Mechanical Subcooling Research Articles

Thermodynamics of a vapor-compression refrigeration cycle with mechanical subcooling

Refrigeration and air-conditioning systems, when operating under large temperature differences between the condenser and evaporator, consume significant amounts of energy. A vapor-compression refrigeration cycle with a mechanical subcooling loop to increase system performance and reduce energy consumption is investigated by using both the first and second laws of thermodynamics. Although the first-law (energy-balance) approach to system analysis shows improvement in the system coefficient of performance (COP) with an increase in the temperature difference between the condenser and evaporator, it fails to locate sources of losses. Identifying and quantifying these sources can be a useful design tool, especially in developing or investigating new, more complex refrigeration cycles. A second-law analysis (in terms of irreversibility) has been carried out for both the simple and the vapor-compression refrigeration cycle with a mechanical subcooling loop. It is found that the performance of the system can be significantly improved by reducing the irreversibilities due to the expansion process. The low-temperature refrigeration system, when operating at the optimum subcooler saturation temperature, may have the following features: 1. (i) 85% reduction in power input 2. (ii) 65% percent lower irreversibility rate 3. (iii) 20% reduction in the total refrigerant flow-rate.

Dedicated mechanical subcooling design strategies for supermarket applications

Dedicated mechanical subcooling cycles utilize a small mechanical vapour-compression cycle, coupled to the main cycle at the exit of the condenser, to provide subcooling to the main refrigeration cycle. The amount of subcooling, the thermal lift of the subcooling cycle, and consequently the performance of the overall cycle, can be directly related to the temperature of the subcooling cycle evaporator. In this paper, the optimum value of the subcooling evaporator temperature is predicted using an ideal dedicated subcooling cycle. These results are then compared with those generated from a property-dependent model. The consideration of this optimum subcooling evaporator temperature leads to a design rule for the optimum distribution of heat exchange area for the dedicated subcooling cycle.

Improvement of refrigeration/air-conditioning performance with mechanical sub-cooling

Significant amounts of energy are consumed by refrigeration/air-conditioning systems. An energy-saving approach that can be applied to new or existing refrigeration/air-conditioning installations is discussed to increase system performance and reduce energy consumption. It consists of adding a mechanical subcooling loop to a conventional vapor-compression cycle. The performance of a modified system is demonstrated for three different applications. It was found that the system performance peaks at a sub-cooler saturation temperature midway between the condensing and evaporating temperatures. Simulations show that performance improvement for air-conditioning systems can be as high as 20% during peak periods of high condensing temperatures whereas high-temperature and low-temperature refrigeration systems under these same conditions will provide energy-savings of 20 and 40%, respectively.

4483392 Air to air heat exchanger : Edward Korsmo, Eugene R Boedecker assigned to Xchanger Inc

In this work, an experimental investigation into the effects, in terms of energy, of employing a dedicated mechanical subcooling cycle with a residential 1.5 ton simple vapor compression refrigeration system is presented. A comparative analysis of the experimental cycle performance is conducted with and without the dedicated subcooler cycle when the room temperature is kept between 18 and 22 °C. This is done in order to ascertain the percentage increase in efficiency due to use of a dedicated subcooling loop. R22 is employed as the refrigerant in the main cycle whereas R12 is flowing in the dedicated subcooling cycle. The experimental outcomes indicate that the load carrying capacity of the evaporator increased by approximately 0.5 kW when R22 was subcooled, in the main cycle, by 5–8 °C. It was also noted that, by using the subcooling, the second-law efficiency of the cycle increased by an average of 21%. Furthermore, the general trend indicated that this percentage increase is inversely proportional to the ambient temperature variation. The experimental work proves that dedicated subcooling can be used for increasing cooling capacity and efficiency.