HVAC for Educational Testing Service Expansion

As part of a large expansion of its Princeton, New Jersey campus, Educational Testing Services (ETS) researched various heating, ventilation, and air-conditioning (HVAC) systems in its goal to save on energy costs and to improve its energy maintenance. With the help of The Hillier Group, an engineering consulting company, ETS, the largest non-profit testing and educational measurement organization in the United States, decided to use electric rotary screw chillers with ice storage. This thermal energy storage system, manufactured by The Trane Company, has allowed ETS to save significant money and energy in its 315,000 ft² (29,264 m²) office expansion on its 370-acre (1.5 km²) campus. The basic principle of thermal energy storage is to produce ice during the off-peak hours, when electricity costs are lowest, and to melt it during the peak hours to replace or supplement the normal source of chilled water. Currently, the chiller produces ice from 10 p.m. until 6 a.m. At 6 a.m., the system reverts to the chilled water mode. The chiller then operates at 100% capacity while the excess load is augmented by melting ice. The use of ice storage for shifting HVAC loads from peak to off-peak has allowed ETS greater energy use management. This thermal energy storage project has a simple payback of 3.1 years. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) have recognized the achievements of this project with an ASHRAE Technology Award.

Technical Data

The primary equipment includes two ~827-kW (235-ton) rotary screw chillers (Series R(r) CenTraVac(r) Helical-Rotary Chillers), two~196-kW (20-hp) primary chilled/glycol solution pumps, two ~392-kW (40-hp) secondary chilled/glycol solution pumps, two ~196-kW (20-hp) condenser water pumps, 16 ice storage tanks, and one double-cell, induced-draft cooling tower. The ice storage systems is designed to supply 20% of the kWh needed on a design cooling day. The ice is produced during off-peak periods when electricity rates are their lowest.

Energy Data

By using thermal energy storage, ETS was able to downsize the chillers for the system by 15%, further cutting energy consumption. Because the new office areas are not individually metered, it is impossible to provide precise energy savings data. However, a very rough estimate is 3,000,000 kWh annually.

Economic Data

The 315,000 ft² (29,264 m²) expansion of office space on the ETS campus took the form of two new buildings. Without individual metering of the buildings, it is not possible to have precise data on energy savings. However, considering that there is a $9.72(USD)/kW/month on-peak demand charge but no intermediate or off-peak demand charges, it is apparent that using the thermal energy storage system to produce ice during off-peak hours significantly reduces what would otherwise be the energy costs. A system analysis estimates that simple payback for the project is about 3.1 years.

Contacts:

Educational Testing Service Paul Weichler Rosedale Road Princeton, NJ 08541 609-921-9000 609-734-410 (Fax) http://www.ets.org	The Trane Company Michael J. Pawelski 3600 Pammel Creek Road La Crosse, WI 54601-7599 608-787-3445 608 787 4644 (Fax) http://www.trane.com
The Hillier Group Fred Broberg 1212 South Abington Road Clarks Summit, PA 18411 570-586-4000 570-587-5110 (Fax) http://www.hillier.com

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