U.S. patent application number 11/144869 was filed with the patent office on 2006-12-07 for method of dehumidifying an indoor space using outdoor air.
This patent application is currently assigned to Lennox Manufacturing Inc.. Invention is credited to James P. Cavanagh, Stephen A. Walter.
Application Number | 20060273183 11/144869 |
Document ID | / |
Family ID | 37493203 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060273183 |
Kind Code |
A1 |
Cavanagh; James P. ; et
al. |
December 7, 2006 |
Method of dehumidifying an indoor space using outdoor air
Abstract
A method for dehumidifying air in an indoor space using outside
air is comprised of the steps of: sensing whether there is a demand
for dehumidification in the space; in response to a demand for
dehumidification, determining whether outdoor air is suitable for
dehumidification of the space; if the outdoor air is determined to
be suitable, admitting outdoor air into the air supplied to the
space; and selectively temperature conditioning the supply air in
accordance with a predetermined temperature condition therefor. The
method is disabled in response to a demand for heating or sensible
cooling in the space. Further, the ratio of outdoor air to return
air in the supply air is kept relatively constant, irrespective of
whether the predetermined temperature condition is satisfied.
Inventors: |
Cavanagh; James P.; (North
Billerica, MA) ; Walter; Stephen A.; (Flower Mound,
TX) |
Correspondence
Address: |
W. Kirk McCord, Esq.;Intellectual Property Counsel
Lennox International Inc.
P. O. Box 799900
Dallas
TX
75379-9900
US
|
Assignee: |
Lennox Manufacturing Inc.
|
Family ID: |
37493203 |
Appl. No.: |
11/144869 |
Filed: |
June 3, 2005 |
Current U.S.
Class: |
236/44C ;
62/176.6 |
Current CPC
Class: |
F24F 13/15 20130101;
F24F 2110/22 20180101; F24F 2110/10 20180101; F24F 2221/34
20130101; F24F 3/153 20130101; F24F 2110/20 20180101; F24F 11/30
20180101; F24F 2110/12 20180101 |
Class at
Publication: |
236/044.00C ;
062/176.6 |
International
Class: |
F25B 49/00 20060101
F25B049/00; F25D 17/04 20060101 F25D017/04 |
Claims
1. A method of dehumidifying air in an indoor space, comprising the
steps of: sensing whether there is a demand for dehumidification in
the space; in response to said demand for dehumidification,
determining whether outdoor air is suitable for dehumidification of
the space; if the outdoor air is determined to be suitable,
admitting outdoor air into the space; and selectively temperature
conditioning the outdoor air prior to admitting it into the space
in accordance with a predetermined temperature condition for air
supplied to the space.
2. The method of claim 1 wherein said determining includes
determining whether the temperature of the outdoor air satisfies a
predetermined outdoor air temperature condition.
3. The method of claim 1 wherein said determining includes
determining whether the humidity of the outdoor air satisfies a
predetermined outdoor air humidity condition.
4. The method of claim 1 wherein said admitting includes
controlling the amount of outside air admitted into the space.
5. The method of claim 1 wherein said selectively temperature
conditioning includes sensing the temperature of the air supplied
to the space and heating the air supplied to the space as needed to
maintain said predetermined temperature condition, even in the
absence of a demand for heating in the space.
6. The method of claim 1 wherein said admitting includes
introducing a predetermined amount of outdoor air into the air
supplied to the space.
7. The method of claim 6 wherein said introducing includes
maintaining a relatively fixed proportion of outdoor air in the air
supplied to the space.
8. The method of claim 1 further including sensing whether there is
a demand for temperature conditioning of the air in the space and
in response to said demand for temperature conditioning, disabling
said method.
9. In a system for conditioning air in an indoor space, a method of
dehumidifying the air in response to a demand for dehumidification
in the space, comprising the steps of: sensing whether there is a
demand for heating or cooling in the space; in the absence of a
demand for heating or cooling in the space, determining whether
outdoor air is suitable for dehumidification of the space; if the
outdoor air is determined to be suitable, admitting outdoor air
into the system; and selectively temperature conditioning the
outdoor air prior to admitting it into the space in accordance with
a predetermined temperature condition for air supplied to the
space.
10. The method of claim 9 wherein said determining includes
determining whether the temperature of the outdoor air satisfies a
predetermined outdoor air temperature condition.
11. The method of claim 9 wherein said determining includes
determining whether the humidity of the outdoor air satisfies a
predetermined outdoor air humidity condition.
12. The method of claim 9 wherein said admitting includes
controlling the amount of outdoor air admitted into the space.
13. The method of claim 9 wherein said selectively termperature
conditioning includes sensing the temperature of the air supplied
to the space and heating the air supplied to the space as needed to
maintain said predetermined temperature condition, even in the
absence of a demand for heating in the space.
14. The method of claim 9 wherein said admitting includes
introducing a predetermined amount of outdoor air into the air
supplied to the space.
15. The method of claim 14 wherein said introducing includes
maintaining a relatively fixed proportion of outdoor in the air
supplied to the space.
16. In an air conditioning system for supplying conditioned air to
an indoor space, a method of dehumidifying supply air to the space,
comprising the steps of: sensing whether there is a demand for
dehumidification in the space; in response to said demand for
dehumidification, determining whether outdoor air is suitable for
dehumidification of the space; if the outdoor air is determined to
be suitable, introducing a predetermined amount of outdoor air into
the supply air; and selectively temperature conditioning the supply
air in accordance with a predetermined temperature condition.
17. The method of claim 16 wherein said determining includes
determining whether the temperature of the outdoor air satisfies a
predetermined outdoor air temperature condition.
18. The method of claim 16 wherein said determining includes
determining whether the humidity of the outdoor air satisfies a
predetermined outdoor air humidity condition.
19. The method of claim 16 wherein said selectively temperature
conditioning includes sensing the temperature of the supply air and
heating the supply air as needed to maintain said predetermined
temperature condition, even in the absence of a demand for heating
in the space.
20. The method of claim 16 wherein said introducing includes
maintaining a relatively constant proportion of outdoor air in the
supply air, irrespective of whether said predetermined temperature
condition is satisfied.
21. The method of claim 16 further including sensing whether there
is a demand for temperature conditioning of the air in the space
and in response to said demand for temperature conditioning,
disabling said method.
Description
TECHNICAL FIELD
[0001] This invention relates generally to space conditioning
systems for conditioning the temperature and humidity of an indoor
space and in particular to a method of dehumidifying the space
using outdoor air.
BACKGROUND ART
[0002] Central air conditioning systems, including systems that use
a vapor compression refrigerant to cool air circulated to an indoor
space, often require relatively accurate control of humidity in the
air within the space. In one such system, as described in U.S. Pat.
No. 6,644,049, a reheat heat exchanger is positioned downstream of
the system evaporator to reheat air that is cooled and dehumidified
by the evaporator. Therefore, dehumidified air can be delivered to
the space without appreciably cooling the space.
[0003] In the system described in U.S. Pat. No. 6,644,049, outdoor
air is not admitted into the system in response to a demand for
dehumidification in the space. In the air conditioning system
described in U.S. Pat. No. 6,427,461, outdoor air is admitted into
the supply air stream in response to a demand for dehumidification
if the enthalpy of the outdoor air is suitable. Typically, if the
enthalpy of the outdoor air is suitable for dehumidification, it is
cooler than the desired temperature of the space. If as a result of
introducing cooler outdoor air into the supply air stream, the
supply air temperature drops below a predetermined setpoint, the
amount of outdoor air admitted into the system is reduced to try to
prevent overcooling of the space. However, there is no provision to
heat the supply air in the absence of a demand for heating in the
space.
SUMMARY OF THE INVENTION
[0004] In accordance with the present invention, a method is
provided for dehumidifying an indoor space using outdoor air. The
method is comprised of the steps of: sensing whether there is a
demand for dehumidification in the space; in response to a demand
for dehumidification, determining whether outdoor air is suitable
for dehumidification of the space; if the outdoor air is determined
to be suitable, admitting outdoor air into the space; and
selectively temperature conditioning the outdoor air prior to
admitting it into the space in accordance with a predetermined
temperature condition for air supplied to the space.
[0005] In accordance with one embodiment of the invention, the
method includes determining whether the temperature of the outdoor
air satisfies a predetermined outdoor air temperature
condition.
[0006] In accordance with another embodiment of the invention, the
method includes determining whether the humidity of the outdoor air
satisfies a predetermined outdoor air humidity condition.
[0007] In accordance with still another embodiment of the
invention, the method includes sensing the temperature of the air
supplied to the space and heating the air supplied to the space as
needed to maintain the predetermined temperature condition for the
supply air, even in the absence of a demand for heating in the
space.
[0008] In accordance with yet another embodiment of the invention,
the method includes sensing whether there is a demand for
temperature conditioning of the air in the space. In response to a
demand for temperature conditioning of the air in the space, the
dehumidifying method is disabled.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a schematic showing the circulation of air in an
air conditioning system;
[0010] FIG. 2 is a block diagram showing the control for the air
conditioning system of FIG. 1; and
[0011] FIG. 3 is a flow diagram depicting the dehumidification
operation in accordance with the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0012] The best mode for carrying out the invention will now be
described with reference to the accompanying drawings. Like parts
are marked in the specification and drawings with the same
respective reference numbers. In some instances, proportions may
have been exaggerated in order to depict certain features of the
invention.
[0013] Referring now to FIG. 1, there is illustrated an air
conditioning system in accordance with an embodiment of the present
invention and generally designated by numeral 10. Air conditioning
system 10 is shown, by way of example, as a so-called "rooftop"
system having a generally rectangular box-like cabinet 12 adapted
to be mounted on a generally horizontal surface such as a rooftop
14. Air conditioning system 10 is adapted to deliver conditioned
air to an enclosed space 16 by way of an opening 18 and air within
the enclosed space 16 is returned to system 10 by way of an opening
19 to cabinet 12 for conditioning by system 10.
[0014] System 10 preferably includes a vapor compression
refrigeration unit 20, including a compressor (not shown) for
circulating a conventional refrigerant fluid between indoor and
outdoor heat exchanger coils. Indoor heat exchanger 32 is disposed
within cabinet 12 and is arranged in the path of the air flow
through cabinet 12, as shown by the arrows. When system 10 is
operated in a cooling mode, indoor coil 32 functions as an
evaporator to transfer heat from the air flowing through coil 32 on
the outside thereof to the refrigerant flowing inside coil 32.
Evaporator 32 is typically disposed downstream of a suitable air
filter 33, which is also disposed in the air flow path between
return opening 19 and supply opening 18 for space 16.
[0015] Air conditioning system 10 further includes a reheat heat
exchanger coil 38, through which heated refrigerant gas may be
circulated directly from the system compressor. Reheat coil 38
extends over a portion (e.g., 50%) of the area of evaporator 32 and
is downstream thereof. Reheat heat exchanger 38 is used to reheat
air cooled and dehumidified by evaporator 32 when system 10 is
operated in a mechanical reheat mode in response to a demand for
dehumidification of space 16. The use of a hot refrigerant gas to
reheat air cooled and dehumidified by the evaporator is known in
the art and is described, for example, in U.S. Pat. No. 6,427,461,
the relevant portions of which are incorporated by reference herein
to further describe operation of reheat coil 38. A drain pan 53 is
located beneath coil 32 for collecting condensate runoff from coil
32.
[0016] System 10 also includes a motor-driven blower 48 of
conventional construction and a suitable electric drive motor 50.
In a preferred embodiment, as shown, blower 48 is disposed within
cabinet 12 in a space 52 downstream of evaporator 32 and reheat
heat exchanger 38 for returning conditioned air to space 16 through
opening 18. However, blower 48 may be disposed upstream of
evaporator 32 and reheat exchanger 38 in an alternate embodiment.
Blower 48 is shown mounted on a heater unit 51, whereby air
returned to enclosed space 16 by way of opening 18 may be
conditioned by heater unit 51, if desired. Heater unit 51 may be
one of several types of conventional heater units, wherein air
discharged from blower 48 passes over suitable heat exchange
surfaces when heater unit 51 is operable. Heater unit 51 is mounted
on a discharge or supply air duct part 48a, which is in
communication with opening 18. Heater unit 51 preferably includes
one or more electrically resistive heating elements, but may also
include a combustible fuel (e.g., gas) heater.
[0017] A suitable sensor 54 is preferably interposed in duct part
48a or may, depending on the configuration of system 10, be
disposed in a suitable air supply duct farther downstream from and
connected to duct part 48a, but upstream of space 16. The location
of sensor 54 and duct part 48a is exemplary. Sensor 54 is
preferably a temperature sensor for measuring the temperature of
the supply air.
[0018] Upstream of evaporator 32 is an enclosed space 55 within
cabinet 12, through which air from space 16 may flow by way of
opening 19 and spaces formed between a set of moveable louvers or
dampers 56, which are mechanically linked to each other and to
linkage 58, for example, connected to a suitable actuator or
positioning motor 60. Positioning actuator or motor 60 is also
connected via linkage 62 to a damper comprising a second set of
moveable louvers or dampers 64 for controlling the entry of ambient
outdoor air into space 55 and discharge into space 16. The
apparatus comprising the aforementioned sets of louvers 56, 64 and
actuator motor 60 connected thereto is also sometimes known in the
art as an "economizer". Outdoor ambient air (represented by arrow
65) may be admitted to space 55 by way of a rain shroud 66, a
suitable filter screen 68 and an enclosed space 70, which is
partitioned from a space 72 by a suitable transverse partition
74.
[0019] A sensor 76 is disposed in space 70. In one embodiment,
sensor 76 is a temperature sensor for sensing the temperature of
ambient outdoor air admitted to space 70. In an alternate
embodiment, sensor 76 is a humidity sensor instead of a temperature
sensor for sensing the humidity of outdoor air admitted to space
70. A suitable humidity sensor 78 is preferably disposed in return
air space 72 or may, alternatively, be disposed within space 16,
for sensing the humidity of air in space 16. A conventional air
conditioning temperature sensor 80 (which may be a thermostat) is
disposed in a suitable location within space 16 for sensing and
controlling the temperature of the air in space 16 as determined by
an adjustable setpoint of sensor 80.
[0020] A suitable pressure relief damper 73 in FIG. 2, for space 72
may be provided to minimize any pressure increase in space 16 if
outdoor air is introduced into space 55 by blower 48 for
circulation to space 16. In a preferred embodiment of the
invention, when outdoor air is introduced into the system in
response to a demand for dehumidification in space 16, the relative
proportion of outdoor air to return air is relatively fixed (for
example, 40% outdoor air to 60% return air) so that louvers 56, 64
are controlled to maintain the fixed proportion of outdoor air to
return air.
[0021] Referring also to FIG. 2, system 10 is controlled by a
microcomputer-based controller 90 in accordance with a preselected
control program. Controller 90 is responsive to inputs from outdoor
air sensor 76, space temperature sensor 80, space humidity sensor
78 and supply air temperature sensor 54 for controlling the
operation of dampers 56, 64, blower 48 and heating unit 51.
[0022] Referring also to FIG. 3, in accordance with an embodiment
of the present invention, outdoor air may be used to help
dehumidify space 16 if the outdoor air is suitable for
dehumidification. The term "FAH" in FIG. 3 stands for "Fresh Air
Heating" and refers to an operating mode of system 10 wherein fresh
(outdoor) air is brought into system 10 in response to a demand for
dehumidification in space 16 and the supply air may be heated as
necessary to maintain the supply air temperature above a
predetermined threshold. If the outdoor air is cooler than the
indoor air, then the humidity of the outdoor air is usually lower
than the humidity of the indoor air. In that case, the outdoor air
may be used to provide "free dehumidification" without having to
operate the system compressor. However, the cooler outdoor air may
lower the supply air temperature below an acceptable limit,
resulting in overcooling of space 16. Therefore, it may be
necessary to add heat to the supply air.
[0023] Controller 90 executes an iterative process as shown in FIG.
3. If fresh air heating (FAH) is enabled at decision point 100 in
response to a demand for dehumidification, dampers 56, 64 are
opened to a preset value at step 101 to admit outdoor air into the
supply air stream in a predetermined ratio of outdoor air to return
air (for example, 40% outdoor air to 60% return air). The preset
value may be selected by the system installer or may be determined
by the default setting in the system control program. Controller 90
then determines at decision point 102 whether the supply air
temperature is less than a predetermined temperature threshold (for
example, 68.degree. F.) in response to the input from supply air
temperature sensor 54.
[0024] If the supply air temperature is less than the threshold,
heating unit 51 (preferably, one or more electrical heating
elements) is activated at step 104 to heat the supply air. However,
if the supply air temperature is not less than the threshold,
heating unit 51 is deactivated in accordance with step 106. In
either case, the process then proceeds to decision point 108.
However, if FAH has not been enabled at decision point 100, dampers
56, 64 are operated in accordance with the normal "economizer"
mode, wherein dampers 56, 64 are controlled automatically, as
represented by step 107. The process then proceeds to decision
point 108. If FAH is not enabled, system 10 cannot be operated to
dehumidify the space using fresh (outdoor) air.
[0025] At decision point 108, controller 90 determines whether
there is a demand for heating or sensible cooling in space 16 in
response to the input from space temperature sensor 80. In response
to a demand for either heating or sensible cooling in space 16, FAH
is disabled at step 110 and the process returns to decision point
100. However, if there is no demand for heating or sensible cooling
in space 16 at decision point 108, controller 90 determines whether
there is a demand for latent cooling (dehumidification) in space 16
at decision point 112. If there is no demand for dehumidification
in space 16, all "Reheat" modes, including FAH and mechanical
reheat modes using the system compressor, are disabled at step 114
and the process returns to decision point 100.
[0026] If there is a demand for latent cooling in space 16 at
decision point 112, the process proceeds to decision point 116,
where controller 90 determines whether the outdoor air is suitable
for dehumidification. This determination is based on input from
outdoor air sensor 78, which senses either temperature or humidity
of the outdoor air. If the temperature or humidity, as the case may
be, of the outdoor air satisfies a predetermined condition (for
example, outdoor air temperature is 45.degree. F. or less), the
outdoor air is determined to be suitable for dehumidification and
FAH is enabled (or remains enabled, if already enabled at step 100)
at step 118. The process then returns to decision point 100.
[0027] If the outdoor air is determined to be unsuitable for
dehumidification of the space at decision point 116, FAH is
disabled at step 120 and a selected mechanical reheat mode is
enabled at set 122 in response to the dehumidification demand in
space 16. The mechanical reheat mode involves the use of the system
compressor to first cool and dehumidify the supply air using the
system evaporator 32 and then to reheat the dehumidified air by
circulating heated refrigerant gas through reheat coil 38.
Alternatively, the mechanical reheat mode may use a heat source
other than reheat coil 38 such as a gas heating section or
electrical heating elements to reheat the dehumidified supply air.
After the selected mechanical reheat mode is enabled at step 122,
the process returns to decision point 100.
[0028] One skilled in the art will recognize that in accordance
with the present invention, fresh (outdoor) air may be used for
dehumidifying an indoor space if the outdoor air is suitable from a
temperature and/or humidity standpoint and in the absence of a
demand for heating or sensible cooling in the space. To prevent
overcooling the space from the introduction of cooler outdoor air
into the supply air, the supply air temperature is monitored and is
adjusted to maintain a predetermined supply air temperature
condition.
[0029] Although the preferred embodiment of the invention has been
described with reference to heating the supply air as necessary to
maintain the predetermined temperature condition, the invention
contemplates that in some cases the supply air may need to be
cooled instead of heated. For example, if the suitability of the
outside air for dehumidification is determined based on its
humidity rather than on its temperature, in some climates, the
outdoor air may be warmer and drier than the indoor air, so that if
outdoor air is brought in to help dehumidify an indoor space, the
supply air may need to be cooled instead of heated to maintain a
predetermined temperature condition.
[0030] The best mode for carrying out the invention has now been
described in detail. Since changes in and modifications to the
above-described best mode may be made without departing from the
nature, spirit and scope of the invention, the invention is not to
be limited to the above-described best mode, but only by the
appended claims and their equivalents.
* * * * *