Energy Recovery Ventilation

Proper ventilation is essential for maintaining good indoor-air quality, yet it places an additional burden on heating and cooling equipment, which must condition air that will soon be exhausted from the building. Energy recovery ventilation (ERV) systems capture thermal energy and moisture from the exhaust (inside to outside) airstream and transfer it to the intake (outside to inside) airstream, saving energy and potentially improving humidity control.

The first step to deploying ERV is to perform an energy analysis on the building. If you can’t afford a full energy analysis, look into demand-controlled ventilation (DCV) as an alternative. As a general rule, if the building’s occupation fluctuates, choose DCV; if occupancy is mostly constant, invest in ERV.

Although the savings from ERVs vary depending on climate, geographic locations with hot, humid summers are particularly well suited to these systems. Other benefits of ERV systems include:

  • Reduced HVAC energy consumption. ERV systems save energy by reducing the need to cool or heat outside air. Although energy consumption from fans can rise after an ERV system installation, the savings in heating and cooling energy generally far outweigh any increases.
  • Reduced peak demand. HVAC systems are some of the biggest contributors to peak demand—electricity use during the times of day when the utility is required to produce the most energy and when rates are highest. By reducing the amount of air that the HVAC must heat or cool, an ERV system can help lower a building’s peak demand, thereby lowering its electric bill even further.
  • Improved humidity control. ASHRAE and others have documented a growing discrepancy between building humidity load and air-conditioner sensible heat ratio (the HVAC unit’s ability to dehumidify the air). Improved building energy efficiency has decreased sensible cooling loads (for example, heat produced by inefficient lighting and plug loads), but latent loads—including occupant respiration and moist ventilation air—have remained essentially the same. Unfortunately, the HVAC industry still hasn’t entirely kept up. Today’s HVAC units are required to remove more latent heat than they were designed for, leading to higher indoor humidity levels. By predrying the incoming ventilation air, ERV systems can mitigate these conditions.
  • Appropriate ventilation. In some cases, HVAC systems may not be bringing in enough outside air to provide proper ventilation. Because an ERV system reduces the energy needed to condition outside air, you can increase ventilation air intake, thereby improving indoor-air quality. ERV systems also help you meet updated building codes without increasing energy consumption.
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