1.3.4 Criteria for choosing a working fluid 1.3.4.1 Vapor pressure The choice of working fluid to the saturation temperature and corresponding saturation pressure at condensation and evaporation lie in the right area in relation to the application.It is important that the evaporation pressure is not lower than atmospheric pressure,so that there is a risk of intake of air(and therefore moisture)in the plant by,for example,packing boxes.This can cause interference in the process,which among other things can take that icing in the valves,with the risk of clogging and depletion of oil and working fluid (acid formation).Any sacked in air will also be collected in the condenser,resulting in higher total pressure for the process. Condensation pressure is limited by the fixed component pressure rating.Heat pumps use extensively the standard refrigeration equipment,which is largely designed for maximum pressure of around 25 bar(PN 25).Figure 1.27 shows vapor pressure curves for some working fluids,i.e.the curves for the saturation pressure [bar]as a function of condensing temperature [C]. 40 10 --R-744 35 NH =R40 R22 8- ==R-717 30 0-R-407C 7,38 Mpa -R-22-------=- 25 R-290 [edw] 6 --R-134电 —R-12 NHs 20 CO. 月12 /R22 日134a R410A 15 R290 2,5 Mpa R134a 10 2 R407 R12 0 0aata欧 40 50 60 70 80 40 -20 0 20 0 60 80 100 Condensing temperature [C] Saturation temperature,t[C][C] Figure 1.27 Saturation Pressure as a function of temperature for some working fluids A limit of 25 bar previously limited the use of ammonia in the heat with temperature requirements higher than approx.60C.40 bar piston compressor,however,was introduced on the market in 1992,and has increased the temperature limit to approx.77C.This has led to a renaissance for ammonia heat pumps in Norway,with many installations in commercial buildings and district heating systems. Operation pressure in CO-systems is typical 5 to 10 times higher than with use of HFC and ammonia and therefore normal refrigeration and heat pump systems are limited to approx 28C condensing temperature.Also it necessary with actions to handle high deadhead pressure during longer stops.1.3.4 Criteria for choosing a working fluid 1.3.4.1 Vapor pressure The choice of working fluid to the saturation temperature and corresponding saturation pressure at condensation and evaporation lie in the right area in relation to the application. It is important that the evaporation pressure is not lower than atmospheric pressure, so that there is a risk of intake of air (and therefore moisture) in the plant by, for example, packing boxes. This can cause interference in the process, which among other things can take that icing in the valves, with the risk of clogging and depletion of oil and working fluid (acid formation). Any sacked in air will also be collected in the condenser, resulting in higher total pressure for the process. Condensation pressure is limited by the fixed component pressure rating. Heat pumps use extensively the standard refrigeration equipment, which is largely designed for maximum pressure of around 25 bar (PN 25). Figure 1.27 shows vapor pressure curves for some working fluids, i.e. the curves for the saturation pressure [bar] as a function of condensing temperature [° C]. Figure 1.27 Saturation Pressure as a function of temperature for some working fluids A limit of 25 bar previously limited the use of ammonia in the heat with temperature requirements higher than approx. 60 ° C. 40 bar piston compressor, however, was introduced on the market in 1992, and has increased the temperature limit to approx. 77 ° C. This has led to a renaissance for ammonia heat pumps in Norway, with many installations in commercial buildings and district heating systems. Operation pressure in CO 2 -systems is typical 5 to 10 times higher than with use of HFC and ammonia and therefore normal refrigeration and heat pump systems are limited to approx 28°C condensing temperature. Also it necessary with actions to handle high deadhead pressure during longer stops