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buffalobillpatrick · 11-05-14, 01:22 PM

http://www.danfoss.com/NR/rdonlyres/...ompressors.pdf

p122

"For R290 experience shows the need for a
capillary flow rate almost similar to R404A. At
least this is a good starting point for optimization.
As with R134a, R404A and R600a 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."

11-05-14, 01:22 PM	#49
buffalobillpatrick Master EcoRenovator Join Date: Mar 2014 Location: Florissant, Colorado Posts: 599 Thanks: 814 Thanked 59 Times in 55 Posts	http://www.danfoss.com/NR/rdonlyres/...ompressors.pdf p122 "For R290 experience shows the need for a capillary flow rate almost similar to R404A. At least this is a good starting point for optimization. As with R134a, R404A and R600a 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."