-
- author "me"
- tags "Cooling 101"
- description ""
- fileName "Tech method lesson 1b"
- freezingBlueDBID -1.0
- Subcooling measurement
- When you remove heat from a vapor, it condenses into a liquid.
- too much refrigerant in the high side will cause refrigerant to back up in the condenser limiting the ability of the condenser to reject heat.
- This quickly raises the condensing temperature and allows more time for the liquid too cool before reaching the outlet of the condenser.
- Resulting in high subcooling.
- The higher the subcooling the more refrigerant that is contained in the high side of the system.
- Some subcooling is required to ensure a steady flow of liquid to the metering device however too much will reduce the capacity of the condenser.
- Cold air flowing through the condenser coil increases its ability to reject heat and increases its capacity.
- Under cold ambient conditions it is necessary to simulate design ambient temperature by blocking off part of the coil to achive a condensing temperature of 100 - 110 degrees.
- Most gauges have both temperature and pressure scales get in the habit of reading the temperature instead of pressure think in terms of condensing temperature not head pressure.
- In most systems anything over 15 degrees subcooling is considered excessve consult the manufactures specifications.
- Excessive subcooling is caused by;
- Noncondensables,
- Overcharge,
- Restriction.
-
Noncondensables
- Air or other noncondensables add pressure to the system without raising the temperature which distorts the pressure/temperature relationship.
- Pump the system down to ensure all the refrigerant is in the condenser coil then disable the compressor and run the outdoor fan till air in/out of the coil are the same when compare the pressure to a PT Chart if there is a higher pressure than the temperature (5 degrees) then there are non condensable in the system.
- Symtoms of non condensables in the system.
- Low side = normal side pressure and saturation temp. Normal superheat.
- high side = high discharge pressure, high subcooling
-
Excess refrigerant
- If subcooling is high and the system does not contain non-condensable then we have excess refrigerant in the high side of the system.
- The system may be overcharged or the excess refrigerant has been borrowed form the low side (restriction)
-
Over charge
- If the subcooling is excessive we must check superheat to dtermine if the system is over charged or restricted.
- Excessive subcooling with a high superheat would indicate a restriction.
- Xcessive subcoolng with a low superheat (fixed metering device) or normal superheat (txv) would indicate an over charge.
-
Condenser airflow
- Measure the air temperature entering the condenser and the air temperature leaving the condenser the difference should be no more than 20 degrees.
- The slower the air moves across the condenser coil the more time the air has to absorb heat.
- Causes;
- Dirty coil, improper fan blade or position in shroud, wrong RPM motor or wrong rotation motor.
High efficiency unit is not more than 15 degrees dfference.
|
|
