U.S. patent application number 10/353947 was filed with the patent office on 2003-09-25 for economizer control.
This patent application is currently assigned to Edwards Systems Technology, Inc.. Invention is credited to Schell, Michael B., Valenta, Rod J..
Application Number | 20030181158 10/353947 |
Document ID | / |
Family ID | 28046447 |
Filed Date | 2003-09-25 |
United States Patent
Application |
20030181158 |
Kind Code |
A1 |
Schell, Michael B. ; et
al. |
September 25, 2003 |
Economizer control
Abstract
An economizer control for controlling air quality. The
economizer control includes a sensor that senses characteristics of
air, a damper located relative to the sensor so that the damper can
control air flow of outside air and re-circulated air to the
sensor, and a controller in communication with the sensor and the
damper. The controller controls the opening and closing of the
damper according to conditions sensed by the sensor.
Inventors: |
Schell, Michael B.; (Santa
Barbara, CA) ; Valenta, Rod J.; (Santa Barbara,
CA) |
Correspondence
Address: |
BAKER & HOSTETLER LLP
Suite 1100
Washington Square
1050 Connecticut Avenue, N.W.
Washington
DC
20036
US
|
Assignee: |
Edwards Systems Technology,
Inc.
|
Family ID: |
28046447 |
Appl. No.: |
10/353947 |
Filed: |
January 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60352857 |
Feb 1, 2002 |
|
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|
60352593 |
Jan 31, 2002 |
|
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Current U.S.
Class: |
454/229 ;
236/49.3 |
Current CPC
Class: |
F24F 2011/0006 20130101;
F24F 11/30 20180101; F24F 2011/0002 20130101; Y02B 30/767 20130101;
Y02B 30/70 20130101; F24F 11/0001 20130101; F24F 2110/70 20180101;
F24F 3/0442 20130101; F24F 2110/20 20180101 |
Class at
Publication: |
454/229 ;
236/49.3 |
International
Class: |
F24F 007/00; F24F
007/007; F24F 007/06; F24F 011/02 |
Claims
What is claimed is:
1. An economizer control comprising: a sensor that senses
characteristics of air; a damper located relative to said sensor so
that said damper can control air flow of outside air and
re-circulated air to said sensor; and a controller in communication
with said sensor and said damper, said controller opening and
closing said damper according to conditions sensed by said
sensor.
2. The economizer control as recited in claim 1 wherein said damper
comprises: an outside damper that allows outside air to enter a
mixed air section of an air handler when said outside damper is
open, and prevents outside air from entering the mixed air section
when said outside damper is closed.
3. The economizer control as recited in claim 1 where said damper
comprises: an inside damper that allows re-circulated air to enter
a mixed air section of an air handler when said inside damper is
open, and that prevents re-circulated air to enter the mixed air
section when said inside damper is closed.
4. The economizer control as recited in claim 1 wherein said sensor
measures temperature, enthalpy and occupancy level.
5. The economizer control as recited in claim 1 wherein said sensor
comprises: a temperature sensor, an absolute humidity control
sensor and a CO.sub.2 sensor.
6. The economizer control as recited in claim 1 wherein said
controller adjusts said damper to limit the amount of outside air
entering a mixed air section of an air handler when said sensor
senses a humidity level above a predetermined range.
7. The economizer control as recited in claim 1 wherein said
controller adjusts said damper to limit the amount of outside air
entering a mixed air section of an air handler when said sensor
senses a temperature outside a predetermined range.
8. A method for controlling an economizer comprising the steps of:
sensing characteristics of air; and controlling a damper to control
the air flow of outside air and re-circulated air in accordance
with the sensed characteristics of the air.
9. The method as recited in claim 8 wherein said step of
controlling the damper comprises the steps of: opening an outside
damper to allow outside air enter a mixed air section of an air
handler; and closing the outside damper to prevent outside air from
entering the mixed air section.
10. The method as recited in claim 8 wherein said step of
controlling the damper comprises the steps of: opening an inside
damper to allow re-circulated air to enter a mixed air section of
an air handler; and closing the inside damper to prevent
re-circulated to enter the mixed air section.
11. The method as recited in claim 8 wherein the step of sensing
characteristics of air comprises the step of sensing the
temperature, enthalpy and occupancy level.
12. The method as recited in claim 8 wherein the step of sensing
characteristics of air comprises the step of sensing the
temperature, absolute humidity and CO.sub.2 level of the air.
13. The method as recited in claim 8 wherein the step of
controlling the damper comprises the step of adjusting the damper
to limit the amount of outside air entering a mixed air section of
an air handler when a humidity level above a predetermined range is
sensed.
14. The method as recited in claim 8 wherein the step of
controlling the damper comprises the step of adjusting the damper
to limit the amount of air entering a mixed air section of an air
handler when a temperature outside a predetermined range is
sensed.
15. A system for controlling an economizer comprises: a means for
sensing characteristics of air located in a mixed air section of an
air handler; a means for controlling a damper to control the air
flow of outside air and re-circulated air in accordance with sensed
characteristics of the air.
16. The system as recited in claim 15 wherein said means for
controlling the damper comprises: a means for opening an outside
damper to allow outside air enter a mixed air section of an air
handler; and a means for closing the outside damper to prevent
outside air from entering the mixed air section.
17. The system as recited in claim 15 wherein said means for
controlling the damper comprises: a means for opening an inside
damper to allow re-circulated air to enter a mixed air section of
an air handler; and a means for closing the inside damper to
prevent re-circulated air from entering the mixed air section.
18. The system as recited in claim 15 wherein said means for
sensing characteristics of air comprises a means for sensing
temperature, enthalpy and occupancy level of the air.
19. The system as recited in claim 15 wherein said means for
sensing characteristics of air comprises a means for sensing the
temperature, absolute humidity and CO.sub.2 level of the air.
20. The system as recited in claim 15 wherein said means for
controlling the damper comprises a means for adjusting the damper
to limit the amount of outside air entering a mixed air section of
an handler when a humidity level above a predetermined range is
sensed.
21. The system as recited in claim 15 wherein said means for
controlling the damper comprises a means for adjusting the damper
to limit the amount of air entering a mixed air section of an
handler when a temperature outside a predetermined range is sensed.
Description
PRIORITY
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/352,857, filed on Feb. 1, 2002. The
aforementioned application is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to an improved
economizer control of HVAC (Heating, Ventilation and Air
Conditioning) systems. More particularly, the present invention
relates to an improved economizer HVAC system control resulting in
increased energy efficiency and a more comfortable environment than
current economizer controls provide, while also ensuring good
indoor air quality.
BACKGROUND OF THE INVENTION
[0003] A unitary heating, ventilation and air conditioning
[Hereafter unitary HVAC] system is one type of HVAC system that is
deemed "unitary" because it is generally configured in an
integrated manner so that this one system provides heating, cooling
and air movement in a single package. This unitary HVAC system can
easily be placed on the rooftop of a building. In a typical system,
air intake dampers are adjusted to provide a fixed outside air
component to air circulated through the system. The amount of
outside air required is usually determined by determining the
design occupancy of the space and multiplying this times a
cfm/person (cfm=cubic feet per minute) recommended ventilation rate
required by local codes and standards. Typically, most spaces
require 15 cfm per person. This amount of outside air is determined
by a design engineer and adjusted by the contractor that actually
performs installation of the system. Typically, this adjustment of
the outside air intake results in a 20% to 30% mix of outside air
together with recirculated air.
[0004] Another common type of HVAC system is the unit ventilator.
Unit ventilators are a smaller version of unitary air handling
equipment that have been designed to serve a single space. Rather
than being rooftop mounted, these devices are typically mounted
through a wall and are popular in applications such as servicing
the HVAC needs of school classrooms and hotel rooms. These devices,
like the unitary HVAC, are also integrated units designed to
provide heating, cooling and ventilation. The unit ventilator,
however, services the heating and cooling requirements for a more
limited area than a unitary system can. Unit ventilators are
popular because they have a lower initial cost than a centralized
system and they allow for specific control of a single zone. Unit
ventilator systems can be operated continuously or on an as needed
basis for both heating and cooling.
[0005] Most HVAC systems are only capable of being controlled based
on temperature and occupancy (manual turn off/on or timed
operation). Humidity control has not been historically a
consideration and most manufacturers do not have strategies for
dealing with humidity. Finally, accurate, dependable and low cost
humidity sensors have not been available on the marketplace that
have the low-cost, low maintenance and long life characteristics
demanded by these applications.
[0006] The combination of all the factors above have resulted in
the increased manifestation of unwanted growth of mold, mildew and
other bacterial entities in indoor spaces that can compromise the
quality of indoor air and the health of building occupants. The
presence of excessive moisture can also result in the deterioration
of physical components of a building including drywall, ceilings
and wooden structural components.
SUMMARY OF THE INVENTION
[0007] It is therefore a feature and advantage of the present
invention to provide an economizer control for controlling the air
quality for a space. In one embodiment of the invention, the
economizer control includes a sensor that senses characteristics of
air, a damper located relative to the sensor so that the damper can
control air flow of outside air and re-circulated air to the
sensor, and a controller in communication with the sensor and the
damper. The controller controls the opening and closing of the
damper according to conditions sensed by the sensor.
[0008] In another embodiment of the invention a method for
controlling an economizer includes the steps of sensing
characteristics of air; and controlling a damper to control the air
flow of outside air and re-circulated air in accordance with the
sensed characteristics of the air.
[0009] In an alternate embodiment of the invention, a system for
controlling an economizer includes a means for sensing
characteristics of air located in a mixed air section of an air
handler, and a means for controlling a damper to control the air
flow of outside air and re-circulated air in accordance with sensed
characteristics of the air.
[0010] There has thus been outlined, rather broadly, the more
important features of the invention in order that the detailed
description thereof that follows may be better understood, and in
order that the present contribution to the art may be better
appreciated. There are, of course, additional features of the
invention that will be described below and which will form the
subject matter of the claims appended hereto.
[0011] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the arrangements of
the components set forth in the following description or
illustrated in the drawings. The invention is capable of other
embodiments and of being practiced and carried out in various ways.
Also, it is to be understood that the phraseology and terminology
employed herein, as well as the abstract, are for the purpose of
description and should not be regarded as limiting.
[0012] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an illustration of one embodiment of the
invention.
[0014] FIG. 2 is an illustration of another embodiment of the
invention.
[0015] FIG. 3 is a chart showing the results of a study for
economizers serving a retail space.
[0016] FIG. 4 is a graph illustrating a pattern of CO2 buildup.
[0017] FIG. 5 is a flow diagram showing an embodiment of economizer
control.
[0018] FIG. 6 is a graph of enthalpy per pound of dry air.
[0019] FIG. 7 is a graph of enthalpy per pound of dry air with a
shaded region showing a 50% loss with a change of 10 degrees.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0020] One embodiment of the invention includes the use of system
supply air pressure to move an air sample to an air return sensor,
thereby enabling use of same sensors for measurement of one or more
air quality parameters for both supply air and return air
measurement using pressure to drive reciprocating sampling. One
such embodiment of the invention is generally illustrated in FIG.
1.
[0021] FIG. 1 illustrates an HVAC system or air handler having an
economizer control in accordance with one embodiment of the
invention. The HVAC system or air handler includes a fan 100,
heating coil 102 and cooling coil 104. A supply air duct 106 leads
to the space or building to be supplied air. A return air duct 108
leads from the space being supplied air back to a mixed air chamber
110 through a return air damper 112. An exterior air damper 114 is
provided between the mixed air chamber 110 and exterior air. In
this embodiment of the invention, an actuator 116 is provided to
open and close return air damper 112 and exterior air damper 114. A
controller/sensor 118 is located between supply air duct 106 and
return air duct 108. Based on the positions of return air damper
112 and exterior air damper 114, controller/sensor 118 will receive
exterior air, return air or a mix of exterior air and return air
through conduits 120. In some instances, return air damper 112 may
be closed so that return air cannot enter mixed air chamber 110. In
this case pressure relief damper 122 opens to exhaust the return
air.
[0022] Control/sensor 118 controls fan 100, heating coil 102 and
cooling coil 104. Return air damper 112 and exterior air damper 114
are also controlled by control/sensor 118 using actuator 116. In
one embodiment of the invention a thermostat/CO2 sensor 124 relays
information to controller/sensor 118 to control the characteristics
of air being supplied.
[0023] In another embodiment of the invention as depicted in FIG.
2, the HVAC system or air handler includes a fan 200, heating coil
202 and cooling coil 204. A supply air duct 206 leads to the space
or building to be supplied air. A return air duct 208 leads from
the space being supplied air back to a mixed air region 210 through
a return air damper 212. An exterior air damper 214 is provided
between the mixed air chamber 210 and exterior air. In this
embodiment of the invention, an actuator 216 is provided to open
and close return air damper 212 and exterior air damper 214. A
controller 218 is located between supply air duct 206 and return
air duct 208. In some instances, return air damper 212 may be
closed so that not enough return air enters mixed air chamber 210.
In this case pressure relief damper 222 opens to exhaust the return
air.
[0024] Controller 218 controls fan 200, heating coil 202 and
cooling coil 204. Return air damper 212 and exterior air damper 214
are also controlled by controller 218 using actuator 216. In one
embodiment of the invention, a sensor 224, which could be a
temperature/absolute humidity sensor, receives outside air, return
air or mixed air based on the positioning of return air damper 212
and exterior air damper 214. The sensor 224 then relays information
to controller 218 to control the dampers for proper airflow.
[0025] The invention as described above is capable of configuration
in several embodiments for use in several different HVAC system
economizer control applications. One such application concerns the
improved economizer control of unitary equipment. Another
embodiment of the present invention results in the improved control
of other HVAC systems such as unit ventilators, to control
conditions within a classroom or hotel room. The present invention
may take the form of a device integrated into a unit ventilator or
similar system, or as a wall or surface mounted control.
[0026] One or more of sensors for smoke and measurement of other
air quality parameters including temperature control rely on
imbedded micro-processors for their measurement and control
functions. One embodiment of the present invention enables the
integration of many or all of these functions into a single device
that can share microprocessing power enabling multi-parameter
sensing which results in an increased understanding of what is
happening in a building, and thereby provides better control of the
indoor building environment.
[0027] The present invention enables the use of CO2 level
measurements in return and supply air to calculate and set the
outside air damper position. The current invention also facilitates
input and control of remote CO2 sensors.
[0028] Carbon dioxide (CO2) is one of the common constituents of
the air in our atmosphere. The concentration of CO2 in our
atmosphere is typically 380 to 400 parts per million. Due to the
natural tendency of gas molecules to readily diffuse and equalize
in air, worldwide levels tend to remain relatively constant and
generally within the aforementioned range of concentrations.
Because the outside CO2 level is relatively constant, the outside
CO2 level can be used as a reference value for outside air.
[0029] CO2 is also produced by humans at a relatively constant and
predictable rate based on a given activity level. An individual
exhales approximately 40,000 PPM of CO2 with each breath. A more
active individual contributes even more CO2 to a given space. Since
people are the most significant contributor of indoor CO2, the
concentration level of indoor CO2 is a good indicator of occupancy
within a space. For example, doubling the number of people in a
space will also double the amount of CO2 produced in the same
space.
[0030] An inside measurement of CO2 concentration levels provides a
dynamic means to measure the number of people occupying a space
(contributing CO2) and the amount of low concentration of outside
air being drawn into the space to provide fresh air and dilute
contaminants. As a result, CO2 can be used to measure and control
the amount of outside air that is provided to the space.
[0031] Because the CO2 contribution is very predictable based on a
common activity level, the measure of CO2 is directly related to
the cfm/person of outside air delivered to the space.
[0032] When CO2 control is applied to a unitary air handling
system, CO2 can be measured in the return air before the air intake
dampers and/or in the space. The CO2 sensor is then used to
modulate the outside air damper to deliver the proper amount of
outside air for the occupancy of the space. Typically this approach
allows the damper to be adjusted below the fixed position typically
set assuming "design occupancy". Energy savings are realized here
because a portion of outside air does not have to be conditioned.
Yet the required ventilation rates established on a per person
basis can still be maintained thus ensuring acceptable indoor air
quality. A CO2 sensor modulates the air intake damper between an
upper limit (typically 20-30% outside air) and a lower limit of
about 5% outside air.
[0033] Another benefit is that the invention enables use of H2O
level measurements in return and supply air to calculate
differential enthalpy and/or to control to dewpoint conditions.
[0034] FIG. 3 is a chart showing the results of a study for
economizers serving a retail space. FIG. 3 shows the relative HVAC
cost using no economizer, a 55 drybulb economizer system, a 65
drybulb economizer system, an enthalpy economizer system and a
differential enthalpy economizer system. The study revealed that
drybulb economizer systems showed HVAC cost savings over a system
without an economizer system. The study revealed that both enthalpy
based economizer systems showed greater cost savings than the
drybulb based systems and that the differential enthalpy system
provided the most HVAC cost savings.
[0035] One embodiment of the invention includes a sensor to be
affixed to a building or one of the interior walls of a space (such
as a building or a room) to measure temperature, absolute humidity
and CO2 levels. The aforementioned air quality parameter
measurements are used to 1) sense occupancy within the space
(CO2)2) control outside air ventilation in the space (CO2) 3)
maintain humidity levels below the point where moisture related
damage may occur when the room is unoccupied and 4) to maintain
temperatures when the room is occupied. This particular embodiment
is particularly useful to monitor and control spaces like but not
limited to hotel rooms where occupancy is unpredictable and current
control schemes strictly operate the system in an on/off mode.
[0036] The invention enables use of a CO2 level sensor for
occupancy determination within a space. The invention determines
occupancy within a space by comparing CO2 concentration levels over
a period of time and detecting patterns in the variations of the
concentration levels that are typical of one or more people in the
space. Such a sensor could also be combined with a simple occupancy
sensor that could indicate initial occupancy and the CO2 sensor
could measure and control for on-going occupancy.
[0037] The invention also could be coupled with a simple occupancy
sensor to provide a baseline for initial occupancy of the space and
where the invention measures occupancy continuously and controls
the HVAC system to maintain the proper ventilation rate
accordingly.
[0038] The invention enables use of a CO2 sensor in the measurement
and control of ventilation rates on a per person basis. CO2 levels
in a space increase to a predictable level in a predictable
exponential manner to a CO2 level that corresponds to a given
ventilation rate per person in the space. Conventional CO2 control
and measurement approaches generally must wait for CO2 levels to
reach the peak or leveling off point of CO2 concentrations (called
the equilibrium level) before ventilation rates can be accurately
predicted. FIG. 4 shows this pattern of CO2 buildup and leveling
off depending on the ventilation rate. The present invention,
however, uses a predictive algorithm to look at the rate of rise of
CO2 and predict where the leveling point or equilibrium level was
and allowing a prediction of the current ventilation rate. This
method of measuring ventilation overcomes the traditional problem
of waiting for CO2 levels to build up and level off, instead
providing a real time indication of the ventilation rate within the
space. The calculation is based on the rate of change of CO2 over a
fixed period of time ranging from one minute or less to every 15
minutes or more. Variables of the predictive algorithm include the
human activity level anticipated in the space, the typical design
densities expected, and the mathematical function for the
exponential buildup of CO2 concentration levels within a space. The
invention allows for calculation and control on a real-time basis
of the actual ventilation rate/person to the space. This could be
used both as a control parameter and a display parameter to
occupants of the space. Such a parameter could also be indicated on
a display in a graphical format which would indicate if a space was
over or under ventilated or ventilated just right. It would provide
a much more relevant indication of ventilation as compared to
providing just a CO2 concentration.
[0039] In the present invention, sensors can be placed in the
return air to compare differential conditions by adjusting dampers
to allow a proper measurement of exterior air to determine if
outside temperature and humidity conditions (combined measurement
is often called enthalpy) are sufficient to utilize outside air for
free cooling. If sensors are provided outside, the sensors would
not last long due to the extreme conditions they are exposed to.
Another embodiment of the present invention includes an absolute
humidity sensor and temperature sensor in the mixed air section of
the air handler or air handling system. In this arrangement, the
sensors continually monitor the conditions of the mixture of return
air and supply air.
[0040] One such control strategy, as depicted in FIG. 5, controls
an economizer as illustrated in FIG. 2. In step 500, the economizer
is in cooling mode. In step 502 the controller 218 periodically
opens the exterior dampers to a consistent position above the
current or minimum airflow setting. In step 504, the temperature
detected by sensor 224 is transmitted to controller 218 to make a
determination as to whether the temperature is within an acceptable
range for economizer control (e.g. between 55 F. and the return air
temperature (70 F.)). If the temperature is not within an
acceptable range the exterior air intake damper 214 is returned to
a minimum air flow position in step 506. If the temperature is
within an acceptable temperature range, the absolute humidity is
determined in step 508 from sensor 224. If the absolute humidity
concentration is within an acceptable range, the external air
intake damper 214 continues to open in step 510. Otherwise, the
exterior air intake damper 214 returns to a minimum air flow
position.
[0041] Another variation of this approach is designed to only
continue opening of the damper if temperature is acceptable and the
absolute humidity level remains the same or is dropped. If the
temperature and or the absolute humidity levels increase, the
dampers or outside airflow rate will go back to the minimum
position. If outside air is used for cooling, CO2 control of the
dampers can be overridden by the economizer control.
[0042] The sensor in the mixed air may also be used to sense and
control the latent heat and sensible heat cooling characteristics
of an air handling system by determining the moisture level of air
before it enters the cooling coil. The ability for the coil to cool
or remove humidity from the air can be controlled by a number of
factors including: controlling the velocity of air through the
coils, controlling the temperature of liquid in the coils, or
staging the operation of a multiple combination of coils to achieve
the desired performance level. This allows for much better control
of humidity levels than current control methods provide.
[0043] Humidity buildup in buildings in summer or any time in humid
climates can occur when equipment is placed on a setback or off
cycle during evening and weekends. As long as the temperature
remains high, humidity concentrations are not a concern. However,
when a system is activated and cooling begins, the temperature will
be reduced, significantly reducing the moisture holding capacity of
the air. The result is that condensation will occur on the coldest
parts of the building (such as on slab on grade floors, around
cooling ducts). This condensation can lead to mold and mildew
contamination that can affect air quality.
[0044] The conditions necessary to cultivate a hospitable
environment for bacterial or fungal growth include warm
temperatures (temperatures of 60.degree. to 90.degree. ),
availability of source of nutrients (dust, dirt and organic human
byproducts), and the presence of bacterial or mold spores (they
come from outside but are everywhere), all of which are readily
available in most indoor environments. The missing ingredient that
makes it all work is and enzyme solvent, namely water. When
conditions in a building reach a point where water condenses on a
cold surface in a building the final ingredient to a self-starting
science project has been added. Once this growth starts, the
contamination will continue to survive regardless of the future
presence of water.
[0045] Air has a limited capacity to hold water vapor based on its
temperature. As illustrated in FIGS. 6 and 7, if the air
temperature decreases just 10.degree. F., the air loses half of its
ability to hold moisture. Once air becomes saturated, it will
condense on the coldest surfaces. It is exactly the same effect
that occurs to a cold drink held in the humid summer air.
[0046] In a building it's a bit more complicated but the same
principle applies. When a room is unoccupied and the system is
turned off, the room heats up and humid air from outside enters the
room. Because the air is warm it can hold lots of moisture. But
when the cooling system turns on, the air conditioning quickly
cools the room to the set-point temperature. Unfortunately the
system is unable to dehumidify the room as fast as it cools the
room and as a result, water begins to form on the coldest surfaces
in the room. The coldest surfaces of a room can include areas such
as those on and around the air conditioner, slab-on-grade floors
(in the carpets) and on bathroom fixtures. Water vapor that has
seeped into walls and furniture within the space also reaches the
condensation point and begins to break down the material. Humid air
that has seeped behind the walls through electrical outlets and
other pathways now starts to condense inside the walls on the
rapidly cooling drywall further helping its deterioration and
allowing unseen microbes to grow unhindered.
[0047] The best way to avoid all these problems is to never allow
water vapor levels to build up in a space so that condensation can
occur when the room reaches its cooling set-point. In one
embodiment of the present invention absolute humidity is measured
in the space so as not to allow absolute concentrations of water
vapor to exceed a certain threshold that will result in
condensation occurring at normal daytime cooling temperatures.
[0048] The many features and advantages of the invention are
apparent from the detailed specification, and thus, it is intended
by the appended claims to cover all such features and advantages of
the invention which fall within the true spirits and cope of the
invention. Further, since numerous modifications and variations
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
illustrated and described, and accordingly, all suitable
modifications and equivalents may be resorted to, falling within
the scope of the invention.
* * * * *