Energy Recovery Systems

What are Energy Recovery Systems?

Energy recovery systems transfer heat from outgoing air to incoming air in the winter and from incoming air to outgoing air in the summer, lowering heating and cooling costs and overall energy use. There are different types of systems, all featuring a heat exchanger, controls, and one or more fans to move air through the machine.

Energy recovery technologies include heat-recovery ventilators (HRV) and energy-recovery ventilators (ERV). Large ventilation systems with dedicated or shared duct systems may contain small, wall or window-mounted units. ERVs transfer a portion of the water vapor, along with heat energy, while HRVs transfer heat only.^[1]

Common design configurations include:

• Flat-plate heat exchanger systems that transfer energy between the incoming and exhaust air streams using a fixed heat exchanger.^[2]
• Run-around coil systems utilize waste heat in the process cooling water from an application such as laboratory equipment and supply domestic hot water and space heating for facilities.
• Regenerative heat wheels consist of revolving discs filled with an air-permeable medium that transfer heat and moisture from one air stream to the next reducing warm air infiltration or heat and moisture loss from buildings.

Figure 1 – Energy Recovery System Diagram[3] (Source: DPoint Technologies)

How to Implement Energy Recovery Systems

Proper installation, sizing, and placement of ducts and regular maintenance impacts performance.^[4] In cold climates, energy recovery ventilators must have a device to prevent freezing and frost formation.^[5] Experienced and qualified HVAC contractors should install, properly test, and balance the system. Regularly clean exchangers to ensure high performance and prevent mold and bacteria buildup.^[6]

Example

Waterfront Technology Center – Camden, NJ

The LEED-Core & Shell Gold Certified Waterfront Technology Center in Camden, NJ, includes an ERV incorporated into its rooftop mechanical room. This five-story, 100,000 square foot facility leases to a range of tenants including offices and wet labs.

Panasonic Corporation of North America, Newark, NJ

The Panasonic building utilized expert guidance and financial incentives offered through the NJ Clean Energy Pay for Performance Program and incorporated an energy recovery ventilation thermal wheel system, resulting in 15 percent less energy use compared to a minimally code-compliant building.

Benefits

Energy recovery systems can recover about 70-80% of the energy in exiting air and transfer it to incoming air reducing energy consumption and costs.^[7] By controlling humidity and cycling in fresh air to replace stale or contaminated indoor air, ERV’s can improve indoor air quality and occupant thermal comfort, which is often linked to increased occupant satisfaction and productivity.

Costs

Climates with extreme temperatures or areas with high heating and cooling costs make energy recovery systems most cost-effective.^[8] Properly designed systems can reduce the size of the HVAC system by 50%, and energy use by 33%, achieving a life-cycle cost savings of zero to three years.^[9]  Typical cost savings and project cost associated with various heat recovery systems, both industrial and commercial, can be found on the DOE IAC database.^[10]

Financial paybacks depend on the following:

• Added capital costs for ERV equipment
• Avoided capital costs that result from HVAC equipment downsizing
• Net annual energy savings provided by ERV systems
• Incremental annual maintenance cost increases due to ERV systems^[11]

Resiliency

Energy recovery systems offer an indirect resiliency benefit to buildings by reducing heating and cooling loads, thereby reducing stress on the grid, and the likelihood of brownouts.

^[1] National Resources Canada (NRCan): Heat/Energy Recovery Systems

https://www.nrcan.gc.ca/energy/products/categories/cooling-ventilating/ventilating/hrv/16197 (accessed Dec 17, 2018).

^[2] US EPA. School Advanced Ventilation Engineering Software. https://www.epa.gov/iaq-schools/school-advanced-ventilation-engineering-software-saves(accessed April 16, 2018).

^[3] US DOE Energy Savers. Whole House Ventilation. https://www.energy.gov/energysaver/weatherize/ventilation/whole-house-ventilation (accessed April 16, 2018).

^[4] University of Minnesota (UMN). Minnesota Sustainable Housing Initiative. Heat and Energy Recovery Ventilators http://www.mnshi.umn.edu/kb/scale/hrverv.html (accessed April 16, 2018).

^[5] US DOE Energy Savers. Whole House Ventilation. https://www.energy.gov/energysaver/weatherize/ventilation/whole-house-ventilation (accessed April 16, 2018).

^[6] US DOE Energy Savers. Whole House Ventilation. https://www.energy.gov/energysaver/weatherize/ventilation/whole-house-ventilation (accessed April 16, 2018).

^[7] US DOE Energy Savers. Whole House Ventilation. https://www.energy.gov/energysaver/weatherize/ventilation/whole-house-ventilation (accessed April 16, 2018).

^[8] Ibid.

^[9] Lawrence Berkley National Laboratory. Energy Recovery. http://ateam.lbl.gov/Design-Guide/DGHtm/energyrecovery.htm (accessed April 16, 2018).

^[10] US DOE. 2018. “Energy Recovery Systems.” Industrial Assessment Center.   https://iac.university/searchRecommendations?arcCode=2.24 & https://iac.university/recommendationTypes/2.24 (accessed Dec 17, 2018).

^[11] US EPA. School Advanced Ventilation Engineering Software. https://www.epa.gov/iaq-schools/school-advanced-ventilation-engineering-software-saves (accessed April 16, 2018).