Advances in HVAC Improve Indoor Air Quality and Reduce Energy Use
Dedicated outside air systems (DOAS) apply the concept of separating heating and cooling from the ventilation system, which allows for optimal control of each of these critical building functions. A very high efficiency DOAS (also referred to as VHE DOAS) improves this concept by focusing on efficiency and pairing a high-performance heating and cooling system, such as a heat pump or VRF, with a very high efficiency heat recovery ventilator (HRV) or energy recovery ventilator (ERV). The HRV/ERV provides ventilation to occupied spaces independently from heating and cooling, and pre-conditions incoming fresh air by recapturing heat (or rejecting it when in cooling mode) from the outgoing air stream. This configuration significantly reduces commercial building energy use, allows for a more compact system and smaller ducts, and improves the building’s indoor air quality with 100-percent fresh, outside air for ventilation.
Energy Savings Potential in the Pacific Northwest
Preliminary analysis of eight pilot projects conducted in the Pacific Northwest shows an average of 41 percent whole building energy savings and 63 percent HVAC savings over code minimum replacement of the existing equipment. For modeled prototypes with electric heat using the same baseline comparison case,
whole-building savings averaged 22 percent, with HVAC savings averaging 53 percent.
The Many Ways High-Performance DOAS Saves Energy
Because it is coupled with an HRV/ERV, very high efficiency DOAS achieves its most substantial savings from right-sized (or down-sized) high-efficiency heating and cooling equipment. And by separating ventilation from heating and cooling, there’s additional energy savings from reductions in fan energy for heating and cooling and ventilation.
The reduced volume of air running through the heating and cooling equipment requires less energy to meet the combined space load and reduced load of the ventilation air, which is delivered a few degrees from room temperature. There are also significant potential peak-demand reductions depending on the existing system type and climate.
Ideal Building Applications
Very high efficiency DOAS is ideal for most small-to-medium commercial new construction buildings, major renovations, and in retrofit applications. Packaged rooftop unit (RTU) replacements in small and medium commercial buildings are an ideal application for this high-performance HVAC concept. In existing buildings, this system replaces conventional, simple HVAC equipment, like RTUs, through a system conversion. In new construction, it is included in the planning and design process from the outset. Some building uses such as restaurants, hospitals and warehouses are less ideal for this application and require careful analysis and design to be effective.
- Lowers energy bills by decoupling the ventilation from the heating and cooling system, allowing for smaller equipment
- Utilizes the highest efficiency HRV/ERV technology available
- Improves indoor air quality due to 100 percent outside air with no recirculation
- Maintains verifiable control of ventilation supply, while minimizing contaminant spread
- Enables demand control ventilation (DCV) to ensure rates reflect occupancy patterns and rely less on pre-programmed schedules
- Fewer components combined with advanced controls help simplify or reduce system maintenance and operation