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Energy consumption and the potential for energy conservation in school buildings in Hellas
Energy Vol. 19. No. 6. pp. 653-660. 1994 Copyright 0 1994 Elscvicr Scicncc Ltd Printed in Great Britain. All rights rescrvcd 0360-5442/94 $7.00 + 0.00
Pergamon
ENERGY ENERGY
CONSUMPTION AND THE POTENTIAL FOR CONSERVATION IN SCHOOL BUILDINGS IN HELLAS
SANTAMOURIS,
M.
Department
C.
of Applied
A.
BALARAs,t E.
Physics,
University
DASCALAKI,
of Athens,
A.
Ippokratous
ARGIRIOU, and A. 33, GR
(Received 28 June 1993; received for publication 5 November
106 80 Athens,
GAGLIA Greece
1993)
Abstract-School
buildings (238) in Hellas were audited for construction, heating, cooling, lighting, and mechanical and electrical systems. The annual average total energy consumption is 93 kWh/m’, of which approximately 72% is consumed for space heating. The assessment of various energy-conservation techniques shows a potential for 20% overall energy conservation.
INTRODUCTION Public and commercial buildings in the European Community the total energy. It is possible to improve the existing situation
consume an estimated and establish guidelines
40% of for new
buildings in order to increase the use of renewable energy sources which can satisfy portion of the building energy needs, while maintaining necessary comfort conditions
a major for the
occupants.’ To achieve these objectives and evaluate possible scenarios for intervention, it is first necessary to document the existing situation in the building sector. For this reason, an extensive short monitoring campaign of over 1000 public and commercial buildings in Hellas was initiated in 1987. The audits included air-conditioned and naturally ventilated offices and commercial, hospital, hotel, and school buildings. Each type of building exhibits individual characteristics and problems due to specific operational needs. As a result, different design guidelines are required in order to construct an energy-efficient building of a given type. The average annual energy consumption hotels3
in the Hellenic
187 kWh/m*
buildings
in offices,4
varies from 406.8 kWh/m’
152 kWh/m’
in commercial
in hospitals,2 buildings,’
273 kWh/m*
to 93 kWh/m”
in in
schools.
METHODOLOGY Monitoring of buildings was done using standard reporting forms and questionnaires addressed to building occupants5 We collected relevant architectural information, descriptions of the heating and cooling systems (including central and individual units, kerosene heaters, fans) and hot-water (lighting, elevators,
systems
(electrical,
solar,
etc.),
as well as data
on electrical
systems
escalators, office equipment, etc.). The number of units and their respective power consumption were recorded, along with annual energy-consumption data. The audits yielded values for the total electrical and thermal energy consumption. The
electrical energy consumption for each subsystem (lighting, air-conditioning and other equipment) was extracted from the total value through calculations based on power consumption and hours of operation. The total energy consumption was also calculated for a series of simulations, using the computer software SPIEL6 developed for the Commission of the European Communities. Using the information which resulted from these simulations and tTo whom
all correspondence
should be addressed. 653
654
M.
Table
I.
Distribution
SANTAMOURIS
et al
of annual average energy consumption
(kWh/m’)
Type of
Lighting
Equipment
Cooling
Electrical
Thermal
Total
building
(kWh/ m’)
(kWh/ m’)
(kWh/ m’)
heating
heating
(kWh/
(kWh/ m’)
(kWh/ m’)
m’) All buildings
I6
8
2
5
62
93
Air conditioned
30
9
42
4
9.5
180
Electrically
20
7
1
49
21
98
I6
8
2
2
68
96
Thermally
heated heated
calculations, it was possible to estimate energy consumption of the various subsystems for each building. For example, electrical energy consumption for lighting was calculated from the total hours of operation and power consumption of each lamp in the building. The information collected is available in a data base.’ The primary data were analysed to assess the applicability, potential and limitations of energy-conservation techniques and the use of high-efficiency energy systems. The energy-savings calculations are based on the assumption that the building operates inside the standard ASHRAE thermal comfort zones during the heating and cooling periods. Also, visual comfort standards for school buildings are used.
ENERGY
CONSUMPTION
IN
SCHOOL
BUILDINGS
The audited buildings have been classified into four categories, based on the energy system utilized. The first category includes all 238 buildings. The second includes 16 buildings with cooling systems (central or independent A/C units). The third includes 24 buildings with electrical heating systems, while the fourth includes 138 thermally heated buildings (central combustion systems). Table 1 summarizes the breakdown of the annual average energy consumption for each category of buildings. School buildings consume the lowest amounts of energy, which may be attributed to the fact that the majority of the school buildings are not equipped with cooling systems and operate for 9 months during the year. For all audited buildings, the frequency distribution of the annual average total energy consumption per m* is shown in Fig. 1; 27% of the buildings consume less than 100 kWh/m*, while 47% consume between 100 and 200 kWh/m2. The frequency distribution of the annual average electrical energy consumption per m* is shown in Fig. 2. The average annual electricity consumption is less than 20 kWh/m* for 52% of the buildings, while 20% consume between 20
Total 100
energy
consumption .-+-
Ok
+-+
700 kWh / SQ.M.
Fig. I.
Frequency
distribution
of the annual average total energy consumption
per rn’.
Energy
Electrical
energy
conservation
655
in school buildings
Thermal
consumption
energy
consumption _+Af
/+-+ t-t
+I t/ t' / t
07 0
’
’
20
’
40
60
’
80
’
’
’
’
100120140160
’
’
01”
’
0
180 200220
20
”
40
60
”
80
electrical
distribution
”
120
”
I60
140
I80
’
200
kWh I SQ.M
kWh I SQ.M. Fig. 2. Frequency
100
of the annual
energy consumption
average
per m2.
Fig. 3. Frequency distribution of the annual thermal energy consumption per m’.
average
and 40 kWh/m2. The frequency distribution of the annual average thermal energy consumption per m2 is similar to that shown in Fig. 3. Approximately 45% of the buildings consume less than 40 kWh/m*, while 33% consume from 40 to 80 kWh/m*. Analysis
The majority of the school buildings do not have central air-conditioning systems. However, this audit included some buildings which are so equipped. Air conditioning is a major cause of energy consumption. In order to evaluate its impact, a comparison has been made between 222 naturally-ventilated (N/V) and 16 air-conditioned (A/C) buildings. The annual average energy consumption of the N/V buildings is 119 kWh/m’, while the corresponding value for the A/C buildings is 180 kWh/m*. Thus, the use of A/C systems increases consumptidn by approximately 40-50 kWh/m2. A comparison of the cumulative distributions for the electrical energyconsumption of the N/V and A/C buildings is shown in Fig. 4. Approximately 87% of the N/V buildings and 46% of the A/C buildings consume less than 50 kWh/m2. The impact of the ventilation system to indoor air quality in school buildings has not been investigated. However, results are available in Ref. 4 from a similar study conducted in office buildings. In total, 478 employees in 30 office buildings were questioned and reported health symptoms associated with their working environment. Employees in naturally ventilated buildings exhibit a higher percentage of eye irritation and disturbed concentration than in A/C buildings. This is primarily due to the fact that most of the audited buildings are located in
Electrical
energy
naturally
100
t2
80
0 z 3
60
bldgs
$
2
OY 0 20
40
60
80
100
I20
140
160
60
0
I80
I 0
50
distribution naturally
EGY 19:6-E
_tl’
150
100
200
2.50
kWh I SQ.M.
kWh / SQ.M. Fig. 4. Cumulative
bldgs
t-t
80
0
/ +
energy consumption
air conditioned
_
IO0
-+-t-t-
t-t
tt _/I’ , , Electrical
consumption
ventilated
of the annual
ventilated
(N/V)
average
electrical
and air-conditioned
energy consumption (A/C)
buildings.
(kWh/m’)
for
I
M. SANTAMOURIS et al
6.56
100 -
Thermal energy consumption insulated buildings
2 ._
xo-
IO0 -
+-f
+-+/
$
+
I SO
Thermal energy consumption non-insulated buildings ,+-+-+--+--f +/
?A-
,,,-b L
I I 00
I 150
I 200
/ +
0
I 100
50
kWh I SQ.M. Fig.
downtown traffic. Thermal
5. Cumulative
Athens,
I I 150 200
I 250
I 300
I 350
I 400
kWh f SQ.M.
distribution of the annual average thermal energy consumption for heating (kWh/m’) for insutated and non-insulated buitdings.
an area with poor
insulation
+-+
can
also
play
outdoor
air quality
a significant
role
and high noise in reducing
levels due to heavy
energy
consumption
by
minimizing heat losses during the winter and heat gains during summer. An analysis has been performed for buildings with and without thermal insulation. This investigation included 180 non-insulated and 58 insulated buildings, which is representative of the country since building insulation has been mandatory only since 1979. For insulated school buildings, the thermal energy consumption for heating insulated
was 40% less than in uninsulated buildings. The cumulative distributions and uninsulated buildings are shown in Fig. 5. Over 88% of the insulated
school buildings have an average thermal to 79% for the uninsulated buildings.
energy
consumption
below
100 kWh/m2
as compared
One of the main energy users in school buildings is lighting. The cumulative distribution is shown in Fig. 6, which illustrates that 50% of the buildings consume less than 11 kWh/m’, while approximately 75% of the buildings consume less than 20 kWh/m*. The energy consumption by various office and other electrical energy-consuming equipment may play an important role in the energy budget. For example, the introduction of computers in schools may increase the electrical energy consumption significantly. According to Ref. 8, the installed power in highly computerized spaces can reach 100 W/m2. Approximately 20% of the total energy is consumed by office equipment (personal computers, typewriters, copying machines)
and other
electrical
systems
such as elevators,
Electrical
which are difficult
to eliminate.
energy consumption for lighting
+_+-+-+
100
O-0 kWh I SQ.M. Fig. 6. Cumulative
distribution of the annual average electrical energy consumed for (kWh/m’).
lighting
Energy conservation in school buildings
ENERGY
Significant
energy
reductions
CONSERVATION
in school buildings
systems and alternative energy technologies estimated for heating, lighting, and cooling,
657
can be achieved
when more efficient
are used. The energy-savings potential as well as for combined scenarios.
energy
has been
Energy savings from heating The annual Possible
average
heating
energy
energy
consumption
conservation
for electrical
was estimated
and thermal
ouerall heat-transfer coeficient-Addition
of the proper
an overall
than that required
heat-transfer
result in thermal double-glass
energy
windows
High-efficiency
coefficient
greater
conservation
will result
of 43.9%,
heating systems-An
increase
amount
of the
of insulation period
with a payback efficiency
was 67 kWh/m*.
results:
by the current
with a payback
in 6.1% conservation
heating
with the following
(i) Reduced
to buildings building
with
code will
of 6-8 years. The use of period
of the
of 4-7 years.
heat-production
(ii) and
distribution systems by 10% may result in overall heat conservation of 6%. This can be easily achieved by proper operation and maintenance of the production unit and optimization of the control system. Additional benefits can be achieved by using appropriate equipment controls, well insulated boilers and piping systems, etc. Energy conservation from artificial lighting The annual average energy consumption for lighting was 16 kWh/m*. Twenty-six different types of lamps were investigated with technical characteristics obtained from Ref. 9. The following results were obtained: (i) Improved fluorescent lamps-The light quality of these lamps is very good with an output of 80Im/W. With these lamps, the average annual energy-consumption is 10.8 kWh/m* (30.7% reduction). lamps-These lamps produce 117 lm/W. The average 8.6 kWh/m* (45% reduction). (iii) Electronic fluorescent
(ii) Super metal-halide, fluorescent annual energy consumption equals ballasts-Electronic ballasts increase
the energy efficiency of fluorescent lamps and use 47% of the energy of a common ballast. The average annual energy consumption equals 13.7 kWh/m* (12.6% reduction). (iv) Improved luminaries (fluorescent lamps with improved performance, i.e. increased ballast reflectivity, improved difluser design, use of parabolic reflectors without diffuser, etc.)-Fluorescent lamps with 100% improved luminaries can increase the efficacy of the lamps to 100 Im/W. The average annual energy consumption equals 9.5 kWh/m* (39% reduction). (v) Occupancy sensors-Several areas in a school building, with different occupational schedules, may remain unoccupied for several hours. Leaving the lights on results in a significant waste of electrical energy. The installation of occupancy sensors to turn lights on and off reduces the energy consumption for lighting. (vi) Daylighting-The use level of natural lighting depends on the architecture of the building and the influence of neighbouring buildings. Natural lighting provides 120-130 Im/W. In a properly designed building, daylighting may reduce the electric energy consumed for lighting by 80% in comparison with a building that uses incandescent lights. Energy conservation from cooling The annual
average
total energy
consumption
for cooling
in air-conditioned
buildings,
was
42.2 kWh/m*, compared to an average value of 2.8 kWh/m* for all audited buildings. Possible energy conservation using several techniques and alternative systems was estimated with the following results: (i) Reduced external loads-Protecting interior spaces from direct solar gains by proper external shading of the opaque building walls can reduce the cooling load by 30%. Thermal insulation, according to the building code, can also reduce heat gains. (ii) Reduced internal loads-Internal heat gains from human activity and equipment are inflexible since they depend solely on the function of the building. However, heat gains from artificial lighting can
658
M. SANTAMOURIS et al
be reduced if fluorescent lamps (80 lm/W) with low heat emissions are used, resulting in a 9% reduction of the cooling load. (iii) Natural cooling techniques--Indirect evaporative coolers can provide an important reduction of the cooling load.“’ Performance data on indirect evaporative coolers have shown that energy savings of up to 60% can be achieved compared to compression-refrigeration systems. ’ I However, simulations of the performance of indirect evaporative coolers indicate that due to climatological constraints, such systems can operate during half of the cooling period. I2 The use of alternative cooling technologies such as ground cooling (using ground-air heat exchangers in places where there is available space) and indirect evaporative cooling systems (in areas with low air humidity levels) can also be used to cover a significant amount of the cooling load. During summer, excessive daytime natural ventilation, should be avoided due to high ambient temperatures which may cause overheating. ” Natural ventilation of buildings located in urban areas may pose additional problems for indoor air quality due to outdoor pollution. (iv) Night-ventilation techniques--Ventilating the building during the night hours can satisfy an important part of the cooling load while contributing to increased indoor comfort during daytime.14 Night ventilation removes the heat stored into the thermal mass of the building and precools it so that it starts its following diurnal cycle at a lower temperature. Building simulations using CASAMO” have shown that it is possible, using night-ventilation techniques, to reduce the maximum indoor-air temperature by approximately 1-2?ZL6 We have calculated for A/C buildings that night-ventilation (with 6 air changes per hour) can reduce the energy consumed for cooling by almost 50%, resulting in an annual average value of 21.41 kWh/m’. (v) Ceiling fans-The use of ceiling fans in interior spaces extends the comfort zone close to 29°C by increasing air circulation. ” The systems have low initial, operational and maintenance costs with a very short payback period. The use of ceiling fans (installed in administration offices, classrooms, large concentration areas, and hallways), combined with proper shading of the building, practically eliminates the need for airconditioning under the prevaiting weather conditions in most cities. The annual average consumption can be reduced to 14 kWh/m* (97% reduction).
OVERALL
ENERGY
CONSERVATION
The impacts of combined measures have also been simulated. A total of three scenarios for reducing energy consumption in audited school buildings was selected and investigated, including the following: (i) Scenario l-Lower End Energy Conservation-Use night ventilation in all A/C buildings, increase the thermal performance of the thermal heating systems by lo%, and use electronic fluorescent ballasts. (ii) Scenario 2-Average Energy ConservationUse night ventilation in all A/C buildings, increase the thermal performance of the thermal heating systems by lo%, use high-power fluorescent lights, and reduce by 10% the thermal losses through the building cell. (iii) Scenario 3-Higher End Energy Conservation-Use ceiling fans in A/C buildings, increase the thermal performance of the heating systems by lo%, use high-power fluorescent lights, and insulate the buildings according to the code. The calculated annual average energy consumption is shown in Fig. 7. Applying the first scenario to all audited buildings resulted in total energy conservation of 11.6%; the second reduces the total energy consumption by 19% and the third by 42.2%. For the air-conditioned buildings, the first scenario reduces energy consumption by 20.6%, the second by 26% and the third by 55%. For electrically-heated buildings, the first scenario reduces energy consumption by 8.7%, the second by 19.2% and the third by 51.9%. For thermally-heated buildings, the first scenario reduces energy consumption by 12.1%, the second by 18.9% and the third by 41.7%.
Energy conservation
Energy
in school buildings
consumption
(kWh
659
/ sq.m.)
250
I Em
200
Actual
I
Scenario
I.50
100
50
-L-
0
Air-conditioned
Fig. 7. Calculated three
overall
energy-conservation
Electrically
annual average energy consumption scenarios.
Each
scenario
includes
healed
for different several
Thermally
types of buildings,
changes
in the
heared
for the
buiidings
as
described in the text.
CONCLUSIONS
The average energy consumption in school buildings is 93 kWh/m*. This is less than similar results obtained for other types of buildings since most of the school buildings are not equipped with cooling systems and operate for only 9 months per year. Heating consumes 72.4% of the total energy, lighting 17%, while 8.7 and 2.1% are consumed by electrical equipment and cooling, respectively. Several energy-conservation measures were investigated. Energy consumption for heating can be reduced 43.9% by adding insulation to the buildings, 6.1% by using double glass windows, and 6.1% by increasing the heat-production and distribution efficiencies by 10%. Energy consumption for lighting can be reduced 30.7% by using improved fluorescent lamps (80Im/W), 45% by using super metal halide fluorescent lamps, 12.6% by using electronic fluorescent ballasts, and 39% by using improved luminaries. Energy consumption for cooling can be reduced 30% by proper shading of the building, 9% by using fluorescent lamps and reducing internal gains, 50% by using night-ventilation techniques, and 97% by using ceiling fans. Acknowled~emenls-This and the Hellenic
investigation
Productivity
Centre,
was funded by the Ministry as part of the CEC
Valoren
of Industry,
Research.
Technology
and Commerce
Programme.
REFERENCES
C. A. Balaras, “State of Energy Efficient Building in Hellas.” in The European Directory of Energy Eficient Building. James & James, London (1993). 2. M. Santamouris, E. Dascalaki, C. A. Balaras. A. Argiriou. and A. Gaglia, Energy Comers. Mgmt 35, 293 (1994). 1.
660
M.
SANTAMOURIS
et al
3. M. Santamouris, E. Dascalaki, C. A. Balaras, A. Agiriou, and A. Gaglia, “Performance Assessment and the Potential for Energy Conservation and the Use of Alternative Energy Sources in Buildings,” Proc. 3rd European Conf. on Architecture: Solar Energy in Architecture and Urban Planning, Florence, Italy (17-21 May 1993). 4. M. Santamouris, A. Argiriou, E. Dascalaki, C. A. Balaras, and A. Gaglia, Sol. Energy (in press, 1994). 5. A. Argiriou, C. A. Balaras, E. Dascalaki, A. Gaglia, G. Gountelas, K. Moustris, M. Santamouris, and M. Vallindras, “Energy Audits in Public and Commercial Buildings in Hellas,” Proc. 3rd European Symposium: Soft Energy Action at the Local Level, Chios, Hellas (11-14 September 1991). 6. C. Green, “The Simulation Tool SPIEL”, Ecotech, U.K. (1991). 7. M. Santamouris, M. Vallindras, A. Gaglia, E. Dascalaki, and J. Sigalas, “Energy Conservation in Final Report, Ministry of Industry, Research, Technology and Public and Commercial Buildings,” Commerce, Athens, Hellas (1992). Swedish Council for Buildings Research, 8. M. Holtz “Electrical Energy Savings in Office Buildings”, D17, Stockholm (1990). 9. J. Benya, Prog. Archit. 7, 320 (1989). 10. M. Antinucci, B. Fleury, J. Lopez d’Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. M. Santamouris ed., Building 2000 Yannas, ‘State of the Art of Passive Cooling of Buildings,” Research Programme, Commission of the European Communities, D.G. 12, Brussels (1991). 11. D. Pescod and R. Prudhoe, Telecommuns J. Aust. 30, 2 (1980). 12. M. Santamouris, “Natural Cooling Techniques,” in “Passive Cooling,” E. Aranovich, E. de Ohveira Fernandes, and T. C. Steemers eds., Commission of the European Communities, D.G. 12, Ispra, Italy (1990). “Natural Ventilation Techniques for Buildings in Greece,” in “Natural Cooling 13. B. Fleury, Techniques in Greece,” M. Santamouris, ed., The Centre for Renewable Energy Sources, Athens, Hellas (1990). 14. M. Antinucci, B. Fleury, J. Lopez d’Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. Yannas, Int. J. Sol. Energy 11, 251 (1992). 15. “Dialogic: Description Manual of CASAMO-CLIM,” Centre d’Energetique, Ecole Nationale Superieure des Mines de Paris, France (1988). 16. G. Agas, T. Matsaggos, M. Santamouris, and A. Argiriou, Energy Sldgs 17, 321 (1991). 17. D. Scheatzle, H. Wu, and J. Yellot, ASHRAE Trans. 95, 360 (1989).
Pergamon
ENERGY ENERGY
CONSUMPTION AND THE POTENTIAL FOR CONSERVATION IN SCHOOL BUILDINGS IN HELLAS
SANTAMOURIS,
M.
Department
C.
of Applied
A.
BALARAs,t E.
Physics,
University
DASCALAKI,
of Athens,
A.
Ippokratous
ARGIRIOU, and A. 33, GR
(Received 28 June 1993; received for publication 5 November
106 80 Athens,
GAGLIA Greece
1993)
Abstract-School
buildings (238) in Hellas were audited for construction, heating, cooling, lighting, and mechanical and electrical systems. The annual average total energy consumption is 93 kWh/m’, of which approximately 72% is consumed for space heating. The assessment of various energy-conservation techniques shows a potential for 20% overall energy conservation.
INTRODUCTION Public and commercial buildings in the European Community the total energy. It is possible to improve the existing situation
consume an estimated and establish guidelines
40% of for new
buildings in order to increase the use of renewable energy sources which can satisfy portion of the building energy needs, while maintaining necessary comfort conditions
a major for the
occupants.’ To achieve these objectives and evaluate possible scenarios for intervention, it is first necessary to document the existing situation in the building sector. For this reason, an extensive short monitoring campaign of over 1000 public and commercial buildings in Hellas was initiated in 1987. The audits included air-conditioned and naturally ventilated offices and commercial, hospital, hotel, and school buildings. Each type of building exhibits individual characteristics and problems due to specific operational needs. As a result, different design guidelines are required in order to construct an energy-efficient building of a given type. The average annual energy consumption hotels3
in the Hellenic
187 kWh/m*
buildings
in offices,4
varies from 406.8 kWh/m’
152 kWh/m’
in commercial
in hospitals,2 buildings,’
273 kWh/m*
to 93 kWh/m”
in in
schools.
METHODOLOGY Monitoring of buildings was done using standard reporting forms and questionnaires addressed to building occupants5 We collected relevant architectural information, descriptions of the heating and cooling systems (including central and individual units, kerosene heaters, fans) and hot-water (lighting, elevators,
systems
(electrical,
solar,
etc.),
as well as data
on electrical
systems
escalators, office equipment, etc.). The number of units and their respective power consumption were recorded, along with annual energy-consumption data. The audits yielded values for the total electrical and thermal energy consumption. The
electrical energy consumption for each subsystem (lighting, air-conditioning and other equipment) was extracted from the total value through calculations based on power consumption and hours of operation. The total energy consumption was also calculated for a series of simulations, using the computer software SPIEL6 developed for the Commission of the European Communities. Using the information which resulted from these simulations and tTo whom
all correspondence
should be addressed. 653
654
M.
Table
I.
Distribution
SANTAMOURIS
et al
of annual average energy consumption
(kWh/m’)
Type of
Lighting
Equipment
Cooling
Electrical
Thermal
Total
building
(kWh/ m’)
(kWh/ m’)
(kWh/ m’)
heating
heating
(kWh/
(kWh/ m’)
(kWh/ m’)
m’) All buildings
I6
8
2
5
62
93
Air conditioned
30
9
42
4
9.5
180
Electrically
20
7
1
49
21
98
I6
8
2
2
68
96
Thermally
heated heated
calculations, it was possible to estimate energy consumption of the various subsystems for each building. For example, electrical energy consumption for lighting was calculated from the total hours of operation and power consumption of each lamp in the building. The information collected is available in a data base.’ The primary data were analysed to assess the applicability, potential and limitations of energy-conservation techniques and the use of high-efficiency energy systems. The energy-savings calculations are based on the assumption that the building operates inside the standard ASHRAE thermal comfort zones during the heating and cooling periods. Also, visual comfort standards for school buildings are used.
ENERGY
CONSUMPTION
IN
SCHOOL
BUILDINGS
The audited buildings have been classified into four categories, based on the energy system utilized. The first category includes all 238 buildings. The second includes 16 buildings with cooling systems (central or independent A/C units). The third includes 24 buildings with electrical heating systems, while the fourth includes 138 thermally heated buildings (central combustion systems). Table 1 summarizes the breakdown of the annual average energy consumption for each category of buildings. School buildings consume the lowest amounts of energy, which may be attributed to the fact that the majority of the school buildings are not equipped with cooling systems and operate for 9 months during the year. For all audited buildings, the frequency distribution of the annual average total energy consumption per m* is shown in Fig. 1; 27% of the buildings consume less than 100 kWh/m*, while 47% consume between 100 and 200 kWh/m2. The frequency distribution of the annual average electrical energy consumption per m* is shown in Fig. 2. The average annual electricity consumption is less than 20 kWh/m* for 52% of the buildings, while 20% consume between 20
Total 100
energy
consumption .-+-
Ok
+-+
700 kWh / SQ.M.
Fig. I.
Frequency
distribution
of the annual average total energy consumption
per rn’.
Energy
Electrical
energy
conservation
655
in school buildings
Thermal
consumption
energy
consumption _+Af
/+-+ t-t
+I t/ t' / t
07 0
’
’
20
’
40
60
’
80
’
’
’
’
100120140160
’
’
01”
’
0
180 200220
20
”
40
60
”
80
electrical
distribution
”
120
”
I60
140
I80
’
200
kWh I SQ.M
kWh I SQ.M. Fig. 2. Frequency
100
of the annual
energy consumption
average
per m2.
Fig. 3. Frequency distribution of the annual thermal energy consumption per m’.
average
and 40 kWh/m2. The frequency distribution of the annual average thermal energy consumption per m2 is similar to that shown in Fig. 3. Approximately 45% of the buildings consume less than 40 kWh/m*, while 33% consume from 40 to 80 kWh/m*. Analysis
The majority of the school buildings do not have central air-conditioning systems. However, this audit included some buildings which are so equipped. Air conditioning is a major cause of energy consumption. In order to evaluate its impact, a comparison has been made between 222 naturally-ventilated (N/V) and 16 air-conditioned (A/C) buildings. The annual average energy consumption of the N/V buildings is 119 kWh/m’, while the corresponding value for the A/C buildings is 180 kWh/m*. Thus, the use of A/C systems increases consumptidn by approximately 40-50 kWh/m2. A comparison of the cumulative distributions for the electrical energyconsumption of the N/V and A/C buildings is shown in Fig. 4. Approximately 87% of the N/V buildings and 46% of the A/C buildings consume less than 50 kWh/m2. The impact of the ventilation system to indoor air quality in school buildings has not been investigated. However, results are available in Ref. 4 from a similar study conducted in office buildings. In total, 478 employees in 30 office buildings were questioned and reported health symptoms associated with their working environment. Employees in naturally ventilated buildings exhibit a higher percentage of eye irritation and disturbed concentration than in A/C buildings. This is primarily due to the fact that most of the audited buildings are located in
Electrical
energy
naturally
100
t2
80
0 z 3
60
bldgs
$
2
OY 0 20
40
60
80
100
I20
140
160
60
0
I80
I 0
50
distribution naturally
EGY 19:6-E
_tl’
150
100
200
2.50
kWh I SQ.M.
kWh / SQ.M. Fig. 4. Cumulative
bldgs
t-t
80
0
/ +
energy consumption
air conditioned
_
IO0
-+-t-t-
t-t
tt _/I’ , , Electrical
consumption
ventilated
of the annual
ventilated
(N/V)
average
electrical
and air-conditioned
energy consumption (A/C)
buildings.
(kWh/m’)
for
I
M. SANTAMOURIS et al
6.56
100 -
Thermal energy consumption insulated buildings
2 ._
xo-
IO0 -
+-f
+-+/
$
+
I SO
Thermal energy consumption non-insulated buildings ,+-+-+--+--f +/
?A-
,,,-b L
I I 00
I 150
I 200
/ +
0
I 100
50
kWh I SQ.M. Fig.
downtown traffic. Thermal
5. Cumulative
Athens,
I I 150 200
I 250
I 300
I 350
I 400
kWh f SQ.M.
distribution of the annual average thermal energy consumption for heating (kWh/m’) for insutated and non-insulated buitdings.
an area with poor
insulation
+-+
can
also
play
outdoor
air quality
a significant
role
and high noise in reducing
levels due to heavy
energy
consumption
by
minimizing heat losses during the winter and heat gains during summer. An analysis has been performed for buildings with and without thermal insulation. This investigation included 180 non-insulated and 58 insulated buildings, which is representative of the country since building insulation has been mandatory only since 1979. For insulated school buildings, the thermal energy consumption for heating insulated
was 40% less than in uninsulated buildings. The cumulative distributions and uninsulated buildings are shown in Fig. 5. Over 88% of the insulated
school buildings have an average thermal to 79% for the uninsulated buildings.
energy
consumption
below
100 kWh/m2
as compared
One of the main energy users in school buildings is lighting. The cumulative distribution is shown in Fig. 6, which illustrates that 50% of the buildings consume less than 11 kWh/m’, while approximately 75% of the buildings consume less than 20 kWh/m*. The energy consumption by various office and other electrical energy-consuming equipment may play an important role in the energy budget. For example, the introduction of computers in schools may increase the electrical energy consumption significantly. According to Ref. 8, the installed power in highly computerized spaces can reach 100 W/m2. Approximately 20% of the total energy is consumed by office equipment (personal computers, typewriters, copying machines)
and other
electrical
systems
such as elevators,
Electrical
which are difficult
to eliminate.
energy consumption for lighting
+_+-+-+
100
O-0 kWh I SQ.M. Fig. 6. Cumulative
distribution of the annual average electrical energy consumed for (kWh/m’).
lighting
Energy conservation in school buildings
ENERGY
Significant
energy
reductions
CONSERVATION
in school buildings
systems and alternative energy technologies estimated for heating, lighting, and cooling,
657
can be achieved
when more efficient
are used. The energy-savings potential as well as for combined scenarios.
energy
has been
Energy savings from heating The annual Possible
average
heating
energy
energy
consumption
conservation
for electrical
was estimated
and thermal
ouerall heat-transfer coeficient-Addition
of the proper
an overall
than that required
heat-transfer
result in thermal double-glass
energy
windows
High-efficiency
coefficient
greater
conservation
will result
of 43.9%,
heating systems-An
increase
amount
of the
of insulation period
with a payback efficiency
was 67 kWh/m*.
results:
by the current
with a payback
in 6.1% conservation
heating
with the following
(i) Reduced
to buildings building
with
code will
of 6-8 years. The use of period
of the
of 4-7 years.
heat-production
(ii) and
distribution systems by 10% may result in overall heat conservation of 6%. This can be easily achieved by proper operation and maintenance of the production unit and optimization of the control system. Additional benefits can be achieved by using appropriate equipment controls, well insulated boilers and piping systems, etc. Energy conservation from artificial lighting The annual average energy consumption for lighting was 16 kWh/m*. Twenty-six different types of lamps were investigated with technical characteristics obtained from Ref. 9. The following results were obtained: (i) Improved fluorescent lamps-The light quality of these lamps is very good with an output of 80Im/W. With these lamps, the average annual energy-consumption is 10.8 kWh/m* (30.7% reduction). lamps-These lamps produce 117 lm/W. The average 8.6 kWh/m* (45% reduction). (iii) Electronic fluorescent
(ii) Super metal-halide, fluorescent annual energy consumption equals ballasts-Electronic ballasts increase
the energy efficiency of fluorescent lamps and use 47% of the energy of a common ballast. The average annual energy consumption equals 13.7 kWh/m* (12.6% reduction). (iv) Improved luminaries (fluorescent lamps with improved performance, i.e. increased ballast reflectivity, improved difluser design, use of parabolic reflectors without diffuser, etc.)-Fluorescent lamps with 100% improved luminaries can increase the efficacy of the lamps to 100 Im/W. The average annual energy consumption equals 9.5 kWh/m* (39% reduction). (v) Occupancy sensors-Several areas in a school building, with different occupational schedules, may remain unoccupied for several hours. Leaving the lights on results in a significant waste of electrical energy. The installation of occupancy sensors to turn lights on and off reduces the energy consumption for lighting. (vi) Daylighting-The use level of natural lighting depends on the architecture of the building and the influence of neighbouring buildings. Natural lighting provides 120-130 Im/W. In a properly designed building, daylighting may reduce the electric energy consumed for lighting by 80% in comparison with a building that uses incandescent lights. Energy conservation from cooling The annual
average
total energy
consumption
for cooling
in air-conditioned
buildings,
was
42.2 kWh/m*, compared to an average value of 2.8 kWh/m* for all audited buildings. Possible energy conservation using several techniques and alternative systems was estimated with the following results: (i) Reduced external loads-Protecting interior spaces from direct solar gains by proper external shading of the opaque building walls can reduce the cooling load by 30%. Thermal insulation, according to the building code, can also reduce heat gains. (ii) Reduced internal loads-Internal heat gains from human activity and equipment are inflexible since they depend solely on the function of the building. However, heat gains from artificial lighting can
658
M. SANTAMOURIS et al
be reduced if fluorescent lamps (80 lm/W) with low heat emissions are used, resulting in a 9% reduction of the cooling load. (iii) Natural cooling techniques--Indirect evaporative coolers can provide an important reduction of the cooling load.“’ Performance data on indirect evaporative coolers have shown that energy savings of up to 60% can be achieved compared to compression-refrigeration systems. ’ I However, simulations of the performance of indirect evaporative coolers indicate that due to climatological constraints, such systems can operate during half of the cooling period. I2 The use of alternative cooling technologies such as ground cooling (using ground-air heat exchangers in places where there is available space) and indirect evaporative cooling systems (in areas with low air humidity levels) can also be used to cover a significant amount of the cooling load. During summer, excessive daytime natural ventilation, should be avoided due to high ambient temperatures which may cause overheating. ” Natural ventilation of buildings located in urban areas may pose additional problems for indoor air quality due to outdoor pollution. (iv) Night-ventilation techniques--Ventilating the building during the night hours can satisfy an important part of the cooling load while contributing to increased indoor comfort during daytime.14 Night ventilation removes the heat stored into the thermal mass of the building and precools it so that it starts its following diurnal cycle at a lower temperature. Building simulations using CASAMO” have shown that it is possible, using night-ventilation techniques, to reduce the maximum indoor-air temperature by approximately 1-2?ZL6 We have calculated for A/C buildings that night-ventilation (with 6 air changes per hour) can reduce the energy consumed for cooling by almost 50%, resulting in an annual average value of 21.41 kWh/m’. (v) Ceiling fans-The use of ceiling fans in interior spaces extends the comfort zone close to 29°C by increasing air circulation. ” The systems have low initial, operational and maintenance costs with a very short payback period. The use of ceiling fans (installed in administration offices, classrooms, large concentration areas, and hallways), combined with proper shading of the building, practically eliminates the need for airconditioning under the prevaiting weather conditions in most cities. The annual average consumption can be reduced to 14 kWh/m* (97% reduction).
OVERALL
ENERGY
CONSERVATION
The impacts of combined measures have also been simulated. A total of three scenarios for reducing energy consumption in audited school buildings was selected and investigated, including the following: (i) Scenario l-Lower End Energy Conservation-Use night ventilation in all A/C buildings, increase the thermal performance of the thermal heating systems by lo%, and use electronic fluorescent ballasts. (ii) Scenario 2-Average Energy ConservationUse night ventilation in all A/C buildings, increase the thermal performance of the thermal heating systems by lo%, use high-power fluorescent lights, and reduce by 10% the thermal losses through the building cell. (iii) Scenario 3-Higher End Energy Conservation-Use ceiling fans in A/C buildings, increase the thermal performance of the heating systems by lo%, use high-power fluorescent lights, and insulate the buildings according to the code. The calculated annual average energy consumption is shown in Fig. 7. Applying the first scenario to all audited buildings resulted in total energy conservation of 11.6%; the second reduces the total energy consumption by 19% and the third by 42.2%. For the air-conditioned buildings, the first scenario reduces energy consumption by 20.6%, the second by 26% and the third by 55%. For electrically-heated buildings, the first scenario reduces energy consumption by 8.7%, the second by 19.2% and the third by 51.9%. For thermally-heated buildings, the first scenario reduces energy consumption by 12.1%, the second by 18.9% and the third by 41.7%.
Energy conservation
Energy
in school buildings
consumption
(kWh
659
/ sq.m.)
250
I Em
200
Actual
I
Scenario
I.50
100
50
-L-
0
Air-conditioned
Fig. 7. Calculated three
overall
energy-conservation
Electrically
annual average energy consumption scenarios.
Each
scenario
includes
healed
for different several
Thermally
types of buildings,
changes
in the
heared
for the
buiidings
as
described in the text.
CONCLUSIONS
The average energy consumption in school buildings is 93 kWh/m*. This is less than similar results obtained for other types of buildings since most of the school buildings are not equipped with cooling systems and operate for only 9 months per year. Heating consumes 72.4% of the total energy, lighting 17%, while 8.7 and 2.1% are consumed by electrical equipment and cooling, respectively. Several energy-conservation measures were investigated. Energy consumption for heating can be reduced 43.9% by adding insulation to the buildings, 6.1% by using double glass windows, and 6.1% by increasing the heat-production and distribution efficiencies by 10%. Energy consumption for lighting can be reduced 30.7% by using improved fluorescent lamps (80Im/W), 45% by using super metal halide fluorescent lamps, 12.6% by using electronic fluorescent ballasts, and 39% by using improved luminaries. Energy consumption for cooling can be reduced 30% by proper shading of the building, 9% by using fluorescent lamps and reducing internal gains, 50% by using night-ventilation techniques, and 97% by using ceiling fans. Acknowled~emenls-This and the Hellenic
investigation
Productivity
Centre,
was funded by the Ministry as part of the CEC
Valoren
of Industry,
Research.
Technology
and Commerce
Programme.
REFERENCES
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660
M.
SANTAMOURIS
et al
3. M. Santamouris, E. Dascalaki, C. A. Balaras, A. Agiriou, and A. Gaglia, “Performance Assessment and the Potential for Energy Conservation and the Use of Alternative Energy Sources in Buildings,” Proc. 3rd European Conf. on Architecture: Solar Energy in Architecture and Urban Planning, Florence, Italy (17-21 May 1993). 4. M. Santamouris, A. Argiriou, E. Dascalaki, C. A. Balaras, and A. Gaglia, Sol. Energy (in press, 1994). 5. A. Argiriou, C. A. Balaras, E. Dascalaki, A. Gaglia, G. Gountelas, K. Moustris, M. Santamouris, and M. Vallindras, “Energy Audits in Public and Commercial Buildings in Hellas,” Proc. 3rd European Symposium: Soft Energy Action at the Local Level, Chios, Hellas (11-14 September 1991). 6. C. Green, “The Simulation Tool SPIEL”, Ecotech, U.K. (1991). 7. M. Santamouris, M. Vallindras, A. Gaglia, E. Dascalaki, and J. Sigalas, “Energy Conservation in Final Report, Ministry of Industry, Research, Technology and Public and Commercial Buildings,” Commerce, Athens, Hellas (1992). Swedish Council for Buildings Research, 8. M. Holtz “Electrical Energy Savings in Office Buildings”, D17, Stockholm (1990). 9. J. Benya, Prog. Archit. 7, 320 (1989). 10. M. Antinucci, B. Fleury, J. Lopez d’Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. M. Santamouris ed., Building 2000 Yannas, ‘State of the Art of Passive Cooling of Buildings,” Research Programme, Commission of the European Communities, D.G. 12, Brussels (1991). 11. D. Pescod and R. Prudhoe, Telecommuns J. Aust. 30, 2 (1980). 12. M. Santamouris, “Natural Cooling Techniques,” in “Passive Cooling,” E. Aranovich, E. de Ohveira Fernandes, and T. C. Steemers eds., Commission of the European Communities, D.G. 12, Ispra, Italy (1990). “Natural Ventilation Techniques for Buildings in Greece,” in “Natural Cooling 13. B. Fleury, Techniques in Greece,” M. Santamouris, ed., The Centre for Renewable Energy Sources, Athens, Hellas (1990). 14. M. Antinucci, B. Fleury, J. Lopez d’Asiain, E. Maldonado, M. Santamouris, A. Tombazis, and S. Yannas, Int. J. Sol. Energy 11, 251 (1992). 15. “Dialogic: Description Manual of CASAMO-CLIM,” Centre d’Energetique, Ecole Nationale Superieure des Mines de Paris, France (1988). 16. G. Agas, T. Matsaggos, M. Santamouris, and A. Argiriou, Energy Sldgs 17, 321 (1991). 17. D. Scheatzle, H. Wu, and J. Yellot, ASHRAE Trans. 95, 360 (1989).