Building Management Hawaii - (Page 27)

What to Know About Chiller Plants Many buildings lack the certification required by code BY JOHN ARIZUMI M Think of the control system as the conductor of a symphony. You can have the best violinists, cellists, bassists, brass section, percussion, etc., but without a great conductor it is hard to make great music. replacement in lieu of oil changes. In addition, most mag-bearing chillers do not have seismic certification required by many building codes. Many consider variable frequency drives (VFDs) are the panacea to energy savings. We should be aware of range of speed reduction when comparing a centrifugal chiller and a screw chiller. A centrifugal compressor behaves by the same HVAC any buildings in Hawaii have reached more than 25 years in age and many are renovating and upgrading their air conditioning chiller plants. With many "energy warriors" offering expertise and products, building owners and engineers should be knowledgeable of what they are getting. This article will shed some light on making better decisions. There are lots of discussions about variable speed chillers as it provides improved energy efficiencies. And there is talk about magnetic-bearing chillers, which adds to the confusion on improving energy efficiency. No way-magnetic bearings only eliminate the use of lubricant oil, but be aware mag-bearing chillers have maintenance costs for its bearing capacitors that need periodic The right chiller plant can improve energy efficiency laws as for centrifugal fans (h.p. proportional to cube of rpm, pressure proportional to square of rpm, and flow rate proportional to rpm). Unlike positive displacement compressors such as screw or reciprocating compressors, centrifugals use pressure "lift" to create the pressure differential. Therefore, VFD centrifugals can only reduce compressor speeds by 35 percent by virtue of design and the rest of the load reduction is accomplished by the time-proven inlet guide vanes. In addition, because centrifugal compressor speeds determine the head pressure (lift) to transfer heat, in Hawaii variable speed reduction for centrifugals is not as significant as in cooler climates. With variable-speed screw chillers, the speed turndown is 75 percent and is not dependent on the weather but is proportional to the load, so it offers better energy savings because of the range of speed reduction depending on the load, not the weather. Another interesting point is screw chillers have quick response and can drop from 100 percent to 25 percent in less than a minute. Centrifugals will take seven to 10 times longer, which most likely means nuisance safety shutdowns and alarm codes during fast-changing conditions, such as tower fan failure or low water temperature. Integrated part-load value (IPLV) is value established by AHRI 550/590, so one can easily compare part-load efficiencies for different chillers of the same capacities. Chillers rarely run at full load. Keep in mind the weather data of AHRI 550/590 originally was compiled in Atlanta, whose weather is very different from Hawaii. Even with the present use of 29 cities averaged, it is far different. For example, in Atlanta 55 percent of the annual hours have entering condensing water temperatures less than 70F; in Hawaii it is less than 2.5 percent. In addition, IPLV is based on single chiller plant operation at AHRI 550/590 conditions. Today, most plants have multiple chillers and IPLV is an inaccurate way BMH February-March 2015 27

Table of Contents for the Digital Edition of Building Management Hawaii

Editor’s Note: Energy Management
Insider’s Guide to Picking a Security Company for Your Property
Industry News
Dealing with Graffiti and Glass Damage
Hawaii’s High-Tech Roofing Products
Building and Management Expo Set
Installing New & Improved Windows
Window Film Cuts Glare, Energy Bills
Reassessing Hurricane Preparedness
An ESA Can Deliver Peace of Mind
Checking a Building’s Energy Score
Managing PV Energy Consumption
The Ultimate Energy-Efficient Building
What to Know About Chiller Plants
New Trends Emerge in HVAC Systems
Walk-throughs Vital to Engineers
Trapped in the Web of Act 326
Faces: The IREM Banquet

Building Management Hawaii