DA-13-C020 -- Dedicated Outside Air System (DOAS) - Design vs. Actual Operation (Are Aggressive Energy Targets Achievable?) PDF

A ground source heat pump and heat wheel energy recovery rooftop unit was used for a DOAS in a LEED Gold Campus Police station. Electrical submetering and a comprehensive EQuest energy model allowed detailed comparison of predicted to actual building energy performance. The DOAS was found to be operating greatly in excess of its modeled fan and compressor horsepower. Although some 40 zones of terminal air control should have reduced airflow at partial occupancy, utilizing demand controlled ventilation strategies, very little turndown was observed during those periods.

Investigation into the project history suggested that initial design decisions were modified during value engineering with little evaluation of performance impacts. Also, the contractor and a third party commissioning agent worked without a clear understanding of the construction and performance details necessary to achieve the owner's energy performance goals. Sheet metal construction details were consequently inadequate to deliver the desired performance. Lessons learned are described, including which specific details are necessary in our code required design intent and basis of design documents to achieve a successful project.

Improvements resulting from repairs and control modifications are presented, with an assessment of the achievable benchmarks relative to fan and compressor horsepower metrics in a DOAS using demand controlled ventilation (DCV). It is hoped this will be of value to establish future design targets.