The Mysterious Ventilators
– aka hrv, erv, or “the hvac” as many mistakenly call them -
Shrouded in fog and the deeply hidden secret files of the Illuminati, the hrv (heat recovery ventilator) is often introduced to homeowners when they walk in to their new home and, for the first time, they see a control on the wall they don’t recognize. Lots of people will tell you what to do with them, but they only give you settings advice without telling you what it actually does. So let’s have a look at different kinds of ventilators, and what each of them do. Understanding what each of them do and how they work will help you know how to adjust them so they do… whatever it is that they do. You can often find out which kind of ventilator you have by looking at the front of the unit.
Air exchanger: These are often sold in hardware stores. Air exchangers are essentially a fan-in-a-box. They remove stale air from within the home and replace it with outdoor air using a fan. That’s it.
HRV (Heat Recovery Ventilators): These units take air exchangers a step further and introduce a core that exchanges heat between the stale indoor air leaving the home and the fresh outdoor air coming in. This makes it more efficient to run than an air exchanger.
ERV (Energy Recovery Ventilators): Finally the erv gets even more efficient. Its core not only exchanges heat between the stale indoor air and fresh outdoor air, it exchanges humidity, making it more efficient in summertime than an hrv.
Not so scary yet. It sounds like a good idea on paper. Rather than cracking open windows for fresh air, let’s use a machine to do it more efficiently. Let’s get further into how to apply that information in your home.
When the HRV turns on in wintertime, it brings in cold dry air and exchanges some heat between the stale indoor air that’s leaving the home and the fresh outdoor air entering the home. So you’re replacing the more humid indoor air with less humid outdoor air. But what happens in summer? Your air conditioners biggest job by far is removing humidity, and secondly, dropping the temperature. If your hrv turns on, it will bring in hot humid air from outside and expel the cooler dry air from inside the home. It will exchange temperature, but it’s just added piles of humidity that your poor overworked air conditioner now has to remove before it can drop the temperature. That’s why the hrv should be off in summer. The “summer” setting on your control could really just say “off”.
When an ERV turns on in wintertime, it brings in cold dry air and exchanges some heat between the stale indoor air that’s leaving the home and the fresh outdoor air entering the home. So you’re still replacing the more humid indoor air with less humid outdoor air, but since it has the ability to exchange moisture, you lose less humidity. That makes it sound worse but… in summertime it works more efficiently than an hrv so you can continue to use it without as much energy loss. The hot humid air from outside that’s replacing your indoor air is pre-dehumidified to some extent. This means an erv can be used efficiently all-year-round without overworking the air conditioner.
Always remember what the unit is doing when you’re thinking about changing your settings. Our next blog post will delve into the real reason people want to understand air exchangers… how to get condensate off your windows.
