Superheat & Subcooling – Explanation & Role in HVACR Efficiency
Do you know that your compressor was designed to handle only vapor, and the presence of liquid refrigerant can damage your compressor?
Proper control of subcooling and superheating helps protect your compressor, optimize the efficiency, control temperature, and save energy for the HVAC and refrigeration cycle.
But how to control these two parameters? The answer is an expansion valve, please read what is expansion valve first.
Besides, Before understanding superheating and subcooling, you also need to know what is a refrigeration system.
What is Subcooling in HVACR?
Subcooling is lowering the liquid refrigerant temperature below its saturation or condensing temperature.
After the refrigerant gas is condensed into the liquid state, it flows through the expansion device and into the evaporator.
Knowing subcooling is essential to ensure that when the liquid finally gets over to the metering device, it is a complete liquid with no vapor present.
If vapor is present, it is inefficient for the refrigeration cycle.
What is Superheat in HVACR?
Superheating means the temperature increases in vapor form in the evaporator coil.
It is the process of heating a vapor refrigerant above its boiling temperature to ensure that it is fully vaporized before it enters the compressor so there is no liquid.
Superheating is essential because it helps prevent liquid refrigerant from entering the compressor, which can cause damage as it is designed to handle only vapor.
What Is the Correct Level of Subcooling and Superheating?
Determining your correct level of subcooling and superheating depends on the indoor and outdoor temperature.
Some systems may need up to 16° of subcooling for the highest efficiency.
Still, the most common subcooling is 10-12° and generally between 10° to 25 for superheating, depending on the application.
The correct level of subcooling for an air conditioner system is 10°F to 18°F that uses a thermostatic expansion valve.
The superheat for AC application usually should be 10°F and 15°F(electronic expansion valve), though it depends on ambient temperature.
For most fridges, the recommended superheat is 10°F to 20°F to ensure efficiency, and the recommended subcooling is 10°F to 20°F.
The subcooling temperature is not a fixed value so you can calculate it for your specific system.
What is the right level of Subcooling and Superheating, you need to know how to choose the right expansion valve.
How Do You Calculate Subcooling and Superheating?
Positive values for subcooling and superheating mean that the refrigerant is in a fully liquid or vapor state, while negative values for subcooling suggest a potential issue.
So you need to measure temperatures at specific points in the refrigeration cycle and use these superheat and subcooling calculating formulas.
Subcooling = Boiling point – Current Temperature
Suppose the boiling point temperature is 90°F and the current temperature is 100°F, so the subcooling = 90°F−100°F = −10°F.
Superheat = Current Temperature – Boiling Point
If the actual temperature is 40°F and after the vaporization of refrigerant, the temperature becomes 20°F, Superheat = 40°F−20°F = 20°F.
To help you better calculate superheat and subcooling, you should understand how expansion valves work.
How to Adjust Subcooling and Superheating?
Properly adjusting subcooling and superheating is crucial for the efficient and reliable operation of the HVACR system.
We take the internally balanced thermostatic expansion valve as an example to explain how to adjust the subcooling and overheating.
If you use an externally balanced thermostatic expansion valve, please understand what an internal and external thermostatic expansion valve is before making adjustments.
Adjust the subcooling and superheat on TXV(thermostatic expansion valve), ensure proper subcooling, required pressure drop, and correct bulb placement.
For minor adjustments, locate the hex cap at the base of the adjustable valve.
To increase superheat, turn clockwise, and to decrease, turn counterclockwise.
Make half-turn adjustments to stabilize and then recheck the superheat.
Different types of expansion valves have different adjustment methods, so please know the different types of expansion valves first.
Additionally, it is essential to know equipment-specific considerations and manufacturer recommendations for the proper subcooling and superheating adjustment.
Relationship Between Subcooling, Superheating, and Compressors
Superheat and subcooling have a relationship with the compressor, and liquids can cause significant damage or increase efficiency in the compressor.
Subcooling ensures refrigerant entering the compressor is in its liquid state, and superheating guarantees that the compressor receives fully vaporized refrigerant and saves compressor components from damage.
Maintaining a full liquid line for expansion device subcooling optimizes refrigeration cycle efficiency and ensures no liquid refrigerant in the compressor; superheating enhances the compressor’s efficiency.
Of course, there are many brands of refrigerant compressors in the world, such as
Relationship Between Subcooling, Superheating, and Expansion Valve
To help you better understand the relationship between expansion valve and superheat and cooling.
The opening of the expansion valve determines the superheat and subcooling of the refrigeration and air conditioning system.
The degree of superheat and subcooling determines the opening of the expansion valve.
The expansion valve mainly regulates the flow and speed of the refrigerant.
If there is less refrigerant in the evaporator, it means the degree of superheat is large.
If there is more refrigerant in the evaporator, it means the degree of subcooling.
Therefore, the function of the expansion valve is to continuously change the valve opening to control the refrigerant entering the evaporator, thereby controlling the degree of superheat and subcooling.
Watch a video on how an expansion valve works here to better understand subcooling and superheating.
If you have any expansion valve brand needs, please contact us today.