AEA Tech Insight: Ventilating High Performance Buildings: HRVs and ERVs
Ventilating High Performance Buildings: HRVs and ERVs
High performance buildings of all shapes and sizes are increasingly prevalent in today’s construction and renovation market. With high performance there comes the need to provide adequate and efficient mechanical ventilation in these buildings, and the old ventilation strategies and systems of the past are not going to cut the mustard.
Exhaust ventilation is needed to expel moisture, odors, and indoor pollutants from a building but, with these contaminants, out goes the energy used to condition that air. Conversely supply air is needed to make up the air that has been expelled from the building but, in with this air come external moisture, heat or cold, pollutants, and more.
Wouldn’t it be great if we could precondition this incoming air with the exhaust air that we have already conditioned?
That’s exactly what heat recovery ventilation (HRV) or enthalpy (or energy) recovery ventilation (ERV) systems do.
There has been a recent surge of HRV and ERV systems to hit the market. These systems provide balanced (both supply and exhaust) ventilation to a building without the severe energy penalty associated with traditional balanced systems. They do this by utilizing a heat exchanger or core that preconditions the incoming ventilation air with outgoing exhaust air, while keeping the two air streams physically separated. The tempered supply air is then ducted through the building to deliver clean fresh air to living spaces.
The magic that makes this happen takes place in the core. The core is comprised of narrow and alternating channels that facilitate the heat exchange between the two air streams. Typical units have two fans, one on the exhaust and the other on the supply, that draw or push their respective air streams through the core.
Depending on the manufacturer and model, these systems can recover up to 90% of the conditioned air before it exits the building.
However similar in appearance and basic operation, the cores found in HRV and ERV systems are different, and are designed to operate in different climate zones. ERV systems are designed to operate in mixed-humid and humid climates, and their core is designed to allow moisture transfer between air streams. This moisture transfer allows the cool dry exhaust air to dehumidify the incoming warm humid supply air, thus reducing the mechanical cooling and dehumidification load on the building.
Now that you are familiar with the basic operation of these ventilation systems, be sure to read the next issue of The Trainer, where we will explain how to determine whether an HRV or ERV is right for your building.