Heat Recovery Ventilators (HRVs) have become mandatory, according to energy codes in several U.S. states, and many other counties and states have the requirement built into upcoming energy regulations. Canada has been requiring HRVs, and its cousin Energy Recovery Ventilators (ERVs), for years. It’s estimated that there are 25,000 HRVs installed in the U.S., whereas Canada has nearly eight times that amount operating. Commercial HRVs have been used for years and the quality and performance of the equipment is improving steadily.
What Are They?
The objective of HRVs is to enable air to be exhausted from the building, while fresh air is introduced into the building through the same system. HRVs include a fan, filters, controls, and ductwork. Sound familiar? Each also includes a heat or energy recovery media, or core, that captures heat in the winter and cooling in the summer before it’s exhausted from the building. HRVs provide the air exchanges and recapture lost heat, while the differentiating factor of ERVs is the removal of moisture from the air.
HRVs offer some benefits that are universal to all of our customers, but before we can install these units, we have to sell some. Consumers will buy HRVs or ERVs as we present them with the following benefits:
• Everybody loves the idea of fresh air in his or her home or office
• As buildings are made tighter, the need to introduce fresh air and ventilation has increased
• Indoor air quality is in demand as the health consciousness of our population increases
• A neutral, or slightly positive, pressure is maintained by an HRV. This keeps the building clean and without excess humidity
• HRVs control the sources of ventilation air to ensure outside air enters from a clean and healthy source, not from the attic or stinky crawl space
• Dilution of pollution. Out with the old air, in with the new air
• Some energy efficiency benefits are achieved as the BTUs from the exhaust is captured in the recovery core of the equipment and is brought back into the building with the fresh air.
Proper engineering requires a blower door test, calculation of air changes per hour, due to the leakiness of the envelope divided by the desired air changes per hour. But there are two rules of thumb for HRV sizing.
Rule 1 — 15 CFM per room. Example: 12 rooms in a home x 15 cfm per room = 180 CFM.
Rule 2 — One CFM/ 100 sq. ft. of floor space. Example 2400 sq. ft. x 1 CFM = 240 CFM. CAUTION: HRV airflow often will decrease by up to 50% after one month of use, due to the core and pre-filters becoming dirty. You may want to consider this fact when sizing HRV airflow.
Identify a solid manufacturer and study their product line. Select a trustworthy distributor that knows the product and understands HRV design and maintenance. Inquire about their relationship with the manufacturer. Interview your territory manager to be sure he understands the product and is able to back you up with the manufacturer and service products.
Buy One Yourself
If you intend to get into this market, nothing replaces personal experience. Install one in your home and office.
There’s nothing really new to learn here. HRV installation parallels HVAC system installation. Duct must be tight and oversized (compared to the rest of the industry) and avoid excessive elbows, etc. Any duct located in unconditioned space must be well insulated (especially if the fan speed is intended to be continuous — consider R-19 wrap). Make solid connections at exterior walls. Be certain the inlet pulls airflow from a clean location (away from flues, dryer vents, standing water, or near exhaust fumes).
Of course duct design and installation must include balancing dampers to each register or grille to enable the system to be properly tested and balanced.
To quote one of my e-mail tags, “Comfort and Efficiency Don't Have Model Numbers,” so measure the system to be certain the system works as you designed it. For your own knowledge, check it again a month later and document the decrease in airflow from the debris accumulated in the core and pre-filters. Using basic air balancing techniques you can actually measure the BTUs recaptured by your HRV or ERV.
If the fan is designed to run continuously, monthly filter changes are recommended, and the core should be replaced quarterly from most units. Always provide a service agreement when selling an HRV or ERV. Maintenance costs can be significant.
One cost study claimed an HRV system costs $80-$180 per year for a typical home. Well maybe with a perfect installation, but if any of the ducts are located in the attic, and if the fan is running 12 hours or more a day, costs may be four times that amount. We recommend installations of HRVs for comfort. Some units claim to recover up to 85% of the energy that would be lost compared to an exhaust fan only. The efficiency claims of most HRVs may be questionable, at best.
Fresh Outside Air
One of the best uses of HRVs is for fresh air ventilation. This application is ideal for HRVs or ERVs in the more humid areas of the country for residential or commercial applications. The same system can also be used to positively pressurize a building. Return 30% or more of the exhaust airflow from the system into the return duct of the HVAC system to pressurize the building.
As you increase your knowledge of these IAQ devices, and complete the preparation steps to offer this product, including installing one in your own home, your convictions of their benefits will increase and your ability to sell profitable jobs will multiply.
Rob “Doc” Falke serves the industry as president of National Comfort Institute a training company specializing in measuring, rating, improving and verifying HVAC system performance. If you're an HVAC contractor or technician and have questions or comments about this article, contact Doc at firstname.lastname@example.org or call him at 800/633-7058. Go to NCI’s website at www.nationalcomfortinstitute.com for free information, technical articles and downloads.