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International Journal of Refrigeration 28 (2005) 1259–1265 Residential CO2 heat pump system for combined space heating and hot water heating Jørn Stene* SINTEF Energy Research, Department of Energy Processes, 7465 Trondheim, Norway Received 29 November 2004; received in revised form 29 June 2005; accepted 6 July 2005 Available online 2 November 2005 www.elsevier.com/locate/ijrefrig Abstract A theoretical and experimental study has been carried out for a residential brine-to-water CO2 heat pump system for combined space heating and hot water heating. A 6.5 kW prototype heat pump unit was constructed and extensively tested in order to document the performance and to study component and system behaviour over a wide range of operating conditions. The CO2 heat pump was equipped with a unique counter-flow tripartite gas cooler for preheating of domestic hot water (DHW), low-temperature space heating and reheating of DHW. The CO2 heat pump was tested in three different modes: space heating only, DHW heating only and simultaneous space heating and DHW heating. The heat pump unit gave off heat to a floor heating system at supply/return temperatures of 33/28, 35/30 or 40/35 8C, and the set-point temperature for the DHW was 60, 70 or 80 8C. Most tests were carried out at an evaporation temperature of K5 8C, and the average city water temperature was 6.5 8C. The experimental results proved that a brine-to-water CO2 heat pump system may achieve the same or higher seasonal performance factor (SPF) than the most energy efficient state- of-the-art brine-to-water heat pump systems as long as: (1) the heating demand for hot water production constitutes at least 25% of the total annual heating demand of the residence, (2) the return temperature in the space heating system is about 30 8C or lower, (3) the city water temperature is about 10 8C or lower and (4) the exergy losses in the DHW tank are small. q 2005 Elsevier Ltd and IIR. All rights reserved. Keywords: Air conditioning; Heat pump; Water-water; Heating; Hot water; CO2; Transcritical cycle; Design; Experiment Syste`me a` pompe a` chaleur re ́sidentiel au CO2 utilise ́ pour le chauffage et le chauffage d’eau sanitaire Mots cle ́s : Conditionnement d’air ; Pompe a` chaleur ; Eau-eau ; Chauffage ; Eau sanitaire ; CO2 ; Cycle transcritique ; Conception ; Expe ́ rimentation * Tel.: C47 73591642; fax: C47 73593959. E-mail address: jorn.stene@sintef.no. 0140-7007/$35.00 q 2005 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2005.07.006 1. Introduction In recent years a number of universities, research institutions and companies have been evaluating and testing various types of residential CO2 heat pump systems. The applications include air-to-air CO2 heat pump systems forPDF Image | Residential CO2 heat pump system space and hot water heating
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