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Figure 7 shows experimental data from Stene (2005) together with simulated data obtained with the optimization routine developed in this study, where the minimum temperature pinch is adjusted to reproduce the experimentally measured COP at ππ =70 Β°C, and using πποΏ½ = β5 Β°C, ππ d evap comp = 54 % and ππa = 6.5 Β°C. Based on Figure 7, a 2 K minimum pinch temperature (ππmin,pinch) is used as base case, and minimum pinch range from 1 to 10 K is used in the sensitivity study (see Table 2). Figure 7. COP for ππππ =60Β°C, 70Β°C, 80Β°C as reported by Stene (2005), and modelled COP values where ππππππππ,ππππππππh is adjusted to reproduce the experimentally measured COP at ππππ=70Β°C. Feedwater temperature (ππ ) is studied in the range from 2 to 30 Β°C, and the average temperature a 2.3 Summary of Design Variables β Study Range and the Base Case varying space and water heating loads, a large range in heating ratios (ππ ) has been set to describe reported by Stene (2005), at 6.5 Β°C, is used as a base case. Heat pumps operate differently with COP in both DHW mode (ππ =0) and space heating mode (ππ =β). This article only studies cases heat οΏ½ heat heat where the average evaporation temperature ππ = 0 Β°C, space heating is operating with ππ = 35 Β°C evap f and ππe = 30 Β°C, and the feedwater is warmed to ππd = 70 Β°C. The other design variables, which are listed in Table 2, are varied in the sensitivity study. Parameter (ππ) Refrigerant (π π refrig) Space to water heating ratio (ππheat) Table 2. Design and case variables used in sensitivity tests. Feedwater temperature (ππ ) a Study range CO2 and R410A 0to10 2 to 30 Β°C 1 to 10 K 0 to 0.5 bar 55 to 75 % 17to34% Base case - - 6.5 Β°C 2.0 K 0.2 bar 70% 25% Minimum pinch temperature (ππmin,pinch) Pressure drop in heat exchangers (Ξππex) Compressor efficiency (ππcomp) Ejector efficiency (ππejec) 3 Results Modelled integrated heat pump data is first presented for different CO2-based systems. The base case with three gas coolers (ABC), is then modelled in a sensitivity study comparing CO2 and R410A. 3.1 System Design for CO2-Based Heat Pumps Figure 8 shows how the COP varies for different designs with three gas coolers (ABC) and other systems with two (AB and BC). All designs are modelled with and without an ejector, using the base case parameters defined in Table 2. Results based on the CD1000H compressor vendor efficiency are also presented for the ABC system. Figure 9 illustrates how the optimized pressures and ππ and ππ are not unique if ππ < 0.1, i.e. where space heating can be integrated with ππ > ππ . 4 5 heat pinch min,pinch temperatures vary for two cases (with and without an ejector). Note that the optimal temperatures 10PDF Image | CO2 Heat Pump Performance
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