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Methods for Improving the Cycle Efficiency
Published in Reinhard Radermacher, Yunho Hwang, Vapor Compression Heat Pumps, 2005
Reinhard Radermacher, Yunho Hwang
When zeotropic mixtures are used, the subcooling has two effects on the evaporator inlet conditions. As with pure fluids, subcooling reduces the enthalpy and increases the capacity of the evaporating fluid. At the same time, as a result of the glide, the inlet temperature to the evaporator is reduced, as shown in Figure 4.1.3. With increased subcooling from 4 to 4a, the evaporator inlet state point changes from 5 to 5a. As can be seen in Figure 4.1.3, the temperature T5a is lower than T5. However, depending on the slope of the two-phase isotherm in this portion of the two-phase region, the decreased inlet temperature effect can be more or less pronounced. Figure 4.1.4 shows examples of isotherms for two different refrigerant mixtures, A and B. The isotherm TA of refrigerant mixture A has an almost horizontal slope in the low quality region close to the saturated liquid line. TB and TB2 of mixture B have a relatively steep slope. Thus, the effect of subcooling on reducing the evaporator inlet temperature as shown in Figure 4.1.3 is much less pronounced for a mixture that exhibits an isotherm of type TA. There is essentially no difference in temperature between points 5a and 5. For an isotherm of type TB, however, point 5a is located on the lower temperature isotherm TB while point 5 lies on TB2, TB < TB2.
Heat Pump Systems for Drying
Published in Vasile Minea, Industrial Heat Pump-Assisted Wood Drying, 2018
As a mass of refrigerant accumulates in the form of subcooled liquid at condenser exit, the two-phase heat exchange internal area of the condenser is reduced. This yields an increase in saturation temperature (not shown in Figure 10.6) while the liquid refrigerant exiting the condenser is cooled below saturation temperature (T5<T3). The increase in subcooling is a result of both reduction of condenser exit temperature and increase of saturation temperature.
Refrigeration and Air Conditioning
Published in Kenneth E. Heselton, Boiler Operator’s Handbook, 2020
Subcooling is accomplished by removing heat from a liquid that has just condensed from a vapor to a temperature lower than the saturation temperature. Subcooling is normally accomplished in the condenser but other provisions and equipment can be utilized to subcool the liquid. A system can, for example, include a heat exchanger that uses the cool vapor coming out of the evaporator to help cool the liquid refrigerant. The cool gas is simply superheated a little more as it absorbs the heat from the liquid. It’s also possible to have an independent subcooler to cool the liquid refrigerant.
Thermal storage subcooling for CO2 booster refrigeration systems
Published in Science and Technology for the Built Environment, 2019
John Bush, Vikrant Aute, Reinhard Radermacher
The work described above focuses on DR wherein the capacity delivered to the load is interrupted for some period. However, the use of thermal storage may allow load shifting in a way that does not interrupt the delivered capacity to the end use. Permanent load shifting refers to regular shifting of energy consumption from one period in time to another, in a way that can be done routinely such as every day. This is often done with thermal storage, for example, using ice storage for chiller plants. A state-of-the-art study by Arteconi et al. (2012) describes thermal storage opportunities and points out that ice and water storage are the methods with most of the market share (ice being the largest) for thermal storage today. Refrigerant subcooling using thermal storage is one approach that has been studied (e.g., Huang et al. 2007; Chieh et al. 2004) and in conventional-refrigerant applications the coefficient of performance (COP) benefits are in the range of 8% using an ice storage subcooler.
Experimental study of a heat pump with high subcooling in the condenser for sanitary hot water production
Published in Science and Technology for the Built Environment, 2018
Miquel Pitarch, Emilio Navarro-Peris, José Gonzálvez-Maciá, José M. Corberán
Applications with a high degree of subcooling has some peculiarities that must be taken into account when designing the system. The condenser was selected in order to produce high degrees of subcooling (part of the condenser is used for subcooling and other part for condensing) without a significant increase in the condensing pressure. Figure 2 shows a theoretical representation of the water and refrigerant temperature profile in the condenser as a function of the normalized heating capacity. The water is warmed up from 10°C to 60°C, and three different subcooling are considered (5, 45, and 55 K). For subcooling of 5 K, there is only one pinch point in the vapor saturated point. For the subcooling of 45 K, the outlet refrigerant temperature is close to the water inlet temperature. At this point, the condensing temperature slightly increases. More subcooling can be obtained, but the condensing temperature considerably increases.
Decision-making on HVAC&R systems selection: a critical review
Published in Intelligent Buildings International, 2018
Mehdi Shahrestani, Runming Yao, Geoffrey K Cook, Derek Clements-Croome
Wang et al. (2008) developed a decision-making model to select an optimal cold storage system for air-conditioning systems. In this study, four alternatives were investigated. The first three alternatives were: ice cold storage, chilled water cold storage and Phase Change Materials cold storage. These systems were designed to respond directly to the cooling demand. However, the fourth alternative was a chilled water cold storage that was designed to subcool the liquid refrigerant leaving the condenser of the refrigeration cycle. This subcooling process improves both the energy performance and cooling capacity of the cooling system and indirectly contributes to the delivery of chilled water demand (Chen et al. 2006).