Robert Tozer

Combined cooling heat and power in supermarkets

Abstract With recent initiatives from the UK government on reduced energy use, energy efficient systems such as combined heat and power (CHP) have been considered for new applications, including supermarkets. In these commercial buildings, the seasonal demand for heat results in underutilisation of the CHP equipment, limiting the primary energy savings that may be achieved. To increase the utilisation time, it has been proposed that heat generated by the CHP unit could be used to power an absorption refrigeration system providing cooling for the refrigerated cabinets. The application of an integrated CHP/absorption scheme or combined cooling heat and power (CCHP) in the supermarket is the subject of this paper. The paper initially describes the cooling/heating/power requirements of a typical supermarket and then reviews a number of CCHP options involving the use of different cooling and engine technologies. The investigation calculates and compares the energy savings/capital costs of the different options against typical conventional supermarket technology.

Fundamental thermodynamics of ideal absorption cycles

Abstract Starting from the representation of a real absorption refrigeration cycle on a temperature-entropy diagram, step-by-step idealisations of the binary mixture, together with the thermodynamic transformations are considered, in order to derive the ideal thermodynamic absorption cycle performance and temperature formulae. It is demonstrated that the ideal absorption cycle is the combination of a Carnot driving cycle with a reverse Carnot cooling cycle. The resorption cycle is analysed in the same manner. Information is included on absorption cooling with heat recovery cycles, heat pumps and temperature amplifiers. From the analysis of single-stage cycles, and by superimposing absorption cycles operating at different temperatures and utilising specific residual heat of the higher temperature sub-cycles, the performance and temperature relations of double, triple and multistage cycles are derived. Special attention is given to three types of triple-stage cycle and their ideal equivalence is demonstrated and represted on the pressure-temperature-concentration (PTX) diagram. A simple hybrid absorption-compression cycle is analysed and the results are compared with those of ideal cold generation cycles (combinations of driving and cooling cycles). Consideration is also given to cold generation systems. Finally, the validation of the fundamental thermodynamics of absorption cycles is presented by applying an exergy analysis. This paper presents the thermodynamic principles involved to obtain simple formulae, in a similar way to the Carnot cycle in order to convey the ideal theoretical limitations.

Cooling tower : an energy conservation resource

In this paper an investigation is made using measurements of the mass transfer rates and pressure drops for a comprehensive range of PVC plastic packings producing an economic comparison to find the best geometry and range. In order to do this, mass transfer and pressure drop for turbulent conditions in fills used in the modern cooling tower have been studied. A new method of comparison of existing cooling tower fills has been developed and the performance of the best packing has been expressed in relation to the ideal packing.

A review of research concerning the use of PCMS in air conditioning and refrigeration engineering

Publisher Summary Phase Change Materials (PCMs), which are an alternative to sensible storage, are finding new inroads into the large air conditioning scheme applications. Several novel methods of applying phase change materials in cooling systems are employed to improve the energy saving potential of PCMs. This chapter presents a scheme where thermal storage is incorporated into the cooling tower circuit that enables the system to charge the thermal store at night when there are lower wet bulb temperatures. The stored cold energy is released into the heat rejection circuit during the day, which produces lower condensing temperatures and higher efficiency. This method can reduce both peak energy and power use by as much as 35%. The chapter also discusses a scheme that uses night sky radiant cooling within the heat rejection water circuit. The lower effective temperature of the night sky is used as a heat sink with long wave radiation taking place between the condenser water and the night sky. With the use of thermal storage cold energy can be released during daytime hours to improve energy efficiency.

Heat powered refrigeration cycles

The technology and application of absorption refrigeration, single and multistage cycles, and systems into which they are integrated such as CHP, are reviewed. The fundamental thermodynamics is established in terms of Carnot cycles (direct and reverse). This theory was then merged with Carnot theory to establish a universal law of cold generation systems: combinations of driving and cooling cycles which produce cooling from a combustion process. The applications of direct fired absorption chillers, cold generation systems, and their integration into combined heat and power (CHP) systems are analysed. Direct fired chillers have been proved to be economically feasible; the analysis of cold generation cycles indicated the feasibility of certain plant configurations. For the CHP analysis, the exergy costing method was selected as very appropriate and was used to determine the most cost effective application. Finally theoretical and economic conclusions are presented regarding the equivalence of vapour compression and absorption cycles.