FALL 2017

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temperature of one fluid and outlet temperature of the other. In a plate and frame type heat ex- changer, the minimum recommended temperature approach is 2 F. Although a plate and frame heat exchanger can, in theory, be designed for a closer ap- proach, it will have a great impact on the size and cost. For example, going from a 2 degree approach to 1 degree results in doubling the size of the heat exchanger. Also, many system instal- lations cannot support measurements closer than 2 degrees. KEYS TO SYSTEM DESIGN In selecting a plate and frame heat ex- changer for an HVAC system there are a number of factors to consider: > Load — the total amount of heat rejected into the atmosphere by the cooling tower or the building load. > Pressure drop — typically, the high- er the allowable pressure loss through the plate and frame heat exchanger, the smaller and less expensive it will be. > Approach — the temperature differ- ence between the inlet temperature of one fluid and outlet temperature of the other fluid. The closer the temperature approach, the heat exchanger becomes larger and more expensive. AHRI 400 SEAL OF APPROVAL Third-party certification is another important consideration in selecting heat exchangers. Certification provides assurance that the equipment will per- form accurately and consistently and ensures all manufacturers are design- ing to the same tolerances. The Air Conditioning, Heating & Refrigeration Institute's Liquid to Liquid Heat Exchanger certification program is based on AHRI Standard 400 for gasketed plate and frame type heat exchangers. ASHRAE Standard 90.1-2010 or newer requires waterside economizers to comply with ANSI/ AHRI Standard 400. The scope of the AHRI LLHE certifi- cation program includes gasketed plate heat exchangers that use water or sea water as the operating fluids and where the heat load is <= 240,000,000 Btu/hr and both flow rates are <= 20,000 gpm. As more states enact stricter regula- tions for HVAC energy efficiency, and building owners realize cost savings and operational efficiencies with free cooling practices, waterside econo- mizers will play an important role in sustainable HVAC system design. John Boyer is the commercial team man- ager, Heat Transfer at Xylem Inc. Mike Kissel is global product manager, Heat Transfer at Xylem Inc. bubble-tight done right Square blades mean lower pressure drop Greenheck introduces a true square bubble-tight damper for square and rectangular duct, plenum, or wall-mount installations. Model HBT221 is factory tested for bubble-tight leakage protection per AMCA 500-D up to 10 in. wg (2.5kPa). When open, the revolutionary square blades offer more free area and lower pressure drop compared to circular or oval blades. That's big for saving energy and maximizing airfl ow…and ideal for medical facilities, universities, test labs and food processing. Learn more from your local rep or on our website. Fans | Energy Recovery | Packaged Ventilation | Make-up Air Kitchen Ventilation | Lab Exhaust | Dampers | Louvers | Coils 715.359.6171 • greenheck.com Damper Innovation! © 2017 Greenheck CIRCLE ID #15 ON READER SERVICE CARD OR GO TO HVACPPRODUCTS.COM/MARKET This gasketed plate and frame heat exchanger is used for cooling a power plant gas turbine.

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