230

Storage cost ($)

428,750

820,000

605,820

1(2 units)(1,080 Ton-Hrs/units)($150/Ton-Hr) = $324,000

Note: The values in this table vary slightly from those in the text from additional significant digits.

1(2 units)(1,080 Ton-Hrs/units)($150/Ton-Hr) = $324,000

Note: The values in this table vary slightly from those in the text from additional significant digits.

Ton-Hr including piping and installation4 (note that this provides 2,160 Ton-Hrs compared to the needed 2,144 Ton-Hrs).

Sizing the storage system utilizing the phase change materials or eutectic salts is completed just as the ice storage system. The EPRI study states that the eutectic salt storage tanks had average daily heat gains approximately the same as that of the chilled water systems. To allow for these heat gains a conservative value of 20% is added to the actual storage capacity5. This increases storage requirements to 1,715 Ton-Hrs. Assuming there are 12,000 Btu's per Ton-Hr, this yields: (1,715 Ton-Hrs)*(12,000 Btu's/Ton-Hr) = 20.58 x 106 Btu's.

The eutectic system also utilizes the latent heat of fusion like the ice system and the temperature differential shown in Figure 19.5a is not used in the calculation. The C1 now becomes:

5.15 x 105 lbm

Volume of Mass

density = water) Density 62.5 lbm/ft3

The actual volume of eutectic salts needed would need to be adjusted for density differences in the various combinations of the salts. Eutectic systems have not been studied in great detail and factory sized units are not yet readily available. The EPRI report7 studied a system that required 1,600 Ton-Hrs of storage which utilized approximately 45,000 eutectic "bricks" contained in an

80,600 gallon tank of water. For this situation, a similar eutectic storage unit will be purchased for approximately $250/Ton-Hr including piping and installation. The ratio of Ton-Hrs required for partial storage and the required tank size will be utilized for sizing the full and optional partial storage systems.

Table 19.9 summarizes the sizes and costs of the different storage systems and the actual chiller systems for each of the three storage arrangements. The values presented in this example are for a specific case and each application should be analyzed thoroughly. The cost per ton hour of a water system dropped significantly as the size of the tanks rises as will the eutectic systems since the engineering and installation costs are spread over more capacity. Also we ignored the sensible heat of the ice and eutectic systems.

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