ANALYSIS OF CYCLING EFFECTS OF RESIDENTIAL AIR CONDITIONERS
Abstract
Extensive laboratory testing on a single 3-ton (10.5 kW) split air conditioner was conducted at steady state and part load cyclic conditions. The test facilities were capable of maintaining the constant temperature conditions as prescribed by the current Department of Energy air conditioner rating procedures. Based on the numerous pressure and temperature measurements which were made, the transient phenomena were first evaluated qualitatively. Separate cyclic losses were identified and their values were estimated for the unit under test. Finally, mathematical simulations of the indoor section (less an evaporator model), the whole system during shutdown, and the compressor, condenser and capillary tubes were programmed on a computer. These models could investigate the system response under shutdown conditions, the indoor sections temperature profiles during all phases of cycling, and the high side transient response after compressor start up. It was determined that refrigerant pressure equalization during shutdown was a primary cause of almost all the unsteady start up characteristics, either directly or indirectly. The cyclic losses for this unit consisted almost completely of cooling capacity degradation. Excess power consumption accounted for less than 10% of the total losses. The computer simulations were quite accurate in predicting the transient pressures and temperatures. The shutdown system model indicated that lightweight heat exchanges could best minimize cycling loss. In addition, a pressure equalizer valve, or similar device, can seriously degrade cyclic efficiency. The start up model confirms that a heavy condenser does not produce any beneficial results to overall cyclic efficiency. In addition, the length of the liquid line has a significant influence on capacity by delaying the flooding of the expansion device and increasing the time it takes the air conditioner to reach steady state conditions.
Degree
Ph.D.
Subject Area
Mechanical engineering
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