Specifications

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6720649497 SM HP270-1 2012/09 en
7.2 Evaporator under performance
The evaporation process is sensitive and potentially unstable. Minor changes in performance have major effect on
the system performance (COP).
A one-degree change in the evaporation temperature changes the COP by approximately 3% and an unstable
process could also cause the evaporation temperature to fluctuate, with a potential risk of freezing in the
evaporator. The critical parameter for the system performance is the saturated pressure at the compressor inlet.
Check Points:
- Check the installation
- Check the evaporation temperature at the compressor inlet
Use compressor data to compare with cooling data
- Check the evaporation pressure at the evaporator outlet
Compare the evaporation pressure at the outlet with the evaporating pressure at the compressor inlet. This
difference should be kept to a minimum to avoid unnecessary losses in cooling capacity. This should be
measured in the suction side of the compressor (pressure gauge available). By measuring the temperature
in the evaporator and knowing the calculated pressure drop, we can check actual pressure drop.
- Check the amount of superheat
A high level of superheating could indicate that the expansion valve is not releasing enough floe to the
evaporator or vice-versa.
- Check the expansion valve and the positioning of the bulb
Make sure that the valve is able to regulate. If the bulb is too close to the evaporator, the evaporation
temperature may fluctuate. The bulb should never be placed on the bottom of the suction line, because refrigerant
droplets may evaporate at this point, affecting the regulation and causing punctual low temperatures.
- Check fins alignment and no dirtiness deposition, because it will cause an underperformance due to the
lack of heat exchange between air temperature (between +5 and + 35ºC or -10 and + 35ºC according to the
correspondent model) and the liquid gas inside of evaporator area.
Pict.58 – Expansion valve detail (cut model)
Evaporator
Condenser
Bulb capillary