Energy Recovery Ventilators: What you need to know

As energy efficiency becomes a priority in commercial buildings, many facility teams and engineers are turning toward solutions like dual fuel heat pump rooftop units (RTUs) equipped with energy recovery ventilators (ERVs). However, misconceptions about how ERVs perform in Minnesota’s cold climates, their maintenance, and building type applications can create hesitations around installations. This blog addresses some of the common questions and concerns about ERVs in commercial buildings, offering clarity on their benefits, their energy-saving potential, and how they are designed to perform.

 

What is an energy recovery ventilator?

An ERV is a type of technology designed to be integrated with and improve the efficiency of ventilation systems while reducing energy consumption. By recovering heat and energy from exhaust air, ERVs minimize waste and act as passive heat exchangers. Unlike heat recovery systems, ERVs also help maintain indoor humidity levels, offering an approach to both temperature and air quality control.

Unitized ERVs, which are either bolted on or fully integrated into RTUs, are an ideal choice for buildings that rely on RTUs for their primary HVAC systems. Whether as a factory-installed feature or a field-installed option, unitized ERVs are compatible with all RTUs.

How do ERVs work?

ERVs act as a passive heat exchanger between the incoming fresh outdoor air and exhausted indoor air. By conditioning the incoming fresh air, an ERV saves energy by reducing the amount that the RTU needs to condition (heat or cool) the fresh air that enters the building. ERVs also possess a few non-energy benefits such as improving comfort by balancing humidity, circulating fresh outdoor air to the building, and potentially reducing the required HVAC tonnage for a building.

Do ERVs work in cold climates?

Yes, ERVs are designed to function in cold climates, even when temperatures drop below zero. Most ERVs include features to prevent freezing or have defrost capabilities when conditions are present to create frost on the membrane.

Do ERVs improve indoor air quality?

Yes, ERVs enhance indoor air quality by moving stale indoor air outside and bringing in fresh outdoor air. These two airstreams cross paths through the wheel or stationary core, which exchanges energy. This process preconditions the incoming air, reducing the load on the HVAC system and lowering energy consumption.

Are ERVs suitable for existing buildings?

ERV systems can be installed in both new construction and existing buildings. ERVs can be bolted onto newly installed or existing RTUs with minimal changes to the roof infrastructure. Professional installers can design a solution for each building case.

Do ERVs only provide energy savings with high volumes of outdoor air?

Not at all. Energy modeling conducted by Center for Energy and Environment’s research team has shown ERVs can provide energy savings for outdoor air percentages below 20%. For more information on this modeling, please review the report.

Do ERV controls work well with standard RTU controls?

Manufacturers specify an installation protocol that details operation of the ERV with the RTU controls. Most manufacturers have preferred ERV models with which their units can operate and integrate their controls for the best performance.

Do ERVs reduce operational costs?

All ERVs reduce operational costs and have a payback period because they significantly reduce the energy used to condition a space by bringing in outside air for ventilation. Without an ERV, it’s like leaving a window open and trying to condition the space. Using an ERV preconditions the incoming ventilation air to reduce the energy needed to condition the space to the right temperature, leading to energy savings over time. Monthly utility bills are typically reduced by 10% or more with the installation of an ERV.

Are ERV installations difficult and complicated?

ERVs for RTUs can be easily integrated into RTUs through bolt-on applications. Manufacturers typically recommend specific ERV manufacturers that can work with their RTUs in bolt-on applications. The misconception that it is difficult is mainly due to a lack of familiarity with ERV products.

Do ERVs require expensive maintenance and more frequent servicing?

ERVs are easy to maintain. Aside from the motor, there are few or no moving parts, depending on whether they use a wheel or stationary core. Maintenance involves cleaning the filters and cores, which can be done during routine RTU filter replacements. ERV cores are simple to remove and can be cleaned with water. Maintenance and replacement of filters are recommended for longevity of equipment. Depending on the size of filter and airflow, filters may need to be changed every 4–6 months. Annual or biannual inspections are recommended as well.

 

Efficient technologies like RTUs with integrated or bolt-on ERVs are key to achieving both cost savings and better indoor air quality. By tackling common myths and beliefs, building owners, facility teams, and engineers can adopt a solution to enhance their building performance and meet sustainability goals. When the right systems are installed and maintained correctly, buildings can remain comfortable and efficient throughout the year, for many years, making ERVs a good investment for long-term success.

If you have more questions, contact us at nextgenrtu@mneta.org, visit the ETA Next Gen RTU page, and stay connected by subscribing to our newsletter.