Specifications

24
RG SERIES ENGINEERING GUIDE
Hot Gas Reheat Dehumidifi cation Overview cont.
Hot Gas Reheat Dehumidification
Overview cont.
Btu/hr may be converted to lbs/hr or grains per hour as shown in
the equations below.
11,900 Btu/h / 1,069 Btu/lb of water vapor
at 80/67 DB/WB°F = 11.13 lbs/hr
11.13 lbs/hr x 7,000 grains/lb = 77,910 grains/hr
External Static Pressure Adjustment
With a reheat coil option installed an adjustment for external static
pressure (ESP) needs to be made. The following table will show the
reduction in ESP for any model relating coil air velocity and ESP.
Variable speed ECM models will generally compensate up to their
maximum ESP of 0.5 in. wg. for 1/2 hp and 0.75 in. wg. for 1 hp.
Model VS048, 1500 cfm,
H x W = SA
20 x 40 = 800 in.
2
= 5.56 ft.
2
Where H=fin height of air coil, W=fin length of air coil, SA=fin surface area
Adjustment must be made for dehumidification mode, 85% of cfm,
1500 x 0.85 = 1,275 cfm
Calculate air velocity, fpm, cfm / SA
1,275 cfm / 5.56 ft.
2
= 229 fpm
Refer to the ESP vs. Coil Velocity Table and look up the fpm to
find ESP increase. If air velocity is below 250 cfm assume 0.10
increase in ESP. Interpolation of data within the table is permitted.
ESP vs. Coil Velocity Table
Coil Velocity (fpm) 250 300 350 400
ESP Increase (in. wg.) 0.10 0.14 0.17 0.20
Hot Gas Bypass with Hot Gas Reheat Layout
Compressor
Reheat
Valve
RV
TXV
Suction
Discharge
Check
Valve
Coax
Air
Coil
Reheat Coil
Hot Gas
Bypass Valve