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 CHIKARA 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% of 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 of 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 of the out- door-air ventilation rate. The analysis was made by computer simulation on a given de- partment store located in Tokyo (floor area 30,000 m 2, seven storeys above and two storeys bellow ground). The number of visitors was recorded by actual observation.

POPULATION OF THE DEPARTMENT STORE AND ITS OUTDOOR-AIR REQUIREMENT

For the computer simulation, we surveyed the daily fluctuation of visitors to the depart-

12

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 calcula- tion 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:

| i |

I r Iffflll l/I,AI .tlf J,i ,Jll, iAl., • " , y v v , " v ~ V ' q I

I i i i i i i i1 i i i i i i i i II I| I i I J I n . Feb. M i r . A p r . M W . J u n . Ju l . A u g . .SIp. O c t . N o v . Dec.

Fig. 1. Daily fluctuation of visitors to the depar tment store.

15'

14 •

15

12

11

C ,

~ 5 o

5

2,

I

o Time 10

~hour8~

• f •

khollday /

20 10 20 10 20 10 20 10 20 10 20 10 20 J | * i m i , t i ~ J t *

S u n . M o r t . T u e . W e d . T ~ u . F r l . S a t .

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

1 0 0

J r~

0 i , 8 0 0 1 0 0 0

R o o m C 0 2 c o n c e n t r a t i o n ( p p m )

Fig. 3. Proportional control of outdoor air damper.

(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

People

Outdoor air

Operation time

Operation season

Cooling 26 °C (DB) 50% (r.h.) Heating 22 °C (DB) 50% (r.h.)

36 .4 W / m 2

refer to Fig. 2 1,100 staff

14,000 visitors (max)

Case 1: fixed to the dasii~ ' supply rate ( 6 9 0 , 0 0 0 m /h)

Case 2: manual control Case 3: automatic control

1 0 : 0 0 ~ 1 9 : 0 0 (s ta r t at 9 :00 )

Cooling June 1 - Sep. 30 Heating Dec. 1 - Mar. 31

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 com- puter is shown in Table 2 in each of cases 1 - 3.

For building cooling, the Table shows case 3 can save 25% of 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

Energy consumption for cooling (106 kcal/month or season)

Room cooling Outdoor (a) + (b) Reduction COOLING load (a) air load (b) rate

Reduction (%)

(b) (a) + (b)

June Fixed 279 142(124) 421 Manual 279 129(117) 408 Automatic 279 128(116) 407

July Fixed 545 635(559) 1180 Manual 545 475(413) 1020 Automatic 545 299(266) 844

Aug. Fixed 608 782(636) 1390 Manual 608 582(473) 1190 Automatic 608 366(301) 974

Sep. Fixed 450 386(338) 836 Manual 450 306(272) 756 Automatic 450 199(179) 649

S e a s o n

June 1 Fixed 1882 1945(1657) 3827 to Manual 1882 1492(1275) 3374 Sep. 30 Automatic 1882 992(862) 2874

A13(A7) A14(A8)

A160(A146) A336(A293)

A200(A163) A416(A335)

~80(A66) A187(A159)

A453(A382) A953(A795)

9.2(4.9) 9.9(5.6)

25.2(23.0) 52.9(46.1)

25.6(20.8) 53.2(42.8)

20.7(17.1) 48.4(41.2)

23.3(19.6) 49.0(40.0)

m

3.1 3.3

13.6 28.5

14.4 29.9

9.6 22.4

11.8 24.9

HEATING

Dec.

Jan.

Feb.

Mar.

Season Dec. 1 to Mar. 31

Fixed 25 794(359) 819 Manual 25 502(232) 527 Automatic 25 214(102) 239 Fixed 31 810(373) 841 Manual 31 533(250) 564 Automatic 31 278(133) 309 Fixed 25 626(266) 651 Manual 25 396(175) 421 Automatic 25 196(92) 221 Fixed 20 502(200) 522 Manual 20 302(124) 322 Automatic 20 129(50) 149

Fixed 101 2732(1198) 2833 Manual 101 1733(781) 1834 Automatic 101 817(377) 918

w

A292(A127) A580(A257)

A277(A123) A532(A240)

A230(A91) A430(A174)

A200(A76) A373(A150)

A999(A417) A1915(A821)

36.8(16.0) 73.0(32.4)

34.2(15.2) 65.7(29.6)

36.7(14.5) 68.7(27.8)

39.8(15.1) 74.3(29.9)

36.6(15.2) 70.1(30.1)

35.7 70.8

32.9 63.3

35.3 66.1

38.3 71.5

35.3 67.6

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 consump- tion of energy, as indicated in our computer simulation.

Figure 5 shows the relation between out- door air and CO2 concentration under the automatic damper control designed for case 3. In Fig. 5, the minimum 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, referring to Fig. 4.

Equilibrium equation for CO2 concen- tration:

Locai exhaust" ai, ~

I I

Toihm I Kitchens I

I I

! t

Minimum o~tcloor Outdoor Exhcult air air air

Air condltioct~r

L--- ' I CO 2 Mmpier

C - '~ -Vr

Room

Fig. 4. System diagram.

M.mq. I00 + Vs.N, + Vf.Noa - - V~.N~ - - Vb .Nr

d - - VfN, = 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),

i" Outdoor air

~j] Damper motor

I

L _ : . . . .

Controller CO 2 analyzer

Fig . 6. O u t d o o r a i r r a t e c o n t r o l b y CO2 c o n c e n t r a t i o n .

Return air

~----~ Supl~y air

70

60

5O

¢D

.~ 40.

~o

~ 5o

20.

10 ̧

Design supply rate of O.A (690D00 m3/4nr)

¢ : ; : C0 2 concentration

Supply rate of O.A (automatically controlled)

.... ~ Supply rate of O.A (manual controlled)

Proportional band of 0(3 z concentration

Minimum 0 .A (26Z000Tc~/hr)

Regular

holiday

10 20 10 20 10 20 10 20

Sun. Mon. Tue. Wed.

Fig. 5. Cont ro l led o u t d o o r air ra te and CO 2 concentration.

10 20 10 20 10 , * i i

Thu. Fr i • S a t .

20

1400

1200

1000

800

500

400

200

o~ .,4

fi

o

Vb: discharged air from toilets, kitchens etc. (m3/h),

Q: room volume (56,700 ms) , CO2 concentration of supply air: N,,

V~.No,, + (V, -- Voa)JV~ N, = (2)

v,

N;: r o o m CO2 concentration one interval of calculation before,

Vo~ : outdoor air supply (m a/h). Room CO2 concentration: Nr converting eqn. (1):

M.mq.lO0 + V~, .N, + Vf .N~ N r = + v , + v f

+ Nr,_( .M'mq' IOO+V"Ns+Vf 'N°a)X y , + v f

e x p ( V s + V r ) 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.

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 motor 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.

Fig. 7. CO2 analyzer.

TABLE 3

Cost of outdoor air rate control

CO 2 analyzer Proportional controller

Control dampers Electric work Installation

Total

400,000 Yen 100,000 Yen 600,000 Yen

300,000 Yen 300,000 Yen

1,700,000 Yen

Return air

Outdoor [ ~ Sup~y air 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 de- par tment store which has a total floor area of 30,000 m 2 .

8

TABLE 4

Economic effect o f ou tdoor rate control

Annual savings using the control system Regular cost of the control system

COOLING

Calories (Table 2) Centrifugal refrigating

machine - - COP Electricity consumption a

(refrigerating machine) Price of electricity Saving for cooling

HEATING

Calories (Table 2) Boiler efficiency Fuel oil consumption a

(boiler) Price of fuel oil Saving for heating

TOTAL SAVING (cooling and heating)

953 Gcal

3.2 346 × 103 kWh

30 Yen/kWh 10,400,000 Yen

1,915 Gcal 0.75 286 × 103 litres

35 Yen/litre 10,000,000 Yen

20,400,000 Yen

Assuming that the control system is attached to each of nine air conditioners

Installation cost 15,000,000 Yen 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

3,957,000 Yen

300,000 Yen

4,257,000 Yen

aHeat loss (or heat gain) of pipeline, duct, pump, and fan are neglected. bUnknown for new product . Conversion factor 15 = 220 Yen (April 1978)

CONCLUSIONS

The control of outdoor air has a high po- tential saving on the air-conditioning energy in a building such as a department store,

where the occupancy rate varies greatly be- cause of the fluctuation in the number of visitors. Such a control system also has eco- nomic advantages in the use of inexpensive devices as shown in this paper.