1. DEMAND COOLING Copeland Discus Demand Cooling
From Emerson Climate Technologies
Application Engineering Bulletin AE R4

2. APPLICATION
Required for all R-22, R407A, and R407C low temperature systems*
With saturated suction temperatures below -10°F
Prevents excessive compressor discharge temperatures
Is compatible with conventional and parallel rack units
Cost effective solution to compressor cooling
HCFC-22 can present problems as a low temperature refrigerant because under some conditions the internal compressor discharge temperature exceeds safe temperature limit for long term stability of refrigeration oil.

3. PROCESS OF DE-SUPERHEATING
The Demand Cooling System uses modern electronics to provide a reliable cost effective solution to the problem of high compression ratios.
The Module uses the signal of a discharge head temperature sensor to monitor discharge gas temperature. If a critical temperature is reached, the module energizes an injection valve which meters a controlled amount of saturated refrigerant into the compressor suction cavity to cool the suction gas. If for some reason, the discharge temperature rises above a preset maximum level, the Demand Cooling module will turn th ecompressor off (requiring a manual reset) and actuate its alarm contact.

4. COMPONENT ACRONYMS CM IV TS
On control diagrams, these demand cooling components will usually be labeled with acronyms. The CM is for Control Module, the IV is for Injection Valve, and the TS stands for Temperature Sensor. TS

5. DEMAND COOLING MODULE Reads sensor input and operates solenoid
Energizes alarm relay for faults (after 1 minute time delay) :
Discharge temperature reaches preset point
A shorted sensor
An open sensor
In order to avoid nuisance trips, a one minute time delay is provided before alarm after a continuous high or low resistance reading or over temperature conditions. The module relay uses a single-pole-double-throw contact. “L” is Common, “M” is normally closed. “A” is normally open and closes on alarm.

6. TEMPERATURE SENSOR
Uses a precision Negative Temperature Coefficient (NTC) Thermistor
Thermistor resistance drops on temperature rise to provide temperature signals to the CM
Working range is usually Ω(HOT) to 90,000Ω (ROOM TEMPERATURE)
All demand cooling systems can use the same sensor, however there are 2 sizes of leads. Three foot shielded cable (standard) and ten foot shielded cable (optional).

7. THE INJECTION VALVE
Injection valve orifices have been carefully chosen for each body style to be large enough to provide the necessary cooling when required but not so large that dangerous amounts of liquid are injected, or that excessive system pressure fluctuation occurs during injection valve cycling. Normally, pressure fluctuations are greater than 1 to 2 psi. It is important to use the correct valve for each compressor body style.

8. DEMAND COOLING SET POINTS
A complete troubleshooting guide for bench-testing each component is included in the bulletin AE1287. You will also find the component part numbers included in the tables of that publication.

9. DISCHARGE LINE TEMPERATURES
-25° F Evaporator – Temperature taken 6” from discharge valve
The thermometer sensor must be insulated for this test, otherwise the results may be off by as much as 30°.
System design and operating conditions may cause a deviation in results from the table above, however, anything within 5-10% is acceptable.
When operating under published conditions, the discharge temperature should never be more than 280°F or less than 200°F.

10. AREAS OF EXPECTED INJECTION
A table containing adjustment factors is included in the AE1287 demand cooling bulletin to allow the service technician to fully troubleshoot and monitor the system operation.

11. DEMAND COOLING Copeland Discus Demand Cooling
From Emerson Climate Technologies
Application Engineering Bulletin AE R4