Refrigeration is basically the elimination or removal of heat from a particular space or substance or material so as to lower its temperature corresponding to the surrounding temperature.
Refrigeration is a cycle which the refrigerant goes through and passes various stages in a piped and sealed system.
Basic Refrigeration Cycle
- Starts at the compressor
- Low pressure vapor refrigerant is compressed and discharged out of the compressor.
- The refrigerant at this point is a high temperature, high pressure, “super-heated” vapor.
- The high pressure refrigerant flows to the condenser by way of the “Discharge Line”.
- The condenser changes the high pressure refrigerant from a high temperature vapor to a low temperature, high pressure liquid and leaves through the “Liquid Line”.
- The high pressure refrigerant then flows through a filter dryer to the Thermal Expansion valve or TXV.
- The TXV meters the correct amount of liquid refrigerant into the evaporator.
- As the TXV meters the refrigerant, the high pressure liquid changes to a low pressure, low temperature, saturated liquid/vapor.
- This saturated liquid/vapor enters the evaporator and is changed to a low pressure, dry vapor.
- The low pressure, dry vapor is then returned to the compressor in the “Suc0on line”.
- The cycle then starts over.
There are 4 important components in a refrigeration cycle:
- Metering Device
The compressor is the heart of
The compressor has two inlets namely Suction and Discharge.
The discharge line is the outlet line of the compressor. After the vapor is compressed it becomes a high presssure vapor and goes through the discharge line to the condenser.
The compressor acts as a pump of the refrigerants
The “Discharge Line” leaves the compressor and runs to the inlet of the condenser. Because the refrigerant was compressed, it is a hot high pressure vapor (as pressure goes up – temperature goes up). The hot vapor enters the condenser and starts to flow through the tubes.
Cool air is blown across the outside of the finned tubes of the condenser (usually by a fan or water with a pump). Since the air is cooler than the refrigerant, heat jumps from the tubing to the cooler air (energy goes from hot to cold – “latent heat”).
As the heat is removed from the refrigerant, it reaches it’s “saturated temperature” and starts to “flash” (change states), into a high pressure liquid. The high pressure liquid leaves the condenser through the “liquid line” and travels to the “metering device”. Some0mes running through a filter dryer first, to remove any dirt or foreign par0cles.
The Evaporator is located inside the medium to be cooled or the room.This is where the heat is removed from the surrounding into the refrigerant.
The low pressure liquid from the metering device goes into the evaporator inlet. The evaporator carries the cooler refrigerant in its tubes thus it absorbs the warm air in the room and this changes the temperature of the refrigerant.
Metering devices regulate how much liquid refrigerant enters the evaporator . Commonly used metering devices are, cap tubes (small copper tubes), TXV’s (thermal expansion valves), and single opening orifices.
The metering device tries to maintain a preset temperature difference or “super heat”, between the inlet and outlet openings of the evaporator. As the metering devices regulates the amount of refrigerant going into the evaporator, the device lets small amounts of refrigerant out into the line and loosens the high pressure it has behind it. The metering device tries to maintain a preset temperature difference or “super heat”, between the inlet and outlet openings of the evaporator.
Now we have a low pressure, cooler liquid refrigerant entering the evapora0ve coil (pressure went down – so temperature goes down).
A very common type of metering device is called a TX Valve (Thermosta*c Expansion Valve). This valve has the capability of controlling the refrigerant flow. If the load on the evaporator changes, the valve can respond to the change and increase or decrease the flow accordingly.
The TXV has a sensing bulb a`ached to the outlet of the evaporator. This bulb senses the suc0on line temperature and sends a signal to the TXV allowing it to adjust the flow rate. This is important because, if not all, the refrigerant in the evaporator changes state into a gas, there could be liquid refrigerant content returning to the compressor.
This can be fatal to the compressor. Liquid cannot be compressed and when a compressor tries to compress a liquid, mechanical failing can happen. The compressor can suffer mechanical damage in the valves and bearings. This is called “liquid slugging”.
Normally TXV’s are set to maintain 10 degrees of superheat. That means that the gas returning to the compressor is at least 10 degrees away from the risk of having any liquid.