Energy Recovery

Energy Efficiency and Energy Recovery

Energy recovery systems typically incorporate heat exchange equipment to reduce energy costs by extracting heat from the facility's exhaust air stream before it is vented outside. Energy recovery from the laboratory's exhaust should be considered when significant portions of operating hours are at ambient temperature of 50°F (10°C) and below. Another recoverable energy source is provided by chiller/DX condensers. Water cooled condensers can be piped to reject waste back into the labs HVAC system to provide reheat capacity, to augment run-around coil systems, and to dry regenerative heat wheels. When properly designed, these energy recovery systems can reduce installed HVAC system capacity by one-half; reduce operating energy from one-third to two-thirds, depending upon mode of operation; and have life-cycle cost paybacks from immediate to three years. The four major energy recovery systems include run-around coil systems, regenerative heat wheels, heat pipes, and fixed-plate exchangers. [Waller, 1999] [Basich, 1997] [Lumpkin, 1997] [Brown, 1993; Industrial Ventilation: A Manual of Recommended Practice - 22nd Edition, 1995]

These systems can recover energy in other ways besides recapturing the heat in the exhaust air. For example, waste heat in the process cooling water from the laboratory equipment can be recovered. Water chiller waste heat can provide domestic hot water and space heating for laboratories and offices with a run-around coil system. [Schicht, 1991]

The following types of energy recovery systems require side-by-side exhaust and supply ducting.

A regenerative heat wheel is a revolving disc filled with an air-permeable medium including a desiccant. When the air passes through the medium, heat energy and moisture are transferred to the medium. As the medium rotates into the opposing air stream, the warmed, moist medium transfers the heat and moisture to the opposite-flowing air stream. Therefore, a heat wheel can either: reduce entry of warm, moist outside air into the lab building, or recover heat and moisture that would have been simply exhausted for the building. There has been a renewed interest in heat wheels since molecular sieve coatings have been used that ensure minimal contaminant transfer. [Industrial Ventilation: A Manual of Recommended Practice - 22nd Edition, 1995; Besant and Johnson, 1995] [Busby, 1996]

Regenerative Heat Wheel

Heat pipes offer a unique, compactly sized method of energy recovery that requires no external energy; however, they are not often used because of the restrictions they place on location of supply and exhaust air streams. [Cockerham, 2000]

Typically, fixed-plate energy recovery systems are coated, air-to-air aluminum heat exchangers; they may have to be quite large to perform effectively. [Stanke, 2000]


Laboratory energy recovery selection factors

Run-around systems

Desiccant heat wheels

Heat pipes

Fixed-plate systems

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