Consulting-Specifying Engineer - February 2008 - (Page 44)

Case Study Going with the counterflow AT A GLANCE fficials at Regina General Hospital, Regina, Saskatchewan, look well into the future to provide progressive and innovative care for the people of southern Saskatchewan. A recent major expansion and renovation of the hospital added significant new facilities, including an emergency ward, MRI and Energy Center, a tunnel connecting buildings, and nurses’ residences. And the same progressive approach applies to the hospital’s mechanical system. Faced with an aging chiller plant that cost too much to maintain and too much to operate, hospital officials needed new equipment to serve the facility cost-effectively and meet its requirements for the next 25 to 50 years. A cost analysis of several different systems provided the answer: two McQuay 1,350-ton dual-compressor centrifugal chillers arranged in series counterflow. “We had been using natural gas absorption chillers installed in 1997,” said Rick Pearce, chief engineer, Regina General Hospital, now retired, “but they had become too expensive to operate and time-consuming to maintain. The price of natural gas alone had gone up 52% over the year prior to the project, which made the switch to electricity easier. When we learned that we could save $11.9 million (Canadian) over the lifecycle of the equipment—about CA $500,000 annually—it was an easy decision to make.” The gas absorption chillers are still installed, but are used as backup only. The lifecycle analysis estimated a savings of CA $500,000 annually. Actual savings are about CA $200,000 annually. Peter Whiteman, manager, Energy Centre and Building Automation for the Regina Qu’Appelle Health Region, said, “We’re saving approximately $200,000 annually. As we switched from absorption cooling to centrifugal, our natural gas consumption has been reduced by approximately 12%. However, our electrical has risen about 6%. In these large institutions, it is difficult to quantify the energy savings on any particular project exactly. However, we believe we experience a net savings O around 35,000 gigajoules of energy.” (1 gigajoule = 278 kWh) In addition to meeting the long-range goal in terms of lifecycle cost, the Saskatchewan Ministry of Health, the governing body of all health facilities in the province, instilled another requirement. According to the department’s new policy, all chillers in its health system must use a refrigerant that is not scheduled for phase-out under the terms of the Montreal Protocol. McQuay chillers use HFC-134a refrigerant, which has no ozone depletion potential or phase-out schedule. Series counterflow is the answer With low lifecycle costs as a primary requirement, Shawn Lamb, engineer, Stantec Consulting, Regina, conducted a capital and operational cost analysis of bids submitted from several manufacturers. “We made the final decision based on a ‘total net present value calculation’ using 2006 dollars. This took into account the capital cost of the equipment and 25-year operating costs, assuming maintenance costs are equal,” Lamb said. Most of the systems considered were designed as a parallel arrangement. After calculating payback amounts for a period of 25 years, it was apparent that the series counterflow arrangement of the chillers provided the lowest lifecycle costs. The new centrifugal chillers are used from April through October. They are usually offline during the winter season. “With the new chillers in place, it’s not only a relief to get away from the high maintenance of the old chillers, it’s also satisfying to know that we are keeping our energy costs as efficient as possible,” Pearce said. “We’re getting much more out of our HVAC system these days.” With its new efficiencies, Regina General has a clean bill of health that will continue well into the future. Information provided by McQuay International, Minneapolis. After a review, Stantec engineers concluded that series counterflow chillers are the best options for Regina General Hospital. The McQuay chillers installed have a relatively low internal pressure drop that makes the series counterflow arrangement much more viable. On an overall system level, the primary evaporator loop pressure drop is 60 ft H2O, while the primary condenser loop pressure drop is 55 ft H2O. The McQuay chillers reduce energy in this application, because each chiller produces only a portion of the temperature change required. While single-compressor chillers are most efficient at or near 100% capacity, and often require hot-gas bypass to unload, a dual-compressor centrifugal chiller is most efficient at 50% to 60% capacity and can easily unload much further. The dual-compressor centrifugal chillers use two compressors on a common refrigeration circuit, which is the reason for the part load efficiency gain. 44 Consulting-Specifying Engineer • FEBRUARY 2008

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - February 2008

Consulting-Specifying Engineer - February 2008 Contents Viewpoint News M/E Roundtable How To Write Control Sequences Mentoring Engineers: Myths, Motivations, and Models Keep Young Electrical Engineers Grounded Protecting a Vulnerable Population Codes & Standards Case Study New Products Equipment Lifecycles Advertisers Index Green Space

Consulting-Specifying Engineer - February 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.