A very good method of troubleshooting is to enter the received data into a pressure/enthalpy diagram (see Figure 9.1). When the compression cycle has been plotted, it can be analyzed and compared with a "normal" cycle. It is also easy to compare the plotted data with data from the suppliers' software.
Refrigerant Side Parameters
To plot the compression cycle in a diagram, five measurements are required:
- Suction pressure (at evaporator outlet/compressor inlet)
- Suction temperature
- Discharge pressure (at compressor outlet/condenser inlet)
- Discharge temperature
- Liquid temperature (at condenser outlet/expansion valve inlet)
Liquid Side Parameters
To evaluate the BPHE heat exchanger performance, two additional temperatures are required for each BPHE:
- Liquid temperature into the evaporator
- Liquid temperature out of the evaporator
- Liquid temperature into the condenser
- Liquid temperature out of the condenser
To evaluate the heat exchanger performance, the system capacity must be known. This can be established in several ways:
- The easiest, and normally most accurate, way is to process compressor data through the manufacturer's software with measured data as input. Nominal data and tables are normally based on other conditions.
- Estimate the flow of liquid from:
- Flow meters
- Pressure drop over valves
- Pump characteristics
- Differential pressure over pumps The capacity can be calculated from the liquid flow and the temperatures (see chapter 1.3).
- Measure the electrical input to the compressor (pumps and fans excluded). Use compressor software to calculate the capacity.
The first method is by far the easiest, and it is very accurate provided the pressures and temperatures are measured correctly and the compressor is not damaged. This can be verified by checking the compressor efficiency in the diagram, provided the normal compressor efficiency is known.