To understand the principle of energy recovery it is necessary to recognize the relationship between Sensible Heat, Latent Heat and Enthalpy.
The energy in our air comprises:
• Sensible heat – the heat we can feel and can be measured with a thermometer.
• Latent heat – this is the heat contained in the airborne moisture. For example, it is the energy absorbed when water is evaporated and stored in the resultant steam. A thermometer cannot measure latent heat. The higher the room humidity, the greater the latent heat present.
• Enthalpy is the total of both the sensible and latent heat, that is, the total heat contained in air.
Whenever fresh outdoor air is introduced into a building, it results in the same volume of air being exhausted. This conditioned exhaust air carries with it heat which can be recovered and transferred to the incoming fresh air. This process is called ‘energy recovery’ or ‘heat recovery’.
Energy recovery is effected by passing the exhaust air and the incoming air through separate air streams across a heat exchanger, enabling the energy to transfer while maintaining separation of the two air streams.
The media for effective heat exchange needs to be carefully selected to provide the required outcomes.
Sensible Heat Exchange Media
Sensible Heat Exchange Media is used for heat recovery where there must be an absolute separation of the air in applications such as:
• Bathroom/toilet exhaust – where contaminated exhaust air must not be reintroduced through the fresh air
• Indoor swimming pool enclosures – which require the introduction of fresh air to reduce the indoor humidity levels.
Sensible media can be manufactured from aluminium and polypropylene materials. The selection is influenced by the corrosive level of the air and the condensation that may occur during the heat recovery process. The correct heat exchange media must be specific to the application to enable the correct outcome.
Enthalpy Heat Exchange Media
Enthalpy Heat Exchanger Media allow both sensible and latent heat energy components to be recovered. This design features a specially constructed capillary surface that traps moisture. This ensures that a proportion of the humidity in the air leaving a ventilated room is trapped and transferred back into the room with the supply air allowing the room humidity level to be maintained.
Rotary Heat Exchangers
A Rotary Heat Wheel, as the name suggests, is a rotating wheel which picks up the energy as it rotates through the exhaust air stream, and transfers this energy as it rotates through the incoming air stream. This continuous process is generally recognised as the most efficient process to recover energy.
Rotary Heat Wheels can utilize either sensible media or enthalpy media. The selection should be carefully matched to the project requirement. The rotational speed also can be modulated to give the greatest efficiency for differing types of media. Specialist engineering assistance should be obtained when designing and selecting Rotary Heat Exchange media.
Contact our Sales Department for assistance with your design.