Balanced Ventilaton, Heating and Insulation Design Essentials

With domestic homes being designed to tighter fenestration rates and minimised air leakage rates as well as insulation standards increasing, the requirement for balanced mechanical ventilation as part of the design is critical.

The tighter the building structure the more moisture that is generated within the home — through respiration — remains in the home and this has to be removed somehow.

Failure to do this will result in damp and mouldy interior conditions that are uncomfortable and very hard to heat. Water has a specific heat capacity of 4.12 — in other words it is almost four times harder to heat the moisture in a damp home than a dry one and this adds significantly to energy usage.

This occurred in the United States in the early 80s where houses were tightened up and insulated but not ventilated and this resulted in a similar situation to our wet building syndrome with catastrophic structural failures. 

Balanced ventilation systems generally also include heat recovery cores either HRV (heat recovery ventilators) or ERV (energy recovery ventilators).

Heat Recovery Ventilators

Heat Recovery Ventilators use non permeable plastic or metal cores, require a fitted drain and recover sensible heat only.

Energy Recovery Ventilators

Energy Recovery Ventilators use semi-permeable cores, don’t require a drain as they operate above the dew point and recover both sensible and latent heat.

So which one?

Both systems have advantages and disadvantages. HRV are generally better for moisture removal while ERV have more potential to recover energy.

Efficiencies depend on the difference between indoor and outdoor psychrometric conditions (approach) and claims of high efficiency energy recoveries of 80% and above should be questioned closely.  50 to 60% are more realistic figures.

An energy efficient primary heat source (heat pump, pellet fire, condensing gas appliance) must be operating for the balanced ventilators to recover any energy and remove moisture during winter months. Simply ventilating and insulating your home will not improve living conditions.

Attention by designers to all three disciplines — heating, ventilation and insulation — along with the correct operation by the client will ensure warm, dry and healthy home environments.