Energy and economic assessment of district cooling ...

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system in the form of chilled water. Due to lower electricity tariff imposed by Tenaga Nasional. Berhad (TNB) during off-peak period, there are two types of DCS ...
Science & Engineering Technology National Conference 2015

Energy and economic assessment of district cooling system in Malaysia Mohd Hazzah Ahmad Siron1,a, Muhammad Hamdi Haron2,b Heating, Ventilation,Air Conditioning & Refrigeration Section, Universiti Kuala Lumpur, Malaysia France Institute, 43600 Bangi, Selangor, Malaysia. a

[email protected], [email protected]

Abstract District cooling system (DCS) distributes cooling energy to buildings from a centralized production system in the form of chilled water. Due to lower electricity tariff imposed by Tenaga Nasional Berhad (TNB) during off-peak period, there are two types of DCS currently in operation here, i.e. district cooling ice thermal storage system (DCSISS) and district cooling chilled water storage system (DCSCWSS). The DCS operator will imposed a certain tariff to the buildings that utilizes their chilled water supply. This study examines both DCS systems from the stand point of their energies and economics. Energy and economic analysis between conventional system and ice thermal storage system had been analyzed previously which showed that even though DCSITSS consumed more energy than conventional chiller system, it is much more cost saving.. A hypothetical DCSISS and DCSCWSS system and their respective offices will be modeled based on two district cooling operators in Malaysia i.e. ‘Pantai District Cooling’ at Kuala Lumpur ( DCSISS operator) and ‘Naditech Sdn Bhd’ at Bandar Baru Bangi (DCSCWSS operator). The objectives will be on total energy consumption, off-peak electricity consumption, capital and running costs, and life cycle cost (LCC). Finally, a suitable chilled water supply tariff will be determined that generate a win-win situation for both DCS operator and the offices. Both chilled water and ice storage systems will be analysed based on full and partial storage strategies. The results indicated that DCSCWSS full storage strategy has a lower life cycle cost and tariff compared to DCSISS (partial and full strorage) and DCSCWSS (partial storage). The result concludes that DCSCWSS (full storage) is the most suitable DCS system in Malaysia.

Keywords – District cooling system, Chilled water storage, Ice thermal storage, Life cycle cost.

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1. Introduction District cooling system distributes (DCS) thermal energy from a central source to residential, commercial, and/or industrial consumers for use in space cooling [1]. It is a system consists of chillers system, thermal energy storage (TES), piping system and multiple buildings of different cooling load requirement connected together as one system. A simple configuration of DCS is shown in Figure 1. TES is a technology that store thermal energy in a storage medium so that it can be used later. TES shifts some of the electricity from the peak period to off-peak period. However, this system will only benefit if the country has two different electricity tariffs, on and off peak tariff. Currently, electricity supplied by Tenaga National Berhad the Malaysian electricity service provider offers two different tariffs; on and off peak tariffs. The off peak period starts from 10.00 p.m. and ends at 8.00 a.m.[2]. There are two types of TES currently operated in Malaysia; i.e. ice (ISS) and chilled water (CWSS) storage system. An earlier studies conducted on the energies and economics of DCS utilizing ice storage system (ISS), centralized chiller system and package unit system [3], revealed that DCSISS partial storage strategy proved to be the most economical and potential for commercialization. An ice storage system is a system utilizing latent thermal energy storage technology. Another study on the comparison between centrifugal chiller with and without ice storage system were conducted in Universiti Malaysia Sarawak campus [4]. It was found that by applying ICSS, their electricity consumption can be saved up to 5.5%. Another comparison on a building in Malaysia between conventional chiller system and ice thermal storage[5] showed that by installing a full ice storage strategy, the building can save up to 35% of total annual costs. Another review on cooled thermal storage system (CTES) [6] indicated that ice on coil is the most desirable CTES system. CTES consumed about 29% more energy compared to the conventional system. However, due to the present of on and off peak tariffs, the electricity cost can be reduced by approximately 55%.

On the other hand, chilled water storage system is a system utilizing a sensible storage technology. The system coefficient of performance (C.O.P.) is almost equivalent to the conventional chiller system due to similar evaporation temperature. A review was carried out to compare various types of thermal storage system indicated that ice thermal storage system C.O.P. is lower than chilled water storage system [7]. Its advantage is that it can store a larger storage capacity. A study conducted at Cornell University U.S.A. [8] showed that by installing chilled water storage system, there are some energy penalties on the added pumps energies, thermal losses at the storage tank and mixing of the supply and return chilled water inside the tank. To further minimized the losses, the tank water level shall be the highest point in the system [9]. Up to date, published literatures on comparing between ISS and CHWS are lacking. Most of the literatures only discussed the benefits of CTES compared to conventional chiller system. Since both systems of CTES i.e. ISS and CWSS have been implemented in Malaysia, a further energy and economic assessment need to be studied in order to justify which system is much more feasible as a commercial DCS. The objectives of this paper are to carry out the feasibility studies on the implementation of DCSISS and DCSCWSS (full or partial storage system) plants in Malaysia. The first part is to determine the energy and life cycle cost analyses of DCSISS and DCSCWSS on hypothetical commercial buildings in Malaysia. The second part is to determine the chilled water supply tariff determination for the DCSISS and DCSCWSS plant (full or partial storage system) for potential implementation in Malaysia as commercial cooling service. The study will serve as a guide for DCS operators in their investment to embark into supplying chilled water business in the future.

Fig.1 Configuration of a typical DCS plant[1]

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2. Method 2.1 Research methodologies Table 1 shows the list of hypothetical buildings used in the study. Each office floor is set at 1750 m2 which is a norm for a typical commercial floor in Kuala Lumpur. Table 1Cooling capacities for the hypothetical buildings

DCSISS and DCS CWSS plant are divided into two modes i.e. full and partial storage system. For full storage system, the entire daily cooling load requirements are provided by the stored ice or chilled water. The chillers charge the ice only at night during the off-peak period i.e. from 2200 to 0800 on the following day. As for partial storage system, load leveling mode will be employed with the chillers and their auxiliary equipment are operating for 24 hours a day. The chillers will charge the ice during off –load period i.e. from 1800 to 0800 and they provide direct cooling during the on –load period i.e. from 0800 to 1800. The additional load during the on-load period will be handled by the stored ice or chilled water. The type of ice storage system is an encapsulated ice storage system which is similar to ‘Pantai District Cooling’ and the chilled water storage is similar to ‘Naditech Sdn Bhd’ the plant operator in ‘German Malaysian Institute’. The plant configuration for full and partial storage systems is shown in Fig.3. All the input data were taken for ‘Pantai District Cooling’ and ‘Naditech Sdn Bhd’ and they are not shown in this paper. As for the calculation of equipment’s capacities, input powers capital and running cost, energy cost, engineering economics and tariff determination, their equations used are shown in the next section. AHU

Fig. 3 Basic configuration of DCSTES[10]

2.2 Equations used in the analysis a. Equipment’s capacity and their input power The buildings’ cooling loads were hypothetically assigned based on the number of floor to be justified with typical commercial buildings in Malaysia. Its equation is: 10.8 (1) 𝑇𝐶𝐿 = 𝐶𝐿𝐼 × 𝑇𝐹𝐴 × 𝑁𝐹 × 12,000 where TCL is the total cooling load in TR, CLI is the cooling load intensity i.e. 60 Btu/hr ft2, TFA is the total floor area per floor i.e. 1750 m2 [11] and NF is the no of floors. Multiple chillers (Full ice storage) connected in parallel in the district cooling plant to charge ice during off-peak hour period only. During on-peak period the chillers are on standby mode. The nominal capacity is calculated by using this equation: 𝑇𝐸𝐶 (2) 𝐶ℎ𝐶 = 𝐶𝐹 × 𝐹𝐻1 × 𝐶𝑄 where ChC is the chiller refrigerating capacity in TR, TEC is the total energy consumed in TR-hr i.e. Building TCL × DF × OH, CF is the chiller derating factor i.e. 0.65, DF is the diversity factor i.e. 0.85, FH is the freezing hour i.e. Total no of hours chillers are energized to make ice only during off-peak period i.e. 2200 to 0800, OH is the operating hours of the commercial building i.e. 0800 to 1800 Monday to Friday and CQ is the chiller quantity. Full chilled water storage chillers is calculated by using this equation [15]: 𝑇𝐸𝐶 (3) 𝐶ℎ𝐶 = 𝐹𝐻2 × 𝐶𝑄 Multiple chillers (partial ice storage) connected in parallel in the district cooling plant to charge ice during of-peak hour period. During on-peak period the chillers are also run. Chillers run for 24 hour period. Its capacity is calculated based on this equation[15]: 𝑇𝐸𝐶 (4) 𝐶ℎ𝐶 = (𝐶𝐹 × 𝐹𝐻 + 𝐶𝐶𝑂𝐻) × 𝐶𝑄 where CCOH is the conventional chillers operating hours i.e. 0800. to 1800 and FH2 is the freezing hour i.e. 1800 to 0800.

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Partial chilled water storage chiller capacity is calculated by using this equation[12]: 𝑇𝐸𝐶 (5) 𝐶ℎ𝐶 = 24 × 𝐶𝑄 Chillers input powers are related to their running capacity and types of chillers. In these analyses, centrifugal chiller was selected due to its high efficiency. The chillers input powers are calculated by this equation[13]: IP = ChC × EP (6) where IP is the input power in kW and EP is the effective power i.e. 0.65 kW/TR Chillers used in the analysis were of water cooled type chillers. It involved with chilled water and condenser water flow. The flow rate can be calculated by this equation[10]: 𝐶ℎ𝐶 × 12,000 (7) 𝐶𝑊𝐹𝑅 = 𝜌 × 𝐶𝑝 × Δ𝑇 or 𝐶ℎ𝐶 × 12,000 𝐶𝑊𝐹𝑅 = (8) 𝐶1 × Δ𝑇 𝐶ℎ𝐶 × 𝐶𝐹𝑟 × 12,000 (9) 𝐶𝑜𝑊𝐹𝑅 = 𝜌 × 𝐶𝑝 × Δ𝑇 or 𝐶ℎ𝐶 × 𝐶𝐹𝑟 × 12,000 𝐶𝑜𝑊𝐹𝑅 = (10) 𝐶1 × Δ𝑇 where CWFR is the chilled water flow rate in usgpm, CoWFR is the condenser water flow rate in usgpm, CFr is the condenser factor i.e. 1.25, ρ is the fluid density in lbm/ft3, Cp is the fluid specific heat in Btu/lbm R, ΔT is the temperature difference between chilled water inlet and outlet temperature in F and C1 is a constant. For water equals to 500 and for 30% glycol –water solution equals to 450. Cooling tower is heat rejection equipment, rejecting heat from the condenser water which in turn absorbs heat from the chillers condensers. Its capacity can be calculated from the following equation[14]: 𝐶𝑇 = 𝐶ℎ𝐶 × 𝐶𝐹𝑟 (11) Cooling tower input power can either be selected based on any catalogues or by using the following equation[14]: 𝐶𝑇𝑝 = 𝐶𝑇 × 𝐶𝑇𝑃𝐶 (12) where CT is the cooling tower capacity in TR, CTp is the cooling tower input power in kW, CTPC is the cooling tower power coefficient i.e.0.035 to 0.04

Pump is used to circulate the water between the chillers to the respective air handlers via piping networks. The required pressure can be calculated based on the following equation[14]: 𝑃ℎ = 𝑃𝑙 × 𝐹𝑅 × 1.8 + 𝐸𝐿 (13) where Ph is the pump head in m, PL is the longest pipe run in the network in m, FR is the friction rate i.e. 1.2 m pressure loss/30m run and EL is the total equipment’s pressure drop in m. Pump input power can be calculated by using this equation[10]: 𝑃𝑝 = (𝑉 ̇ × 𝐻 × 𝑆𝐺 × 0.746)/ (3960 × 𝜂𝑝 × 𝜂𝑚 ) (14)

where Pp is the pump power in kW, 𝑉̇ is the volumetric flow rate in usgpm, H is the pump pressure head in ft, SG is the specific gravity of the fluid, 𝜂𝑝 is the pump efficiency i.e. 87% and 𝜂𝑚 is the motor efficiency i.e. 80%. Ice tank function is to store energy in term of ice in a closed steel container. The quantity of the ice tank is estimated by the following equation[12]: 𝑇𝐸𝐶 𝐼𝑇𝑄 = (15) 𝑇𝐶 where ITQ is the ice tank quantity and TC = ice tank rated capacity by manufacturers (Ton-hr) Chilled water tank storage size is calculated by using this equation[1]: 𝑉 = (𝑋 ̇ × 12000 × 𝐵𝑡𝑢/𝑡𝑜𝑛𝐻𝑟)/(𝐶𝑝 × 𝛥𝑇 × 𝑆𝐺 (624 𝑙𝑏/𝑓𝑡3)𝑒𝑓𝑓)

(16)

where V is the TES tank volume in ft3, X is the amount of thermal capacity required in Ton-hr, and eff is the storage efficiency typically 0.9 Air handling units are responsible to distribute air to the respective conditioned area. Chilled water generated either by the chillers or ice tank will flow through the AHU and absorb heat from the circulating air. Its capacity is calculated based on the following equation: 𝑇𝐹𝐴 × 𝐶𝐿𝐼 𝐴𝐶 = (17) 𝐴𝑄 × 12,000 where AC is the air handling unit capacity in TR, AQ is the no of air handling units per floor. Its input power is calculated based on the following equation[14]: 𝐴𝑝 = 𝐴𝐶 × 0.25 (18) where Ap is the air handling unit input power in kW.

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b.

Plant and buildings capital and running cost

The capital costs for HVAC installation can be quite tedious and time consuming to be determined. A capital cost of a system will be known accurately once a firm contract or a purchase order has been given to particular suppliers. Therefore, it is quite not practical to ask the every supplier for the price every time an analysis is to be carried out. Therefore certain approach has to be adopted in determining the capital which is known as proportionality method [13]. The reference plant is ‘Pantai District Cooling’ for ISS and ‘German Malaysian Institute’ for CWSS.

For the consumers building and buildings that utilize conventional chillers systems, the plant room cost/opportunity cost was calculated by using this equation: 𝑅 =𝑆 × 𝑟 (23) where R is the rental per month in RM, S is the size of the plant room in m2 and r is the rental per month per m2 in RM. Land rental per month in Kuala Lumpur is taken to be RM6.50 per ft2 [11] The operating strategy of full and partial storage are shown in Figure 4 and 5 respectively.

Capital costs i.e. costs on buildings and equipment for the hypothetical plants were calculated by using the following equation[13]: 𝑆 𝑚 𝐶 = 𝐶𝑟 × ( ) (19) 𝑆𝑟 where C is the estimated cost of the plant in RM, Cr is the cost of a reference plant in RM, S is the size of the plant in TR, Sr is the size of the reference plant in TR and m is the exponent i.e. 0.6 for Partial and full storage.

Fig.4 Full storage operating strategy[1]

Running cost of a plant or a building comprised of several costs such as maintenance and electricity costs. Maintenance costs were also based on equation (19) and electricity cost in Malaysia consists of on-peak tariff, off-peak tariff and maximum demand charge. The plant and buildings electricity charges were calculated by using the following equation: 𝑂𝑛𝑃𝐸𝑈 = 𝑂𝑛𝑃𝐸𝑃 × (𝑘𝑊)𝑜𝑛 × (𝑂𝐻)𝑜𝑛 𝑂𝑓𝑃𝐸𝑈 = 𝑂𝑓𝑃𝐸𝑃 × (𝑘𝑊)𝑜𝑓𝑓 × (𝑂𝐻)𝑜𝑓𝑓

(20) (21)

𝑀𝐷𝐶 = 𝑘𝑊𝑚𝑎𝑥 × 𝐷𝐶 (22) where OfPEU is the off peak electricity use in kWh, OnPEU is the on peak electricity use in kWh, Kwon is the equipment input power that operate during on-peak period in kW, Kwoff is the equipment input power that operate during on-peak period in kW, OHon is the equipment operating hours during on-peak period in hr, OHoff is the equipment operating hours during off-peak period in hr, kWmax is the maximum cumulative kW of equipment operate during on-peak period, MDC is the maximum demand charge in RM i.e. RM 45.1 per kW, DC is the demand charges in RM/kW, OfPEP is the off peak electricity price in RM i.e. RM 0.224 per kWhr and OnPEP is the on peak electricity price in RM i.e. RM 0.365 per kWhr.

Fig.5 Partial storage operating strategy[1] c.

Engineering economic analysis

An engineering economic analysis is carried out in order to study whether the selected system is viable for commercialization. To implement the giant system such as district cooling systems, huge capital investment is needed and the investment scheme must be quite attractive to investors in term of capital returns. Furthermore, the tariff selected must be beneficial to both the DCS plant operators and the consumers. Therefore, it is quite imperative to study the selected plant with respect to engineering economic analysis. The cost efficiency curve is determined by calculating a life cycle cost (LCC) for each system

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based on their initial and running cost. The LCC is the sum of investment cost and the annual operating cost discounted over the lifetime of the equipment. LCC is calculated by the following equation[17]: 𝐿𝐶𝐶 =

(𝐼𝐶 × 𝐶𝑅𝐹 × 𝐸𝐿𝑆) + (𝐸𝐿𝑆 × 𝑂𝐶) 𝐸𝐿𝑆 × 𝑃𝐿𝐶

(24)

where LCC is the life cycle cost, ELS is the equipment life span i.e. 20 years for chillers system, IC is the investment cost i.e. Total equipment plus buildings costs in the system in RM, PLC is the plant capacity in TR, OC is the annual operating cost in RM, CRF is the capital recovery factor. Refer to equation (27). Capital recovery factor is the correlation between the real discount rate and the lifespan of the plant. It is the amount that the bank would recover in giving the loan or it is the amount per year that the borrower will pay to the bank. It can be calculated by using this equation[18]: 𝑖 𝐶𝑅𝐹 = (25) 1 − (1 + 𝑖)−𝑁 where CRF is the capital recovery factor, i is the interest rate imposed by local banks per year i.e. 7 % per year and N is the no of year the loan spread i.e. taken to be plants lifespan.

d.

Tariff determination

This subsection will provide some equations used in tariff determination for the chilled water supplied by the DCS operator. Capacity charge also known as the connection charge is the equivalence of the amount of installing chillers plant spread over the required payback period and is charged monthly to the consumers’ buildings. Its amount is fixed depends o the amount of refrigerating required by the consumers. It can be calculated by using these equations: 𝑇𝐼𝑛𝑣 × 𝐶𝑅𝐹 × 𝑌𝑟 𝑇𝐶𝐶 = (26) 𝑌𝑟 × 12 𝑚𝑜𝑛𝑡ℎ 𝑈𝐶𝐶 =

𝑇𝐶𝐶 𝑃𝐿𝐶 × 0.85

(27)

𝐶𝐵𝐶𝐶 (𝑅𝑀) = 𝑈𝐶𝐶 𝑥 𝐴𝐶 (28) where CBCC is the consumer building capacity charge in RM, AC is the air conditioning maximum consumption in TR i.e. Buildings’ cooling capacity X 0.85, TCC is the total capacity

charge per month in RM, UCC is the unit capacity charge, TInv is the total amount invested in installing the DCS plant and Yr is the no of years that the plant investment loan to be spread i.e. 10 years. Consumers building expenditure are comprised of fixed and running cost over the life span of the equipment. The expenditures of the individual buildings in utilizing the conventional chillers are calculated by the following equation: 𝐸𝑥𝑝_𝑦𝑟 = (𝐼𝑛𝑣_𝑐𝑐 × 𝐶𝑅𝐹) + (𝐸. 𝐶 + 𝑀. 𝐶. +𝑅) × 12 (29)

where Invcc is the initial investment on the plant in RM, (Exp)yr is the expenditure per year in RM, E.C is the electricity cost per month kWhr/month X RM/kWhr, M.C. is the maintenance cost per month in RM and R is the space rental for installing the chillers plant in RM. The expenditure of the individual buildings in utilizing the chilled water supplied by the DCS plant is calculated by using the following equation: 𝐸𝑥𝑝𝑦𝑟 = (𝐼𝑛𝑣𝑜𝑡 × 𝐶𝑅𝐹) + (𝐶. 𝐶 + 𝐸. 𝐶 + 𝑀. 𝐶. +𝑇. 𝐶. +𝑅) × (30)

12

where C.C. is the capacity charge per month, Invot is the investment on cooling equipment installed, T.C is the chilled water tariff charge per month;RM/kWrhr × kWrHr/month, kWrhr is the kilowatt hour of refrigeration and RM/kWrh is the tariff charged by the DCS operator The acceptable tariff for each consumer building is calculated by setting eq. (3.34) and (3.35) to be equal and solved to find T.C. Then use the following equation to find unit tariff charge: 𝑇𝐶 =

𝐼𝑛𝑣𝑐ℎ × (𝐶𝑅𝐹)20 𝑦𝑒𝑎𝑟𝑠 + (Δ𝐸𝐶 + Δ𝑀𝐶 + Δ𝑅) 12 − 𝐶𝐶 (31)

𝑈𝑇𝐶𝐵 =

𝑇𝐶 𝐸𝐶

(32)

where Invch is the investment on chillers system only, ΔR is the plant room rental difference between using conventional chillers and DCS for buildings per month, ΔEC is the electricity price difference between using conventional chillers and DCS for buildings per month, ΔMC is the maintenance price difference between using conventional chillers and DCS for buildings per month, TC is the tariff charge per month, (UTC)B is the unit tariff charge on building in RM/Ton-hr and EC is the building energy consumption per month in Ton-hr. U.T.CB. is the maximum tariff

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that the DCS operator can impose on each consumer’s building. The district cooling plant total expenditure and net saving can be calculated by using these equations: (𝐸𝑥𝑝)𝑦𝑟 = (𝐸. 𝐶. + 𝑀. 𝐶. ) × 12 𝑚𝑜𝑛𝑡ℎ + (𝐼𝑛𝑣)𝑦𝑟

(33)

(𝐼𝑛𝑐)𝑦𝑟 = (𝐶. 𝐶 + 𝑇. 𝑇. 𝐶. ) × 12 𝑚𝑜𝑛𝑡ℎ (34) (𝑁𝑆)𝑦𝑟 = (𝐼𝑛𝑐)𝑦𝑟 – ( 𝐸𝑥𝑝)𝑦𝑟 (NS)yr ROI = (Inv)yr

(35) (36)

(𝑁𝑆)〗_𝑟𝑦𝑟 = ((𝐼𝑛𝑐)_𝑦𝑟 − ((𝐸. 𝐶. + 𝑀. 𝐶. )𝑥 12 + ((𝐼𝑛𝑣)_𝑦𝑟 𝑥 𝐶𝑅𝐹)) × 𝑃𝑊𝐹 (37)

where CC is the total capacity charge, TTC is the total tariff charge; (UTC)DCS X (Kwrhr)total /month,(NS)yr is the net saving per year, (NS)ryr is the real net saving per year, (Inv)yr is the total initial investment / Equipment lifespan, (Inc)yr is the income to DCS plant per year, (Exp)yr is the DCS plant expenditure per year and ROI is the return of investment.

Fig. 6 Electricity consumption per day

The minimum tariff selected shall make return on investment equivalent to what the market offer on any investment. To select a suitable tariff the following equation is to be used: (𝑈𝑇𝐶)𝐷𝐶𝑆 =

𝑅𝑂𝐼 × (𝐼𝑛𝑣)𝑦𝑟 + (𝐸𝑥𝑝)𝑦𝑟 12 × 𝑘𝑊𝑟𝐻𝑟



𝑇𝐶𝐶 𝑘𝑊𝑟𝐻𝑟

(38)

where ROI is the return on investment i.e. Current investment return in the present market which is set at 7%, (kWrHr)t is the total kilowatt-hr of refrigeration supplied by DCS per month and (UTC)DCS is the unit tariff charged by DCS plant operators to consumers. The DCS can be considered viable as a utility cooling plant only if: (UTC)DCS < (UTC)B (39) If (UTC)DCS > (UTC)B (40) Then it is economical for each consumer’s buildings to use conventional chillers. 3. Results and discussion This section is divided into two subsection. The first subsection is the energy analysis and the second subsection is the economic analysis. 3.1 Energy analysis Figure 6 shows the total energy consumption and Figure 7 shows the on-peak energy consumption of each plant.

Fig. 7 Energy usage during on-peak period From Figure 6, DCSCWSS (partial storage) consumes the least amount of energy. It is 34% lower than DCSISS (full storage), 17% lower than DCDISS (partial storage) and 5% lower than DCSCWSS (full storage). However, it is 7.5% higher than centralised chiller system [3]. The reason DCSCWSS (partial storage) total energy consumption in this analysis to be lowest is due to its C.O.P. is higher as compared to DCSISS (full and partial storage) and lower input power compared to DCSCWSS (full storage). In the ice charging mode, the chiller capacity will be reduced by approximately 35% [15]. Furthermore, DCSISS uses glycol solution which impart higher pressure drop and lower heat transfer performances as compared to DCSCWSS [16]. From Figure 7, DCSCWSS (full storage) consumes the least power during on-peak period. It is lower by 52% compared to DCSISS (partial storage), 44% compared to DCSCWSS (partial storage) and 15% compared to DCSISS (full

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storage). A full storage system shifts most of its equipment operation during the off-peak period. DCSCWSS (full storage) is lower than DCSISS (full storage) due to its higher equipment efficiency. 3.2 Economics analysis Figure 8 shows the total fixed cost for the systems.

From Figure 9, DCSCWSS (full storage) is the lowest running costs. It is lower by 12% compared to DCSCWSS (partial storage), 25% compared to DCSISS (partial storage and full storage). The reason is due almost 40% lower electricity tariff during the off-peak period. Figure 10 shows the life cycle cost of the systems per annum. Life cycle cost is summation of initial investment cost and running cost and spread over the life span of the system which is 20 years.

Fig.8 Total fixed cost for the system From Figure 8, DCSCWSS (partial storage) is the lowest fixed or installation cost for the systems. It is lower by 23% compared to DCSCWSS (full storage), 24% compared to DCSISS (partial storage) and 50% compared to DCSISS (full storage) systems. It is due to DCSISS (partial storage uses smaller equipment compared to full storage system. Full storage chiller plant equipment run for only 10 hours whereas for the partial storage it runs for 24 hours. DCSCWSS systems is lower than DCSISS systems due to the absence of primary heat exchangers in the chiller plant, reduced pumps size (absence of glycol solution) and reduced chiller and cooling tower size (increase chiller C.O.P.).

Fig.10 Life cycle cost of the systems per annum From Figure 10, DCSCWSS (full storage) is the lowest life cycle cost. It is 2% lower than DCSCWSS (partial storage), 19% lower than DCSISS (partial storage) and 28% lower than DCSISS (full storage). From the life cycle cost diagram, DCSCWSS (full storage) is the most suitable to be adopted as a DCS plant. Figure 11 shows the chilled water supply tariff comparison between the DCS plant and the buildings.

Figure 9 shows the total running costs for the systems annually. Total running costs are the summation of the electricity cost, system maintenance, maintenance staffs’ salaries and land rental that is used to construct the DCS plant.

Fig.11 Chilled water supply tariff per 1000 kWrhr

Fig.9 Total running costs of the systems

From Figure 11, office D is the highest tariff at RM 0.13 per 1000 kWhr and DCSCWSS full storage is the lowest at RM 0.04 per 100 kWrhr. All DCS plant tariffs with the exception of DCSISS

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full storage are lower than the office tariffs. It is therefore, the respective DCS can be commercialized with DCSCWSS full storage being the best option.

4. Conclusion With reference to the result presented in the previous section, it can be concluded that: I. As shown in Fig. 7, DCSISS and CWSS full storage will shift 40-50% of the electricity consumption toward off-peak period. As such, it will reduce the burden on T.N.B. in providing electricity during the peak period. II. DCSCWSS full storage is the best option for potential commercialization in Malaysia due to its lowest tariff as compared to other district cooling thermal storage system . III. As shown in Fig. 11, the recommended tariff to be charged to consumers is RM 0.09 per 1000 kWrhr. These studies provide as a framework for implementation of district cooling system for commercialization. Even though the studies only involve with commercial sectors that operate during day time only (8 a.m. to 6 p.m.), the same benefits can also be extended to other sector that operate for more than 10 hours daily such as shopping centers, hospitals, factories etc. Other recommended studies to be carried out in the future are for the energy and economic analysis between DCSCWSS full storage and cogeneration systems in Malaysia.

ACKNOWLEDGEMENT The author acknowledge the support and data given by “Pantai District Cooling’ and ‘Naditech Sdn Bhd’ in preparing this studies.

[4] M.O. Abdullah, L.P. Yii, E. Junaidi, G. Tambi, M.A. Mustafa, “Electricity cost saving comparison due to tariff change and ice thermal storage (ITS) usage based on a hybrid centrifugal-ITS system for buildings: A university district cooling perspective”. Energy and building, vol 67, 2013, pp 70-78. [5] B. Rismanchi, R. Saidur, H.H. Masjuki, T.M.I. Mahlia, “Cost-benefit analysis of using cold thermal energy storage systems in building applications”, proceeding of ICAEE 2011, Bangkok, Thailand, 2011, pp 493-498. [6] B. Rismanchi, R. Saidur, G. Boroumandjazi, S. Ahmed, “Energy, exergy and environmental analysis of cold thermal energy storage (CTES) systems”, renewable and sustainable energy review, vol 16, 2012, pp 5741-5746. [7] Y.H. Yau, Behzad Rismanchi, “A review on cool thermal storage technologies and operating strategies”, Renewable and sustainable energy review, vol 16, 2012, pp 787-797. [8] W.P. Bahnfleth, W.S. Joyce, “Energy use in a district cooling system with stratified chilledwater storage”, ASHRAE transaction: Symposia, 1994, pp 1767-1778. [9] Kent W. Peterson, “Chilled water TES hydraulic”, ASHRAE journal, February 2015, pp 40-43. [10] Shan K. Wang, “Handbook of air conditioning and refrigeration”, 2nd ed., McGraw Hil, U.S.A. 2000. [11] Williams, C.H., Talhar & Wong., “Another Mega Deal by WTW”, Kuala Lumpur, 2007. [12] B.Silvetti, “Application Fundamental of IceBased Thermal storage”, ASHRAE Journal, pp 30-35, 2002

REFERENCES

[13] J.F. Kreider, “Handbook of heating, ventilation and air conditioning”, CRC Press LLC., 2001.

[1] American Society of Heating, Refrigerating and Air Conditioning Engineer, “Handbook of System and Equipment”, Atlanta, Georgia, 2012, chapter 12.

[14] A.Bell, “HVAC, equation, Data nad Rules of Thumb’, Mc Graw-Hill Company, 2002.

[2] Tenaga Nasional Berhad, “Tariff book”, Kuala Lumpur, 2006, p2. [3] M.H. Siron, “Energy and economic analysis of district cooling ice thermal storage system in Malaysia”, Master dissertation, Universiti Malaya, 2008.

[15] M.A. Habeebullah, “Economic feasibility of ice thermal storage system”, Journal of energy and building, Saudi Arabia, 2006, pp 355363. [16] A. Melinder, “Thermo-physical properties of liquid secondary refrigerants”, Internal institute of refrigeration, France, 1997, pp 25120.

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R.C.Dorf, “Engineering economic and management”, The engineering handbook, CRC Press, LLC, Boca Raton, 2000. [18] American Society of Heating, Refrigerating and Air Conditioning Engineer, “Handbook of Application”, Atlanta, Georgia, 2007 [17]