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Table 2-3: Typical Cast Iron Radiator Capacities
Design Water
Btuh per
Temperature,
sq ft
°F [°C]
110 [43]
30
120 [49]
50
130 [54]
70
140 [60]
90
180 [82]
170
200 [93]
210
FAN COIL UNITS
Fan coil units (or air handlers) consist of a hot water coil and/or
chilled water coil (usually copper tubing with aluminum fi ns) and
a fan or blower to move the air over the coil. The term "fan coil
unit" typically applies to smaller units, which are installed in the
zone or area where the heating or cooling is needed. The term
"air handler" normally refers to larger units. Fan coils are available
in many different confi gurations, sizes and capacities from a number
of manufacturers. Some are designed to be connected to a
ductwork system and can be used to replace a forced air furnace.
Others are designed for use without ductwork, and are mounted
in a suspended ceiling space with only a grill showing in place of
a ceiling tile. There are also console type fan coils that can be
mounted on a wall under a window or fl ush with the wall surface.
A typical horizontal fan coil illustration is shown in fi gure 2-14.
Figure 2-14: Typical Horizontal Fan Coil
Table 2-4: Fan Coil Heating Water Temperature
Capacity Correction Factor Table
EAT
°F [°C]
100 [38]
110 [43]
65 [18]
0.318
0.409
68 [20]
0.295
0.386
70 [21]
0.272
0.363
Bryant Geothermal Heat Pump Systems
Part II: Load Side Design / Distribution Design
Watts per
sq m
95
158
221
284
536
663
EWT °F [°C]
120 [49]
130 [54]
140 [60]
0.500
0.591
0.478
0.568
0.455
0.545
Water-to-Water System Design Guide
Fan coils and air handlers typically have one or two coils and
a blower. Air is heated by hot water circulated through a hot
water coil. Chilled water is circulated through the coil if cooling
is needed. Depending upon the application, the unit will include
one coil for both heating and cooling (hot water/chilled water) or
a coil dedicated to heating (hot water) and another coil specifi cally
for cooling (chilled water). Blowers can be provided to fi t various
applications, with or without ductwork. Unit heaters (small, wall-
mounted fan coils) typically use axial fans in applications where
ductwork is not needed.
Fan coil units have been used to heat buildings using water
temperatures as low as 90-100°F [32-38°C]. As with radiators/
baseboard convectors, heating capacities fall dramatically when
operated below design temperatures. Table 2-4 shows the heating
correction factors for lower water temperatures. For example, a
fan coil designed for 180°F [82°C] entering water temperature and
70°F [21°C] entering air temperature would have only 36% of its
original heating capacity when operated at 110°F [43°C] entering
water temperature. For this reason, two coils are recommended if
the fan coil will be used for forced air space heating, one for heating,
one for cooling. Careful consideration should be given to fan coil
selection, since the heating and cooling coils could be signifi cantly
different in physical size. Proper fan coil selection may involve
selecting a larger model with multiple fan speeds in order to satisfy
the capacity requirements without providing too much airfl ow.
Manufacturers' literature will be necessary for proper selection.
In a retrofi t situation when replacing a conventional boiler, care
must be taken to ensure that any air handlers or fan coil units in
the building will heat the building with cooler water temperatures,
and will be able to handle the increased fl ow rates if necessary. If
the insulation levels of the building are being upgraded, the existing
coils may meet the lower heat loss of an upgraded building with
lower water temperatures.
145 [63]
150 [66]
0.682
0.728
0.773
0.659
0.705
0.750
0.636
0.682
0.727
180 [82]
1.045
1.023
1.000
29
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