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15
VII ARI/ISO 13256-1 Conversion
Performance standard ARI/ISO 13256-1 became
effective on January 1, 2000 and replaced the exist-
ing ARI Standards 320 Water-Loop Heat Pumps
(WLHP), 325 Ground-Water Heat Pumps (GWHP),
and 330 Ground-Loop Heat Pumps (GLHP).
The ARI/ISO Standard incorporates a consistent
rating methodology for including fan and pump
energy for calculating cooling capacity, heating
capacity, and energy efficiency ratios (EER). This
simplifies the use of rating data for heat pump per-
formance modeling in seasonal energy analysis cal-
culations, and allows for direct rating comparisons
across applications.
a) ISO Capacity and Efficiency Equations
The following equations are used to calculate and
correct cooling capacity, heating capacity, and
respective EER:
ISO Cooling Capacity = (Cooling Capacity in
Btuh) + (Fan Power Correction in Watts x 3.412)
ISO Cooling EER = (ISO Cooling Capacity in
Btuh/3.412)/(Power Input in watts – fan power
correction in watts + pump power correction in
watts) = Watts/Watts
NOTE: Do not divide ISO Cooling Capacity by
3.412 to obtain Btuh/Watts.
ISO Heating Capacity = (Heating Capacity in
Btuh) – (Fan Power Correction in Watts x 3.412)
ISO Heating EER = (ISO Heating Capacity in
Btuh/3.412)/(Power Input in watts – fan power
correction in watts + pump power correction in
watts) = Watts/Watts
NOTE: Do not divide ISO Heating Capacity by
3.412 to obtain Btuh/Watts.
b) Identify the design conditions corrected for air and
water conditions.
Airflow Cfm = 308 Cfm
Water Flow
(Based upon 10 F rise in temp) = 3.1 GPM
External Static Pressure = 0.0 in. wg (non-ducted
application)
Water Pressure Drop = 3.7 ft of head
Power input = 1,067 watts
Cooling Capacity = 11,741 Btuh
c) Perform Fan Power Correction Adjustment
Use the following formula to calculate Fan Power
Correction:
Fan Power
Correction = (Cfm x 0.472) x (External Static
Pressure x 249)/300 = Watts
= (308 x 0.472) x (0 x 249)/300
= 0 Watts
d) Perform Pump Power Correction Adjustment
Use the following formula to calculate Pump
Power Correction:
Pump Power
Correction = (GPM x 0.0631) x (Pressure Drop
x 2,990)/300
= Watts
= (3.1 x 0.0631) x
(3.7 x 2,990)/300
= 7.2 Watts
e) Perform capacity and EER calculations
Use the following formula to calculate capacity
and EER:
ISO Cooling
Capacity = (Cooling Capacity) + (Fan Power
Correction x 3.412)
= 11,741 + (0 x 3.412)
= 11,741 Btuh
f) Perform Corrections by using the ISO Equations
ISO EER = (ISO Cooling Capacity/3.412)/
(Power Input – Fan Power Correc-
tion + Pump Power Correction)
= Watts/Watts
NOTE: Do not divide ISO Cooling Capacity by
3.412 to obtain Btuh/Watts.
= (11,741/3.412)/(1,067 – 0 + 7.2)
= 3.20 Watts/Watt
= 10.93 Btuh/Watt