Abstract
The use of cascade heat pumps for hot water generation has gained much attention in recent times. The big question that has attracted much research interest is how to enhance the performance and energy saving potential of these cascade heat pumps. This study therefore proposed a new cycle to enhance performance of the cascade heat pump by adopting an auxiliary heat exchanger (AHX) in desuperheater, heater and parallel positions at the low stage (LS) side. The new cascade cycle with AHX in desuperheater position was found to have better performance than that with AHX at heater and parallel positions. Compared to the conventional cycle, heating capacity and coefficient of performance (COP) of the new cascade cycle with AHX in desuperheater position increased up to 7.4% and 14.9% respectively.
Highlights
The application of boilers and electric heaters in space heating and hot water generation for domestic and industrial use is expensive, energy intensive and mostly poses a major threat to the climate and environment
When auxiliary heat exchanger (AHX) was adopted in the low stage (LS), heat transfer to secondary fluid of the high stage (HS) cycle occurred in two stages
The first part went into the AHX for heat exchange with the HS secondary fluid, while the other part went into the cascade heat exchanger for heat exchange with the HS refrigerant
Summary
The application of boilers and electric heaters in space heating and hot water generation for domestic and industrial use is expensive, energy intensive and mostly poses a major threat to the climate and environment. Air source heat pumps operate at lower outdoor temperatures in winter and higher outdoor temperatures in summer seasons. These operating conditions decrease the performance of heat pumps by increasing their irreversibility during compression and decreasing the refrigerant mass flow rate [2]. Heat pumps used in such applications operate between very low evaporating and higher condensing temperatures, resulting in higher temperature lifts and pressure ratios beyond the applicable limits of single stage heat pumps. Such harsh operating conditions make single-stage heat pumps inefficient and expose compressors to higher discharge temperatures and damage
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