Patent Grant
6928389
The present invention relates to compressor performance and, in particular, to calculating performance parameters for new and existing compressors.
Whether troubleshooting or replacing a compressor in an existing system or selecting a compressor for a new system, it is desirable to know how the compressor performs. The performance of a compressor can be captured generally by four operating parameters: Capacity (Btu/hr), Power (Watts), Current (Amps) and Mass Flow (lbs/hr). The following equation can be used to describe each of the above-listed parameters in relation to the others: Result=C0+C1*TE+C2*TC+C3*TE2+C4*TE*TC+C5*TC2+C6*TE3+C7*TC*TE2+C8*TE*TC2+C8*TE*TC2+C9*TC3, where TE=Evaporating Temperature (F), TC=Condensing Temperature (F) and C0-C9 are the rating coefficients for each parameter. For this equation, there exists unique rating coefficients for each compressor and for each parameter.
Traditionally, compressor performance data is obtained through reference to large binders of hardcopy performance data, or by using a modeling system, which requires the use of compressor rating coefficients. The difficulty with both of these methods is that the compressors are rated at standard conditions, which means that the sub-cool temperature and either the return gas or the super-heat temperatures remain constant. Neither the hardcopy performance data nor the data derived from the rating coefficients in the modeling system will reliably indicate a suitable compressor when actual conditions are not standard. To modify the standard conditions the sub-cool temperature the return gas or the super-heat temperatures must be manually converted to reflect actual conditions. This conversion requires the understanding of thermodynamic properties as well as knowledge of refrigerant property tables.
In addition, because there are thousands of compressors commercially available, the maintenance of hardcopy binders and modeling systems for each of the compressors is an insurmountable task given rapid industry and product changes. Further, compressor rating coefficients are often re-rated, compounding the difficulty in maintaining accurate data.
The present invention provides a method for determining the performance of a compressor using an updateable performance calculator with a convenient user interface. The performance calculator allows the user to select a compressor either by using a model number or by entering specific design conditions. Additionally, the performance calculator includes a lockout feature that assures the calculator is using the latest and most up-to-date data and methods.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application or uses.
Performance calculator 30 is shown schematically as including controller 12, computer 14, and memory device 20, but more or fewer computers, controllers, and memory devices may be included. For example, controller 12 of cooling system 10 maybe a processor or other computing system having the ability to communicate through communication platform 15 or internet connection 16 to computer 18, which is shown external to cooling system 10 and typically at a remote location. Computer 14 is shown located locally, i.e., proximate controller 12 and cooling system 10, but may be located remotely, such as off-premises. Alternatively, computer 14 and computer 18 can be servers, either individually or as a single unit. Further, computer 14 can replace controller 12, and communicate directly with system 10 components and computer 18, or vice versa. Also, memory device 20 may be part of computer 14.
Internal to cooling system 10, condenser 22 connects to compressor 24 and a load 26. Compressor 24, through suction header 25 communicates with load 26, which can be an evaporator, heat exchanger, etc. Through one or more sensors 28, controller 12 monitors system conditions to provide data used by performance calculator 30. The data gathered by sensors 28 can include the current, voltage, temperature, dew point, humidity, light, occupancy, valve condition, system mode, defrost status, suction pressure and discharge pressure of cooling system 10, and additionally can be configured to monitor other compressor performance indicators.
As one skilled in the art can appreciate, there are numerous possibilities for configuring cooling system 10. Although the above-described system is a cooling system, the performance calculator 30 is suitable for other systems including, but not limited to, heating, air conditioning, and refrigeration systems.
Referring to
As previously mentioned, the rating coefficients are calculated at standard conditions and are often re-rated after the compressor is commercially released for sale. In addition, as compressors are continually developed, their rating coefficients and application parameter limitations need to be added to database 40. To assure database 40 includes the most up-to-date data, the performance calculator 30 includes a lockout feature that disables operation after a predetermined period, usually ninety days, until the database is updated. Optionally, updates to the performance calculator 30 can be made by retrieving data via the internet or from any other accessible recording medium.
To begin the calculation process, the user selects a compilation route at step 50. Two examples of compilation routes are selecting a compressor by model number via step 60 or entering design conditions via step 70. Entering design conditions will return a list of compressors suitable for a particular application. Both of the example compilation routes are discussed in detail below.
Continuing the calculation process in
Returning now to
Referring again to the beginning of the process in
In addition, at data entry points 100 and 101, the user may select a capacity rate and a capacity tolerance percentage, respectively. Compressor capacity is expressed in terms of its enthalpy, which is a function of a compressor's internal energy plus the product of its volume and pressure. More specifically, the change in compressor enthalpy multiplied by its mass flow defines its capacity. The tolerance percentage refers to its capacity in Btu/hr.
Lastly, at selection point 102, the user may elect to narrow the selection list of compressors by selecting a compressor by category. For example, the user may only be interested in compressors that are OEM production, service replacement or internationally available models.
When all selections are complete, the user activates the select button 104, which initiates at step 120 a query of database 40 for records that match the design criteria. As discussed previously, each compressor's rating coefficients are representative of the compressor when measured at standard conditions. For example, 65° F. return gas and 0° F. sub-cool, or some other standard at testing. To the extent the specified design conditions differ from standard, conversions are performed to reflect the condition changes. The conversions alter the standard conditions to the new design conditions such as, for example, 25° F. superheat and 10° F. sub-cool. The conversions are derived from thermodynamic principles such as, Q=mΔh, where Q=Capacity, m=mass flow, and Δh=enthalpy change. The query returns a list, after which the user may select a compressor and continue with the performance calculation process.
Returning to
Compressor performance is often expressed in terms of saturated suction and discharge temperatures. For compressors that use glide refrigerants, such as R407C, it is advantageous to determine the appropriate temperatures that define the suction and discharge conditions. There are generally two ways to accomplish this, by midpoint or dew point temperatures. The midpoint approach is expressed by using temperatures that are midpoints of the condensation and evaporation processes. While this is a valid approach for non-glide refrigerants the performance data for compressors using glide refrigerants is more accurate when determined at dew point. The term “glide”, as used herein, is widely used in industry to describe how the temperature changes, or glides, from one value to another during the evaporation and condensation processes. Numerous refrigerants possess a gliding effect. In some, the glide is relatively small and normally neglected, but in others, such as the R407 series, the glide is measurable and can have an effect on a refrigeration cycle and compressor performance data.
At step 125 in
Once all data is inputted, an operating envelope check is performed at step 130 on the data to verify that it is within compressor operating limits. Each compressor has design and application limits that are predetermined and are defined by evaporating and condensing temperature limits. Each application has an operating envelope, and the check verifies that the compressor selected can run within its operating envelope. The code used for the verification of compressor operating limits performed at step 130 is shown in the Appendix. The operating envelope will be described in detail below.
After final parameter selections are made, the user orders performance calculator 30 to calculate the Capacity, Power, Current, Mass Flow, EER and Isentropic Efficiency for the compressor selected 140. The user can also select from the main selection interface 300 another compressor using the model number method, or by the application condition method previously discussed. Additional features include creating data tables representing a compressor's operating envelope, graphically showing the operating envelope and checking the rated amperage for the compressor selected.
As briefly explained earlier, each application has an operating envelope. The purpose of the envelope is to define an area that encompasses the operating range for each compressor. An example of an operating envelope is graphically represented in FIG. 6. The envelope is defined by a series of points that represent the lower and upper limits of the evaporating and condensing temperatures for a given compressor. If an evaporating or condensing temperature is selected that is outside the operating envelope, such as at point 132, which represents an evaporation temperature of −30° F. and a condensing temperature of 45° F., a message appears in a display window 110 (shown in FIG. 4). The message informs the user that the conditions are outside the operating envelope, in which case no performance calculations are returned. An example of a set of temperatures that falls within the operating envelope, and returns performance results, is located at point 134, where the evaporating temperature is −60° F. and the condensing temperature is 35° F.
Several additional features of the performance calculator 30 are available at the main selection interface 300 of FIG. 4. One such feature is the create tables function, which is shown in FIG. 7. The function generates a table that displays the following parameters: Capacity (Btu/hr) 140, Power (Watts) 142, Current (Amps) 144, Mass Flow (lbs/hr) 146, EER (Btu/Watt-hr) 148 and Isentropic Efficiency (%) 150 for an entire operating envelope. Referring to cell A in
Another feature available from main selection interface 300 of
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
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| Number | Date | Country | |
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| 20040068390 A1 | Apr 2004 | US |
