- Email: [email protected]
Effect of energy conservation by controlled ventilation: Case study in a department store
Energy and Buildings, 2 (1979) 3 - 8 © Elsevier Sequoia S.A., Lausanne - - Printed in the Netherlands
Effect of Energy Conservation by Controlled Ventilation: Case Study in a Department Store SYOGO OGASAWARA, HIROMI TANIGUCHI and C H I K A R A SUKEHIRA
Sanki Engineering Co. Ltd., Sanshin Bldg., 4-1 Yurakucho, 1-Chome, Chiyoda-ku, Tokyo 100 (Japan) (Received December 24, 1977)
The outdoor-air load in a large building uses 30 to 40% o f the total cooling or heating energy. It can be highly effective, therefore, to reduce the outdoor-air load to save energy when air-conditioning a building. One way o f doing this is to control the outdoor ventilation rate in relation to the occupancy rate (persons/m 2) since in many conventional buildings, the supply rate of outdoor air is fixed. This report refers to the energy saving in a department store through control o f the outdoor-air ventilation rate. The analysis was made by computer simulation on a given department store located in Tokyo (floor area 30,000 m 2, seven storeys above and two storeys bellow ground). The number o f visitors was recorded by actual observation.
ment store shown in Fig. 1. We modelled the fluctuation in a week shown in Fig. 2 on hourly observations. The 1100 staff of the store and the visitors' total, obtained from this weekly model, was used for the calculation of the cooling load for the building. The maximum outdoor-air requirement in this department store was calculated as 690,000 m s/h, on the assumption that an adult person exhales CO2 at 0.046 m~/h and that the occupancy rate was 0.3 to 0.5 persons/m 2 . This air requirement was used as the design supply rate for outdoor air in the simulation.
COMPUTER SIMULATION PROCEDURES
In this simulation, the energy saving performance was measured as the difference in energy consumption of the refrigerating machines or heating boilers between the following three cases of damper control:
POPULATION OF THE DEPARTMENT STORE AND ITS OUTDOOR-AIR REQUIREMENT
For the computer simulation, we surveyed the daily fluctuation of visitors to the depart12
| i
I r
|
Iffflll
•
",y
I
ii JIn.
ii Feb.
v v
ii Mir.
l/I,AI ,"v
i1 Apr.
~
,Jll, iAl.,
V'q
ii MW.
.tlf J,i
I
ii Jun.
Fig. 1. Daily fluctuation o f visitors to the department store.
ii Jul.
ii Aug.
II .SIp.
I| Oct.
Ii Nov.
I Dec.
15' 14
•
15 12 11
C
,
~
5
o •
•
5
khollday/
2,
f
I
o
Time 10
~hour8~
20
10
20
10
20
J
|
*
i
m
Sun.
Mort.
Tue.
10 i
20
10
20
10
20
10
,
t
i
~
J
t
Wed.
T~u.
Frl.
20 *
Sat.
Fig. 2. Weekly model of visitors' total.
Case 1: Fixed damper opening (conventional type) Outdoor-air ventilation rate fixed to the design supply rate of outdoor air. Case 2: Manual damper control Damper manually controlled according to the fluctuation of visitors number. Here, we assumed that the maximum rate of outdoor air would be supplied on Sundays (the busiest day) and half of this on weekdays. Case 3: Automatic damper control Damper automatically controlled according to the fluctuation of CO2 concentration
(average), measured at the point of return duct or elsewhere in the building. In case 3, a damper control related to the COs concentration was designed as shown in Fig. 3 so that the concentration would be maintained below 1000 p.p.m. (In Japan, CO2 concentration must be below 1000 p.p.m, by law). TABLE 1 Conditions for simulation Inside design condition Lighting
Cooling 26 °C (DB) 50% (r.h.) Heating 22 °C (DB) 50% (r.h.) 36.4 W / m 2
100
People
refer to Fig. 2 1,100 staff 14,000 visitors (max)
Outdoor air
Case 1: fixed to the dasii~' supply rate ( 6 9 0 , 0 0 0 m /h) Case 2: manual control Case 3: automatic control
J
r~
0
i
, 800
Room
C02
concentration
1000 (ppm)
Fig. 3. Proportional control of outdoor air damper.
Operation time
10:00
Operation season
Cooling June 1 - Sep. 30 Heating Dec. 1 - Mar. 31
~
19:00
( s t a r t at 9 : 0 0 )
In cooling-load calculation, the response factor method was adopted and the input data shown in Table 1 were used. Weather conditions used here were those of Tokyo metropolitan area for 1966, published by The Society of Heating, Air-Conditioning and Sanitary Engineers of Japan.
OUTCOME
OF COMPUTER
SIMULATION
Energy consumption calculated by computer is shown in Table 2 in each of cases 1 - 3.
For building cooling, the Table shows case 3 can save 25% o f the energy required in case 1 (the reduction is 49% when confining it to outdoor-air load) in the season from June to September. Case 2 can save 12% of the energy in case 1 (23% in outdoor-air load). For building heating, case 3 saves as much as 68% of the energy required in case 1 (70% in outdoor-air load) in the season from December to March. Case 2 can save 35% (37% in outdoor-air load). In a department store, the heating load is small, because internal heat gains within the
TABLE 2 Reduction of energy consumption by outdoor air rate control Reduction (%)
Energy consumption for cooling (106 kcal/month or season) COOLING June
Room cooling load (a)
Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic
279 279 279 545 545 545 608 608 608 450 450 450
June 1 Fixed to Manual Sep. 30 Automatic
1882 1882 1882
July
Aug.
Sep.
Outdoor air load (b) 142(124) 129(117) 128(116) 635(559) 475(413) 299(266) 782(636) 582(473) 366(301) 386(338) 306(272) 199(179)
(b) (a) + (b) 421 408 407 1180 1020 844 1390 1190 974 836 756 649
(a) + (b)
Reduction rate m
9.2(4.9) 9.9(5.6)
3.1 3.3
A160(A146) A336(A293)
25.2(23.0) 52.9(46.1)
13.6 28.5
A200(A163) A416(A335)
25.6(20.8) 53.2(42.8)
14.4 29.9
~80(A66) A187(A159)
20.7(17.1) 48.4(41.2)
9.6 22.4
A453(A382) A953(A795)
23.3(19.6) 49.0(40.0)
11.8 24.9
A292(A127) A580(A257)
36.8(16.0) 73.0(32.4)
35.7 70.8
A277(A123) A532(A240)
34.2(15.2) 65.7(29.6)
32.9 63.3
A230(A91) A430(A174)
36.7(14.5) 68.7(27.8)
35.3 66.1
A200(A76) A373(A150)
39.8(15.1) 74.3(29.9)
38.3 71.5
A999(A417) A1915(A821)
36.6(15.2) 70.1(30.1)
35.3 67.6
A13(A7) A14(A8)
S e a s o n
1945(1657) 3827 1492(1275) 3374 992(862) 2874
HEATING
Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic
25 25 25 31 31 31 25 25 25 20 20 20
Fixed Manual Mar. 31 Automatic
101 101 101
Dec.
Jan.
Feb.
Mar.
794(359) 502(232) 214(102) 810(373) 533(250) 278(133) 626(266) 396(175) 196(92) 502(200) 302(124) 129(50)
819 527 239 841 564 309 651 421 221 522 322 149
w
Season
Dec. 1 to
2732(1198) 2833 1733(781) 1834 817(377) 918
M.mq. I00 + Vs.N, + Vf.Noa
store are very large. Most of the energy is consumed by heating the outdoor air. The reduction of outdoor air, therefore, leads directly to the reduction of the consumption of energy, as indicated in our computer simulation. Figure 5 shows the relation between outdoor air and CO2 concentration under the automatic damper control designed for case 3. In Fig. 5, the m i n i m u m outdoor air is calculated as the total discharged air from toilets, kitchens, tearooms (cigarette smoke) and food booths in the basement floor. Calculation of CO2 concentration takes the following procedure, referringto Fig. 4. Equilibrium equation for CO2 concentration:
- -
VfN,
-
-
V~.N~
-
-
Vb .Nr
d
Q.-:-:-.N,
=
(1)
Clr
where Nr: room COs concentration (%), No.: outdoor CO2 concentration (0.03%), AT,: CO2 concentration of supply air (%), M: population in the building (persons/h), mq: exhaled CO2 per person (0.046 m3/ person/h), V,I~ volume of supply air (2.3 X 10 8 m3/h), Vr: return air (m°/h), Vf: infiltration (45,000 ma/h),
Minimum o~tcloor Outdoor Exhcult air air air Return air Locai exhaust"
ai,
Air condltioct~r
~ ! t
Outdoor
air
-'~-Vr Toihm Kitchens
i"
L---' I CO2 Mmpier
C
I I
~----~
Supl~y air
~j] Damper motor
I I I I
Room
I
L_: .... Controller CO2 analyzer
Fig. 4. System diagram.
F i g . 6. O u t d o o r
air rate control by CO2 concentration. 1400
70 Design supply rate of O.A (690D00 m3/4nr)
60
¢
:
; :
1200
C0 2 c o n c e n t r a t i o n Supply
.... ~
rate
of O . A
(automatically
controlled)
Supply rate of O.A (manual controlled)
1000
5O ¢D
.~
Proportional
b a n d o f 0(3z c o n c e n t r a t i o n
40.
800
~o
~
o~
.,4
fi
5o
500 o
M i n i m u m 0 .A
(26Z000Tc~/hr)
20.
400 Regular holiday
10 ¸
10
20
10
20
10
20
10
200
20
10
20
,
Sun.
Mon.
Tue.
Wed.
Fig. 5. C o n t r o l l e d o u t d o o r air r a t e a n d CO 2 concentration.
Thu.
10
20
10
*
i
i
Fr i •
20 Sat.
Vb: discharged air from toilets, kitchens etc. (m3/h), Q: room volume (56,700 ms), CO2 concentration of supply air: N,, N, =
V~.No,, + (V, -- Voa)JV~
(2)
v,
N;: r o o m CO2 concentration one interval of calculation before, Vo~ : outdoor air supply (m a/h). R o o m CO2 concentration: Nr converting eqn. (1): Nr=
M.mq.lO0 + V~, .N, + Vf.N~ v,+vf
+
+ Nr,_(.M'mq'IOO+V"Ns+Vf'N°a)X y,+vf exp(Vs+Vr) G N~t: initial value of N~ N~ in eqn. (2) is the value of Nr one hour earlier. N; is induced to adjust time lag in the ducting system.
Fig. 7. CO2 analyzer. TABLE 3 Cost of outdoor air rate control
ECONOMIC EFFECT OF THE OUTDOOR AIR CONTROL
Figure 6 shows an example of automatic outdoor-air control, in which the damper is controlled automatically according to room CO2 concentration. Motor dampers, attached to an outdoor air duct, a return duct and an exhaust air duct, control outdoor air without affecting the supply of air volume. These three dampers drive directly or in reverse according to the CO2 concentration measured in the return duct. Total costs for this control system can be kept below 1,700,000 Yen by using such a simple CO2 analyzer as shown in Fig. 7 (see Table 3). When the outdoor-air/return-air ratio is small, more concise control systems can be applied. Figure 8 shows an example in which only the m o t o r damper of outdoor air is automatically controlled. Here, the air supply volume will decrease. In this case the system costs are reduced by 20 to 30% compared with the system in Fig. 6.
400,000 Yen 100,000 Yen 600,000 Yen 300,000 Yen 300,000 Yen 1,700,000 Yen
CO 2 analyzer Proportional controller Control dampers Electric work Installation Total Return air
Outdoor[ ~ air
Sup~y air
Controller
CO 2 anJyzJ¢
Fig. 8. Outdoor air rate control by CO2 concentration (for small ON rate).
Table 4 shows the energy conservation effect (a) and the economic effect (b) of the outdoor air control in the case of a department store which has a total floor area of 30,000 m 2 .
8 TABLE 4 Economic effect o f o u t d o o r rate control Annual savings using the control system
Regular cost o f the control system
COOLING
Assuming that the control system is attached to each o f nine air conditioners
Calories (Table 2) Centrifugal refrigating machine - - COP Electricity consumption a (refrigerating machine) Price o f electricity Saving for cooling
953 Gcal 3.2 346 × 103 kWh 30 Yen/kWh 10,400,000 Yen
HEATING Calories (Table 2) Boiler efficiency Fuel oil consumption a (boiler) Price o f fuel oil Saving for heating
1,915 Gcal 0.75 286 × 103 litres
TOTAL SAVING (cooling and heating)
20,400,000 Yen
Installation cost c - r . f = 0.2638 minimum life (estimation) = 5 years b annual interest = 10% Fixed cost (15,000,000 Yen × 0.2638) Maintenance (15,000,000 Yen × 0.02) Total
15,000,000 Yen
3,957,000 Yen 300,000 Yen 4,257,000 Yen
35 Yen/litre 10,000,000 Yen
aHeat loss (or heat gain) o f pipeline, duct, pump, and fan are neglected. b U n k n o w n for new product. Conversion factor 15 = 220 Yen (April 1978)
CONCLUSIONS
The control of o u t d o o r air has a high potential saving on the air-conditioning energy in a building such as a department store,
where the occupancy rate varies greatly because o f the fluctuation in the number of visitors. Such a control system also has economic advantages in the use o f inexpensive devices as shown in this paper.
Effect of Energy Conservation by Controlled Ventilation: Case Study in a Department Store SYOGO OGASAWARA, HIROMI TANIGUCHI and C H I K A R A SUKEHIRA
Sanki Engineering Co. Ltd., Sanshin Bldg., 4-1 Yurakucho, 1-Chome, Chiyoda-ku, Tokyo 100 (Japan) (Received December 24, 1977)
The outdoor-air load in a large building uses 30 to 40% o f the total cooling or heating energy. It can be highly effective, therefore, to reduce the outdoor-air load to save energy when air-conditioning a building. One way o f doing this is to control the outdoor ventilation rate in relation to the occupancy rate (persons/m 2) since in many conventional buildings, the supply rate of outdoor air is fixed. This report refers to the energy saving in a department store through control o f the outdoor-air ventilation rate. The analysis was made by computer simulation on a given department store located in Tokyo (floor area 30,000 m 2, seven storeys above and two storeys bellow ground). The number o f visitors was recorded by actual observation.
ment store shown in Fig. 1. We modelled the fluctuation in a week shown in Fig. 2 on hourly observations. The 1100 staff of the store and the visitors' total, obtained from this weekly model, was used for the calculation of the cooling load for the building. The maximum outdoor-air requirement in this department store was calculated as 690,000 m s/h, on the assumption that an adult person exhales CO2 at 0.046 m~/h and that the occupancy rate was 0.3 to 0.5 persons/m 2 . This air requirement was used as the design supply rate for outdoor air in the simulation.
COMPUTER SIMULATION PROCEDURES
In this simulation, the energy saving performance was measured as the difference in energy consumption of the refrigerating machines or heating boilers between the following three cases of damper control:
POPULATION OF THE DEPARTMENT STORE AND ITS OUTDOOR-AIR REQUIREMENT
For the computer simulation, we surveyed the daily fluctuation of visitors to the depart12
| i
I r
|
Iffflll
•
",y
I
ii JIn.
ii Feb.
v v
ii Mir.
l/I,AI ,"v
i1 Apr.
~
,Jll, iAl.,
V'q
ii MW.
.tlf J,i
I
ii Jun.
Fig. 1. Daily fluctuation o f visitors to the department store.
ii Jul.
ii Aug.
II .SIp.
I| Oct.
Ii Nov.
I Dec.
15' 14
•
15 12 11
C
,
~
5
o •
•
5
khollday/
2,
f
I
o
Time 10
~hour8~
20
10
20
10
20
J
|
*
i
m
Sun.
Mort.
Tue.
10 i
20
10
20
10
20
10
,
t
i
~
J
t
Wed.
T~u.
Frl.
20 *
Sat.
Fig. 2. Weekly model of visitors' total.
Case 1: Fixed damper opening (conventional type) Outdoor-air ventilation rate fixed to the design supply rate of outdoor air. Case 2: Manual damper control Damper manually controlled according to the fluctuation of visitors number. Here, we assumed that the maximum rate of outdoor air would be supplied on Sundays (the busiest day) and half of this on weekdays. Case 3: Automatic damper control Damper automatically controlled according to the fluctuation of CO2 concentration
(average), measured at the point of return duct or elsewhere in the building. In case 3, a damper control related to the COs concentration was designed as shown in Fig. 3 so that the concentration would be maintained below 1000 p.p.m. (In Japan, CO2 concentration must be below 1000 p.p.m, by law). TABLE 1 Conditions for simulation Inside design condition Lighting
Cooling 26 °C (DB) 50% (r.h.) Heating 22 °C (DB) 50% (r.h.) 36.4 W / m 2
100
People
refer to Fig. 2 1,100 staff 14,000 visitors (max)
Outdoor air
Case 1: fixed to the dasii~' supply rate ( 6 9 0 , 0 0 0 m /h) Case 2: manual control Case 3: automatic control
J
r~
0
i
, 800
Room
C02
concentration
1000 (ppm)
Fig. 3. Proportional control of outdoor air damper.
Operation time
10:00
Operation season
Cooling June 1 - Sep. 30 Heating Dec. 1 - Mar. 31
~
19:00
( s t a r t at 9 : 0 0 )
In cooling-load calculation, the response factor method was adopted and the input data shown in Table 1 were used. Weather conditions used here were those of Tokyo metropolitan area for 1966, published by The Society of Heating, Air-Conditioning and Sanitary Engineers of Japan.
OUTCOME
OF COMPUTER
SIMULATION
Energy consumption calculated by computer is shown in Table 2 in each of cases 1 - 3.
For building cooling, the Table shows case 3 can save 25% o f the energy required in case 1 (the reduction is 49% when confining it to outdoor-air load) in the season from June to September. Case 2 can save 12% of the energy in case 1 (23% in outdoor-air load). For building heating, case 3 saves as much as 68% of the energy required in case 1 (70% in outdoor-air load) in the season from December to March. Case 2 can save 35% (37% in outdoor-air load). In a department store, the heating load is small, because internal heat gains within the
TABLE 2 Reduction of energy consumption by outdoor air rate control Reduction (%)
Energy consumption for cooling (106 kcal/month or season) COOLING June
Room cooling load (a)
Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic
279 279 279 545 545 545 608 608 608 450 450 450
June 1 Fixed to Manual Sep. 30 Automatic
1882 1882 1882
July
Aug.
Sep.
Outdoor air load (b) 142(124) 129(117) 128(116) 635(559) 475(413) 299(266) 782(636) 582(473) 366(301) 386(338) 306(272) 199(179)
(b) (a) + (b) 421 408 407 1180 1020 844 1390 1190 974 836 756 649
(a) + (b)
Reduction rate m
9.2(4.9) 9.9(5.6)
3.1 3.3
A160(A146) A336(A293)
25.2(23.0) 52.9(46.1)
13.6 28.5
A200(A163) A416(A335)
25.6(20.8) 53.2(42.8)
14.4 29.9
~80(A66) A187(A159)
20.7(17.1) 48.4(41.2)
9.6 22.4
A453(A382) A953(A795)
23.3(19.6) 49.0(40.0)
11.8 24.9
A292(A127) A580(A257)
36.8(16.0) 73.0(32.4)
35.7 70.8
A277(A123) A532(A240)
34.2(15.2) 65.7(29.6)
32.9 63.3
A230(A91) A430(A174)
36.7(14.5) 68.7(27.8)
35.3 66.1
A200(A76) A373(A150)
39.8(15.1) 74.3(29.9)
38.3 71.5
A999(A417) A1915(A821)
36.6(15.2) 70.1(30.1)
35.3 67.6
A13(A7) A14(A8)
S e a s o n
1945(1657) 3827 1492(1275) 3374 992(862) 2874
HEATING
Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic Fixed Manual Automatic
25 25 25 31 31 31 25 25 25 20 20 20
Fixed Manual Mar. 31 Automatic
101 101 101
Dec.
Jan.
Feb.
Mar.
794(359) 502(232) 214(102) 810(373) 533(250) 278(133) 626(266) 396(175) 196(92) 502(200) 302(124) 129(50)
819 527 239 841 564 309 651 421 221 522 322 149
w
Season
Dec. 1 to
2732(1198) 2833 1733(781) 1834 817(377) 918
M.mq. I00 + Vs.N, + Vf.Noa
store are very large. Most of the energy is consumed by heating the outdoor air. The reduction of outdoor air, therefore, leads directly to the reduction of the consumption of energy, as indicated in our computer simulation. Figure 5 shows the relation between outdoor air and CO2 concentration under the automatic damper control designed for case 3. In Fig. 5, the m i n i m u m outdoor air is calculated as the total discharged air from toilets, kitchens, tearooms (cigarette smoke) and food booths in the basement floor. Calculation of CO2 concentration takes the following procedure, referringto Fig. 4. Equilibrium equation for CO2 concentration:
- -
VfN,
-
-
V~.N~
-
-
Vb .Nr
d
Q.-:-:-.N,
=
(1)
Clr
where Nr: room COs concentration (%), No.: outdoor CO2 concentration (0.03%), AT,: CO2 concentration of supply air (%), M: population in the building (persons/h), mq: exhaled CO2 per person (0.046 m3/ person/h), V,I~ volume of supply air (2.3 X 10 8 m3/h), Vr: return air (m°/h), Vf: infiltration (45,000 ma/h),
Minimum o~tcloor Outdoor Exhcult air air air Return air Locai exhaust"
ai,
Air condltioct~r
~ ! t
Outdoor
air
-'~-Vr Toihm Kitchens
i"
L---' I CO2 Mmpier
C
I I
~----~
Supl~y air
~j] Damper motor
I I I I
Room
I
L_: .... Controller CO2 analyzer
Fig. 4. System diagram.
F i g . 6. O u t d o o r
air rate control by CO2 concentration. 1400
70 Design supply rate of O.A (690D00 m3/4nr)
60
¢
:
; :
1200
C0 2 c o n c e n t r a t i o n Supply
.... ~
rate
of O . A
(automatically
controlled)
Supply rate of O.A (manual controlled)
1000
5O ¢D
.~
Proportional
b a n d o f 0(3z c o n c e n t r a t i o n
40.
800
~o
~
o~
.,4
fi
5o
500 o
M i n i m u m 0 .A
(26Z000Tc~/hr)
20.
400 Regular holiday
10 ¸
10
20
10
20
10
20
10
200
20
10
20
,
Sun.
Mon.
Tue.
Wed.
Fig. 5. C o n t r o l l e d o u t d o o r air r a t e a n d CO 2 concentration.
Thu.
10
20
10
*
i
i
Fr i •
20 Sat.
Vb: discharged air from toilets, kitchens etc. (m3/h), Q: room volume (56,700 ms), CO2 concentration of supply air: N,, N, =
V~.No,, + (V, -- Voa)JV~
(2)
v,
N;: r o o m CO2 concentration one interval of calculation before, Vo~ : outdoor air supply (m a/h). R o o m CO2 concentration: Nr converting eqn. (1): Nr=
M.mq.lO0 + V~, .N, + Vf.N~ v,+vf
+
+ Nr,_(.M'mq'IOO+V"Ns+Vf'N°a)X y,+vf exp(Vs+Vr) G N~t: initial value of N~ N~ in eqn. (2) is the value of Nr one hour earlier. N; is induced to adjust time lag in the ducting system.
Fig. 7. CO2 analyzer. TABLE 3 Cost of outdoor air rate control
ECONOMIC EFFECT OF THE OUTDOOR AIR CONTROL
Figure 6 shows an example of automatic outdoor-air control, in which the damper is controlled automatically according to room CO2 concentration. Motor dampers, attached to an outdoor air duct, a return duct and an exhaust air duct, control outdoor air without affecting the supply of air volume. These three dampers drive directly or in reverse according to the CO2 concentration measured in the return duct. Total costs for this control system can be kept below 1,700,000 Yen by using such a simple CO2 analyzer as shown in Fig. 7 (see Table 3). When the outdoor-air/return-air ratio is small, more concise control systems can be applied. Figure 8 shows an example in which only the m o t o r damper of outdoor air is automatically controlled. Here, the air supply volume will decrease. In this case the system costs are reduced by 20 to 30% compared with the system in Fig. 6.
400,000 Yen 100,000 Yen 600,000 Yen 300,000 Yen 300,000 Yen 1,700,000 Yen
CO 2 analyzer Proportional controller Control dampers Electric work Installation Total Return air
Outdoor[ ~ air
Sup~y air
Controller
CO 2 anJyzJ¢
Fig. 8. Outdoor air rate control by CO2 concentration (for small ON rate).
Table 4 shows the energy conservation effect (a) and the economic effect (b) of the outdoor air control in the case of a department store which has a total floor area of 30,000 m 2 .
8 TABLE 4 Economic effect o f o u t d o o r rate control Annual savings using the control system
Regular cost o f the control system
COOLING
Assuming that the control system is attached to each o f nine air conditioners
Calories (Table 2) Centrifugal refrigating machine - - COP Electricity consumption a (refrigerating machine) Price o f electricity Saving for cooling
953 Gcal 3.2 346 × 103 kWh 30 Yen/kWh 10,400,000 Yen
HEATING Calories (Table 2) Boiler efficiency Fuel oil consumption a (boiler) Price o f fuel oil Saving for heating
1,915 Gcal 0.75 286 × 103 litres
TOTAL SAVING (cooling and heating)
20,400,000 Yen
Installation cost c - r . f = 0.2638 minimum life (estimation) = 5 years b annual interest = 10% Fixed cost (15,000,000 Yen × 0.2638) Maintenance (15,000,000 Yen × 0.02) Total
15,000,000 Yen
3,957,000 Yen 300,000 Yen 4,257,000 Yen
35 Yen/litre 10,000,000 Yen
aHeat loss (or heat gain) o f pipeline, duct, pump, and fan are neglected. b U n k n o w n for new product. Conversion factor 15 = 220 Yen (April 1978)
CONCLUSIONS
The control of o u t d o o r air has a high potential saving on the air-conditioning energy in a building such as a department store,
where the occupancy rate varies greatly because o f the fluctuation in the number of visitors. Such a control system also has economic advantages in the use o f inexpensive devices as shown in this paper.