Energy Recovery Ventilation is the process of exchanging the energy contained in normally exhausted building or space air and using it to treat the incoming outdoor ventilation air in residential and commercial HVAC systems. The benefit of using energy recovery is the ability to meet the ASHRAE ventilation & energy standards, while improving indoor air quality, and reducing total HVAC equipment capacity.

Methods of transfer

An Energy Recovery Ventilator (ERV) is a type of air-to-air heat exchanger that not only can transfer sensible heat but also latent heat. Since both temperature and moisture is transferred, ERVs can be considered total enthalpic devices. On the other hand, a Heat Recovery Ventilator (HRV) is limited to only transferring sensible heat. HRVs can be considered sensible only devices because they only exchange sensible heat.

Types of energy recovery devices

**Total Energy Exchange only available on Hygroscopic units

Rotary air-to-air enthalpy wheel

The rotating wheel heat exchanger is composed of a rotating cylinder filled with an air permeable material resulting in a large surface area. The surface area is the medium for the sensible energy transfer. As the wheel rotates between the ventilation and exhaust air streams it picks up heat energy and releases it into the colder air stream. The driving force behind the exchange is the difference in temperatures between the opposing air streams which is also called the thermal gradient. Typical media used consists of polymer, aluminum, and synthetic fiber.

The Enthalpy Exchange is accomplished through the use of desiccants. Desiccants transfer moisture through the process of adsorption which is predominately driven by the difference in the partial pressure of vapor within the opposing air-streams. Typical desiccants consist of Silica Gel, and molecular sieves.

Plate heat exchanger

Fixed plate heat exchangers have no moving parts. Plates consist of alternating layers of plates that are separated and sealed. Typical flow is cross current and since the majority of plates are solid and non permeable, sensible only transfer is the result.

Enthalpy plates were introduced 2006 by Paul, a special company for airing systems for passive houses. A crosscurrent countercurrent air to air heat exchanger built with a humidity permeable material.

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