Handbook of air conditioning and refrigeration / Shan K

System Description
AC SYSTEMS: PACKAGED AND DESICCANT-BASED SYSTEMS 29.33
40 gr/lb), and a dew point of 43°F (6.7°C). Using conventional dew point, there is a 22°F (12.2°C)
reheat and a dedicated refrigeration system.
Busby (1996) reported a desiccant-based air conditioning system for a six-room operating suite at
Straith Hospital, Southfield, Michigan, as shown in Fig. 29.7. The process airstream is an outdoor
airstream of 7600 cfm (3586 L/s) at an inlet with a temperature of 95°F (35°C) with a humidity ratio
of 0.0142 lb/lb (kg/kg or 100 gr/lb). It flows through a prefilter of medium efficiency and a water
sensible cooling coil; the outdoor air is sensibly cooled to 80°F (26.7°C) and 0.0142 lb/lb
(kg/kg or 100 gr/lb). Before entering the rotary desiccant dehumidifier, the process air is divided
into two airstreams: a dehumidified airstream and a bypass airstream. At summer design conditions,
the bypass air flows through the bypass dampers at 400 cfm (189 L/s). The desiccant used in the
rotary dehumidifier is titanium silica gel. After dehumidification in the rotary dehumidifier, the temperature
of the process air is raised to 138°F (58.9°C) and the humidity ratio reduced to 0.005 lb/lb
(kg/kg or 36 gr/lb). Both the dehumidified and bypass airstreams are extracted by the supply fan,
at the outlet of the supply fan, the process air temperature is increased to 140°F (60°C), and its humidity
ratio is raised to 0.0057 lb/lb (kg/kg or 40 gr/lb).
The process air then flows through the evaporator end of the heat pipe, and its temperature drops
to 95°F (35°C). When the process air flows through a water-cooling coil, its temperature is sensibly
Filter
95%
eff.
7200 cfm
53� F
40 gr/lb
Water
cooling
coil
95� F
40 gr/lb
Heater DDC
controller
Humidifier
Heat-pipe heat exchanger
T H
EA
140� F
40 gr/lb
OA
Supply
fan
Operating room
65� F f � 50%, 46 gr/lb
Gas
heater
138� F
36 gr/lb
Rotary desiccant dehumidifier
Reactivated
fan
Chilled
water
80� F coil
100 gr/lb
FIGURE 29.7 A desiccant-based air conditioning system for a six-room operating suite at Straith Hospital,
Southfield, Michigan.
Filter
OA
95� F
7600 cfm
100 gr/lb