As part of a program to explore new energy efficient strategies, the San Francisco Marriott Hotel is working with Pacific Gas & Electric to take full advantage of cool storage technology and PG&E's experimental real-time electricity pricing scheme.
The hotel has participated in the Real-Time Pricing Project since March, 1992. Its utility bill savings from the rate strategy were already at $150,000 per year prior to the installation of a FAFCO IceStor System, which is expected to add an additional $135,000 in annual savings.
Under a year-long contract with PG&E, real-time pricing participants, like the Marriott Hotel, pay for electricity and demand through a charge per kWh that varies hourly. Each day the utility transmits the next day's different hourly rates to participants. In summer months, hourly real-time prices typically range from 4.5 up to about 13 cents per kWh, but the utility can set higher rates on up to 10 days a year during unusually high demand periods. Additionally, PG&E is allowed up to 25 "transmission and distribution" days per year to reduce demand when the capacity of its power transmission and distribution network is strained. Peak rates on these days may go as high as 40 to 50 cents per kWh.
Real-time pricing participants must regulate electrical usage to avoid the high hourly rates as much as possible, and shift maximum usage to low cost periods. In order for the Marriott to take maximum advantage of the rate structure, FAFCO installed an 1,800 ton-hour ice storage system, which can provide up to 450 tons of cooling per hour through a plate-and-frame heat exchanger.
The Marriott ice storage system utilizes six of FAFCO's model 590C IceStorTM units, which were assembled on-site to minimize demolition costs.
Under real-time pricing, the peak daily rates only last for two or three hours. Since the hotel's average load is about 450 tons, the ice storage system can handle the entire cooling loan during these peak periods. If the hotel were operating under the utility's regular time-of-use schedule, the peak period would be considerably longer, and storage capacity would have to be greater to cover peak period cooling needs. In this case, the hotel did not even have room for a larger thermal storage system, so real-time pricing fit the circumstances ideally.
Hotel management also uses pre-cooling to its advantage. Operators check the following day's hourly rate schedule against how hotel space if being utilized. If large rooms are to be in use about the time of the highest rates, the rooms are pre-cooled with the conventional chilled water system prior to the peak period.
The storage system's installation cost $390,000 and was eligible for a $140,000 rebate from Pacific Gas & Electric. The hotel paid the net cost of $250,000 in a lump sum and expects to recoup its investment in just over 22 months.
