8
This section provides capacity tables for the 42BHC unit.
Capacity tables are based on nominal cfm. Correction
factors are provided for other operating conditions as
explained in the following selection example.
For applications outside the range provided in this
catalog, please consult the factory.
FORMULAS:
TC = TCb x Ct x Et
SC = SCb x Cs x Es
Where:
Cs = Sensible Airflow Correction Factor
Ct = Total Airflow Correction Factor
Es = Sensible Elevation Correction Factor
Et = Total Elevation Correction Factor
SC = Sensible Capacity
SCb = Base Sensible Capacity from Base Cooling Capaci-
ties by gpm charts
TC = Total Capacity
TCb = Base Total Capacity from Base Cooling Capacities
by gpm charts
EXAMPLE:
I Rate unit performance.
To rate the performance at sea level for an 42BHC16
unit with a four-row coil at 80 F/67 F EAT, 45 F EWT,
7 gpm water flow, and 1500 cfm:
a) Enter the Base Cooling Capacities by Gpm, 4-Row
Capacity Units table on 80 F/67 F EAT and
45 F EWT.
b) Locate the appropriate row for unit size 16 and
7 gpm.
Record the tabulated base performance.
TCb = 43.8 MBtuh
SCb = 34.9 MBtuh
∆
T = 12.5 F
c) Divide CFM Actual by CFM Nominal to determine
Cfm Ratio.
Cfm Ratio = 1500/1600 =.9375
II Select CFM correction factors.
Select the Cfm correction factors, Ct and Cs, from the
Air Flow Correction Factors table. (Interpolation may
be required.)
Ct = .9625
Cs = .96
Select the elevation correction factors, Et and Es, from
the Elevation Correction Factors table. (No correction
necessary in this example, unit is at sea level.)
Et = 1.00
Es = 1.00
III Calculate actual performance.
TC = TCb x Ct x Et
= 43.8 x .9625 x 1.00
= 42.16 MBtuh
SC = SCb x Cs x Es
= 34.9 x .96 x 1.00
= 33.50 MBtuh
a) Calculate water pressure drop (or refer to the Water
Pressure Drop for Cv Factor and Water Flow Rate
table on page 18). From the Cv Factor by Coil and
Unit Size table on page 17, find the Cv value for
unit size 16 with four rows.
Cv = 7.2
P = [GPM/(0.658 x Cv)]2
= [7.0/(0.658 x 7.2)]2
= 2.18 feet of H
2
O
b) For selections other than those listed here, please
contact the factory.
IV Determine motor and drive.
To determine motor and drive selection requirements
and obtain the cfm for a specific application, the
total static pressure (TSP) for that application must be
determined.
The TSP is the sum of the internal static pressure (ISP)
and the external static pressure (ESP) measured in
inches of water column. ISP is sum of the static resis-
tance of the components of the unit — the cabinet,
coil and filter. ESP is the static resistance of the exter-
nal components of the unit, including, but not limited
to, duct work, grilles and additional filtration. For non-
ducted applications, the ESP is 0 in. wg.
After the TSP has been calculated (see the following
example), use the motor horsepower table to deter-
mine the actual horsepower (HP) for your Belt Drive
unit. Horsepower offerings are limited to
1
/
4
,
1
/
3
,
1
/
2
,
3
/
4
, 1, 1
1
/
2
, 2 and 3.
The standard selection is the nearest offering above the
actual HP shown in the table.
Using the TSP of the table, match the unit size with the
cfm row to determine the correct motor for your spe-
cific application. Drive sheaves and the required belt
assembly will be provided to meet your design require-
ments. Drive sheaves are set at the factory.
Calculate the HP and drive selection required to deliver
1500 cfm on a 42BHC16 unit equipped with a
4-row hydronic cooling coil and a 2-in. pleated filter in
a ducted application at .38 in. ESP, including duct and
grille losses.
Using the Component Static Resistance table on
page 17, the ISP is calculated as follows:
Cabinet
.09-in. wg
4-row Wet Coil
.30-in. wg
2-in. Filter
.12-in. wg
ISP
.51-in. wg
ESP
.38-in. wg
TSP
.89-in. wg
Selection procedure
