by Mr. Eric Mayert MD
Published 3 years ago
Updated 2 years ago
If we measure the temperature on the liquid line exiting the condenser coil then we know the end temperature after the refrigerant has lowered in temperature. Subtract the lower temperature measured on the liquid line from the saturated temperature and you have subcooling!Apr 8, 2020
How do you measure subcooling?
Record the actual temperature of the liquid leaving the condenser with a surface temperature probe. Subtract the liquid pipe temperature (at the exit of the condenser) from the converted temperature (from the high side pressure using the pressure/temperature comparator). The difference is the amount of sub cooling.
What is meant by subcooling?
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled".
What is subcooling and why is it important?
The most basic meaning of subcooling is any temperatures below the saturation temperature. Generally, the lowest temperature a condenser can achieve, the better. In other words, the colder the refrigerant is as it flows into the evaporator coil, the more heat it will be able to absorb.
What is a good range for subcooling?
Subcooling on systems that use a thermostatic expansion valve (TXV) should be approximately 10°F to 18°F. Higher subcooling indicates excess refrigerant backing up in the condenser.
What happens if subcooling is too high?
If the subcooling is too high, the system will be overcharged, reducing performance, efficiency, and ultimately damaging compressor valves and start components.
What causes high subcooling?
High Subcooling is an indication that more than the designed amount of refrigerant is “backing up” or “packed” into the condenser. This can be caused by overcharge, restriction (such as a contaminated line drier or kinked liquid line), or an undersized or failing closed metering device.
Does adding refrigerant increase subcooling?
The difference between the measured liquid line temperature and the saturated condensing temperature is the liquid subcooling. Add refrigerant to increase subcooling.
What is a subcooling in HVAC?
Subcooling occurs when you cool a vapor below the temperature at which it turns into a liquid. Let's use the same refrigerant with a high pressure boiling point of 120 degrees for the following example: The refrigerant is a 140 degree vapor heading into the condenser.
What is normal subcooling for 410a?
Most heating and cooling systems should operate at a superheat of 10F at the evaporator and between 20F to 25F at the compressor. if your HVAC system has a thermostatic expansion valve (TXV), the subcooling should be between 10F and 18F.
How do you fix low subcooling?
Low superheat with low subcooling indicates that your evaporator is low on heat and has limited refrigerant in the condenser. To increase superheat, you can try turning the adjusting screw clockwise on the valve setting. Then, add a refrigerant to increase subcooling.
Does subcooling change with temperature?
Since both superheat and subcooling are changes in temperature, they are both sensible heat processes.
What does a negative subcooling mean?
When a negative subcooling value exists, it is a reflection of the cooling system's failure to properly decrease the refrigerant's temperature throughout the subcooling process.
What is subcooling and superheat?
What are superheat and subcooling? Superheat is defined as the amount of heat added to a vapor above its boiling point. Subcooling is defined as the amount of heat removed from a liquid below its condensing point.
What is sub cooling HVAC?
Subcooling occurs when you cool a vapor below the temperature at which it turns into a liquid. Let's use the same refrigerant with a high pressure boiling point of 120 degrees for the following example: The refrigerant is a 140 degree vapor heading into the condenser.
What is the normal superheat and subcooling?
“Typically” on TXV systems the Superheat will range between 8 to 28 degrees with a target of about 10 to 15 degrees. The Subcool range on TXV systems will range from about 8 to 20. Although this is not enough information to charge a system, it does give a technician a better understanding of the systems operation.
What is normal subcooling for 410a?
Most heating and cooling systems should operate at a superheat of 10F at the evaporator and between 20F to 25F at the compressor. if your HVAC system has a thermostatic expansion valve (TXV), the subcooling should be between 10F and 18F.
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