Engineered Systems - April 2008 - (Page 42)

This Time, Water Cooled Was All Wet 500-ton air cooled VFD chillers in parallel and five nominal 170-ton dry fluid coolers in series with the air cooled chillers. You can see in Figure 1 the final layout we actually applied in the final design. The following sequence was modeled: When the outdoor drybulb temperature was 57°, the air cooled chillers would handle the entire load. Between approximately 47° and 57° drybulb, a portion of the load would be handled by the dry coolers, which, as you may recall, would be in series with the air cooled chillers. As the drybulb temperatures drops, the proportion of essentially free cooling to cooling requiring the compressors would increase. Below 47° drybulb, the dry coolers would handle the entire load. Now, the caveat of “essentially free” cooling is applied here since in actuality there will always be a minimal amount of dry cooler or cooling tower fan energy that is required. But this is drastically less than the otherwise requisite compressor energy. THE BOTTOM LINE Looking at Table 2, the higher energy usage seen in the South in all cases could be attributed to fewer available economizer hours. But notice that while the two concepts were essentially even in the North, the air cooled plant proved significantly less attractive in the relatively warmer Carolina locale. This observation was validated in a recent article that appeared in HPAC Magazine, which applied the same concept in a data center using chillers with integrated dry coolers. In that same article, there is a fascinating graphic showing an approximate air cooled Mason-Dixon line that I strongly encourage you to take a look at. But energy use is only part of the equation. We then ran the 15-year LCCA using the following approximate utility rates: Electricity at both locations $0.10 kWh. Water at $2.50/100 cu ft in PA and $2.90/100 cu ft in NC. Sewage at $1.70/100 cu ft in PA and $2.60/100 cu ft in NC. Refer to Table 3 for the results. Now, the dramatic impact of cutting out water usage floated to the top (pun painfully intended). In the North, the air cooled system’s favorable spread was what we expected based on the energy use. But we were surprised that even with higher energy use in the South, when you factored in the relatively high local water and sewer rates, the air cooled option defied conventional wisdom and won out again. CONCLUSION Ultimately, after all of my feverish machinations, the impartial computer proved the mad concept designer’s hunch. He would have told you that you could have saved yourself the trouble, but to his credit he was magnanimous. He was a little insufferable, but hey, he was a pain even before we ran the numbers (I kid because I love). So lesson learned. The less obvious choice of an air cooled chilled water system ultimately was less costly in both locations. This could primarily be attributed to the lower first costs, the relatively high number of available economizer hours, and to a lesser but no less surprising extent, the relatively high water and sewer costs at both sites. Not only was it cheaper, but the system would be easier to operate and maintain. The simplicity of the automatic economizer changeover was worth the price of admission alone. Since it would basically be automatic, it would certainly be preferable to a waterside economizer and/or a system with a changeover sequence that requires a weather station, a pair of unloaded dice, and access to a Magic 8-Ball just to determine when conditions will be just right for just long enough to commit the system to the whims of Mother Nature. As the project evolved, a number of other interesting opportunities and equally interesting solutions were realized. But more on that next month. In the end, it was, to paraphrase my Russian counterpart, a freaking thing of beauty (FToB). Of course I would be remiss if I didn’t identify my tormenter/comrade. The guy with the sixth sense and unwavering conviction was and is Alex Balsam. Alex is a principal with Sigma7 Design Group, a New Yorkbased consulting firm that specializes in mission critical design. You can contact him for your next data center project at www.sigma7design.com. Or you can contact me, but don’t expect any guarantees. ES I GAINED 60 TONS. HOW COOL IS THAT? That’s how much extra cooling we gained – all found money. How? By using Goodway’s CoilPro® to clean our air conditioning coils. It reduces our waste by 37%. I call that Fat City. To find out more, call Goodway today! Dickens is a deputy director specializing in mission critical design for Jacobs Engineering Group’s Architecture and Engineering Practice. Reach him at kevin.dickens@jacobs.com. BIBLIOGRAPHY American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Thermal Guidelines for Data Processing Environments. Atlanta.2004. CITED WORKS 1. Whitmore, Graham. HPAC Magazine. “Green HVAC Designs for Data Centers.” December 2007: 20-24. ® Run Leaner. Run Cleaner. Call 1-800-333-7467 or visit us online at www.goodway.com FREE INFO: 34 42 En gi neer ed S y stem s April 2008 http://www.sigma7design.com http://www.goodway.com http://www.goodway.com

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Engineered Systems - April 2008 Contents Editor’s Note Back2Basics HVAC Challenge Case In Point Commissioning Building Automation Energy Wiz HVACR Designer Tips This Time, Water Cooled Was All Wet Cleanroom Design In 10 Easy Steps It's Not The Heat, It's The Humidity Issues & Events Computers and Software Products Glossary Classifieds Advertiser Index Tomorrow’s Engineer

Engineered Systems - April 2008

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