3055 -- A Comparative Study of the Performance of Temperature-Based and Enthalpy-Based Economy Cycles PDF

Deciding whether to use an economy cycle and then whether to use a temperature-based or an enthalpy-based economy cycle is a problem that many HVAC designers face today. The controversy about ,which type of economy cycle should be used was demonstrated at a recent ASHILAE meeting when one author recommended the use of enthalpy-based economy cycles (Sud 1984) while another discouraged their use in favor of temperature-based economy cycles (Haines 1984.) This study quantitatively examines the potential energy savings for two prototypical buildings due to both types of economy cycles. This was done in a systematic manner in order to give designers the guidance that they need.

Two different buildings, one more core-dominated than the other, were studied at five different locations, using the Building Loads Analysis and System Thermodynamics (BLAST) program (Hittle 1979). Two different types of systems, terminal reheat and variable air volume (VAV), were simulated, each with and without economy cycles. For all locations except Houston, the temperature-based economy cycle achieves most of the savings that can be achieved by the enthalpy-based economy cycle.

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