U.S. patent application number 12/741910 was filed with the patent office on 2010-09-23 for method and apparatus for improving dehumidification.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20100236262 12/741910 |
Document ID | / |
Family ID | 40626021 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100236262 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
September 23, 2010 |
METHOD AND APPARATUS FOR IMPROVING DEHUMIDIFICATION
Abstract
Comfort temperature and humidity levels in a conditioned space
are controlled by cycling the speed of an evaporator fan motor in
such a manner that, during time periods when higher sensible
capacity is desired, the time in which the fan motor operates at a
higher speed is increased, and during time periods when a higher
latent capacity is desired, the time in which the fan motor
operates at a lower speed is increased. The fan motor may be a
single speed motor that is switched between on and off positions,
or it may be a multiple speed motor that is cycled between a higher
speed and a lower speed.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
40626021 |
Appl. No.: |
12/741910 |
Filed: |
November 8, 2007 |
PCT Filed: |
November 8, 2007 |
PCT NO: |
PCT/US07/23543 |
371 Date: |
May 7, 2010 |
Current U.S.
Class: |
62/89 ; 236/44C;
62/186; 62/426 |
Current CPC
Class: |
F24F 11/77 20180101;
F24F 3/1405 20130101; Y02B 30/70 20130101; F24F 11/30 20180101;
F24F 2110/10 20180101; F24F 2110/20 20180101; F24F 2003/1446
20130101 |
Class at
Publication: |
62/89 ; 62/186;
62/426; 236/44.C |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25D 17/04 20060101 F25D017/04; F24F 3/14 20060101
F24F003/14 |
Claims
1. A method of controlling the humidity and temperature in a
conditioned space comprising the steps of: providing an air
conditioning system having an evaporator and an associated
evaporator fan motor; and selectively operating said fan motor by
rapidly cycling between a first speed and a second speed, with said
second speed being higher then said first speed, to change the
latent or sensible capacity.
2. A method as set forth in claim 1 and further wherein, when a
higher sensible capacity is desired, the time in which the fan
motor operates at said second speed is increased, and when a higher
latent capacity is desired, the time in which the fan motor
operates at said first speed is increased.
3. A method as set forth in claim 1 wherein said evaporator fan
motor is a single speed motor and further wherein said first speed
comprises an "off" disengaged condition and said second speed
comprises an "on" engaged condition.
4. A method as set forth in claim 3 wherein said evaporator fan
motor is brought to a complete stop before starting the next
consecutive cycle.
5. A method as set forth in claim 3 wherein said evaporator fan
motor is not brought to a complete stop before starting the next
consecutive cycle.
6. A method as set forth in claim 3 wherein said evaporator fan
motor is electrically engaged and disengaged.
7. A method as set forth in claim 3 wherein an associated
evaporator fan is mechanically engaged and disengaged from said
evaporator fan motor.
8. A method as set forth in claim 7 wherein the engagement and
disengagement mechanism is a clutch.
9. A method as set forth in claim 1 wherein said evaporator fan
motor is a multiple speed motor and further wherein said first
speed comprises a lower speed from an available set of speeds for
the fan motor and said second speed comprises a higher speed from
an available set of speeds for the fan motor.
10. A method as set forth in claim 9 wherein said multiple speed
motor comprises a dual speed fan motor.
11. A method as set forth in claim 1 wherein said step of
selectively operating said evaporator fan motor is accomplished by
way of a relay, a contactor, an electro-magnetic switch or an
optical switch.
12. A method as set forth in claim 1 wherein the fan motor cycling
frequency is defined by at least one of reliability considerations
for cycled components, temperature variations in a conditioned
space, humidity variations in a conditioned space, airflow
fluctuations, and evaporator freeze conditions.
13. A method as set forth in claim 1 wherein the time interval at
which fan operates at said higher speed is defined by at least one
of the latent capacity requirement and sensible capacity
requirement.
14. A method as set forth in claim 1 wherein the time of a full
cycle of operation for said fan motor comprised of the time of
operation at said first speed plus the subsequent time of operation
at said second speed is in the range of 5 seconds to 2 minutes.
15. Apparatus for controlling the humidity and temperature in a
conditioned space, comprising: an air conditioning system having an
evaporator and an associated evaporator fan motor; a switch capable
for rapidly switching said fan motor between a first speed and a
second speed; and a controller for selectively operating said
switch by rapidly cycling between said first speed and said second
speed, with the second speed being higher then the first speed, to
change the latent or sensible capacity.
16. Apparatus as set forth in claim 15 wherein said controller
operates said switch in such a manner that, when a higher sensible
capacity is desired, the time in which the fan motor operates at
said second speed is increased, and when a higher latent capacity
is desired, the time in which the fan motor operates at said first
speed is increased.
17. Apparatus as set forth in claim 16 wherein said evaporator fan
motor comprises a single speed motor and further wherein said first
speed comprises an "off" disengaged condition and said second speed
comprises an "on" engaged condition.
18. Apparatus as set forth in claim 17 wherein said evaporator fan
motor is brought to a complete stop before starting the next
consecutive cycle.
19. Apparatus as set forth in claim 17 wherein the evaporator fan
motor is not brought to a complete stop before starting the next
consecutive cycle.
20. Apparatus as set froth in claim 17 wherein said evaporator fan
motor is electrically engaged and disengaged.
21. Apparatus as set forth in claim 17 wherein an associated
evaporator fan is mechanically engaged and disengaged from said
evaporator fan motor.
22. Apparatus as set forth in claim 21 wherein the engagement and
disengagement mechanism is a clutch.
23. Apparatus as set forth in claim 15 wherein said evaporator fan
motor comprises a multiple speed motor and further wherein said
first speed comprises a lower speed from an available set of speeds
for the fan motor and said second speed comprises a higher speed
from an available set of speeds for the fan motor.
24. Apparatus as set forth in claim 23 wherein said multiple speed
motor comprises a dual speed motor.
25. Apparatus as set forth in claim 15 wherein said switch
comprises a relay, a contactor, an electro-magnetic switch or an
optical switch.
26. Apparatus as set forth in claim 1 wherein the fan motor cycling
frequency is defined by at least one of reliability considerations
for cycled components, temperature variations in a conditioned
space, humidity variations in a conditioned space, airflow
fluctuations, and evaporator freeze conditions.
27. Apparatus as set forth in claim 1 wherein the time interval at
which fan operates at said higher speed is defined by at least one
of the latent capacity requirement and sensible capacity
requirement.
28. Apparatus as set forth in claim 1 wherein the time of a full
cycle of operation for said fan motor comprised of the time of
operation at said first speed plus the subsequent time of operation
at said second speed is in the range of 5 seconds to 2 minutes.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to air conditioning systems
and, more particularly, to control of an indoor fan to obtain
improved dehumidification.
BACKGROUND OF THE INVENTION
[0002] In air conditioning systems, it is known that the gross
cooling capacity of the refrigerant system, or the overall cooling
capacity of an evaporator, is increased with indoor fan speed. This
higher capacity is the result of higher indoor airflow moving over
the evaporator external surfaces and therefore improving overall
evaporator heat transfer coefficient.
[0003] It is also known that, when an evaporator fan is operating
at a lower speed, with less air being passed over the evaporator,
evaporator operates at a lower sensible heat ratio. In other words,
the latent capacity component in the overall evaporator capacity is
increased while the sensible capacity component is reduced, such
that more moisture will be removed from each unit of the air on a
relative basis and the overall relative humidity will be
reduced.
[0004] There are many techniques to provide the desired levels of
temperature and relative humidity comfort in conditioned spaces or
climate-controlled zones. However, such techniques are quite often
very complicated, involve additional expensive components and
require complex control logic.
[0005] What is needed is a simple and inexpensive approach to
controlling the temperature and relative humidity in a
climate-controlled space by a conventional air conditioning system
comprised of standard components.
DISCLOSURE OF THE INVENTION
[0006] Briefly, in accordance with one aspect of the invention, the
respective levels of temperature and humidity in a conditioned
space are controlled by selectively operating an evaporator fan by
periodically switching between the first speed and the second
speed, with the second speed being higher than the first speed.
Furthermore, when higher cooling capacities are desired, the period
of time associated with the indoor fan operation at the second
speed is increased, and when lower relative humidity levels are
desired, the period of time associated with the indoor fan
operation in the first speed is increased.
[0007] For a multi-speed evaporator fan motor, the first speed is
one of the lower available speeds and the second speed is one of
the higher available speeds. For a single speed evaporator fan
motor, the first speed is zero and the second speed is the only
operational speed of that evaporator fan motor.
[0008] The frequency of switching between the first speed and the
second speed may be determined based on reliability considerations
and variations of temperature and humidity in the conditioned
space.
[0009] In the drawings as hereinafter described, a preferred
embodiment is depicted; however, various other modifications and
alternate constructions can be made thereto without departing from
the spirit and scope of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic illustration of an air conditioning
system with the present invention incorporated therein.
[0011] FIG. 2 is a graphic illustration of the manner in which the
evaporator fan motor is controlled in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The invention is shown generally at 10 as incorporated into
an air conditioning system 11 which includes, in serial flow
relationship, a compressor 12, a heat rejection heat exchanger 13,
an expansion device 14 and a heat accepting heat exchanger 16. The
heat rejection heat exchanger assembly includes a motor driven
air-moving device or fan 17 and the heat accepting heat exchanger
assembly includes an air-moving device or fan 18 driven by an
electric motor 15. As known, the heat rejection heat exchanger 13
is a condenser for subcritical applications and a gas cooler for
transcritical applications, while a heat accepting heat exchanger
16 is generally known as an evaporator. In operation, the basic
conventional air conditioning system 11 is typically utilized to
provide cooling to a conditioned space 19. While the indoor airflow
driven by the indoor fan 18 passes over external surfaces of the
evaporator 16 and is delivered to the conditioned space 19, it is
cooled and typically dehumidified, prior to entering the
conditioned space 19. In the cooling mode of operation, the focus
is typically on providing cooling to the conditioned space 19,
while dehumidification occurs as a side effect of this cooling
process. In many cases, it is desired to shift the focus from
cooling to dehumidification, or in other words, rebalance sensible
and latent capacity components in the overall capacity provided by
the air conditioning system 11. Therefore, the operation of the
evaporator fan motor 15 is controlled in a manner which allows for
selectively controlling the humidity level in the conditioned space
19 when desired.
[0013] Within the conditioned space 19, there is provided a
temperature sensor 21 and a humidity sensor 22 whose sensed values
are sent along the respective transmission lines 23 and 24 to a
control 26. The control 26 then responsively operates a relay 27 to
control the speed of the evaporator fan motor 15 in a manner to be
described hereinafter. In this regard, it should be recognized that
the relay 27 is only representative of various other types of
switching devices that can be used for this purpose. For example,
an electronic switch or an optical switch could also be used in
place of the relay 27.
[0014] It is recognized that, during periods of high demand for
cooling such as high ambient temperature conditions or high heating
thermal load in the conditioned space 19, there will be a need for
higher cooling capacity of the air conditioning system 11 and
accordingly higher sensible cooling performance of the evaporator
16. In order to obtain that higher sensible cooling, the evaporator
fan motor 15 is operated at full speed for a single speed motor or
at the highest speed for a multi-speed (e.g. two-speed) motor, so
as to obtain the maximum amount of air being passed over the
external surfaces of the evaporator 16. During this mode of
operation, the increased evaporator airflow and elevated saturation
suction temperature of the refrigerant will provide maximum
evaporator capacity, but on a relative basis, its latent component
will be reduced such that the relative humidity in the space 19 may
tend to increase. Since in this mode of operation, the focus is on
sensible cooling, the humidity sensor feedback potentially showing
slight relative humidity increase will be overridden.
[0015] On the other hand, during other periods of operation, the
heat load in the conditioned space 19 may be at a moderate level or
environmental conditions may not be that severe (relatively low
ambient temperatures). In these cases, the full cooling capacity
provided by the air conditioning system 11 and full sensible
capacity of the evaporator 16 are not required. Thus, during these
operational periods of the reduced cooling demands, the system may
be controlled to operate with the focus on dehumidification to
primarily reduce the relative humidity in the conditioned space 19.
To accomplish this task, the evaporator fan motor 15 is switched
between the first lower speed and the second higher speed, in order
to obtain a reduced overall time-averaged speed. At a reduced
time-averaged speed of the evaporator fan motor 15, a lower
time-averaged airflow is passing over external surfaces of the
evaporator 16 resulting in a lower refrigerant saturation suction
temperature. As known, at lower saturation suction temperatures (or
suction pressures), the latent component of the evaporator capacity
is increased, on a relative basis, which, in turn, tends to reduce
the relative humidity in the conditioned space 19. At the same
time, the reduced time-averaged airflow causes sensible component
of the evaporator capacity to decrease, which is acceptable since
the higher cooling capacity is not required during this time
periods of reduced cooling demands. The two phenomena mentioned
above, of course, promote lower sensible heat ratios (SHR) as
desired.
[0016] For a multi-speed evaporator fan motor, the first speed is
one of the lower available speeds and the second speed is one of
the higher available speeds. The switching may be performed between
any of the lower speeds and any of the higher speeds. For a single
speed evaporator fan motor, the first speed is zero and the second
speed is the only operational speed of that evaporator fan
motor.
[0017] The frequency of switching between the first speed and the
second speed may be determined based at least on reliability
considerations and variations of temperature and humidity in the
conditioned space. On one hand, too frequent switching may reduce
reliability of the air management components of the air
conditioning system 11. On the other hand, prolonged operational
time intervals at each speed may cause excessive temperature and
humidity fluctuations in the conditioned space 19. The time spent
at each speed level within one cycle determines time-averaged speed
for the evaporator fan motor 15 and time-averaged sensible and
latent components of the capacity for the evaporator 16.
[0018] It has to be pointed out that, if the switching technique
described above is implemented to a single speed motor, the
evaporator fan 15 does not have to be brought to a complete stop
and may be engaged again in a consequent cycle while still rotating
due to inertia that would assist in a starting torque and power
consumption reduction in a subsequent cycle. Further, the
evaporator fan motor 15 may be engaged and disengaged by shutting
off electric power provided to the evaporator fan motor 15 or an
evaporator fan 18 may be engaged and disengaged by mechanical means
such as an electro-magnetic clutch.
[0019] Further, it has to be understood that air conditioning
system 11 depicted in FIG. 1 is a very basic system and shown for
illustrative purposes only. In reality, air conditioning system 11
may have many enhancement features and design options. All such
systems are within the scope and can equally benefit from the
invention. For instance, to further control capacity, the air
conditioning system 11 may have various unloading options known in
the art, such as hot gas bypass, suction modulation, multiple
circuits, vapor injection, economizer-to-suction bypass, digital
scroll compressor, two-stage compressor, cylinder unloading for a
reciprocating compressor, etc. All these unloading options can be
used in combination with indoor fan cycling to control latent and
sensible components of the capacity for the evaporator 16.
[0020] Referring now to FIG. 2, there is shown a graphic
illustration of the method in which the evaporator fan motor 15 is
controlled in a simple and efficient manner to obtain the speed
changes corresponding to required thermal load demands in the
conditioned space 19 as described hereinabove.
[0021] The evaporator fan motor 15 may be a single speed motor or a
multiple speed motor (e.g. two speed motor). As explained above, if
the evaporator fan motor 15 is a single speed motor, the motor is
cycled alternately between the on and off positions as shown in
FIG. 2 wherein: [0022] T--time interval of a single cycle [0023]
t.sub.1--time interval when the evaporator fan is off or disengaged
[0024] t.sub.2--time interval when the evaporator fan is on or
engaged
[0024] t.sub.1+t.sub.2=T
[0025] Alternatively, if the evaporator fan motor 15 is a
multi-speed motor, it is selectively cycled between one of the
higher available speeds and one of the lower available speeds as
shown in FIG. 2. In this case, the values T, t.sub.1 and t.sub.2
have the following meaning: [0026] T--time interval of a single
cycle [0027] t.sub.1--time interval when the evaporator fan is
operating at a lower speed [0028] t.sub.2--time interval when the
evaporator fan is operating at a higher speed
[0028] t.sub.1+t.sub.2=T
[0029] In both cases time-averaged speed is defined as follows:
S=(S.sub.i*t.sub.i+S.sub.2*t.sub.2)/T [0030] S.sub.1--a lower
operational speed [0031] S.sub.2--a higher operational speed
[0032] The values of T, t.sub.1 and t.sub.2 can be selectively
varied as desired to accomplish the desired result of achieving
latent and sensible components of the evaporator capacity while
satisfying reliability requirements as well as temperature and
humidity variations in the conditioned space. That is, the time
ratio of t.sub.1/t.sub.2 can vary from 0 to .infin.. For instance,
in a variety of applications, the period of a single cycle, T, can
be varied within a range of 5 second to 2 minutes. As mentioned
above, the cycle frequency is determined by the reliability
requirements in order not to overheat or wear cycling components as
well as limitations imposed on variations of temperature and
humidity in the conditioned space, while the time at the higher
speed t.sub.2 is defined by the latent and sensible components of
the evaporator capacity required to satisfy thermal load demands in
the conditioned space.
[0033] Since an air conditioning system and an associated
conditioned space have significantly large thermal inertia, such
evaporator fan cycling and airflow fluctuations should not affect
environmental parameters in the climate-controlled space. Further,
the provided time-averaged airflow should not deviate much from the
mean value preventing uncomfortable conditions for an occupant of
the conditioned space. Since the air duct system has significant
volume, such airflow fluctuations will be reduced well before
reaching the conditioned environment.
[0034] As known in the art, extremely low airflows may cause
evaporator surface temperature to fall below a freezing point.
Therefore, conventional methods of control, such as low suction
pressure cutoff or low saturation suction temperature threshold,
may be utilized to prevent evaporator frosting conditions.
[0035] It should be recognized that, the present invention is
applicable to all types of air conditioning systems such as
commercial and residential air conditioning and heat pump systems
as well as mobile applications. Also, no new hardware is required
to implement the invention.
[0036] While the present invention has been particularly shown and
described with reference to a preferred embodiment as illustrated
in the drawing, it will be understood by one skilled in the art
that various changes in detail may be effected therein without
departing from the spirit and scope of the invention as defined by
the claims.
* * * * *