part of the building's energy budget. According to the international experience, the mean installed power of equipment in office buildings is close to 10 W / m 2, [5]. However, for highly computerized offices, the installed power can reach values close to 100 W / m 2, [ 5 ]. The cumulative distribution of the installed power in the audited buildings is given in Fig. 4. As shown, 60% of the buildings are below 20 W / m 2, while 80% of them are below 30 W / m 2. As has already been mentioned, the mean annual consumption of the office equipment is calculated close to 35 k W h / m 2. This amount includes the energy used for vertical transportation, (7 k W h / m 2) and the energy consumed for hot water purposes (0.6 kWh/m2). When energy statistics are limited to air conditioned and highly computerized buildings, the specific energy consumption of the office equipment increases dramatically and approaches values close to 64 k W h / m 2.
5. ENERGY SAVINGS FOR LIGHTING
An analysis of the collected data has shown that important energy reductions can be achieved in office buildings when more efficient energy systems and alternative energy technologies are used. A study of the energy savings potential has been carried out separately for each energy consumption sector (heating, cooling, lighting, and office equipment), while combined scenarios have also been examined to identify the overall energy savings potential. Electricity savings for lighting can be obtained by either using more efficient lighting devices or by increasing the natural lighting in the buildings, if possible. In order to investigate the use of daylight in the audited buildings, the necessary energy to artificially illuminate all the interior spaces of the buildings, at lighting levels
- -
(%)
100
80
60
40
20
0
f i
10
close to 400 lux, has been calculated. The lighting schedule and the type of lighting devices in each building have been taken into account. Then, the net energy needs to illuminate the building were calculated by performing a simulation of the daylight penetration. As a result, it was possible to estimate the available energy from the daylight components. The calculations were performed using the accurate building's simulation tool, SPIEL [6]. To classify the obtained results, all buildings have been grouped in accordance with the location and orientation of their openings. It was found that, for buildings equipped with fluorescent lamps and operating from 7 A.M. to 5 P.M., the energy contribution from daylighting varies from 40-95% of the overall lighting load. Specifically, when daylight is provided by one side of the building, the energy contribution is close to 40%. In cases where daylight enters from two, three, or four sides of the building, the mean annual contribution is close to 63, 87, and 95%, respectively. In cases where the building's operation schedule is extended from 7 A.M. to 8 P.M., the energy contribution ranges between 29-68% of the overall lighting load. These values cannot be directly considered as energy gains, because the base case for comparison (a building with only artificial lighting), is not realistic. However, the present analysis provides comparative information that can contribute to the evaluation of the impact of daylighting in office buildings. To evaluate the possible energy savings from the use of high efficiency lamps and improved lighting systems, the lighting energy consumption of each building has been calculated considering 15 different types of lamps, with an efficiency ranging between 20-117 lm/ W. Details on the various types of these lamps were obtained from [7]. In addition, the impact of using electronic fluorescent ballasts and improved luminaires on the electric consumption of the buildings was also simulated. Electronic ballasts use only 47% of the energy core ballasts, [ 8 ], while improved luminaires can provide the required lighting levels with half the number of fixtures, [ 5 ]. Simulation results have shown that the replacement of the existing lamps with fluorescent lamps producing 80 lm/W, will reduce the total energy requirements for lighting to about 35%. The use of very high efficacy lamps, 117 lm/W, will provide a reduction of the total lighting load to about 55%. This type of lamp offers a very good warm color of 3300 K and is one of the higher efficacy types. The use of electronic fluorescent ballasts, where possible, can reduce the total lighting load to about 8%. Finally, the use of conventional fluorescent lamps, having an efficacy close to 50 lm/W, combined with improved luminaires, can reduce the lighting load to about 48%. 6. ENERGY SAVINGS FOR COOLING
I
i
20
30
I
i
40
50
(W/SOUARE
I
i
60
70
i
i
80
90
100
METER)
Fig. 4. Cumulative distribution of the installed office equipment power.
A reduction of the cooling load of office buildings can be achieved by improving the building envelope, by using alternative cooling techniques, or by using more efficient air-conditioningsystems. Sixteen differ-
Energy-savingpotential in offices ent scenarios, including improvement of the shading devices, use of high efficacy lighting devices, use of night ventilation techniques, installation of ceiling fans, and use of natural cooling techniques like indirect evaporative coolers and earth to air heat exchangers, have been considered. The detailed results of all these simulations are reported in [9 ]. Appropriate shading of buildings provides a significant reduction of the buildings' cooling load. It is found that almost all the studied buildings dispose movable internal shading devices like curtains, blinds, etc. Also, more than 80% of the buildings dispose fixed shading devices and overhangs. An evaluation of the possible reduction of the cooling load by using more efficient shading was performed for each building. It was found that it is possible to reduce the total cooling load of the air conditioned buildings by approximately 7%. The use of efficient lighting devices can substantially decrease the cooling load of buildings. It was estimated that the use of fluorescent lamps (80 l m / W ) in the air conditioned buildings, can reduce the total cooling load to about 9%. Night ventilation techniques can satisfy an important part of the buildings' cooling load, while contributing to increased indoor comfort during daytime [ 10 ]. Simulations of buildings using the accurate computer software CASAMO [11], have shown that it is possible, using night ventilation techniques, to reduce the peak temperature of a building by approximately 1 to 2 C [ 12 ]. This daytime temperature reduction permits the operation of the building inside the comfort zone, and therefore it is possible to dramatically reduce the cooling load. Calculations have shown that the use of night ventilation techniques, when possible, reduce the total cooling load of the air conditioned buildings to about 11 kWh / m 2, which corresponds to 30% of the buildings' cooling load. Calculations have been based on the assumption that six air changes per hour are applied during the night period. Any further increase of the air changes does not contribute in a significant reduction of the building's temperature. In cases where mechanical ventilation systems are used in the building, the energy consumption of the fans should also be considered. Use of increased natural ventilation levels during the daylight period cannot be considered due to the high ambient temperatures. As shown in [ 13 ], natural ventilation of office buildings during daytime creates important overheating problems and therefore should be avoided. Use of ceiling fans in buildings permits extension of the comfort zone to a maximum temperature close to 29.5°C [ 14]. The use of this type of fan is considered as one of the best alternatives to reduce the building cooling load [ 15 ]. The impact of use of ceiling fans, when possible, is simulated for all the air conditioned buildings. It is found that the mean annual cooling load of the buildings is reduced to about 3 k W h / m 2. Therefore, the energy conservation is close to 90%. The use of natural cooling techniques and especially of the indirect evaporative coolers, can provide, under
63
certain conditions, an important reduction of the cooling load [ 16 ]. Performance data on indirect evaporative coolers show that energy savings of up to 60% can be achieved compared to compression refrigeration systems [ 17 ]. Simulations of the performance of indirect evaporative coolers have shown that due to climatological constraints, such a system can operate during half of the cooling period [ 18 ]. 7. ENERGY SAVINGSFROM OFFICE EQUIPMENT The decrease of the energy consumed by office equipment is primarily associated with the use of new equipment, presenting a lower energy consumption. Although new office equipment is characterized by important improvements [ 19 ], the continuous increase of the installed equipment and especially in relation to information technology, do not permit any significant reductions in absolute values. On the other hand, in Greece, an increase of the energy consumption should be expected because the country's office buildings cannot be considered as equipment saturated. Important energy consumption increases due to office equipment have also been reported in other countries. Reports coming from the United States identify computer loads as a potential source of about 125 TWh in added electricity consumption between the early 1980s and the early 1990s [20,21 ]. Studies on the possibilities to reduce future energy consumption of office equipment conclude that more efficient hardware and operating systems should be used in the future, reducing the per-user power to about 70% for computers, and 50% for I / O [19]. 8. ENERGYSAVINGSFOR HEATING The energy consumption for heating of the office buildings can be reduced by improving the buildings' envelope and the efficiency of the heating systems, as well as using passive solar systems and techniques. In order to investigate the possible energy conservation resulting from improvements of the buildings' envelope, two scenarios were studied. The first scenario deals with the addition of insulation to decrease the overall heat transfer coefficient of each building to about 10%. Using simulation techniques, it was found tfiat the mean energy consumption of the buildings can be reduced by 4.9 k W h / m 2, which represents 5% of the overall energy consumption for heating. The second scenario deals with the insulation of all the noninsulated buildings, according to the Greek code. Simulations have shown that the mean annual energy gains are 17 k W h / m 2, which corresponds to 18% of the energy consumed for heating purposes. Use of high efficiency combustion systems for heating and their appropriate maintenance, can contribute significantly in reducing the energy consumption of the buildings. Based on the results of this investigation, it was found that almost all buildings maintain their combustion system once per year. However, it is identified that important improvements can be achieved using more appropriate control, insulation of the boiler
M. SANTAMOURISel al.
64
Table 2. Energy consumption of the buildings when scenario 1 is applied
Group A Group B Group C Group D Group E
Lighting
Cooling
Heating
Office equipment
Total
Reduction
15 16 14 15 15
5 11 11 16 6
86 87 85 85 81
48 66 78 89 50
154 180 188 205 152
17.6% 20.3% 16.4% 18.0% 19.1%
and pipes, etc. To identify the impact of the combustion systems efficiency on the overall energy consumption of the buildings, several simulations of buildings with various efficiencies heating systems were carried out. Accordingly, it has been found that an increase of the combustion efficiency to 10% will decrease the mean energy consumption of the buildings equipped with a combustion system to about 9 k W h / m E, which corresponds to 9% of their thermal consumption. Use of passive solar systems can provide an important part of the building's load. Application of such systems in multistory buildings, located in highly dense urban environments, is a difficult task due to the low availability of solar radiation and the orientation of the buildings. However, south-oriented buildings receive important solar gains which, together with internal gains, contribute significantlyto the thermal load of the buildings. Simulations of the audited office buildings have shown that the mean solar gains for all buildings are close to 12 k W h / m E, while internal gains contribute 29 k W h / m Eon an annual basis. Therefore, solar gains cover 8-9%, while free gains cover 29% of the overall heating load. 9. GLOBAL ENERGY SAVINGS In order to identify the comprehensive potential for energy savings in office buildings, the impact of combined measures has also been simulated. From the overall analysis, it is deduced that night ventilation and ceiling fans are the more promising alternative cooling techniques. Also, the use of high efficacy lighting devices and the appropriate maintenance and control of the heating system are simple, but efficient, measures concerning lighting and heating of the buildings. Two scenarios have been created and simulated for all five groups of office buildings, defined in section 3. The first scenario deals with the use of night ventilation techniques in air conditioned buildings, when possible, combined with an increase of 10% of the efficiency of
the combustion heating systems and use of high efficacy lighting (80 l m / W ) for all the buildings. The second scenario deals with the use of ceiling fans in air conditioned buildings, when possible, together with the use of high efficacy lighting systems (80 lm/W) and the improvement of the efficiency of the combustion heating systems to about 10%. The calculated values of the specific energy consumption for each group of buildings are given in Tables 2 and 3, for the first and second scenario, respectively. Global energy savings vary from 16-24% of the total energy load. Important energy gains are calculated and identified for air conditioned buildings, for both scenarios. Because the consumption of the office equipment and of the special electrical uses can be considered inflexible (because they are directly dependent on the function of the building), the achieved reduction of the load for heating, cooling, and lighting purposes is between 22-37%. 10. LIMITATIONS The use of natural ventilation techniques and especially of night ventilation in urban environments is subject to important limitations. Opening of windows can be the source of various problems, the most important of which is related to the increased concentration of outdoor pollutants in the interior spaces. The impact of the ventilation systems and techniques to the indoor air quality of office buildings has been investigated using questionnaire techniques. A total of 30 office buildings were audited in the Athens greater metropolitan area, including 12 naturally ( N / V) and 18 mechanically ventilated ( M / V ) buildings, In total, 478 employees were questioned. The results for the number of the main health symptoms reported by employees in each type of buildings are given in Fig. 5 [22]. Naturally ventilated buildings exhibit a higher percentage of symptoms such as eye irritation and disturbed concentration. This is primarily due to the fact that most of the buildings that have been au-
Table 3. Energy consumption of the buildings when scenario 2 is applied
Group A Group B Group C Group D Group E
Lighting
Cooling
Heating
Office equipment
Total
Reduction
15 16 14 15 15
1 3 1 2 1
89 87 85 85 81
48 66 78 89 50
150 172 178 191 147
19.8% 23.9% 20.9% 23.6% 21.8%
Energy-savingpotential in offices NATURALLY VENTILATED OFFICE BUILDINGS
MECHANICALLY VENTILATED OFFICE BUILDINGS
A
E
A
B
D
65
E
C
B
D
C
SYMPTOMS: A : Eye Irritation D : Dizziness
B : Headaches E : Drowsiness
C : Disturbed C o n c e n t r a t i o n F : Unusual Fatigue
Fig. 5. Percent of reported symptoms by employees in office buildings.
dited are located in the downtown area, where the outside air quality is poor. Using statistical techniques, it is found that there is a statistically significant difference between the occurrence of a symptom from its nonoccurrence, except for the symptom of headaches in naturally ventilated buildings. Therefore, the symptom of headaches exhibited by employees in N / V buildings is not related to the type of ventilation system, but rather is caused by the poor air quality of the outdoor air that is allowed into the building. With regard to thermal comfort, it is found that the percentage of dissatisfied people in N / V buildings is substantially higher than the corresponding percent for the M/V buildings. In N / V buildings, only two audited buildings were reported by half of their employees, as providing thermal comfort. On the other hand, in only two mechanically ventilated buildings, the employees were unsatisfied. Correlations have been attempted between the reported employee health symptoms and the buildings' global energy consumption. No significant relationship
Z
~8 7
+
6
+
+
++
2
+
1
~5 7°
++
+
0
....... 0
I I. CONCLUSIONS
Detailed energy consumption data from 186 office buildings in Greece have been presented. The impact of the used energy systems, techniques, and components is investigated. It is found that half of the energy consumption of all buildings is consumed for heating purposes, while 10.7 and 12.6% are consumed for lighting and cooling purposes, respectively. In addition, 25.9% of the total energy consumption is due to office equipment and other electrical equipment of the office buildings. The potential effectiveness of various energy conservation techniques has been assessed, taking into account the specific limitations for each building. The possible reduction of the load for heating, cooling, and lighting purposes is found to be between 22-37%. The applicability of natural ventilation techniques in high density urban areas and the impact of office equipment to the indoor air quality of the buildings has also been investigated. It is found that natural ventilation techniques may cause important indoor air quality problems when the quality of the outdoor air is polluted. Also, the increased use of office equipment may be the direct cause for a number of employee health problems.
i
L 100 ELECTRICAL
has been identified for either naturally or mechanically ventilated buildings. However, an important correlation has been found between the reported health symptoms and the electrical energy consumption of the buildings (Fig. 6). This can be attributed to the impact of increased office equipment use, which is an important source of indoor air quality problems [ 23 ].
200 CONSUMPTION
300
(kWh/SQ.M,)
Fig. 6. Correlation between reported symptoms and electrical energy consumption.
Acknowledgments--The present work has been funded by the Ministry of Industry, Energy and Research and was carried out under a contract with the Greek Productivity Center. The authors wish to express their gratitude to both Institutions.
M. SANTAMOUR1Sel al.
66 REFERENCES
1. J. Campbell, Use of passive solar energy in offices. In: P. O'Sullivan (ed), Passive solar energy in buildings. The Watt Committee on Energy. Elsevier Applied Science Publ. (1988). 2. P. O. Fanger, Thermal comfort analysis and application in environmental engineering. Krieger, Malabar (1982). 3. P. O. Fanger, J. Lauridsen, P. Bluyssen, and G. Clausen: Air pollution sources in offices and assembly halls quantified by the olf unit, Energy and Buildings, 12, 7 ( 1988 ). 4. A. Hedge, E. M. Sterling, and T. D. Sterling, Building illness indices based on questionnaire responces, In: Engineering solutions to indoor air problems, pp. 31-43, Proeeedings ASHRAE IAQ 88 Conference, Atlanta, GA (1988). 5. M. Holtz, Electrical energy savings in office buildings, Swedish Council for Buildings Research, D17 (1990). 6. C. Green, The simulation tool SPIEL, Ecotech, UK. 7. J. R. Benya, Light loads, Progressive Architecture. 7 (1989). 8. B. L. Capehart, Florida's new ballast standard saves on commercial lighting, Energy Engineering. 86, 21 (1989). 9. M. Santamouris, A. Argiriou, M. Vallidras, A. Gagglia, E. Dascalaki, and G. Sigalas, Energy conservation in office buildings, Final Report, Greek Productivity Center and Ministry of Industry, Research and Technology (1992). 10. M. Antinucei, B. Fleury, J. Lopez d'Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. Yannas, Passive and hybrid cooling of buildings--State of the art, Int. J. Solar Energy, in press ( 1992 ). 11. Dialogic: Description manual ofCASAMO-CLIM (1988). 12. G. Agas, T. Matsaggos, M. Santamouris, and A. Argiriou, On the use of the atmospheric heat sinks for heat dissipation, Energy and Buildings, 17, 321 ( 1991 ).
13. B. Fleury, Natural ventilation techniques for buildings in Greece. In: M. Santamouris (ed), Natural cooling techniques in Greece. Valorin Programme, CRES (1990). 14. D. Scheatzle, H. Wu, and J. Yellot, Extending the summer comfort envelope with ceiling fans in hot arid climates, ASHRAE Transactions, 95, 1 (1989). 15. S. Chandra, Fans to reduce cooling cost in the Southeast. Florida Solar Energy Center, EN- 13-85 ( 1985 ). 16. M. Antinucci, B. Fleury, J. Lopez d'Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. Yannas, State of the art of passive cooling for buildings. In: M. Santamouris (ed), Building 2000 research programme. Commission of the European Communities, DGI2 ( 1991 ). 17. D. Pescod and R. K. Prudhoe, Telecommunications Journal Australia, 30, 2 (1980). 18. M. Santamouris, Natural Cooling Techniques, In: E. Aranovich, E. de Oliveira Fernandes, and T. C. Steemers, (eds), Workshop on passive cooling, CEC, DGI2, 143 (1990). 19. L. Norford, A. Hatcher, J. Harris, J. Rotunier, and O. Yu. Electricity Use in Information Technologies, Annu. Rev. Energy, 423 (1990). 20. E. R. Berndt, Aggregate energy, efficiency and productivity measurement, Annu. Rev. Energy. 3, 225 (1978). 21. U. S. Energy Inf. Admin., Monthly Energy Rev., Washington DC, U.S. Dept Energy, various years. 22. A. Argiriou, C. Balaras, E. Dascalaki, A. Gaglia, G. Goudelas, K. Moustris, M. Santamouris, and M. Validras, A survey of indoor air quality in office buildings in Athens, Greece. In: J. N. Lester, R. Perry, and G. L. Reynolds, (eds), Quality ~f the indoor environment. Athens, 587 (1992). 23. T. Godish, Indoor airpollution control, Lewis Publishers (1989).
0038-092X/94 $6.00 + .00 Copyright © 1993 Pergamon Press Ltd.
Printed in the U.S.A.
E N E R G Y CHARACTERISTICS AND SAVINGS POTENTIAL IN OFFICE BUILDINGS M. SANTAMOURIS,A. ARGIRIOU,E. DASCALAKI,C. BALARAS,and A. GAGLIA Laboratory of Meteorology, Department of Applied Physics, University of Athens, Ippokratous 33, 106 80, Athens, Greece Abstract--The present paper reports the findingsof a monitoring campaign in 186 officebuildingsin Greece. The specific energy consumption of the buildings for heating, cooling, and lighting purposes, as well as the consumption of the officeequipment is reported. The impact of the used systems,techniques,and components is investigated. The potential and the limitations of various energy conservation systems and alternative techniques is assessed. The present study provides useful information for efficientenergy planning, as well as appropriate design and equipment selection, in office buildings.
1. I N T R O D U C T I O N
building engineers in order to choose energy efficient systems and techniques applicable to office buildings.
Residential and commercial buildings consume more than one-third of Europe's primary energy budget. Commercial buildings, and primarily office buildings, are classified among the buildings presenting the highest energy consumption. Typical primary energy values for offices in Northern Europe, [1], fall between 270 and 350 kWh per year and m 2. Energy in office buildings is consumed mainly for heating, cooling, and lighting purposes, while a significant portion is devoted to the consumption of office equipment. Application of energy conservation techniques, as well as use of solar or ambient alternative energy sources in offices, require knowledge of the specific energy characteristics of the buildings. The frequency distribution of the building's final energy con: sumption, the specific energy requirements for each type of use, and the characteristics of the installed systems are amongst the necessary information. In order to assess information on energy consumption and identify the main energy characteristics, as well as the potential for energy conservation in office buildings in Greece, an extensive campaign based on short monitoring techniques has been designed and executed. Detailed data from 186 representative office buildings from around the country have been collected and analyzed. The potential effectiveness of various energy conservation techniques has also been assessed, taking into account the specific limitations for each building. The aim of this paper is to describe the energy consumption characteristics of the office buildings in a representative Southern European country, to provide specific information on the potential for energy conservation, and, finally, to investigate the technical, environmental, and social limitations of the existing technologies for energy conservation. The results of the present study provide the necessary information to energy planners in order to effectively design energy conservation policies. It can also provide useful knowledge to building designers and
2. M E T H O D O L O G Y
Short monitoring of buildings has been performed by a trained panel of engineers using standard reporting forms and an extensive questionnaire addressed to the building occupants. The following information has been collected from each building: 1. General information about the occupants and the building: this include the name, address, legal status, owner, the construction year, the number of stories, the heated surface and volume, and the daily occupation profile. 2. General and specific information about the building envelope: for each side of the building, the orientation, the vicinity with heated or unheated space, and the type of glazing and shading were recorded. A detailed description of each exterior building element, walls, ceiling, and floors was also included. 3. Information about the heating, cooling, and lighting systems. Here, the type, the power, and the operational profile was recorded. The duration of the heating and cooling period, the control type and the set points, as well as the maintenance policy were also noted. 4. Information about the office equipment. The type and the power of the used office equipment was recorded in each building. Also, information about specific appliances like water heaters, refrigerators, fans, and pumps were collected. 5. The energy consumption of the building. The quantity of every type of fuel and the consumed electricity in each building was recorded. The exact data were taken from the monthly electricity and fuel consumption official receipts kept in each building. In parallel with the standard forms, a specific questionnaire was designed in order to collect information 59
60
M. SANTAMOURIS el
about the thermal comfort and the indoor air quality inside the office buildings. The opinion of the occupants regarding the thermal comfort inside the building during the heating and the cooling seasons was separately recorded. The seven steps of the thermal comfort scale proposed in [2] were used. To study the applicability of natural ventilation techniques in high density urban areas and the impact of office equipment to the indoor air quality of the buildings, a specific study has been carried out. This investigation has been executed in 30 buildings located in the central Athens area. Two questionnaires were used for this purpose. The first one dealt with the outdoor and indoor air quality perceived by the visiting staff. The questionnaire and the methodology proposed in [ 3 ] has been used to collect this type of information. The purpose of the second questionnaire was to record the health symptoms of the building occupants to investigate the impact of the used energy options, and more generally of the indoor and outdoor environment, to the occupants' health. For this purpose, the questionnaire and the methodology proposed in [4] for office buildings has been used. A data base has been created using the information recorded from all the buildings. The collected primary data have been analyzed in order to identify the energy characteristics of the office buildings in Greece and then to assess the applicability, potential, and limitations of some important energy conservation techniques and use of high efficiency energy systems. Energy savings calculations are based on the assumption that the building operates inside the standard ASHRAE thermal comfort zones during the heating and cooling period. Also, the visual comfort standards for office buildings are used. 3. ENERGY CONSUMPTION OF OFFICE BUILDINGS
The audited office buildings have been classified in the following five groups based on the utilized energy systems: 1. Group A includes the whole set of buildings. In total, 186 buildings have been audited. 2. Group B includes only the buildings that are equipped with conventional air conditioning systems. In total, 89 buildings or 48% of the total number of buildings were included in this group. 3. Group C includes only the buildings that are equipped with electrical heating systems. In total,
al.
29 buildings or 16% of the total number of buildings were included in this group. 4. Group D includes only the buildings that are equipped with both an electrical heating system and an A / C system. In total, 24 buildings or 13% of the total number of buildings were included in this group. 5. Group E includes only the buildings that are equipped with a combustion fuel based heating system. In total, 153 buildings or 82% of the total number of buildings were included in this group. The characteristics of a sixth group, F, including the "nonAC buildings" have been also analyzed. The annual energy consumption per square meter of building for each one of the above groups as well as for each specific energy use is given in Table I. The mean energy consumption of the office buildings is close to 187 k W h / m 2. The frequency distribution of the annual energy consumption of all the office buildings, is shown in Fig. 1. Accordingly, 39% of the office buildings have an energy consumption lower than 100 k W h / m E, while for 36% of the buildings the energy consumption ranges between 100-200 kWh / m E. The electrical energy consumption for 44% of the office buildings is lower than 50 k W h / m E, while for 24% of the buildings it ranges between 50-100 k W h / m 2. The thermal energy consumption for 45% of the office buildings is lower than 50 k W h / m E, while for 22% of the buildings it ranges between 50-100 k W h / m 2. Over half of the total energy consumption (50.8%) is consumed for heating purposes, while 10.7 and 12.6% are consumed for lighting and cooling purposes, respectively. Also, 25.9% of the total consumption is due to the office equipment and the other electrical equipment in the office buildings. Buildings that are equipped with air conditioning systems (Group B) exhibit a mean annual energy consumption increase of about 226 k W h / m E. In this case the percentage for the heating and cooling of the buildings are 44 and 15.6%, respectively. Similar figures are also obtained for buildings equipped with an electrical heating system (Group C). Buildings equipped with a conventional A / C and an electrical heating system (Group D) exhibit the highest energy consumption, reaching a value equal to 250 k W h / m 2. In this case, heating represents 37.5% of the total energy consumption, while for cooling this corresponds to 17.5%. The total energy consumption of the buildings
Table 1. Energy conservation of the buildings (kWh/m2)
Group A Group B Group C Group D Group E Group F
Lighting
Cooling
Heating
Office equipment
Total
24 25 21 23 22 15
20 36 36 44 15 0
95 99 90 94 101 100
48 66 78 89 50 34
187 226 225 250 188 149
Energy-savingpotential in offices +
(%)
+
100
100
80
80
60
60
40
40
20
20
0
i
i
i
i
170
340
510
680
61
N/V
z~
A/C
ol 0
850
170
340
510
680
850
(W/S.M)
(W/S.M)
Fig. 1. Cumulative distribution of the annual energy consumption in kWh/m 2 for all the monitored office buildings.
Fig. 2. Cumulative distribution of the annual electric consumption in kWh/m 2 for the naturally ventilated and the air conditioned office buildings.
equipped with a combustion heating system (Group E) is close to 188 k W h / m 2. Approximately 27% is consumed by the office and other electrical equipment, while for satisfying the heating, cooling, and lighting requirements of the buildings the consumed energy in each case represents 53.4, 8. l, and 11.9%, respectively. Finally, the total energy consumption of the "'nonAC" buildings, group F, is close to 149 kWh per square meter. Almost 67% of the annual energy is consumed for heating purposes, while almost 10% is the lighting consumption. Also, 23% is used by the office and other electrical equipment.
office building stock in the country. It is found that insulated buildings in Athens present a mean annual energy consumption for heating purposes close to 81 kWh/m 2, while the corresponding consumption of the noninsulated buildings is approximately 23% higher, with a value of 100 k W h / m 2. The cumulative distribution of the annual energy consumption for heating purposes given in Fig. 3 for insulated and noninsulated buildings shows that 80% of the insulated buildings and 70% of the noninsulated buildings present a heating consumption less than 100 k W h / m 2 per year. The type of devices used for lighting determines the corresponding energy consumption of the office buildings. The overall analysis has shown that 155 buildings use fluorescent lighting devices, 19 buildings use both fluorescent and incadescent lights, and 12 buildings use only incadescent lights. However, the specific energy consumed in every building for lighting purposes also depends on other factors, like the percentage of used daylight and the lighting schedule of the building. Therefore, a comparison between the lighting consumption of the various buildings should not be attempted. On the other hand, it is very useful to know
4. A N A L Y S I S O F S P E C I F I C P A R A M E T E R S
The use of conventional cooling systems is a major source of energy consumption. To analyze the impact of air conditioning to the overall energy consumption of the office buildings, a comparison has been performed between the naturally ventilated and the air conditioned buildings. The mean annual energy consumption of the naturally ventilated ( N / V ) buildings is close to 179 k w h / m 2 while the corresponding consumption for the A / C buildings is 226 k W h / m 2. Subsequently, the use of A / C in office buildings increases the annual energy consumption by approximately 4050 k W h / m 2. A comparison of the cumulative distribution of the electrical consumption of the N / V and A / C buildings is shown in Fig. 2. It is calculated that 55% of the naturally ventilated and 43% of the A / C buildings, present a total electrical consumption lower than 50 k W h / m 2. In addition, 80% of the N / V and 67% of the A / C buildings present an electrical consumption lower than 100 k W h / m 2. To examine the impact of thermal insulation on the buildings' energy consumption, a separate analysis has been performed for buildings with and without thermal insulation. Insulation in buildings has been obligatory in Greece since 1979. Insulation levels are determined as a function of the surface-to-volume ratio and the climatological zone. The overall study has been performed in 136 noninsulated and 50 insulated buildings. This sample is almost representative of the
LIGHTING - -
CONSUMPTION
(%) E~.JILDINS
100
J
i
0
10
20
30
40
50
60
K WH/M2
Fig. 3. Cumulative distribution of the annual electric energy consumed for lighting purposes, in kWh/m2.
62
M. SANTAMOURIS el a/.
the distribution of the lighting consumption of the buildings. Figure 3 shows the cumulative distribution of the electrical energy consumption for lighting purposes in all the audited office buildings. Accordingly, 50% of the buildings present a lighting consumption less than 11 k W h / m 2, while for the majority of the buildings (86%) the consumption is less than 20 k W h / m 2. Energy consumption by the office equipment represents an important part of the building's energy budget. According to the international experience, the mean installed power of equipment in office buildings is close to 10 W / m 2, [5]. However, for highly computerized offices, the installed power can reach values close to 100 W / m 2, [ 5 ]. The cumulative distribution of the installed power in the audited buildings is given in Fig. 4. As shown, 60% of the buildings are below 20 W / m 2, while 80% of them are below 30 W / m 2. As has already been mentioned, the mean annual consumption of the office equipment is calculated close to 35 k W h / m 2. This amount includes the energy used for vertical transportation, (7 k W h / m 2) and the energy consumed for hot water purposes (0.6 kWh/m2). When energy statistics are limited to air conditioned and highly computerized buildings, the specific energy consumption of the office equipment increases dramatically and approaches values close to 64 k W h / m 2.
5. ENERGY SAVINGS FOR LIGHTING
An analysis of the collected data has shown that important energy reductions can be achieved in office buildings when more efficient energy systems and alternative energy technologies are used. A study of the energy savings potential has been carried out separately for each energy consumption sector (heating, cooling, lighting, and office equipment), while combined scenarios have also been examined to identify the overall energy savings potential. Electricity savings for lighting can be obtained by either using more efficient lighting devices or by increasing the natural lighting in the buildings, if possible. In order to investigate the use of daylight in the audited buildings, the necessary energy to artificially illuminate all the interior spaces of the buildings, at lighting levels
- -
(%)
100
80
60
40
20
0
f i
10
close to 400 lux, has been calculated. The lighting schedule and the type of lighting devices in each building have been taken into account. Then, the net energy needs to illuminate the building were calculated by performing a simulation of the daylight penetration. As a result, it was possible to estimate the available energy from the daylight components. The calculations were performed using the accurate building's simulation tool, SPIEL [6]. To classify the obtained results, all buildings have been grouped in accordance with the location and orientation of their openings. It was found that, for buildings equipped with fluorescent lamps and operating from 7 A.M. to 5 P.M., the energy contribution from daylighting varies from 40-95% of the overall lighting load. Specifically, when daylight is provided by one side of the building, the energy contribution is close to 40%. In cases where daylight enters from two, three, or four sides of the building, the mean annual contribution is close to 63, 87, and 95%, respectively. In cases where the building's operation schedule is extended from 7 A.M. to 8 P.M., the energy contribution ranges between 29-68% of the overall lighting load. These values cannot be directly considered as energy gains, because the base case for comparison (a building with only artificial lighting), is not realistic. However, the present analysis provides comparative information that can contribute to the evaluation of the impact of daylighting in office buildings. To evaluate the possible energy savings from the use of high efficiency lamps and improved lighting systems, the lighting energy consumption of each building has been calculated considering 15 different types of lamps, with an efficiency ranging between 20-117 lm/ W. Details on the various types of these lamps were obtained from [7]. In addition, the impact of using electronic fluorescent ballasts and improved luminaires on the electric consumption of the buildings was also simulated. Electronic ballasts use only 47% of the energy core ballasts, [ 8 ], while improved luminaires can provide the required lighting levels with half the number of fixtures, [ 5 ]. Simulation results have shown that the replacement of the existing lamps with fluorescent lamps producing 80 lm/W, will reduce the total energy requirements for lighting to about 35%. The use of very high efficacy lamps, 117 lm/W, will provide a reduction of the total lighting load to about 55%. This type of lamp offers a very good warm color of 3300 K and is one of the higher efficacy types. The use of electronic fluorescent ballasts, where possible, can reduce the total lighting load to about 8%. Finally, the use of conventional fluorescent lamps, having an efficacy close to 50 lm/W, combined with improved luminaires, can reduce the lighting load to about 48%. 6. ENERGY SAVINGS FOR COOLING
I
i
20
30
I
i
40
50
(W/SOUARE
I
i
60
70
i
i
80
90
100
METER)
Fig. 4. Cumulative distribution of the installed office equipment power.
A reduction of the cooling load of office buildings can be achieved by improving the building envelope, by using alternative cooling techniques, or by using more efficient air-conditioningsystems. Sixteen differ-
Energy-savingpotential in offices ent scenarios, including improvement of the shading devices, use of high efficacy lighting devices, use of night ventilation techniques, installation of ceiling fans, and use of natural cooling techniques like indirect evaporative coolers and earth to air heat exchangers, have been considered. The detailed results of all these simulations are reported in [9 ]. Appropriate shading of buildings provides a significant reduction of the buildings' cooling load. It is found that almost all the studied buildings dispose movable internal shading devices like curtains, blinds, etc. Also, more than 80% of the buildings dispose fixed shading devices and overhangs. An evaluation of the possible reduction of the cooling load by using more efficient shading was performed for each building. It was found that it is possible to reduce the total cooling load of the air conditioned buildings by approximately 7%. The use of efficient lighting devices can substantially decrease the cooling load of buildings. It was estimated that the use of fluorescent lamps (80 l m / W ) in the air conditioned buildings, can reduce the total cooling load to about 9%. Night ventilation techniques can satisfy an important part of the buildings' cooling load, while contributing to increased indoor comfort during daytime [ 10 ]. Simulations of buildings using the accurate computer software CASAMO [11], have shown that it is possible, using night ventilation techniques, to reduce the peak temperature of a building by approximately 1 to 2 C [ 12 ]. This daytime temperature reduction permits the operation of the building inside the comfort zone, and therefore it is possible to dramatically reduce the cooling load. Calculations have shown that the use of night ventilation techniques, when possible, reduce the total cooling load of the air conditioned buildings to about 11 kWh / m 2, which corresponds to 30% of the buildings' cooling load. Calculations have been based on the assumption that six air changes per hour are applied during the night period. Any further increase of the air changes does not contribute in a significant reduction of the building's temperature. In cases where mechanical ventilation systems are used in the building, the energy consumption of the fans should also be considered. Use of increased natural ventilation levels during the daylight period cannot be considered due to the high ambient temperatures. As shown in [ 13 ], natural ventilation of office buildings during daytime creates important overheating problems and therefore should be avoided. Use of ceiling fans in buildings permits extension of the comfort zone to a maximum temperature close to 29.5°C [ 14]. The use of this type of fan is considered as one of the best alternatives to reduce the building cooling load [ 15 ]. The impact of use of ceiling fans, when possible, is simulated for all the air conditioned buildings. It is found that the mean annual cooling load of the buildings is reduced to about 3 k W h / m 2. Therefore, the energy conservation is close to 90%. The use of natural cooling techniques and especially of the indirect evaporative coolers, can provide, under
63
certain conditions, an important reduction of the cooling load [ 16 ]. Performance data on indirect evaporative coolers show that energy savings of up to 60% can be achieved compared to compression refrigeration systems [ 17 ]. Simulations of the performance of indirect evaporative coolers have shown that due to climatological constraints, such a system can operate during half of the cooling period [ 18 ]. 7. ENERGY SAVINGSFROM OFFICE EQUIPMENT The decrease of the energy consumed by office equipment is primarily associated with the use of new equipment, presenting a lower energy consumption. Although new office equipment is characterized by important improvements [ 19 ], the continuous increase of the installed equipment and especially in relation to information technology, do not permit any significant reductions in absolute values. On the other hand, in Greece, an increase of the energy consumption should be expected because the country's office buildings cannot be considered as equipment saturated. Important energy consumption increases due to office equipment have also been reported in other countries. Reports coming from the United States identify computer loads as a potential source of about 125 TWh in added electricity consumption between the early 1980s and the early 1990s [20,21 ]. Studies on the possibilities to reduce future energy consumption of office equipment conclude that more efficient hardware and operating systems should be used in the future, reducing the per-user power to about 70% for computers, and 50% for I / O [19]. 8. ENERGYSAVINGSFOR HEATING The energy consumption for heating of the office buildings can be reduced by improving the buildings' envelope and the efficiency of the heating systems, as well as using passive solar systems and techniques. In order to investigate the possible energy conservation resulting from improvements of the buildings' envelope, two scenarios were studied. The first scenario deals with the addition of insulation to decrease the overall heat transfer coefficient of each building to about 10%. Using simulation techniques, it was found tfiat the mean energy consumption of the buildings can be reduced by 4.9 k W h / m 2, which represents 5% of the overall energy consumption for heating. The second scenario deals with the insulation of all the noninsulated buildings, according to the Greek code. Simulations have shown that the mean annual energy gains are 17 k W h / m 2, which corresponds to 18% of the energy consumed for heating purposes. Use of high efficiency combustion systems for heating and their appropriate maintenance, can contribute significantly in reducing the energy consumption of the buildings. Based on the results of this investigation, it was found that almost all buildings maintain their combustion system once per year. However, it is identified that important improvements can be achieved using more appropriate control, insulation of the boiler
M. SANTAMOURISel al.
64
Table 2. Energy consumption of the buildings when scenario 1 is applied
Group A Group B Group C Group D Group E
Lighting
Cooling
Heating
Office equipment
Total
Reduction
15 16 14 15 15
5 11 11 16 6
86 87 85 85 81
48 66 78 89 50
154 180 188 205 152
17.6% 20.3% 16.4% 18.0% 19.1%
and pipes, etc. To identify the impact of the combustion systems efficiency on the overall energy consumption of the buildings, several simulations of buildings with various efficiencies heating systems were carried out. Accordingly, it has been found that an increase of the combustion efficiency to 10% will decrease the mean energy consumption of the buildings equipped with a combustion system to about 9 k W h / m E, which corresponds to 9% of their thermal consumption. Use of passive solar systems can provide an important part of the building's load. Application of such systems in multistory buildings, located in highly dense urban environments, is a difficult task due to the low availability of solar radiation and the orientation of the buildings. However, south-oriented buildings receive important solar gains which, together with internal gains, contribute significantlyto the thermal load of the buildings. Simulations of the audited office buildings have shown that the mean solar gains for all buildings are close to 12 k W h / m E, while internal gains contribute 29 k W h / m Eon an annual basis. Therefore, solar gains cover 8-9%, while free gains cover 29% of the overall heating load. 9. GLOBAL ENERGY SAVINGS In order to identify the comprehensive potential for energy savings in office buildings, the impact of combined measures has also been simulated. From the overall analysis, it is deduced that night ventilation and ceiling fans are the more promising alternative cooling techniques. Also, the use of high efficacy lighting devices and the appropriate maintenance and control of the heating system are simple, but efficient, measures concerning lighting and heating of the buildings. Two scenarios have been created and simulated for all five groups of office buildings, defined in section 3. The first scenario deals with the use of night ventilation techniques in air conditioned buildings, when possible, combined with an increase of 10% of the efficiency of
the combustion heating systems and use of high efficacy lighting (80 l m / W ) for all the buildings. The second scenario deals with the use of ceiling fans in air conditioned buildings, when possible, together with the use of high efficacy lighting systems (80 lm/W) and the improvement of the efficiency of the combustion heating systems to about 10%. The calculated values of the specific energy consumption for each group of buildings are given in Tables 2 and 3, for the first and second scenario, respectively. Global energy savings vary from 16-24% of the total energy load. Important energy gains are calculated and identified for air conditioned buildings, for both scenarios. Because the consumption of the office equipment and of the special electrical uses can be considered inflexible (because they are directly dependent on the function of the building), the achieved reduction of the load for heating, cooling, and lighting purposes is between 22-37%. 10. LIMITATIONS The use of natural ventilation techniques and especially of night ventilation in urban environments is subject to important limitations. Opening of windows can be the source of various problems, the most important of which is related to the increased concentration of outdoor pollutants in the interior spaces. The impact of the ventilation systems and techniques to the indoor air quality of office buildings has been investigated using questionnaire techniques. A total of 30 office buildings were audited in the Athens greater metropolitan area, including 12 naturally ( N / V) and 18 mechanically ventilated ( M / V ) buildings, In total, 478 employees were questioned. The results for the number of the main health symptoms reported by employees in each type of buildings are given in Fig. 5 [22]. Naturally ventilated buildings exhibit a higher percentage of symptoms such as eye irritation and disturbed concentration. This is primarily due to the fact that most of the buildings that have been au-
Table 3. Energy consumption of the buildings when scenario 2 is applied
Group A Group B Group C Group D Group E
Lighting
Cooling
Heating
Office equipment
Total
Reduction
15 16 14 15 15
1 3 1 2 1
89 87 85 85 81
48 66 78 89 50
150 172 178 191 147
19.8% 23.9% 20.9% 23.6% 21.8%
Energy-savingpotential in offices NATURALLY VENTILATED OFFICE BUILDINGS
MECHANICALLY VENTILATED OFFICE BUILDINGS
A
E
A
B
D
65
E
C
B
D
C
SYMPTOMS: A : Eye Irritation D : Dizziness
B : Headaches E : Drowsiness
C : Disturbed C o n c e n t r a t i o n F : Unusual Fatigue
Fig. 5. Percent of reported symptoms by employees in office buildings.
dited are located in the downtown area, where the outside air quality is poor. Using statistical techniques, it is found that there is a statistically significant difference between the occurrence of a symptom from its nonoccurrence, except for the symptom of headaches in naturally ventilated buildings. Therefore, the symptom of headaches exhibited by employees in N / V buildings is not related to the type of ventilation system, but rather is caused by the poor air quality of the outdoor air that is allowed into the building. With regard to thermal comfort, it is found that the percentage of dissatisfied people in N / V buildings is substantially higher than the corresponding percent for the M/V buildings. In N / V buildings, only two audited buildings were reported by half of their employees, as providing thermal comfort. On the other hand, in only two mechanically ventilated buildings, the employees were unsatisfied. Correlations have been attempted between the reported employee health symptoms and the buildings' global energy consumption. No significant relationship
Z
~8 7
+
6
+
+
++
2
+
1
~5 7°
++
+
0
....... 0
I I. CONCLUSIONS
Detailed energy consumption data from 186 office buildings in Greece have been presented. The impact of the used energy systems, techniques, and components is investigated. It is found that half of the energy consumption of all buildings is consumed for heating purposes, while 10.7 and 12.6% are consumed for lighting and cooling purposes, respectively. In addition, 25.9% of the total energy consumption is due to office equipment and other electrical equipment of the office buildings. The potential effectiveness of various energy conservation techniques has been assessed, taking into account the specific limitations for each building. The possible reduction of the load for heating, cooling, and lighting purposes is found to be between 22-37%. The applicability of natural ventilation techniques in high density urban areas and the impact of office equipment to the indoor air quality of the buildings has also been investigated. It is found that natural ventilation techniques may cause important indoor air quality problems when the quality of the outdoor air is polluted. Also, the increased use of office equipment may be the direct cause for a number of employee health problems.
i
L 100 ELECTRICAL
has been identified for either naturally or mechanically ventilated buildings. However, an important correlation has been found between the reported health symptoms and the electrical energy consumption of the buildings (Fig. 6). This can be attributed to the impact of increased office equipment use, which is an important source of indoor air quality problems [ 23 ].
200 CONSUMPTION
300
(kWh/SQ.M,)
Fig. 6. Correlation between reported symptoms and electrical energy consumption.
Acknowledgments--The present work has been funded by the Ministry of Industry, Energy and Research and was carried out under a contract with the Greek Productivity Center. The authors wish to express their gratitude to both Institutions.
M. SANTAMOUR1Sel al.
66 REFERENCES
1. J. Campbell, Use of passive solar energy in offices. In: P. O'Sullivan (ed), Passive solar energy in buildings. The Watt Committee on Energy. Elsevier Applied Science Publ. (1988). 2. P. O. Fanger, Thermal comfort analysis and application in environmental engineering. Krieger, Malabar (1982). 3. P. O. Fanger, J. Lauridsen, P. Bluyssen, and G. Clausen: Air pollution sources in offices and assembly halls quantified by the olf unit, Energy and Buildings, 12, 7 ( 1988 ). 4. A. Hedge, E. M. Sterling, and T. D. Sterling, Building illness indices based on questionnaire responces, In: Engineering solutions to indoor air problems, pp. 31-43, Proeeedings ASHRAE IAQ 88 Conference, Atlanta, GA (1988). 5. M. Holtz, Electrical energy savings in office buildings, Swedish Council for Buildings Research, D17 (1990). 6. C. Green, The simulation tool SPIEL, Ecotech, UK. 7. J. R. Benya, Light loads, Progressive Architecture. 7 (1989). 8. B. L. Capehart, Florida's new ballast standard saves on commercial lighting, Energy Engineering. 86, 21 (1989). 9. M. Santamouris, A. Argiriou, M. Vallidras, A. Gagglia, E. Dascalaki, and G. Sigalas, Energy conservation in office buildings, Final Report, Greek Productivity Center and Ministry of Industry, Research and Technology (1992). 10. M. Antinucei, B. Fleury, J. Lopez d'Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. Yannas, Passive and hybrid cooling of buildings--State of the art, Int. J. Solar Energy, in press ( 1992 ). 11. Dialogic: Description manual ofCASAMO-CLIM (1988). 12. G. Agas, T. Matsaggos, M. Santamouris, and A. Argiriou, On the use of the atmospheric heat sinks for heat dissipation, Energy and Buildings, 17, 321 ( 1991 ).
13. B. Fleury, Natural ventilation techniques for buildings in Greece. In: M. Santamouris (ed), Natural cooling techniques in Greece. Valorin Programme, CRES (1990). 14. D. Scheatzle, H. Wu, and J. Yellot, Extending the summer comfort envelope with ceiling fans in hot arid climates, ASHRAE Transactions, 95, 1 (1989). 15. S. Chandra, Fans to reduce cooling cost in the Southeast. Florida Solar Energy Center, EN- 13-85 ( 1985 ). 16. M. Antinucci, B. Fleury, J. Lopez d'Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. Yannas, State of the art of passive cooling for buildings. In: M. Santamouris (ed), Building 2000 research programme. Commission of the European Communities, DGI2 ( 1991 ). 17. D. Pescod and R. K. Prudhoe, Telecommunications Journal Australia, 30, 2 (1980). 18. M. Santamouris, Natural Cooling Techniques, In: E. Aranovich, E. de Oliveira Fernandes, and T. C. Steemers, (eds), Workshop on passive cooling, CEC, DGI2, 143 (1990). 19. L. Norford, A. Hatcher, J. Harris, J. Rotunier, and O. Yu. Electricity Use in Information Technologies, Annu. Rev. Energy, 423 (1990). 20. E. R. Berndt, Aggregate energy, efficiency and productivity measurement, Annu. Rev. Energy. 3, 225 (1978). 21. U. S. Energy Inf. Admin., Monthly Energy Rev., Washington DC, U.S. Dept Energy, various years. 22. A. Argiriou, C. Balaras, E. Dascalaki, A. Gaglia, G. Goudelas, K. Moustris, M. Santamouris, and M. Validras, A survey of indoor air quality in office buildings in Athens, Greece. In: J. N. Lester, R. Perry, and G. L. Reynolds, (eds), Quality ~f the indoor environment. Athens, 587 (1992). 23. T. Godish, Indoor airpollution control, Lewis Publishers (1989).