7/28/2019 AE1306
1/2
1 2010 Emerson Climate Technologies
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
AE4-1306 March 2000Reformatted November 2010
Application Engineering
B U L L E T I N
7/28/2019 AE1306
2/2
2 2010 Emerson Climate Technologies
Printed in the U.S.A.
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
Recommended