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Very High Efficiency Dedicated Outdoor Air Systems (VHE DOAS)

Packaged roof-top units (RTUs) need replacing every 10-15 years. Replace your aging RTU with a VHE DOAS system, a cutting edge, new HVAC system that separates the ventilation from the heating and cooling, allowing you to downsize your heating and cooling equipment and bring in fresh, outside air. This new system includes a high efficiency heat recovery ventilator (HRV) that dramatically lowers heating and cooling costs, when coupled with a ‘right-sized’ high efficiency heating and cooling system.

VHE DOAS Benefits:

Better air quality (IAQ)
Increased comfort
Reduced maintenance costs and requirement
Simplified controls
Lower HVAC energy costs
Meets 2017 Washington code requirements for new construction or retrofit HVAC installations, which requires Dedicated Outside Air Systems (DOAS)

How It Works

The illustration to the left demonstrates how VHE DOAS works when installed on the roof of your commercial building. 

*This drawing is for illustration purposes only and does not represent the sizing or depth of the system or frame for all manufacturers' products. Check with manufacturer for exact measurements and specifications.

Download Systems Overview (PDF)

High Performance Heat Recovery Ventilator (HRV)

Using a high-performance and separated heat recovery ventilation (HRV) system is key to significantly downsizing the HVAC using the VHE DOAS approach. The HRV's aluminum micro-channel counter-flow heat exchanger pre-heats incoming supply air with outgoing exhaust air, keeping the temperature differential between supply and exhaust between 3-5 degrees. This results in the heating and cooling system working less hard to condition the fresh, incoming air as it’s already close to the indoor temperature. Ventacity's HRV system, pictured to the left, can achieve over 90% efficiency—substantially higher than other HRVs currently available in North America, which have an average 60% efficiency. 

Right-Sizing Equipment

To the left, an old packaged RTU is removed to make room for VHE DOAS. In a typical RTU, the compressor is located at one end of the unit and condenser coils are wrapped around it or in close proximity. Low-pressure refrigerant arrives at the compressor as a gas. It compresses into a hot, high-pressure gas as it flows into the condenser coil, giving off heat. The coil acts as a heat sync and the condenser fan blows the waste heat up and away from the building. The return air travels through the ductwork into the rooftop unit, while some fresh air is added for ventilation purposes.  

To the left, a new VHE DOAS is pictured in place of the old RTU, demonstrating the component separation approach and significant system downsizing.