Pompe à chaleur air-eau à Haute Température. Phase 2: cycle à injection optimisé, essai journaliers et compreseur booster. Analyse thermo-économique.

The project High Temperature Heat Pump has been completed in 2 phases. First a new type of scroll compressor with adapted injection port for vapor injection, was tested with an air-water heat pump (fig 2.2, 2.3). This type of heat pump reaches the extreme running conditions for the retrofit of existing fuel boilers at air (a) -12°C and water (W) 65°C with very satisfying performances (Final Report, Phase 1). In this report a second improved compressor could be tested: with a COP of 2.74 (was 2.58) at A2W50r.h.93% (normalized conditions) and at A-12W65 (without defrosting) the COP has reached 2.07 (was 1.91) with a base heat output of 10 kW. The setup for the intermediate injection was continuously improved by implementing a capillary tube (sect. 3.3.5) and by reconnecting the economizer heat exchanger (chap. 4). Continuous tests including multiple frosting cycles and 24h tests with modulated external conditions were also conducted on the same test fascility (chap. 6 and 7). A second approach studied in this project is the implementation of a booster compressor (open scroll type) mounted at the suction line of the main compressor (chap. 8, fig. 8.3). Test at A-12W65 show the large improve of heat output raising from 9.7 kW (heat pump with intermediate injection) up to 15.7 kW! For this configuration, the existing heat exchangers are not properly designed anymore and slight losses in COP are seen, even if the performances of the compressor are acceptable (fig 8.6). In the second part of this report a thermo-economic analysis has been undertaken in order to compare the proposed concepts for a monovalent heating case (heat pump only) and by optimizing the size of an electric direct heating device. Zurich was chosen for the climatic conditions of the heating season. The heat pump characteristics are calculated for a heat curve (passing through the point A-12W60 and a heating limit at Text=15°C), losses of defrosting and auxiliaries (ventilator and pump) are included. Cost functions for the heat pump and its main elements have been proposed. The economic performance (cost price per kWh heat output) has been calculated for different electric prices and residence sizes. The optimization gives the best choice of relative the size of the booster compressor and the electrical heat supply. For the monovalent heating a seasonal COP of 2.71 (one-stage HP), 287 (HP with intermediate injection) and 3.09 (booster type HP). The optimal booster size is depending on the optimization criteria. For an optimal choice of the heat supply the cost price reache 8.8 ctsSFr/kWhth (on -stage), 8.5 ctsSFr/kWth (injection) and 7.9 ctsSFr/kWhth (booster) (fig. 7.4). The electric supply covers >50% of the base heat output and will consume 10% - 13% of the electricity during the heating period. The choice of a heat pump for the substitution of a oil or gaz boiler represents a raise of 7% - 19% of the cost price (sect. 7.3).