Optimal temperature between high and low stage cycles for R134a/R410A cascade heat pump based water heater system

Single-stage air-source heat pumps have some disadvantages such as a deteriorated heating capacity and low coefficient of performance at low ambient temperatures. To overcome these disadvantages, a cascade cycle has been suggested; this cycle exhibits a better performance at low ambient temperatures. Many studies have investigated the cascade heat pump system. However, little information is available regarding experimental verification of the optimal intermediate temperature levels based on experimental results. In this study, an AWHP (air-to-water heat pump) was studied numerically and experimentally. The high and low cycles of the AWHP adopted R134a and R410A as refrigerants, respectively. Numerical analysis of the optimal intermediate temperature was performed and the experiment was conducted under various operating conditions: ambient temperature, condenser water inlet temperature, and heating capacity. The numerically optimized intermediate temperature accurately predicted the experimental data. (C) 2013 Elsevier Inc. All rights reserved.