Thermal Energy Storage - Dodging the Energy Crisis

Engineering Foresight and Thermal Storage - Looking Back After 10 Years

In 1990, construction began on a 24 story, 430,000 square foot office building known as 801 Towers in downtown Los Angeles. As means of shifting peak loads and qualifying for incentives and off-peak rates offered by the Los Angeles Department of Water and Power (LADWP), the building was designed to include 8,300 ton hours of thermal energy storage (TES). As installed, the system is actually capable of approximately 11,000 ton hours of capacity, which in hindsight, was a stroke of engineering prudence that has paid off as the California energy crisis drags on.

Flack and Kurtz of San Francisco, the principal engineer, and the Los Angeles Department of Water and Power (LADWP) may not have seen the current crisis coming. Looking back today, however, this system has proven to be a prime example of engineering foresight. The engineer, building owner and local utility designed in  flexibility to deal with the uncertainties in electrical supplies that are now exacerbated by deregulation of electricity markets. Leadership shown by LADWP with incentives and off-peak rates was part of an overall business plan that has shielded customers in that service territory from many of the problems faced today by ratepayers elsewhere in the State. Energy supply uncertainties and the need for design foresight have become the norm in California and promise to spread nationwide and to continue for some time to come. http://www.cryogel.com/

801 Towers during construction

After incentive payments from the LADWP, the system cost approximately $640,000 more than a non-storage air conditioning system. With the capability to shift approximately 2,000 kW of electrical demand to off-peak periods, the additional costs amount 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. This cost per kW represents a bargain compared to the cost of new generation capacity currently under consideration by electricity suppliers in the U.S. and in developing international energy markets.

Inside the storage tank before filling with Ice Balls

The system includes a 180,000 gallon concrete tank with a polyethylene liner and approximately 750,000 spherical ice containers (Cryogel Ice Balls^TM) as well as two 700 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 with most civic centers, parking is a premium in downtown L.A. This tank configuration and ice storage technology was chosen because the tank could be installed in a manner that would not consume parking spaces in the garage. Eight years after initial start-up in 1993, the system functions virtually unknown and invisible to visitors and tenants of the building.

The concrete tank was fitted with a one-eighth inch thick polyethylene liner to prevent leaks in the underground concrete tank due to normal thermal expansion and contraction. The liner also allowed for one and one-half inches of Styrofoam board insulation between the liner and the internal tank wall. This unique solution to insulating an underground tank offers double-wall leak security as well as a vapor barrier for the insulation.

Today, engineers and utilities across the country have seen the effects of deregulation in California. They have the benefit of studies done by the California Energy Commission which show thermal storage as both a conservation tool and an environmentally friendly and economically attractive alternative to new generation capacity. Today's designers also have the benefit of years of proven success with TES systems and equipment. Designing in the flexibility to deal with future uncertainties in electrical supply and prices is not only a prudent HVAC engineering decision, it is also prudent energy policy. Time-of-use rates, real-time-pricing, time sensitive meters and thermal energy storage have proven benefits and deserve greater attention as policy makers search for solutions to the energy crisis.