# Fan efficacy and ERVs

| Posted in Building Code Questions on

what classification does a erv/hrv have if it doesn’t have a ECM motor
it is not exempt from the efficacy requirement. so, does it a bathroom utility roon fan efficacy

Panasonic whisper comfort erv uses an ac motor .
its fan efficacy is 40 cfm@ 0.1 esp/ 23 watts = 1.75 ?

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### Replies

1. GBA Editor
| | #1

Kevin,
Your question is a little confusing.

HRVs and ERVs can be rated according to their thermal efficiency. It's also possible to calculate the cfm/watt for any fan -- the more cfm per watt, the less electricity required to move the air.

In your example, a 40 cfm fan drawing 23 walls is moving 1.75 cfm/watt.

A Panasonic FV-08VKS1 fan rated at 80 cfm and drawing 11.3 watts is moving 7 cfm/watt.

The Home Ventilating Institute rates HRVs and ERVs according to several efficiency criteria:

Sensible Recovery Efficiency (SRE): The net sensible energy recovered by the supply airstream as adjusted by electric consumption, case heat loss or heat gain, air leakage, airflow mass imbalance between the two airstreams and the energy used for defrost (when running the Very Low Temperature Test), as a percent of the potential sensible energy that could be recovered plus the exhaust fan energy.

This value is used to predict and compare Heating Season Performance of the HRV/ERV unit.

Adjusted Sensible Recovery Efficiency (ASRE): The net sensible energy recovered by the supply stream as adjusted by case heat loss or heat gain, air leakage, airflow mass imbalance between the two airstreams and the energy used for defrost (when running the Very Low Temperature Test), as a percent of the potential sensible energy that could be recovered. This value should be used for energy modeling when wattage for air movement is separately accounted for in the energy model.

Total Recovery Efficiency (TRE): The net total energy (sensible plus latent, also called enthalpy) recovered by the supply airstream adjusted by electric consumption, case heat loss or heat gain, air leakage and airflow mass imbalance between the two airstreams, as a percent of the potential total energy that could be recovered plus the exhaust fan energy. This value is used to predict and compare Cooling Season Performance for the HRV/ERV unit.

Adjusted Total Recovery Efficiency (ATRE): The net total energy (sensible plus latent, also called enthalpy) recovered by the supply airstream adjusted by case heat loss or heat gain, air leakage and airflow mass imbalance between the two airstreams, as a percent of the potential total energy that could be recovered. This value is used to predict and compare Cooling Season Performance for the HRV/ERV unit. This value should be used for energy modeling when wattage for air movement is separately accounted for in the energy model.

To see a list of certified HRV and ERV models that have been rated by the HVI, visit the web site: HVI Products Directory.

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