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01-21-15, 12:31 PM | #1 |
Master EcoRenovator
Join Date: Mar 2014
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http://www.danfoss.com/NR/rdonlyres/...ompressors.pdf
r290 pressure level and critical temperature are almost like R22. However, the discharge temperature is much lower. This gives the opportunity to work at higher pressure ratios, means lower evaporating temperatures, or at higher suction gas temperatures. Refrigerant R290 is used with polyolester oil in Danfoss compressors, so material compatibility is almost identical to R134a or R404A situation from oil side. R290 is chemically inactive in refrigeration circuits, so no specific problems should occur there. Solubility with ester oil is good. Direct material compatibility is less problematic. To keep the refrigerant flow speed within the recommended range of 3 to 5 m/s it may be necessary to adopt the cross flow sections Special care has to be taken when designing the accumulator in the system. When using R22 or R134a the refrigerant is heavier than the oil used, while with R290 the refrigerant is less heavy, as can be seen in the data table 1. This can lead to oil accumulation if the accumulator is too large, especially too high, and has a flow path which does not guarantee emptying sufficiently during startup phase of the system. the suction line heat exchanger is very important for system energy efficiency of R290, which it was not for R22, see fig. 5. The figure shows increase of COP with superheat from few K up to +32 °C return gas temperature, where a range from +20 °C to approx. +32 °C is usual for small hermetic systems. This large increase in COP for R290 is caused by a high vapour heat capacity. In combination with the need for keeping the refrigerant charge close to maximum possible in the system, thus giving no superheat at evaporator outlet, the suction line heat exchanger has to be very efficient for preventing air humidity condensation on the suction tube. In many cases an elongation of the suction line and capillary gives efficiency improvements. The capillary itself has to be in good heat exchanging contact with the suction line for as long a part of total length as possible. At high superheat, with good internal heat exchange, the theoretical COP of R290, R600a and R134a is higher than for R22. At very low superheat the COP of R290, R600a and R134a is lower than for R22. The R290 behaviour is similar to R134a, with respect to internal heat exchange. Generally the same rules for evacuation and processing are valid as for R22, R134a or R404A systems. The maximum allowable content of non condensable gases is 1 %. Too high level of non condensables increases energy consumption because of higher condensing temperature and a portion of the transported gas being inactive. It can additionally increase flow noise The 3rd paragraph on Suction Line Accumulator, oil being heavier than Propane & probable accumulation of oil in Accumulator makes me VERY hesitant to use the LARGE 60oz one that I have bought! I have a large Refrigeration Research BH750 for use as SLHX, 7.5hp (19K btu/h) The suction line pipe in the middle of it is 15" long x 1.625" ID (31.1 cubic inch) I'm thinking of positioning it vertical with evaporator output 3/4" pipe into bottom, so it would also be a burp / slobber reciever tank. This would be a 6.76x increase in pipe volume for 15", thus the refrigerant would slow down by about the same ratio. Good idea or bad ??? Last edited by buffalobillpatrick; 01-21-15 at 03:33 PM.. |
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