Self-Test System For Qualifying Refrigeration Chiller System Performance

Abstract

A chiller or cooler is disclosed, including a self-test mechanism to simulate a sampling of normal operations and to compare the operating parameters resulting from such sampling against factory operational parameters adjusted for differences in operating parameters so as to eliminate unnecessary servicing or maintenance events.

Claims

1. a chiller having an integrated self-testing system comprising: a) a controller; b) memory connected to the controller, the memory including preloaded factory operational parameters; c) At least one chiller operational sensor for providing in situ operational parameters for comparison to the preloaded factory operational parameters; d) At least one sensor for recording ambient condition data; e) An output interface for providing a signal for determining whether servicing the chiller is desired based upon adjusting the factory operational parameters based upon the ambient condition data and the comparing of the adjusted factory operational parameters and the in situ operational parameters.

2. The chiller of claim 1, wherein the in situ operational parameters correspond to operational parameters over a plurality of time intervals.

3. The chiller of claim 1, wherein the signal provided by the output interface includes a graphical comparison of the in situ operational parameters adjusted by the ambient condition data versus the factory operational parameters.

4. The chiller of claim 1, wherein the signal provided by the output interface includes a graphical comparison of the in situ operational parameters versus the factory operational parameters adjusted by the ambient condition data.

5. The chiller of claim 1, wherein the signal provided by the output interface includes at least one end user service recommendation.

6. The chiller of claim 5, wherein the at least one end user diagnostic recommendation includes an automated adjustment of in situ operational parameters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 mechanical schematic a chiller in accord with the first preferred embodiment.

[0021] FIG. 2 is a flow diagram of the self-test process of the chiller as shown in FIG. 1.

[0022] FIG. 3 is a diagram showing a prophetic example of the comparison of adjusted factory operating characteristics in comparison with the in situ operating characteristics being analyzed.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0023] As can be seen in FIG. 1, the present invention comprises chiller assembly 10 for supplying temperature regulation to an instrument or equipment (not shown). The chiller 10 includes the basic components of a compressor 20, a condenser 30 a pump 40, an evaporator 50, and a fan 70. The chiller further includes a controller unit 60 which receives inputs from various sensors related to each of these components. In this embodiment, the sensors include a suction pressure transducer 22, and a suction temperature sensor 24 for measuring the input to the compressor 20, as well as a fluid temperature sensor (P1) 42 downstream from pump 40.

[0024] At time of manufacture, a series of tests are performed which accurately measures and stores certain performance criteria for the chiller. (These readings taken are called pull-up, stability, pull-down parameters, and are all in units of time and temperatures). This measurement data is stored in the chiller and remains with the chiller for its lifetime stored within controller unit 60, as a signature of its performance.

[0025] An example of the self-test process 100 in accord with the embodiment shown in FIG. 1 is shown in the flow chart of FIG. 2. First is the step 110 of the system 10 receiving an input from a user initiating a self-test sequence. This step can be initiated by a button or a soft key (not shown) which is connected to the controller unit. As an additional option, the controller unit 60 can prompt the user to remind him of the need to initiate the self-test, e.g., prompting or querying the end user at regular time intervals. Once the end user initiates the self-test the chiller system 10 instructs itself to follow the following temperature set points (autonomously).

[0026] In a pre-test step 120, the controller unit 60 turns compressor 20 off, turns the pump 40 off and turns the fan 70 on. Then, once the discharge temperature sensor 26 reading is stable, e.g., +1-0.1 C for longer than 60 seconds, the controller unit 60 records the reading from that sensor, which represents the ambient air temperature environment where the chiller 10 is located.

[0027] The next self-test initiation step 130 is simply to enable the chiller 10 to operate as normal, under control of the controller unit 60 under an autonomous chiller set point in order to begin the sequencing of operational tests.

[0028] The next step 140 initiated by the controller unit 60 is a stability at +20 C. measurement. This step, solely for purposes of this preferred embodiment, involves the controller unit 60 increasing the set point to 20 C. from its current level, waiting for the fluid temperature sensor (P1) 42 to achieve that set point, and to wait five minutes at that set point. The controller unit 60 measures temperature stability of the fluid temperature sensor (P1) 42 over this time period. Stability, for purposes of this embodiment, is fluid temperature degrees Celsius spread, where spread equals (maximum fluid temperatureminimum fluid temperature)/2, where the maximum and minimum temperatures derived over the five minute set point.

[0029] The next step 150 is a pull down measures the efficiency of changing (decreasing) temperatures. This step involves the controller unit 60 decreasing the set point to +10 C., i.e., 10 degrees below the point of step 140, and waiting for the fluid temperature sensor (P1) 42 to achieve that set point, and measuring the time required to achieve that set point.

[0030] The next step 160 is a pull down stability measurement which involves waiting for five minutes at the +10 C. of step 150, above, and having the controller unit 60 measuring temperature stability over this time period.

[0031] The next step 170 is a time for pull-up measurement which involves going back from the +10 C. to a +20 C. set put, wherein the controller unit 60 measuring the amount of time required for the fluid temperature sensor (P1) 42 to achieve that set point.

[0032] Next, the process 100 includes a analysis step 180 involving comparing each of the time and stability readings of steps 140, 150, 160 and 170 against the results stored in the controller unit 60 from the same tests recorded at the time of manufacture for the chiller 10, with such results being adjusted to account for differences between the operating parameters as of the date of manufacture. That is, this step by the processor first adjusts time and stability readings from the date of manufacture to account for differences in operating parameters (e.g., changes in ambient air temperature or pressures).

[0033] An example of how the differences between the adjusted factory readings and the in situ readings may be used in accord with the present invention is shown in FIG. 3. In this prophetic example, pull down function of the chiller system 10 as of the date of manufacture is represented by figure element 210. The processor 60 uses the discharge temperature sensor to account for degradation in the performance of the chiller that is due to, for instance, a higher pressure or ambient air temperature than the conditions in recording of the factory readings. Additional sensor readings, such as suction pressure transducer 22 and/or suction temperature sensor 24 can optionally be logged during the self-test for separate diagnostic use by technicians, but are unnecessary for use in the self-test as separate pass/fail criteria.

[0034] The resulting adjusted factory pull down reading is shown in figure element 220. The comparison in this example is then made between the adjusted factory pull down reading 220 and the in situ pull down reading 230 (corresponding to step 150). The slope deviation between 220 and 230 is the measure for warning in pull up or pull down. For instance a slope deviation between 220 and 230 of less than 10% in this example would be considered a pass or OK reading, while a deviation of between 10-20% would be a yellow or caution reading, and a slope deviation of greater than 20% would trigger a service required prompt as per step 200, below. In this preferred example, slope deviation as calculated by processor 60 would be used for pull up and pull down comparisons, while absolute deviation could be used as the measure for warning in temperature set point maintenance.

[0035] An example of this prophetic calculation of the effects of ambient temperature on chiller performance follows. In this preferred example, by using AHRI methods for calculating refrigeration compressor performance and making certain assumptions to simplify calculations, the operation of the present invention can calculate that chiller cooling capacity may be de-rated by 1.3% per C. rise in ambient temperature. This calculation for purposes of this example makes a number of assumptions, namely: [0036] 1. The calculation is directed to effects of rising ambient temperature on cooling capacity at fixed chiller leaving water temperatures (set point temperature); [0037] 2. Parasitic heat gains (e.g., heat absorption from hoses) presented to the chiller will rise with ambient temperature. The increased heat load will be offset to some extent by other effects, noted in Assumptions #3 and #4; [0038] 3. As compressor cooling capacity is diminished by rising ambient temperature, the refrigerant evaporator becomes effectively oversized with respect to compressor cooling capacity; [0039] 4. As compressor cooling capacity is diminished by rising ambient temperature, refrigerant condenser becomes effectively oversized with respect to compressor cooling capacity; [0040] 5. For purposes of this prophetic example, one can assume that the effects described in Assumption #2 will be offset to some degree by the effects described in Assumptions #3 and #4; [0041] 6. Based on Assumption #5, suction dew point temperature (aka saturated suction) is assumed to be fixed with respect to leaving water temperature; and [0042] 7. Based on Assumption #5, discharge dew point temperature (aka saturated discharge) is assumed to operate at a fixed differential from the ambient temperature (i.e. a 1 F. rise in ambient temperature results in a 1 F. rise in discharge dew point).

[0043] With these assumptions in place for this prophetic example, one can estimate compressor performance using established AHRI equations, so along as regression coefficients known and supplied by the compressor manufacturer are available, along with suction dew point and discharge dew point temperatures. An example of such an equation to establish instantaneous efficiency is set forth below:

Section 5. Rating Requirements

[0044] 5.1 Published Ratings. The Published Rating of the Compressor shall consist of the following individual ratings which are established through coefficients provided by the manufacturer that are to be used in Equation 1 and tested as specified in Section 4 meeting the uncertainty in Section 5.4. [0045] 5.1.1 Power Input, W, W [0046] 5.1.2 Refrigerant Mass Flow Rate, Ibm./h, kg/s [0047] 5.1.3 Refrigerating Capacity, Btu/h, W [0048] 5.2 Polynomial Equation. The polynomial equation that shall be used to present the Published Ratings is a third degree equation of ten coefficients in the firm of:

X=C.sub.1+C.sub.2.Math.(t.sub.S)+C.sub.3.Math.t.sub.D+C.sub.4.Math.(t.sub.S.sup.2)+C.sub.5.Math.(t.sub.S.Math.t.sub.D)+C.sub.6(t.sub.D.sup.2)+C.sub.7.Math.(t.sub.S.sup.3)+C.sub.8.Math.(t.sub.D.Math.t.sub.S.sup.2)+C.sub.9.Math.(t.sub.S.Math.t.sub.D.sup.2)+C.sub.10.Math.(t.sub.D.sup.3)1 [0049] Where: [0050] C.sub.1 through C.sub.10=Regression coefficients provided by the manufacturer [0051] t.sub.D=Discharge dew point temperature, F., C. [0052] t.sub.S=Suction dew point temperature, F., C. [0053] X=Individual Published Ratings shown in Sections 5.1
(Source: AHRI Standard 540 from the 2015 Standard for Performance Rating Of Positive Displacement Refrigerant Compressors and Compressor Units)

[0054] In this prophetic example, one can generic coefficients for a representative compressor as specified by the AHRI and set forth below, though of course such coefficients will vary based upon the manufacturer: [0055] 7. Based on Assumption #5, discharge dew point temperature (aka saturated discharge) is assumed to operate at a fixed differential from the ambient temperature (i.e. a 1 F. rise in ambient temperature results in a 1 F. rise in discharge dew point).

[0056] With these assumptions in place for this prophetic example, one can estimate compressor performance using established AHRI equations, so along as regression coefficients known and supplied by the compressor manufacturer are available, along with suction dew point and discharge dew point temperatures. An example of such an equation to establish instantaneous efficiency is set forth below:

Section 5. Rating Requirements

[0057] 5.1 Published Ratings. The Published Rating of the Compressor shall consist of the following individual ratings which are established through coefficients provided by the manufacturer that are to be used in Equation 1 and tested as specified in Section 4 meeting the uncertainty in Section 5.4. [0058] 5.1.1 Power Input, W, W [0059] 5.1.2 Refrigerant Mass Flow Rate, Ibm./h, kg/s [0060] 5.1.3 Refrigerating Capacity, Btu/h, W [0061] 5.2 Polynomial Equation. The polynomial equation that shall be used to present the Published Ratings is a third degree equation of ten coefficients in the firm of:

X=C.sub.1+C.sub.2.Math.(t.sub.S)+C.sub.3.Math.t.sub.D+C.sub.4.Math.(t.sub.S.sup.2)+C.sub.5.Math.(t.sub.S.Math.t.sub.D)+C.sub.6(t.sub.D.sup.2)+C.sub.7.Math.(t.sub.S.sup.3)+C.sub.8.Math.(t.sub.D.Math.t.sub.S.sup.2)+C.sub.9.Math.(t.sub.S.Math.t.sub.D.sup.2)+C.sub.10.Math.(t.sub.D.sup.3)1 [0062] Where: [0063] C.sub.1 through C.sub.10=Regression coefficients provided by the manufacturer [0064] t.sub.D=Discharge dew point temperature, F., C. [0065] t.sub.S=Suction dew point temperature, F., C. [0066] X=Individual Published Ratings shown in Sections 5.1
(Source: AHRI Standard 540 from the 2015 Standard for Performance Rating Of Positive Displacement Refrigerant Compressors and Compressor Units)

[0067] In this prophetic example, one can generic coefficients for a representative compressor as specified by the AHRI and set forth below, though of course such coefficients will vary based upon the manufacturer:

TABLE-US-00001 COEFFICIENT CAPACITY C1 7801.696 C2 93.15076 C3 42.714 C4 1.264949 C5 0.4885953 C6 0.1130572 C7 0.006240552 C8 0.006111 C9 0.00450243 C10 9.26E04

[0068] Using these stated assumptions and AHRI compressor capacity calculation methodology, one can calculate compressor cooling capacities across a range of ambient temperatures. Based on stated assumptions, an arbitrary value of 40 F. was chosen for the suction dew point, as this is well within normal operating parameters. A discharge dew point temperature of 100 F. was chosen to represent a nominal ambient condition, and this is shown to rise by the same increments as the ambient temperature, in accordance with stated assumptions.

[0069] The results of this calculation (shown below) provide a result whereby the compressor capacity can be stated as decreasing by 0.7% per F. ambient rise. This approximates a 1.3% performance reduction per C.

TABLE-US-00002 Rise Above Nominal Suct Dewpoint Disch Dewpoint Cooling % Capacity Ambient Temp t_s t_D CAPACITY De-rate from % Capacity De-rate per F. F. F. F. Btu/hr Nominal Rise Above Nominal Amb Nominal 40.00 100.00 8651.13 At Nominal At Nominal 2.00 40.00 102.00 8523.51 1.5% 0.7% 4.00 40.00 104.00 8395.80 3.0% 0.7% 6.00 40.00 106.00 8268.07 4.4% 0.7% 8.00 40.00 108.00 8140.34 5.9% 0.7% 10.00 40.00 110.00 8012.67 7.4% 0.7% 12.00 40.00 112.00 7885.11 8.9% 0.7% 14.00 40.00 114.00 7757.68 10.3% 0.7% 16.00 40.00 116.00 7630.45 11.8% 0.7% 18.00 40.00 118.00 7503.45 13.3% 0.7% 20.00 40.00 120.00 7376.73 14.7% 0.7% 22.00 40.00 122.00 7250.33 16.2% 0.7% 24.00 40.00 124.00 7124.30 17.6% 0.7%

[0070] These results validate the capacity approximation used in a first simplified embodiment of the present invention whereby the expected reduction of capacity as a function discharge dew point temperatures can be determined. Thus, the present invention compares such calculate changes in capacity at a first factory tested ambient condition and compares such results (shown as slope S1 on FIG. 3) and compares such results with in situ changes in capacity as a function of temperature (as defined by slope S2 on FIG. 3). If the ratio of the slopes S1/S2 exceeds one or more predetermined values (e.g., 1.1 for yellow conditions or 1.2 for red conditions) then the system can recommend dispositions, remedies or corrective actions to replace or maintain the safe operation of the system as required.

[0071] As shown by this prophetic example, if the temperature stability or pull up or pull down times obtained from the self-test process steps differ obtained from the stored factory parameters as adjusted for differences in operating parameters beyond a preselected limit (such as the deviation percentages set forth above), the controller unit 60 performs the step 190 of reporting a service required or fail indicator to the end user so that the chiller can be serviced promptly. In the alternative, if the self-test process step results are sufficiently similar to the stored factory parameters, then the controller unit 60 performs the step 200 of reporting a pass or OK signal. These service indicators are preferably reported to both the user and the manufacturer, though persons of skill having these teachings can understand that the notifications provided under the present invention may not necessitate automatic notices to all such parties. Additionally, these indicators can include, but do not have to include graphical results of the type shown in FIG. 3. Moreover, while the present invention does not require any automated maintenance in response to a service required indicator, one alternative embodiment of the present invention provides for the present service indicator to be linked to the self-cleaning filter invention taught in the application entitled REFRIGERATION CHILLER SYSTEM WITH SELF-CLEANING FILTER and owned by the assignees of the present invention. The teachings of that application are incorporated herein by reference, and provide an example of how the indicator of the present invention can be linked to an automated filter so as to further eliminate false maintenance indicators, e.g., instances in which the filter needs to be replaced, as opposed to performance degradation due to malfunction. Alternatively, another embodiment of the present invention can prompt a user to provide non-automated service support (e.g., changing filters or moving the location of the chiller to provide better airflow) so as to similarly eliminate unnecessary service events.

[0072] The differences between these two sets of data provide a confident determination of chiller performance and possible maintenance steps to investigate to maintain best chiller performance. The process thus allows the manufacturer and the user the ability to determine whether the chiller requires a return to factory for factory maintenance and repair/return or not. Thus, the Chiller Self-Test Procedure of the present disclosure may be used by various personnel to determine whether a chiller is operating within expected normal parameters, or else determine that the chiller is in need of further examination.

[0073] In other preferred embodiments, various preferred processes involving the application of the present invention are focused upon testing one of the more significant criteria for chiller operation, the Cooling Rate. The Cooling Rate is the rate at which energy, in the form of heat, can be removed from the chiller's process fluid. Cooling rate follows the form:

P=(m*C.sub.P*delta_T)/time

[0074] Where,

[0075] P: Cooling Rate (Power);

[0076] C.sub.P: specific heat capacity of cooling fluid;

[0077] m: mass of cooling fluid;

[0078] delta_T: temperature change observed in cooling fluid; and

[0079] time: time interval of observation

[0080] Two significant sources of variation exist that the present disclosure eliminates or normalizes in order to make a useful comparison between two observed cooling rates: 1) the thermal mass of cooling fluid; and 2) the normal change in cooling capacity due to differing ambient temperatures. Variable 1), thermal mass, is the product of the mass (m) and specific heat capacity (C.sub.P) of the cooling fluid. It is controlled procedurally, by specifying that cooling rate tests, including Chiller Self Tests and production quality assurance testing as disclosed herein, must be conducted with a measured amount of a specified fluid such as a predefined mixture of water and glycol. This constrains both the mass and specific heat capacity of the fluid.

[0081] Variable 2), change in capacity due to varying ambient, is generally not feasible to control, so it may vary significantly between tests. In order to compensate for expected performance variations at different ambient temperatures, an ambient compensation factor is applied.

[0082] With the mass and specific heat of the cooling fluid constrained procedurally, the cooling rate of the chiller is thus proportional to the observed drop in temperature (delta_T) divided by the time over which this temperature drop is measured. Within the Self-Test Procedure, the measured cooling rate is specified in degrees Celsius per minute.

[0083] As part of end of line production quality assurance testing, a cooling rate is measured between two predefined fluid temperatures, using the same fluid type and amount that are specified for the particular chiller. The ambient temperature observed at the beginning of the test is also recorded. This measured cooling rate is known as the Born on Performance, and may also be referred to as the Reference Cooling Rate. The ambient temperature measured for this test is referred to as the Reference Ambient Temperature. These recorded parameters are stored in the memory of the chiller controller 60 for use in future Chiller Self Tests.

[0084] Upon initialization of a Chiller Self-Test Procedure by a chiller user, the ambient temperature is recorded and stored in the memory of the chiller controller. This is referred to as the Self-Test Ambient Temperature. The chiller controller will then compute and store in memory an Ambient Temperature Compensation Factor based off of the difference between Self-Test Ambient Temperature and Reference Ambient Temperature, multiplied by a coefficient equal to 1.3% per C. (or 0.013/ C.). This calculation of the Ambient Temperature Compensation Factor follows the form:

Ambient Temperature Compensation Factor=1+((Reference Ambient Temperature)(Self-Test Ambient Temperature))*0.013/ C.

[0085] Example Calculation:

[0086] Reference Ambient Temperature=20 C.

[0087] Self-Test Ambient Temperature=22 C.

Ambient Temperature Compensation Factor=1+(2022 C.)*0.013/ C.

[0088] Ambient Temperature Compensation Factor=0.974

[0089] During the Chiller Self-Test Procedure, the chiller controller multiplies the Ambient Temperature Compensation Factor by the Reference Cooling Rate, with the chiller controller registering the result in memory as the Expected Cooling Rate. The calculation of Expected Cooling Rate follows the form:

Expected Cooling Rate=(Reference Cooling Rate)*(Ambient Temperature Compensation Factor)

[0090] Example Calculation:

[0091] Reference Cooling Rate=5 C./minute

[0092] Ambient Temperature Compensation Factor=0.974

Expected Cooling Rate=5 C./minute*0.974

[0093] Expected Cooling Rate=4.87 C./minute

[0094] As part of the Chiller Self-Test Procedure, the chiller controller 60 will actuate components within the chiller such as motors and valves (such as the valves shown in FIG. 1) such that the chiller's cooling fluid will be cooled between the same two temperatures as used in the end of line production quality assurance test that was previously used to derive the Reference Cooling Rate and Reference Ambient Temperature. The cooling rate observed during the Chiller Self-Test will be registered in the memory of the chiller controller as the Self-Test Cooling Rate.

[0095] Upon completion of the Chiller Self-Test Procedure's actuation of electromechanical circuits, the chiller controller 60 includes an interface (whether graphical, such as FIG. 3, and/or digital) that will provide the user with diagnostic information. The chiller controller will provide different diagnostic information depending on comparison of the Self-Test Cooling Rate and the Expected Cooling Rate. One or more thresholds below the Expected Cooling Rate may be established by the chiller controller, such that different actionable instructions will be presented to the user, based on the comparison between the Self-Test Cooling Rate and these threshold levels. A threshold level, will provide tolerance for variances in site and normal wear, such that false negative results are minimized. For instance, the chiller controller may instruct the user at the conclusion of the Chiller Self-Test that the chiller needs further service if the Self-Test Cooling Rate is less than 95% of the Expected Cooling Rate. Additional thresholds may be defined within the chiller controller, in order to instruct the user as to differing levels of problem severity.

[0096] While the disclosure is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and have herein been described in detail. It should be understood, For instance, there is a number of variants in terms of which operational parameters can be sampled (e.g., discharge temperature, air flow volume, fan speed, etc.). Likewise, there is no special attachment to the particular order of tests in the self-test, or the composition of the tests employed (or the temperature quantities involved). Further, it will be understood that the present invention could encompass an adjustment of the in situ readings as opposed to the factory readings so as to enable the appropriate comparison of performance. There is no intent to limit the disclosure to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.