A Different Perspective

I was very disappointed to read the January 21article inThe Newsentitled “Maximizing Efficiency in Chillers, Rooftop Systems.” Many people in our industry do not understand how the entire system works together to save energy and reduce operating cost in a chiller plant.

The article states that energy efficiency in a chiller is all about head (“head” or “lift” is related to the pressure ratio Pcond/Pevap that the compressor is required to produce). This leads the reader to believe that a reduction in chiller head will result in chiller energy savings. This is true, but what is not stated is that, many times, that head reduction comes at a very high price. That high price results from a drastic increase in the power consumption of the other items in the system, such as the pumps, towers, and air handlers. The goal of a responsible chiller system design should not be to reduce head, it should be to reduce the operating cost (or life cycle cost) of the entire system. The vast majority of the time, reducing the chiller head does not coincide with reduced system operating cost.

The article also sings the praises of part load value (IPLV) and how it represents “real world operation.” This is a marketing term, not a technical term. We must be extremely careful as an industry to not rely on overly simple single number representations to take the place of real energy analysis. There is no way that an IPLV can show you if you will save money for your application — it is simply not that easy. With demand charges today as much as 60% of the electrical cost of operating a chiller, full load chiller performance is easily as important as part load [is] on your electrical bill. Full load and part load are both important. That is why ASHRAE/IESNA Standard 90.1 contains both full and part load requirements, and states that both must be met.

The bottom line is, we must do the right thing as an industry when it comes to designing chiller plants. A real economic analysis looks at not only weather, but solar loads, building loads, people loads, and ventilation loads, and then applies these elements in the chiller system with pumps and towers to minimize energy consumption. Relying on “too simple” solutions like IPLV to do the work for us will only cause harm to our industry and, more importantly, our customers.

Mike Thompson, Marketing Manager — Centrifugal and Absorption Chillers, Trane, La Crosse, WI

Unbiased On IAQ

I just read B. Checket-Hanks’ article on the IAQ forum at ASHRAE’s Winter Meeting [“Hospitality IAQ Forum Inspires Passionate Debate,” Jan. 28]. I attended this meeting and just wanted to tell you that the article is as accurate and evenhanded as anyone could hope for.

David Gau, Vice President, Titus, Richardson, TX

Publication date: 03/04/2002