HRV Efficiency: No Matter the Measurement, Zehnder Tops the Scores

Once you’ve made the decision to use a heat recovery ventilator (HRV), what is the next step? Finding the right system. Many new and familiar brands offer a plethora of options for recovery ventilators. What sets one choice apart from the others? Performance! Various measurement criteria come together to point towards a clear winner, and that winner is Zehnder. Here are the measurements and what they mean when selecting an HRV system.

MEASUREMENT CRITERIA #1: APPARENT SENSIBLE EFFECTIVENESS

HVI ratings

Longer pathways maximize heat transfer which translates into increased energy savings

Recovery ventilation is rated by efficiency, or the ratio of energy transferred between the two air streams compared with the total energy moved through the heat exchanger. There are several metrics to look at to get a clear view of total unit efficiency. The big number that all the manufacturers tout is their Apparent Sensible Effectiveness, or ASEF. The Home Ventilating Institute, HVI, reports Zehnder’s ASEF as 93%; this is among the highest in HVI’s directory, quickly establishing it as a top contender. A key factor in Zehnder achieving this high of a rating is the counter-flow heat-exchanger, which allows the air to travel a longer pathway than a cross-flow style core and maximize heat transfer. This translates to massive energy savings as it reduces the amount of heating energy used to raise outside air temperatures, so the higher the ASEF number, the higher the savings.

MEASUREMENT CRITERIA #2: SENSIBLE RECOVERY EFFICIENCY

To really get a clear look at how efficient a heat recovery ventilator is as an entire system, it is necessary to take into consideration other factors affecting performance that could influence energy savings. An HRV with a great heat exchanger is only part of the picture; the entire HRV’s build quality can negatively influence savings if it underperforms in other key areas. HVI calculates this performance as the Sensible Recovery Efficiency, or SRE. The SRE scoring accounts for waste heat generated by fan motors being introduced to the air stream, leakage across incoming and outgoing air streams, and case leakage which is the occurrence of heat transferring from outside of the box to the airstream inside. Zehnder really begins to shine here, and the build quality and smart engineering are reflected in the ComfoAir 350’s SRE score of 88 percent. In fact, compared to all other strictly HRV systems listed, Zehnder holds the top two scores for Sensible Recovery Efficiency, and has the most potential for energy bill savings.

MEASUREMENT CRITERIA #3: CUBIC FEET PER MINUTE PER WATT

When you bring in the airflow per watt measurement (CFM/W) , Zehnder solidifies its place at the top of the charts. This measurement shows the relationship between how much air is moved (CFM) and how much energy is used (Watts, or ‘W’). This is important to look at because while some units may boast a high ASEF, they may be relying on pushing more cubic feet of air to achieve that apparent efficiency, at the expense of using more wattage. In fact, the top Zehnder unit listed, the ComfoAir 350 HRV, achieves an impressive 3 CFM/W! For perspective, Energy Star criteria calls for a minimum 1 CFM/W, and most of the other high performing HRVs only have air delivery efficiencies between 1-2 CFM. Furthermore, Zehnder’s efficiencies can be expanded upon by utilizing the variable fan speed settings. With 3 different custom settings, plus an extra-low away setting, air delivery efficiencies can be dialed in to meet demands and criteria set forth by clients or code. These three measurements combined give an overall view of the effectiveness of any HRV by detailing the impact on energy use. The more energy an HRV can effectively recover, while also using as little energy to run itself, the more money it can save on energy bills.

SOME IMPORTANT THINGS THAT ARE HARDER TO MEASURE

Decibel levels of Zehnder ComfoAir 350 by setting compared to common sound levels. Note these measurements are at the air connections, not at the registers, where the noise levels are much lower

Beyond the obvious benefits of efficiency, there are a few other factors that make Zehnder a desirable system choice. All the necessary installation components are made available through Zehnder’s distributors, such as Small Planet Supply. Many of these components are designed to help Zehnder systems operate quietly while maintaining high efficiency and ease of installation. For example, Zehnder’s choice of ComfoFlex tubing allows for installation in two by four interior walls and meets the International Mechanical Code requirement for ducting to be UL181 rated fireproof. This ComfoFlex is installed in a “home run” configuration, where a single continuous duct connects each supply and return directly to the HRV. Compared to a traditional “Trunk and Branch” design, this greatly helps control noise on an already quiet system. Using DC motor fans, sound levels are kept low at the source, 19dB at the lowest setting for a CA350, upwards of 59dB at the highest setting, where most households run the units at around 50% speed (speed level 5 in the chart at the right). This is sound emission measured at the air connections, and is much lower at the registers. The operational sound level is so low that customers have called to ask if the units are working!

By now it is hopefully clear that a Zehnder HRV is the best option in North America today, be it for energy savings or the health benefits of increased airflow in tight homes. Additionally, Zehnder backs up all their products with outstanding customer service and support. For more information about how a Zehnder system can benefit your next project, you can request contact by email, schedule a complimentary consultation or call either of our Small Planet Supply locations.

This blog post was written by Small Planet Supply’s Josh Palmer.