Public Services Building 155 N First Avenue Hillsboro, OR March 2012

Transcription

1 Public Services Building 155 N First Avenue Hillsboro, OR March 2012 Tests and report done by: Joel Klobas Emerging Energy Solutions Technical Director joelk@eeswest.com

2 Contents Introduction... 3 Description of Equipment... 3 Flow Chart of the System and Readings... 4 March 2012 Test... 5 The post measurement test show:... 6 Sub-Cooling... 6 Pre-test Pre-test Post-test... 7 Condenser performance... 8 Pre-test Pre-test Post-test Comparison chiller dt condensing - cooling water Compressor performance Pre-test Post-test Comparison table Nominal Data Rating condition comparison: Conclusions P a g e

3 Introduction The purpose of this chiller analysis is to compare test data from before and after repairs that were made to the system. The first test was performed in May of 2011 indicating the system was low on refrigerant and may have some type of non-condensable (air or nitrogen) mixed with the refrigerant. Between May of 2011 and September 2011 when we conducted our second test the condenser tubes were cleaned on the water side and the filter drier was replaced. During our second test it was evident that the problem of non-condensables remained. March of 2012 repairs were again performed to address the non-condensable issues. The repairs to the system included: Removal of all contaminated refrigerant. Remove old filter driers and installation of new ones. Remove old compressor oil and install new oil. Repair leaks. Evacuation of the system to 40 microns. Charge the system with new R-22 refrigerant to the factory recommendation of 60lbs. While the technician was recovering the old refrigerant it was noted that only 30lbs of refrigerant was removed from the system. The manufacturer s recommended charge of this system is 60lbs. The recovered refrigerant was not sent out to be tested for non-condensables. After all the above repairs were concluded, ClimaCheck was hooked up to the system to verify all recommended changes had been completed correctly. Additionally the final test would indicate the actual savings that were achieved by doing the repairs. The ClimaCheck PA Pro performance analyzer is a data logger that uses a multitude of temperature sensors, pressure transducers, and electrical analyzing equipment which all take readings and measurements that are then converted to data. This data is then collected and imported into a software program. The software then uses thermodynamic laws which make calculations similar to the types of calculations used in a research and development labs. All readings were taken with the ClimaCheck Pa Pro. All conclusions were made by inspection and research of this data using some nominal data supplied by the manufacturer. Description of Equipment The Equipment is a McQuay water cooled chiller built in This chiller is refrigerating a Glycol loop providing cooling to a server room. This system has two refrigerant circuits, one compressor on each circuit, a desuperheater on each circuit, a condenser for each circuit, and a common evaporator cooled by both circuits. The two desuperheaters provide heat for a heating loop in the building and preheating for a potable hot water heater. Water provided to the condensers comes from an evaporative condenser outside controlled by a fan cycle control. Normally the 3 P a g e

4 water inlet temperature is controlled at 74 F; however the sensor was not working during the final test causing the fan on the evaporative condenser to run continuously. Only circuit 1 was tested. There are three test dates noted in this report, May 18 th, October 2011, and March The data collected for these tests was taken on circuit one at full load with the desuperheater loop on. Compressor two never ran during the test, it was forced off. Flow Chart of the System and Readings Single Compressor Flow Chart The above diagram is a flow chart representative of the system tested. The yellow triangles represent where ClimaCheck temperature probes were attached. The blue circle is the low Pressure and the red circle is the high pressure. Pressure transducers were connected to each point. There also was a power meter attached to record voltage and Amperage. 4 P a g e

5 March 2012 Test There should only be a 10 difference between the two Saturated Condensing Temperature Exiting Water Temperature Sub-Cool 18.7 F Adding refrigerant to system System is stable and showing good readings This graph shows the start-up and charging of the system. The last 20 minutes shows very stable operation at full charge. All abnormal unstable data shown indicates times when refrigerant was being added to the system. It is important to point out that the difference between saturated condensing temperature and leaving water temperature of the condenser stayed about the same throughout the charging of the system. This indicates poor heat transfer between the refrigerant and the cooling water in the condenser. 5 P a g e

6 The post measurement test show: Sub-Cooling - During the latest repairs the system was charged to manufacturer s specification of 60 lbs. The system is now operating at a sub-cool of 18.7 F, (shown above). This sub-cool would be expected to be at the high end range of most chillers. No significant increase of dt between water and condensing temperature was shown during charging of the system (graph above). Pre-test 1 Pre-test 1 showed a sub-cool ranging from 13 F to 0 F averaging about 6 F. 6 P a g e

7 Pre-test 2 Pre-test 2 showed a 4.5 F sub-cool averaging almost 4 F. For the entire test the liquid line sight glass was flashing rapidly. You cannot have higher than 0 F sub-cool with a flashing sight glass. This fluctuation is a strong indication of non-condensables in the system. Post-test Post-test showing 19.2 F to 18.6 F of sub-cool. This reading is a little higher than would be expected. This high sub-cool is an indication of poor heat transfer between the refrigerant and the cooling water in the condenser. 7 P a g e

8 Condenser performance - The condenser has a low performance with almost 20 F difference between exiting water and condensing. However the condenser is operating better with the correct refrigerant charge. There is no longer any indication of non-condensables in the refrigeration circuit. 8 P a g e

9 Pre-test 1 dt condensing - cooling water. This is the difference of the saturated condensing temperature and the leaving condenser water (cooling water). There is an 18.6 F average. Pre-test 2 dt condensing - cooling water. This is the difference of the saturated condensing temperature and the leaving condenser water (cooling water). There is a 19.5 F average. 9 P a g e

10 Post-test dt condensing - cooling water. This is the difference of the saturated condensing temperature and the leaving condenser water (cooling water). There is a 19.6 F average. Notice the stability in this graph is much different than the two prior, this is due to the evaporative condenser fan never shutting off due to the bad sensor mentioned earlier. All three graphs show a large difference indicating very poor heat transfer in the condenser. Comparison chiller dt condensing - cooling water Here we see a test done on a very similar chiller the dt condensing - cooling water ranged from 7 F to 10 F. This would be an expected operating range. 10 P a g e

11 Compressor performance - Compressor Isentropic Efficiency of 65-67% is in line with what is expected of a good semi-hermetic compressor (typical range 64-72%) at similar operating condition. Pre-test 2 The isentropic efficiency of the compressor during the pretest is showing 87 96% effeciency. This is immpossible for a reciprocating compresors which is expected to run between 64-72% efficiency. It is clear that noncondensables are present. Post-test 11 P a g e

12 Now the non-condensables have been removed from the system and the isentropic efficeincy is right where you would expect from this 24 year old compressor 65-68%. Comparison table Parameter Pre-test 1 Pre-test 2 Post-test Difference May 18 Sept 9 March 9 Pre-test 2 and post Chilled water in F Chilled water out F Chilled water dt F (12.5%) Evaporation F dt chilled water evaporation F Cooled water in Cooled water out Cooled water dt F (+17%) Condensing F dt condensing - cooling water Power input KW (-4%) The following can be noted as improvements: There are some differences in operation between Pre-test 2 and Post-test: A. Post-test has a lower chilled water inlet temperature of 1.2 F B. Post-test has a lower chilled water exiting temperature of 1.9 F (difference is caused by higher capacity) C. Post-test has lower cooling water of 6.1 F D. Post-test has lower cooling water out temperature of 4.1 F (difference is caused by higher capacity) The above table indicates that the chiller has increased in performance significantly with the non-condensables removed and new refrigerant added to the correct manufacturer specifications. Compared to the first two tests and last test, the condenser performance has increased its performance slightly but is still significantly below where it should be. 12 P a g e

13 Nominal Data WHR040D Selection guidelines (page 15) 1. Ratings may be interpolated for any chilled water temperature between 42 F and 50 F but cannot be extrapolated. 2. Chilled water quantities - Ratings are based on a 10 degree chilled water range and are applicable from a minimum of 8 F to a maximum of 12 F differential between entering and leaving chilled water temperature. 3. Condenser water quantities - Ratings are based on a 10 F rise in condenser water temperature and are applicable from 1 ½ to 4 gpm/ton (20 F to 7.5 F rise) except as limited by pressure drop in Chart 2. Capacity data note that data is given in first table at entering water and in second at exiting water temp with a dt of 10 F e.g. the two first two columns are equivalent and given for a 5 F higher exiting water temperature than listed. The flow is lower than nominal but within range. A lower flow than table will be beneficial for performance when rating tables are based on existing water. 13 P a g e

14 Rating condition comparison: Operating conditions (temperature and flow) is within the given range of the chiller but with lower water temperature than tabulated. Exiting water temp is approx. 5 F below tabled data. Based on extrapolation of table At 5 F higher exiting water temperature the rated EER is 17.6 whereas ClimaCheck measured the EER at 14.5 which is an increased energy consumption of 18%. Extrapolation of table always include an increased uncertainty but it can be noted that 5 F lower exiting water condensing has an estimated impact of an additional 5% increased EER. Conclusions The McQuay Chiller performance improved significantly when the non-condensable gases were recovered and the system was charged with new refrigerant. The capacity has increased % There is a decrease in power consumption of a 4 % This equates to a 15 to 25% performance improvement. However there is still room for improvement in the system. If the condenser was brought to manufacturers specifications there is a possibility of an additional savings of 20%. No data on evaporation or condensing temperatures versus water temperatures was found in manufacturers manual which makes it impossible to - with certainty specify cause of decreased performance to condenser. There are a number of possibilities that could cause pour performance of this condenser: A leak on the condenser water gasket allowing flow to occur between inlet and outlet water before passing through the condenser tubes, (a shortcut). Cavitation of the water circulation pump that is circulating cooled water from the evaporative condenser, (water tower). This is a likely problem due to the design of the water system but is very easily detected as when cavitation occurs you can hear the bubbles being produced in the pump. There was no indication of cavitation while the tests were performed. Air in the water side of the condenser that is trapped. This is unlikely since the water side of the condenser barrel is tubes and the refrigerant is in the barrel. Poor original design. After reading the design specifications of this chiller this is very unlikely A build-up of scale on the inside of the condenser tubes that has not been able to be removed during cleaning causing poor heat transfer between refrigerant and cooling water. 14 P a g e