District Energy - 2005 First Quarter

capacity from 3,500 to 60,000 ton-hours;

● the median TES capacity per installation is 16,000 ton-hours;

● the average TES capacity per installation is 19,431 ton-hours;

● the average peak cooling-load shift per installation is 2,776 tons;

● the average peak electric-demand reduction per installation is 2. 1 MW;

● the total peak cooling-load shift is nearly 203,000 tons; and

● the total peak electric-demand reduction is more than 152 MW.

Latent-heat TES, in which cooling is stored as the phase change of a storage medium (generally as ice), represents nearly 400,000 ton-hours ( 22 percent) of TES capacity installed on campus. Of the installations using this technology,

● 86 individual installations range in TES capacity from 320 to 93,200 ton-hours;

● the median TES capacity per installation is 2,350 ton-hours;

● the average TES capacity per installation is 4,526 ton-hours;

● the average peak cooling-load shift per

A Note on
Survey Methodology

Courtesy of Chicago Bridge & Iron Co.

This 30,000-ton-hour stratified chilled-water TES installation at the University of Texas in El Paso began operation in 1999. It was designed to complement the architectural style prevalent on campus. Such installations are often sited remotely from the main campus chiller plants, allowing the TES to function as a satellite chiller plant during on-peak discharge periods. In this manner, TES can act not only to peak-shave electric power demand but also to enhance campus distribution network capacity.

Campus Sensible-Heat TES by TES Storage Medium

Type of TES TES Storage Total Campus TES Installations by TES Supplier Technology Medium No. Avg. (ton-hr) Total (ton-hr) (% of total)

Sensible-Heat TES CHW 71 19,230 1,365,312 96% Sensible-Heat TES CHW (LTF*) 4 40,300 161,200 11% Sensible-HeatTES LTF 1 40,000 40,000 3% Sensible-HeatTES HW 1 13,167 13,167 1%

All Sensible- all media 73 19,431 1,418,479 100% Heat TES

Initially operating as CHW TES, but also designed for potential future expansion as LTF TES.

Although some of the system data in this survey was obtained directly from the owners and operators, most of the information was compiled by the author over a number of years and then recently expanded and confirmed through a survey of all the leading suppliers of latent-heat (ice) TES and sensible-heat (chilled-water or low-temperature fluid) TES systems.

The author notes the following caveats regarding the data:

¹. The survey was conducted only through September 2004.

². The survey was limited to college and university campuses, plus a few national (U.S. and non-U.S.) research laboratory campuses. At this time, other campus applications are not included, such as grade K- 12 educational facilities, medical complexes (other than those on university campuses), museums, airports, and military, administrative and other government campuses. The database also does not include campuses that purchase chilled water from district energy utilities that may themselves employ TES.

³. Data from all leading TES equipment suppliers was included. For those who did not respond to the survey directly, a detailed review of their published literature was done to collect data.

⁴. Though it does not identify 100 percent of campus TES systems, the database includes the vast majority (perhaps 90 percent or more) of U.S. TES installations and a lesser number of non-U.S. installations.

⁵. Quantitative data on individual installations are sometimes approximate, due to the necessary use of estimates in a few instances. In those very few instances where no quantitative individual data was available, the average value from similar installations was assumed. Cumulative data (e.g., totals, averages and means) are judged to be relatively accurate.

⁶. On average, peak thermal-load shifts (in tons) are estimated to be the ton-hour capacity divided by seven hours. On average, peak electric-load shifts are calculated at the rate of 0.75 k W/ton (including chillers, condenser water pumps and cooling tower fans).