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Printed in the U.S.A.
AE4-1306
Application Engineering
B U L L E T I N
New hermetic compressors have been developed forthe application
with R-404A refrigerant suitable foruse in Low Temperature
applications. It must be notedhowever, that under low evaporating
conditions, theoperating envelope for these models will be
restrictedespecially in comparison to semi-hermetic
compressorstypically used in similar applications. The
operatingenvelope and restrictions are shown in Figure 1.
Note: These compressors do not meet the starting
and maximum load run down requirements for theuse with R-507
refrigerant therefore they are notapproved for R-507.
For a given saturated suction temperature, themaximum condensing
temperature, the maximumreturn gas temperature, and the maximum
dischargeline temperature as outlined in Figure 1 must not
beexceeded! Operation beyond these limits will causehigh
compression ratios and/or excessive internalcompressor temperatures
resulting in overheating,connecting rod wear and premature
compressor failure.
If the system design is such that operation within these
guidelines cannot be guaranteed, then the followingadditional
controls must be added:
1. Discharge Line Thermostat: Located 6 from thecompressor and
set to cut-out the compressor at225 maximum.
2. Low Temperature Pressure Control: Set to cut-outat 7 psig
minimum.
Superheat Requirements
In order to ensure that liquid refrigerant does notreturn to the
compressor during the running cycle,attention must be given to
maintain proper superheat
at the compressor suction inlet. Emerson ClimateTechnologies
recommends a minimum of 20Fsuperheat, measured on the suction line
6 inches fromthe suction valve, to prevent refrigerant
floodback.
Another method to determine if liquid is coming back tothe
compressor is to accurately measure the differencein temperature
between the compressor oil crankcaseand the return line. If this
delta can be kept at a minimumof 50F, no liquid will be present in
the crankcase.
Suction Accumulator Requirements
Through our development testing we have found thecombination of
HFC refrigerants and polyol ester oildevelop very high cylinder
pressures during floodedstart conditions. As a result of this
testing, we have setthe maximum charge limit to be 3 lbs.
Any system that exceeds the charge limit requiresa suction
accumulator and/or pumpdown cycle. The
purpose of these precautions is to prevent damage to
thecompressor due to continuous floodback and/orfloodedstart
conditions. An accumulator is an effective measureagainst floodback
and provides some protection againstflooded starts; however, the
pumpdown cycle is the mostpositive means of preventing flooded
start conditions.
Crankcase Heater Requirements
Crankcase heaters are recommended on all outdoorapplications or
indoor applications if expected tooperate in ambients below 40F,
orany system withan accumulator.
Lubricants
The HFC refrigerant such as R-404A will require polyolester
lubricants to provide proper miscibility and lubricity.Emerson has
approved only the following lubricants atthis time:
Copeland Ultra 22CC
Mobile Arctic EAL 22CC
ICI Emkarate RL32CF
Thermal Zone 22CC
Should a system require the addition of lubricant forany reason,
only the lubricants specified above shouldbe used.
Practical Considerations
The application restrictions imposed on these modelswill require
careful system design. Some considerationsfor the designer are:
1. Units operating at low evaporator temperatures willbe
susceptible to overheating with dirty condensersand/or restricted
airflow. Large condensers (with
Application Guidelines for RF LowTemperature Refrigeration
Compressors
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Application Engineering
B U L L E T I N
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2 2010 Emerson Climate Technologies
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AE4-1306
Application Engineering
B U L L E T I N
low TDs) should be designed into systems usingthese compressors
and proper condenser coilmaintenance will be more critical.
2. Minimum suction line pressure drops will be importantto
maintain Saturated Suction Temperature limits atthe compressor.
3. Traditional superheat settings at the ThermalExpansion Valves
may be too high to maintain thereturn gas temperature limits
specified.
4. Suction lines should be well insulated.
5. Suction line to liquid line heat exchangers may notbe
desirable if the return gas temperatures specifiedare to be
maintained.
Figure 1
Evap Temp Max Return Max Cond Max Disch
(SST)*(F) Gas (F) Temp (F) Line (F)
10 40 140 225
5 40 140 225
0 40 140 225
-5 40 140 225
-10 40 140 225
-15 40 140 225
-20 40 130 225
-25 40 125 225-30 40 120 225
6 0
7 0
8 0
9 0
1 0 0
1 1 0
1 2 0
1 3 0
1 4 0
1 5 0
-4 0 - 3 0 - 2 0 - 1 0 0 1 0 2 0 3 0 4 0
EVAPORATING TEMPERATURE ( oF)
CONDENSING
TEMPERATURE(oF)
CF EnvelopeRF Envelope
