Page 100 - Sustainable On-Site CHP Systems Design, Construction, and Operations

78 CHP B a s i c s

3.0 50,000
Steam flow COP
45,000
2.5
Steam: 150 psig 40,000
Output: 2,000 tons
Chilled W: 44°F 35,000
2.0
30,000
1.66
COP 1.5 1.49 25,000 Steam flow (Ib)

1.21
20,000
1.0
15,000
10,000
0.5
5,000
0.0 0
55 60 65 70 75 80 85
Condenser water temp (°F)
FIGURE 4-7 Steam turbine effi ciency versus condenser water temperature. (Courtesy of Integrated
CHP Systems Corporation.)

saved due to increased chiller efficiency can be used for other purposes. Figure 4-7 provides
a graph of efficiency versus condenser water temperature for a 2000-ton steam turbine
chiller using 150-psig steam at full load. At full load and a condenser water temperature
of 70°F, the steam turbine chiller will operate at a COP of over 1.6.
The steam turbine chillers also have relatively low condenser water flow require-
ments compared to absorbers at 3.5 gpm/ton which are similar to electric chillers. In
addition, the turbine chiller can produce low chilled water temperatures well below
40°F without suffering significant capacity or efficiency losses.
Steam turbine chillers are available sizes ranging from 700 to 2500 tons, are gener-
ally more expensive per ton in smaller sizes and only become cost competitive with
absorption above 1000 tons. If the condenser is located above the evaporator these
chillers have approximately the same footprint as an electric chiller and smaller than an
absorber. The ability to provide low temperature chilled water and to take advantage of
low ambient conditions to increase efficiency make them suitable for larger distributed
energy type CHP applications.

Desiccant Dehumidifiers
Desiccant systems are thermally driven air conditioners that remove the moisture from
an air stream by absorbing or adsorbing the water into a desiccant material. They come
in two types—liquid and solid—with each type having slightly different characteristics.
Liquid desiccant systems typically use a lithium chloride (LiCl) and water solution to
absorb the water in an air stream thereby to dry the air. The diluted LiCl solution is then
directed to a hot water–driven regeneration process, where the water is expelled and the