Executive Summary. Number of Low Number of High Number of Faults , Number of OK

Transcription

1 Unit Lower limit Upper limit Air on Model no evap. F Air off evap. F dt air evap. F Executive Summary Evapo. F This is a summary chart for quick reference and view of all the systems tested. Red boxes indicate measured levels that were out of range. There were faults in evaporator dt, condenser dt, superheat, subcool, and isentropic efficiency of the compressors. Fault levels are determined from manufacturer s recommendations and testing experience. EER at Ambient Temperatures dt air- Super Air on Air off dt air Conde dt air- Sub cool Comp evap heat cond. F cond. F cond. F n. F cond F eff. AH 10 C1 Model# 50HJQ AH 10 C2 Model# 50HJQ GE 2 Model#48TJE GE 3 Model# 48TJE GE 7 Model# 48TJD GE 8 Model# 48TJD GE 13 Model# 48TJD GE 15 C1 Model# 48TJD GE 15 C2 Model# 48TJD Mean Max Min Number of Low Number of High Number of Faults , Number of OK EER Power kw Cooling cap Note: these are measured EER, not equipment rating. This graph shows the EER each circuit was operating at during the test at the average ambient. It would be expected to see a drop in EER the further to the right the units get, as EER should drop as ambient temperature rises.

2 EER and Return Air Temperature Note: these are measured EER, not equipment rating. This graph shows the EER of each circuit during the test with the Return air to the evaporator. You would expect to see a drop in EER the further right each unit gets, as the higher the return air temperature gets the lower the EER should be. 2 P a g e

3 Measured EER Results AH-10 C1 AH-10 C2 GE-2 GE-3 GE-7 GE-8 GE-13 GE-15 C1 GE-15 C2 ClimaCheck Measured EER Nominal EER for the compressor at measured conditions (Copeland Compressor design EER) Expected Nominal EER This Graph shows three different EER metrics. ClimaCheck takes multiple measurements then uses thermodynamic calculations to get the EER level. A Copeland software program was used to calculate design EER levels for the compressor. A compressor in Copeland s software was chosen that was closest in comparison to the compressor on the Carrier unit, but as it is not identical, the data will vary somewhat. Measurements that the ClimaCheck took were imported into the software to get the nominal EER level. This is essentially the EER that the compressor should be running in these conditions. The expected EER was derived from the software by averaging data from multiple conventional RTUs with no known problems that were tested previously with the ClimaCheck. This is not a perfect calculation, but a reasonable expectation of unit performance if there are no problems. Below are the averages used for Expected Nominal EER. Evaporation Temperature = evaporator entering air -35 F (the average delta T entering air to evaporation temperature on previous units tested without issues) Condensing Temperature = ambient Temperature + 25 F (the average delta T entering air to condensing temperature on previous units tested without issues) Superheat = Average temperature of 10 F Subcool = Average temperature of 15 F 3 P a g e

4 Compressor Isentropic Efficiency Compressor isentropic efficiency is a comparison of the actual compression process efficiency vs. the theoretical efficiency of a perfect compression process. This compressor is averaging about 63% isentropic efficiency. Most of the other compressors in this test were around 70%. This unit and GE-3 are the only two units tested that have Tecumseh compressors. It is interesting to see that these two units also have the lowest EER of all units tested. The difference between 63% and 70% is only 7% but the difference in performance is actually 11%. 4 P a g e

5 GE-15 GE-15 conditions a large break room with refrigerated vending machines in it that produce a constant load. This unit conditions with 2-stage mechanical cooling and natural gas heat. Refrigeration Process Discharge Temp Circuit 1 Discharge Temp Circuit 2 Superheat Circuit 1 Superheat Circuit 2 This unit has two stages of cooling using the same evaporator and condenser coils though the refrigeration circuits are separate. Both refrigeration circuits are almost identical and should run almost identical. However, this graph shows that this is not the case during this test. Circuit 2 has 0 superheat. Superheat this low brings the discharge temperature down. 5 P a g e

6 Superheat Superheat Circuit 1 Avg. 22 F Superheat Circuit 2 Avg. 0 F Most RTUs are efficient between F of superheat and many manufacturers suggest this range. However, with Carrier s Acutrol fixed orifice metering device the refrigerant charge is the greatest determining factor of the superheat level. As outside ambient temperatures and indoor space temperatures change this affects the superheat and causes it to change as well. Circuit 1 is averaging about 22 F of superheat. The charging chart on page 59, shows the superheat should be at about 9 F (±5 suction temp) in these conditions. Circuit 2 rapidly drops to 0 of superheat as the test starts. The charging chart on page 58 shows this circuit should be operating at about 11 F of superheat (±5 suction temp). 6 P a g e

7 Subcool Subcool Circuit 2 Avg. 25 F Subcool Circuit 1 Avg. 17 F Both refrigeration circuits should have the same refrigerant charge in them. If the circuits have the same charge and are operating the same you would see the subcool of both circuits at the same level. It would be expected that with the very low superheat of circuit 2, it would have a lower subcool as well because too much refrigerant is in the evaporator and not the condenser. That is not the case. Circuit 2 has high subcool that may be causing the low superheat. Similar units to this one would run around F subcool in these conditions, however, all of the units on this roof have issues with condenser coil corrosion. It is difficult to measure the level of corrosion so it is very difficult to say where the subcool should be with a corroded condenser coil. If the refrigerant charge is correct it would be expected that the worse the corrosion is the higher the subcool would be. Although evaporator air inlet temperature would have to be taken into account as well. 7 P a g e

8 Condenser Condensing Temperature circuit 2 Condensing Temperature circuit 1 Avg. DT of 40 F Avg. DT of F Air inlet temperature at Condenser The blue and green at the top of the graph shows the condensing temperature of circuits 1 and 2. At the bottom of the graph, (in light blue) is the air temperature at the inlet of the condenser. The difference of these would be referred to as the delta T air inlet to condensing temperature. During the test the delta T air inlet to condensing averaged close to 40 F on circuit 1 and F on circuit 2. A new higher efficiency RTU with good controls could run F dt. Older units are usually around 20 to 25 F dt. This higher dt level than usually seen on DX air conditioners and may indicate a problem with the condenser s ability to transfer heat. The 60 F dt of circuit 2 is indicating a major problem. 8 P a g e

9 Evaporator Evaporation Temperature Circuit 2 Evaporation Temperature Circuit 1 The high pressure side of the system and the low pressure side of the system are only separated by the fixed orifice metering device (Carrier Acutrol) on this system. If the high pressure increases, there will be more gas forced through the metering device at a higher pressure causing the low pressure side of the system to rise in pressure as well. On the condenser graph on previous page circuit 2 is operating at a higher condensing temperature than circuit 1. This higher temperature comes from a higher pressure. The evaporator shows evidence of this as well circuit 2 has a higher evaporation temperature than circuit 1. This higher evaporation temperature comes from a higher suction pressure that is caused by a higher condensing pressure. The saturated suction pressure of circuit 2 is higher than circuit 1 because the condensing temperature and pressure of circuit 2 are very high. 9 P a g e

10 Charging Chart GE-15 Circuit 1 and 2 Suction line temperature = 46 R-22 refrigerant at 65# psig = = 9 super Suction line temperature = 54 R-22 refrigerant at 73# psig = = 11 superheat This is a Carrier Charging Chart. All Carrier units have this sticker mounted on them to help a technician make sure there is a correct refrigerant charge. The red is plotted on the chart from test data. The green represents where the plot should be. Circuit 1 chart shows refrigerant should be added to the circuit. Circuit 2 shows that refrigerant should be removed from the circuit. They also indicate that the superheat on circuit 1 should be 9 F and circuit 2 should be 11 F at these temperatures and pressures. It is not recommended that the unit run at this superheat. If refrigerant were to be added and removed the pressures and temperatures will change causing the superheat to change. 10 P a g e

11 Conclusion Superheat The superheat of circuit 1 is dangerously low and will be causing lubrication issues in this compressor every time it runs. These lubrication issues will damage the compressor and shorten its life expectancy. Condenser The difference between condenser air inlet temperature and condensing temperature are very high. This would indicate poor heat transfer at the condenser coil between the air and the refrigerant on circuit 1. However, Circuit 2 is much worse and both circuits are using the same condenser. There were no visual conditions of the condenser to suggest either circuit would get more or less air flow or heat transfer than the other. Summary The condenser coil is where heat is removed from the conditioned space and released into the ambient conditions. The better the heat transfer is at the coil the more efficient the unit is. As the heat transfer drops at the coil the unit becomes less efficient. GE-15 had 69 F air onto the evaporator and 74 F air onto the condenser with 113 F and 132 F condensing temperatures. This was a low load situation and the unit should not have produced condensing temperatures this high under these conditions. With these problems this unit would be extremely inefficient at higher load conditions and may cause damage or compressor failure. It is evident this condenser coil has serious problems transferring heat. Efficiency would be increased if this condenser coil was replaced. Circuit 2 seems to have more problems than just poor heat transfer between the refrigerant and the air at the condenser coil. The manufacturers charging chart suggests removing refrigerant from this circuit. It is a good recommendation, but with a condensing temperature this high, it would be expected that the subcooling would be much higher than it is. It is possible for non-condensables in the refrigerant circuit to cause this. The ClimaCheck is a great tool for detecting non-condensables, such as air or nitrogen in a refrigeration circuit, even in very small amounts. Typically, the isentropic efficiency would rise to a fictitious range and conversions such as superheat and subcool could show impossible negative readings. The superheat dropped to 0 F, which is the lowest level possible and stayed right there without going below 0 F. The isentropic efficiency was in an expected range. This is a good indication there are not any non-condensables in the system. The compressor of circuit 2 is in danger of failure running the way it is now. It would be much more cost effective to take action now than wait for it to fail, costing the owner replacement cost, down time, and occupant discomfort. Even with all of the problems circuit 2 has shown, it is only running about 2.5% less efficient than circuit 1. Circuit 1 averaged a 12.9 EER and Circuit 2 averaged a 12.6 EER. Both of these EER levels should be higher in these conditions. The issue with the condenser is the reason for the lower than expected EER levels. The ClimaCheck only measures the actual performance of the unit in real time at the conditions during the test. It is hard to estimate what the unit should run at under different conditions or with no problems opposed to problems. On the next page, there are illustrations to help show performance at different conditions. The three illustrations below show the compressor data for the compressors in GE-15. This is nominal data supplied by Copeland software, the manufacturer of the compressors in GE-15. The top illustration shows the temperatures and pressures of circuit 1 and the expected performance of the compressor with a EER. The second illustration shows the expected performance at these conditions with a EER. If this unit was operating at this EER, it would be a 20% increase in performance at these conditions. The second chart shows the temperatures and pressures circuit 2 running at and the expected performance of the compressor with a EER. The bottom chart shows temperatures and pressures that would be expected of this unit under these conditions, if there were no issues. It shows an EER of 14.93, this is a 43% increase in performance at these conditions. 11 P a g e

12 Example: nominal running performance at these conditions Circuit 1 Example: nominal running performance at these conditions Circuit 2 12 P a g e

13 Example: expected nominal performance at these conditions Circuits 1 and 2 13 P a g e