Bubbles at the NBIL! Evaporative Sidecar Testing for Retrofitting Rooftop Units

We have seen the future and it is bubbly. This summer we’ve been busy testing the effectiveness of using an indirect evaporative air conditioner to retrofit an existing 5-ton rooftop unit (RTU) in the western Washington and Oregon climate. Testing is ongoing at the NBI Laboratory (NBIL), a 1000 square foot RTU testing facility where NBI has tested high performance RTUs and variable speed components in previous years. The picture above shows the evaporative unit at initial start-up (a surfactant similar to a soap is used to ensure initial wetting of the evaporative media which results in a few bubbles; they go away after the first hour or so). The testing was scoped to include two evaporative units though only one, the Coolerado M50, will be tested in 2013. The Greenaire CRS2500 Air2O unit did not arrive in time for 2013 testing but will be tested in 2014.

RTUInitial results are promising. The unit runs as a two stage system with the evaporative unit as the first stage. The tests are designed to evaluate the energy savings and water usage of the approach as well as the economic benefit resulting from reduced run-time on the RTU components (particularly the compressor). NBI has created a controlled space to replicate the internal sensible gain (i.e. space heaters that simulate loading of people and equipment at a total of 62.8 kWh per day; pretty high for such a small space) and so we can compare the evaporative plus RTU configuration versus the baseline of RTU only which we established earlier in the summer.

The unit is indirect-only so there is no impact on humidity. The Air2O has a direct stage (where water is blown into the supply airstream) and so we will be curious to see how this impacts humidity.Preliminary conclusions are that the energy savings are significant but that the cost/benefit analysis will be a close call. Stay tuned! More information may bubble up soon…