8/18/2014

The Benefits of Heat and Energy Recovery Ventilation in Southern Climates

With a product name of “Heat Recovery Ventilator” or “Energy Recovery Ventilator,” it’s a common initial assumption that the primary benefit of the heat exchanger is to reduce heating loads and heating costs. However, in hot Southern climates (or any hot summer climate) the opposite benefits are true as well.  The heat exchanger greatly reduces the cooling loads and cooling costs of an air conditioning system.

Why use an HRV/ERV as part of a strategy for a comfortable indoor temperature during the hot summer?

With building codes and energy efficiency strategies increasing the tightness of a home’s envelope, ventilation is becoming an increasingly important factor for indoor air quality and comfort. You need a ventilation strategy or the indoor air quality will suffer. Sometimes exhaust-only ventilation (bath fans) is used as a ventilation strategy but the drawback is that you are unnecessarily exhausting the comfortable air-conditioned air from the house and replacing it through cracks and building openings with uncomfortable hot (and humid) make-up air. The make-up air is often coming from pretty unattractive places: potentially under floors, between insulated walls, attics and other unattractive places to get outside air from.   Therefore, the air conditioning needs to run more to bring down the temperature of the uncomfortable hot (and humid) make-up air infiltrating the home.

As an alternative ventilation solution, an HRV/ERV breaks the inefficient cycle of wasting the comfortable air-conditioned temperature (and money) to the outside. The HRV/ERV recovers most of the comfortable room temperature and uses it to pre-cool the incoming air. Therefore, the incoming air to the home is already close to room temperature when it is distributed to living spaces. The air conditioning needs to be run far less for cooling.  By distributing the pre-cooled air evenly through rooms, hot spots in the home are reduced, and it’s a lot more comfortable for inhabitants.

ERV or HRV for Southern Climates?

Most often, southern climates use an energy recovery ventilator because, in addition to transferring temperature, an Energy or Enthalpy exchanger transfers humidity from one airstream to the other. The Zehnder Enthalpy exchanger transfers the humidity as water vapor by diffusion from the high to the low partial vapor pressure side.  As this process occurs, it also prevents cross-contamination of the air streams, so that the exhaust air (gases, odors, etc.)  is not recirculated into your fresh air stream. The pores are just large enough for a small water vapor molecule to fit through but too small for larger air constituents or VOC molecules to fit through.

Energy recovery ventilators help maintain a comfortable and healthy home by reducing the temperature and humidity of the fresh incoming air during the hot, humid summertime. This is an important energy saving method. It’s a healthier and more comfortable alternative to excessively running air conditioning to combat high humidity and temperature infiltrating a home through cracks and openings in the building.