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Selection of prime mover type was investigated for use in combined cooling, heat and power systems. Selection was determined from comparison of performance criteria for economic, energy and emissions savings. Simulations were run for three different types of prime movers in one climate zone and compared to a reference case with a typical separate heating and power system in the same climate zone. A hybrid load following method was implemented, with a suggested improvement. Performance parameters were compared and results indicated emissions and energy savings for all three prime movers. The prime mover types were reciprocating internal combustion engine (ICE), micro-turbine and phosphoric acid fuel cell. The climate zone was chosen to be a cold, humid climate represented by Chicago, IL. Economic savings were seen for both the ICE and micro-turbines. Emissions savings for carbon, nitrogenoxides and methane, for all three types, were greater than 9%, 12%, and 13%, respectively. Primary energy consumption savings for all three were greater than 8%.

Combined Cooling Heat and Power (CCHP) attained significant attention among energy professionals and academicians recently due to its superior thermal, economic and environmental benefit in comparison with conventional energy producing systems (internal combustion engine (ICE), micro-turbine, etc). Despite the abundance of literature on CCHP, only a few studies emphasized on the selection of appropriate prime mover for an economically sustainable CCHP system. Furthermore, the effect of part load efficiencies is commonly neglected during CCHP analysis. We had introduced these two new concepts of economic sustainability of specific prime mover and part load effects on efficiency to CCHP system in our previous paper. An algorithm based on hybrid load following method was utilized to determine the optimum prime mover for a particular location and weather type. No studies explored the effects of efficiency parameters and the selection strategies of prime mover in different building types for any particular location using this newly developed algorithm. Since building types dominates the electric, heating and cooling demand extensively, it is imperative to extend the prime mover selection analysis for building types for efficient CCHP operation. Economic, energy, and emission performance criteria have been utilized for the prime mover selection systems in different building types. Computer simulations were conducted for five different building categories (primary school, restaurant, small hotel, outpatient clinic and small office buildings) for each of three different types of prime movers (reciprocating internal combustion engine (ICE), micro-turbine and phosphoric acid fuel cell) in a cold climate zone (Minneapolis, MN). The simulation results of different prime movers were compared with the outcomes of a reference case (for each building in the same climate zone) that has a typical separate heating and power system. The cold climate zone (Minneapolis, MN) helped to explore the heating load effects on economic, energy, and emission performance of the buildings in comparison to other energy demands (i.e. electric and cooling demand). A hybrid load following method was executed, using improvements shown in our previous article. Performance parameters and other outcomes of this study showed that economic savings were observed for the ICE in all building types, and the micro-turbine in some building types. Internal rate of returns of ICE are 22.4%, 14.7%, 20.5%, 14.6% and 6.5% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. ICE also shows highest energy savings among all three prime movers with an energy savings of 20%, 17.2%, 25.7%, 23.8% and 9.7% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. For all types of prime mover based CCHP systems, lower CO2 emission was observed for all building types. However, unlike ICE, which is preferable in terms of economic and energy savings, emission analysis shows that micro-turbine poses better emission characteristics compared to other types of prime movers. CO2 emission for micro-turbine savings are 67.1%, 62.2%, 82%, 43.2% and 81.4% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. The relationship between the power and thermal demand of the different buildings was determined to be a significant factor in CCHP system performance. A sensitivity analysis determining the effects of heat exchanger and heating coil efficiencies on the performance of CCHP systems shows that the economic performance was most sensitive to the heat exchanger efficiency, while energy consumption and emissions was most sensitive to the heating coil and boiler efficiency.

A laboratory-experimental and theoretical-modeling investigation was conducted of isobaric, radiative cooling of cloud-like water mists to a remote heat sink, similar to what can happen at the tops of clouds. For mist initially at 20°C cooled by a radiative sink at –20°C, the mean (D43) mist droplet diameter grew from 5.5 to 8.4 μm and the mist temperature decreased from 20° to 3°C in just 80 s. Modeling showed that conventional assumptions were able to predict the measured temperature decrease reasonably well but not droplet size changes, suggesting that bulk radiative cooling was being reasonably well-modeled but not detailed, droplet-size-dependent behavior. Theoretically, Lewis-number near-unity was exploited to obtain an analytic expression for quasi-steady supersaturation that agrees with Davies (1985) but is simpler and a function of only droplet size distribution, surface tension and solute parameters, not radiative transfer. A simpler expression for the corresponding time constant was also found that is a function of only the binary diffusion coefficient and D31-moment of the droplet diameter distribution. The time constant was found to be in milliseconds, not seconds. Simply modifying quasi-steady supersaturation (i.e., applying droplet cooling effects uniformly to all droplet sizes) was shown not to be an acceptable substitute for including droplet-specific radiation terms in the droplet growth equation. These results confirm that radiative cooling at cloud top can have a significant effect on droplet size evolution and temperature change and provide data and analytical simplifications for use in further needed investigations of radiation modeling assumptions and parameterizations.

This chapter includes the basic configuration of combined cooling heat and power (CCHP) systems and provides performance analysis based on energy, economic and environmental consideration applicable to buildings. The performance parameter for energy savings measure used for the analysis is primary energy consumption (PEC) of CCHP system. Parameters used for economic analysis are the simple payback period (SPP), annual savings (AS), internal rate of return (IRR) and equivalent uniform annual savings (EUAS). The emissions savings are determined for carbon dioxide (CDE), nitrogen oxides (NO X ), and methane (CH 4 ). Economic, energy, and emission performance criteria have been utilized for three types prime movers in five different building types, consisting of a primary school, a restaurant, a small hotel, an outpatient clinic, and a small office building. Performance for economic analysis indicated that economic savings career, unlike ICE, which is preferable in terms of economic and energy savings, emission analysis shows that micro-turbine poses be observed for the ICE in all building types, and the micro-turbine in some building types. For all types of prime mover based CCHP systems, lower CO 2 emission is observed for all building types. However, emission characteristics compared to other types of prime movers. Overall, CCHP system with optimum use of its appropriate prime movers can provide potential energy, economic and environmental benefit in buildings.