Energy Recovery Ventilation vs. Heat Recovery Ventilation
What's the difference?
Ventilation systems provide comfortable living spaces by supplying clean, fresh air from outside while exhausting stale, waste air from inside. Heat Recovery Ventilation (HRV) units are designed to enhance the amount of heat energy exchanged between these two air flows. In winter, the warm exhaust air preheats the supply air as it enters the building. In summer, the warm supply air will be cooled by the exhaust air.
Energy Recovery Ventilation (ERV) units also recover heat. However they also allow for moisture exchange between the supply and exhaust air flows. This allows for the regulation of humidity which can prevent or mitigate excessive dryness, particularly over the winter months. So Energy recovery is the combination of Heat recovery and Moisture recovery.
Counterflow Heat Exchanger (HRV)
Counter-flow heat exchangers push air flows through parallel plates arranged in a row. The supply air and exhaust air flow alternatively between the fins for maximum energy transfer area without actually mixing the two air flows. Warm air flow transfers its energy via the plate to the cold air flow resulting in the supply air being preheated during the winter months, and excess heat being rejected outside by the exhaust air during the hotter months.
As warmer air can hold more water, and counter-flow heat exchangers recover heat but not moisture (i.e. they are HRV units), incoming air being warmed by the heat exchanger will decrease in relative humidity. This can lead to excessive drying of the internal environment. The significance of this phenomenon can be reduced slightly due to diffusion of moisture through the fins of some heat exchangers.
The integrated controls automatically open a bypass damper around the counter-flow core during the summer months. This stops the preheating of incoming air to keep your property cooling down overnight.
Rotary Wheel Energy Exchangers (ERV)
Rotary wheel energy exchangers consist of a pure aluminium wheel with a honeycomb matrix of holes on the face as well as two channels which contain warm and cool air flows respectively. Heat transferred into the matrix by the warm air is later recovered with by the cool air once the wheel rotates between the two channels.
In cooler months, the warm exhaust air will transfer heat to the incoming cool air to preheat it. This increase in temperature allows the air to hold more moisture which results in a lower relative humidity. However condensation occurs in the exhaust channel which is transferred to the supply channel by the rotation of the wheel where it is reabsorbed by the incoming air. This recovery of humidity prevents the interior air from becoming too dry, improving its quality.
In warmer months, the cool air being exhausted from the building will intercept some of the heat and moisture absorbed from the incoming warm air, removing it from the system before it enters the interior and keeping the house cool on warmer days and minimising excessive drying of the indoor environment.
The integrated controls automatically switch the heat exchanger rotary wheel on during the day and off overnight, which prevents the preheating of warm air in the summer months and helps to keep the interior cool.
Matrix Core Heat Exchangers (ERV)
Matrix core heat exchanges deposit heat into a core by forcing air through it with a fan. The matrix face splits the airflow to maximise the surface area in contact with the core, facilitating more efficient heat transfer. The core itself is made of a ceramic material to allow for a greater amount of heat storage.
This heat is then recovered by periodically reversing the direction of the fan. When it is hot outside and cool inside, the supply air from outside will deposit heat in the core which will then be reabsorbed and removed from the system by the exhaust air when the fan changes direction. When it is cold outside and warm inside, the exhaust air being removed from the house will deposit heat in the core which is used to preheat the supply air from outside when the fan changes direction.
Any condensation which occurs in the core due to the cooling of airflow will be recovered when the fan changes direction. This means that moisture is either recovered or expelled to maintain comfortable interior humidity levels.