Transient behavior and dynamic performance of cascade heat pump water heater with thermal storage system

At low ambient temperature, air-source heat pump water heater suffers from decrease of both heating capacity and coefficient of performance, and increase in compressor’s pressure ratio and discharge temperature. A cascade air-source heat pump water heater with phase change material (PCM) for thermal storage application was designed to ensure the reliable operation under various weather conditions and enhance the system performance at low ambient temperature. Dynamic experiments were carried out under various operating conditions in accordance with China National Standard GB/T23137-2008. Transient operating characteristics were adopted to analyze the performance of cascade heat pump system. Dynamic performance of the heat pump water heater in single stage mode and cascade mode was compared and discussed. The heating COP values in single stage mode ranged from 1.5 to 3.05, while in cascade mode, the heating COP values ranged from 1.74 to 2.55. Based on the transient heating COP values, critical switching curve from single stage mode to cascade mode was founded for the code of the system controller. Furthermore, energy performance between water tanks with and without PCM was compared to clarify the contribution of PCM.

[1]  E. Groll,et al.  Two-stage air-source heat pump for residential heating and cooling applications in northern U.S. climates , 2008 .

[2]  Luisa F. Cabeza,et al.  Energetic and exergetic analysis of a domestic water tank with phase change material , 2008 .

[3]  Ruzhu Wang,et al.  Experimental performance analysis and optimization of a direct expansion solar-assisted heat pump water heater , 2007 .

[4]  Xing Ziwen,et al.  Study on performance of a heat pump water heater using suction stream liquid injection , 2009 .

[5]  Zhengguo Zhang,et al.  Study on paraffin/expanded graphite composite phase change thermal energy storage material , 2006 .

[6]  Fengrui Sun,et al.  Performance optimization for a two-stage thermoelectric heat-pump with internal and external irreversibilities , 2008 .

[7]  I. Sakai,et al.  Solar space heating and cooling with bi-heat source heat pump and hot water supply system , 1976 .

[8]  Ruzhu Wang,et al.  Study on a direct‐expansion solar‐assisted heat pump water heating system , 2003 .

[9]  P. Nekså,et al.  CO2-heat pump water heater: characteristics, system design and experimental results , 1998 .

[10]  Tin-Tai Chow,et al.  Domestic air-conditioner and integrated water heater for subtropical climate , 2003 .

[11]  Reinhard Radermacher,et al.  Comparison of CO2 heat pump water heater performance with baseline cycle and two high COP cycles , 2010 .

[12]  K. F. Fong,et al.  Modeling and application of direct-expansion solar-assisted heat pump for water heating in subtropical Hong Kong , 2010 .

[13]  Ruzhu Wang,et al.  Experimental performance analysis on a direct-expansion solar-assisted heat pump water heater , 2007 .

[14]  Jerzy Banaszek,et al.  Numerical analysis of the paraffin wax-air spiral thermal energy storage unit , 2000 .

[15]  X. Py,et al.  Paraffin/porous-graphite-matrix composite as a high and constant power thermal storage material , 2001 .

[16]  S. Chaturvedi,et al.  Thermal performance of a variable capacity direct expansion solar-assisted heat pump , 1998 .

[17]  L. Cabeza,et al.  Experimental evaluation of commercial heat exchangers for use as PCM thermal storage systems , 2009 .