Consider a building with 250 tons of peak cooling load. On a peak-cooling day, the cooling load occurs for 8 hours with a load factor of 75 percent. During the entire year, there are 1,000 equivalent full-load hours. Cooling is required only during the on-peak periods of the utility rate structure.

The utility rate structure includes (i) demand charge of $10/Kw with 12 months ratchet period and (ii) the energy charge differential between on-peak and off-peak is $0.05/kWh. The installed cost of a chiller is $60/ton. The cost of a storage system is $60/ton-hr. Consider that the efficiency of the chiller is on average 1 kW/ton.

i. Determine the cost-effectiveness (using a simple payback analysis) of installing

(a) a full storage system and

(b) a partial storage system with 50 percent undersized chiller. For the partial storage system, assume that only 400 of equivalent full-load hours (relative to the new chiller size) have to be supplied by the chiller during the on-peak period.

ii. Determine the effect of the number of hours that the chiller has to be used during the on-peak period on the cost-effectiveness of the partial storage system.