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 ???