The discharge superheat can be calculated with the temperature difference.
Discharge Superheat = Discharge line temperature at compressor – Temperature of saturated liquid
The discharge line temperature is measured at the service valve provided on the compressor’s discharge. The thermocouple (Temperature measurement device) is used to measure the temperature of the discharge.
The saturated temperature can be obtained by measuring the pressure gauge pressure. This pressure value is converted into the temperature using the pressure-temperature chart.
What is discharge superheat?
It is a critical concept to understand the performance of a system
The total superheat is measured accurately in the system to know negligible energy loss or gain
difference between the two temperatures. The first one is the discharge temperature measured on the compressor discharge line. The second temperature is the saturation temperature of the working fluid in the system.
Discharge superheat temperature
In superheat, the temperature plays a vital role in the system’s performance.
The discharge temperature should be less than 225 ° F. If the temperature is increased more than 225 ° F, the system’s performance is decreased.
Most of the compressors used in refrigeration and air conditioning can withstand temperatures up to 225 ° F. An increment in the temperature of more than 225 ° F can cause some damage to the system.
The higher temperature can cause oil breakdown, formation of the acid and failure of rings. The compressor will be considered overheated above this temperature limit. The system will work efficiently by continuous monitoring the discharge temperature of the compressor.
The following are the probable reasons for the overheating of the compressor:
- The compression ratio is higher
- The condensing pressure is very high
- The suction pressure is too low
- The compressor superheat high
Discharge superheat formula
It is obtained from the difference in the temperature.
Discharge Superheat = Discharge line temperature at compressor – Temperature of saturated liquid
It is measured at the service valve provided at the outlet of the compressor. This service valve is six inches far from the compressor outlet.
The saturation temperature is founded by using the P-T chart. The saturation pressure is noted at the suction line with the help of the bourdon tube pressure gauge.
This superheat is necessary to calculate the performance of the compressor and system.
What causes low discharge superheat?
The low discharge superheat can be caused for the following reasons.
- The refrigerant is excessive in the system.
- There is less heat absorbed in the evaporator coil
- Insufficient insulation over sensing bulb of a thermal expansion valve
- Excessive refrigerant feeding into the metering system
- There is less airflow through the evaporator than the actual requirement
- There is less airflow through the condenser than the actual requirement
- The component failure like poor motor bearing, obstruction in the system etc.
- The system components are dirty, corroded, inefficient etc.
If the system possess low superheat, then the following problem may arise in the system,
- The working of the thermal expansion valve is inefficient
- The condenser pressure is increased and affects the system’s performance
- The discharge pressure is highly decreased
- The heat load is increased due to insufficient heat transfer
- The overfeeding of the compressor
How to calculate discharge superheat?
The calculation of the this is similar to the super cool and superheat in the system
It is calculated by measuring discharge superheat and subtracting it from the suction superheat.
It is a difference in the temperatures. The equation of the this superheat is given by the following equation.
Discharge Superheat = Discharge line temperature at compressor – The temperature of saturated liquid
It is used to measures the compressor performance. The compressor is the essential mechanical component of most of refrigeration and the air conditioning system. The efficiency of system is highly dependent on the compressor’s performance.
The compressor can withstand efficiently at the temperature 225 ° F. If the temperature of the discharge is increased above 225 ° F, the compressor’s performance degrades accordingly.
How to calculate compressor discharge superheat?
The compressor superheat calculated similarly to normal superheat
The compressor discharge superheats, and the discharge superheat is the same. Discharge Superheat = Discharge line temperature at compressor – Temperature of saturated liquid
How to increase discharge superheat?
This superheat can be increased with the following different steps.
- Decrease the overfeed of refrigerant
- Clean the evaporator coil if it gives less heat transfer
- clean the condenser coil if the heat transfer is insufficient
- decrease the refrigerant if it is excessive in the system
- Provide proper insulation over the sensing bulb of the thermal expansion valve
- Keep the appropriate airflow through the evaporator
- Maintain the proper airflow over the condenser coil
- Remove the dirt and corrode tubes from the system and repair
Why is discharge superheat importantly?
This superheat’s monitoring is required in any refrigeration system
It affects the performance of the system. If it is low, then the system may fail to work efficiently.
This superheat is highly affecting the working of the compressor. There are some technical reasons for insufficient discharge superheat. It is crucial to maintain discharge superheat for efficient system’s working.ong>
Discharge superheat range
The range of the discharge depends on the scale of the system.
The compressor can withstand efficiently at the temperature 225 ° F. If the temperature of the discharge is increased above 225 ° F, the compressor’s performance degrades accordingly.
The discharge superheat depends on many factors, so it is difficult to decide any range for discharge superheat. The compressor’s discharge temperature should not increase more than 225 ° F. The continuous measuring and monitoring of the temperature can control the discharge superheat.
Screw compressor discharge superheat
The screw compressor is a special type of compressor for particular applications.
The discharge superheat is always lower in the screw compressor than the reciprocating compressor due to low discharge temperature.
In a screw compressor, the oil is injected into the compressor; the oil cools the system. The temperature of discharge in the screw compressor is low.
In a reciprocating compressor, there is no oil injection system. The temperature at discharge in the reciprocating compressor is more than the screw compressor.
The discharge temperature also depends on the pressure ratio, even if suction superheat is constant.
I am Deepak Kumar Jani, Pursuing PhD in Mechanical- Renewable energy. I have five years of teaching and two-year research experience. My subject area of interest are thermal engineering, automobile engineering, Mechanical measurement, Engineering Drawing, Fluid mechanics etc. I have filed a patent on “Hybridization of green energy for power production”. I have published 17 research papers and two books.
I am glad to be part of Lambdageeks and would like to present some of my expertise in a simplistic way with the readers.
Apart from academics and research, I like wandering in nature, capturing nature and creating awareness about nature among people.
Also refer my You-tube Channel regarding “Invitation from Nature”
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