Consulting-Specifying Engineer - April 2008 - (Page 38) asked “Where are you measuring pressure?” When I told him, he explained the exit and entry losses and suggested that moving the gauges or using a pump test to set the flow might provide a better result. When we crosschecked the flow via a pump test of the dedicated evaporator pump, we discovered that its results indicated that the flow was at design. Doing the math on the loss from the pipe into and out of the water box at design flow and then adding those losses to the reading on our gauges verified the result; i.e., the measured pressure drop based on the waterbox gauges plus the entry and exit losses resulted in a number that was in the same ballpark as the manufacturer’s specified pressure drop at design and cross-checked with the pump test. Leveraging details for ongoing improvements Appreciating and understanding the implications of the piping details in campus chilled water systems during construction and start-up is only the beginning. Paying attention to details and learning from the experience can lead to ongoing improvements in the operation and efficiency of your chiller plant, as illustrated by the results of ongoing commissioning efforts at the San Diego Marriott Hotel and Marina (see Figure 7). The bottom line is that even in the largest of systems, the smallest of details can matter. And the reality is that because the physical principles behind the details apply irrespective of system size, the lessons learned by the big boys on their campus systems can have merit on any system were fluid flows through a conduit, including yours. Additional reading 1. Cooling Tower Fundamentals, http://spxcooling.com/pdf/Cooling -Tower-Fundamentals.pdf. 2. David Seller’s blog, “A field guide for engineers,” www .csemag.com Sellers is a member of CSE’s editorial advisory board. His background includes more than 30 years of experience with commissioning, design engineering, facilities engineering, mechanical and control system contracting, and project engineering in a wide array of facilities. Sellers also provides technical training and develops technical guidelines on retrocommissioning and commissioning field techniques and engineering fundamentals in a number of venues. This article was developed in collaboration with the Building Commissioning Assoc. 2.50 Pre MRCx original plant kW per ton 2.00 Modified plant kW per ton, option 1 Post MRCx original plant kW per ton Overall plant kW per ton Modified plant kW per ton, option 3 1.50 1.00 0.50 0.00 0 100 300 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 Load, tons Figure 7: This graph illustrates the kW per ton profile (excluding tower fans) for the central chilled water plant serving the San Diego Marriott Hotel and Marina building complex. The red line illustrates where the plant started and the purple line is where the plant will be when completed. The operating team got from one point to the other by paying attention to the details. Source: David Sellers 38 Consulting-Specifying Engineer • APRIL 2008 http://spxcooling.com/pdf/Cooling-Tower-Fundamentals.pdf http://spxcooling.com/pdf/Cooling-Tower-Fundamentals.pdf http://www.csemag.com http://www.csemag.com
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