Patent Application
20110219790
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Heating, ventilation, and air conditioning systems (HVAC systems) may utilize refrigerants in thermodynamic processes to cool and/or heat fluids for use in conditioning a temperature and/or a humidity of spaces serviced by the HVAC systems. Some HVAC systems may comprise substantially closed refrigeration systems that perform better when a particular mass of refrigerant is contained within the substantially closed refrigeration system. The particular mass of refrigerant or so-called “charge” of refrigerant needed by a particular HVAC system to perform well may be dependent upon the volume and/or configuration of various components of the HVAC system that accept refrigerant, including any refrigerant conduits used to join the various components of the HVAC system. It is known that some HVAC systems may require adjustment of the mass and/or charge of refrigerant retained within the HVAC system during the course of installing, repairing, and/or maintaining the HVAC system.
While there are many well-known methods of providing a mass of refrigerant to HVAC systems (or methods of “charging” an HVAC system), existing methods may fail to charge an HVAC system accurately even though the methods are adhered to strictly. Some well-known methods of charging an HVAC system include charging an HVAC system based primarily on a weight of refrigerant, adjusting an HVAC system charge in response to a measured subcooling, and adjusting an HVAC system charge in response to a measured superheat. The above-listed methods of charging an HVAC system may fail to properly charge an HVAC system due to the environment in which the HVAC system operates (i.e., temperatures, humidity, and/or other environmental factors), due to variations in the physical configuration of the HVAC system as actually installed compared with the physical configuration assumed to be adhered to by the methods (i.e., prescribed distances between components and/or prescribed height differences between components), and/or due to variations in actual operation of the HVAC system as compared to the operation assumed to be adhered to by the methods (i.e., providing prescribed air flow across particular heat exchangers).
In some embodiments a method of charging an HVAC system by determining a relationship between a liquid line temperature of the HVAC system, a suction line pressure of the HVAC system, and an ambient outdoor temperature of the HVAC system is provided.
In other embodiments, a method of charging an HVAC system by adjusting a mass of refrigerant in the HVAC system to approach a target minimum liquid line temperature is provided.
In still other embodiments, a method of charging an HVAC system by testing the HVAC system according to at least three sets of test parameters, two of the three sets of test parameters comprising testing the HVAC system at substantially a same outdoor ambient temperature and at least one of the remaining set of test parameters comprising testing the HVAC system at a different outdoor ambient temperature is provided.
For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.
Some methods of charging HVAC systems fail to properly charge HVAC systems even when the methods are adhered to strictly. Further, some HVAC systems continue to perform substantially as desired even though the HVAC systems are not appropriately charged with refrigerant. For example, some HVAC systems comprising spine fin heat exchangers and/or other heat exchangers having substantially traditional total refrigerant volumes may continue to perform, albeit less effectively, in overcharged states (more than an optimum amount of refrigerant) or undercharged states (less than an optimum amount of refrigerant) that result from being charged according to a subcooling charging method.
However, some HVAC systems that comprise micro-channel heat exchangers are less likely to perform substantially as desired when inappropriately charged, even when the charge is only slightly greater than or slightly less than an appropriate mass of refrigerant. Accordingly, there is a need for a system and method of charging an HVAC system that improves the accuracy with which an HVAC system is charged. Further, the same need may be more critical for HVAC systems comprising micro-channel heat exchangers. The present disclosure provides systems and methods for properly charging HVAC systems by adjusting a charge of an HVAC system to achieve a target minimum liquid line temperature and by primarily using suction line pressure and ambient outdoor temperature as feedback for determining what target minimum liquid line temperatures should be attained.
Further, a charge port 128 is configured to selectively allow refrigerant flow into and out of the suction line 122 through the charge port 128. The charge port 128 may be equipped with a check valve, such as a Schrader valve, to selectively allow fluid flow through the charge port 128. A refrigerant output of the compressor 112 is connected to an input of the outdoor heat exchanger 114 via a discharge line 130. An output of the heat exchanger 114 is connected to an input of the flow restrictor 110 via a liquid line 132. In this embodiment, a liquid line service valve 134 is configured to selectively allow refrigerant flow into and out of the liquid line 132 through a liquid line pressure tap 136. An output of the flow restrictor 110 is connected to an input of the indoor heat exchanger 106.
In some embodiments, the HVAC system 100 further comprises a suction line pressure gauge 138 configured to determine and/or display a pressure of the refrigerant within the suction line 122, a liquid pressure gauge 140 configured to determine and/or display a pressure of the refrigerant within the liquid line 132, a liquid line thermometer 142 configured to determine and/or display a temperature of the liquid line 132, and an ambient temperature sensor 144 configured to measure and/or display a temperature of the environment immediately surrounding the outdoor unit 104. In some embodiments, a location of the ambient temperature sensor 144 may be selected in a manner that improves measurement of the ambient environmental temperature as influenced by operation of the outdoor unit 104. In some embodiments, a maximum separation distance between the ambient temperature sensor 144 and the outdoor unit 104 (i.e., the outdoor heat exchanger 114) may be about 6 inches or less. The HVAC system 100 further comprises an indoor temperature sensor 148 configured to determine and/or display an ambient indoor temperature associated with the indoor unit 102.
In some embodiments, the HVAC system 100 may be installed so that the refrigerant input into the indoor unit 102 (i.e., the portion of the liquid line 132 generally connected to the indoor unit 102) may be located vertically offset from the refrigerant output of the outdoor unit 104 (i.e., the portion of the liquid line 132 generally connected to the outdoor unit 104). Such a vertical offset between the input to the liquid line 132 and the output of the liquid line 132 may be generally be referred to as a lift distance 146. The lift distance 146 may be generalized as being dependent upon the circumstances of a particular installation of an HVAC system 100. For example, where an outdoor unit 104 rests substantially at ground level, the lift distance 146 may be negligible when the indoor unit 102 is also installed substantially at ground level. However, in an installation of an HVAC system 100 where the outdoor unit 104 rests substantially at ground level and the indoor unit 102 is installed well above ground level (i.e., on a second or higher level of a building and/or in an attic of a building) the lift distance 146 may be significant. In some embodiments, the lift distance 146 may have a value of between about zero to about fifty feet, alternatively about zero to about thirty feet, or any other value. While the lift distance 146 shown in
Further, in some embodiments, the lengths of each of the suction line 122 and the liquid line 132 may be generalized as being substantially similar insofar as each of the suction line 122 and the liquid line 132 may generally be provided to have lengths necessary to join the indoor unit 102 to the outdoor unit 104. A so-called overall “line length” that each of the suction line 122 and the liquid line 132 must extend to accomplish the above-described joining of the indoor unit 102 to the outdoor unit 104 may be a value of about less than 10 feet to about 200 feet, alternatively about less than 10 feet to about 60 feet, or any other suitable length necessary to join the indoor unit 102 to the outdoor unit 104.
In some embodiments of the HVAC system 100, at least one of the indoor heat exchanger 106 and the outdoor heat exchanger 114 may be a so-called “micro-channel” heat exchanger. Micro-channel heat exchangers may be of the type disclosed in U.S. Patent Publication No. 2005/0269069 A1 to Stephen S. Hancock published on Dec. 8, 2005, which is incorporated by reference herein in its entirety. It will be appreciated that in embodiments of the HVAC system 100 where at least one of the indoor heat exchanger 106 and the outdoor heat exchanger 114 are micro-channel heat exchangers, charging the HVAC system 100 with an appropriate mass of refrigerant may be more critical to achieving desired performance of the HVAC system 100 as compared to embodiments where the HVAC system 100 does not comprise a micro-channel heat exchanger. The above-described increased HVAC system 100 performance sensitivity may be due at least in part to the micro-channel heat exchanger comprising significantly less internal volume for housing refrigerant as compared to other types of heat exchangers such as so-called “spine fin coil” heat exchangers. As explained in greater detail below, the HVAC system 100 may be charged according to one or more of the charging methods described herein.
Most generally, this disclosure provides HVAC system charging methods that allow HVAC systems, including, but not limited to, HVAC systems such as HVAC system 100 to be charged primarily by altering a refrigerant charge of an HVAC system with a goal of achieving a target minimum liquid line temperature where the target minimum liquid line temperature is determined as a function of an outdoor ambient temperature and a suction line pressure. Most generally, the operational and/or equipment differences among combinations of various models and/or variations of indoor units 102 and outdoor units 104 may result in the target minimum liquid line temperature of one HVAC system having a first combination of indoor unit 102 and outdoor unit 104 to be different from the target minimum liquid line temperature of a different HVAC system having a second combination of indoor unit 102 and outdoor unit 104. Accordingly, it will be appreciated that some methods of charging an HVAC system as disclosed herein may first require determining a set of recommended target minimum liquid line temperatures for a particular HVAC system 100. In other words, it will be appreciated that while different HVAC systems 100 may be charged according to the method described above, different HVAC systems 100 may need to be charged according to different target minimum liquid line temperature values even when operational conditions, outdoor ambient temperatures, and/or suction line pressures of the different HVAC systems are substantially the same. As such, some methods of charging an HVAC system 100 may comprise determining a plurality of target minimum liquid line temperature values as functions of outdoor ambient temperatures and suction line pressures of the HVAC system 100.
Most generally, for any particular HVAC system, a plurality of target minimum liquid line temperature values may be determined as functions of outdoor ambient temperatures and suction line pressures of the particular HVAC system. Such relationships may be successfully and predictably utilized because the suction line pressure and the outdoor ambient temperature (i.e., as measured by the suction line pressure gauge 138 and ambient temperature sensor 144, respectively) have been discovered to be substantially independent functions of the operation of the HVAC system and/or environmental factors affecting operation of the HVAC system. Put another way, the suction line pressure and the outdoor ambient temperature, while in some embodiments may not be wholly independent functions, any interdependence of the suction line pressure and the outdoor ambient temperature is practically and/or statistically insignificant. More specifically, it has been discovered that a variation in the suction line pressure does not necessarily correspond to a predictable and/or statistically significant change in the outdoor ambient temperature, and similarly, a variation in the outdoor ambient temperature does not necessarily correspond to a predicable and/or statistically significant change in the suction line pressure. The above discovery, in combination with the further discovery that a liquid line temperature (i.e., as measured by liquid line thermometer 142) is substantially predictable based on the suction line pressure and the outdoor ambient temperature, allows for creation and useful implementation of the above-mentioned plurality of target minimum liquid line temperature values.
In one embodiment, target minimum liquid line temperature values may be determined by testing an HVAC system under at least three sets of conditions. It will be appreciated that the HVAC system testing described herein may be accomplished either experimentally, through simulation, and/or both. Most generally, a first test of the HVAC system may be conducted according to a first set of operational parameters including conducting the first test at a first selected outdoor ambient temperature. The first test may be conducted to determine a functional relationship between the outdoor ambient temperature, the suction line pressure, and the liquid line temperature as a result of testing the HVAC system according to the first set of operational parameters. Next, the same HVAC system is tested according to a second set of operational parameters including conducting the second test at the first selected outdoor ambient temperature wherein the second set of operational parameters are selected to result in different resultant suction line pressure values even though the same outdoor ambient temperature was used in both the first test and the second test. It will be appreciated that any of a plethora of operational conditions may be varied between the first test and the second test to produce the above described different suction line pressure results, including, but not limited to, varying an airflow through the indoor heat exchanger 106, varying an airflow through the outdoor heat exchanger 114, varying a refrigerant flow rate through the compressor 112, varying the environmental conditions (such as indoor ambient temperature as measured by indoor temperature sensor 148) related to the indoor unit 102, varying the lift distance 146, varying the length of the suction line 122, varying the length of the liquid line 132, and/or any of many other variables known to have an impact on suction line pressure of an HVAC system. Regardless of which of the many variables are varied between the first test and the second test, the first and second test share the operational variable of having run the first test and the second test at a same first outdoor ambient temperature. Finally, a third test may be run according to a third set of operational parameters wherein the outdoor ambient temperature of the third test is not equal to the outdoor ambient temperature value used in the first test and the second test.
Each of the first test, the second test, and the third test are configured at least to collect data regarding the suction line pressure, outdoor ambient temperature, and the liquid line temperature as the suction line pressure is varied in response to one or more changes in operational parameters. As such, each of the first test, the second test, and the third test may be generalized as at least providing data points for use in a Cartesian coordinate chart 200 of suction line pressure on an X-axis and liquid line temperature on a Y-axis as shown in
The above discussion relates to determining a particular function and/or equation that generally represents liquid line temperature as a function of outdoor ambient temperature and suction line pressure and that provides resultant liquid line temperature estimates suitable for providing guidance in charging an HVAC system. It will be appreciated that other equations, functions, and/or relationships may be determined from the data gathered according to the first test, the second test, and the third test. In other embodiments, estimations of the liquid line temperature may be more or less accurate than the estimates provided by the methodology stated above while still effectively enabling charging of an HVAC system in response to the estimates of liquid line temperatures. While the above describes the use of three tests to determine the relationships, it will be appreciated that more than three tests may be utilized to determine the relationships.
In some embodiments, the above-described first test, second test, and third test may be substantially conducted as the so-called “B,” “C,” and “A” tests, respectively, of the substantially standardized testing methods, such as, but not limited to the tests disclosed in 10CFR430 Appendix M as described by DOE in the Federal Register and/or as disclosed in AHRI Standard 210/240. Accordingly, the information and/or data necessary to determine the above-described relationships for estimating liquid line temperatures as a function of outdoor ambient temperature and suction line pressure may be obtained through testing that would otherwise already need to be performed to obtain satisfactory commercial rating certifications. According to the B, C, and A tests prescribed by at least one of the tests disclosed in 10CFR430 Appendix M as described by DOE in the Federal Register and/or as disclosed in AHRI Standard 210/240, the B test (or first test) may be conducted with an 82° F. outdoor ambient temperature, an 80° F. indoor dry bulb temperature, and a 67° F. indoor wet bulb temperature. The C test (or second test) may be conducted with an 82° F. outdoor ambient temperature, an 80° F. indoor dry bulb temperature, and an indoor wet bulb temperature of 57° F. or less (such as with an indoor wet bulb temperature of about 47° F.). The A test (or third test) may be conducted with a 95° F. outdoor ambient temperature, an 80° F. indoor dry bulb temperature, and a 67° F. indoor wet bulb temperature.
With the above-described data and relationships established between the liquid line temperature, suction line pressure, and outdoor ambient temperature, any of a variety of equations may be derived to represent the liquid line temperature as a function of outdoor ambient temperature and suction line pressure. In one embodiment, an equation may be derived to estimate liquid line temperature as a function of outdoor ambient temperature and suction line pressure as follows:
and where the constant, C, is determined from the test results of the first test, the second test, and the third test.
It will be appreciated that regardless of what function and/or equation is ultimately garnered from conducting the three tests, the resultant functions and/or equations may be applied to generate a graphical chart and/or matrix of values of target minimum liquid line temperatures where the target minimum liquid line temperatures are calculated as functions of possible combinations of outdoor ambient temperatures and suctions pressures. As such, the above-described discovery may, in some embodiments, be distilled into a simple to use graph and/or chart that may guide an HVAC system installer and/or technician to appropriately charge an HVAC system.
Referring now to
Referring now to
Referring now to
The method 500 of charging an HVAC system 100 of
The method 500 starts at block 502 and continues to block 504. At block 504, the indoor ambient temperature and the outdoor ambient temperature may be checked to verify that the temperatures are within prescribed ranges that will allow for proper charging of the HVAC system 100 according to the method 500. In some embodiments, the outdoor ambient temperature may need to be about 60° F. or above while the indoor ambient temperature may need to be between about 70° F. and 100° F. If the indoor ambient is not within the prescribed range, the indoor ambient temperature should be altered to conform with the prescribed range prior to continuing the method 500. If the outdoor ambient temperature is lower than 60° F., the HVAC system 100 may be charged according to a charging chart using 60° F. and a suction line pressure of 115 PSIG.
At block 506, the HVAC system 100 should be stabilized by operating the system in cooling mode for a minimum of about 10 minutes.
At block 508, each of the outdoor ambient temperature, the suction line pressure, the liquid line pressure, and the liquid line temperature should be measured.
At block 510, a charging chart appropriate for the HVAC system 100 being charged should be selected (see
At block 512, the measured outdoor ambient temperature should be located along the top of the selected charging chart (see
At block 514, the measured suction line pressure should be located along the left side of the charging chart (see
At block 516, a target minimum liquid line temperature should be determined at the intersection of the located measured outdoor ambient temperature on the charging chart and the located measured suction line pressure on the charging chart (see
At block 518, if the target minimum liquid line temperature falls between two listed temperatures on the charging chart, a target minimum liquid line temperature should be estimated (see
At block 520, a maximum liquid line pressure should be located on the charging chart (see
At block 522, if a target minimum liquid line temperature was estimated, a maximum liquid line pressure should similarly be estimated (see
At block 524, any charge adjustment needed should be determined and provided. This determination may be made by comparing the measured liquid line temperature against the target minimum liquid line temperature. If the measured liquid line temperature is above the target minimum liquid line temperature and the maximum allowable liquid line pressure has not been exceeded, refrigerant should be added to the HVAC system 100. If the measured liquid line pressure is higher than the maximum allowable liquid line pressure, refrigerant should be removed from the HVAC system 100. Further, if the measured liquid line temperature is lower than the target minimum liquid line temperature, refrigerant should be removed from the HVAC system 100.
To add refrigerant to the HVAC system 100, liquid refrigerant should be added to the HVAC system through the charging port 128 until the measured liquid line temperature is within 1 to 2° F. of the target minimum liquid line temperature. In alternative embodiments of an HVAC system 100 that comprises no charging port 128, refrigerant may be added through the suction line pressure tap 126.
At block 526, the HVAC system 100 should again be stabilized by running the HVAC system 100 in cooling mode for at least 10 minutes.
After stabilizing the HVAC system 100, the method 500 stops at block 528.
It will be appreciated that the method 500 should be repeated until at block 524, no charge adjustment is needed.
It will further be appreciated that any of the methods of charging an HVAC system disclosed herein may be used to charge so-called heat pump HVAC systems as well as non-heat pump and/or other conventional HVAC systems.
At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, RI, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=RI+k*(Ru−RI), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention.
