U.S. patent application number 11/995128 was filed with the patent office on 2008-08-21 for system reheat control by pulse width modulation.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20080196426 11/995128 |
Document ID | / |
Family ID | 37771893 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080196426 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
August 21, 2008 |
System Reheat Control by Pulse Width Modulation
Abstract
A refrigerant system is provided with a reheat circuit. A pulse
width modulation control is provided to achieve variable reheat
capacity and thus to satisfy a wide spectrum of temperature and
humidity levels in an environment conditioned by a refrigerant
system. The pulse width modulation signal provided for the reheat
flow control device achieves incremental amounts of reheat while
avoiding temperature and humidity variations in the conditioned
space.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Lifson; Alexander; (Manlius,
NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
37771893 |
Appl. No.: |
11/995128 |
Filed: |
August 23, 2005 |
PCT Filed: |
August 23, 2005 |
PCT NO: |
PCT/US2005/030603 |
371 Date: |
January 9, 2008 |
Current U.S.
Class: |
62/173 |
Current CPC
Class: |
F25B 2400/0403 20130101;
F25B 2600/2521 20130101; F24F 3/153 20130101 |
Class at
Publication: |
62/173 |
International
Class: |
F25B 29/00 20060101
F25B029/00 |
Claims
1. A refrigerant system comprising: a compressor, a condenser
downstream of said compressor, an expansion device downstream of
said condenser and an evaporator downstream of said expansion
device, a reheat circuit for selectively receiving refrigerant
through a reheat heat exchanger, an air-moving device passing air
over said evaporator and said reheat heat exchanger; and a control
for selectively operating a valving system to deliver refrigerant
through said reheat heat exchanger, and said control being operable
to utilize pulse width modulation signal to operate the valving
system to achieve levels of temperature and humidity control
between the levels of control with said reheat circuit being
continuously operational, and the levels of control without said
reheat circuit being operational.
2. The refrigerant system as set forth in claim 1, wherein said
reheat circuit receives refrigerant in a serial flow arrangement
relative to said condenser.
3. The refrigerant system as set forth in claim 2, wherein said
reheat circuit receives refrigerant from a location upstream of
said condenser.
4. The refrigerant system as set forth in claim 2, wherein said
reheat circuit receives refrigerant from a location downstream of
said condenser.
5. The refrigerant system as set forth in claim 1, wherein a bypass
is provided for selectively bypassing at least a portion of
refrigerant around said condenser.
6. The refrigerant system as set forth in claim 5, wherein said
bypass is controlled by a pulse width modulation valve.
7. The refrigerant system as set forth in claim 1, wherein said
reheat circuit is controlled by a three-way valve.
8. The refrigerant system as set forth in claim 1, wherein said
valving system consists of at least one valve.
9. The refrigerant system as set forth in claim 8, wherein said at
least one valve is a three-way valve.
10. A method of controlling a refrigerant system comprising the
steps of: (1) providing a compressor, a condenser downstream of
said compressor, an expansion device downstream of said condenser,
an evaporator downstream of said expansion device, a reheat circuit
to selectively receive a refrigerant through a reheat heat
exchanger, and an air-moving device to move air over said
evaporator and said reheat heat exchanger; and (2) operating said
refrigerant system by selectively actuating said reheat circuit to
pass refrigerant through said reheat heat exchanger, and operating
a control to utilize pulse width modulation signal to operate a
valving system to direct refrigerant to said reheat circuit to
provide levels of temperature and humidity control intermediate
discrete levels provided by actuating or not actuating said reheat
circuit.
11. The method as set forth in claim 10, further including the
steps of selectively bypassing said condenser by routing at least a
portion of refrigerant around said condenser.
12. The method as set forth in claim 11, wherein said bypass is
controlled by a pulse width modulation valve.
13. The method as set forth in claim 10, wherein said reheat
circuit receives refrigerant in a serial fashion relative to said
condenser.
14. The method as set forth in claim 13, wherein said reheat
circuit receives refrigerant from a location upstream of said
condenser.
15. The method as set forth in clam 13, wherein said reheat circuit
receives refrigerant from a location downstream of said
condenser.
16. The method as set forth in claim 10, wherein said valving
system consists of at least one valve.
17. The method as set forth in claim 16, wherein said at least one
valve is a three-way valve.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to a pulse width modulation control
that allows for continuous or precise stepwise reheat capacity to
be provided by a refrigerant system.
[0002] Refrigerant systems are utilized in many applications such
as to condition an environment. Air conditioners and heat pumps are
used to cool and/or heat the air entering an environment. The
cooling or heating load on the environment may change with ambient
conditions, and as the temperature and/or humidity levels demanded
by an occupant of the environment vary. Obviously, the refrigerant
system operation and control have to adequately reflect these
changes to maintain stable temperature and humidity conditions
within the environment.
[0003] In some cases, while the system is operating in a cooling
mode, the temperature level of the indoor air stream to provide a
comfortable environment in a conditioned space may need to be
higher than the temperature that would provide the ideal humidity
level. On the other hand, by lowering the temperature of the air
stream, more moisture can be removed from the air. These
contradicting trends presented challenges to refrigerant system
designers. One way to address such challenges is to utilize various
schematics incorporating reheat coils. In many cases, a reheat
coil, placed in the indoor air path downstream of the evaporator,
is employed for the purposes of reheating the air supplied to the
conditioned space, after it has been cooled in the evaporator, and
where the moisture has been removed.
[0004] In the prior art, controls can be programmed to optionally
actuate the reheat function. However, the capacity provided by the
reheat circuit is increased or decreased in steps. It would be
desirable to provide the ability to vary the reheat capacity and
overall system performance between these discrete steps.
[0005] While pulse width modulation controls have been provided for
various purposes in refrigerant systems, they have not been
utilized to provide varying steps in a reheat capacity.
SUMMARY OF THE INVENTION
[0006] In a disclosed embodiment of this invention, a pulse width
modulation control is provided for selectively varying capacity
provided by a reheat circuit and thus overall system performance.
The "on/off" cycle time interval is selected such that the overall
effect on the system in terms of external operational
characteristics, due to system thermal inertia, is negligible. That
is, an occupant of an environment being conditioned would not
recognize that the flow of refrigerant to the reheat circuit is
being periodically turned on and off.
[0007] In various embodiments, the control is operable to vary the
width of the pulse to achieve a desired time interval for a flow
control device such as a valve being opened to direct refrigerant
to the reheat heat exchanger. In this manner, a broad range of
reheat capacities can be covered and variable reheat control can be
provided.
[0008] In specific schematics, the present invention may also be
provided in combination with a circuit that allows for bypass of
refrigerant around a condenser to allow for additional operational
flexibility in the reheat functionality and control.
[0009] 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
[0010] FIG. 1 shows a first schematic.
[0011] FIG. 2 shows a second schematic.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] A refrigerant system 20 is illustrated in FIG. 1 including a
compressor 22 compressing refrigerant and delivering it to a
downstream condenser 24. A fan 25 blows air over the condenser 24.
Refrigerant passes from the condenser 24 to a downstream expansion
device 26, then to an evaporator 28, and finally returns to
compressor 22. A three-way valve 30 is placed on a discharge
refrigerant line, and as illustrated, between the compressor 22 and
the condenser 24. The three-way valve 30 is controlled by a control
38 for a purpose that will be described below. When the three-way
valve is in an open position, it will deliver refrigerant through a
reheat heat exchanger 34 and a check valve 35, and then return the
refrigerant back to a position 31 still upstream of the condenser
24. As is known, a fan 36 blows air over the evaporator 28, and the
reheat heat exchanger 34 is placed such that it is in the path of
that air stream behind the evaporator 28.
[0013] The purpose of the reheat heat exchanger 34 is to allow the
evaporator 28 to cool the air passing over it to a level that is
lower than may be desired by an occupant of an environment and
requested through a thermostat 32 in order to remove sufficient
amount of moisture from the air and maintain desired humidity level
in the environment. Lower temperatures of air passing over the
evaporator 28 result in more moisture been removed from the air.
The air then passes over the reheat heat exchanger 34, and is
reheated back towards the desired temperature. In this manner,
utilization of a reheat circuit provides both desired temperature
and humidity levels in the conditioned environment.
[0014] The control 38 sends a pulse width modulation signal to the
valve 30. The valve 30 is of a three-way type that is typically in
a normally open position (during a cooling mode of operation)
communicates refrigerant from the compressor 22 directly to the
condenser 24, and may be driven to an alternate position (during a
reheat mode of operation) at which it allows refrigerant to flow
from the compressor 22 through the reheat heat exchanger 34 to the
condenser 24. When a pulse width modulation signal is provided by
the control 38 to the valve 30, it moves the valve to this
alternate position. Since the control 38 is determining the
required reheat capacity, the control can then determine the width
of the pulse and the time interval between the pulses sent to the
valve 30, such that the valve 30 can be in the open position
precisely for an amount of time to provide this required reheat
capacity. In this manner, just the right reheat capacity is
provided, and temperature and humidity in a conditioned environment
are precisely controlled. The present invention thus offers a
relatively inexpensive and efficient method of providing a variable
reheat function with essentially an infinite number of reheat
stages.
[0015] FIG. 2 shows another embodiment 37, which is similar to the
FIG. 1 embodiment, however, rather than having a three-way valve,
conventional on/off solenoid valves 38 and 40 are controlled by the
pulse width modulation signal. When a reheat branch is active, the
valve 40 is opened and the refrigerant is tapped from a point 100
and is returned to point 102 of the main circuit. The pulse width
modulation is controlled in a manner similar to that described with
the FIG. 1 embodiment.
[0016] Valve 40 may be opened and closed to achieve a variable
reheat capacity similar to the three-way valve 30 in FIG. 1. Valve
38 may also be operated by the pulse width nodulation signal and
allows control over the refrigerant flow in a main refrigerant
circuit in conjunction with the valve 40.
[0017] The FIG. 2 schematic also provides the option of including a
condenser bypass line 42 passing through a bypass valve 44 to allow
rerouting of at least a portion of refrigerant around the condenser
24. The bypass valve 44 is activated when dehumidification is
desired with little or no cooling of the air. The operation and
control of the bypass valve 44 is as known in the art, however the
provision of the condenser bypass function that can also be
operated by the pulse width modulation signal along with the
variable pulse modulation control for the reheat circuit itself
provides increased flexibility in operation to precisely achieve
desired parameters (in terms of temperature and humidity) in an
environment conditioned by the refrigerant system 37.
[0018] Obviously both embodiments shown in FIGS. 1 and 2 may be
configured either with a three-way valve or a pair of solenoid
valves. Further, although only two reheat concepts are disclosed,
any known reheat schematic can benefit from the invention.
[0019] Pulse width modulation controls are known, and valves
operated by the pulse width modulation signal are known. The
present invention utilizes this known technology in a unique manner
to achieve goals and benefits as set forth above.
[0020] Although a preferred embodiment of this invention has been
disclosed, a worker of ordinary skill in this 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.
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