Abstract:
An air conditioner and filtering unit produces a positive or negative pressure to create an isolation space. A common air intake plenum has first and second inlets for admitting return air from the space or outside air which may be from a building main A/C system supply. Sanitized, cleaned and conditioned air is returned to the conditioned space; and condenser air is exhausted outside the conditioned space. The air intake plenum may be common to both the condenser air flow and to the evaporator air flow. A HEPA filter cleans the air suppled to both the condenser and the evaporator. A slide damper or other arrangement selectively opens and closes air flow through the first and second air inlets into the common intake plenum. This permits creation of overpressure, underpressure, or an intermediate pressure in the conditioned space. All air supplied to the room and all air exhausted from the room is cleaned and sanitized. The unit is self-contained and portable.

Description:
Priority is claimed of U.S. Provisional Application No. 60/591,135, filed Jul. 27, 2004, the disclosure of which is incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   The invention concerns room air conditioning and filtration equipment, and in particular is directed to a unit that can operated in a positive pressure mode, a negative pressure mode, or a normal mode. The invention is also concerned with units that clean and condition the room air as well as remove or kill airborne pathogens, and which have a mechanism for introducing make-up air to create a positive pressure or overpressure in the room relative to the outside ambient air, or exhausting some of room air to create a negative pressure relative to the outside air. At least one of the inventors is the patentee of U.S. Pat. No. 5,884,500, Mar. 23, 1999 and U.S. Pat. No. 5,987,908, Nov. 23, 1999, which are incorporated herein by reference. 
   High Efficiency Particulate Air (HEPA) filters are used extensively in industrial, commercial and residential applications to filter out dust and dirt from the air which can harbor harmful bacteria or other micro-organisms. These filters are capable of filtering out more than 99.99% of the particles in the air. 
   Recently, due to the occurrence of terrorist strikes and outbreaks of contagious diseases such as SARS, there has been a heightened concern about contaminants in the indoor air, and about the ability to exclude or confine contaminants in a given area. Also, medical services are required in sufficient capacity and of the appropriate quality to handle extraordinary events or circumstances. Each community needs to have a surge capacity plan for handling a large number of emergency patients. If a terrorist event or outbreak of disease occurs, it will become necessary to isolate at least some of the patients. Some patients will need to be isolated in a fashion to keep any airborne contaminants within a confined area to protect others from the contagion. Other patients, e.g., burn patients, will need to be protected from outside contaminants reaching the patient area. Hospitals today lack sufficient numbers of hospital rooms that can be used for isolation of patients, whereas the need to isolate patients from the general public or from one another is critical in controlling the situation, whether the patients are in surge capacity facilities or in traditional hospitals. 
   Most hospitals today have only a few isolation rooms out of the hundreds of patient rooms in the facility. One reason for this is because isolation rooms are very expensive to build because they conventionally require separate, independent HVAC systems for each room to prevent the spread of contaminants to other areas of the hospital. In those cases where the patient is susceptible to contaminants, the room must operate at a positive pressure, whereas when the patient is infected with a contagious pathogen, the room must be under a negative pressure to protect other patients and hospital workers. However, even with isolation HVAC systems the rooms are not easy to convert from positive pressure to negative pressure or vice versa. These rooms are generally built either for positive pressure only or for negative pressure only, and this limits the flexibility of a hospital to deal with emergency situations. 
   Other applications could include laboratories within a hostile environment that may need a positive pressure, e.g., in a paper mill. Other examples include museum archiving rooms that need a positive pressure. 
   The inventor herein proposes to convert a room air conditioning unit, similar in some ways to the type described in the above-mentioned U.S. Pat. Nos. 5,884,500 and 5,987,908 to be suited for use in converting a standard, typical hospital room to an isolation room, and which can be provided with neutral pressure (equaling outside air pressure), a negative pressure relative to outside air pressure, or a positive pressure relative to outside air pressure. 
   These units, known commercially as HEPAir units, are used extensively in clean room situations to control airborne contaminants while maintaining temperature and humidity control for critical processes such as the sterile packaging of medical devices or pharmaceuticals. These units are also used extensively in the manufacture of semiconductor devices. These are not simple portable air conditioning units, but are industrial in nature and capable of handling relatively large volumes of air against a high static pressure such as that encountered with high efficiency particulate air (HEPA) filters, and are capable of attaining an air exchange rate that is sufficient to assure dilution and purge. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is an object to provide a unit for cleaning and conditioning of air in a room that can be easily installed in an existing room to create an isolation space having net positive pressure or net negative pressure, as needed, and which avoids the drawbacks of the prior art. 
   It is another object to provide a unit to convert an existing room to an isolation room, in which the air exiting the unit into the room and any air exhausted from the unit to outside the room is sanitized, filtered, and cleaned. 
   It is a more particular object to create a self-contained unit that can be easily and reliably installed by hospital personnel with only a minimum of special training and without need for special tools. 
   In one aspect of the invention, the hospital environmental control unit of the present invention could employ the existing HEPAir cabinet design and organize the internal components in a way that allows it to perform the operations needed in this application. The evaporator fan or room air fan (or blower) draws return air from the room, through a pre-filter, then past a UV lamp or battery of UV lamps, then through a HEPA filter and the cooling or evaporator coil. A supplemental heating coil may be used for warming the air. Then the treated, filtered air is supplied to the hospital room, fully conditioned and filtered. Particles in the air are subjected to the killing effect of the UV light as they pass through the W illuminated zone, and are further exposed when captured on the HEPA filter. The heating and cooling coils work to control the patient room at the desired temperature. The separate condenser fan draws air from outside or from the building system through the condenser coil by means of flexible ductwork. The condenser air picks up the waste heat from the unit, and then the air is discharged into the outside air or else into the building HVAC system. If outside air is used, the building air conditioning system must be sealed off. If the building system is used, it will effectively be isolated from the room and only used as condenser air plus makeup air. 
   According to one aspect of the present invention, an air passage or air plenum is added to provide a controllable passageway which allows fresh air to be drawn into the evaporator system to positively pressurize the room, or to draw off some of the conditioned air from downstream of the evaporator fan to negatively pressurize the room. Since the make-up air enters upstream of the UV tubes and upstream of the HEPA filter, it is treated before it enters the room so as to protect the patient. The amount of this fresh air is controlled by adjusting a slide damper inside the cabinet. If the slide damper is moved to another position, the damper closes the fresh air passageway to the evaporator return plenum, and opens a passageway from the supply plenum to the condenser air plenum. In this position the room can be negatively pressurized. A portion of the supply air, which has been treated by the UV tubes and the HEPA filter, is drawn into the condenser air flow, and the condenser fan exhausts it outside the room, either to the outside air or into the building HVAC system with the rest of the condenser air. The air evacuated from the room is UV treated and filtered, which protects persons outside from contamination or contagion. 
   According to another aspect of this invention, an air conditioner and filtering unit is provided for creating a positive pressure, negative pressure, or neutral pressure in a hospital room or other conditioned space. Inside a housing for the unit, a refrigeration circuit has a compressor, a condenser coil, and an evaporator coil. A common air intake plenum has a first return air inlet for admitting return air from the conditioned space into the common plenum, a second return air inlet for admitting outside air into the plenum, and a supply duct connecting the second return air inlet to an air source outside the conditioned space. A supply air outlet exhausts cleaned and conditioned air into the conditioned space. An exhaust air duct exhausts condenser air, also cleaned, to an outlet outside the conditioned space; an inside airpath, i.e., evaporator airpath within the housing leads from the common intake plenum to the supply outlet, the inside air path including a HEPA filter arrangement, and in many cases a UV sterilizer, for cleaning the air in the inside air path, the evaporator coil, and an evaporator fan for drawing the air through said HEPA filter arrangement and said evaporator coil. The evaporator fan then exhausts the cleaned and conditioned air through the supply air outlet into the conditioned space. A condenser air path leads from the common intake plenum to the exhaust air duct. The condenser air path includes a HEPA filter arrangement for cleaning the air in the condenser air pathway, the condenser coil, and a condenser fan for drawing the condenser air through the HEPA filter arrangement and through the condenser coil. The consenser fan then exhaust the condenser air outside the conditioned space as cleaned air. A slide damper or other suitable means to open or close the intake ports or vents can be employed selectively opening and closing air flow through the first and second return air inlets into the common intake plenum to create selectively an overpressure, an underpressure, or neutral pressure in the conditioned space. 
   Important features of the units of this system which permit them to function in this application are high volume and high static pressure fans; two completely separate fans, one for the evaporator and one for the condenser; relatively small size and portability of the units (e.g., mounted on wheels), and requiring only application of standard 115 v single-phase AC electric power and light-weight flexible ducts for the condenser air; corrosion-free all-aluminum or plastic cabinet construction; completely self-contained system, with heating and air conditioning, UV sterilization, HEPA filtration, and positive and negative pressurization, all contained in the housing. Some optional equipment features include humidity control (humidifier) and flexible duct kits for the supply and return room air. 
   These units, which may be referred to as hospital environmental control units have a net cooling capacity of e.g., 5000 BTU/H and a 1000 W heater. The dimensions are favorably 18 inches wide, 30 inches deep, and 48 inches high. The unit is provided with wheels for mobility, and weights about 150 pounds. The unit is provided with a six foot 115 v power cord, and draws about 15 amperes. Flexible ducts eight to ten inches in diameter are employed to connect the condenser inlet and outlet with the building system, or to reach the outside air via a window. 
   In one embodiment, a slide baffle controls the communication of air between the return plenum or the supply plenum and the pressurization control plenum, which in turn communicates with the condenser air pathway. The slide baffle can be moved to positions for positive pressure, negative pressure, or neutral. This can be done by hand, or by means of a linear motor. Openings on the slide baffle line up with vent openings on the side of the return plenum and the supply plenum, depending on whether positive or negative pressure is needed. These can be partially or fully aligned, so that the amount of pressurization can be controlled. 
   In another embodiment, the slide baffle can control the air flow into the common intake plenum from a first (room-air) inlet and a second (outside-air) inlet, which may be connected via a duct to the supply ducting of the building air conditioning. By moving the slide, one inlet or the other is opened, and the other closed, and this controls whether the room has a net positive pressure or net negative pressure. It is possible to move the slide baffle to a mid-way or neutral position so that both are partly open, which can be used to create a neutral room pressure. 
   The above and many other objects, features, and advantages of this invention will become apparent from the ensuing description of selected preferred embodiments, which should be read in connection with the accompanying Drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Reference is made to the drawing Figures, in which 
       FIG. 1  is a top plan schematic view of an embodiment of the invention. 
       FIG. 2  is a schematic view of this embodiment, partly cut away and with some panels removed. 
       FIGS. 3 ,  4 , and  5  are views showing the position of the slide baffle for neutral, positive pressure, and negative pressure, respectively. 
       FIGS. 6 and 7  are schematic views showing the unit of this invention employed in a hospital room to create an isolation area, with positive pressurization and negative pressurization, respectively. 
       FIG. 8  is a perspective view showing another embodiment. 
       FIGS. 9 ,  10 , and  11  are schematic views of this embodiment for explaining its operation. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the drawing Figures,  FIGS. 1 and 2  show the general construction of the hospital environmental control unit of one possible embodiment, with a housing or enclosure  10 , and an indoor or evaporator side  12  and an outside air or condenser side  14 . The indoor evaporator side  12  has an intake grille  16 , which serves as inlet for return air from the conditioned room environment, and the grille may incorporate a pre-filter. This leads to a return plenum  18  in which there are UV tubes  20  that provide sterilizing ultraviolet radiation for killing airborne pathogens. After this the return air passes through a HEPA filter  22  and then through an evaporator coil  24  that chills and dehumidifies the air. An electric heat coil  25  may be present for reheating the air, as necessary to control room temperature. The UV tubes  20  also illuminate the HEPA filter  22  to kill any bacteria or other pathogens that become trapped on the filter. After this, a supply plenum  26  includes a fan or blower  28 , plus associated baffles, that induce air flow through the return plenum  18 , into the supply plenum  26 , and then out through a supply duct  30  back to the room environment. A partition  32  separates the supply plenum from the condenser side  14  of the unit. 
   The condenser side  14  provides a flow of outside air (or air from the main building air conditioning system) for carrying away exhaust heat. The outside (or main building) air enters through an intake duct  34  into a condenser air inlet plenum  35 . A compressor  36  is shown located here, in advance of a condenser coil  38 . Other electric and refrigerant control equipment (not shown here) could be located at this plenum  35  also. After the outside air has passed through the condenser coil  38 , a condenser fan or blower  40  exhausts the air through an exhaust duct  42  to the outside air (or back to the building central air conditioning system). 
   In this embodiment, there is a slide baffle environmental control system for controlling the relative pressurization of the conditioned space, which may for example be a hospital room or other controlled environment. 
   Here, an environmental pressure-control plenum or bypass plenum  44  is positioned along one side of the unit, extending along and communicating with the return plenum  18 , the supply plenum  26  and the outside or condenser air inlet plenum  35 . A wall of the unit has a port  46  that communicates with the return plenum  18 , a port  48  that communicates with the supply plenum  26 , and a port  50  that communicates with the condenser inlet plenum  35 . A pressure-control slide baffle  52  is positioned alongside this internal wall, and selectively blocks or opens the supply port  48  and the return port  46 . As better shown in  FIGS. 3 ,  4 , and  5 , in a neutral pressure or normal position, the slide damper is positioned so that both the supply port  46  and the return port  48  are closed ( FIG. 3 ). Because of the action of the fan or blower  28 , the supply plenum  26  air is above ambient pressure, and the return plenum  18  air is below ambient pressure. The slide baffle  52  can be moved to a positive pressure position, shown in  FIG. 4 , in which the return port  46  is aligned with a control opening  54  of the slide baffle, so that some outside air will be drawn as make-up air through the condenser side port  50  and the bypass plenum  44  and port  46  into the return plenum of the unit. For negative pressurization, the slide baffle  52  can be moved to a position as shown in  FIG. 5  in which the supply port  48  is aligned with another control port  56  on the slide baffle, and there is some exhaust air flow from the supply plenum  26 , through the port  48  and the bypass plenum  44  to the condenser air port  50  where a portion of the room air is exhausted from the conditioned space. The two control openings  54  and  56  of the slide baffle  52  are positioned so that the return and supply ports  46 ,  48  cannot both be opened at the same time into the control plenum  44 . As also shown in these views, there may be a handle  60  at a top side of the slide baffle  52  so that a hospital worker can easily move the slide baffle to the desired position. 
     FIG. 6  schematically shows one practical application of the hospital environmental control unit of this invention, here arranged to create a positive pressure or overpressure in a normal or typical hospital room  62 . This permits the room to be made into an isolation room for a burn victim or other hospital patient that must be protected from infection from airborne pathogens that may be present in the air outside the patient&#39;s room. The slide baffle is in the positive pressure position, so that there is air flow from the condenser side  14 , through the bypass plenum  44 , into the return plenum  18 . The flow into or from the supply plenum  26  is blocked. This means that a portion of the outside air or main building conditioned air will constitute make-up air. The room air is positively pressurized, so that any air flow is in the direction out of the room. It should be noted that all the make-up air as well as all the return air from the room that enters the return plenum  18  will flow past the UV tubes  20  and through the HEPA filter  22  so that the airborne pathogens are removed and destroyed. 
     FIG. 7  schematically shows the unit arranged to create a negative pressure or underpressure in the same hospital room  62 , here creating an isolation room in which a patient who carries an infectious disease, for example, may be maintained in isolation and the rest of the hospital environment may be protected from contamination. In this case, the slide baffle is placed in the negative pressure position, so that a portion of the indoor air flows out from the supply plenum  26 , into the bypass plenum  44 , and then into the condenser side  14  where that air is exhausted with the condenser air into the outside air or into the building central air. Air flow from the bypass plenum  44  into the return plenum  18  is blocked. As shown here, with the room kept at a relative negative pressurization, any flow of air is in the direction into the room, keeping contaminants inside the room. It should also be noted, that all air in the supply plenum  26  will have flowed past the UV lamps  20  and HEPA filter  22 , and is free of airborne pathogens, so only clean air is exhausted from the isolation space into the outside air or into the hospital central air system. 
   In some cases, the position of the baffle may be placed at a partway position, so that the port  46  and baffle opening  54  or the port  48  and baffle opening  56  are partly aligned. This enables the unit to create a controlled level of underpressure or overpressure, if that is needed. Also, the shapes of the ports and openings are not limited to the vertical rectangular shapes illustrated here. 
   Another possible embodiment of this invention is shown in perspective in  FIG. 8 , and schematically in  FIGS. 9 ,  10 , and  11 . Here, elements that correspond to similar elements in the first embodiment are identified by similar reference numbers but raised by 100. 
   This embodiment is a self-contained unit in which the room air and air from the main air conditioning system are fed into a common intake plenum, and all of that air is cleaned and filtered. Then the air is fed from that through both an evaporator side, in which the air is conditioned and returned to the room and through a condenser side, in which the air picks up waste heat and is exhausted as cleaned, filtered air into the return ductwork of the building air conditioning system. The relative amounts of room air and of A/C system supply air that is fed into the common intake plenum determines the room pressure relative to the ambient pressure outside the room. If room air only is used for both the condenser side air and the evaporator side air flows, then a negative room pressure will result, which means there will be a net leakage into the room and there will be no contaminated air leaking out of the room. If building AC supply air only is used for both the condenser side and the evaporator side air flows, then there will be a net positive pressure, so all leakage will be out from the room, and there will be no potentially contaminated air leaking into the room from the outside environment. The relative amounts of room air and building AC air into the common intake plenum can be adjusted, if desired, to produce a desired positive or negative room pressure or a neutral pressure. 
   In some possible applications, outside non-conditioned air can be used instead of building AC supply and return air. However, the use of building AC system air can relieve some of the cooling load that the unit would otherwise have to bear, and this allows the compressor and coils to be of a smaller capacity with smaller electrical load requirements. Also, this permits the unit to be used in rooms or spaces that may not have access to outside air. 
   As shown in  FIG. 8 , one possible embodiment of the hospital environmental control unit of this invention has a housing or enclosure  110 , which is illustrated here partly cut away to reveal an evaporator side or pathway  112  (in the front) and a condenser side or pathway  114  (in the rear). At the base there is a room air intake vent  116  and an outside air intake duct  117  which both connect with a common air intake plenum  118  in the lower part of the unit. The duct  117  is is shown in ghost here, as it may be omitted in a negative-pressure-only application. This plenum  118  is common to both the evaporator side  112  and the condenser side  114 , so that air from this plenum is divided and part of the air flows through each of the evaporator pathway and the condenser pathway. Within the plenum  118  there is a pre-filter or coarse filter  119 , and a bank of UV fluorescent tubes  120 . Above this, i.e., downstream is a HEPA filter assembly  122  which filters microscopic contaminants, including bacteria and virus, from the air before proceeding through the evaporator and condenser pathways. This HEPA filter assembly may have a single HEPA filter or may be separate HEPA filters for the two airflow pathways. 
   Above the HEPA filter assembly  122  are an evaporator coil  124  and a fan or blower  128  located on the evaporator side for chilling and dehumidifying the air that is to be discharged into the patient room through a supply air grille or supply outlet  130 . In this embodiment, the supply outlet  130  is located at the top of the unit. 
   A partition  132  rises vertically behind the evaporator coil  124  and fan  128  and divides the front or evaporator side  112  from the rear or condenser side  114 . Here, there is a condenser coil  138  disposed above the HEPA filter assembly  122  and behind the evaporator coil  124 , and a condenser air fan  120  that draws the air through the HEPA filter assembly and through the condenser coil  138  into a condenser air plenum  141  that is located behind the partition  132 . An exhaust air duct or conduit  142  connects the condenser air plenum  141  with a means for accepting the discharged condenser air. In this embodiment, the duct  142  connects to the building air conditioning system return air ductwork, but in other embodiments it could connect with a general air discharge ducting, or could simply be exhausted to the outdoor air. 
   While not specifically shown here, the unit would also include a refrigerant compressor, which could be located at a convenient place within the cabinet  110 . An electric heating element in the evaporator side could be used as necessary to preheat air being returned to the hospital room. Other controls, which are understood to be present, are omitted from this illustration. 
   The unit of this embodiment is shown schematically in  FIGS. 9 ,  10 , and  11 . There a slide damper  152  is shown with one position across the outside air intake  117  and another across the room air intake  116 , and is moved to an appropriate position to control the amount of air being drawn into the intake plenum  118 . As shown here, the sterilized and filtered air having passed through the UV tube bank  120  and HEPA filter assembly  122  splits and passes through each of the condenser side (from which it is exhausted from the conditioned space) and through the evaporator side (from which it is discharged back into the conditioned space). The exhaust air duct  142  is always connected between the condenser air plenum  141  and the outside of the conditioned space (e.g., the building A/C return ductwork). The pressure within the room can thus be controlled by adjusting the position of the slide damper  152 . 
     FIG. 10  illustrates a net over-pressure setting, in which the slide damper is moved to block the air flow from the conditioned space into the common plenum  118 , so that all the air is supplied from a source outside the room, e.g., from the building A/C supply ducting. The airflow from the outside source then flows through both the evaporator and condenser sides  112 ,  114 , such that part of the air flow is exhausted into the room as cleaned and sanitized conditioned air, and part is exhausted outside the room together with the waste heat from the condenser coil  138 , as cleaned and sanitized exhaust air. In this condition, the air pressure in the room is higher than in the general building environment, and the direction of air leakage is from inside the room to outside the room. This setting would be used for patients that must be protected from contamination from outside the room. 
     FIG. 11  illustrates a net under-pressure setting, in which the slide damper  152  is moved to permit air flow from the conditioned space into the common plenum  118  but block the air flow from outside the conditioned space (such as through the duct  117 ). Again, part of the air flow passes through the evaporator side  112  and part through the condenser side  114 , so that part of the air is returned to the room as cleaned, sanitized conditioned air, and part is exhausted from the room, through the exhaust air duct  142 , as cleaned and sanitized exhaust air. As the net air flow is out of the room, the air pressure within the room is reduced below the ambient building pressure. The negative room pressure means that any air leakage is into the room. This setting would be used for quarantining a patient with a contagious disease so that contaminants in the isolation room do not escape to other spaces within the hospital or other building. 
   It is also possible to set the slide damper  152  at an intermediate position (e.g., as in FIG.  9 ) which allows some air from outside and some air from inside the room to be admitted to the common intake plenum  118 . This permits the level of underpressure or overpressure to be modulated. A neutral room air pressure can be achieved. 
   In the hospital environmental control units of this invention, all the air flowing through the unit is cleaned and sanitized, i.e., all the air flows past the UV tube bank  120  and all the air flows through the HEPA filter assembly  122 . Consequently, all the air being returned to the room from the supply grille  130  is cleansed and sanitized, and in addition all the air flowing through the condenser coil and into the condenser plenum  141 , and all the air passing in the exhaust air duct  142  is also cleansed and sanitized. This minimizes the risk of contamination of air if there is a leak in the housing  110  or in any associated ducting. 
   The slide damper  152  shown here is optional. The desired effect can be achieved by connecting up the outside air intake duct  117 , or not, and covering or capping the room air intake  116  or the outside air intake duct opening. Otherwise, other air valving or damper arrangements can be employed to achieve modulation of air flow. A cap or closure  154  is shown in dash lines in  FIG. 11 , in place over the outside air intake  117 . In a positive pressure configuration, the cap  154  could be used over the room air intake  116 . 
   Also shown in  FIG. 8 , the enclosure  110  is mounted on wheels or casters  156  so it can be wheeled easily into the isolation room. 
   These and other objects, features, and advantages of this invention would be apparent to persons who work in this field. While the invention has been described with reference to preferred embodiments, many modifications and variations would present themselves to persons skilled in this art without departing from the scope and spirit of this invention, which is to be ascertained from the appended claims.