The Heat Recovery Ventilator: improving indoor air quality & reducing energy consumption.
Today I am going to share some basic information about the “what,why, how” of a heat recovery ventilator or HRV system. This special ventilation system is becoming common in newly built homes and in renovations. We all live in a climatic zone that is perfect for this device. It is important to note that these are highly specialized systems. Therefore, you need to use HVAC professionals for installation and maintenance.
Why do I need it?
Most homes built today are much more airtight than older homes. Since older homes had less insulation, unsealed openings and old inefficient windows, these homes leaked tons of air. If people felt cold, they would just crank up the heat until they saw their monthly heating bill. When this initial shock subsided, these people would then pull out sweaters for the rest of the winter.
To combat leaky and inefficient heating/cooling, we build modern homes airtight. But what about the quality of the air that people in these modern homes need to breathe?
A breath of fresh air: the heat recovery ventilator.
Fresh clean air is crucial for leading a healthy life. Dirty moist air leads to health problems and damage to the home. For those of us who suffer from breathing issues, this is paramount. Therefore, as we build more airtight homes we have to solve for bad air issues. Adding a heat recovery ventilator helps airtight homes operate properly.
A heat recovery ventilator is a special mechanical ventilation device that provides continuous fresh air inside the home. At the same time it exhausts stale moist air and indoor air pollutants.
How does it work?
Let’s begin from the outside and work our way inside. The diagram below should help you visualize the sequence:
- A fan draws fresh outside air into a duct penetration on the exterior of the home.
- This air passes through a filter to remove any pollutants.
- Then the air passes through a heat exchanger. This air passes by the stale exhausted air. During this time, a transfer of some heat occurs between the stale exhausted air into the fresh incoming air.
- Finally, the air leaves the heat exchanger pre-warmed and circulated in the home. Pre-warmed air doesn’t over-cool the home and reduces the need to overuse the heating system.
From inside the home, the reverse happens. The exhausting stale indoor air passes through a filter and then reaches the heat exchanger. Which then pulls heat (and moisture) out of the exhausted indoor air. The extracted heat pre-warms incoming fresh air. Consequently, the warm fresh air helps to lower heating costs. While at the same time raising the indoor air quality.
Does it work in the summer?
Yes, during the summer cooling season a heat recovery ventilator can reverse the process of the heat exchanger. It will remove some of the heat from the incoming outdoor air and transfer it to the outgoing exhaust air. However, it will not perform as well as air-conditioning.
Heat recovery ventilator removes moisture too
Besides providing fresh air, a heat recovery ventilator also removes moisture out of the exhausted stale air. This happens inside the heat exchanger. As the warm exhaust air passes next to the cool incoming fresh air, condensation occurs. This is why the unit has a drain on the bottom. If a new airtight home does not have a heat recovery ventilator, it can retain lots of moisture. Without a way to remove stale moist air, moisture has nowhere to go. Eventually organic growth (mold) develops, which leads to structural damage and health issues.
A heat recovery ventilator is an ideal system for anyone interested in living in a healthy and energy efficient airtight home.
Thanks for reading, until next time.
Author: Geoff Bohaker for Shelter West Home Inspections