ASHRAE Journal - December 2009 - 63

The figure shows the piping of the refrigerant liquid and the reheat coil. The reheat coil is part of the refrigerant liquid line, and the additional refrigerant charge is equal to the volume of the coil tubes and additional piping. If a winter heating source is located upstream of the refrigerant liquid reheat coil, the refrigerant circuit must be checked to ensure that the refrigerant has a relief path and is not blocked by isolation valves. The advantages of the refrigerant subcooling/air reheating dehumidification enhancement are: • There are no water circuits to freeze or ethylene glycol charges to maintain; • No electrical connections are required; • Controls are not required for many systems; • Only a single coil is required somewhere in the airstream leaving the main cooling coil; and • Air resistance is approximately onehalf that of heat pipe, water or glycol runaround coils or rotary heat exchanger wheels.1 A good application of LSCARH is residential air conditioning in moist (humid) climate zones 1A, 2A, 3A and 4A.2 Many homes in humid climate zones have marginally acceptable relative humidity conditions in the home. The 95% increase in moisture removal with LSCARH can change a marginally acceptable humidity level to an acceptable relative humidity condition in the home. Is LSCARH a new technology? No. It is discussed in textbooks of the 1940s, including a thorough discussion by William Goodman.3 Patent protection for the basic LSCARH cycle ended in the 1950s. Conclusion LSCARH is an old technology that has not been widely used. The fact that dehumidification performance in systems using R-410A is approximately 50% better than with R-22 may result in more LSCARH systems. LSCARH appears simple. However, there are many variations including the selection of optimum evaporator airflow and refrigerant inventory management. The authors may explore these variations in a future article. LSCARH recuperative dehumidification, as with most other recuperative dehumidification technologies, requires additional operating cost. The reheat energy is nearly free but, at the same time, the system sensible cooling capacity is reduced. The consequences are that equipment runtime and operating cost are increased. References 1. Dieckmann, J., K. McKenney, J. Brodrick. 2009. “Energy-efficient dehumidification.” ASHRAE Journal 51(8):78 – 80. 2. IECC. 2006. International Code Council, www.iccsafe.org. 3. Goodman, W. 1943. Air Conditioning Analysis With Psychrometric Charts & Tables. New York: Macmillan Co. Donald P. Gatley, P.E., is a retired consulting engineer and moisture consultant. He is author of Understanding Psychrometrics, 2nd edition, published by ASHRAE. Jason LeRoy is a modeling and analysis team leader with Trane Residential Solutions in Tyler, Texas. www.info.hotims.com/25211-18 December 2009 ASHRAE Journal

ASHRAE Journal - December 2009

Table of Contents for the Digital Edition of ASHRAE Journal - December 2009