What is the Difference between HRV and ERV?

A ventilation system in your house can provide many advantages. For example, it keeps indoor air fresh, reduces pollutants and allergens and adjusts moisture level. The two most popular types of ventilation systems are heat recovery ventilator (HRV) and energy recovery ventilator (ERV). In this article we will explore the difference of both systems and how you can decide which one is right for you.

• Function difference between energy recovery ventilator and heat recovery ventilator

• Core difference between energy recovery ventilator and heat recovery ventilator

• Which is better to choose?

Function difference

ERVs and HRVs look the same and you can hardly tell them by their appearance. And ERVs are pretty similar to HRVs in terms of how they function. They have the same function of bringing fresh outdoor air into your home and removing the stale air out while recovering energy from the exhausted air.

Though they are very similar, there is some difference. An energy recovery ventilator transfers heat and water vapor through the incoming and outgoing airstreams. It can recover sensible heat and latent heat from the exchanged air, which is also referred to as enthalpy. While an HRV transfers only heat through the incoming and outgoing airstreams. It can only recover the sensible heat from the exchanged air.

Related:

• Sensible heat: the heat content of air itself, which you can feel it, or sense it. It can be measured with a thermometer. Sensible heat is involved in temperature changes.

• Latent heat: the energy contained in the air moisture. It is the heat required for an object to change phase （evaporate, condensate). Latent heat is involved in phase changes such as water evaporation. Latent heat can be measured by a wet-bulb thermometer. The higher the room humidity, the greater the latent heat is.

• Enthalpy is the sum of the sensible and latent heat contained in air-vapor mix.

We can conclude that energy recovery ventilators recover enthalpy heat, whereas HRVs recover only sensible heat.

The key function difference between them is that ERVs transfer heat and water vapor through incoming and outgoing airstreams while HRVs only transfer heat. That is, ERVs will also allow moisture to pass from one airstream to the other, but HRVs can't.

Core difference

If we go deeper, we may find the main reason for their function difference is because of their central core, which is also called heat exchangers.

ERVs have Enthalpy Cores.

Energy recovery ventilator cores are made of polymer membrane, which is highly moisture permeable.

In cold winter, an energy recovery ventilator system transfers the humidity from the extracted air to the incoming fresh dry air to help keep the internal humidity level at a reasonable value.

In summer, the humidity transfer in an ERV reverses and the humidity in outside air is removed before it is injected into the house.

HRVs have Aluminum Cores.

HRV cores are made of aluminum alloy, which is non permeable. It doesn't allow the transfer of moisture from one side to the other. So if it's humid outside and you have your air conditioning run inside and you're running an hrv, all that hot humid air is coming into your home. Yes, it's not as hot when it comes into the house, but it's still carrying all of that humidity into your house. And then your air conditioner has to work even harder to get rid of it. Whereas if you have an energy recovery ventilator, that moisture will partly be transferred into the outgoing air, so your air conditioner won't be working as hard now.

ERV vs. HRV - Which is better?

The best choice between an ERV and an HRV relies on the local climate and particular requirements.

Here is another simple rule for you to make decision: if you heat more than you cool, choose an HRV. If you cool more than you heat, choose an ERV.

I hope I answered all of your questions, if not please leave me comments. I'd be more than happy to help.