Energy Recovery: A Clear Solution for Improved IAQ In Existing Buildings

by Tyler Mancl, P.E. |

As building occupancy has shifted and changed in many sectors since the COVID-19 pandemic, a heightened awareness remains to improve the quality and safety of the air we breathe. The most proven and longstanding method of doing this is by increasing the amount of ventilation, or fresh air, that we bring into a space. It might seem intuitive that this can be accomplished by simply opening doors and windows to provide “natural ventilation”. However, natural ventilation can introduce unwanted particles such as dust and pollen and provides no control over the temperature and humidity entering the space. Open doors and windows also create a security risk in buildings, such as schools, that must keep the perimeter secure for overall occupant safety.


Improving indoor air quality through mechanical ventilation is expensive as mechanical ventilation systems are large consumers of electricity and gas loads. Increasing ventilation in existing buildings presents even more challenges as there is a limit to how much additional fresh air we can bring in through the mechanical system before exceeding heating and cooling capacities, making the resulting temperature and humidity in the space uncomfortable.


For new buildings, these challenges are addressed in evolving codes and best practice standards such as ASHRAE 62.1 for ventilation and ASHRAE 90.1 for building energy efficiency. But what about all of our existing--and often outdated--buildings?


An Energy Recovery Ventilator (ERV) provides the solution to significantly increase the amount of fresh air delivered to a building while still operating within the capacities of the existing equipment. Energy recovery is the process of transferring energy between the conditioned return air from the space and the fresh, outdoor air that imposes the load on mechanical equipment. Fresh, outdoor air passes through the ERV where an energy recovery wheel or core treats the air before entering the heating and cooling equipment.


Energy recovery units can be used in conjunction with other HVAC equipment in a retrofit application. Whether ducting into terminal units, air handlers, or directly feeding into a rooftop unit, an ERV provides the ability to reduce the ventilation loads on those systems. (Figure 1)

Energy Recovery Application

Existing System vs. ERV Retrofit
Figure 1


In existing buildings, this load reduction creates an opportunity to increase ventilation within the limits of the existing heating and cooling equipment capacities. The result is an increase in fresh air delivered to the space without increasing the heating and cooling equipment sizes, a win-win! The table below highlights the potential increase in ventilation based on geographic location. All examples are using a polymer, total energy recovery wheel with 75% total enthalpy recovery, the highest-performing energy recovery device on the market.


Ventilation Increase
Table 1

When specifying an ERV for a retrofit application to introduce more fresh air into an existing building, it’s important to ensure an equal amount of air is exhausted to keep the building pressure in check. Doing so will also optimize the performance of the energy recovery device. Additionally, it’s always best to verify energy recovery performance in the AHRI 1060 certification database. This ensures that the unit you are specifying performs as submitted through third-party validation.

Greenheck’s representatives and application engineers are happy to assist with any design questions you may have to optimize your system.

For more information on Greenheck energy recovery ventilators, click here or contact your local Greenheck representative

Energy Recovery
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Tyler Mancl, P.E.
Tyler Mancl, P.E.
Tyler Mancl, P.E.
Tyler Mancl, P.E. is a Principal Application Engineer with Greenheck’s Customer Insights Team. He holds a bachelor’s degree in mechanical engineering from the University of Wisconsin—Platteville and is an ASHRAE member. Tyler has 12 years of experience in the HVAC industry including contracting, consulting, and manufacturing roles.
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