Study: Hybrid systems for HVACs

The Energy Center of Wisconsin's report reveals that a hybrid HVAC system is more energy-efficient than a standard system, but is also more expensive.

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The Energy Center of Wisconsin, with support from the U.S. Dept. of Energy and the University of Wisconsin Solar Energy Laboratory, spent more than a year working on hybrids and how they can save energy for HVAC systems. They found in their report that in the long term ground source heat pump (GSHP) as a hybrid is very cost-effective with an average rate of return of 10%. If they had fully invested in a GSHP without the hybrid, the return averaged about 3%.

However, going to a hybrid does have high initial costs, especially when you invest in a ground heat exchanger (GHX). Compared to the conventional HVAC system used now, it is more expensive, but not as expensive as a full investment in GSHP, according to the study by East Career and Technical Academy, a vocational high school in Las Vegas. The first cost savings were an estimated $1 million by going to a hybrid system.

Among the lessons learned from the study include cooling towers being at variable speed so they can shut off shortly after substantial cooling and boilers being placed downstream from a GHX and set 5 to 10 F cooler than the GHX temperature.

- Edited by Chris Vavra, Consulting-Specifying Engineer, www.csemag.com