WO2005005895A1

WO2005005895A1 - Humidity control utilizing heat pump concept

Info

Publication number: WO2005005895A1
Application number: PCT/US2004/020130
Authority: WO
Inventors: Thomas J. Dobmeier; Michael F. Taras
Original assignee: Carrier Corporation
Priority date: 2003-06-30
Filing date: 2004-06-24
Publication date: 2005-01-20
Also published as: US20040261429A1; JP2007527494A; CN1826498A; EP1642068A1

Abstract

A vapor compression system for allowing humidity control includes a plurality of vapor compression circuits including at least one cooling circuit and at least one heat pump operable circuit; the plurality of circuits being adapted to act upon a stream of air whereby a first portion is cooled by the at least one cooling circuit (14, 16) and a second portion is heated by the heat pump operable circuit (12) whereby the stream of air can be dehumidified while maintaining a desired air stream temperature. As a result, such a system can have three modes of operation; cooling, heating and dehumidification with low sensible capacity as well as multiple steps of unloading. Furthermore, system reliability and complexity are improved and operation and control functions are enhanced.

Description

HUMIDITY CONTROL UTILIZING HEAT PUMP CONCEPT

BACKGROUND OF THE INVENTION The invention relates to a vapor compression system and, more particularly, to a system and method for operating same to provide control of humidity and sensible capacity. Vapor compression systems such as those incorporated into heating, ventilation, air conditioning and refrigeration (HVAC&R) systems, are frequently required to provide humidity control as well as temperature control. The humidity control function is typically provided by cooling a stream of air so as to condense moisture out of the stream of air as desired. Unfortunately, this results in substantial cooling of the air stream which can be beyond that desired by the user. Various methods are known for addressing this problem, most involving re-heating the cooled and dehumidified stream of air utilizing hot gas from the vapor compression circuit. This hot gas can be heat exchanged with the cooled and dehumidified air so as to re-heat the air and provide the desired end product. Unfortunately, such systems have issues, especially during low ambient conditions, in connection with refrigerant charge migration and significant variation of the system performance at different environmental conditions. Other methods, utilizing refrigerant bypass around the condenser coil, have similar issues. Furthermore, other methods, such as "warm liquid" reheat, do not allow for maintaining of low sensible capacity. The need remains, therefore, for an improved system and method for operating same whereby temperature control and humidity control are readily accomplished. It is therefore the primary object of the present invention to provide such a system and method. It is a further object of the present invention to provide a system and method which are versatile in being useful for cooling, heating and/or dehumidification. Other objects and advantages of the present invention will appear hereinbelow.

SUMMARY OF THE INVENTION In accordance with the present invention, the foregoing objects and advantages have been readily attained. According to the invention, a vapor compression system is provided for allowing humidity control, comprising a plurality of vapor compression circuits including at least one cooling circuit and at least one heat pump operable circuit; said plurality of circuits being adapted to act upon a stream of air whereby a first portion is cooled by said at least one cooling circuit and a second portion is heated by said heat pump operable circuit whereby said stream of air can be dehumidified while maintaining a desired air temperature. In further accordance with the invention, a method is provided for controlling temperature and hum.i dity of a stream of air, comprising the steps of providing a stream of air to be treated; providing a vapor compression system comprising a plurality of vapor compression circuits including at least one cooling circuit and at least one heat pump operable circuit; feeding a first portion of said stream of air to said at least one cooling circuit so as to provide a cooled dehumidified stream; and feeding a second portion of said stream of air to said at least one heat pump operable circuit so as to provide a heated stream; whereby said stream of air can be dehumidified while maintaining a desired air temperature.

. BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of preferred embodiments of the present invention follows, with reference to the attached drawing, wherein: Figure 1 schematically illustrates a system in accordance with the present invention.

DETAILED DESCRIPTION The invention relates to a vapor compression system and method for operating same which allow for dehumidification and, advantageously, cooling, heating and reduction in sensible capacity, as desired. In accordance with the invention, this functionality is provided by adapting a circuit of a multiple-circuit system to operate as a heat pump, preferably in a reversible manner, whereby a portion of air to be conditioned can be heated while other vapor compression circuits cool the air so as to dehumidify same. This can be done sequentially or separately as desired. Figure 1 schematically illustrates a system 10 in accordance with the present invention which includes a plurality of circuits 12, 14, 16 each illustrated as having a compressor 18, an outdoor coil 20, an expansion device 22 and an indoor coil 24. A stream of air 26 is passed through indoor coil 24 so as to treat this air as desired. In accordance with the invention, the plurality of circuits 12, 14, 16 includes one circuit 12 which is operable as a heat pump, in this embodiment through the positioning of a reversing valve 28 in the circuit. Other circuits, in this instance circuits 14, 16, are configured to provide the desired cooling function. Thus, circuits 14, 16 in this embodiment serve to cool portions 30, 32 of evaporator air 26, thereby removing moisture from same. At the same time, circuit 12 which is operable as a heat pump serves to heat portion 34 of evaporator air 26, and downstream combination of these portions of air results in a stream of air with reduced humidity and capable of reduced or substantially avoided sensible capacity as desired. The drawing shows separate or parallel treatment of portions 30, 32 and 34 of stream 26. It is well within the scope of the invention to sequentially treat stream 26 instead, for example by feeding stream 32 to stream 30 and then to stream 34 for reheating. Also, stream 26 can be treated both sequentially and in parallel through the same method, by connecting two portions in series and the third in parallel. In addition stream 26 or portions thereof can be mixed with untreated air if desired, for example outside air and/or air that is not treated with coil 24. Circuits 12, 14, 16 as illustrated in Figure 1 operate as is well known to a person of ordinary in the art through passing refrigerant along refrigerant lines between the various components which act upon the refrigerant to provide the desired function at coils 20, 24. System 10 in accordance with the present invention advantageously allows refrigerant to be used as a heating medium in coil 24 through which portion 34 passes, in combination with the remainder of the unit wherein circuits 14, 16 are operated as cooling circuits for dehumidification of portions 20, 32. System 10 permits the return air to be cooled in order to remove moisture (latent load) from the conditioned air by the cooling circuits. In the meantime, the heat pump circuit is used to add heat and consequently reduce the overall sensible capacity of the unit, so that the desired dry bulb condition can be maintained in the occupied space once the cooled and heated air streams are mixed, for example in a supply fan plenum. It should be appreciated that circuits 12, 14, 16 can advantageously be controlled so as to allow for three independent modes of operation of system 10. First, system 10 can be operated in a full cooling mode, wherein reversing valve 28 is configured to operate circuit 12 as a cooling circuit along with circuits 14 and 16. In this mode, full cooling capacity is provided to allow for dehumidification and cooling as desired. It should be appreciated that without switching capacity for circuit 12, this same function can be provided by taking circuit 12 offline and independently operating only circuits 14, 16. A second mode of operation is as described above, which is referred to herein as a low sensible dehumidification mode, wherein dehumidification of the air stream is provided with minimal cooling to the stream of air due to re-heat using the heat pump operable circuit. It should be understood that low sensible capacity cooling or heating can be obtained, depending on the number of heat pump and cooling circuits operating at a particular instance of time. Finally, system 10 can be operated in a heating mode through the use of circuit 12 configured to operate as a heat pump, with circuits 14, 16 being substantially inactive. This flexibility of system 10 in accordance with the present invention provides a substantial advantage. Furthermore, problems encountered in conventional systems are overcome. As set forth above, hot gas systems typically can have problems with refrigerant migration at low ambient conditions and significant capacity variation. The system of the present invention eliminates this problem and improves reliability in system performance at low ambient conditions . Additionally, system reliability and the control function are improved due to more precise matching of the specified conditions and significant reduction in a number of start/stop cycles. Also, it should be noted that each of the circuits, in heating or cooling, can be provided with internal means of unloading, or capacity reduction, further improving system operation. Similarly, in a system using warm liquid, the problem of space overcooling which is typical with these systems is eliminated. It should readily be appreciated that the present invention provides improved dry bulb control and humidity removal, and furthermore that the present invention allows for cost reduction and reduction in system complexity as well. It should be appreciated that although system 10 as illustrated in Figure 1 shows three circuits, one of which can be configured between a cooling circuit and a heat pump, it is well within the scope of the present invention to provide additional circuits, wherein one or more can be operated as heat pumps and one or more can be operated in a cooling mode. It should further be appreciated that although the present invention as shown allows for treatment of a portion of the stream of air with cooling circuits, and a different portion with the heat pump circuit, it is within the scope of the present invention to instead treat this air sequentially, that is, to treat the entire flow at a cooling coil followed by treatment of the entire flow at the heat pump coil. It should be appreciated that air treated by heating and cooling circuits can be combined or mixed with a portion of untreated air and either of these portions of air can be brought from an outside environment of re-circulated from a conditioned space . It should also be understood that the system can be configured of any number of cooling and heating circuits and these can be provided having components of different sizes. It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.

Claims

WHAT IS CLAIMED IS:

1. A vapor compression system for allowing humidity control, comprising: a plurality of vapor compression circuits including at least one cooling circuit and at least one heat pump operable circuit; said plurality of circuits being adapted to act upon a stream of air whereby a first portion is cooled by said at least one cooling circuit and a second portion is heated by said heat pump operable circuit whereby said stream of air can be dehumidified while maintaining a desired air stream temperature.

2. The system of claim 1, wherein said at least one heat pump operable circuit is selectively operable as a cooling circuit and as a heat pump circuit, whereby said system can be operated in at least three modes of operation including a cooling mode wherein said plurality of circuits are operated as cooling circuits, a low sensible dehumidification mode wherein said at least one cooling circuit is operated to cool said first portion and said at least one heat pump operable circuit is operated to heat said second portion, and a heating mode wherein said at least one heat pump operable circuit is operated as a heat pump and said at least one cooling circuit is inactive.

3. The system of claim 1, wherein said, circuits have internal unloading capability whereby temperature and humidity of said stream or air can be controlled.

4. The system of claim 1, wherein said circuits are arranged to sequentially treat a single stream of air.

5. The system of claim 1, wherein said circuits are arranged to treat said first portion and said second portion in parallel .

6. The system of claim 1, wherein said circuits are arranged to treat said stream of air in a combination of sequential and parallel portions including said first portion and said second portion.

7. A method for controlling temperature and humidity of a stream of air, comprising the steps of: providing a stream of air to be treated; providing a vapor compression system comprising a plurality of vapor compression circuits including at least one cooling circuit and at least one heat pump operable circuit; feeding a first portion of said stream of air to said at least one cooling circuit so as to provide a cooled dehumidified stream; and feeding a second portion of said stream of air to said at least one heat pump operable circuit so as to provide a heated stream, whereby said stream of air can be dehumidified while maintaining a desired air temperature.

8. The method of claim 7, wherein said first portion and said second portion are treated separately and then combined to provide a combined air stream.

9. The method of claim 8, further comprising selectively controlling flow rate in said first portion and said second portion whereby temperature and humidity of said combined air stream can be controlled.

10. The method of claim 7, wherein said stream of air is fed as said first portion to said at least one cooling circuit and sequentially fed as said second portion to said heat pump operable circuit.

11. The method of claim 7, further comprising treating said stream of air in a combination of sequential and parallel portions including said first portion and said second portion.

12. The method of claim 7, further comprising mixing an untreated stream of air with at least one of said first portion and said second portion.