Dedicated Outside Air Systems and HRVs
Within their emerging technologies research program, BPA staff is studying alternatives to existing roof top units for commercial end-users. They are testing a systems approach to separating ventilation control from building heating and cooling. The approach includes an efficient Heat Recovery Ventilation (HRV) system and a hydronic or variable refrigerant flow (VRF) for building heating and cooling. The BPA field research team is evaluating a very high efficiency dedicated outdoor air systems (DOAS) using a HRV system with variable refrigerant flow or ductless heat pump heating and cooling systems.
An HRV’s fans pull fresh air into a building while simultaneously exhausting stale air from the building. Heat is transferred from the warmer air stream (the exhaust air in winter, the supply air in summer) to the cooler air stream. The two air streams are not mixed.
A DOAS supplies only the outdoor ventilation air necessary to maintain high ventilation standards, while independent heating and cooling coils inside the building take care of conditioning the space. Since a smaller volume of air needs to be moved in a heating and cooling system, a smaller capacity air handling unit can be used, reducing the fan energy consumed. And since the amount of outside air introduced can be modulated for demand, less air is needed for heating and cooling, resulting in further energy consumption savings.
In most cases, a building that is not well sealed will not benefit from the installation of an HRV as the leaks will bypass much of the benefits of the system. It is important to ensure that the building is well sealed to optimize the HRV system operation.
If you are interested in learning more about HRVs, decoupled ventilation and what that means for you, get in touch with Air Northwest. If you are a utility please consider participating in the BPA Field Test for this technology and help the pipeline with a new conservation measure.
If you are a Washington state contractor don’t forget that the DOAS section of the building code is no longer optional after July 1, 2017. It becomes prescriptive. If you like more information about the code changes, reach out to us and we will help you get the right information.