Depressurization control

DEPRESSURIZATION CONTROL

RELATED APPLICATION

This invention relates the application No. 09/ (Attorney Docket R23-25355) filed contemporaneously with this present application. The contents thereof are incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to make-up air equipment. More specifically, this invention relates to equipment which provides make-up air and the control of such equipment.

Make-up air equipment supplies additional outside air to a building space. Make-up air is needed when an exhaust producing appliance within the building is operated. This make-up air equipment keeps the building from becoming depressurized. If depressurization of the building occurs, potentially dangerous situations may exist. Most importantly, spillage and back drafting of combustion by-products can occur - a very hazardous situation. This is generally true of all fossil fuel appliances like furnaces, water heaters, and wood burning equipment, etc.

In addition to the potentially hazardous situation mentioned above, an imbalance between the indoor and outdoor pressure can create uncomfortable conditions for the building occupants and can negatively impact the building structure. As is well known, air will move from spaces with a higher pressure to spaces with a lower pressure. Small openings in the building envelope allow for air to move through the wall to the lower pressure side. Depending on the indoor and outdoor temperature and dew point conditions, this may lead to condensation occurring within the wall and eventually to a degradation of the building structure. Imbalanced air pressures can also make doors and windows difficult to open and close and, in some cases prevent them from being held open or closed as desired. Consequently, it is desirable to utilize appropriate equipment to maintain indoor pressure equal to outdoor pressure.

Make-up air equipment generally consists of a fan and damper arrangement, sometimes utilizing a heater to condition outdoor air prior to delivery indoors. However, a control system does not presently exist for automatically adjusting the amount of make-up air to maintain neutral indoor air pressure (relative to outdoors). As a result, make-up air systems typically are manually controlled by simply turning a switch on or off. Such systems are often not turned on when needed, and do not respond to variable demand when, for example, multiple exhausting devices are used simultaneously. Other present make-up air systems may be interlocked with exhausting devices, but still lack the ability to respond to variable demand.

SUMMARY OF THE INVENTION

In order to maintain a pressure balance, a control system directs a make-up air apparatus to allow matching the volume of air brought into the building to the amount of air exhausted from the building. Thus, overpressurization or under pressurization of the controlled space within the building is avoided. More specifically, the invention provides a system for controlling the pressure of air in the controlled building space. A sensor is used for sensing a decrease in pressure of air in the controlled space and a controller is used for appropriately operating the make-up air apparatus. Alternatively, a sensor can be used which monitors the flow of air as it is exhausted from the controlled building space.

The make-up air apparatus includes a blower for drawing air into the controlled space. The blower operates as required to maintain the pressure within the controlled space substantially equal to the pressure outside. If the pressure in the controlled space is determined to be greater than or equal to the pressure outside this will indicate a need to deactivate the make-up air apparatus. More specifically, the blower and a preheater are deactivated, while the backflow damper is closed. Thus, additional make-up air is not provided to the controlled space, and the pressure is not increased. Alternatively, if an airflow sensor is used and it is determined that no air is being exhausted, the make-up air apparatus will be similarly shut down.

Preferably, the make-up air apparatus includes a variable speed blower and a control for the blower wherein the speed of the blower and the amount of air flow into the controlled space can be regulated. The pressure differential between the controlled space and the environment outside the controlled space is monitored and is used to control the blower speed. The air flow is gradually increased until the pressure in the controlled space is at a predetermined level, preferably substantially equal to the pressure outside the controlled space.

As necessary, the temperature of the make-up air can be monitored, so that the make-up air can be heated (or cooled) prior to delivery. A preheater associated with the make-up air apparatus can be used for heating the air being drawn into the controlled space when the temperature of the controlled space is below a predetermined level. If necessary, a cooling device could be similarly used.

A sensor can be mounted in a location relative to a vent from the building to monitor exhaust air volume. When the sensor determines that air is being exhausted from the controlled building space, the operation of the make-up air equipment is activated. Thus, a fairly constant air pressure can be maintained within the controlled building space. Other mounting locations are clearly possible.

The sensor is selected to be at least one of a pressure sensor, infrared sensor, or Hall effect sensor. Other sensors which detect air flow may also be used. One or more sensors are located in a strategic location in or related to the controlled building space. Preferably, the sensor is located in a vent pipe which is used to exhaust air from the building. This type of vent pipe is typically associated with an appliance which, when operable, normally exhausts air from the building. For example, the appliance may be a furnace, a vent hood, an exhaust fan, etc.

It is an object of the present invention to provide a pressurization control which will maintain the pressure within a controlled building space substantially equal to the pressure in the environment outside of the controlled building space. The specific system provided is directly responsive to this differential pressure and the variable conditions typically encountered.

It is a further object of the present invention to provide a system which utilizes a variable speed blower to provide variable amounts of make-up air to a controlled building space. In this way, a system can quickly respond to varying conditions as they are encountered.

The foregoing and other objects, features, and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments which makes reference to several drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the system, apparatus and equipment and one possible control scenario.

Figure 2 illustrates the system, apparatus and equipment and another control strategy.

Figure 3 shows a pipe placed between the outside and the room where the combustion appliances are located in a controlled building space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the preferred embodiments reference is made to the accompanying drawings which form the part thereof, and in which are shown by way of illustration of specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional changes may be made without departing from the scope and spirit of the present invention.

A make-up air system is shown in Figure 1 and generally referenced as 10. Make-up air system 10 is used to provide make-up air to a controlled building space 1 1 and to control the amount of make-up air as necessary. By providing make-up air in this way, depressurization can be avoided. More specifically, make-up air is provided to insure that the pressure difference between the controlled space 1 1 and the environment outside the controlled space 17 (the "Differential Pressure") is minimized. System 10 includes a depressurization sensor 12 for sensing when the pressure within the controlled building space 11 is lower than the pressure outside the controlled space 17, and a controller 32 for coordinating the overall operation of the components. Also included is a make-up air device 30 which actually provides make-up air to the controlled building space 11. Make-up air device 30 includes a blower 14 for drawing air into the controlled building space 11. The blower 14 can operate selectively for a predetermined time or for predetermined time intervals within a greater time period. Make-up air device 30 also includes a preheater 15 for heating the make-up air that is provided to controlled building space 11. As can be seen in Figure 1, blower 14 draws airflow 18 through damper 16, and preheater 15 before it is provided to controlled building space 11.

Whenever the Differential Pressure, as sensed by sensor 12, or another sensor, is above a predetermined level, this indicates a need to shut down make-up air device 30. Specifically, blower 14, and preheater 15 are deactivated and backflow damper 16 is closed. Stated alternatively, when the sensed pressure within the controlled building space 11 is equal to or above a predetermined level, the make-up air device 30 is shut down. This sensed condition simply indicates that there is no longer a need for make-up air.

Blower 14 is operated by a motor 22 which is either a fixed speed motor as shown in Figure 1 or variable speed motor as shown in Figure 2. As seen in both Figures 1 and 2, controller 32 is attached to motor 22 (and other components of make-up air device 30) via connections 20. In the case where a variable speed motor is used, controller 32 controls motor 22 to regulate the amount of air flow into the space 11. The air flow is gradually increased until the pressure in the building space 11 is at a predetermined level, preferably substantially equal to the pressure outside the building space 11.

A temperature sensor 23 for monitoring the outside air temperature can also be used in make-up air system 10. Temperature information is provided to controller 32 so that preheater 15 can be appropriately operated for heating the air being drawn into controlled building space 11 when the temperature of air outside the controlled building space 11 is below a predetermined level. The differential pressure is measured and is used to control the speed of the blower 14. Depressurization sensor 12 can be mounted in numerous locations to detect depressurization conditions. For example, depressurization sensor 12 could be mounted relative to a vent 13 from controlled building space 11 such that the exhaust of air from controlled building space 11 can be monitored. Signals indicative of exhaust can then be communicated to controller 32 for appropriate action.

Alternatively, the need for make-up air can be determined by monitoring the amount of exhaust air being produced. Consequently, depressurization sensor 12 may include an air flow sensor for monitoring exhaust air. By monitoring this exhaust air, the control system can determine the amount of make-up air required, and appropriately control variable speed motor 22. As should be clear, a single depressurization sensor could be used, or multiple depressurization sensors could be positioned at appropriate locations.

The depressurization sensor 12 is selected to be at least one of a pressure sensor, infrared sensor, Hall effect sensor. One or more sensors can be located in strategic locations in or related to the controlled building space 11. Depressurization sensor 12 is preferably located in one or more vent pipes 24 and 25 from the building. The vent pipe 24 is associated with respective device 26 and 27, which, when operable normally exhaust air from the building. Alternatively, a depressurization sensor 112 can be placed in a location which is not directly related to an exhaust related appliance. This could simply be a vent pipe 25 which is intended to provide a mechanism to compare the controlled space 11 air pressure to the outside environment 17 air pressure.

In Figure 1, the make up air equipment 30 brings in a fixed amount of outside air until the depressurization condition is substantially corrected. Again, the make-up air device 30 consists of the blower 14, heating element 15, and back flow damper 16. Also, a control panel 19 provides for appropriate system connections 20 and has controller 32 mounted thereon. A signal from the depressurization sensor 12 activates the equipment as follows: control panel receives signal from sensor back flow damper opens air temperature data evaluated preheater activated if required blower activated, air brought into building

When the depressurization condition within the building 11 is satisfied the control could time the blower 14 to remain on for a certain time interval to reduce short cycling situations. Alternatively, when the sensor 12 determines a large over pressurization situation indicating the exhaust air flow was shut off, the sensor 12 issues a shut down signal to the control panel 19. This causes the blower 14 and preheater 15 to deactivate, and the back flow damper 16 closes.

Figure 2 illustrates a different control strategy involving a variable speed blower. A control panel 19 relays signals to the make up air device 10 when sensor 12 determines a depressurization condition occurred within the building 11. A speed control board 28 within the equipment 10 receives the signal from the control panel 19. The make up air device contains a variable speed motor 22 to regulate the amount of airflow to the building 11. The equipment also includes a damper 16 and heating element 15.

When a signal is received the following scenario occurs: control panel receives signal from sensor back flow damper opens air temperature data evaluated preheater activated if required blower activated, air brought into building

The speed of the blower 14 is a function of the amount of depressurization. Airflow could gradually be increased until the pressure inside the building 11 is substantially equal to the pressure outside. At this point the blower speed is held constant. As the pressure differential changes the blower speed changes. A shut down signal is given at some threshold or predetermined level of over pressurization. This causes the blower 14 and preheater 15 to deactivate and the back flow damper 16 closes. Multiple possibilities exist to sense when a back draft condition exists. One such situation requires a mass airflow sensor 12 located within the main vent 24 of multiple atmospherically vented appliances 26 and 27. The sensor 12 determines directionality and quantity of airflow within the vent 24. If an appliance 26 or 27 is back drafting, the sensor triggers a make up air device 10 to come on and bring outside air into the building 11 until the depressurization effect is corrected. Other sensing technologies such as pressure, infrared, and Hall effect are utilized to accomplish the same objective. It is also possible to locate the sensor 42 in a location other than a vent pipe. One such possibility could be a small diameter («2") pipe that is placed between the outside and a room where combustion appliances are located as shown by Figure 3.

The foregoing description of the preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.