Cooling heat pump

Some small cooling circuits have reversing refrigerant flow (i.e. cooling/ heat pump) and may work at reduced gas flow for capacity control. Under such conditions it may not be possible to maintain the minimum velocity to carry oil back to the compressor, and it will settle in the circuit. Arrangements must be made to increase or reverse the gas flow periodically to move this oil. 

A refrigeration system is a heat pump in which heat is absorbed below ambient temperature. Thus the appropriate placement principle for heat pumps applies in exactly the same way as for refrigeration cycles. The appropriate placement for refrigeration cycles is that they also should be across the pinch. As with heat pumps, refrigeration cycles also can be appropriately placed across utility pinches. It is common for refrigeration cycles to be placed across a utility pinch caused by maximizing cooling water duty. 

Most refrigeration systems are essentially the same as the heat pump cycle shown in Fig. 6.37. Heat is absorbed at low temperature, servicing the process, and rejected at higher temperature either directly to ambient (cooling water or air cooling) or to heat recovery in the process. Heat transfer takes place essentially over latent heat profiles. Such cycles can be much more complex if more than one refrigeration level is involved. 

Heat Pumps. Because of added capital and complexity, heat pumps are rarely economical, although they were formerly commonly used in ethylene/ethane and propylene/propane spHtters. Generally, the former spHtters are integrated into the refrigeration system the latter are driven by low level waste heat, cascading to cooling water. 

The system s AHp should tall within the pump s primary or. secondary sweet zone. At the beginning of the operation, with the cold reactor vessel, the pump operates to the right of the BEP but within the. sweet zone, and as the reactor ve.s.sel is heated, the pump migrates on its curve toward the left, crossing the BEP, to the other extreme of its sweet zone. When the reaction is completed and the tank cools, the pump... 

C 0.35 Recovery of low level waste heat f space heating, district heating syste Absorption cooling. Recovery of steam condensate and flash steam. Heat pump for evaporation, drying, etc. 3r m. 

In summary, heat-driven cycles for cooling or heat pumping can have energy saving and environmental benefits. There are also niche applications in developing countries or remote areas. Adsorption cycles using active carbons are one of a number of approaches that might be economically viable. 

Whilst the above analysis is detailed and quite complex, there are general trends that become apparent relating to how both the carbon properties and the operating conditions affect the OOP s of adsorption heat pumps and refrigerators. The cooling available from the cycle is approximately proportional to the difference between the high and low concentrations and to the latent heat of the refrigerant. The heat input to the cycle has three components the sensible... 

Some heat pumps, called thermoelectric heat pumps, employ the Peltier effect, using thermocouples. The Peltier effect refers to the evolution or absorption of heat produced by an electric current passing across junctions of two suitable, dissimilar metals, alloys, or semiconductors. Presently, thermoelectric heat pumps are used only in some specialized applications. They have not been developed to a point to make them practical for general heating and cooling of buildings. 

Schematic of cooling cycle for a heat pump system.

In the summer, the COP of an air-to-air heat pump decreases as the outdoor temperature rises, reducing the cooling capacity. Normally the thermal needs of the building are met since it is common practice to size a heat pump so that it will deliver adequate cooling capacity in all but the most extreme summer conditions. The winter heating capacity of the system is then determined by this tradeoff, and if the heating capacity is inadequate, supplemental electric or fossil fuel heat is required. 

Electric utilities did have a vested financial interest in heat pumps, since most designs used electricity for heating and cooling. But utilities were not manufacturers or consumers. Despite their attempts to promote heat pumps with articles and showcase system installations, they failed to create the demand for the product. 

---