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Residential Products Technical Guide
About AHRI/ISO/ASHRAE 13256-1
About AHRI/ISO/ASHRAE 13256-1
AHRI/ASHRAE/ISO 13256-1 (Air-Conditioning and Refrigeration Institute/American Society of Heating, Refrigerating and Air Conditioning
Engineers/International Standards Organization) is a certifi cation standard for water-source heat pumps used in the following applications:
• WLHP (Water Loop Heat Pump – Boiler/Tower)
• GWHP (Ground Water Heat Pump – Open Loop)
• GLHP (Ground Loop Heat Pump – Geothermal)
The directory at http://www.ahrinet.org/ is constantly being updated and immediately available on the Internet. All ratings are submitted by the
manufacturer for certifi cation, and must be approved by AHRI. Therefore, there is a signifi cant difference between AHRI “certifi ed” and AHRI
“rated.” Thirty percent of a manufacturer’s basic models must be tested each year. AHRI selects models at random from stock for testing on
the basis of its evaluation of a participant’s certifi cation data.
Units that fail one or more certifi ed test (90% of declared performance or lower) may be declared defective. If the initial failure is a
performance test, the manufacturer must obsolete all units within the same basic model group or elect to have a second sample tested. If the
second unit fails a performance test, it must be obsoleted, together with all units within the same basic model group. Bryant Geothermal takes
certifi cation seriously. We were recently awarded a certifi cate for consecutive years of no AHRI failures.
Temperatures used in AHRI certifi cation standards are S.I. (Système International – metric) based. For example, typical catalog data for cooling
is shown at 80°F DB/67°F WB [26.7°C DB/19.4°C] entering air temperature, but the AHRI standard for cooling is 80.6°F DB/66.2°F WB
[27°C DB/19°C], since it is based upon whole numbers in degrees Celsius. Water and air temperatures for the standard are shown below.
Data certifi ed by AHRI include heating/cooling capacities, EER (Energy Effi ciency Ratio – Btuh per Watt) and COP (Btuh per Btuh) at the
various conditions shown above. Pump power correction is calculated to adjust effi ciencies for pumping Watts. Within each model, only one
water fl ow rate is specifi ed for all three groups, and pumping Watts are calculated using the formula below. This additional power is added
onto the existing power consumption.
• Pump power correction = (gpm x 0.0631) x (Press Drop x 2990)/300
Fan power is corrected to zero external static pressure using the equation below. The nominal airfl ow is rated at a specifi c external static
pressure. This effectively reduces the power consumption of the unit and increases cooling capacity but decreases heating capacity.
• Fan Power Correction = (cfm x 0.472) x (esp x 249)/300
Capacities and effi ciencies are calculated using the following equations:
• ISO Cooling Capacity = Cooling Capacity (Btuh) + [Fan Power Correction (Watts) x 3.412]
• ISO EER Effi ciency (Btuh/W) =
ISO Cooling Capacity (Btuh)/[Power Input (Watts) – Fan Power Correction (Watts) + Pump Power Correction (Watts)]
• ISO Heating Capacity = Heating Capacity (Btuh) – [Fan Power Correction (Watts) x 3.412]
• ISO COP Effi ciency (Btuh/Btuh) =
ISO Heating Capacity (Btuh) x 3.412/[Power Input (Watts) - Fan Power Correction (Watts) + Pump Power Correction (Watts)]
Test Condition Comparison Table
WLHP GWHP GLHP
Cooling
Entering Air Temperature - DB/WB °F [°C]
Entering Water Temperature - °F [°C]
Fluid Flow Rate
80.6/66.2 [27/19]
86 [30]
*
80.6/66.2 [27/19]
59 [15]
*
80.6/66.2 [27/19]
77 [25]
*
Heating
Entering Air Temperature - DB/WB °F [°C]
Entering Water Temperature - °F [°C]
Fluid Flow Rate
68 [20]
68 [20]
*
68 [20]
50 [10]
*
68 [20]
32 [0]
*
*Flow rate is specifi ed by the manufacturer