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19
H.
HOT WATER CALCULATION FORMULAS
1. Refer to Table 11:
a. To determine the heating capacity (Btu/hr) of a
unit heater at a water temperature and/or entering
air temperature other than standard conditions of
200°F entering water temperature, 60°F entering
air temperature.
b. To fi nd actual unit heater capacity when
operating at non-standard (actual) conditions:
Btu
A
= Btu
S
x Heating Capacity Factor
c. To select a heater capacity based on standard
conditions to meet a heating capacity at non-
standard (actual) conditions:
Btu
S
= Btu
A
/ Heating Capacity Factor
2. Refer to Table 12:
a. To determine how water temperature drop affects
heat capacity in Btu, water fl ow rate is in GPM
and pressure drop in feet of water. These factors
should be applied to the values at actual entering
water and air temperature conditions.
b. To fi nd actual unit heater capacity or fl ow rate
or pressure drop when operating at non-standard
(actual) conditions:
Btu
A
= Btu
S
x Btu Correction Factor
GPM
A
= GPM
S
x GPM Correction Factor
WPD
A
= WPD
S
x WPD Correction Factor
c. To select a heater capacity based on standard
conditions to meet a heating capacity at non-
standard (actual) conditions:
Btu
S
= Btu
A
/ Btu Correction Factor
d. Other useful formulas:
FAT
A
= EAT
A
+ [(460 + EAT
A
) x (Btu
A
) / (576 x
Cfm
S
)] For BH units only
FAT
A
= EAT
A
+ [(460 + EAT
A
) / (576 x Cfm
S
/
Btu
A
)-1)] For BV Units only
3. Refer to Table 13:
a. To determine how glycol solutions affect heater
capacity. These factors should be applied to the
heater capacity at actual entering water and air
temperature conditions.
b. To fi nd actual unit heater capacity when operated
with glycol solution:
Btu
AG
= Btu
S
(or Btu
A
) x Glycol Correction
Factor
c. To select a heater capacity based on standard
conditions to meet a heating capacity with glycol
solution:
Btu
S
(or Btu
A
) = Btu
AG
/ Glycol Correction
Factor
4. Refer to Table 14:
To determine how water temperatures other than
200°F affect mounting height of unit.
Max. Mounting Height
A
= Max. Mounting
Height
S
x Correction Factor
5. Terminology:
a. Btu
A
= Capacity at non-standard (actual)
conditions
b. Btu
AG
= Capacity with Glycol solution
c. Btu
S
= Capacity at standard conditions (200°F
entering air temperature, 60°F entering air
temperature) from Tables 9 and 10
d. Cfm
S
= Unit airfl ow as found in Tables 9 and 10
e. EAT
A
= Entering air temperature at actual
conditions
f. FAT
A
= Final air temperature at actual conditions
g. GPM
A
= Water fl ow rate at actual conditions in
GPM
h. GPM
S
= Flow rate at standard conditions (200°F
entering water temperature, 60°F entering air
temperature) from Tables 9 and 10
i. Max. Mounting Height
A
= Maximum mounting
height at actual conditions
j. Max. Mounting Height
S
= Maximum mounting
height at standard conditions
k. WPD
A
= Water pressure drop at non-standard
(actual) conditions
l. WPD
S
= Water pressure drop at standard
conditions (200°F entering water temperature,
60°F entering air temperature) from Tables 9 and
10