Performance of ejector heat pumps

Abstract

An ejector-compression heat pump can use low-grade thermal energy in the neighbourhood of 93.3°C (200°F) to provide space cooling and heating. This paper applies the existing ejector theory to estimate the performance of an ejector heat pump system at various operating conditions. The study includes parametric, sensitivity and off-design analyses of the heat pump performance. The performance enhancement options and desired ejector geometry are also examined. Refrigerants 11, 113 and 114 are three of the halocarbons most suitable for the ejector heat pump system. The estimated coefficients of performance for a simple ejector heat pump are 0.3 for the cooling mode and 1.3 for the heating mode at a sample operating condition in which the refrigerant (R-11) boiling temperature is 93.3°C (200°F), condensing temperature 43.3°C (110°F) and evaporating temperature 10°C (50°F). A 24 per cent performance improvement is predicted for a heat pump with two-stage ejectors and regenerative heat exchangers. The off-design performance is relatively insensitive to the evaporator temperature variations.