Can Ventilation Energy Loss Be Avoided or Recovered?
Ventilation energy demand can be reduced considerably by adopting a variety of energy efficient ventilation techniques. These include:
Minimising the need for ventilation: Energy demand may be curtailed by ensuring that the need for ventilation is reduced. This means minimising emissions from avoidable pollutant sources. Any extra ventilation needed to dilute and remove avoidable pollutants can be equated directly against conditioning load.
Avoid uncontrolled air infiltration losses: Poor building air-tightness results in excessive air infiltration and resultant uncontrolled energy loss. In many Countries building air-tightness can be improved considerably without detriment to indoor air quality. Infiltration driven by stack effect is particularly high when the difference between inside and outside temperature is at its greatest. This often corresponds to periods of maximum thermal conditioning need.
Demand controlled ventilation: If the dominant pollutant can be identified and measured, then the ventilation rate can be automatically adjusted to respond to need by means of demand controlled ventilation. This is especially successful at tracking metabolically produced carbon dioxide in densely and transiently occupied buildings (e.g. offices, schools and theatres). In dwellings, moisture sensors are used with varying success to control the rate of ventilation in bathrooms and kitchens.
Heat recovery: As much as 70% of the energy lost through mechanical balanced or extract ventilation can be recovered by the use of ventilation heat recovery systems. However potential savings must be equated against capital cost, ongoing maintenance needs and electrical (fan and/or heat pump) load. Their performance can also be destroyed by poor building air-tightness. The cost effectiveness of heat recovery systems is largely dependent on the severity of outdoor climate, the quality of the building envelope and the ventilation need.
Ground pre-conditioning of the supply air: Tempering of the supply air is possible by passing the supply air duct underground. Thermal gain must be equated against additional pressure loss introduced into the ventilation system. This approach has been applied to both single family and multi family (apartment) buildings.