Picking an ERV

With the ducts in place and sealed it’s time to think about the energy recovery ventilator (ERV). Actually the thinking, i.e. the product selection, already happened a few weeks back.

How does an ERV work?

The ERV is basically an air to air heat exchanger. The idea is to achieve effective air exchange in a building while minimizing the heat energy losses.

ventilation-15

Image source: Little Deschutes Lodge

The heat exchanger in the ERV transfers heat energy from the exhaust air to the incoming, fresh supply air. In other words, fresh, cold winter air will be preheated by the exhaust air, while hot, incoming summer air will be cooled down.

While the ERV is yet another gadget drawing electricity, it actually contributes to substantial energy savings through its ability to reduce heat loss, not to mention the auxiliary benefits of maintaining good indoor air quality (IAQ) and moisture management.

To maximize the energy savings benefits, it is important to us to find a highly efficient unit, efficient in heat recovery and efficient in its operation.

The Motor

An ERV, or for that matter a heat recovery ventilation (HRV) requires a blower motor that can run at variable speeds to meet the specific ventilation requirements.

The typical motor option is the PSC (permanent-split capacitor), which provides the variable speed option and runs on alternating current (AC).

A significantly more efficient option is the ECM (electronically commutated motor). It also runs at variable speeds but is powered by direct current (DC).

With the knowledge of these two motor options at hand, I limited the product search to ERV’s with ECM motors only.

The product options

I came across an ERV called the ComfoAir HRV/ERV System by Zehnder America.

This rather expensive unit has all the bells and whistles I could wish for.

It runs very efficiently, has a very high heat recovery rate and comes with a summer by-pass cooling option. The cooling option basically turns the heat exchanger off once its senses that the outside air is cooler than the inside air. It also comes with the option of geothermal preconditioning, also known as earth tubes.

My problem is that this unit has been developed in Europe and not yet re-engineered for the North American market. As much as I liked the bells and whistles, I was not in the mood to accommodate the 220 volt requirement and deal with the metric connections.

There is a North American alternative I stumbled upon. It is the UltimateAir RecoupAerator. At the writing of this post, it appears to be the most efficient HRV readily available on the market, particularly at the lower airflow rates.

  • 50 watt draw to deliver 65 cubic feet per minute (cfm)
  • 75 watt draw to deliver 100 cfm
  • 250 watt draw to deliver 200 cfm
See also: Product performance data

GreenBuildingAdvisor.com lists anther metric that rates the UltimateAir efficiency at 2.04 cfm/watt.

The heat recovery rate is listed at around 80% or 95% for sensible recovery efficiency and apparent sensible effectiveness, respectively.

The UltimateAir also comes with bells and whistles, including a number of controls and an EconoCool option that senses cool summer night air and delivers it into the building.

One of the optional features that caught my eye is a Water-to-Air Coil Module or heat exchanger. We could upgrade our ERV system with this module if our indoor air becomes too hot and muggy, despite our airtight and well insulated building envelope.

I might come back to the Water-to-Air heat exchanger sometime down the road.

Conclusion

The price point of the UltimateAir fits our budget. It meets our energy requirements, in terms of heat recovery and electrical usage.

What I particularly like is the flexibility – the option to provide additional cooling and dehumidification if required with the Water-to-Air heat exchanger module.

Well, all what’s left is to place the order, wait for the delivery install the ERV.

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About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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