If you experience unexpected or unrealistic data it is important to methodically check data and possible sources of error. All analysing of performance will regardless of method depend on both the accuracy of input and the use of proper calculations. The calculations is in the case of ClimaCheck defined by the used template and there are different templates for different applications. With ClimaCheck you can use the following troubleshooting method if you experience a deviation from expected or references values.
1. Check measurement by measurement that each value is realistic. The best way to do this is obviously with a second meter if you have a specific issue but there are several means of identifying issues by looking at the measurements.
a. Pressure sensors are typically quite linear with the most common error affecting offset. This means that it is often enough to checked versus atmosphere pressure but comparing with a traceable reference is always best.
i. At stand still the pressure normally equalise if there is no solenoid. If both pressure sensors show the same you can almost be certain the measurements are good as it is a low likelihood two sensors with different ranges should show the same. You can also run pump/fans and stop compressor pressure should then equalise with the temperature of incoming air/water.
ii. It is normally also know what pressure is expected at a given exiting air/water temp of evaporator/condenser. Small deviations of pressure measurements has a low impact on performance and large should be identified by strange pressure readings.
b. Temperature sensors/measurements with ClimaCheck is done with high accuracy Pt1000 class A sensors these can best be checked versus a known traceable reference.
i. If you run the system with some flash gas at the sight glass the sub cool should be near zero.
c. Power measurement most often creating “problems”. There are many computations with 3-phase power measurements and it is more seldom alternative measurement equipment with high accuracy is available.
i. The easiest way to check is to compare power with compressor manufacturer data (the leading manufacturers often have softwares with reliable data whereas some offer less reliable data. It is important if you want to have high accuracy to be aware of that inaccuracy increase if you are below 20% of range of current transformers.
ii. You can check the power with a multimeter Volt/Amp measurement together with an assumption of 0.8-0.85 as normal power factor if you do not have detailed info. But this is more of an estimate.
2. The only assumption the ClimaCheck method use is the energy balance over the compressor and the 93% will be a good assumption for heat losses for hermetic and semi hermetic compressors (the maximum identified in a survey was 10% and minimum 3% e.g. the error will be maximum 3-4% at extreme cases). This is only true if there is no additional cooling e.g. heat exchange with ambient air in a cabinet/room or external cooling through special devices such as oil or water cooling. External cooling can be:
a. Liquid carry over from evaporator. This will give a warning for low superheat but also give a fictive high compressor efficiency (also gives warning) and fictive high COP/Capacity. Very few if any compressor manufacturers accept liquid carry over as this will drastically affect compressor lubrication as the liquid carry over will increase the refrigerant content of the oil which decrease the viscosity that result in increased wear and shortened lifetime expectance. Liquid carry over is a common problem on air to air and air to water heat pumps that are often originally designed for.
b. Air cooling; if forced air is blown over the compressor the heat losses will increase in particular if the air is cold. This can be the case on condensing and low temperature semi hermetic compressors with fans to cool cylinder head. This can be handled:
i. By shielding the compressor from the forced air flow if the pressure ratio is not so high that extra cooling is required or by shutting of the fan if the conditions allow this e.g. if the discharge is monitored to stay within allowable limits. Shielding is often easily done with a sheet of insulation or cardboard or similar. There is no requirement to make it tight just to remove the forced air as this increase the heat losses drastically.
ii. By adjusting the heat losses in the constant sheet. To identify what heat loss to use there are several means either experience can be used or comparison with the what is the measurement if the system can be monitored under known condition without fan.
c. Oil/water cooling. This is common on larger compressor in particular in the industry and require additional measurements and special templates for calculations see special information on this.
d. Liquid injection. To inject liquid injection can extend envelope of a compressor but as it decrease efficiency to inject liquid refrigerant it should only be used when necessary e.g. extreme conditions. This is often controlled by discharge or motor temperature. These systems require special calculations and accuracy can be significantly affected if effect of liquid injection is not known and taken into account.