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Ideal temperature intervals of Entering/Leaving water temperatures is from5 to7 degrees C but sometimes the interval becomes close to each other.
> What is superheat?
Superheat refers to the number of degrees a vapor is above its saturation temperature (boiling point) at a particular pressure.
> Why is it important to know the superheat of a system?
Superheat gives an indication if the amount of refrigerant flowing into the evaporator is appropriate for the load. If the superheat is too high, then not enough refrigerant is being fed resulting in poor refrigeration and excess energy use. If the superheat is too low, then too much refrigerant is being fed possibly resulting in liquid getting back to the compressor and causing compressor damage.
> What is subcooling?
Subcooling is the condition where the liquid refrigerant is colder than the minimum temperature (saturation temperature) required to keep it from boiling and, hence, change from the liquid to a gas phase.
The amount of subcooling, at a given condition, is the difference between its saturation temperature and the actual liquid refrigerant temperature.
> Why is it important to know the subcooling of a system?
Subcooling increases the efficiency of the system since the amount of heat being removed per pound of refrigerant circulated is greater. In other words, you pump less refrigerant through the system to maintain the refrigerated temperature you want. This reduces the amount of time that the compressor must run to maintain the temperature. The amount of capacity boost which you get with each degree of subcooling varies with the refrigerant being used.
Also subcooling is beneficial because it prevents the liquid refrigerant from changing to a gas before it gets to the evaporator. Pressure drops in the liquid piping and vertical risers can reduce the refrigerant pressure to the point where it will boil or "flash" in the liquid line. This change of phase causes the refrigerant to absorb heat before it reaches the evaporator. Inadequate subcooling prevents the expansion valve from properly metering liquid refrigerant into the evaporator, resulting in poor system performance.
Degree superheat and sub cooling beyond the saturation temperature is found in Refrigeration systems wherein it is required to have lower temperatures for freezing and other lower process temperatures required.
In Airconditioning the lowest point is approximately 4.4 deg C, and that is called comfort cooling and freezing the water beyoond such temperatures.
However when we use glycol it is achieved to have lower temperatures for TES-Thermal Energy Storage systems where DC District Cooling and Ice banks are employed using Heat Exchangers.
Super heat and sub cooling are related to refrigeration status, both have impact on performance of refrigeration cycle, and on the Qadd in the evaporator and Qrej from the condenser, the more sub cooled/super heated the water entering and leaving evaporator the more Qadd in the evaporator which maximize the performance and efficiency but on the other hand it also maximize the Qrej required to be removed in the condenser and thus maximize the condenser size and related fans or pumping power.....and this is kind of irrelevant to water entering and leaving temperatures from the evaporator as this is more related to the size of FCU/AHU and how well the control system is designed and integrated with HVAC equipments to maintain a minimum water temperature difference and thus save pumping power on building side
