Heat recovery in ventilation: where does the potential energy saving come from?

When warm indoor air is removed from a home and replaced with colder outdoor air, the new air needs to be heated. The purpose of heat recovery, or HRV, is to utilize the heat from the exiting air. This way, part of the heat can be reused instead of being completely lost through ventilation.

Heat recovery can reduce the need for ventilation heating energy, but the efficiency declared for the device does not directly indicate the change in the home's energy bill. The actual impact depends on the starting situation, implementation, and usage.

What does efficiency tell us?

Various brochures may mention things like temperature efficiency or seasonal efficiency, for example. They should not be interpreted as the same thing. A figure describing a single operating situation and an estimate covering the entire heating season answer different questions. Always ask for information on what the stated percentage measures and under what conditions.

According to Motiva, the annual efficiency of HRV describes the proportion of the heating energy needed for ventilation that is covered by heat recovery. The assessment takes into account the entire heating season, the location of the building, and the effect of freeze prevention. More information is available In Motiva's detached house planning guide.

Why doesn't the heating bill decrease by the same percentage?

Heating energy in a home is used for more than just ventilation. Heat escapes through the building envelope, and heating domestic hot water consumes energy. Therefore, the efficiency of ventilation heat recovery cannot be directly determined from the home's annual energy bill.

Illustrative calculation example: if the heating energy requirement for ventilation were 1,000 kilowatt-hours and 70 percent of it were covered by heat recovery, the recovered share would be 700 kilowatt-hours. The figures in the example are fictitious. They do not describe the performance of the Freshin device, the savings of a specific home, or the change in the electricity bill.

The starting point affects the comparison

When comparing, you must ask what kind of ventilation the home had before the modification. It is different to supplement a functioning system than to fix a situation where the air does not change sufficiently relative to needs. If the ventilation improves at the same time, merely comparing total consumption does not tell how much heat recovery reduces the heating energy need of the new situation.

Therefore, ask for clear assumptions for the potential savings estimate: what is being compared, with what airflow rates, operating hours, and energy prices? In addition, the electricity consumption of the equipment as well as maintenance and filter costs must be taken into account when evaluating the total costs.

How does this relate to Freshin's devices?

In Freshini's product range, heat recovery is specified for both Flow and Spin devices. The devices have different applications, so the choice is made based on the needs of the rooms and the planned overall solution. Explore To Freshin's products and ask for the technical specifications of the device along with the quote.

A good question for the designer is: how is the current ventilation of this home taken into account, and what is the potential energy calculation based on? Instead of just looking at the highest percentage shown in the brochure, it is worth examining the implementation and its operating conditions.

Operation and maintenance affect performance

The cleanliness of filters and equipment, as well as correct settings, are part of a functioning ventilation system. Follow the operating and maintenance instructions for your specific device. Energy saving should not be pursued by closing necessary ventilation routes or by reducing ventilation too much. The task of ventilation is to serve the home also during the heating season.

Find out the potential of your own home

When you want to evaluate the suitability of heat recovery for your home, start From Freshi's design service. A site-specific assessment helps combine ventilation needs, equipment selection, and a realistic understanding of energy impacts. For the continuation of use, you can also explore to maintenance services.