US20080022705A1

US20080022705A1 - Device and method for managing indoor air quality via filtration and dehumidification

Info

Publication number: US20080022705A1
Application number: US11/492,459
Authority: US
Inventors: Roger Dale Clearman
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-07-25
Filing date: 2006-07-25
Publication date: 2008-01-31

Abstract

A device and method are specified for managing indoor air quality. More particularly, to promote health, comfort, and air quality, a device and method are proposed for filtering and dehumidifying air in an indoor environment, e.g., air that flows through an HVAC system.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to managing indoor air quality, especially in connection with heating, ventilation, and air conditioning (HVAC) systems. More particularly, a device and method are proposed for filtering and dehumidifying air in an enclosed (indoor) space—for example, the air that flows through an HVAC system—so as to improve indoor air quality and promote health and comfort.
Managing indoor air quality is a well-established but continually evolving field of technology. Particularly in industrialized nations, populations have become largely “indoor societies,” with many people spending substantial portions of most days indoors. Millions of people work in homes or offices. Millions attend schools. Many senior citizens spend a majority of their day indoors. Many young children spend large amounts of time indoors, whether at home or in other indoor environments.
Consequently, indoor air quality is an area of growing importance and concern. The United States Environmental Protection Agency (EPA) has identified indoor air pollution as one of the top five serious environmental health risks, and mold as a health threat of growing concern within the indoor environment. “Most Americans do not have a clear sense of the significant health risks of indoor pollution. They also do not know what they can do to reduce risk for asthma, cancer, and other serious diseases caused by indoor pollutant exposure.” See Healthy Buildings, Healthy People, EPA Document #402-K-01-003 (October 2001).
A variety of indoor air pollutants are known to exist. Some of these include bioaerosols, dust mites, animal dander, volatile organic compounds, carbon monoxide, mold, bacteria, viruses, fungi, etc. In some circumstances and concentrations, air pollutants are capable of producing a variety of effects undesirable to humans. Certain environmental factors are known or suspected to play a role in either inhibiting or promoting the proliferation of such pollutants in an indoor setting. Regulating or compensating for such factors is known as environmental control or management of air quality.
Ventilation is a primary consideration in managing indoor air quality. Without ventilation, pollutants within a closed environment have little means of escape and can become more concentrated over time. Appropriate ventilation, then, can be an important step toward reducing indoor air pollution. Outside air may be introduced into an indoor air space, subject to whatever additional environmental control processes may be in use.
Filtration of indoor air is another important component in maintaining acceptable air quality. Mechanical filtration systems are commonly rated according to the size of airborne particulates they are capable of removing and their particulate arrestance percentage. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has promulgated a widely-used “Minimum Efficiency Reporting Value” (MERV) Standard 52.2 to quantify these filter performance characteristics. For example, commonly recommended air filtration systems for newer commercial and residential buildings might typically carry a rating around MERV 11, indicating a capability to remove particles about 1 to 3 microns in diameter with an arrestance rate of about 95% or better. To remove even smaller particulates, a more discriminating filter such as a High Efficiency Particulate Air (HEPA) filter with a rating at or near MERV 20 can be employed. To meet HEPA standards, a filtration device must be able to capture at least 99.97% of all airborne particles 0.3 microns or more in diameter that enter it.
Irradiation may also offer certain environmental control benefits. Naturally occurring sunlight includes ultraviolet (UV) rays which inhibit the growth of many microbes in out-of-doors environments. Artificial germicidal UV light can be similarly applied in indoor air quality management to inhibit the growth of bacteria, viruses, molds, etc. UV-C, the germicidal wavelength of UV light, can damage the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in their DNA. The formation of such bonds prevents the DNA from being unzipped for replication, hindering the organism from reproducing.
Proper humidity control is an important but often-overlooked consideration in indoor air quality management. Various organisms, health concerns, and other reactions can increase or decrease with the indoor relative humidity level. See Criteria for Human Exposure to Humidity in Occupied Buildings, Dr. Elia Sterling (1985). “Biological air pollutants are found to some degree in every home, school, and workplace.” “A number of factors allow biological agents to grow and be released into the air. Especially important is high relative humidity, which encourages house dust mite populations to increase and allows fungal growth on damp surfaces.” See Indoor Air Pollution, EPA Document #402-R-94-007 (1994). The basic refrigeration process that allows dehumidification of moisture-laden air has been known for some time—i.e., compressing and condensing refrigerant gas and then allowing this gas to evaporate in a controlled manner through some pressure-drop metering device—but effectively integrating targeted dehumidification into the overall processes of indoor air quality management is not common at this time.
The basic process of refrigeration to achieve dehumidification can be understood by description of a typical implementation of this process. A simple dehumidification system would typically include a refrigerant compressor, an evaporative coil (a refrigerant-to-air heat exchanger, also known as a dehumidification coil), a condenser coil (another refrigerant-to-air heat exchanger, also known as a reheat coil), a refrigerant metering device, assorted tubing connecting the system components so as to make a sealed or closed system, and an air blower or fan. The blower or fan operates in conjunction with the compressor and moves air that is to be dehumidified through the system. The refrigeration system, being closed, recycles the refrigerant through several system components so that various changes of state are induced to achieve the removal, addition, and conversion of energy in the form of latent and sensible heat.
In such a system the compressor receives superheated vapor and compresses this vapor to a point beyond its condensing or liquefying point, yet this compressed gas will not condense to a liquid state without the removal of heat; heat is removed as the gas moves through the condenser coil where the energy required to condense is exchanged with the moving air stream. The liquid's temperature is further reduced (sub-cooled) before leaving the condenser. The sub-cooled liquid being at relative high pressure in the system is passed through a metering device (e.g., a valve, capillary tube, or other specialized orifice) to create a drop in pressure, allowing the refrigerant to change state and evaporate. The evaporation process requires energy (heat) to be added back to the refrigerant, and this occurs in the evaporator coil. The source of the energy or heat is a stream of air moving through the system; because the evaporator is colder that the air stream, heat (both sensible and latent) is removed from the air. The latent heat removal results in water being removed from the air stream in the form of liquid, typically referred to as condensate. Thus some dehumidification of the air has been achieved. The gas—now super-heated beyond its point of evaporation—is returned the compressor, where the cycle is then repeated.
Such a dehumidification process can be enhanced to higher operational efficiency with the addition of an air-to-air heat exchanger (AXA) in the system. With the addition of an AXA the ratio of sensible and latent heat removed can be adjusted. Increasing the latent heat removal capacity allows for a greater volume of moisture removal in each system cycle without the need to increase the overall operational capacity of the refrigeration system. The AXA pre-cools the incoming air stream before the air enters the evaporator coil, and because of the air is pre-cooled the coil itself may typically operate at a lower temperature so that it will be removing a greater amount of latent heat from the air. As a result more water will condense and be removed from the air. The air stream is then directed back through the AXA where it is reheated while serving as the source (“sink”) to cool the incoming air stream. In other aspects this high-efficiency dehumidification process operates similarly to the basic process described before.
The present invention provides several novel combinations of some of the above air quality management techniques, in a manner suited to achieve improved performance over many existing environmental control systems. That the present invention is a distinct improvement over solutions in the prior art will become more apparent from this specification.

SUMMARY OF THE INVENTION

To adequately handle the challenges of managing indoor air quality, more than temperature must be addressed. Yet in the majority of air conditioned buildings today, temperature is the only air quality variable that is precisely monitored or regulated. Successfully controlling the sources of indoor air pollution must involve precise regulation of at least humidity as well. Systems disclosing temperature and/or humidity control are exemplified by such references as U.S. Pat. No. 5,598,715, issued Feb. 4, 1997, to Edmisten; U.S. Pat. No. 5,088,295, issued Feb. 18, 1992, to Shapiro-Baruch; and U.S. Pat. No. 2,255,292, issued Sep. 9, 1941, to Lincoln.
Humidity control is a basic building block of the present invention. Humidity that is too low can promote proliferation of some indoor pollutants such as ozone and certain bacteria and viruses. At extremely low humidity levels, incidence of respiratory infections tends to rise. On the other hand, humidity that is too high can promote proliferation of many indoor pollutants as well, including fungi, dust mites, and certain bacteria and viruses. Humidity control to improve overall indoor air quality thus becomes something of a balancing act of avoiding relative humidity extremes at either end of the range. Current data and experience suggest that an optimally balanced indoor humidity level for many environments may fall in the area of 40% to 60% relative humidity. Adjusting this range in either direction may be desirable in some applications, e.g., where certain specific pollutants are considered to be of greater significance and concern than others. Dehumidification aspects of the invention are further described below.
In addition to temperature and humidity control, air should be filtered and circulated to remove airborne particulate matter, and fresh outside air may be introduced to dilute concentrations of volatile organic compounds. Other treatments such as irradiation may be employed as well. The present invention addresses some of these important indoor air quality control factors, resulting in improved indoor air quality and further resulting in potential health and comfort benefits.
Filtration alone will not achieve the full air quality benefits of the present invention, yet filtration remains an important component of the overall device and method. Filtration can remove airborne particulate matter and thus help improve air quality. Particulate matter comprises very small particles of solids or liquids that vary in size, chemical composition, and source. Such particles can remain suspended in air for long periods of time; the smaller a particle, the longer it may remain airborne. When inhaled, some fine particles may be deposited in the lower respiratory tract and the gas-exchanging portions of the lung, and can damage respiratory airways.
While various approaches to air filtration exist, certain preferred embodiments of the invention employ one or more mechanical filtration stages including, e.g., a HEPA filter. Another preferred embodiment includes a rubberized gasket around at least one mechanical filter, to form a tight seal inside the system and ensure that air passes through the filter and not around it. In still another embodiment, a system control device incorporating a humidistat will monitor and regulate environmental humidity and may also include an indicator to indicate when a mechanical filter or other expendable system components should be changed.
To achieve suitable ventilation, fresh outside air may be introduced into the indoor air space in a variation of the invention. Preferably the outside air enters the system via a path that allows it to be at least partially filtered and dehumidified before entering the conditioned indoor airspace. Incorporating such ventilation into the process or system of the invention can be a significant step in improving the quality of indoor air, by diluting accumulated indoor pollutants.
Germicidal irradiation is implemented in a further optional embodiment of the invention. An embodiment employs a lamp producing UV light on the order of 265 nanometers, which is considered a wavelength lethal to many airborne microorganisms such as bacteria, viruses, and molds. Wavelength and other lamp characteristics may be modified in accordance with the needs of particular applications. The lamp preferably is positioned so as to expose the evaporator, drain pan, and condensate water to germicidal UV light radiation. Airflow may also be subjected to the radiation. Various safety and convenience features may be included with the UV lamp, such as a lamp shutoff switch, a sight glass for safe and easy lamp inspection, and a protective cover with a safety interlock switch to deactivate the lamp before a person can access or service the device. Preferably the UV lamp is constructed to high quality standards to achieve suitable performance and reliability, including the use of hard glass tubing adapted to optimize UV transmittance levels.
In most variations of the device of the invention, an advanced combination of environmental control techniques is implemented in connection with a separate HVAC system. This can be achieved, for example, by integrating the environmental control solutions into a module that can be relatively easily installed in interface with an existing HVAC system to enhance its operation and utilize its air distribution system (e.g., fans, vents, and ductwork). A common installation configuration places the module in parallel with an existing HVAC airflow path, and may utilize a blower and/or damper to direct airflow through the module at appropriate times. The module may be arranged in a horizontal, vertical, or other configuration as needs may dictate. Enhancement of process control may be achieved through the use of dampers and by providing electrical blower interlock with an existing HVAC system blower. A similar module may be installed somewhere within an indoor air space, for example in a stand-alone configuration.
Embodiments of the device and method of the invention trigger an environmental control process at a suitable time (e.g., when a humidistat or other feedback mechanism senses environmental conditions outside some preselected range). HVAC airflow optionally is at least in part diverted so as to be subjected to aspects of the process. HVAC airflow (together with fresh outside airflow, in some embodiments) is directed through a filtration process for removing airborne particulate matter. Dehumidification is achieved as airflow is directed through stages of an AXA that first cause flowing air to give up some sensible heat, reducing air temperature so that it approaches the dew point. (In some conditions dew point may be reached in the AXA and moisture may condense, a condition which should preferably be accommodated by the device's design, e.g., by appropriate placement of a drain pan.) The air then passes through the first of two refrigeration heat exchanger coils, which preferably operates just above the freezing point to achieve primarily moisture condensation or latent heat removal. The air exits at a low temperature and passes over an irradiating UV lamp, if applicable, then passes through a second stage of the AXA, where it begins a reheating process. Once exiting the AXA, the air is directed through a second refrigeration heat exchanger where it is reheated and the excess heat of refrigeration is added. The air is pulled through a blower and reintroduced (as cleaner, dehumidified air) through the HVAC system to the climate-controlled indoor space. The cycle is continued until a desired humidity level is achieved.
The invention and some of its variations may be more fully understood with reference to the accompanying drawings.

DRAWINGS REFLECTING SOME EMBODIMENTS

FIG. 1 is a side sectional view of a module embodying at least part of a device of the invention, depicted in a horizontal configuration, indicating with arrows a typical airflow.

FIG. 2A is a perspective view of a module embodying at least part of a device of the invention, depicted in a vertical configuration.

FIG. 2B is a front sectional view of the same embodiment as FIG. 2A.

FIG. 2C is a side sectional view of the same embodiment as FIGS. 2A & 2B.

FIG. 2D is an input end view of the embodiment in FIG. 2E.

FIG. 2E is a side sectional view of a horizontally configured embodiment that is essentially the same as FIG. 1, without arrows depicting airflow.

FIG. 2F is an output end view of the embodiment in FIG. 2E.

FIG. 3 is a simplified side view of an embodiment of the invention as in FIGS. 1 & 2E, installed in connection with an existing HVAC ductwork system.

FIG. 4 is a simplified side view of an embodiment of the invention as in FIGS. 1 & 2E, installed partially in connection with an existing HVAC ductwork system, and shown with outside air outside air ventilation and crawl space options.

FIG. 5 is a simplified side view of an embodiment of the invention as in FIGS. 1 & 2E, installed partially in connection with an existing HVAC ductwork system, and shown with outside air ventilation and crawl space options. Also shown is added ductwork for a dedicated airflow return path.

FIG. 6 is a flowchart depicting a method in accordance with the invention.

DESCRIPTION OF SOME EMBODIMENTS

With reference to the drawings, it will be seen that a basic embodiment of the device of the invention consists of a closed refrigeration system including a compressor, dehumidification coil (evaporator), reheat coil (condenser), refrigerant metering device, associated tubing connecting these components (typically copper), and a drain pan (e.g., of stainless steel). Some of the smaller and standardized elements of the system are not labeled in the drawings or given special attention in the discussion of the drawings, such elements being well known in the arts of refrigeration and HVAC engineering. Further aspects of the device of the invention may include a blower, an air-to-air heat exchanger, a pre-filter, a main HEPA filter, and a germicidal UV lamp.
FIGS. 1 and 2E illustrate a basic embodiment of the device of the invention, shown in a horizontal configuration. FIGS. 2D and 2F show opposite end views of the same embodiment.
FIGS. 2A, 2B, and 2C illustrate a functionally similar embodiment of the device of the invention, but in a vertical rather than horizontal configuration. Element labeling numbers for this alternate configuration will be mentioned below in parentheses. See, e.g., blower 190 (290).
The functionality of the elements of these embodiments will be discussed with reference to an airflow passing through the device. Airflow 10 originates in the environment for which air quality is to be regulated, and enters module 100 (200) at intake opening 110 (210). External airflow 5 (from outside ventilation) can optionally be combined with airflow 10. In a preferred embodiment providing more than one filtration step, the airflow 10 (together with external airflow 5, if applicable) passes first through a high-efficiency pre-filter 120 (220) to remove larger airborne particles, and then through a main HEPA filter 130 (230) to remove smaller airborne particles. Various filtration devices could be used interchangeably in the invention, but the configuration illustrated here is a presently preferred embodiment.
Having passed through the filtration devices, airflow 10 is now depicted as filtered airflow 20. Filtered airflow 20 enters an air-to-air heat exchanger 140 (240) and is cooled. Cooled airflow 30 passes across the dehumidification coil/evaporator 150 (250) so that moisture will be removed from the air. In a well-known refrigeration process, refrigerant contained within the system is compressed in compressor 170 (270) and metered through evaporator 150 (250). Moisture from the airflow 30 thus condenses and collects by the operation of gravity in a drain pan 160 (260), which is preferably constructed of stainless steel or another non-corrosive material. UV lamp 165 optionally irradiates the airflow passing by, as well as the drain pan and the liquid collected in it, tending to destroy certain pollutants that might otherwise collect or pass through.
The dehumidified airflow 40 returns through the AXA 140 (240) as described above, being warmed by and in turn cooling airflow 20. The warmed, dehumidified airflow 50 then passes through the reheat coil/condenser 180 (280) where heat is transferred from compressed refrigerant in the condensor 180 (280) to the airflow 50 and it passes on as airflow 60. Blower 190 (290), which serves to actuate the airflows through the overall system, now forces the dehumidified air 60 back toward the indoor environment for which the air quality is being regulated (e.g., by way of ductwork). Electrical controls for the overall system are centralized in control box 185 (285). Other control elements not depicted in the drawings could include a humidistat and other remote sensors and controls, which typically would be in electrical communication with control box 185 (285).
FIG. 3 illustrates how the module 100 (200) can be integrated into existing HVAC ductwork. In a typical HVAC system installation, return duct 300 carries air from the controlled environment back to an air handler, furnace, or similar equipment (not shown). When a device according to the invention is integrated into such a system, air duct material is used to construct a diversion path 310 to carry a portion of the HVAC system return airflow through module 100, and after this diverted airflow has been filtered and dehumidified in module 100 it is returned to the HVAC system return duct 300 by way of insertion path 320.
FIG. 4 elaborates on the illustration of FIG. 3 by showing some additional optional features for integrating the invention into an existing HVAC system. The primary additional feature in this embodiment is the provision of an outside air ventilation input to the system. Intake hood 330 (preferably screened) is provided outside the structure of the environment to admit fresh outside air into the system. Outside air path 332 is constructed to carry this air into the system. Manual damper 334 allows for closing the air flow when necessary. Optional power damper 336 can be integrated into the system control set. Thus, outside air enters through hood 330, passes through path 332 and past damper(s) 334, 336 (when open), into module 100, to be mixed with indoor air for filtration and dehumidification. Another feature here illustrated is an optional partial air return of dehumidified air to an area such as a crawl space or unconditioned basement. Path 342 diverts a fraction of the output airflow from module 100, carrying some air past manual damper 344 and backflow damper 346 (when these are open) into the unconditioned space 340.
FIG. 5 represents an additional variation in which for whatever reason a separate input airflow path into module 100 is needed, rather than a diversion from existing HVAC ductwork 300. Here, a dedicated air return 350 is added, which carries air from the conditioned space to low intake of module 100. The filtered, dehumidified air is then sent back toward the conditioned environment through insertion path 320 via ductwork 300.
Many modifications or expansions upon the invention itself and the various illustrative embodiments herein described still fall within the spirit and scope of the invention, and should be so considered.

Claims

1. In an environment supplied by an airflow, a method comprising:

Determining a satisfactory level of an environmental humidity;

Monitoring said environmental humidity;

So long as said environmental humidity exceeds said satisfactory level: continuously filtering said airflow to remove particulate matter therefrom, and continuously dehumidifying said airflow to remove moisture therefrom;

When said environmental humidity reaches a satisfactory level, ceasing to continuously filter and dehumidify said airflow.

2. A method according to claim 1, wherein said dehumidifying comprises:

causing said airflow to pass a first time through an air-to-air heat exchanger to lower the temperature of said airflow;

causing said airflow to pass through an evaporative dehumidification coil stage to remove moisture from said airflow;

causing said airflow to pass a second time through said air-to-air heat exchanger to raise the temperature of said airflow; and

causing said airflow to pass through a condensing reheat coil stage.

3. A method according to claim 2, further comprising adding to said airflow a supply of air from outside said environment.

4. A method according to claim 3, further comprising irradiating said airflow.

5. A method according to claim 4, wherein said filtering comprises:

causing said airflow to pass through a pre-filtering stage to remove larger particulate matter therefrom;

causing said airflow to pass through a fine-filtering stage to remove smaller particulate matter therefrom;

removing from said airflow at least about 99.97% of all particulate matter greater than about 0.3 microns in diameter.

6. A method according to claim 1, wherein said filtering comprises:

7. A method according to claim 6, wherein said dehumidifying comprises:

causing said airflow to pass through a condensing reheat coil stage.

8. A method according to claim 6, further comprising adding to said airflow a supply of air from outside said environment.

9. A method according to claim 6, further comprising irradiating said airflow.

10. A method according to claim 7, further comprising adding to said airflow a supply of air from outside said environment.

11. For an environment, a device comprising:

A blower to divert an airflow from said environment and cause said airflow to pass through said device;

An intake stage for receiving said airflow into said device;

A filtration stage coupled to said airflow intake stage;

A dehumidification stage coupled to said filtration stage;

An output stage for returning said airflow to said environment;

A control stage for monitoring at least one characteristic of said environment and for regulating operation of said device.

12. A device according to claim 11, wherein said dehumidification stage comprises an air-to-air heat exchanger for pre-cooling said airflow; a compressor for compressing a refrigerant; a dehumidification coil for removing moisture from said airflow; and a reheat coil.

13. A device according to claim 12, wherein said filtration stage comprises a pre-filter for removing larger particulate matter from said airflow and a fine filter for removing smaller particulate matter from said airflow.

14. A device according to claim 13, wherein said intake stage comprises means for receiving a supplemental airflow from outside said environment and combining said supplemental airflow with said airflow received from said environment.

15. A device according to claim 14, further comprising an ultraviolet lamp for irradiating said airflow and at least a part of said device.

16. For an environment to which a duct network is connected, a device comprising:

A blower to divert an airflow from said duct network and cause said airflow to pass through said device;

An intake stage for receiving said airflow into said device;

A filtration stage coupled to said airflow intake stage;

A dehumidification stage coupled to said filtration stage;

An output stage for returning said airflow to said duct network;

17. A device according to claim 16, wherein said filtration stage comprises a pre-filter for removing larger particulate matter from said airflow and a fine filter for removing smaller particulate matter from said airflow.

18. A device according to claim 17, further comprising an ultraviolet lamp for irradiating said airflow and at least a part of said device.

19. A device according to claim 18, wherein said intake stage comprises means for receiving a supplemental airflow from outside said environment and said ductwork, and combining said supplemental airflow with said airflow received from said ductwork.

20. A device according to claim 19, wherein said dehumidification stage comprises an air-to-air heat exchanger for pre-cooling said airflow; a compressor for compressing a refrigerant; a dehumidification coil for removing moisture from said airflow; and a reheat coil.