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 find actual unit heater capacity when operating at
BtuA = BtuS x Heating Capacity Factor
c.To select a heater capacity based on standard conditions to meet a heating capacity at non- standard (actual) conditions:
BtuS = BtuA / Heating Capacity Factor
2.Refer to Table 12:
a.To determine how water temperature drop affects heat capacity in Btu, water flow 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 find actual unit heater capacity or flow rate or pressure drop when operating at
BtuA = BtuS x Btu Correction Factor GPMA = GPMS x GPM Correction Factor WPDA = WPDS x WPD Correction Factor
c.To select a heater capacity based on standard conditions to meet a heating capacity at non- standard (actual) conditions:
BtuS = BtuA / Btu Correction Factor
d.Other useful formulas:
FATA = EATA + [(460 + EATA) x (BtuA) / (576 x CfmS)] For BH units only
FATA = EATA + [(460 + EATA) / (576 x CfmS /
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 find actual unit heater capacity when operated with glycol solution:
BtuAG = BtuS (or BtuA) x Glycol Correction Factor
c.To select a heater capacity based on standard conditions to meet a heating capacity with glycol solution:
BtuS (or BtuA) = BtuAG / Glycol Correction Factor
4.Refer to Table 14:
To determine how water temperatures other than 200°F affect mounting height of unit.
Max. Mounting HeightA = Max. Mounting HeightS x Correction Factor
5.Terminology:
a.BtuA = Capacity at
b.BtuAG = Capacity with Glycol solution
c.BtuS = Capacity at standard conditions (200°F entering air temperature, 60°F entering air temperature) from Tables 9 and 10
d.CfmS = Unit airflow as found in Tables 9 and 10
e.EATA = Entering air temperature at actual conditions
f.FATA = Final air temperature at actual conditions
g.GPMGPMA = Water flow rate at actual conditions in
h.GPMS = Flow rate at standard conditions (200°F entering water temperature, 60°F entering air temperature) from Tables 9 and 10
i.Max. Mounting HeightA = Maximum mounting height at actual conditions
j.Max. Mounting HeightS = Maximum mounting height at standard conditions
k.WPDA = Water pressure drop at
l.WPDS = Water pressure drop at standard conditions (200°F entering water temperature, 60°F entering air temperature) from Tables 9 and 10
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