U.S. patent application number 12/848788 was filed with the patent office on 2011-11-17 for method and system for improved-efficiency air-conditioning.
Invention is credited to Udi Meirav.
Application Number | 20110277490 12/848788 |
Document ID | / |
Family ID | 44910513 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110277490 |
Kind Code |
A1 |
Meirav; Udi |
November 17, 2011 |
Method and System for Improved-Efficiency Air-Conditioning
Abstract
The amount of supply air used by an HVAC system, and hence the
amount of energy used for heating and cooling, while maintaining
desirable air quality and composition, is reduced by removing
unwanted gases, such as carbon dioxide, using scrubbers or other
devices that separate these gases from the circulating air.
Optionally, the air can be further improved with injection of
concentrated oxygen. While in a normal HVAC system frequent
replacement of the building air is performed, scrubbing of CO.sub.2
and other unwanted gases, with or without additional oxygen, would
achieve the same goal, but with less frequent air replacement and
therefore lower thermal load on the HVAC system.
Inventors: |
Meirav; Udi; (Newton,
MA) |
Family ID: |
44910513 |
Appl. No.: |
12/848788 |
Filed: |
August 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61345194 |
May 17, 2010 |
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61351968 |
Jun 7, 2010 |
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Current U.S.
Class: |
62/89 ; 454/337;
62/186; 62/235.1 |
Current CPC
Class: |
B01D 2257/504 20130101;
B01D 2257/708 20130101; F24F 2110/70 20180101; F24F 8/167 20210101;
B01D 2251/30 20130101; B01D 53/72 20130101; F24F 2110/72 20180101;
B01D 53/62 20130101; B01D 2251/604 20130101; B01D 2257/302
20130101; B01D 2257/404 20130101; B01D 2251/304 20130101; B01D
2258/06 20130101; B01D 2252/20484 20130101; F24F 8/158 20210101;
Y02C 20/10 20130101; B01D 2251/606 20130101; B01D 2253/108
20130101; F24F 8/10 20210101; B01D 53/60 20130101; B01D 2257/402
20130101; F24F 8/60 20210101; B01D 2257/502 20130101; Y02C 20/40
20200801; F24F 2110/66 20180101 |
Class at
Publication: |
62/89 ; 454/337;
62/235.1; 62/186 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25B 27/00 20060101 F25B027/00; F25D 17/04 20060101
F25D017/04; F24F 7/00 20060101 F24F007/00 |
Claims
1. A system for controlling temperature of air in an enclosed
environment, comprising: an inlet configured to receive air from
outside the enclosed environment; an air handling unit connected to
receive outside air through the inlet and circulated air from the
enclosed environment and configured to affect the temperature of
the received air; an air circulation system configured to circulate
air from the air handling unit to designated spaces in the enclosed
environment and back to the air handling unit; a gas scrubbing
system configured to reduce the level of unwanted gases in the
circulating air.
2. The system of claim 1, further comprising a control system
responsive to measurements of composition of the circulated air to
control the gas scrubbing system to maintain a desired composition
of the circulated air.
3. The system of claim 2, wherein airflow through the inlet is such
that the desired air composition is maintained with a lower amount
of outside air than would be possible without the gas scrubbing
system.
4. The system of claim 1, wherein the unwanted gases includes
carbon dioxide.
5. The system of claim 4, wherein the unwanted gases further
include at least one of volatile organic compounds, carbon
monoxide, nitrous oxides and sulfur oxides.
6. The system of claim 1, wherein the gas scrubbing system is
connected to the air circulation system to intercept at least a
portion of the circulating air prior to the circulating air
reaching the air handling unit.
7. The system of claim 1, wherein the gas scrubbing system is
connected to the air the air circulation system to intercept at
least a portion of the circulating air after the circulating air is
processed by the air handling unit.
8. The system of claim 1, wherein the gas scrubbing system includes
a molecular sieve and the unwanted gas is reduced by adsorption of
the unwanted gas onto the molecular sieve.
9. The system of claim 8, wherein the molecular sieve is made of a
form of zeolite.
10. The system of claim 8, wherein the gas scrubbing system
includes at least one additional adsorbent.
11. The system of claim 10, wherein the additional absorbent
includes at least one of activated charcoal, silica gel or porous
alumina.
12. The system of claim 10, wherein the additional adsorbent is
placed in a bed that intercepts flow of circulating air.
13. The system of claim 10, wherein the gas scrubbing system
comprises a plurality of beds, wherein each bed intercepts flow of
circulating air, and each bed includes an additional adsorbent.
14. The system of claim 1, wherein the gas scrubbing system
comprises a system for controlling a reversible chemical
reaction.
15. The system of claim 14, wherein the reversible chemical
reaction is a sodium carbonate and sodium bicarbonate cycle.
16. The system of claim 14, wherein the reversible chemical
reaction is an amine-gas cycle.
17. The system of claim 1, where the gas scrubbing system utilizes
one or more bases.
18. The system of claim 17, wherein the base is an alkaline
hydroxide.
19. The system of claim 1, wherein the gas scrubbing system is a
temperature swing adsorption system.
20. The system of claim 1, wherein the gas scrubbing system
includes a purge cycle, wherein a purge gas is applied to the gas
scrubbing system to release the unwanted gas from the gas scrubbing
system.
21. The system of claim 20, wherein the purge gas is heated by
taking heat from a component of a heating, ventilation and
air-conditioning system incorporating the air circulation
system.
22. The system of claim 20, further comprising a heating system
configured to heat the purge gas.
23. The system of claim 22, wherein the heating system uses solar
energy.
24. The system of claim 1, wherein the gas scrubbing system
comprises an adsorbent, and the system further comprises a cooling
system that cools the adsorbent, wherein the cooling system uses a
chilled fluid provided by the air handling unit.
25. The system of claim 1, wherein the gas scrubbing system is
connected to the air circulation system such that a part of
circulating air flows through the gas scrubbing system and another
part of the circulating air bypasses the gas scrubbing system.
26. The system of claim 1, further comprising an oxygen injection
system that injects oxygen concentrated air into the circulating
air.
27. The system of claim 26, further comprising a control system
responsive to measurements of oxygen level in the circulating air
to control the oxygen injection system so as to maintain a desired
level of oxygen in the circulating air.
28. The system in claim 26, wherein the oxygen injection system
comprises a pressure swing adsorption or vacuum swing adsorption
system.
29. A process for controlling temperature of air in an enclosed
environment, comprising: receiving air from outside the enclosed
environment and circulating air from the enclosed environment;
conditioning the received air so as to provide air at a desired
temperature; circulating the conditioned air into and from
designated spaces in the enclosed environment; scrubbing the
circulated air from the enclosed environment to reduce unwanted
gases in the circulated air; recirculating the scrubbed air; and
exhausting a portion of the circulated air from the enclosed
environment.
30. The process of claim 29, wherein the scrubbed air is
conditioned to the desired temperature prior to being
recirculated.
31. A control system for use with an HVAC system having a gas
scrubbing system for removal of an unwanted gas from circulated
air, the control system comprising: a sensor for determining an
amount of the unwanted gas in the circulated air; a controller that
modifies a rate of exhaust of circulating air and intake of outside
air so as to adjust overall air replacement according to the
measured amount of unwanted gas in the circulated air.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a nonprovisional application of, and
claims priority to and the benefit under 35 U.S.C. 119 of,
provisional patent application 61/345,194, filed May 17, 2010, and
provisional patent application 61/351,968, filed Jun. 7, 2010, each
of which is hereby incorporated by reference.
BACKGROUND
[0002] Heating, Ventilation and Air-Conditioning (HVAC) are
standard in virtually every modern building. Indeed, HVAC is often
the largest part of the entire energy budget of most buildings, and
this is particularly the case in extreme climates, both hot and
cold. The goal of HVAC systems is to provide comfortable and
healthy conditions for the building occupants, in terms of
temperature, humidity, composition and cleanliness of the air.
[0003] Central HVAC systems typically include one or more central
air handling unit and an air distribution system, where supply air
is directed to the various parts of the building through a network
of ducts, and return air flows from these spaces, through ducts or
a plenum, back to the air handling unit. In the air handling unit,
air is cooled or heated, as well as filtered and often dehumidified
or humidified, as needed. Thus HVAC systems constantly circulate
air through the building while continually adjusting is temperature
and humidity to maintain comfortable conditions.
[0004] However, in order to maintain good air quality, not all the
air is recirculated: some fraction of the circulating air is
constantly exhausted outside the building--hence exhaust air--and
is replaced by an intake of outside air also known as makeup air,
to make up for the exhaust air. In other places this is also
referred to as "fresh air" or ventilation. This replacement of the
air is done because the occupants of the building and the equipment
consume oxygen and emit carbon dioxide (CO.sub.2) and a variety of
other contaminants that would gradually compromise the quality and
safety of the air. This replacement of the air maintains fresh air
quality.
[0005] Oxygen represents about 21% of atmospheric air and that is
normally the desired level of indoor air as well. On the other hand
CO.sub.2 is present only in very low levels in outside air,
typically a few hundred ppm (parts per million). Once breathing
produces elevated levels of CO.sub.2 and some of the indoor oxygen
is consumed, a fairly significant amount of outside air is used to
bring their respective concentrations close to the desired level.
Indeed, to fully restore oxygen and CO.sub.2 concentration
virtually all the air would need to be replaced.
[0006] The outside air represents an additional, and--depending on
outside climate conditions--often a significant, thermal load on
the air handling unit. In the case of a hot and humid climate, for
example, the outside air injected into the HVAC system requires
additional energy for cooling and dehumidifying the outside air,
and can represent a significant fraction of the entire thermal
load, hence energy usage, of the HVAC system.
[0007] The amount of exhaust air and outside air can adjusted to
meet the air quality standards. A certain minimum amount is often
set to maintain air quality, in terms of levels of oxygen, CO.sub.2
and other contaminants. In the USA, the American Society of
Heating, Refrigeration and Air-conditioning Engineers (ASHRAE)
issues guidelines for the minimum amount of outside air ventilation
recommended for a given space and number of occupants. However, the
greater the rate of air replacement, the more energy is consumed by
the HVAC system.
SUMMARY
[0008] The amount of supply air used by an HVAC system, and hence
the amount of energy used for heating and cooling, while
maintaining desirable air quality and composition, is reduced by
removing unwanted gases, such as carbon dioxide (CO.sub.2), using
scrubbers or other devices that separate these gases from the
circulating air. Optionally, the air can be further improved with
injection of concentrated oxygen. While in a normal HVAC system
frequent extensive replacement of the building air is performed,
scrubbing of CO.sub.2 and other unwanted gases and vapors, with or
without additional oxygen, would achieve the same goal, but with
much lower thermal load on the HVAC system, providing significant
energy saving for the building and reducing demands on the entire
electrical grid.
[0009] In one embodiment, the HVAC system also has an oxygen
injection system that injects oxygen-enriched air into the
circulated air.
[0010] In one embodiment, a control system for use with an HVAC
system has a gas scrubbing system for removal of an unwanted
substance gas from circulated air. The control system includes a
sensor for determining an amount of the unwanted substance gas in
the circulated air. controller modifies a rate of exhaust of
circulating air and intake of outside air so as to adjust overall
air replacement according to the measured amount of unwanted
substance gas in the circulated air. The control system also can
include an oxygen sensor for determining an amount of oxygen in
circulated air, and wherein the controller modifies the rate of
oxygen injection.
[0011] In another embodiment, the system is a modular system can be
connected to an HVAC system that circulates air in an enclosed
environment. The modular system comprises a module for scrubbing
configured to reduce a level of an unwanted substance in the
circulating air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a conventional HVAC system
[0013] FIG. 2A illustrates an HVAC system incorporating CO.sub.2
scrubbing and oxygen injection.
[0014] FIG. 2B illustrates another embodiment of the system of FIG.
2A.
[0015] FIG. 2C illustrates another embodiment of the system of FIG.
2A.
[0016] FIG. 3 shows the configuration of valves and lines allowing
the scrubber to switch from adsorption mode to purge mode.
[0017] FIG. 4 illustrated the addition of an oxygen injection
system into the system of FIG. 2A.
[0018] FIG. 5 is a diagram of the control flow for a controller for
such an HVAC system.
DETAILED DESCRIPTION
[0019] FIG. 1 schematically describes a typical circulating central
HVAC system. A central air handling unit has both heating and
cooling elements, which modify the temperature of the circulating
air as it flows and comes in contact with these elements. Fans or
blowers force the flow of the conditioned supply air through ducts
that distribute the conditioned air throughout the various parts of
an occupied space (an enclosed environment). In this document, a
building is used as an example of an enclosed environment may have
different zones for which the rates of air flow are different.
Return air flows back to the air handling unit, as indicated at 10,
and can be filtered to remove particles, bacteria, and various
fumes. However some of the return air is exhausted outside the
building, through valves that control the amount of exhaust
released. At the same time fresh outside air is pulled in to
replace the exhaust air and maintain the correct overall volume and
pressure of air in the building. Typically 10-15% of airflow is
released as exhaust and replaced, but this number can vary widely.
Indeed some settings like bathrooms and kitchens will exhaust and
replace 100% of the air flow. The constant replacement of exhaust
air with outside air helps maintain good air quality, and in
particular replenish oxygen consumed by the building occupants and
remove carbon dioxide and other compounds generated by the
occupants or the equipment inside the enclosed environment.
[0020] The enclosed environment can be an office building,
commercial building, residential building, house, school, factory,
hospital, store, mall, indoor entertainment venue, storage
facility, laboratory, vehicle, aircraft, ship, bus, theatre,
enclosed arena, education facility, library or other enclosed
structure which can be at times occupied by breathing things, such
as humans or animals.
[0021] FIGS. 2A, 2B and 2C schematically show how to incorporate
scrubbers in the HVAC system in order to allow reduction of exhaust
air and outside air. The scrubber (CS) intercepts some of the flow
of return air, allowing scrubbed air to continue to flow to the air
handling unit and back into the building, but CO.sub.2 and other
compounds are captured or filtered. The scrubber can be implemented
in many ways, as CO.sub.2 scrubbing has been used for decades in
industrial applications as well as in spacecraft and
submarines.
[0022] In one embodiment the CO.sub.2 scrubber utilizes a bed of
adsorbent material, such as synthetic zeolite, placed in a
container, canister or lining the inside of one or more tubes.
Several zeolites have been shown to be effective adsorbents of
CO.sub.2, notably zeolite-13X. These are readily available from a
variety of commercial sources, such as W.R. Grace SYLOBEAD.RTM.
C-Grade 13X, Pingxiang XINTAO Chemical Packing Co., Ltd. In China,
GHCL Ltd., in India, and many others. Indeed, zeolite beds have
been developed to extract CO.sub.2 from a gas stream for various
industrial applications (Ventriglio et al, 1968; U.S. Pat. No.
3,619,130; Reyhing et al, 1971, U.S. Pat. No. 3,808,773; Collins,
1972, U.S. Pat. No. 3,751,878; Shermen et al, 1974, U.S. Pat. No.
3,885,927; Sirkar et al, 1979, U.S. Pat. No. 4,249,915; Grenier et
al, 1991, U.S. Pat. No. 5,137,548). The same underlying
technologies can readily be adopted for this invention, which in
fact is more forgiving in terms of the allowed residual CO.sub.2 in
the outflow. In certain embodiments adding other adsorbents,
including multiple zeolites, porous alumina (Slaugh et al, 1981,
U.S. Pat. No. 4,433,981; Kumar et al, 1986, U.S. Pat. No.
4,711,645) or the long established activated charcoal (Allen, 1921,
U.S. Pat. No. 1,522,480; Bechthold, 1927, 1,836,301) may further
improve air quality or energy efficiency by removing other gases,
volatile organic compounds and humidity or by allowing
lower-temperature release of adsorbates. In some embodiments the
combination of several different adsorbents in the same unit or as
separate units may offer the best performance. As such captured
gases accumulate in the scrubber, at some rate these need to be
removed from the scrubber, in what is commonly called
"regeneration". These unwanted gases can be released to the
atmosphere or otherwise collected and disposed of or sequestered.
In one embodiment the release is achieved by a combination of
heating and purging with air or other purge gas. Thus an
adsorption-desorption cycle sometimes referred to as temperature
swing adsorption. During regeneration the scrubber is isolated from
the HVAC circulation by a set of valves, shown in FIG. 3, and in
turn connected to the incoming and outgoing purging lines. During
the adsorption cycle Valve 1 and Valve 2 are open, connecting the
scrubber to the circulating air flow, while Valves 3 and 4 are
closed. During regeneration Valves 1 and 2 are closed and Valves 3
and 4 are open, flowing purge gas thru the scrubber while isolating
it from the air circulation system. If the scrubber regeneration
interrupts the continual scrubbing process for an unacceptably long
period of time, multiple scrubbers (not shown) may be used to avoid
such interruption, so that when one scrubber is undergoing
regeneration, another scrubber is engaged. However, short
interruptions may not pose a problem, as long as the aggregate
amount of CO.sub.2 removed over periods of several hours is
sufficient. Similar back up may be implemented for the oxygen
concentrator.
[0023] The scrubber adsorbent bed design will include the
appropriate choice of adsorbent material, its amount, its spatial
distribution, the air flow pattern and its overall capacity to be
compatible with the airflow design requirements. There are
tradeoffs to consider in terms of system size and cost versus
throughput, frequency of regeneration and energy requirements for
regeneration. The amount of CO.sub.2 that can be collected and
released in each temperature swing adsorption cycle is dependent on
the amount of active and accessible adsorbent material, as well as
the temperature gap between the adsorption and purge cycle. Thus to
achieve a certain rate of gas capture one use less material and
operate with more frequent purge cycles. However there are natural
kinetic rates for adsorption and desorption that depend on material
and temperature that constrain the cycle time for a given amount of
material. To minimize the energy required, i.e. the energy required
to heat the purge gas, one would design a lower purge gas
temperature, however that would reduce the amount desorbed per
cycle. In an application that is primarily driven by energy
savings, one can start with the temperature and volume of purge gas
that can be produced by the excess heat of the HVAC system and use
that to design the thermal range of the temperature swing cycle,
and based on that and the kinetics of the adsorbent design the
dimensions of the bed. It is anticipated that different embodiments
will be implemented in different settings to address these
tradeoffs.
[0024] Solid adsorbents like zeolite 13X offer a preferred
embodiment but there are many other ways to remove CO.sub.2 as well
as other unwanted gases and vapors. In other embodiments CO.sub.2
scrubbing is achieved by reactions with alkaline hydroxide bases.
In another embodiment CO.sub.2 scrubbing is achieved with amine gas
solutions, such as monoethanolamine or other amines, that are well
known in the art. Another embodiment scrubbing is achieved by a
chemical cycle in which sodium carbonate combines with carbon
dioxide and water to form sodium bicarbonate (Fuchs, 1967 U.S. Pat.
No. 3,511,595). Yet other techniques for removal of CO.sub.2
include selective membranes, for example, PRISM membranes from Air
Products, Inc, or CYNARA membranes from Cameron International Corp.
Since the scrubber is a separate module in this systems, as new
scrubbing technologies emerge they can readily be replaced in such
a system without having to change its other components.
[0025] The scrubber will have to be regenerated and many of the
above techniques require heat for regeneration. Some of that heat
can be obtained by harvesting waste heat produced by other systems
nearby, including the compressor and the air handling unit of the
HVAC system, as well as solar energy. This could further improve
the overall economics of the system. In certain embodiments the
purging of the adsorbent bed utilizes warm air from the cooling
unit to purge the bed during regeneration. In some embodiments
solar energy is collected on a rooftop unit and used to heat the
purge gas. Solar heating and harvesting compressor heat and other
wasted heat can be used in combination, to minimize the energy
usage of the system as a whole. Independent or additional heating
may be performed to achieve a particular purge gas temperature in
which case a heating coil, a furnace or a gas burner can be
incorporated to the system before the entry point of the purge
gas.
[0026] FIG. 2A shows the scrubber (CS) intercepting all of the
return air flow. In an alternative configuration, shown in FIG. 2B,
only some of the return air is diverted to the scrubber while the
rest bypasses the scrubber and flows directly to the air handling
unit. It is not essential that all the air pass thru the scrubber,
as long over time a sufficient fraction of the unwanted gases are
captured. In another configuration, the scrubber is positioned
downstream from the air handling unit, which has the advantage of
colder air entering the scrubber and cooling it. Most scrubbers,
and adsorbents in particular, perform better with lower
temperatures. From an air quality standpoint, the any location of
the scrubber can work, as long as there is over time adequate
amount of contact between the circulating air and the scrubber
somewhere along the flow path of the air before or after the air
handling unit. The scrubber(s) could even be distributed in the
occupied space.
[0027] The scrubber will collect CO.sub.2 and potentially other
substances that can be disposed of in various ways. They could be
released to the atmosphere, or collected in containers for handling
and disposing in another location, or flowed through pipelines to
another location or facility, to be stored, processed or utilized.
For example, CO.sub.2 is beneficial for greenhouses and could be
directed to such greenhouses by pipes or by containers.
Alternatively these byproduct gases can be sequestered indefinitely
simply to avoid releasing them into the atmosphere. However there
will be a higher cost to such disposition of these gases and it
will not necessarily be economically justifiable to do so.
[0028] FIG. 4 illustrates the addition of an oxygen concentrator
(OC) to the system. In this embodiment, an oxygen concentrator
takes its own outside air supply (OA2) and creates a flow of
concentrated oxygen (O), which is directed through an additional
intake valve in to the air handling unit, upstream from the
heating/cooling elements. The oxygen concentrator disposes of
nitrogen and potentially other by-products back to the atmosphere
as indicated at N. The amount of oxygen added to the circulating
air depends on flow rate and the oxygen concentration. The latter
could be well over 90% as is the case in most commercially
available concentrators, but even a lower concentration would
achieve the desired results, with a slightly higher flow rate.
[0029] The oxygen concentrator can be implemented in many ways. In
the preferred embodiment, the technique for oxygen concentration is
Pressure Swing Adsorption (PSA) or Vacuum Swing Adsorption (VSA).
This technique has been known since the 1960's, it is in widespread
commercial use today, and is readily available from a variety of
producers making many products with different sizes and output
capacities, as stand-alone systems for providing concentrated
oxygen directly from air. Example VSA oxygen generating systems
include, but are not limited to, the PRISM VSA oxygen generation
systems from Air Products Inc.; the OXYSWING product line from
Innovative Gas Systems, Inc.; the ADSOSS line of oxygen generators
from Linde; the VPSA oxygen generating system from Praxair Inc.
These PSA/VSA systems utilize highly porous adsorptive solids,
usually a synthetic zeolite bed, in one or more container,
typically shaped as a cylindrical column, and use pumps and
compressors to change the pressure of gases in these containers.
The technique relies on differential adsorption of oxygen and
nitrogen onto the adsorbent. Thus it takes an inflow of normal air
(or other gas mixtures), and generates two separate outputs: oxygen
concentrated air and oxygen depleted air. The advantage of PSA/VSA
is that these systems can continually generate oxygen for extended
periods without much maintenance.
[0030] Other ways to separate or concentrate oxygen exist.
Cryogenic separation is an effective way for large volumes and high
purity, where the different condensation/boiling temperatures of
different gases are used to separate oxygen from air. Selective
membranes and selective diffusion media have also been developed to
separate oxygen from air. Concentrated oxygen can also be generated
from electrolysis of water, where electrical current through water
generates oxygen gas on one electrode and hydrogen gas at the
other. While these are energy intensive processes, pure hydrogen or
nitrogen created as by products and can be collected and utilized
for other applications.
[0031] Even the presence of both the scrubber and the oxygen
concentrator does not mean that exhaust air and outside air are
necessarily eliminated altogether. In certain embodiments, exhaust
air and outside air will be kept at a controlled level, lower than
in a conventional HVAC system but a level that would still be
warranted or desired in order to assure that there is no gradual
deterioration in air quality despite the benefits of the oxygen
concentrator and the scrubber.
[0032] We describe systems both with and without the oxygen
concentrator. Indeed in some embodiments the oxygen concentrator is
eliminated, and the use of a scrubber by itself imparts the
majority of the benefits. At first glance this may not be obvious,
since oxygen consumption and CO.sub.2 emission go hand in hand and
occur in almost identical molecular quantities, which implies that
the drop in oxygen concentration would be commensurate to the rise
in CO.sub.2 levels, and the sum of the two almost constant.
However, as long as makeup air is reduced but not eliminated
altogether, even without a scrubber and an oxygen source, the
oxygen and CO.sub.2 levels will stabilize at certain asymptotical
concentrations that together sum up to 21%, the same as that of
outside air. The asymptotic level of oxygen, X, is given by
X=X.sub.0-B.sub.o/M
Where X.sub.0 is the concentration of oxygen in outside-air,
B.sub.o is the net amount of oxygen consumed (in CFM, liters/second
or any other units) by the occupants and M is the amount of outside
air injected (in same units, CFM, liter/second, etc respectively).
Similarly CO.sub.2 level, Y, would be given by
Y=Y.sub.0+B.sub.c/M
where Y.sub.0 is the concentration of CO.sub.2 in outside-air and
B.sub.c is the net amount of CO.sub.2 exhaled by the occupants.
Looking at the above it is clear that as long as
B.sub.c.apprxeq.B.sub.o, at least approximately, then
X+Y.apprxeq.X.sub.0+Y.sub.0. However, adding a scrubber that
extracts CO.sub.2 at a rate of S.sub.c (in same units, CFM,
liter/second, etc. respectively) will result in
Y=Y.sub.0+(B.sub.c=S.sub.c)/M
[0033] Analogously the impact of an oxygen generator injecting at a
net rate of G.sub.o (in same units, CFM, liter/second, etc.,
respectively) would be to change the asymptotic value of X to
X=X.sub.0-(B.sub.o-G.sub.o)/M
[0034] For example, if outside air is at the normal 21% oxygen, and
occupants consume 2 CFM net oxygen and exhale a similar amount of
CO.sub.2, makeup air is at 100 CFM, and no further scrubbing or
oxygenation are in effect, then oxygen will gradually approach 19%
while CO.sub.2 approaches 2%. But whereas a 19% concentration of
oxygen may be acceptable in some circumstances, a 2% concentration
of CO.sub.2 is clearly not. Thus adding a scrubber with S.sub.c=2
CFM capacity alone could bring CO.sub.2 levels down to normal.
Oxygen will still be at approximately 19%, unless we inject
supplemental oxygen, but even so air quality may be acceptable at
this level even without an oxygen source, and would require less
hardware and less operating costs, therefore might be a preferred
embodiment for some buildings.
[0035] FIG. 5 shows how air quality is maintained through a
feedback system. Sensors (Y) are distributed through the building
space and detect levels of one or more target gases, such as
CO.sub.2 and/or oxygen but potentially also other gases. Sensors
for CO.sub.2 are commercially available, examples include the C7232
sensor from Honeywell Corp., TELAIRE sensors from General Electric.
A central control system (CC) can be human operated, automated or
computerized. The control system detects the signal for said
sensors and, based on these and the various parameters and settings
of the system, controls or modifies any of the following, in order
to achieve targeted conditions: OC power (on/off), OC settings, OC
valves, CS settings, CS regeneration trigger, outside air flow
rate, exhaust air flow rate. The system can have fail safe measures
to prevent unwanted elevation of oxygen, and the ability to shut
down either or both oxygen concentrator and scrubber if needed and
compensate by increasing outside air and exhaust air levels to
those of a conventional HVAC.
[0036] The control system can permit the amount of scrubbing or
injection of oxygen to be adjustable, whether directly or
indirectly, whether electronically or manually. Adjustments can be
achieved by changing the power or settings applied to the various
compressors, pumps, motors, heaters, actuators or valves associated
with the scrubbers and the oxygen concentrators. The adjustments to
the amount of scrubbing or oxygen injection can be automatically
done in response to a measurement of air quality or air composition
in one or more locations. The adjustments to the amount of
scrubbing or oxygen injection can also be automatically done based
on building occupancy, time of day, day of the week, date, season
or outside climate.
[0037] In one embodiment, the scrubber is set to run at a constant
operating mode. The capacity and efficiency of the scrubber in that
mode should be selected based on the occupied space and the amount
of activity in the occupied space, so as to maintain desirable
levels of CO.sub.2 (or other gases). In this embodiment, the
control system now controls the rate of exhaust air and outside air
to either a preset minimum. If the capacity and efficiency of the
scrubber is insufficient to handle the CO.sub.2 load, then the rate
of exhaust air and outside air can be set to a higher level. The
oxygen flow is separately controlled to maintain the target level
of oxygen in the occupied space. Both the control of the exhaust
air valves and the oxygen inflow can be subject to a simple
feedback loop, with a proportional-integral-differential (PID)
algorithm with upper and lower set points. The coupling of the
oxygen concentrator to the air flow manifold can be done using any
tube of duct fitting, with or without a control valve and/or a flow
meter.
[0038] The system can be designed in a modular way so that it can
be retrofitted on a pre-existing or pre-designed HVAC system. This
will enable the benefit of this invention in buildings that already
have HVAC systems, with relatively lower costs. The oxygen
concentrator and scrubber, with a control system, can be installed
and connected to a conventional HVAC system without having to
replace the ductwork or the central air handling unit.
[0039] Having described an example embodiment, it should be
apparent to those skilled in the art that the foregoing is merely
illustrative and not limiting, having been presented by way of
example only. Numerous modifications and other embodiments are with
the scope of ordinary skill in the art and are contemplated as
falling with the scope of the invention.
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