1-s2.0-S0378778813005057-main

Energy and Buildings 67 (2013) 7078

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Energy and Buildings

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Electricity cost saving comparison due to tariff chstorage (ITS) usage based on a hybrid centrifugalbuildin tiv

Mohamm a,Ghazali Ta Faculty of Engb Asset and Ma alaysia

a r t i c l

Article history:Received 24 JuReceived in reAccepted 5 Au

Keywords:Electricity chaCost savingDistrict cooling systemTariff structureIce thermal storage

ct cooed. Inumidrawakoling ty cha

with and without ice-thermal storage (ITS) systems on the buildings were investigated. It was found that,due to the local tariff status, marginally saving can be achieved in the range of 0.083.13% if a new tariffis adopted; and a total of further saving of 1.262.43% if ITS is operated. This marginally saving is mainlydue to the local tariff conditions and lower local temperature range (T) which are less favorable ascompared with those reported in the literature elsewhere.

2013 The Authors. Published by Elsevier B.V.

1. Introdu

The builtions, i.e., bu(occupants)use due to time [1]. Fois due primeither for hcooling sysing systemdemand whThe advantwith indiviothers:

CorresponE-mail add

(M.O. Abdullah

0378-7788 2http://dx.doi.o

Open access under CC BY-NC-ND license.ction

ding industry involves two kinds of energy applica-ilding construction application, and post-constructions

application. The latter consumes much of the energythe energy consumption over a period of much longerr modern buildings, one of the notable energy usagesarily to the electrical-driven air conditioning systems,eating or cooling. For bigger system such as districttems (DCS) application, higher capacity of the cool-s are necessary due to the higher cooling or heatingich necessarily incur enormous electrical energy costs.ages of DCS systems in huge building areas compareddual air-conditioning unit systems are many, among

ding author. Tel.: +60 82 583280; fax: +60 82 583409.resses: [email protected], [email protected]).

Economical advantages: The DCS have overall lower total capitalcost compared to the split cooling that require their own coolingequipment(s) [2,3].

Space conservation: The space required for cooling equipment(s)can become vacant for other purposes for a district cooling sys-tems [2,3].

Noise reduction: The noise that produced by the cooling machinescan be avoided in the consumer buildings [2].

Flexibility: The DCS systems also exible to employ a widerange of inter-related thermal storage technologies such as co-generation, tri-generation, and thermal energy storage (TES)[2,3]. The present paper is primarily concerning with the TESstorage technique.

In respect of energy usage, it was reported that thermal energystorage (TES) not only dramatically reduces the use of peak-periodhigh cost energy; it can also reduce the total energy usage by asmuch as 13% [4,5]. The United State Department of Energy reportedthat many ice storage applications can result in lower rst costand/or with higher system efciency as compared to non-storagesystem [6]. This is because ice-storage allows downsizing of theconventional chiller system [3,7], the resulting cost savings maysubstantially or entirely cover the added incremental cost of thestorage system [7]. MacCracken [8] pointed out that since thermal

013 The Authors. Published by Elsevier B.V. rg/10.1016/j.enbuild.2013.08.008

Open access under CC BY-NC-ND license.gs: A university district cooling perspec

ad Omar Abdullaha,, Lim Pai Yii a, Ervina Junaidiambia, Mohd Asrul Mustaphab

ineering, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysianagement Division, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, M

e i n f o

ne 2013vised form 3 August 2013gust 2013

rge

a b s t r a c t

In this paper, the case study of a distri(lat: 0129; long: 11020E) is presentaround 3235 C coupled with high hcharge for the Universiti Malaysia Samonth. In this paper, a few district coorder to minimize the overall electrici/ locate /enbui ld

ange and ice thermal-ITS system fore

ling system of a university located in a South East Asia region general, the university has high peak ambient temperature ofity of about 85% during afternoon period. The total electricity

Campus is very high amounting to more than $314,911 perschemes are investigated to provide what-if analysis and inrges. Few scenarios designed for the application of centrifugal

M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078 71

Nomenclature

C1 commercial 1C2 C3 CAIS CH DCS FCST MEP MIS N/A S1 S2 S3 SESCO UNIMAST

MeasuremC m2

RM % RT unit $

storage metcost for powwill be reduto non-peak(1) in the ncient than dnight time b

Results fshows an evical major Cas 10% and

Sebzali abuilding in dition. Theythe AC systearound 40%to the advabetween daenergy cost

A hybridErwin Middto able to sof the contlow-interesby completproject usescept with astorage systby carefullywhere the coperation anormal con

Morgan a school wThey investsystems to

building energy costs. The set point temperature during theoccupied periods from 8:30 to 17:00 was at 24 C and 32 C duringunoccupied periods. A 50 ton scroll compressor operates duringthe night (from 02:00 to 08:00) and charges three ice-tanks with

capa. Thebe s

is duptio

to beplicanome of ctricny gaowev

sysive tirderotentvestiIn thS simancd un

factof thund

capenerattran theorin

tarig thhen tructm cig coy, ancommercial 2commercial 3Centre Academic and Information Serviceschillerdistrict cooling systemFaculty Resource Science and Technologymechanical and electrical plantmain intake supplynot availableScenario 1Scenario 2Scenario 3Sarawak Electricity Supply Corporation

Universiti Malaysia Sarawakambient temperature difference

ent unitsdegree Celsiusmeter squareRinggit Malaysiapercentrefrigerant tonkWh (kilowatt-hour)US dollar (USD)

hod operate at full load during the night time, the fuelering the ITS plant during the night (non-peak hours)ced, as the cooling demand is shifted from peak hours

hours. The two main reasons for the saving are thus:ight, the base load plants are much more energy ef-aytime plants; and (2) line losses are less during theecause much less power is transmitted at night.rom the study by the California Energy Commission [9]en higher energy saving potential gures, for two typ-alifornia utilities with energy usage reduction as much

a totalsystemcould savingconsum

It isTES apan ecoMosquing elehave aegy. Hstorageincent

In oness pwas inKong. TRNSYperformgies, andesigntance oThey fostoragebetter is not shorteneighbportingapplyinonly wtariff s

Frofavorincountrcan up to 30% has been reported [9,10].nd Rubini [10] had conducted an investigation in a clinicKuwait, which has hot climates with long summer con-

found out, via computational modeling analysis, thatms consume around 61% of the peak electrical duty and

of the total electricity consumption. The saving is duentage of hot climate and huge temperature differencey and night time, considerably long summer and lows in Kuwait.

chilled water/ice thermal storage plant for the Lucilele School in Colorado, United State, has been reportedave more than $18,000 in energy costs annually. Oneributing saving factors reported is due to the offer oft nancing from the local Florida power authority, andely eliminating chiller demand from the utility bill. The

a exible ice thermal storage management system con- demand limit-controlled, chiller priority, and partialem. This ice storage system optimized energy efciency

avoiding electrical demand peaks caused by the system,hiller/storage match is designed for continuous chillert about 6 C chilled water supply temperature underditions [11].and Krarti [12] reported a TES application study onith total small oor area of 65,000 ft2 (6038.7 m2).igated the inuences of using active and passive TESshift the peak cooling loads to the nights to reduce

Generally, tregions whtemperaturutility compthat incorp

The preearlier in 2parametersdistributionhowever, isaims to seeto the followchange andcation scenand most reyear, i.e. 20

2. The UNI

Universirahan of SarCampus) inpus is approtime (Fig. 1hot tropicacity of 570 tons/h using the internal melt ice-on-coily found that around 47% of the annual electricity costaved by employing the TES systems. This huge coste to the incentive utility rate of $0.0164 kWh1 as a atn rate and a demand charge of $11.24 kW1.

noted that not all the literature came up with favorabletions. Habeebullah [13], for instance, had conductedic feasibility of using the huge ITS system in the GrantMakkah, the results of which show that as the exist-ity rate is xed at $0.07 kWh1, the ITS system does notin neither for the partial nor for the full storage strat-er, the author indicated that by employing the energytem via full load storage strategy combined with anme structured rate, the electricity cost could be reduced.

to evaluate the energy performance and cost effective-ial, a feasible district cooling with ice-storage systemgated by Chan et al. [14] for a hypothetical site in Hongeir works, a parametric study employing DOE-2 andulation software was conducted to evaluate the systeme at different partial storage capacities, control strate-der three different tariff structures. Other than the basicrs, the results from 27 cases studies showed the impor-e tariff structure, the capital cost and electricity costs.

out that the district cooling plant with about 40% ice-acity and chiller-priority control sequence can providegy performance. However, the saving in electricity costctive. The authors further suggested that in order to

payback period, the power supply must come from theg region that provides lower electrical charges and sup-ff structure. This also implies that there is a potential ofe integrated technology in the South China region butthe investment becomes favorable and with supportingure.ted literature and experiences obtained elsewhere,nditions of TES applications can vary from country tod in fact region to region, due to numerous factors.he usage of ice-thermal technology has been higher inere a signicant day and night-time differential in bothe, in the lower price of electricity exists, and with someanies provide cash incentives or rebates to developers

orate TES schemes.sent study is an extension of previous work reported007 [15]. The previous work briey investigated some

inuencing the DCS performance, in particular cool air, chiller capacity, and occupant behavior. This paper,

an extension of the previous work. The current studyk on the overall district cooling saving possibilities dueing two application aspects, viz. (1) the effects of tariff

(2) the effect of ITS usage. For that purpose, few appli-arios are given for comparison. Due to the completenesscent data available, the authors have chosen a typical11 for the analysis.

MAS district cooling system

ti Malaysia Sarawak (UNIMAS) is located in Kota Sama-awak. By completion of new campus (or known as West

the year of 2005, the total build-up area of the new cam-ximately 223,619 m2 and keep expanding from time to). With the location at equatorial climate which providel weather basically on 365 days per year with average

72 M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078

Fig. 1. D

temperaturwas installefortable envcooling sysdistrict cooarea and thMost of thetem that esfrom mechaundergrounend of 2011for cooling chillers fromtan (RT).1 Uof eight cenwith total 9were used fwith ice thedirectly to bplished by replace theof heat tranassist in trachillers andas well as

1 Anyhow, itheir individuabuilding, the ris not econommidnight. Apalike Faculty Realso having th

-

0,000

1,00 0,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

4,500,000

5,000,000

W

Elec tricit y Consu mption (per half hour) vs Time

lectri 2011)

utingve thhe elache

5]), thgatetricitugal-S cae frositysolinThe ptio

re ar, CH00 RT

funcistrict chilled water distribution pipeline for DCS in UNIMAS.

e of 2535C during daytime, air conditioning systemd in almost all of the building spaces to provide com-ironment for both students and staffs [15]. The main

tem which is selected to install in this new campus is

50

Fig. 2. E(August

distribnot hapeak. Tsive, reRef. [1investiall eleccentrifUNIMApipelinunivertrict CoFig. 2. consum

The400 RTCH6-8chillerling system (DCS) due to the extremely huge built-upe potential to expand in future depend on demand.

buildings are operating with the air-conditioning sys-sentially sharing the cooling from the same resourcesnical and electrical plant (MEP) with the piping buriedd for distribution. There are a total of 15 facilities (as) in the compound which were using the same resourcespurpose. The total cooling capacities supplied by base

MEP reached up to approximately 8000 refrigerantp until December 2011 in the MEP, there are a totaltrifugal chillers with total 8500 RT, two brine chillers00 RT, and also 10 cooling towers of total 14,000 RTor provide heat rejection. Brines chillers are connectedrmal storage; while centrifugal chillers supply coolinguildings by chilled water. The heat rejection is accom-using cooling towers with makeup water tank as to

evaporated water in cooling towers. For effectivenesssfer, heat exchangers and pumps also use in MEP tonsporting the cooling to buildings. However, the brine

the ITS are just for backup and not in operating so far,heat exchanges which used to assist brine chillers in

t is to be noted that there are few other standalone buildings havingl cooling systems, for instance the Centre of Information Study (CAIS)equirement of which is to operate 24 hours per day due to which itical for the MEP to supply cooling just for the CAIS building alone atrt from that, some buildings which are located too far from the based,course Science and Technology (FRST) external laboratory buildingeir individual cooling equipments.

(facility). Thto chargingWhile for thtotal of 14,0to replace tare one expthat, there (two units able at the loop used istrifugal chiNevertheleeach consumcentral planing is differis supply vithe central brine chillesystem andrequired tounits distrialso used tointo the folchiller systeconsists of exchanger sing system)throughoutchiller plac0 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0

hr

MIS

MEP

city consumption of the district cooling system for a typical month. MIS, main intake supply; MEP, mechanical and electrical plant.

. This is mainly due to the fact that the current tariff doese different charging rate provision for on peak and offectricity charge of UNIMASs new campus is very expen-d more than $314,911 or more per month (data fromus in the present work, some feasible study are seek to

the effects on the use of different tariff in reducing over-y cost; and to estimate the how much saving if a hybridthermal storage system is used instead. Fig. 1 shows thempus layout plan illustrating the district cooling waterm the Mechanical Electrical Plant (MEP) throughout the

campus. The total electricity consumption of the Dis-g System for a typical month (August 2011) is given inMEP only consumed about 34% while the rest of then goes to the main intake supply (MIS).e eight centrifugal chillers with total of 8500 RT (CH1-2-1300 RT, CH3-1300 RT, CH4-1300RT, CH5-800 RT,, CH7-1300 RT, and CH8-1300 RT), the centrifugaltion as supply direct cooling to consumer buildingsere are also two brine chillers in the MEP which used

the ITS (7000 RTh) with total of 900 RT (450 RT each).e heat rejection system, ten units of cooling towers with00 RT (1400 RT each) applied in central plant. Between,he evaporated water inside the cooling towers, thereansion tank and two make up tank used. Apart fromare also three heat exchangers with a total of 1800 RTwith 450 RT each and another one with 900 RT) avail-MEP which support the brine chiller and the ITS as the

different with that of the direct cooling supply by cen-ller, hence the heat exchanger is become an essential.ss, there is also some quantity of heat exchangers insideer buildings which function as receive cooling from thet. The capacity of the heat exchangers for each build-ent depending on the cooling load received. The coolinga the pipe buried underground which connected fromplant to each buildings. The ITS facility comprises of ar system, an ice thermal storage (Fig. 3), a cooling tower

a heat exchanger system. It generates chilled water meet the cooling load demand for various air-handlingbuted in the buildings. Besides, the brine chillers are

generate ice for the thermal storage plant. It is dividedlowing 5 sections, i.e. (1) brine chiller system, (2) basem, (3) cooling tower system, (4) thermal storage systemone ITS and associated motorized valves, and (5) heatystem. The chilled water system (central air condition-

is networked to have multiple cooling coils distributed the large distributed buildings with the refrigerationed at one base central location.

M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078 73

Fig

In the prencing the distributionhowever, isstudy of thethe overall investigatedmost receni.e. 2011 for

3. UNIMAS

The maipus, the elecas main intaity requireddemand, ansections.

3.1. Monthl

Fig. 4 shoyear 2011 wincrement throughout2011 due toin particula

3.2. Monthl

Table 1 during Monoccurred dumaximum dlic holiday

0.00

,000 .00

,000 .00

,000 .00

,000 .00

,000 .00

,000 .00

700,000 .00

800,000 .00

900,000 .00Demand Charge ($) Usage Charge ($) Tota l Charge ($)

istrib

um 201

ethod

hugee dampuMEPr 201lectritricid ch. Sin

comence ent the pr

off-d th. 3. The ice thermal storage (capacity rated at 7000 RTh).

evious work as reported in [15], many parameters inu-DCS had been briey covered which includes cool air, chiller capacity, and occupant behavior. This paper,

an extension of the previous works which is a detail changing of tariff effect as well as the ITS application tosaving possibilities. Few application scenarios are also. For that purpose and due to the completeness and

t data available, the authors have chosen a typical year,

100

200

300

400

500

600

Char

ge

($)

Fig. 4. D

maximof year

3.3. M

Theysis. Thnew caplant (for yealocal e

Elecdemanchargeused tocondrepres

In tduringdeduce the analysis.

electricity charge for year 2011

n target of the present analysis was UNIMAS new cam-tricitys main intake for UNIMAS new campus is knownke supply (MIS) which supply majority of the electric-. Monthly electrical consumption, monthly maximumd electrical charge are described in the following sub-

y electricity consumption

ws the monthly electricity consumption of UNIMAS forhich was essentially increasing over the months. The

was reasonable due to the increasing of built-up area year 2011. But there were exception for JuneAugust

semester break period where most of the occupants,r the undergraduates are out of the campus for holiday.

y maximum demand

show that monthly maximum demand only occurredday to Thursday. In detail, maximum demand onlyring ofce hour period. Hence, it can be deduced thatemand was impossible to occur on weekend and pub-due to decrease of occupants and overall usage. The

to energy sabenet of othat with a to 06:00 h),to the fact tthermal sto

4. Results

Computhybrid opertively.

4.1. Compu

4.1.1. ApplyIn year 2

MEP centrathe electricout of total equipmentcooling equincluded in

There arUNIMAS is In order to C3, the incrJan Feb March April May Jun e July Aug Sept Oc t Nov Dec

Month

ution of usage charge, demand change and total charge for year 2011.

demand was increased when getting toward the end1, thus the increased of total electricity charge.

ology and data analysis

data is collected for the project and enable further anal-ta includes: (1) monthly electrical charge for UNIMASss (MIS); (2) monthly electrical consumption of central); (3) electricity consumption of UNIMASs new campus1 and schedule of tariff both of which is available fromcal service provider.ty charge of MIS can be divided into usage charge andarge to nd the opportunity to decrease the electricityce huge number of data is involved, Microsoft Excel ispile and analyze the data sets. Standard deviations withinterval of 95% (Error bars with 5% errors) were used tohe distribution of the data.esent study, ice storage tank only chosen to be operatingpeak hour. This is because, from the literature, manyat ice thermal storage not really economical in regardving, but cost earning primarily from the tariff structuren-peak and off-peak hour. In this study, it is assumedtotal daily charging period of 6 h (off peak is from 00:00

the ice tank only able to discharge for about 5.5 h, duehat many literature predicted losses of around 10% forrage.

and discussion

ation of electrical charge and effect of ITS usage on theating system is discussed in Section 4.1 and 4.2, respec-tation of electricity charge

ing different tariff structure011 an average of 39.54% electricity was contributed byl plant alone. As for the overall air-conditioning system,ity consumed by the system will be more than 39.54%consumption, since MEP only generate the main coolings. While the other components like split units, individualipments, air handling unit, fan coil unit, etc. was not

the 39.54% gure.e three tariffs available for UNIMAS as listed in Table 2.applying tariff C2 currently (including year 2011) [16].take advantage from converting from tariff C2 to tariffement of maximum demand charge should overcome

74 M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078

Table 1Occurrence of maximum demand for year 2011.

Date Day Time Maximum electricity consumedper half hour (kW)

January 04-01-2011 Tuesday 09301000 4233.976February 23-02-2011 Wednesday 14301500 4222.604March 16-03-2011 Wednesday 11001130 4387.816April 28-04-2011 Thursday 15301600 4627.604May 10-05-2011 Tuesday 16001630 4590.928June 27-06-2011 Monday 16001630 4452.476July 26-07-2011 Tuesday 09301000 4356.732August 04-08-2011 Thursday 09000930 4441.456September 14301500 4765.392October 08300900 4989.480November 15301600 5217.680December 09000930 5574.548

Average 4655.06

Table 2Tariff structur

Tariff C1 coFor the rFor the neFor each a

Tariff C2 coFor each k

per monFor each u

Tariff C3 coFor each k

month dFor each uFor each u

Note: 1 RM = $

Table 3Savings regard

Tariff C1 tTariff C2 t

by earning fapplying taguity. HencSESCO is es

Appendimonth whiAppendix Biffs as well the Sarawathat total sayear 2011 bof the calcuthe actual tvery close athat there wtariff C2 to by switch fr

Table 4Percentage of

Tariff Pe

C1 10C2 8C3 8

le 4 shows that applying tariff C3 will lead to decrement intage of usage charge, but increment in percentage of maxi-emand charge. Hence, if applying tariff C3, it is importancemore effort in order to decrease the maximum demand duehigh

Equaend1 to he ste bo

ana15-09-2011 Thursday 04-10-2011 Tuesday 16-11-2011 Wednesday 01-12-2011 Thursday

e available for UNIMAS.

Rate per unit

mmercialst 100 units per month RM0.40 ($0.124)xt 4900 unit per month RM0.34 ($0.101)dditional unit per month RM0.30 ($0.093)mmercial demandilowatt of maximum demandth

RM16.00 ($4.96)

nit RM0.25 ($0.078)mmercial peak/off-peak demandW of maximum demand per RM20.00 ($6.200)

Tabpercenmum dto put to the

4.1.2. App

tariff CIn t

calcularelateduring peak periodnit during the peak period RM0.25 ($0.078)nit during the off-peak period RM0.144 ($0.045)

0.31 (exchange rate as per 15 July 2013). $ refer to US dollars.

to tariffs for year 2011.

Cost saving

ariff C2 $136,632ariff C3 $49,272

rom off peak period. By referring to electricity bill whenriff C2, the usage for off peak period is somewhat ambi-e, the detail data obtained from the electricity provider,sential.x A shows an example of calculation on a specicch is August 2011 for different type of tariff structures.

shows the calculated total charge for three different tar-as the reality charge for tariff C2 which obtained fromk Electricity Supply Corporation (SESCO). Table 3 showving of $50,052.37 (RM 158,941.32) can be obtained fory applying tariff C3 rather than tariff C2. The accuracylation was considered high due to the calculated andotal electricity charge for year 2011 with tariff C2 weres $1.92 (RM6.11) whole year. Besides, Table 3 showsas more saving from tariff C1 to tariff C2 compare to

C3. This means that UNIMAS had made a smart choiceom tariff C1 to tariff C2 many years ago.

usage and demand charge for year 2011.

rcentage of usage charge (%) Percentage of demand charge (%)

0 N/A6.14 13.862.46 17.54

the savings

4.1.2.1. Tarsaving per m

Saving, SC

where SC1Cusage (kWnumber of

The follooping the g

Percentage

Percentage

where SC1Cusage (kWh

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

0.22

Sav

ing

($

)

Fig. 5. Vacharge for maximum demand compare to tariff C2.

tion and regression of savingix B and Table 3 show that there is saving from changingtariff C2 as well as from tariff C2 to tariff C3.ubsequent sections, some equations are developed toth of the savings based on the obtained information andlysis. Regression equations were use to relate between

and the inuencing factors.

iff C1 to tariff C2. Eq. (1) is developed to represent theonth by switching from tariff C1 to tariff C2

1C2 = $0.0155 kWh1 U $4.96 kWh1 D + $63.86 (1)

2 = saving from switch tariff C1 to tariff C2 ($),U = totalh),D = maximum demand (kWh) (double the largestkilowatt supplied during any consecutive 30 min).wing equations were required for the purpose of devel-raphs in Figs. 5 and 6:

of maximum demand = DU

100% (2)

of saving = SC1C2TC1

100% (3)

2 = saving from switch tariff C1 to tariff C2 ($),U = total),

Saving vs Perce ntage of Maximum Demand in ($) y = -217114x + 66013

0.23 0.24 0.25 0.26 0.27 0.28 0.29

Perce ntage (%)

riation of saving (C1C2) with percentage of maximum demand.

M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078 75

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0.22

%Perce ntage of Saving vs Perce ntage of M aximum

Demand

Fig. 6. Variatidemand.

D = maxikilowatt sucharge with

The equawhen maximimpossible by switchinwas the int0.31% of mafrom tariff Cwas more thinterval, nopoints for b

4.1.2.2. Tarsaving per m

Saving, SC

where SC2Cpeak usagelargest num30 min).

The follsketching th

Percentage

Percentage

Off peakMaximum

where SC2CU = TotalD = Maxi

kilowatt suTC2 = Ele = Off pGraph in

centage of mindicate thoccur, henctariff C2 tomore than 3

y = -23 .24 x + 7.06 68

0

.5

1

.5

2

2.5

0.22 0.24 0.26 0.28%

Percentage of Saving vs Percentage of Maximum Demand

ariation of savings percentage (C2C3) with percentage of maximum.

graph in Fig. 8 shows the intersection occurred when theas 36.24. The intersection indicates the moment starting ofe value in saving (loss) occur, therefore estimated that it notto sw

ed onifferand

fect o

ITS ondir the. The

5 % lod tha

rev

Pe Demandy = -53 .25 3x + 16 .665

0.24 0.26 0.28%

on of savings percentage (C1C2) with percentage of maximum

mum demand (kWh) (double the largest number ofpplied during any consecutive 30 min),TC1 = electricity

tariff C1 in $.tion line in Fig. 6 shows the maximum saving of 16.66%um demand percentage was zero, but the scenario was

to occur. From the line, the condition of lost occurredg tariff C1 to tariff C2 can be estimated. The conditionersection point between the line and x-axis, which isximum demand. This means it is not worth to switch1 to tariff C2 when the maximum demands percentagean 0.31%. Based on the error bars at the 95% condence

signicant differences were observed between the dataoth Figs. 5 and 6.

iff C2 to tariff C3. Eq. (4) is developed to represent theonth from tariff C2 to tariff C3.

2C3 = $0.0329 kWh1 $1.24 kWh1 D (4)

3 = saving from switch tariff C2 to tariff C3 in $. = Off in kWh.D = Maximum demand in kWh (double theber of kilowatt supplied during any consecutive

owing equations were required for the purpose ofe graphs in Figs. 7 and 8:

D

0

1

%

Fig. 7. Vdemand

Theratio wnegativworth 36.3.

Basicant dFigs. 7

4.2. Ef

Theof air ccost focernedarounding 8demanerature

2.5of maximum demand =U

100% (5)

of saving = SC2C3TC2

100% (6)

usagedemand

= D

(7)

3 = saving from switch tariff C2 to tariff C3 in $. usage in kWh.mum demand in kWh (double the largest number ofpplied during any consecutive 30 min).ctricity charge with tariff C2.eak usage in kWh.

Fig. 7 shows the intersection occurred when per-aximum demand charge was 3.29%. The intersection

e moment starting of negative value in saving (loss)e can be estimated that it was not worth to switch from

tariff C3 if the percentage of maximum demand was.3%.

0

0.5

1

1.5

2

40

%

Fig. 8. Variatidemand.itch from tariff C2 to tariff C3 if the ratio was less than

the error bars at the 95% condence interval, no signif-ences were observed between the data points for both8.

f ice thermal storage (ITS) usage

facility in the MEP was installed during constructiontioning system at new campus, thus required no extra

hybrid cooling application as far as the study is con- 6 h charging period during off peak hour will yieldh discharging of ITS by considering some losses (assum-sses). The discharge period depend on the maximumt occur each month during year 2011. As stated in lit-iew, the applicants of ITS facility do not actually cause

rcentage of Saving vs Off Peak Usage/Maximum y = 0.0797x - 2.863

45 50 55 60 65

on of savings percentage (C2C3) with off peak usage/maximum

76 M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078

-

1

2

3

4

5

0

MW

Fig. 9. MIS eAugust 2011.

energy savipeak and onthe ITS app

The discwith the exrate of 900replacing anfor testing iest cost sa14301630on the year are summa

Scenario 1.14301630

Scenario 2.14301630

Scenario 3.14301630

With thecan be furthcase which 800 RT basedischarge omight be honly perfor

By combing for eachC3 can be ITS with Sce(RM3,673.5$3,954,885.saving is wMEP companario 2 is u

Table 5Estimation sav

Controlling m

ConventionaApply ice thApply ice thApply ice th

Table 6Estimation percentage of usage and demand charge by different controlling methodfor year 2011.

Usage charge (%) Demand charge (%)

Conventional 82.46 17.54Apply ice thermal storage Case 1 S2 83.14 16.86Apply ice thermal storage Case 2 S2 83.00 17.00

compar ison for var ious selected area.

50

60

0:00 2:00 4:00 6:00 8:00 10 :00 12 :00 14 :00 16 :00 18 :00 20 :00 22 :00 23 :00

Time of day, hours

Kuching, Sarawak 2 Aug 201 1Riyadh, Saud i Arabia 2 Aug 201 1Colorida, USA 2 Aug 201 1Kuwait, Ku wait 2 Aug 201 1Riyadh, Saud i Arabia July 199 6

10. Am

s dured tle 5 il out

accus late

ancng teS magingappl

in Targing

halfschaso cantrolling method of the system. Hence, maximum demand

may be further decreased.

High T5 10 15 20 25

time (hr)

Conventional Case 1 Case 2

lectricity consumption with different controlling method for 2nd

ng, but only take advantage with different rate on off peak [9,14]. Hence, for the present study, theoretically,lication will only take advantage in tariff C3.harge of ITS can be 450 RT, 900 RT, 1350 RT or 1800 RTisting heat exchangers. In this project, only discharge

RT be considered in order to simplify the process forother base chiller. There are three scenario developedn order to nd out the scenario that will lead to high-ving. The discharge time is xed at 09001130 and

based on the study for occurrence of maximum demand2011 as shown in Table 2. The three scenarios developedrized as follows:

S1 charge (00000600) and discharge (09001130,) ITS daily.

S2 charge (00000600) and discharge (09001130,) ITS daily except weekend and public holiday.

S3 charge (00000600) and discharge (09001130,) ITS daily except Friday, weekend and public holiday.

discharge of ITS at the rate of 900 RT, the investigationser divided to two cases (Fig. 9): Case 1 is the most likelyis assuming the discharge of 900 RT able to replace an

chiller. Case 2 is optimistic case which assuming thef 900 RT able to replace a 1300 RT base chiller. Case 2appen when the 1300 RT is under performance whichm around 60% of the base load.

0

10

20

30

40

Am

bie

nt

tem

per

atu

re,

C

Fig.

obvioucompain Tabcan faldictedsuch aperformroundithat ITof char

By showndischaaroundstop dimay althe cochargeining two cases of ITS application, the range of sav- scenario compared to conventional method by tariffobtained (Table 5). Table 5 shows that the saving ofnario 2 was within the range of $1,1388.8148,112.299155,200.91). With the total electricity charge of00 (RM12,757,693.55) (with tariff C3) for year 2011, theithin 0.031.22%. But, with the contribution of 39% forre to MIS, the saving in MEP with ITS application Sce-p to 0.083.13%. Here, the saving by applying ITS is not

ings for year 2011 with Ice thermal storage application.

ethod Saving range

l N/Aermal storage S1 $11,379.5557,281.52ermal storage S2 $1,1388.8148,112.29ermal storage S3 $2439.5339,037.44

a

Coo ling load

Fig. 11. Coolinof total load mT and high each graph frobient temperature prole comparison for various selected area.

e to the extreme small capacity of the storage facility aso the main direct cooling facility. Note that the savings having wide range gures, yet the actual saving still

from the range predicted. The saving cannot be pre-rately due to the controlling technique of the system

startup of the chillers. Besides, the ITS will have highere at night time by taking advantage from the lower sur-mperature at night period compare to daytime. It meansy able to discharge more than 5 h per day and by 6 h.ying ice thermal storage, the results of which is asble 6 shows that the demand charge was decreased by

the ITS strategically. Anyhow, by applied ITS facility, of maximum demand will occurred right after the ITSrged. In reality, although the ITS had stop discharged, ituse the late startup of the chiller as well depending onb

B

A

Time of day

Low T

c d

g load meets by storage prole for a full storage scheme. The regioneet by storage (indicated by shaded area) are A and A + B for the lowT prole, respectively. Chiller meets load directly at the regions underm a to b, and c to d.

M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078 77

A view on typical days for the day and night-time differentialin ambient temperature T prole is as given in Fig. 10, it showsthat the local tropical condition (present study) is having narrowerambient temperature difference as compared to other countries.As far as th21 C for Kuand Kuwaittribute to hby the storaregion will the storage

5. Conclus

In this pthe saving campus, in thermal stostudy is theelectricity cdecrease thwhich has tindicated ththe data avthat, UNIM2011 by swto the percC2.

Also, thithe electricmal storagenot in use current tarition is esti(RM3,673.5to charge aday. The sawith respegain by imOverall, bythe ITS fac(RM162,614saving is 1.with $4,00ing can be human behfort.

In summmarginally new tariff iif ITS is oplocal tariff those reporin Refs. [9night-time countries, tatively narrperiods.

6. Recomm

In orderbuildings, tstudy on thvia fuzzy lo

employing Axiomatic design methodology for improvement ofUNIMASs district cooling system, and (2) optimal operation strat-egy of the hybrid based on minimum operating cost of the systemsat various combined working conditions and suitable storage

es. Also, reduction of electricity charge during studentster break can bring about further savings.

wled

grean anding p

paranagangn, UssetSenia (Eleata rawaiated

dix A

First 1Next 4Surplu

Total u

Maximdeman

On peusageOff peusageMaximdeman

um day).

dix B

y

ry

t

ber e present study is concern, the Ts are 8, 12, 14, andching (Sarawak), Riyadh (Saudi Arabia), Colorado (USA)

(Kuwait), respectively. In general, bigger T will con-igher energy savings as more cooling load can be metge (see Fig. 11). Conversely, a country with lower Tgenerally have lower cooling load that can be met by.

ions

aper, a few operating schemes are investigated to studypotential in total electricity charge for UNIMAS newparticular with respect to the tariff change and with therage application. One of the ndings emerge from this

signicance of contribution of demand charge to totalharge in tariff C2 and tariff C3. Effort had been put on toe maximum demand especially when applying tariff C3he highest charge for maximum demand. This projectat tariff C3 is the best option to implement based onailable for year 2011. From the analysis, it was foundAS can save up to $49,271.81 (RM158,941.32) on yearitching to tariff C3. The saving is inversely proportionalentage of maximum demand charge by refer to tariff

s project explains the inuence of ITS application toity charge. The ice thermal storage facility (ice ther-, heat exchanger, brine chiller, brine pump, etc.) aredue to neither energy saving nor cost saving withff applied. But, by switching to tariff C3, ITS applica-mated to be able to save up to $1.138.8148,112.289155,200.91) for year 2011, when the ITS is subjectnd discharge every weekday excluding public holi-ving was calculated to be in the range of 0.083.13%ct to total usage of MEP. There can be more savingposing more detail study on the controlling system.

switching tariff to C3 as well as the application ofility, a saving up to total of $19,410.6297,384.09.91314,142.23) for year 2011 is estimated. The total26%2.43% compare to total electricity charge of MIS4,156.81 (RM12,916,634.86) for year 2011. The sav-done without any initial cost, without changed theavior for users, as well as without scaried users com-

ary, it was found that, due to the local tariff status,saving can be achieved in the range of 0.083.13% if as adopted; and a total of further saving of 1.262.43%erated. This marginally saving is mainly due to theconditions which is less favorable as compared withted in the literature and experience elsewhere (e.g.11]). Furthermore, while there are signicant day anddifferential in ambient temperature that exists in otherhe local tropical condition is having less favorable, rel-ow ambient temperature difference over the day-night

endation for further study

to further reduce the electricity charges in UNIMAShere are few methods can be considered such as (1)e controlling method in relation to the ITS applicationsgic investigation and/or development of a framework

schemsemes

Ackno

Weconcerfollowions, inand MbintiAbDivisioneer, ASwee (Sze Xition). Dand Saapprec

Appen

C1

C2

C3

Maxim(Thurs

Appen

Januar

Februa

March

April

May

June

July

Augus

Septemgments

tly acknowledge Datu Dr. Hatta Solhi for sharing his idea on electrical consumption. We are grateful to the

ersonnel for their useful assistance and fruitful discuss-ticular: Mr. Lawrence Abdullah (Senior Engineer, Assetement Division, UNIMAS), Mdm Dayang Duwiningsih

Abdullah (Electrical Engineer, Asset and ManagementNIMAS), Mr. Pelle Tunggi (Assistant Mechanical Engi-

and Management Division, UNIMAS), Mr. Jong Fungor Mechanical Engineer, JKR Sarawak), and Ms. Liewctrical Engineer, Sarawak Electricity Supply Coopera-

provided by the Asset & Management Division UNIMASk Electricity Supply Corporation (SESCO) is very much.

.

Units (kWh) Charge, RM ($) Total, RM ($)

00 U 100.00 40.00 ($12.4)900 U 4900.00 1666.00 ($516.46)s 3,471,296.28 1,041,388.88

($322,830.55)1,043,094.88($323,359.41)

sage 3,476,296.28 869,074.07($269,412.96)

umd

8882.91 142,126.59($44,059.24)

1,011,200.66($313,472.20)

ak 3,032,208.54 758,052.13($234,996.16)

ak 444,087.74 63,948.64($19,824.08)

umd

8882.91 177,658.24($55,074.05)

999,659.01($309,894.29)

demand occur during: 04-08-2011, 09000930

.

Tariff C1 Tariff C2 Tariff C3 RealityRM ($) RM ($) RM ($) RM ($)

1,051,672.87 1,011,709.62 998,073.86 1,011,710.50($326,018.59) ($313,629.98) ($309,402.90) ($313,630.26)969,180.42 942,602.01 929,477.08 942,598.00($300,445.93) ($292,206.62) ($288,137.89) ($292,205.38)1,167,927.57 1,113,511.42 1,093,264.62 1,113,517.50($362,057.55) ($345,188.54) ($338,912.03) ($345190.43)1,144,220.66 1,101,428.88 1,084,904.64 1,101,425.50($354,708.41) ($341,442.96) ($336,320.44) (341,441.90)1,118,815.96 1,079,084.66 1,065,800.35 1,079,087.00($346,832.95) ($334,516.24) ($330,398.11) ($334,516.97)953,808.85 937,148.27 932,840.68 937,149.00($295,680.74) ($290,515.96) ($289,180,61) ($290,516.19)1,000,574.86 973,056.14 964,865.35 973,048.75($310,178.21) ($301,647.40) ($299,108.26) ($301,645.11)1,043,094.88 1,011,200.66 999,659.01 1,011,202.00($323,359.41) ($313,472,20) ($309,894.29) ($313,472.62)1,138,714.74 1,101,249.83 1,087,535.27 1,101,253.50($353,001.57) ($341,387.45) ($331,135.94) ($341,388.56)

78 M.O. Abdullah et al. / Energy and Buildings 67 (2013) 7078

Appendix B (Continued )

Tariff C1 Tariff C2 Tariff C3 RealityRM ($) RM ($) RM ($) RM ($)

October 1,258,840.75 1,208,525.66 1,189,293.93 1,208,526.00($390,240.4) ($374,642.9546) ($368,681.11) ($374,633.06)

November 1,229,441.94 1,191,329.05 1,178,565.34 1,191,323.25($381,127.00) ($369,312.01) ($365,354.64) ($369,310.21)

December 1,281,089.76 1,245,788.67 1,233,413.41 1,245,732.75($397,137.83) ($386,194.49) ($382,358.16) ($386,177.15)

Total 13,357,383.26 12,916,634.87 12,757,693.54 12,916,573.75($4,140,788.81) ($4,004,156.81) ($3,954,884.00) ($4,004,137.86)

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Electricity cost saving comparison due to tariff change and ice thermal storage (ITS) usage based on a hybrid centrifugal-...1 Introduction2 The UNIMAS district cooling system3 UNIMAS electricity charge for year 20113.1 Monthly electricity consumption3.2 Monthly maximum demand3.3 Methodology and data analysis

4 Results and discussion4.1 Computation of electricity charge4.1.1 Applying different tariff structure4.1.2 Equation and regression of saving4.1.2.1 Tariff C1 to tariff C24.1.2.2 Tariff C2 to tariff C3

4.2 Effect of ice thermal storage (ITS) usage

5 Conclusions6 Recommendation for further studyAcknowledgmentsReferencesAppendix B Appendix IIReferences