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Frank Crawford, CPHD, P.Eng
Energy Efficiency Consultant
Asked a question 2 years ago

What is the difference in testing methods for HRV/ERV between PHI, HVI and PHIUS? I know that PHI is the most stringent and results in the lowest efficiency rating but way is there also a big difference between PHI and PHIUS?

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Hi Frank,

Indeed, I have been speaking to this for many years. Measuring efficiency of H/ERVs is actually much more complicated than most know. That said, there is a fundamental difference between PHI and HVI/AHRI. PHI measures efficiency with the exhaust air stream as the basis, which determines the amount of energy LEAVING THE BUILDING. As opposed to HVI/AHRI which measures the incoming air stream. The incoming air stream has multiple factors that impact the perceived efficiency, such as waste heat from the motors, transfer from exhaust air to incoming air stream, energy transfer from the outside of the unit through the walls to the air stream...  The PHI measurement provides a much better input for energy modeling (PHPP) that is reliable and much more realistic. I will be co-presenting with Berthold Kaufmann from PHI on this exact subject for PH2020. So I would highly recommend signing up for the conference! 

Prudence Ferreira
Passive House Practice Lead - Morrison Hershfield

Frank- Vive la difference! 

Depending on location this issue of testing methods and modeling of ventilators for PH certification can be a pretty big deal for clients when it comes to supply chain and the desire to avoid sole sourcing. The information I'm including below is paraphrased or directly quoted from several sources: 

  1. Morrison Hershfield's Guide to Low Thermal Energy Demand Intensity For Large Buildings53
  2. PHIUS HRV ERV Certification program v0.8 requirements46 and PHIUS Certification Guidebook v2.199
  3. Protocols-for-H_ERV-Use-in-North-America (May 2016 - PHI North American Certifers in partnership with NAPHN and PHI)

When comparing the standards, it is important to understand that there are differences in terminology for the key metrics involved. The terms efficiency and effectiveness  are used throughout these standards. Both are an attempt to measure the  useful  heat  transfer provided by the HRV as a fraction of the theoretical maximum energy that can be  extracted. The  higher the efficiency, the more energy is recovered and used to temper incoming air. The differences arise in what is included in the theoretical maximum energy that can be extracted and what is considered useful heat            . 

The table below summarizes the  differences  between  how  the  terms  are  used  in  each  standard.  HVI's Sensible Recovery Efficiency and PHI's efficiency are the metrics most applicable to energy modeling. The metrics are derived from measurements taken at particular temperatures and flows.

What is the difference in testing methods for HRV/ERV between PHI, HVI  and PHIUS? I know that PHI is the most stringent and results in the lowest efficiency rating but way is there also a big difference between PHI and PHIUS?

It is important to use the metric measured at the flow closest to the design flow rate of the HRV being modeled. For example, HVI often provides efficiency values for a range of flows, in contrast to PHI efficiencies, which are always provided at a specific flow rate. For a multi-speed unit, this would be a calculated flow rate, depending on the minimum and maximum flows. This calculated value is not directly an average, so this can make comparisons between PHI and other ratings difficult for multi-speed units. See the Passive House documentation for details (PHI09).

The largest difference between Sensible Recovery Efficiency (SRE) and Apparent Sensible Recovery Effectiveness (ASRE) (from Table above ) is the inclusion of supply fan heat effects, leakage and cross contamination. A comparison of the differences between SRE and ASRE for several hundred HRVs from the HVI product database is shown below.  There is a strong relationship between SRE/ASRE difference and fan power, as would be expected.

Effects of Fan Power on SRE vs ASRE
Effects of Fan Power on SRE vs ASRE

When it comes to modeling for PHI projects:

  1. Passive House Institute- accredited building Certifiers operating in North America require testing certification results from either HVI or AHRI for all H/ERVs which are not PHI-certified.
  2. Certifiers will not certify buildings with ventilators unless they have independently-tested internal and external air leakage <3%.
  3. Certifiers will accept HVI or AHRI test data (temperature and flow readings) but use the PHI's "N-eff" formula to determine the H/ERV efficiency. Consistent with PHI’s protocol, Certifiers will not include the heat generated by the fan motors in determining the efficiency of non PHI-certified H/ERVs.
What is the difference in testing methods for HRV/ERV between PHI, HVI  and PHIUS? I know that PHI is the most stringent and results in the lowest efficiency rating but way is there also a big difference between PHI and PHIUS?

For modeling PHIUS Projects:

What is the difference in testing methods for HRV/ERV between PHI, HVI  and PHIUS? I know that PHI is the most stringent and results in the lowest efficiency rating but way is there also a big difference between PHI and PHIUS?
  1. For units with HVI certification, use an adjusted SRE for winter performance by adding back the fan power to the SRE equation (add supply fan energy to the numerator, deduct exhaust fan energy from the denominator) as seen above. This method provides for a mathematical adjustment for exhaust air transfer and case heat transfer, while avoiding double counting fan energy. See spreadsheet for calculations33. For units with multiple airflow rating points and efficiencies, PHIUS staff will develop appropriate guidance for selecting the correct efficiency rating to use in modeling.
  2. In climate zones 4 and higher, for units with HVI certification, use winter test point data for latent/humidity recovery efficiency.  If a latent/humidity recovery value is not specified for the ERV, 40% may be used as a default (0% for HRV's). For projects in climate zones 1A, 2A, 2B and 3B, summer test point data per CSA 439 should be utilized to derive apparent sensible effectiveness (ASE) and latent recovery (LR).
  3. For units with only PHI certification, use the PHI efficiency for winter performance, as long as the design airflow is within the range listed on the PHI certificate. Summertime performance TBD.
  4. For commercial units with AHRI certification, use the “Net sensible” and “Net Latent” efficiencies from the AHRI certified rating. All AHRI certified units are rated at 100% airflow and 75% airflow. It is our understanding that AHRI is developing methods for estimating a performance curve for AHRI certified units at various airflows. In the meantime, PHIUS has developed a simple “straight line curve” calculation embedded in WUFI Passive that estimate the performance of these units at airflows other than at the AHRI rated airflow points. AHRI ratings do not include electrical efficiency data. For pre-certification use the design static pressure and airflow to estimate fan energy from manufacturer's fan curve.
  5. For units without HVI or PHI certification, use the “manufacturer’s stated for efficiency (which is typically ASE), less 12 percentage points”.
  6. For Monotair conditioning ERV's, use HVI data however 100% ASE is the maximum efficiency that will be accepted, above 100% and the units is considered to be operating as a space conditioning device. For Build Equinox CERV (no test data as of June 11, 2020) use 75% SRE, 40% LR and 1 W/cfm for the fan motor.

Hope this helps! 

Cheers,

Prudence Ferreira - PH Practice Lead - Morrison Hershfield

 

 

Tim Eian
CPHD at TE Studio and Climate Action Activist

I believe Barry Stephens with Ventacity has dug deep into this subject. Perhaps we can get him to chime in. https://www.linkedin.com/in/barry-stephens-a67701b/29