ENERY COST AND CONSUMPTION IN HOSPITALS

7/31/2019 ENERY COST AND CONSUMPTION IN HOSPITALS

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International Journal on Architectural Science, Volume 5, Number 1, p.11-19, 2004

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ENERY COST AND CONSUMPTION IN A LARGE ACUTE HOSPITAL

S.C. Hu, J.D. Chen and Y.K. ChuahDepartment of Air-Conditioning and Refrigeration Engineering, National Taipei University of Technology1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan ROC

(Received 16 April 2003; Accepted 28 October 2003)

ABSTRACT

This paper presents the measured results of electricity consumption and cost in a large acute hospital in subtropicalTaipei City of Taiwan ROC from August 2001 to July 2002. It was found that air-conditioning is the majorelectricity end use, accounting for more than 50% of the total building energy use. The highest monthly EUI(Energy Use Intensity) value comes out in July with monthly value of 25.5 kWhm-2month-1 and the annual EUIvalue was 259.45 kWhm-2year-1. The highest overall DUI (Demand Use Intensity) value (45.7 Wm-2) that relatesto the electricity contract capacity, appears in August 2001. The highest EUI value found in the region ofOperation Theater (OT), in which the EUI value is about three times higher than that in general place. Some

approaches to shift peak load are proposed and discussed.

1. INTRODUCTIONEnergy efficiency becomes a necessity that cannotbe over emphasized for long-term management. It isalso the fetal factor to meet the agreements from theUnited Nations Framework Convention On ClimateChange. For green buildings, energy efficiency isonly a fundamental requirement. One of thecharacteristics of developed countries is the old agedsociety. The demand for health care and medical

services in these countries is high. Therefore, thecost of health care and medical service occupieslarge percentage of the GDP. The floor area of

hospitals and clinics is increased ever since. Energyrepresents the third largest cost in the health careservice sector behind staff wages and medicines,hence it is recognized as a major cost area. Energyconsumption in hospital buildings exhibit severalcharacteristics in energy use including: (1)air-conditioning and hot water system operate 24hours a day year round, back-up machines arerequired, (2) multi-function services required suchas surgery, diagnostic, healing, monitoring, food

preparation and laundry, (3) some medical treatmentequipment consumes huge electricity such as MRT,X ray etc. and (4) weather, operation mold andusers style affect the cost and consumption greatly.

Open publications regarding detailed electricity

consumption in hospital building are rare.Santamouris et al. [1] reported a survey results of

energy consumption in hospital and clinic buildingsin Hellas area of Greece. Williams et al. [2]surveyed energy cost and consumption in a largeacute hospital in UK. Chen et al. [3] conducted asurvey of electricity consumption of both hospital

and clinic buildings in Taiwan area. In this paper,one of the large educational hospitals in Taipei(Hospital S) is taken as a sample to measure and

analyze the energy consumption and to identify the

possibility of shifting peak load.

2. DESCRIPTION OF THE HOSPITALThe hospital, located in downtown of Taipei city, isa large educational acute hospital. Table 1 showsthe basic data of the hospital, which includesarchitectural data, occupant number, electricity

contract capacity, and temperature set point. Table2 lists the major energy-consumption itemsincluding A/C facilities, utilizes and medicalequipment.

According to the capacities of the characteristics andthe operating mode of the facilities listed in Table 2,the peak load of electricity is estimated as shown inFig. 1. It can be seen from Fig. 1 that if theabsorption chiller is not in use, then theair-conditioning system would consume about 70 %of the total electricity. Among them, the chillers, the

chilled water pumps, and the fan of the cooling

towers would need 43.94% of the total electricity.The lighting system consumes 19.22% of electricity.The elevators and escalators need 2.17% of theelectricity.

3. MEASURED RESULTS ANDDISCUSSION

The monitoring of power consumption was carriedout by using the existing power monitoring system,

and integrated with computer networking to collectthe power consumption data. To analyze the energy

efficiency, the electricity consumption iscategorized as three major items: air-conditioning,lighting, and all others.


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International Journal on Architectural Science

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600RT chiller+pump 3

44%

PC

1%

medical treatment eq.

1%

elevator

2%outlet

1%

FCU

2%exhaust fan

1%

supply fan

2%

package AHU

3%

cooking facility

1%

AHU

13%

zone pump

7%

lighting

19%

Fig. 1: Capacity of all equipments

3.1 Analysis of the Power Consumption

3.1.1 Monthly power consumption

The task starts from August 2001. It can be seenfrom Fig. 2 that in July 2002, the electricityconsumption reaches the peak. In winter, the

electricity consumption gets lower due to the lowertemperature. From March 2002, the weather getswarmer, so the power required in air-conditioning

system is rising. The power consumption in lightingand utility does not show seasonal variations. InFebruary, the power consumption is lower becausethere are only 28 days in this month. The ChineseLunar New Year is also in February.

3.1.2 Daily power consumption

Fig. 3 is the day-by-day analysis of powerconsumption for air-conditioning, lighting, andutility in the month of July 2002. Obviously inholidays, the power consumption is low becausemost of the offices and clinics is closed. Theair-conditioning, lighting, and utility are all in

partial load operation.

3.1.3 Hourly power consumption

Fig. 4 is the hour-by-hour analysis of the energyconsumption in one day. The energy consumption isincreasing from 8 oclock in the morning. Then, it

starts decreasing from 5 oclock in the evening.This trend matches with the activity of the

occupancy.

3.1.4 Analysis of Energy Use Intensity (EUI)

The original definition of Energy Use Intensity (EUI,

with unit of kWhm-2year-1) is the average electricity

consumption in unit area per year. In this report, thetime frame is shrunk to month for comparison. Fig.5 shows the variation of EUI in each month forair-conditioning, utility and lighting. It can be seenfrom this figure that most of the electricity is

consumed by the air-conditioning system. Themonthly trend is similar to the total annual energy

consumption with average EUI value of 259.45kWhm

-2year

-1.

The electricity consumption in operating theaterswas monitored individually in the day of May 142002. The result is shown in Table 3, which revealsthat the air-conditioning region of OT areaconsumes 38.8 kW of electricity, about 3.02% of thetotal electricity consumption due to air-conditioningof the building (1281.72 kW). In terms of electricity

consumption in unit area (EUI), the EUI value forair-conditioning in OT is three times (i.e. 45.06kWhm

-2month

-1/ 15.97 kWhm

-2month

-1) higher

then that in general area. Therefore, the OperatingTheater is the most electricity-consuming area.

3.1.5 Analysis of Demand Use Intensity (DUI)

Fig. 6 shows the monthly electricity peak load. InAugust 2001 the peak load is 3551 kW, more thanany other month. The next step is to analyze dailyelectricity data. The peak load in August 2001 is onAugust 28. Fig. 7 is the instant power monitoringdata on August 28. The peak of the day appeared at9 oclock in the morning. This is because at thatmoment, all the air-conditioning systems is runningat full power. Later, when the temperature reaches

the stable state, the return air becomes cooler, theair-conditioning system can then run in partial load.

The load is then decreased.


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0

200000

400000

600000

800000

1000000

1200000

8 9 10 11 12 1 2 3 4 5 6 7

monthly

monthlyelectricityconsumption(kWh)

A/C equipment lighting

Fig. 2: Monthly electricity consumption

0

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date

electricityconsumption(kW)

A/C equipment lighting total

Fig. 3: Daily electricity consumption in July 2002


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3500

00:00

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00

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00

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HOUR

elec

tricityconsumpt

ion(

kW)


Fig. 4: Hourly electricity consumption

0.00

5.00

10.00

15.00

20.00

25.00

30.00

8 9 10 11 12 1 2 3 4 5 6 7

monthly

kWh/


Fig. 5: Monthly EUI values

Table 3: Electricity consumption and the EUI value in OT

Area (m2)

Electricity consumption(kW)

EUI (kWhm-2

month-1

)

The whole hospital 77695.00 2411.67 23.09

A/C region of thehospital area

59718.00 1281.72 15.97

OT area 640.70 66.27 76.95

A/C region of theOT area

640.70 38.80 45.06


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0

500

1000

1500

2000

2500

3000

3500

4000

8 9 10 11 12 1 2 3 4 5 6 7

monthly

elec

tricityconsump

tion(

kW)


Fig. 6: Monthly peak load

0

500

1000

1500

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3000

3500

4000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

HOUR

electricityconsumption(kW)


Fig. 7: Electricity data on August 28

The definition of DUI is the peak electricity demandper unit area. The unit of DUI is Wm-2. Fig. 8

shows the monthly DUI values of the hospital. Thedata in Fig. 8 includes the total DUI and DUIs for

air-conditioning, utility and lighting. It can be seen

from the figure that the highest overall DUI value(45.7 Wm-2) is in August 2001. The DUI forair-conditioning in Hospital S is higher than utility

or lighting. The trend for air-conditioning is alsosimilar to the overall DUI. While DUI for lighting

and utility remains almost the same throughout theyear, with utility DUI slightly higher than lighting

DUI. Therefore, air-conditioning is responsible for

peak electricity demand per unit area. The demandof air-conditioning decides the contract capacity.


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0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

8 9 10 11 12 1 2 3 4 5 6 7

monthly

W/

A/C equipment lighting

Fig. 8: Monthly DUI values

3.1.6 Comparison of EUI and DUI

The overall power consumption index can beanalyzed by EUI and DEI. From Figs. 5 and 8, it isfound that in June, the air-conditioning consumesthe most power throughout the year. Then, the DUIdecreases gradually until February. The variation

rate (difference between maximum and minimumdivided by the average) is less than 62.4%. If the

variation rate goes over 62.4%, then the system isrunning abnormally and has to be repairedimmediately. In February, the demand inair-conditioning is the least in the year then startsincreasing. This is because the demand isproportional to outside temperature. While thelighting and utility remains the same throughout theyear. It is found that the average monthly EUI is21.08 (kWhm-2month-1 while the yearly EUI is 259kWhm-2month-1. The investigation in ref. 3 shows

that the magnitude of EUI in the medical center in

Northern Taiwan is about 277 kWhm

-2

month

-1

.Compared with the data in ref. 3, Hospital S has alower EUI value. This means that the energymanagement in Hospital S is better. However, thereare still some rooms for improvement and will bediscussed later.

3.2 Analysis of Electricity Consumption by

Facilities

Fig. 9 shows the electricity distribution accumulatedfrom August 2001 to July 2002. It can be seen thatthe air-conditioning takes out 52%, lighting takes

12%, and other utility takes about 36%. The setpoint temperature in air-conditioning spaces is 24

oC

(operating theater is 22oC), the relative humidity is55%.

3.3 Cost Analysis of Energy Consumption

The heat capacity of different energy sources can becalculated as follows. For electricity, one kWhr is

equal to 860 kcal. For natural gas, one cubic meterof natural gas is about 9000 kcal. Gas is primaryenergy so the efficiency is about 30%. Fig. 10shows 88% heat capacity used in the hospital in theform of electricity.

Fig. 11 is the annual energy cost in pie chart form. Itcan be seen from the figure that 65% of the total

energy cost goes to electricity. Although the gasthermal heat capacity only occupies 12% as shownin Fig. 10, the natural gas cost about 19% of the totalenergy. This is because that hot water generationand absorption water chiller uses natural gas as fuel,

and the unit price of natural gas is pretty high.

3.4 Approaches for Reducing the Peak

Hour Demanding of Electricity

3.4.1 Shifting peak load by using absorption

chillers

The measured data shows that when the A/C systemis running with three centrifugal chillers without

turning on the absorption chiller, the electricityconsumption is 2865 kW. The total electricityconsumption could go over the contract capacity of

3300 kW anytime when the other facilities arerunning in full capacity at the same time. With anabsorption chiller, only two centrifugal chillers are


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required. In such a case, the total electricityconsumption can be reduced to 2372 kW. The

absorption water chiller needs 74.5 kW only. Theentire air-conditioning system then has room forreducing the contract capacity to save cost. The fuelof the steam boilers in this hospital is natural gas,

which can provide the heat required by theabsorption chiller. The cost of natural gas is higherthan fossil fuel however, fossil fuel needs extraexpense to abate the exhaust air pollution.

3.4.2 Shifting peak load by energy management

Shutting down some facilities temporary couldreduce peak electricity load. Fig. 11 shows thatreducing chillers load is the most effective methodbecause it contributes 43% of the total electricitycapacity that could be shut down. The next effective

facility is the ventilating fans in parking lot andother exhaust fans, which could contribute 22% of

the total electricity capacity.

lighting

12%

equipment

36%

A/C

52%

Fig. 9: Electricity usage in facilities

gas thermal

capacity

12%

electricity

thermal capacity

88%

Fig. 10: Heat capacity variation of the year 2002

electricity

65%

water

12%

gas

19%

liquid oxygen

4%

Fig. 10: Annual energy cost


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chiller

43%

lighting

16%

supply/exhaust fan

22%

AHU

18% chill water zone pump

1%

Fig. 11: Facilities and their contributions (in terms of percentage of the total electricity capacity),

which may be shut down temporary for shifting peak load

4. CONCLUSION

This study investigates the power consumption andcost in a large-scale acute hospital during the periodof August 2001 to July 2002 by field measurement.

The air-conditioning takes 52%, lighting takes 12%,and other utility takes about 36% of the totalelectricity consumption in this hospital building.About 88% heat capacity used in the hospital is inthe form of electricity. The peak load takes place atnine oclock in the morning of on August 28. Thepeak of the day appeared at 9 oclock in the morning.

To shift the peak load of electricity consumption,adoption of absorption chiller and temporary shutdown of a chiller are the two most effective means.

The highest EUI value is found in the region of theoperation theater, in which the EUI value is about

three times higher then that in general place. Theresults of this study can be used as reference data tosimilar research for other hospital buildings.

ACKNOWLEDGEMENT

The authors would like to acknowledge the financial

support from the Energy Commission of theMinistry of Economic Affairs Taiwan ROC and theChinese Architecture Center. Y.M. Lin, J.S. Fan andK. Lee are also appreciated for their help inpreparing the raw data.

REFERENCES

1. M. Santamoris, E. Dascalaki, C. Balaaras, A.Argiriou and A. Gaglia, Energy performance andenergy conservation in health care buildings in

Hellas, Energy Conservation and Management,

Vol. 35, No. 4, pp. 293-305 (1994).

2. J.M. Williams, A.J. Griffiths, D. Johns and P.N.Eaton, Energy consumption in large acute

hospitals, Energy and Environment, Vol. 6, Issue 2(1995).

3. R.L. Chen, Y.K. Chuah and W.S. Lee, A survey ofthe total energy consumption of health care andshopping mall buildings in Taiwan area, Project

number MOIS 892032, Building Research Institute,Minister of Internal Affairs, October (2000).

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ENERY COST AND CONSUMPTION IN HOSPITALS