USE OF AN ADJUSTABLE EXPANSION VAVLE TO CONTROL DEHUMIDIFICATION

Abstract

A refrigerant system is provided with a control for its expansion device. The control operates the expansion device to adjust the superheat of the refrigerant leaving an evaporator to have desired dehumidification for air being delivered into an environment to be conditioned.

Description

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system incorporating an adjustable expansion valve, and more particularly, to a refrigerant system wherein this adjustable expansion valve is controlled to achieve desired dehumidification within a climate-controlled environment. A typical example of such an adjustable expansion device is an electronic expansion valve.

Refrigerant systems are known in the HVAC&R (heating, ventilation, air conditioning and refrigeration) art, and operate to compress and circulate a refrigerant throughout a closed-loop refrigerant circuit, connecting a plurality of components, to condition a secondary fluid to be delivered to a climate-controlled space. In a basic refrigerant system, refrigerant is compressed in a compressor from a lower to a higher pressure and delivered to a heat rejection heat exchanger (condenser or gas cooler). From the heat rejection heat exchanger, where heat is typically transferred from the refrigerant to an ambient environment, a high-pressure refrigerant flows to an expansion device where it is expanded to a lower pressure and temperature and then is routed to a heat accepting heat exchanger (evaporator), where refrigerant cools a secondary fluid to be delivered to the conditioned environment. From the evaporator, refrigerant is returned to the compressor. One common example of refrigerant systems is an air conditioning system, which operates to condition (cool and often dehumidify) air to be delivered into a climate-controlled zone or space.

Refrigerant systems are utilized to provide temperature control, and often humidity control, for air supplied into an occupied environment. One feature that is important to the reliable and efficient operation of a refrigerant system is the amount of superheat of the refrigerant leaving the evaporator and moving to the compressor. Typically, the superheat, which is defined as a difference between the actual temperature and the saturation temperature of the refrigerant, must be kept within a tight band for most efficient and reliable operation of the refrigerant system. Moreover, it is also typical that for pure temperature control, a refrigerant system operates most efficiently with the lowest safe superheat amount that can be accurately sensed and maintained over a wide range of environmental and operating conditions. For various reasons, the superheat needs to be kept several degrees above zero, and it is typically maintained in the low range from 6 to 12° F.

Control of the evaporator superheat has been provided for a variety of functions, however, the evaporator superheat has not been controlled to control dehumidification of the air being delivered into an environment to be conditioned.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a control for an electronic expansion valve (EXV) achieves a desired refrigerant superheat at the evaporator exit such that the dehumidification provided by the refrigerant system to the air delivered into a conditioned environment can be controlled. In one embodiment, the “dehumidification” mode of superheat control is only entered if a reduced cooling load provided by the refrigerant system is desired. In another embodiment, various conditions for reliable operation of the refrigerant system, such as discharge temperature and saturation suction temperature being within specified respective ranges, have to be satisfied while entering into the “dehumidification” mode of superheat control or continuously operating in the “dehumidification” mode of superheat control.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the basic refrigerant system incorporating the present invention.

FIG. 2 is an example of simplified flowchart of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a refrigerant system 20 incorporating a compressor 22 for compressing a refrigerant and delivering it downstream to a heat rejection heat exchanger 24. From the heat rejection heat exchanger 24, the refrigerant passes through an electronic expansion valve 26, and then to an evaporator 30. As shown, air moving over the evaporator 30 is delivered into an environment to be conditioned 32. The environment to be conditioned 32 is provided with a control 43 that allows an occupant to select desired temperature and/or humidity levels to be provided by the air being delivered into the environment.

A control 28 is shown for the electronic expansion device 26. Moreover, transducers or other sensors 34 and 36 are shown in various locations within the refrigerant system 20. As shown, a transducer 34 is provided downstream of the compressor and may sense the pressure and/or temperature at the discharge of the compressor 22. Similarly, a sensor 36 may sense the pressure and/or temperature downstream of the evaporator 30. The sensors 34 and 36 signals are provided to the control 28. It should be noted that some of these sensors are optional and may not be required for certain system configurations.

Controls are known which operate to control electronic expansion devices to achieve desired superheat values downstream of the evaporator 30. Typically, to achieve desirable performance (total capacity and efficiency) for the refrigerant system 20 while preserving reliability of the compressor 22, it would be desirable to control the evaporator superheat to low positive values, typically in the range from 6 to 12° F.

In this invention, however, the inventors have recognized that by increasing superheat under certain circumstances, could lead to increased dehumidification capability of the evaporator 30 and in turn lower humidity of the air being delivered into the conditioned environment 32. Thus, the present invention utilizes its control of the expansion device 26 to achieve increased dehumidification, at least under certain circumstances.

It should be noted that total capacity of the evaporator 30 decreases when superheat is increased, while a simultaneous capacity shift from the sensible component to the latent component is taking place. As a result, a sensible heat ratio (the ratio of the sensible capacity to the total capacity) provided by the evaporator 30 is reduced. Therefore, by increasing evaporator superheat, operation of the refrigerant system 20 can be focused more on providing dehumidification, if desired, while full cooling sensible capacity is not required. In other words, the sensible heat ratio of the evaporator 30 can be controlled by controlling the electronic expansion valve 26 and consequently adjusting superheat at the exit of the evaporator 30. Therefore, by controlling the electronic expansion valve 26, the total evaporator capacity as well its sensible and latent components can be controlled.

Feedback from the sensors 34 and 36 may be used to ensure that the increased superheat is provided to ensure desired dehumidification while, at the same time, any unreliable or unsafe operational limits are not being approached. For instance, the desired superheat range may be defined by a lower limit and a higher limit, with the lower limit restricted by a minimum value of the evaporator pressure (or saturation temperature) and the higher limit constrained by a discharge temperature threshold. As known, abnormally low evaporator pressure may cause the evaporator freeze-up and excessively high discharge temperature may lead to the compressor damage.

As shown in FIG. 2, the control 28 may normally operate to achieve a desired optimal superheat in a conventional cooling mode, for instance, to provide maximum performance (capacity and efficiency) for the refrigerant system 20 to cool the air delivered to the conditioned environment 32. However, at least under circumstances where a reduced sensible cooling load is demanded, such as, for instance, when the ambient temperature is sufficiently low or/and sensible cooling load demands in the conditioned space 32 are not significant, the control 28 enters a “dehumidification” mode of superheat control. In this “dehumidification” mode, the control 28 may control the expansion device 26, such that superheat is adjusted so that the capacity of the evaporator 30 is shifted from cooling to dehumidification (to lower sensible heat ratios) to reduce humidity of the air being delivered into the zone to be conditioned 32. A worker of ordinary skill in the art would recognize how to control the electronic expansion device 26, given the goals of this application as described above, including maintaining the operation of the refrigerant system 20 within safety and reliability limits.

It should be noted that superheat control may be executed at the compressor suction or compressor discharge. In case of the compressor suction, it can be executed at the location toward the compressor suction instead of the evaporator exit. Further, superheat control can be executed at the compressor discharge, if the relationship between suction superheat and discharge superheat is known. Further, even under circumstances when the desired humidity level cannot be precisely achieved by the evaporator superheat control, it still can be noticeably reduced towards the desired value providing a higher degree of comfort for an occupant of the conditioned space.

It should be pointed out that many different compressor types could be used in this invention. For example, scroll, screw, rotary, or reciprocating compressors can be employed. The refrigerant systems that utilize this invention can be used in many different applications, including, but not limited to, stationary and mobile air conditioning systems as well as heat pump systems. The refrigerant system can also employ vapor injection, liquid injection, multiple circuits, as well as compressors connected in parallel in a tandem fashion.

Although embodiments of this invention have been disclosed a worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims

1. A refrigerant system including:

a compressor for compressing a refrigerant and delivering it downstream into a heat rejection heat exchanger, the refrigerant from said heat rejection heat exchanger passing through an adjustable expansion device, and then through an evaporator, before being returned to the compressor; and

a control for said adjustable expansion device, said control being operable to control dehumidification in an environment to be conditioned by controlling said adjustable expansion device.

2. The refrigerant system as set forth in claim 1, wherein said dehumidification control consists of changing refrigerant superheat.

3. The refrigerant system as set forth in claim 2, wherein said superheat is at least one of suction superheat and discharge superheat.

4. The refrigerant system as set forth in claim 1, wherein said dehumidification control has a limit on the maximum acceptable superheat.

5. The refrigerant system as set forth in claim 1, wherein said adjustable expansion device is an electronic expansion valve.

6. The refrigerant system as set forth in claim 1, wherein said control being provided with feedback of at least one measurement within said refrigerant system.

7. The refrigerant system as set forth in claim 6, wherein said feedback includes feedback from at least one of the pressure and temperature measurement at the discharge of said compressor.

8. The refrigerant system as set forth in claim 6, wherein said feedback includes feedback from at least one of the pressure and temperature measurement in at least one location selected from the following locations: the evaporator, the compressor or between the evaporator and the compressor.

9. The refrigerant system as set forth in claim 1, wherein said control has a dehumidification mode at which it increases the superheat of the refrigerant leaving the evaporator, when full sensible cooling capacity of the refrigerant system is not required, to provide desired dehumidification.

10. The refrigerant system as set forth in claim 1, wherein said control has a dehumidification mode at which it increases the superheat of the refrigerant leaving the evaporator, when full sensible cooling capacity of the refrigerant system is not required, to provide the desired sensible heat ratio.

11. The refrigerant system as set forth in claim 1, wherein said control has a dehumidification mode at which it increases the superheat of the refrigerant leaving the evaporator, when full sensible cooling capacity of the refrigerant system is not required, to provide the desired latent capacity and the desired sensible capacity.

12. A method of operating a refrigerant system including the steps of:

(a) compressing a refrigerant and delivering it downstream into a heat rejection heat exchanger, the refrigerant from said heat rejection heat exchanger passing through an adjustable expansion device, and then through an evaporator, before being returned to the compressor; and

(b) controlling said adjustable expansion device to control dehumidification in an environment to be conditioned by controlling said adjustable expansion device.

13. The method as set forth in claim 12, wherein said control being provided with feedback of at least one measurement within said refrigerant system.

14. The method as set forth in claim 13, wherein said feedback includes feedback from at least one of the pressure and temperature measurement at the discharge of said compressor.

15. The method as set forth in claim 13, wherein said feedback includes feedback from at least one of the pressure and temperature measurement in at least one location selected from the following locations: the evaporator, the compressor or between the evaporator and the compressor.

16. The method as set forth in claim 12, wherein said control moving into a dehumidification mode at which it increases the superheat of the refrigerant leaving the evaporator, when full sensible cooling capacity of the refrigerant system is not required, to provide desired dehumidification.

17. The method as set forth in claim 12, wherein said control moving into a dehumidification mode at which it increases the superheat of the refrigerant leaving the evaporator, when full sensible cooling capacity of the refrigerant system is not required, to provide the desired sensible heat ratio.

18. The method as set forth in claim 12, wherein said control moving into a dehumidification mode at which it increases the superheat of the refrigerant leaving the evaporator, when full sensible cooling capacity of the refrigerant system is not required, to provide the desired latent capacity and the desired sensible capacity.

19. The method as set forth in claim 12, wherein said dehumidification control consists of changing refrigerant superheat.

20. The method as set forth in claim 13, wherein said superheat is at least one of suction superheat and discharge superheat.

21. (canceled)

22. (canceled)