Heating systems/heat pumps

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. 

As with heat pumping, the grand composite curve is used to assess how much heat from the process needs to be extracted into the refrigeration system and where, if appropriate, the process can... 

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. 

Heat Pumps. A heat pump is a refrigeration system that raises heat to a useful level. The most common appHcation is the vapor recompression system for evaporation (qv) (Fig. 14). Its appHcation hinges primarily on low cost power relative to the alternative heating media. If electricity price per unit energy is less than 1.5 times the cost of the heating medium, it merits a close look. This tends to occur when electricity is generated from a cheaper fuel (coal) or when hydroelectric power is available. 

This provides another criterion for testing whether a heat-pump system may be cost-effective. A power plant takes three units of to yield one unit of W. Therefore, to provide any incentive for less overall energy use, Q W must be far in excess of 3. 

Hea.t Pumps. The use of heat pumps adds a compressor to boost the temperature level of rejected heat. It can be very effective in small plants having few opportunities for heat interchange. However, in large faciHties a closer look usually shows an alternative for use of waste heat. The fuel/steam focus of energy use has led to appHcation of heat pumps in appHcations where a broader examination might suggest a simpler system of heat recovery. 

Tc- This may require Carnot engines or heat pumps internal to the system that provide for the reversible transfer of heat from the temperature of the flowing fluid to that of the surroundings. Since Carnot engines and heat pumps are cychc, they undergo uo net change of state. 

Heat pumps are particularly suitable for recycling heat energy in the chemical-process industries. For the outlay of an additional fixed-capital expenditure Cec on a heat-pump system, a considerable reduction in the annual heating cost can be effected. 

The payback period in years for a heat-pump system is the additional feed-capital cost Cpc divided by the annual saving on heating costs. This can be written as... 

Active carbons can be used in both refrigeration and heat pumping cycles, but their potential for use in these applications does not necessarily merit the development of such systems. Before devoting research and development effort into active carbon-based thermodynamic cycles, the interest in both heat-driven cycles in general, and adsorption cycles in particular, must be justified. 

Meunier, F., Second law analysis of a solid adsorption heat pump operating on reversible cascade cycles application to the zeolite-water pair. Heat Recovery Systems, 1985, 5, 133 141. 

Rockenfellcr, U. et al. Advanced heat pump staging for complex compound chemi-sorption systems. In proceedings of Solid Sorption Refrigeration, Paris, HR, 1992, pp,153 159. 

Control Systems Heat and Heating Heat Pumps Insulation Refrigerators and Freezers Water Heating. 

Schematic of cooling cycle for a heat pump system.

There are two major factors that impact the COP temperature difference and system component efficiency. A heat pump requires energy to move heat from a lower temperature to a higher one. As the difference in the two temperatures increases, more energy is required. The COP of a heat pump is high-... 

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