Victor J. Ott, PE, of CRYOGEL Thermal Energy Storage Systems.
Joe Hickman, the Chief Engineer for 801 Towers in
To qualify for peak load shifting incentives and off-peak rates offered by LADWP, the building was designed in 1990 to include 8,300 ton hours of thermal energy storage (TES). The system is actually capable of approximately 11,000 ton hours of capacity, which in hindsight, was valuable engineering judgement that has paid off with ever-changing electricity prices and energy markets.
Flack and Kurtz of San Francisco, the principal engineer, and the Los Angeles Department of Water and Power may not have anticipated all the changes in energy markets during the past two decades. Looking back today, however, this system has proven to be a good example of engineering foresight. The engineer, building owner and electric utility recognized the need for flexibility to deal with the uncertainties in electrical supplies and increasing energy costs. Leadership shown by LADWP with incentives and off-peak rates was part of an overall business plan that shielded customers in that service territory from many of the problems faced by ratepayers elsewhere in the state and the rest of the country. Concern about the reliability of energy supplies and the need for design foresight and peak load shifting may finally become the norm in
Green Benefits of Off-Peak Energy Storage: In addition to the reduction in energy costs, thermal energy storage (TES) is effective in reducing green house gasses and the carbon foot-print of electric generation facilities. This benefit may not have been anticipated by the building designers in 1990 but the positive effects of TES on emissions from power plants has been well documented over the years as concerns about climate change have gained attention. Both of the largest
After incentive payments from LADWP, the TES system at 801 Towers cost approximately $640,000 more than a non-storage air conditioning system. With the reported capability to shift approximately 2,000 kW of electrical demand to off-peak periods, the additional costs can be translated to approximately $320 per kW of peak electrical demand reduction. The net installed cost was approximately $58 per ton hour of actual thermal storage capacity. The cost per shifted kW was a bargain compared to the cost of new generation capacity. Although prices for electricity and equipment have changed over many years, that bargain is even mor
e compelling as costs and environmental impacts associated with new power plants have become more painful and politicized.
The 801 Towers system includes a 180,000 gallon concrete tank with a polyethylene liner and approximately 750,000 spherical ice containers (* Cryogel Ice BallsTM) as well as two 800 ton, Trane three-stage centrifugal chillers. The tank is located three levels below the street and adjacent to the underground parking garage. The roof of the concrete tank is formed by a ramp that connects two garage levels. As in most civic centers, parking is a premium in downtown
Flexibility of the system allows for compliance with changes in utility rate structures. This is apparent when looking back at the original specifications as compared to operational demands now being placed on the system which exceed design intent.
The original design intent was to shift the cooling load for a period of 8 hours. However, today the system is actually shifting load for 10 hours per day. According to Joe Hickman, "the current agreement with LADWP requires us to keep the chillers shut off completely from 10 am to 8 pm. The system has enough capacity to carry the extended hours of operation, even without charging fully every night."
The concrete tank was fitted with a one-eighth inch thick polyethylene liner to prevent leaks due to normal thermal expansion and contraction. The liner allows for 1.5 inches of rigid insulation between the liner and the tank wall. This unique solution to insulating an underground tank offers double-wall leak security as well as a vapor barrier.
Thermal storage is not new technology although proven environmental benefits and energy cost savings are only now gaining the wider attention of design engineers and electric utilities across the nation. TES is increasingly recognized as an environmentally friendly and economically attractive alternative to new generation capacity. Today's designers and regulators have the benefit of years of proven success with TES systems and equipment. Improved efficiency of existing power generation equipment, and means to avoid building new expensive power plants, are major benefits to electric utilities. Lower energy costs and improved reliability stand as major benefits to consumers. Reductions in the use of fossil fuel and the decrease in greenhouse gas emissions are benefits to society that should inspire incentives for thermal storage as part of state and national energy policy.
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