Handbook of air conditioning and refrigeration / Shan K

29.32 CHAPTER TWENTY-NINE
RA
To
store
Gas
OA
Performance
DX-coil
Heat pipe
When the relative humidity sensor senses that the relative humidity of a representative zone exceeds
a preset limit and calls for dehumidification, the entire 10,000 cfm (4719 L/s) of supply air in
the OAU is dehumidified in the desiccant dehumidifier. When relative humidity drops to or below a
preset limit and the dehumidification is not required, the entire 10,000 cfm (4719 L/s) bypasses the
rotary desiccant wheel.
At the Norfolk store, the desiccant-based outdoor ventilation air system provided excellent control
of indoor relative humidity and comfort, generally maintaining relative humidity within 5 percent
of the 45 percent set point. The space temperature was maintained at 78°F (25.6°C). When the two
OAUs were operated in base ventilation mode, the CO 2 level in the store never went above
1000 ppm. During high ventilation air mode, the desiccant wheel removes 0.0065 lb/lb (kg/kg
or 42 gr/lb) from the outdoor air. Despite the fact that the ventilation rate had been raised from
0.15 to 0.30 cfm/ft 2 (2.73 to 5.46 m 3 /h� m 2 ) in the Norfolk store, the energy cost increased only 2.6
percent more.
29.12 CASE STUDY: A DESICCANT-BASED AIR CONDITIONING
SYSTEM FOR OPERATING ROOMS
EA
Indoor Environment of Operating Rooms
OA
OA Outdoor air RA Recirculating air
Because the surgical staff are gowning more heavily to avoid the hazard of infectious diseases such
as AIDS and at the same time there is a higher lighting and electronic equipment load, today surgeons
need 65°F (18.3°C), 45 percent relative humidity, a humidity ratio of 0.0058 lb/lb (kg/kg or
EA
RA
Exhaust air
FIGURE 29.6 An outdoor air unit of a desiccant-based air conditioning system for a large retail store in Norfolk,
Nebraska.
Gas heater
Rotary desiccant dehumidifier
EA
OA
Dampers