Subcool Hvac Definition

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.

Why is subcooling important in HVAC?

Condenser subcooling ensures that there is a liquid seal at the condenser's bottom so the liquid line or receiver will not be fed with vapors. This condition prevents any noncondensables, like refrigerant vapor or air, from leaving the condenser's bottom and entering the receiver or liquid line.

Whats a good superheat and Subcool?

“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.

What does high subcooling mean HVAC?

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.

What is normal subcooling temp?

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. On TXV systems with high superheat, be sure to check the subcooling as refrigerant is added.

What is the purpose of subcooling?

In a refrigeration system, subcooling is used to bring the refrigerant from the condenser to the thermostatic expansion valve (VTX) in a completely liquid form. When exiting the compressor, the refrigerant is in a high temperature and high pressure state.

What happens if subcooling is too low?

A reminder why subcooling is important: Among other things, if the subcooling is too low, the condenser will “run out of” refrigerant prematurely at higher load conditions, overheating the compressor and reducing performance and efficiency.

How do you adjust subcooling?

First remove the adjusting stem cap. If your sub cooling is too low turn the adjustment stem

Does subcooling increase capacity?

Subcooling the main liquid line will increase refrigeration capacity while improving energy efficiency. Subcooling in this document refers to the use of a separate refrigeration source to lower the temperature of the main liquid line.

How do I know if I need subcooling?

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!

What happens if superheat is too low?

A low or zero superheat reading indicates that the refrigerant did not pick up enough heat in the evaporator to completely boil into a vapor. Liquid refrigerant drawn into the compressor typically causes slugging, which can damage the compressor valves and/or internal mechanical components.

What happens if superheat is too high?

Too high of a superheat can cause the heat of compression to increase, causing the temperature at the discharge valves to increase. If the temperature increases beyond its safe operating temperature, it will cause damage to the compressor.

What does it mean if you have low subcooling and low superheat?

If superheat is low and sub-cooling is low: Orifice could be too big, there is no orifice in the unit of the orifice is stuck and refrigerant is by-passing it. Superheat is telling you what is going on in the evaporator. Sub Cooling is telling you what is going on in the condenser.

Does subcooling change with outdoor temperature?

On a system with a thermostatic expansion valve, the subcooling will not be affected very much by the ambient conditions. This is because at higher pressure differentials the TXV will close slightly to maintain the desired superheat. As a result, the subcooling will not change appreciably with the ambient.

Does a dirty condenser cause high subcooling?

Higher Subcooled Liquid Temperatures With a dirty or blocked condenser, even the subcooled liquid temperature coming out of the condenser will be at a higher temperature. This means that the liquid temperature out of the condenser will be further from the evaporating temperature.

Does airflow affect subcooling?

Common HVAC Airflow Problems The air that flows across the coil has to be just right. Otherwise the duct system won't function properly. Occupants will lose comfort, and the building will lose efficiency. Too much air across the evaporator coil will cause low sub-cooling in the HVAC system.

What is the formula for subcooling?

Calculate the subcooling as follows: subcooling = CT – T. For a refrigerant blend use the saturated liquid (bubble) temperature as the condensing temperature. Subcooling will not usually occur in the condenser unless liquid backs up in the condenser.

Can you check subcooling in heat mode?

Subcool and superheat can still be checked in heat mode, the problem is since there are rarely any set guidelines, it is difficult to tell when the charge is set correctly by simply checking subcool or superheat alone.

Will a dirty condenser cause low subcooling?

An air conditioner with a dirty condenser coil may also lose some of its ability to provide cool air. A dirty condenser coil with have a reduced ability to transfer heat to the outside air and this can lead to a less effective cooling system.

What are the advantages of subcooling of refrigerant?

Subcooling is desirable, because it increases refrigerating effect and reduces the required compressor power. Since COP is ratio of refrigerating effect to work done, therefore, COP of system increases.