Abstrict An apparatus is disclosed for an improved air conditioning system
for admitting air from an exterior space, adjusting the temperature
and humidity of the exterior air and delivering the adjusted air
to an interior space of a structure. To compare the energy levels
of these two air streams an improved device brings both air streams
to the same temperature, so just the relative humidity has to be
measured to know which of these two air streams has the higher or
the lower energy level. Using the device in a control system for
a desiccant wheel, at least two temperature sensors are eliminateable.
Claims What is claimed is:
1. A desiccant device, comprising:
a division means for at least locally substantially isolating at
least two areas from each other;
at least one desiccant means for removing moisture from air in
the first of said areas, and for transporting said moisture to the
second of said areas;
humidity sensing means for obtaining the humidity difference between
air from said first area and air from said second area;
first air transport means for transporting air from said first
area to said humidity sensing means;
second air transport means for transporting air from said second
area to said humidity sensing means; and
a control means for controlling the level of activity of said desiccant
means in response to the output of said humidity sensing means,
wherein said first air transport means and said second air transport
means are in a heat exchanging relationship to one another and comprise
a temperature equalising means for substantially equalising the
temperatures of the air from said first area and of the air from
said second area before completing the transport to said humidity
sensing means.
2. A desiccant device according to claim 1 wherein said humidity
sensing means comprises at least one humidity sensor for sensing
relative humidity.
3. A desiccant device according to claim 2 wherein said humidity
sensing means comprise a first humidity sensor for sensing the humidity
of air from said first area and a second humidity sensor for sensing
the humidity of air from said second area.
4. A desiccant device according to claim 1 wherein said control
means provides substantially the same response to any level of output
of said humidity sensing means indicating a positive humidity difference
between air from said first area and air from said second area,
and provides substantially the same reverse response to any level
of output of said humidity sensing means indicating a negative humidity
difference.
5. A desiccant device according to claim 1 wherein said temperature
equalising means further comprise a heat exchanger.
6. Humidity measuring means, comprising:
humidity sensing means for obtaining the humidity difference between
air from a first area and air from a second area;
first air transport means for transporting air from said first
area to said humidity sensing means; and
second air transport means for transporting air from said second
area to said humidity sensing means wherein said first air transport
means and said second air transport means are in a heat exchanging
relationship to one another and comprise a temperature equalising
means for substantially equalising the temperatures of the air from
said first area and of the air from said second area before completing
the transport to said humidity sensing means.
7. Humidity measuring means according to claim 6 wherein said humidity
sensing means comprises at least one humidity sensor for sensing
relative humidity.
8. A desiccant device according to claim 7 wherein said humidity
sensing means comprise a first humidity sensor for sensing the humidity
of air from said first area and a second humidity sensor for sensing
the humidity of air from said second area.
Description FIELD OF THE INVENTION
This invention relates to an improved air treatment system, and
more in particular to a regenerative desiccant based air humidity
controlling system.
BACKGROUND OF THE INVENTION
Air treatment systems, such as air conditioning and cooling systems,
preferably include some means for controlling air humidity. Air
humidity can be just as important to personal comfort as air temperature,
especially in sunny regions close to open water. Also, air humidity
control can be important for the protection of sensitive electronics,
ancient art treasures etc.
Whereas raising air humidity is a relatively straightforward operation,
it takes a lot more to bring it down for the purposes described
above.
Various methods exist for bringing down air humidity. The spraying
of certain chemicals is an non-repeatable and comparatively expensive
method with many additional disadvantages. In general, a repeatable
method is preferred, in the sense that no refuelling is needed,
other than a possible energy supply. Air cooling means may indeed
effect a repeatable drying of air, but since that is inevitably
coupled to the cooling thereof, it will in itself not allow enough
flexibility and fine-adjustment to meet the needs of most applications
described above. On top of that, it makes for a relatively inefficient
and therefore expensive air drying process.
More sophisticated desiccant means have therefore been developed,
that are often but not always used as part of an air cooling system.
Best described are the so-called desiccant wheels, that can for
instance be found in U.S. Pat. No. 5353606 U.S. Pat. No. 4719761
U.S. Pat. No. 4594860 U.S. Pat. No. 3488971 U.S. Pat. No.
3247679 and U.S. Pat. No. 3009684 all deemed to be incorporated
by reference. The thermodynamic process involved in operating these
desiccant wheels are also described therein. Examples of the active
chemical compound used in such desiccant wheels are silica-gel and
lithium chloride.
Most air humidity controlling systems need some form of control
over the level of activity employed at any given time. When drawing
outside air, the humidity and temperature thereof vary and influence
the end result. Also, the end result itself may have to be adjusted
from time to time, for instance depending on personal preference
in the case of comfort control. All forms of level control in an
air humidity controlling system require measurement of air humidity,
be it of the end result, be it at some intermediate stage, be it
of the outside air.
Air humidity measurement is usually performed by comparing the
air humidity in two different areas that indicate the air humidity
before and after treatment with the desiccant means. The comparison
in turn gives an indication of the preferred level of activity.
For instance, one area could be somewhere within a duct for transporting
outside air to the inside of a building, and the other area in another
duct serving the opposite purpose. Or one area could be the inside
of the building itself, so that the end result of the air humidity
control is being measured, and the other measurement could then
possibly be performed outside, in order to give the system an indication
of the difference that should be bridged. In theory, one humidity
sensor placed in between the two different areas of measurement
may do the job. However, the most practical solutions so far make
use of two separate humidity sensors, each located with either of
the two measuring areas.
SUMMARY OF THE INVENTION
The invention relates to air humidity controlling systems in which
air humidity is measured in at least two different areas. Measuring
air humidity at the random temperature, air pressure and air speed
that may commonly occur in areas in and around air humidity controlling
systems, sets high requirements to the quality of the humidity sensor
or humidity sensors involved. In particular, a sensor should be
gauged and should give representative output within the whole range
of temperatures, pressures and wind shield factors to be expected.
Temperatures in both areas constantly and independently fluctuate
with the weather, the required end result, the level of activity
of the desiccant means itself and of humidifiers close by (since
drying and moisturising air influences the temperature thereof),
the presence of water damp sources at the output, the demands made
to the system, any heat sources nearby, to name a few. Air pressures
in both areas constantly and independently fluctuate with the weather,
fan activity, the required end result, and the demands made to the
system. The same holds true for air speed.
Surprisingly, it is now made possible to use more simple and cheaper
humidity sensors in air humidity controlling systems, some of which
sensors have been on the market for longer than air humidity controlling
systems. Also, the humidity sensor or humidity sensors involved
need not necessarily be as accurate as before to obtain the same
quality end result. This has been achieved with a desiccant device
according to the invention, comprising a division means for at least
locally substantially isolating at least two areas from each other,
at least one desiccant means for removing moisture from air in the
first of said areas, and for transporting said moisture to the second
of said areas, humidity sensing means for obtaining the humidity
difference between air from said first area and air from said second
area, first air transport means for transporting air from said first
area to said humidity sensing means, second air transport means
for transporting air from said second area to said humidity sensing
means, a control means for controlling the level of activity of
said desiccant means in response to the output of said humidity
sensing means, wherein said first air transport means and said second
air transport means comprise a temperature equalising means for
substantially equalising the temperatures of the air from said first
area and of the air from said second area before completing the
transport to said humidity sensing means.
In a preferred embodiment of the invention, the desiccant device
comprises humidity sensing means that comprise at least one humidity
sensor for sensing relative humidity. For all practical purposes,
if the air temperatures are equal, an equality of relative humidity
in equals the equality of absolute humidity. Applying this rule
while realising that it predominantly is absolute humidity that
needs to be controlled, and combining this with the insight that,
for all practical purposes here, air temperatures can easily be
made sufficiently equal, has lead to this preferred embodiment of
the invention.
In a further preferred embodiment of the invention the desiccant
device comprises humidity sensing means that comprise a first humidity
sensor for sensing the humidity of air from said first area and
a second humidity sensor for sensing the humidity of air from said
second area.
In a yet further preferred embodiment of the invention the desiccant
device comprises control means that provides substantially the same
response to any level of output of said humidity sensing means indicating
a positive humidity difference between air from said first area
and air from said second area, and provides substantially the same
reverse response to any level of output of said humidity sensing
means indicating a negative humidity difference. It has been found
that simply measuring which of the humidities of both areas is higher,
already provides enough data to effectively control the desiccant
device of this preferred embodiment of the invention. This allows
for cheaper humidity sensors and less complicated control means.
Most effectively for the reason of keeping the control means as
simple as can be, the desiccant device according to a further preferred
embodiment of the invention comprises a heat exchanger as temperature
equalising means. Alternatively, it may be attractive to save on
material by using a heating means instead of or in combination with
a (smaller) heat exchanger, according to another preferred embodiment
of the invention. More specifically, an electrical heating resistor
is even more preferred because it can be controlled relatively easy
and in quick response by electronic control means of the desiccant
device.
The invention is also incorporated in a humidity measuring means,
comprising humidity sensing means for obtaining the humidity difference
between air from a first area and air from a second area, first
air transport means for transporting air from said first area to
said humidity sensing means, second air transport means for transporting
air from said second area to said humidity sensing means, wherein
said first air transport means and said second air transport means
comprise a temperature equalising means for substantially equalising
the temperatures of the air from said first area and of the air
from said second area before completing the transport to said humidity
sensing means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the principles of the operation of a system for controlling
the humidity of air. The system comprises sensors for measuring
the absolute humidity of fresh, outdoor air and sensors for measuring
the absolute humidity of return air as well as a controller unit.
FIG. 2 shows an invention for a system for controlling the humidity
of air. The system comprises a measuring means for determining the
absolute humidity of both the outdoor air and of the return air.
FIG. 3 shows in detail the measuring means for determining the
absolute humidity of both the outdoor air and of the return air.
FIG. 4 shows a diagram of the operation of the controller unit.
DETAILED DISCUSSION
FIG. 1 shows a system 1 for controlling the humidity of air in
a first air duct 2 and a second air duct 3 whereby both air ducts
2 and 3 are connected to each other via an enthalpy wheel 4. The
system 1 further comprises a control unit 5 via which a control
signal S for controlling or regulating a drive unit 6 of the enthalpy
wheel 4 is generated.
Via the operation of system 1 outdoor air flows through the first
air duct 2 into a building whereby the outdoor air flows through
a first inlet 7 in the first air duct 2 and subsequently flows through
a first outlet 8 into the building. Correspondingly, via the operation
of system 1 return air flows through the second air duct 3 whereby
the return air flows through a second inlet 9 in the second air
duct 3 and subsequently flows out of the building through a second
outlet 10.
The controller unit 5 is connected to a first sensor 20 and a second
sensor 21 whereby the first sensor 20 can measure the absolute
humidity of the air between the first inlet 7 and the enthalpy wheel
4 and also whereby the second sensor 21 can measure the absolute
humidity of the air between the second inlet 9 and the enthalpy
wheel 4.
Furthermore the controller unit 5 is connected to a third sensor
22 and with a fourth sensor 23 whereby the third sensor 22 can
measure the absolute humidity of the air between the enthalpy wheel
4 and the first outlet 8 and also whereby the fourth sensor 23 can
measure the absolute humidity of the air between the second outlet
10 and the enthalpy wheel 4.
According to the requirement the system 1 is activated or de-activated
by the controller unit 5 via a signal input 24 and/or a switch 25
and/or a stop button 26.
The implementation of both sensors 20 and 21 for measuring the
absolute humidity of the air by means of the currently known method
is non-trivial and relatively expensive.
According to the invention, FIG. 2 shows a system 1 for controlling
the humidity of air with a controller unit 5 connected to a measuring
means 30 through which the absolute humidity of air is determinable
in the first air duct 2 and in the second air duct 3 whereby the
absolute humidity of the flow in air ducts 2 and 3 is measured before
entry to the enthalpy wheel 4. The measuring means 30 has a first
inlet tube 31 and a second inlet tube 32 whereby both inlet tubes
31 and 32 in the system 1 are installed in a particular way such
that via the first inlet tube 31 air is sampled from a zone between
the first inlet 7 and the enthalpy wheel 4 and similarly, via the
second inlet tube 32 air is sampled from a zone between the second
inlet 9 and the enthalpy wheel 4. The measuring means 30 has outlet
tubes 33 and 34 out through which the air from inlet tubes 31 and
32 respectively is exhausted. The measuring means 30 generates a
first signal WI and a second signal W2 whereby the first signal
WI corresponds to the value of the absolute humidity of the air
in the zone between the first inlet 7 and the enthalpy wheel 4 and
the second signal corresponds to the value of the absolute humidity
of the air in the zone between the second inlet 9 and the enthalpy
wheel 4. Both signals WI and W2 are fed to the controller unit 5.
In FIG. 3 is shown the improved measuring means 30 between the
first inlet tube 31 and the first outlet tube 33 of a first channel
41 and between the second inlet tube 32 and the second outlet tube
34 of a second channel 42. At one end of the first channel 41 next
to the first outlet tube 33 is installed a first humidity sensor
43 whilst at an end of the second channel 42 next to the second
outlet tube 34 is installed a second humidity sensor 44.
Both channels 41 and 42 form a heat exchanger which functions such
that the air in the first humidity sensor 43 is equalized in temperature
with the air in the second humidity sensor 44. The heat exchanger
41 42 functions such that both humidity sensors 43 and 42 measure
the humidity of their respective air streams at the same temperature,
independent of how big is the temperature difference between the
air sampled by the first inlet tube 31 and the air sampled by the
second inlet tube 32. The heat exchanger 41 42 is advantageously
realized as a plate heat exchanger.
Via the measuring means 30 and the heat exchanger 41 42 the temperatures
of the sampled air flows from the first air duct 2 and from the
second air duct 3 are equalized. By this temperature equalization,
the absolute humidity difference can be cost effectively (indirectly)
measured. The cost reduction results from the fact that when the
temperatures of the two air samples are equalized, the determination
of the difference in absolute humidity is (indirectly) measured
with two simple relative humidity sensors 43 and 44. Even though
the absolute humidity is a function of both relative humidity and
temperature the application of two additional temperature sensors
for determining the air temperature in the zone of the first inlet
7 and in the zone of the second inlet 9--or the application of two
expensive sensors 20 and 21 for measuring the absolute humidity
of the air--is unnecessary.
The two humidity sensors 43 and 44 are advantageously realized
as resistive humidity sensors. Resistive humidity sensors for measuring
relative humidity exhibit an electrical resistance which is strongly
dependent upon the humidity of the surrounding air. Resistive humidity
sensors for measuring relative humidity are very cheap compared
with sensors which are used to measure absolute humidity. In the
control unit 5 the absolute humidity of the outdoor air is compared
with the absolute humidity of the return air. The control unit 5
has at least two operational modes namely a dehumidification mode
and a humidification mode.
In FIG. 4 the absolute humidity of the outdoor air is represented
on the ordinate 50 and the absolute humidity of the return air is
represented on the abscissa. The control unit 5 operates in the
dehumidification mode when the absolute humidity of the outdoor
air is greater than the absolute humidity of the return air. The
controller 5 operates in the humidification mode when the absolute
humidity of the outdoor air less than the absolute humidity of the
return air. The hysteresis switching between the two modes is beneficially
adjustable and has a value of 5% for example.
In the dehumidification mode the enthalpy wheel is controlled by
the controller unit 5 such that the enthalpy wheel transfers the
humidity of the air in the first air duct 2 to the air in the second
air duct 3 whereby air in the first outlet 8 is less humid than
the air in the first inlet 7.
In humidification mode the enthalpy wheel 4 is controlled via the
control unit 5 such that the enthalpy wheel transfers energy out
of the warm air from the second air duct 3 to the outdoor air in
the first air duct 2. |