2022 HRV/ERV in Energy Compliance Modeling
We can all agree fresh and filtered air is important to our health and wellbeing. Energy efficiency is also essential for cost savings and building code compliance. Together, indoor air quality and energy efficiency point squarely to Heat Recovery and/or Energy Recovery Ventilation (HRV/ERV), but there are key points to consider for energy code compliance.
Fresh Air for Indoor Air Quality
“Tight” homes are more efficient because conditioned air stays inside, while external temperature swings are kept outside. Balanced Ventilation is when the Supply and Exhaust rates match each other, run continuously, and consistently bring in fresh air while exhausting stale air.
Currently, the standard residential building practice for introducing outside air is through Exhaust Ventilation, where negative pressure draws “fresh air” into our home through leaks by continuously run bathroom exhaust fans. While this is allowable by code, it is inefficient from an energy perspective and does not guarantee quality indoor air.
Supply Ventilation is also a viable strategy but is not often practiced in the field since Exhaust Ventilation is more common and cheaper.
To build tighter envelopes with fresh and filtered air, the best solution is to include a balanced outside air system.
HRV/ERV’s ‘temper’ outside air
An Energy Recovery Ventilation (ERV), or Heat Recovery Ventilator (HRV), is a fan box that brings in fresh air and exhausts stale air. The benefit of an E/HRV is that they include a heat exchanger or enthalpy wheel. This exchange device does not allow the air streams to mix but has them pass each other through a medium that will allow the heat to transfer, typically through a metal or ceramic material.
For example, let’s imagine that it is 50°F outside and a home is heated to a comfortable 68°F: instead of bringing in 50° fresh air, the heat exchanger will transfer some of the warmth of the exhaust air into the incoming cold fresh air. This keeps the heat created within the HVAC system inside the building and prevents heat waste during the process of bringing in fresh air.
Energy Modeling with HRV/ERV’s
California is rewarding the installation of Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV) with Title 24 Part 6 Compliance credit.
When specifying an E/HRV in your Title 24 compliance model the energy consultant will input a few metrics which dictate the system’s credit and effectiveness. These include:
- Cubic Feet per Minute (CFM) delivered
- Watts (W) consumed by the system
- Sensible Recovery Efficiency (SRE)
- Adjusted Sensible Recovery Efficiency (ASRE)
These metrics can be found on the selected system’s cutsheet or specification document. However, the best resource is a Home Ventilating Institute (HVI) Certified product.
https://www.hvi.org/hvi-certified-products-directory/section-iii-hrv-erv-directory-listing/
Here, you will find a searchable database of all HVI certified fans and performance data that can be used for your Energy Model.
An example output from HVI:
| Brand Name | Model | Temp Mode | °C2 | °F2 | Net Airflow (L/s) | Net Airflow (cfm) | Power Consumed (Watts) | SRE | ASRE |
| Zehnder | CA200HRV | HEATING | 0 | 32 | 31.0 | 66 | 34 | 86.0 | 90 |
| Zehnder | CA200HRV | HEATING | 0 | 32 | 41.0 | 87 | 44 | 86.0 | 90 |
| Zehnder | CA200HRV | HEATING | 0 | 32 | 51.0 | 100 | 60 | 86.0 | 90 |
There are two additional checkboxes within the Performance modeling regarding E/HRVs:
Requires that supply air filters, inlets, and H/ERV Cores must be accessible. Without this option you will not receive IAQ Compliance credit.
What this looks like on a Title 24 report:
You will find the IAQ Ventilation system’s E/HRV minimum efficiencies, Accessibility and FID criteria if selected, under the “Required Special Features” table in the Title 24 document.
These features will be verified by a HERS Rater as part of the “Indoor Air Quality Ventilation” HERS Scope.
Additionally, you’ll find a table “Indoor Air Quality (IAQ) Fans” near the end of the T24 document. This table will summarize the modeled system and is the best location to reference during design and bid to assure correct equipment is selected, purchased, and installed.
Accuracy is key!
All members of design, construction, and code enforcement should be aware of the benefits and compliance implications of balanced ventilation systems with E/HRV, as these systems will likely continue to increase in usage. Systems should be modeled correctly, accurately, and consistently with field installation.
For more about this topic or other Energy Code/Title 24 compliance questions, contact a 3C-REN Energy Code Coach.
