Service Engineers’ Section Bulletin No 17

1 Service Engineers Section Bulletin No 17 r410a HANDLING, PROPERTIES, DESIGN, INSTALLATION AND SERVICING 1. INTRODUCTION r410a is now a recognised refrigerant for air conditioning and comfort heating heat pumps in Europe. Many major Original Equipment Manufacturers (OEMs) in this application field, represented in the EU, now supply systems using r410a . r410a is a near azeotropic mixture consisting of two HFC components, R32 and R125 in the proportions 50%/50% by weight. r410a has much higher pressures than R22. System condensing pressures will be 9 to 10 bar higher than with R22. System performance will be similar to R22. To gain the full benefits of r410a the system should be designed to take full advantage of its better heat transfer properties.

2 Servicing with r410a should be straightforward provided the guidelines given below are followed. Systems which use r410a normally have compressors charged with a polyolester (POE) lubricant. There are many manufacturers and grades of POE lubricant. It is therefore very important that any oil added to a system is of the correct grade. Consult the system or compressor manufacturer for guidance on which specific oil to use. 2. PROPERTIES OF r410a Vapour Pressure The high pressure of r410a requires that all system components, gauges and refrigerant cylinders are specified for the proper pressures. System test pressures must be set accordingly. When this is done, the safety risk associated with an r410a system is the same as for any other pressurised system.

3 Retrofitting R22 systems with r410a is not normally possible. Critical Temperature r410a has a critical temperature of C, significantly lower than that of R22. Tests of air conditioning systems carried out at high ambient temperatures have shown that the performance is not unduly affected however (when compared with that of R22). Specific Volume and Mass Flow r410a has higher density (lower specific volume) than R22 under normal A/C system conditions. A similar mass flow is required to achieve the same cooling effect. Table 1 Properties of r410a Property R22 r410a Vapour Pressure @ 25 C, bar gauge Vapour Pressure @ 40 C, bar gauge Boiling Point at 1 Atmosphere Pressure, C Critical Temperature, C Specific Volume of Saturated Vapour @ 5 C, gm3/kg Specific Mass Flow per kW Cooling @ 5/50 C*, g/s/kW * EN12900 Rating point 5 C Evaporating, 50 C Condensing, 10K superheat.

4 No subcooling SES Technical Bulletin 17 1 of 7 April 2004 The lower r410a volume flow rate means that smaller displacement compressors are required for equivalent system capacities, and smaller tubing diameters and associated fittings can be used. The overall result is a smaller refrigerant side system and consequent lower refrigerant charge. Because, in many condensers and evaporators the airside heat transfer coefficient is the limiting one, the surface areas required to transfer heat to the air or water will remain similar to those for R22, as will the compressor motor size. Nevertheless, designing to take advantage of the properties of r410a can lead to reductions in overall heat exchanger size and tubing.

5 Stability and Material Compatibility r410a stability in the presence of metals is excellent. Laboratory tests have shown that it is compatible with steel, copper, aluminium and brass. As with all HFCs the behaviour of r410a in the presence of plastic materials and elastomers varies. Some materials have been evaluated to be completely suitable, some depending on their composition and process may not be suitable. Compatibility data is readily available from wholesalers and component or refrigerant suppliers 3. DESIGN AND INSTALLATION OF r410a SYSTEMS Designers must take into account that the higher design pressures may raise the PED category of the system or component. The maximum allowable pressure for design purposes must be at equal to or above the values shown in Table 2, in accordance with BS EN378:2000.

6 High pressure reduces the impact of pressure drop on system performance. Because there is a much larger pressure difference between the high side and the low side of the system than with R22, longer lines and smaller diameters can be used for vapour flow. For example, there will be r410a saturated suction pressure reduction per 100mb pressure drop compared with with R22. Manufacturing r410a equipment (as well as installation and maintenance) simply requires good refrigeration practice, as is the case for traditional R22 installations. Suitable components (compatible with working pressure, refrigerants and lubricants) should always be used. The components and tools suited for r410a must never be used with other HCFC or CFC refrigerants to avoid any possible risk of contamination in the circuit.

7 Compressors Dedicated r410a compressors should always be used because they will be designed for the higher pressures and incorporate motors of correct size relative to the displacement. Compressors designed for other refrigerants should not be used. Manufacturers can provide information on performance, lubricants, and application details. Heat Exchangers Heat exchanger coils (evaporator or condenser) designed for r410a Service will, due to the properties of r410a , utilise smaller diameter tubing than ones of equivalent Service for R22. In practice it is possible to reduce the number of circuits in a heat exchanger for a given duty when using r410a . Table 2 Maximum Allowable Pressures (minimum) for which r410a systems must be designed (adapted from BS EN378-2:2000).

8 Ambient condition 32 C 38 C 43 C 55 C High pressure side with air cooled condenser bar(g) bar(g) bar(g) bar(g) High pressure side with water cooled or evaporative condenser bar(g) bar(g) bar(g) bar(g) Low pressure side bar(g) bar(g) bar(g) bar(g) Note: for the high pressure side of a heat pump with water cooled condenser the design pressure should be at least equivalent to the saturation pressure at the maximum leaving water temperature +8K. SES Technical Bulletin 17 2 of 7 April 2004 The number of circuits in the coil can typically be reduced by 1/3 compared to R22. In other words, an r410a coil only needs 2/3 of the number of circuits required for R22.

9 This, combined with smaller diameter tubing may give the additional benefit of a lower air side pressure drop. r410a has a significantly higher heat transfer coefficient than R22 and R407C, during both evaporation and condensation, leading to improved performance. For same thermal capacity (refrigeration capacity) the coils need a lower refrigerant side heat exchange surface, leading to more compact design and less material required. Figure 1. Refrigerant side pressure drop for the evaporation process. Given the same pressure drop the r410a coil permits a higher refrigerant mass flux Figure 2. Refrigerant side pressure drop for the condensation process. Given the same pressure drop the r410a coil permits a higher refrigerant mass flux Connecting Tubing As with heat exchangers, smaller diameters may be used for the vapour lines, when designing for for oil return.

10 The higher working pressures of r410a could require thicker-walled tubes (see below). The miscibility between HFCs and POE oils is lower than that of HCFCs with traditional oils and it is even more important to ensure the required velocity of the refrigerant for the oil return and to avoid possible oil traps when designing the pipework and accumulator. Tubing and fittings must be properly pressure rated for r410a use; see Table 2 above. BS 1306:1975 gives the methodology for determining the pressure rating of copper tubing. Based on this the following currently available copper tubing meets pressure requirements for r410a use. (Note: It is important that the pressure ratings of fittings be verified as appropriate before being used) SES Technical Bulletin 17 3 of 7 April 2004 Table 3 Copper Tube Coil Stock Suitability for r410a , based on Pressures in Table 2 and Design Stress 40N/mm2 high side, 41N/mm2 low side, according to BS 1306:1975 and BS EN 13480-3:2002.