Critoph, Robert E., Tamainot-Telto, Zacharie and Metcalf, Steven John (2008) Development of heat driven compressors for heat pump and refrigeration applications. In: International Conference on Energy Technologies and Policy 2008, Birmingham, U.K., Sep 8-10, 2008

Abstract

There is considerable interest in the potential of heat driven refrigeration or heat pump systems to reduce the CO2 emissions associated with heating or cooling and adsorption systems offer one way of achieving these aims. A prototype of a compact adsorption generator using the activated carbon -ammonia pair and based on a plate heat exchanger concept has been designed and built. The novel generator has low thermal mass and good heat transfer. The heat exchanger uses Nickel brazed shims and spacers to create adsorbent layers (4 mm to 12 mm thick) between pairs of liquid flow channels of very low thermal mass. The prototype sorption generator manufactured (Figure 1) was evaluated in term of heat transfer capability and the results were highly satisfactory: the overall generator UA value is about 380 W/K while driven by water as thermal fluid; the cycling period is under 60s. The activated carbon - ammonia pair must be selected for the specific application and operating conditions. The current prototype could be partially dismantled but the final version will be fully welded without the need for bolted flanges. The combination of two or more identical generators operating out of phase, possibly with mass and heat recovery, constitute a Heat Driven Compressor (HD compressor). Such HD compressors are used in three demonstration projects that are ongoing at Warwick University: - Car air conditioning system driven with waste heat from the engine coolant water (at 90oC): The current lab demonstration has produced an average cooling power 1.6 kW (with about 2 kW peaks) and a COP of about 0.23 under the EU typical normal conditions (33oC and 20oC for condensing and evaporating temperatures respectively). - Gas fired heat pump: This demonstration unit is designed for domestic hot water production and space heating. The machine could deliver hot water at a flow rate of 10 litre/min with a temperature rise of 30oC and a nominal heating power of 7 kW (conditions suitable for the majority of homes in UK). The system’s target COP of 1.4 represents substantial fuel savings and emissions reductions over a conventional boiler. - Solar driven mobile container for food conservation: This demonstration solar cooling unit is design to produced 2 kW cooling with 10 m2 solar collector operating in a desert environment (40oC and -10oC for condensing and evaporating temperatures respectively). Preliminary testing will be carried out at Warwick but field tests will follow in desert site.

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