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Dynamic control of dilution ventilation in one-pass, critical environmentsRelated Patent Categories: Ventilation, Having Inlet Airway, Including Automatic Control MeansDynamic control of dilution ventilation in one-pass, critical environments description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070082601, Dynamic control of dilution ventilation in one-pass, critical environments. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE [0001] This is a continuation-in-part of U.S. Provisional Patent Application Ser. No 60/660,245 filed on Mar. 10, 2005. FIELD OF THE INVENTION [0002] This invention relates to systems for controlling ventilation to dilute contaminants within critical environments or spaces such as laboratories and vivariums which utilize a "one-pass" ventilation strategy in which the airflow out of each environment is entirely exhausted without a recirculated air component, and more particularly, to systems and methods for varying the flows of supply and exhaust air into and from these environments for the purposes of controlling the dilution of air contaminants based on changes in the presence of these contaminants as sensed by a facility monitoring system. BACKGROUND OF THE INVENTION [0003] This invention relates to the dynamic control of dilution ventilation in one-pass, critical environments. Critical environments in the context of this invention relate to spaces, areas or rooms in which potentially hazardous materials may be used that could become airborne and impact in some way the health of individuals operating within the space. Examples of such spaces include but are not limited to laboratories where chemicals or biological materials are used as well as vivariums or animal research facilities where animals are housed for research purposes. Other types of applicable areas include but are not limited to: clean rooms, pharmaceutical processing areas, bio-safety facilities, and medical containment and isolation facilities. Furthermore, critical environments may be further narrowed down to those which are strictly one-pass environments, which in the context of this invention refers to those spaces which use one-pass air, in other words no air from the space is returned or recirculated to an air handler or fan system for use again within the building. As such all air introduced to within the space either from a supply system, or as transfer air from another space, is exhausted typically through some sort of exhaust system which takes the room air and exhausts it from the building typically controlled by some sort of room exhaust or special exhaust air flow control device. Specifically, these rooms have no return air grills or return airflow control devices. Control of the room's airflow is thus accomplished through one or more exhaust airflow control devices designated for the space plus one or more supply airflow control devices that although typically are designated for the space, may also be somewhat remote from the room if some of the air from those devices enters the space as transfer air from another space that is provided with supply airflow via a separate air flow control device. Furthermore, a flow of air that is drawn from or supplied to a space or environment may be expressed as a volume of air per unit time, for example, in terms of cubic feet per minute (cfm). [0004] Dilution ventilation as used in the context of this invention refers to the use of airflow supplied to the room either directly or as transfer air that dilutes or reduces the concentration of possible contaminants in the air of the room. Although capture and containment of hazardous vapors is the safest approach to handling hazardous materials, dilution ventilation provides an important backup or secondary form of protection for the critical environment in case the primary or containment control device malfunctions, or else an accident or spill occurs, or the occupants of the space use unsafe practices that introduce contaminants into the air of the room. Dilution ventilation is also sometimes referred to or defined as the minimum level of airflow allowed in the room, or as the airflow corresponding to the critical environment's minimum air change requirement typically expressed as a minimum air changes per hour (ACH) for the space. [0005] As the price of oil, natural gas and other fuel sources has increased over the years, there has been interest in reducing the amount of outside air that is used by buildings to save energy, while still maintaining good indoor environmental quality within those facilities. In the context of this invention outside air is defined as the ambient air outside of the building housing the critical environment that maybe drawn into the building to provide some measure of fresh air ventilation. Since laboratory and vivarium facilities typically use 100% outside air these facilities use extremely large amounts of energy compared to other types of facilities such as office buildings that are able to use return or recirculated air. The purpose of the present invention is to significantly reduce the energy consumption of a critical environment utilizing one-pass or 100% exhaust air for dilution and potentially other purposes while also enhancing the safety of these environments. [0006] As mentioned earlier, one example of a critical environment in which a one-pass, dilution ventilation system may be employed is a laboratory. A laboratory generally is a facility that is designed to permit the safe use of various chemicals, biologicals, toxic compounds and/or other potentially harmful substances for research or other purposes. The laboratory may be equipped with one or more "special exhaust devices" that are designed to exhaust air from the lab to an outside environment to protect lab users from potentially dangerous exposure to harmful substances. For example, a laboratory may include one or more of the following special exhaust devices such as laboratory fume hoods, canopy hoods, glove boxes, or non-recirculating biological safety cabinets, in which potentially harmful substances may be regularly handled. Additionally, exhaust trunks sometimes referred to as snorkel exhausts are special exhaust devices that may be used to exhaust air containing potentially harmful substances from a particular area on a bench top or from an analytical instrument thereby providing local containment and protection. Additionally, a laboratory may include one or more exhausted storage cabinets that are special exhaust devices that are used to store potentially hazardous substances and function to contain harmful fumes or vapors that might leak from the stored substances. The described laboratory environment may be used for many purposes, such as research, teaching, manufacturing or production, quality control, pilot or scale up, or other functions. Additionally the laboratory may contain many types of areas adjacent to or beyond the research areas such as support rooms, equipment rooms, corridors, offices and other types of rooms found in a laboratory building that may also be one-pass environments with all the air from the spaces exhausted to outside the facility. [0007] Another example of a critical environment in which a one-pass dilution ventilation system may be employed is a vivarium as mentioned earlier. A vivarium is generally a facility used to house animals for research purposes. These animals which can include rats, mice, rabbits, larger mammals, and even aquatic life such as fish have many environmental requirements. In addition to proper temperature control and lighting, it is important to use containment and or dilution ventilation to reduce and exhaust odors, animal dander, particles, gases from the animal's metabolic functions, and potentially toxic gases from the animal holding and other rooms that are part of these facilities. In addition to protecting the animals, the reduction and elimination of these contaminants in the air is important to the health and safety of the animal care and research staff who use these facilities. In particular, the exposure of these people to animal allergens, such as rat urine protein (RUP) or mice urine protein (MUP), that is often carried in the air on particulates can over time sensitize the animal care workers and researchers, and create allergic reactions in these individuals from the animals via contaminated air in the facility. The vivarium may also have special exhaust devices, for example the animal cage racks that are often used to house rats and mice for example have cages with filter membrane tops and are also ventilated. In particular, these racks may be directly exhausted into a general exhaust duct via a constant, 2-state, or variable air volume valve or other flow control device like a damper-based system. [0008] Additionally, some vivarium or animal facility rooms may contain biosafety cabinets that may be exhausted, snorkel exhausts or laboratory fume hoods. Vivariums may also have many different functions similar to the lab room functions mentioned above and similarly as mentioned above may have many types of rooms such as support rooms, surgery, examination rooms, cage wash area, corridors, "clean" corridors, "dirty" corridors, offices, and other rooms that are part of the animal or vivarium facility that do not house animals yet still are one-pass environments. [0009] In view of the foregoing, conventional ventilation processes in a laboratory facility, vivarium, or potentially other similar or related critical environments where dilution ventilation is employed, generally involve supplying 100% fresh outdoor air to the environment in the form of supply air ducted directly into the space or supply air that is supplied to other nearby spaces and then passes into the environment as transfer air or as a constant source of offset air. It should be obvious to those who are experienced with building ventilation system technology that this ducted supply air is usually provided via an air handler that contains a fan to move the air, but also will usually include a method for heating, cooling, and filtering the air. Offset airflow is specifically defined as a typically fixed difference in airflow between the ducted supply into the space and the ducted exhausted airflow from the space. Depending on whether the supply is greater than or less than the total exhaust airflow from the space determines whether the environment is at a positive or negative pressure respectively with respect to an adjacent room or corridor. As an example for labs, typically the supply air is controlled to be less than the exhaust to ensure that the lab is at a negative pressure with respect to the corridor. In the context of this invention, corridor is defined as a passageway that may be adjacent to and is in communication with a plurality of rooms or critical environments. [0010] There are three factors that may be typically used to determine the level of supply and exhaust airflow into the critical environment. The first of these factors is the space thermal load. Typically the supply air into the space is conditioned at a temperature such as 55 degrees F. and used for cooling the environment. The heat sources with in the lab can be solar load, lights, people and the so-called plug loads from the heat generated by equipment and instrumentation within the lab. As these loads increase the cool supply air must be increased to maintain a given temperature set point such as 72 degrees Fahrenheit. Occasionally, the lab may be cooled using methods other than the supply air such as from a cooled ceiling or floor or from a local fan coil unit that pulls air from the room, passing this air through cooling coils (typically chilled water coils), and passes it back into the room. In these latter two cases the control of the environment's supply and exhaust airflow would be unaffected by the thermal load factor. For purposes of this invention a single pass environment would not be altered from a pressurization standpoint by adding the aforementioned fan coil and, therefore, would be viewed as being a single pass environment even though it may be connected to a locally recirculating fan coil or other device such as a ductless fume hood, glove box, or other device that locally recirculates air from said environment while having no net influence on the offset airflow to the environment. [0011] A second factor that can determine the environment's required supply and exhaust airflow is the exhaust airflow from any special exhaust devices as described earlier as well as the associated make up air needed to match the exhausted airflow. These sources of exhaust air may be fixed sources such as from storage cabinets or biosafety cabinets, two-state (high/low) sources or air or fully variable sources such as with variable air volume laboratory fume hoods. Alternatively, the space or environment may have no special exhaust devices and thus this factor will not affect the airflows of the space. [0012] The third and final factor affecting the environment's required supply and exhaust airflow is the airflow requirements for dilution ventilation. This requirement is typically expressed as a certain number of air changes per hour (ACH) for the space such as 6 air changes per hour of total exhaust (including special exhaust airflow) or total supply (including offset and transfer) airflow. This number of air changes per hour can then be converted into a specific airflow rate for a given volume space. For example if an environment is 20 feet long by 25 feet wide and 9 feet high, the total volume of the space is 4500 cubic feet. Thus 6 air changes an hour would mean that in 60 minutes the entire volume of 4500 cubic feet would be exchanged 6 times, or equivalently there would be one air change in 10 minutes (60 minutes/6 ACH=10 minutes per air change). For the volume of 4500 cubic feet to be exchanged in 10 minutes would require a total room supply or exhaust flow of 450 cfm (4500 cubic feet/10 minutes per air change=450 cfm). Typical industry accepted required flows for dilution ventilation range from 6 to 12 air changes per hour. [0013] Furthermore, this amount of air changes per hour of airflow is typically a fixed level that is set irrespective of the actual quality of the room air, even though the air exhausted from the lab environment often is clean and safe. Additionally, due to simplicity and costs, some portions of the lab or vivarium environment served by the ventilation system, such as storage areas and support areas, or even offices where there may be no hoods, animals, or active research are also ventilated with one-pass air at these levels, even though the possibility of contaminants being present in these areas is less likely. Accordingly, the minimum fixed air changes requirements for 100% outside air in conventional laboratory, vivarium, or other dilution ventilation systems often results in wasted resources (i.e., fresh outdoor air) and unnecessarily excessive operating costs as well as high up front capital costs for sufficient sizing of the building's heating, ventilating and air conditioning system also referred to as the HVAC system. [0014] The typical approach used to integrate the three factors, or requirements mentioned above, into a single flow requirement for total exhaust or supply is simply to take the highest of the three requirements. If constant volume airflow devices are used then they must be set for the highest of the peak requirements of each the three factors. If variable volume airflow control devices are used, then the environment airflow can vary based on the highest of the actual requirements such as the variation in thermal load. Traditionally, in many one-pass, critical environments, the dominant factor that has been the controlling factor has been either the thermal load or the requirements of the special exhaust devices such as laboratory fume hoods. [0015] As such there have been many inventions and technologies developed to safely vary the environment's airflow to save energy based on either or both of varying airflow to meet the actual thermal load requirements, or varying the airflow through the special exhaust devices. The latter has often been done through the use of variable air volume laboratory fume hoods; such as those described in U.S. Pat. Nos. 4,706,553; 4,893,551. and 5,240,455; since fume hoods have often been the dominant driver behind laboratory airflows. More complex airflow controls involving the sensing of air contaminants in critical environments that would typically be dominated by thermal loads have also been developed to safely vary and recirculate air from critical environments, such as described in U.S. Pat. Nos. 6,609,967 and 6,790,136 through the addition of a return airflow control device to each critical environment to return and reuse clean air in an air handler serving multiple lab rooms. [0016] In the last five to ten years, there have two important trends that have affected the airflow levels in labs. First, the numbers of laboratory fume hoods and related special exhaust devices has decreased. This is partly related to the increased use of computers to model chemical reactions vs. lab experimentation, as well as the use of smaller amounts of chemicals in research. Additionally, more life sciences labs that tend to have less fume hoods are being built today vs. the traditional chemistry lab with many fume hoods. Furthermore, many labs today are built with variable air volume laboratory fume hood control systems to reduce the amount of exhaust and make up air related to the fume hood. As a result the lab ventilation requirements related to special exhaust or fume hood make up air have been reduced significantly, so that in many labs it is not the driving force determining the airflow or ventilation in the lab. [0017] Second, thermal loads in labs have also dropped as more energy efficient technologies are being used in labs. The efficiency and waste heat from lighting for example has dropped significantly as has the power used by lab instrumentation. Although in the early 90's the amount of lab instrumentation increased significantly, over time this equipment has become smaller and more energy efficient. Refrigerators and freezers have in many cases dropped their power consumption by two-thirds, plus LCD displays and laptops have replaced desktop computers and large energy hungry CRT monitors. Many recent studies show this result, such as a study from the Lawrence Berkeley National Laboratory mentioned in the September, 2005 issue of HPAC Engineering entitled "Right-sizing Laboratory HVAC systems". This article demonstrates that labs are often over designed for thermal loads that are 5 to 10 times more than what the lab environment will actually be used for. [0018] As a result of these two trends, the minimum or dilution ventilation requirement has emerged as often the dominant and controlling factor in laboratory airflow requirements. If this level can, on average, be reduced it would save significant amounts of energy in laboratories as well as allowing a smaller HVAC system that would save first cost in the construction of the facility. As a point of fact, the level of minimum air change or dilution ventilation requirements are also usually set somewhat arbitrarily, for example at levels of between 6 to 12 air changes per hour for a laboratory or 10 to 20 ACH's for a vivarium. [0019] Occasionally to save energy, this dilution rate is made a two state flow reduced during unoccupied times to a set lower level such as 4 ACH and then increased during occupied times to a higher level such as 8 ACH. This control can occur by a set time schedule control or through the use of an occupancy sensor such as those commonly used to shut off lights. Although this approach can save energy it has several safety problems that negate its prudent use. For example, a spill or release of hazardous vapors can occur during an unoccupied time increasing the level of contaminants in the air above safe levels. If someone were to walk into the space during this scheduled unoccupied time, they could be injured by the higher level of contaminants in the air. Even with an occupancy sensor or detector, when the individual walked into the room the level of contaminants could be quite high, exposing the individual until the system both detected their presence and more importantly was able to adequately flush out the lab with the higher occupied airflow which could take some time. Furthermore, occupancy detectors can have problems with detecting people in a broken up space with many barriers such as lab shelves and equipment between the sensor and the occupants. They also need to constantly see motion to operate and may fail to see someone quietly reading with insufficient motion to trigger the higher safe airflow. If the flow is dropped due to lack of sufficient motion, the occupant might not notice the flow change and then even worse could possibly be overcome by a higher level of contaminants in the lab. SUMMARY OF THE INVENTION [0020] It is therefore a primary object of this invention to provide a system for controlling ventilation to dilute contaminants within critical environments or spaces, such as laboratories and vivariums which utilize a "one-pass" ventilation strategy in which the airflow out of each environment is entirely exhausted without a recirculated air component. Continue reading about Dynamic control of dilution ventilation in one-pass, critical environments... 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