Energy Recovery Wheels: Design Basics

​An energy recovery wheel is a relatively simple object compared to the complex machinery found throughout an HVAC system. It is, as the name suggests, a wheel or disc that is filled with aluminum (or another metal with a high heat transfer coefficient), synthetic polymer, or some other plastic that can rapidly absorb heat. It’s placed in the system where the supply and exhaust airstreams come into contact, generally before the main heating and cooling equipment that conditions the air for delivery to the building spaces.​

Thanks to the laws of thermodynamics, where systems seek equilibrium and energy can only be transferred, not destroyed, latent and sensible energy is passed from whichever airstream is warmer to the airstream that’s cooler. Latent energy, or moisture, flows in a similar manner, from the moister airstream to the airstream that is drier. This principle works during both winter and summer:

1. During the winter, the hot exhaust gasses passing by the cool supply air from outside will warm it up. This decreases the amount of work that the HVAC system needs to do to reach user settings. It can also keep the building more comfortable and healthier by recovering moisture from the exhaust air to keep the humidity in the building from getting too low.
2. During the summer, the exhaust air is still cooler than the hot and muggy supply air. Not only does the exhaust air help to cool down the incoming summer air, but it can also remove some moisture.

​As mentioned in the summertime example above, energy recovery wheels also play a crucial role in modulating humidity, and reduce the energy consumption needed to dehumidify the air

​Alternative Options

​Energy recovery wheels are the dominant form of energy recovery in modern commercial HVAC systems, but they are certainly not the only option available. For effective transfer of both total and sensible (i.e., including moisture) energy, fixed plate heat exchangers are growing in popularity.​In addition, heat pipes, hydronic glycol runaround energy recovery systems, and other designs are also options for energy recovery. However, only fixed-plate exchangers and energy recovery wheels can effectively exchange moisture or latent energy.

​Benefits in Simple and Complex HVAC Systems

​Energy recovery wheels and their counterparts are crucial parts of the HVAC system because of the ever-growing emphasis on energy efficiency present in both society and new government and industry regulations. The ability to use a relatively passive system like energy recovery wheels in HVAC systems will always limit the strain on other components like compressors, chillers, heat pumps, and furnaces that consume significant electricity and fossil fuels.

Regulatory bodies have taken note. Both the U.S. Green Building Council, which runs the LEED certification program, and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) mandate energy recovery ventilation systems, or ERVs, in new construction on many systems. ASHRAE’s Standard 189.1 also requires minimum efficiency ratings to ensure effective energy recovery installations.

Properly designed ERVs not only reduce the overall energy requirements, but they can make a substantial difference in both new and retrofit projects in terms of the sizes and tonnages of components required.

For example, consider a large auditorium. A properly installed and sized ERV can reduce the room’s HVAC load by about 40 percent for existing components—and lower utility costs as well. This provides more flexibility for engineers who can size smaller air conditioning systems, including air-handling units, fan coil units, and other elements.

​Specify Energy Recovery Wheels for Your HVAC Project

Windy City Representatives represents leading manufacturers of energy recovery wheels for HVAC systems, and we understand how important it is to take multiple considerations like budget and existing systems into account when specifying for these units. Contact us today for a quote or bid.