The following is from a report based on the findings of a ClimaCheck Performance Analysis on 16 Refrigeration Circuits over 4 Water Chillers in order to verify Cooling Capacity and other general performance parameters (COP, Compressor Isentropic Efficiency, etc)__________________________________________________________________________

ClimaCheck Performance Analyser Test Runs

Once steady state conditions had been achieved, each Performance Test was run for a duration of approximately 15 minutes at recording intervals of 30 seconds.

Test Conditions

In order to ensure stable operation and a realistic performance test, each Chiller was run under the maximum load conditions that could be applied with all 4 Compressors running during each individual Compressor/refrigeration circuit test so as to achieve realistic operating conditions for the Evaporator, Condenser and Compressor being tested.

Where Circuit 4 test on Chiller 101 is concerned, we noticed the loss of several kilowatts cooling capacity in comparison with other circuits and conclude that this was due to a slightly reduced building load at that time and a possible disparity in water flow rates through the Condensers/Evaporators for this circuit as a result of the slightly different pipe work length arrangement on the water circuits, as shown in the following photograph:

Condenser Water Pipe Work - Uneven Lengths

Water Chiller No. 102

On initial test of Chiller 102 it became apparent that superheat was rather high on Circuit 1 and we made adjustments to this prior to running the 15 minute recording session. We succeeded in reducing superheat to around 8K, but could not take this any further as the Expansion Valve at this point was fully open. This implies that the Expansion Valves may be slightly undersized at part load conditions due to a lower pressure ratio, but it is anticipated that this will self-correct at higher summer operating conditions when the increased pressure ratio will drive more refrigerant through the Expansion Valve.

During the first set of tests on Wednesday, it was apparent that the performance consistency of each refrigeration circuit was extremely stable and this in turn confirmed that the water flow rate to each of the Heat Exchangers (Condensers and Evaporators) was also consistent.

It is of course important to remember that the cooling capacity of each refrigeration circuit is directly related to the mass flow of water passing through the Plate Heat Exchanger / Evaporator and if this is either higher or lower than design, the Water Chiller will respond proportionally. In other words, an excess water flow rate through one circuit will show this delivering a higher cooling performance than another circuit with a lower water flow rate.

The same is true for the water cooled condensers, where these Heat Exchangers rely on the correct flow rate in order to reject the heat energy to the Cooling Towers. For example, the load imposed at the Evaporator (kW), plus the Power Input (kW) will be forcedly rejected at the Condenser and if the water flow rate is below design, a higher water leaving temperature will be recorded. This would partially impair the performance of that Condenser and the refrigeration performance of this circuit as a whole will be reduced in terms of cooling capacity and COP.

Consequently, in order to balance such machines, it is wise to apply recording instrumentation such as ClimaCheck, with the appropriate sensors located at all inlets/outlets of the Plate Heat Exchangers in order to balance the water flow correctly during the commissioning stage.

Towards the end of the test on Water Chiller No.102 – Circuit 4, minor adjustments were made to the Expansion Valve to improve the performance and this can be seen in the COP column (figures in red) where the COP exceeded 4. The recording file was terminated at this point, but more minor adjustments to improve the machine still further were made thereafter.

Water Chiller No. 1

Once conditions had stabilised on Water Chiller No.1, we commenced our test on Circuit 1 at around 09:40. It was immediately evident that due to the existence of a Heat Exchanger between the Condenser water from the Cooling Towers and the Water Cooled Condensers of the Water Chiller (not the case on Water Chillers 101 and 102) that the entering and leaving water temperatures for the Condensers on this machine was higher than the temperatures experienced on Chillers 101 and 102. Entering water temperatures were in the order of 31°C and a leaving water temperature of around 36°C was apparent at the start of this test. This of course reduced the cooling capacity of the machine, which was in close accord with the Hitachi performance data.

The tests for Water Chiller number 1 were completed at approximately 12:15 and all circuits behaved in a very stable manner. Minor adjustments were made to refrigerant charge on one circuit prior to its performance being recorded, this having brought about a slight improvement in performance. (Minor refrigerant charge adjustments were made to a few circuits prior to recording test results).

Water Chiller No. 2

Testing of all 4 circuits commenced at approximately 12:40.

Digital Flow Meter Readings

Whilst running the final test on Circuit 4 of Water Chiller No. 2, we connected a digital flow meter to the Orifice Plate of the Condenser water supply/return pipe work and read a flow rate of approximately 47l/s. We then compared this with the heat of rejection of Circuit 4 at that time and after multiplying by 4, calculated a flow rate of 54l/s. I am inclined to suspect that the Orifice Plate is not providing a true reading, since this is located too close to a bend and there is also a flow meter within a short distance of the Orifice Plate:

We then conducted a similar test on the chilled water circuit of Water Chiller No. 2, which has a well-installed Orifice Plate. The digital meter showed a flow rate of 38.5 l/s via the Orifice Plate and the ClimaCheck cooling performance on Circuit 4, multiplied by 4, showed a total

mass flow rate of 39.46l/s. Accordingly, in this instance, the percentage error was much smaller than that experienced on the Condenser water circuit.

CLIMACHECK TEST RESULTS

The following ClimaCheck screen dumps show a) the “Table” view of results, the top line of which is the final reading and b) a graphical output of key system parameters across the full test run period of approximately 15 minutes for each Refrigeration Circuit:

Water Chiller No. 101 – Circuit 1

QUESTIONS & ANSWERS

The following questions were raised at the Meeting 9th March and I have responded accordingly:

1. Please provide a simple explanation of how the cooling capacity of a refrigeration machine is derived from the values recorded

The ClimaCheck Performance Analyser consists of a Data Logger capable of recording a number of temperatures, refrigeration system pressures and electrical power values from an auxiliary power meter. The Logger combines a high precision electronic PCBA combined with high precision temperature and pressure transducers in order to accurately record valves at frequencies of 1, 5, 10, 30 and 60 second intervals. The recorded values are stored and also combined with a number of calculations, the results of which are also displayed and recorded.

In essence, for the selected refrigerant, ClimaCheck calculates a series of thermo-physical values such as refrigerant enthalpy at various points of the refrigeration cycle and also predicts theoretical values based on known and accepted laws for the fluid in question. These values can be compared against actual values recorded.

For example, for a given pressure and temperature entering the Compressor, the discharge temperature for a given discharge pressure can be calculated. The true discharge temperature is actually recorded and the variation between these two allows the isentropic efficiency of the Compressor to be calculated.

Once the enthalpy for the refrigerant at various points around the refrigeration circuit is known, it is simply a question of deriving the refrigerant mass flow rate in order to determine cooling capacity and heat of rejection. Accurate measurements of voltage and current are used to derive kW power input to the Compressor. A small percentage allowance is then applied for heat losses from the Compressor body. The remaining electrical power (enthalpy change) must therefore be absorbed by the refrigerant. This increase in enthalpy, in conjunction with the measured enthalpy values for the refrigerant on an instantaneous basis can then be used to derive the mass flow rate.

The patented ClimaCheck Performance Analyser method, known as the Internal Method, after taking into account potential errors in field measurements, heat loss from Compressor body, etc. will provide accurate performance analysis to within 5% - 7% of reality. This percentage error could be positive or negative. It can also be argued that some errors will be positive and some negative and that to some extent these will be self-cancelling, thus rendering the overall system performance values to be accurate to a value better than 5%.

2. It is possible to produce graphs of cooling capacity?

The graphical output of ClimaCheck can be set to include/exclude almost every variable including cooling capacity, power input and heat of rejection. Of the numerous variables available, items such as voltage and current, isentropic efficiency, power factor, etc. can be displayed.

Given that the ClimaCheck file is exportable to Excel, this then allows the user to perform additional functions such as:

a) Summation of the results of 4 separate refrigeration circuits on a single Water Chiller in order to arrive at averages for the 4 circuits as a whole.

b) Production of graphs  based on the tabular data including cooling capacity, power input, heat of rejection and many other variables.

3. Please provide an outline description of the ClimaCheck Performance Analyser

ClimaCheck is the result of 14 years ongoing development originating in Sweden. The Internal Method was conceived in order to combat the problems of inadequate field measurement accuracy and the limitations when attempting to measure the secondary flows for any type of Air Conditioning or Refrigeration system. For example, in order to determine the performance of an Evaporator Coil within an Air Handling Unit, it is necessary to determine entering dry bulb/wet bulb temperature, leaving dry bulb/wet bulb temperature and the air flow rate. These results must then be combined with psychometric calculations in order to arrive at the sensible, latent and total cooling capacity. Air flow measurements are notoriously inaccurate as are wet bulb temperature readings. Moreover, these readings are subject to continual change and it is virtually impossible to calculate these on a dynamic basis whilst also observing many other parameters.

Consequently, the development of the Internal Method means that the primary refrigeration/air conditioning circuit performance can be accurately determined and these results can then be sensibly applied to calculate secondary flows. It is important to note that ClimaCheck does not rely at all on secondary fluid flow rates or temperatures to derive its results.

Another driving reason behind this development was the need to provide refrigeration and air conditioning Engineers with a dynamic and very accurate means of determining exactly what is happening at every point of the refrigeration system on a dynamic basis, since this is the only way to fully optimise performance. Adjustments to refrigerant charge, expansion devices, controls, differentials, low ambient/head pressure control, etc. are all now visible and adjustable.

Moreover, a clear and accurate record of performance of the refrigeration system prior to adjustments and following adjustments can now be safely recorded and stored in an accurate and consistent form across numerous types of air conditioning and refrigeration equipment types.

4. Is the accuracy of the ClimaCheck temperature and pressure sensors validated?

Calibration instrumentation is used by ClimaCheck on all temperature and pressure sensors prior to dispatch and a Validation Certificate is produced documenting these results. This is issued with every ClimaCheck shipment.

During the tests at Bracken House, the high pressure and low pressure transducers were connected to a refrigeration circuit, which was non-operational at the time and the standing pressure of the refrigerant throughout the system, which is precisely at a single pressure value, was recorded by the sensors with an inaccuracy of less than 1%. Similar observations were made on the chilled water temperature sensors where, without the Water Chiller in operation, precisely the same temperature was recorded at both Binder Probe Sensors.

In other words, it is very easy to quickly validate the general accuracy of sensors in the field by conducting such simple tests. For example, pressure transducers can be connected to the Logger, but simply read against atmospheric pressure to enable their accuracy to be determined.

It is also useful to point out that many aspects of refrigeration and air conditioning rely on temperature differences rather than finite temperature values. Accordingly, provided the sensors are accurate in relation to each other, their ability to perform the task within this application is further guaranteed.

Finally, it is important to note that the results recorded during these tests were carefully matched against the Hitachi Performance Data and relatively small capacity differences over several hundred kW were recorded.

5. What values are recorded and what values are calculated?

ClimaCheck records the following:

Suction temperature at Compressor inlet Suction pressure at Compressor outlet Suction temperature at Compressor inlet Discharge temperature at Compressor outlet Liquid temperature upstream of expansion device Voltage on all three phases Current on all three phases

The following items are recorded, these being extremely useful to see in order to determine the performance of Heat Exchangers on the secondary fluid side, but are not required by ClimaCheck:

Inlet temperature to Evaporator Outlet temperature from Evaporator Inlet temperature to Condenser Outlet temperature from Condenser

The following values are calculated:

Power input – kW (per phase and total) Power factor Refrigerant mass flow rate – kg/s Cooling capacity – kW Heat of rejection – kW Compressor isentropic efficiency - % System COP – cooling System COP – heating Superheat – K Sub-cooling – K

ClimaCheck can also calculate and display secondary fluid mass flow rates.

CONCLUSIONS

NM and I took the averages of 4 off 15 minute refrigeration circuit test results on one Water Chiller and then summed these to arrive at the total average Cooling Capacity. We then compared this value against the Hitachi Water Chiller Performance Data, interpolating precisely to compare performance at exactly the same Leaving Chilled Water and Leaving Condenser Water Temperatures and noted only a very small capacity difference. The following extracts from the Test Results File set my finding out in detail:

Additional Conclusions:

1 – All 16 Water Chiller Circuits ran in a stable manner

2 – Improvements to Cooling Capacity and overall performance were achieved by making small adjustments to the TEV / Refrigerant Charge in some cases

3 – The efficient operation of these machines strongly implies long-term reliability

4 – The COP in all cases was very acceptable, which should keep running costs to a minimum

5 – A quick estimate of the building thermal load based on 220000ft2 (20446m2) and 120W/m2

implies a load of 2453kW to which must be added Data Room Loads, etc. A far more accurate value together with a breakdown of loads (and building heat losses) can be achieved with our Quantum Software. However, the Cooling Capacity of the 16 Refrigeration Circuits tested indicates that there is sufficient cooling capacity to handle the peak load of the building. (This is not intended to be a firm declaration).

END

Mike CreamerManaging Director

mike@businessedgeltd.co.uk