Patent Publication Number: US-8974275-B2

Title: Passive ventilation stack

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Phase Application of International Application No. PCT/GB2006/001811, filed May 16, 2006, which claims priority to Great Britain Patent Application No. 0510007.8, filed May 16, 2005, which applications are incorporated herein fully by this reference. 
     The present invention relates to a passive ventilation stack for a room, building or the like, and to a method of ventilating a room, building or the like. 
     Passive stacks are well known as devices for extracting warm air from the upper regions of a room or building, with incoming air being admitted via inlets lower down in the room or building. In winter, such incoming air will need to be heated for the comfort of occupants and this is wasteful. 
     Other systems for ventilating rooms and the like include air conditioning devices. These however are energy intensive devices that can be expensive to operate, and do not function without electrical input. 
     It is therefore desirable to produce a ventilation system that is both relatively efficient and cost effective, and which need not rely on electrical input for power. 
     According to a first aspect of the present invention, there is provided a passive ventilation stack for a room, building or the like, the stack having an interior space, a first opening which in use provides two way fluid communication between the interior space and the room, building or the like to be ventilated, and a second opening which in use provides two way fluid communication between the interior space and ambient atmosphere, and a control device for varying the size of each of the first and second openings. 
     An advantage of this passive ventilation stack is that cooler ventilation air entering the stack from outside is able to mix in the interior space with warmer air from the room or building to be ventilated, such that ventilation air is provided to a room at a controlled temperature that is comfortable to the occupants of the room, without the need for electrical or other form of power to preheat the ventilation air. This in turn can make the system cheaper to operate than prior art systems. 
     Further aspects of the invention are as claimed in claim  3  and claim  4 . 
     The size of the first opening and the size of the second opening may be independently variable. 
     The stack may provide substantially the only inlet of the ambient atmosphere into the room, building or the like to be ventilated. In this manner, the passive ventilation stack operates most efficiently. 
     The control device may comprise an electric stepper motor. The control device may comprise a fluid thermostat. 
     At least two said interior spaces may be provided in series. Preferably, a third independently variable opening is provided between the said interior spaces to provide fluid communication therebetween. 
     The passive stack may include at least one sensor, the output of which provides an input to the control device. The sensor may comprise a temperature sensor. At least one further sensor may be provided in the room, building or the like to be ventilated. The further sensor may comprise a temperature sensor and/or a CO 2  sensor. 
     According to a second aspect of the present invention, there is provided a method of ventilating a room, building or the like having a first variable size opening in an upper region of the said room, building or the like, said first opening providing fluid communication with an interior space substantially adjacent the room, building or the like, said interior space having a second variable size opening providing fluid communication with the atmosphere, the method comprising the steps of controlling the size of the first opening such that room air in said upper region passes via said opening into the interior space, and controlling the size of the second opening such that ventilation air from the atmosphere enters the interior space, to cause heat exchange by mixing in said interior space of relatively warm room air and relatively cool ventilation air, such that warmed ventilation air is passed into the room, building or the like, and room air from the upper region passes to the atmosphere, substantially without external power. 
     Still further aspects of the invention are as claimed in claims  25  and  26 . 
     The first variable size opening and second variable size opening may be independently controllable by a control device. 
     The method may comprise the further step of obtaining air temperature measurements in the interior space, outside of the interior space and in the room or building to be ventilated, and controlling the size of the first opening and the second opening based upon the said air temperature measurements. 
     The method may comprise the further step of obtaining a CO 2  concentration measurement in the room or building to be ventilated, and controlling the size of the first opening and the second opening based upon the said CO 2  concentration measurement. 
     The passive ventilation stack may be installed on a room, building or the like, and the installation may include at least one sensor in the interior space, at least one said sensor in the room, building or the like, and at least one sensor located in the atmosphere external to the interior space. 
     The interior space may include at least two said first openings and at least two said second openings provided at spaced locations on the room, building or the like. This arrangement can be advantageous where large rooms, buildings or the like are to be ventilated. 
     The passive ventilation stack may be located at the top of the room, building or the like. 
     An additional power source may be provided to ensure mixing of air in the interior space. The additional power source may comprise a fan. At least one splitter plate may be provided within said interior space to ensure mixing of air in the interior space. 
    
    
     
       An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic view of a building having a ventilation stack according to the invention; 
         FIG. 2  shows a schematic view of a building having two ventilation stacks according to a second embodiment of the invention; 
         FIG. 3  shows a schematic view of a building having a ventilation stack according to a third embodiment of the invention; 
         FIG. 4  shows a schematic view of a passive ventilation stack according to a fourth embodiment of the invention; 
         FIG. 5  shows a schematic enlarged detail view of the passive ventilation stack of  FIG. 4 ; 
         FIG. 6  shows a schematic view of the passive ventilation stack of the fourth embodiment with an extended partition; and 
         FIG. 7  shows a schematic partial view of a passive ventilation stack according to a fifth embodiment of the invention. 
     
    
    
     Referring to  FIG. 1 , a room or building  10  has a single ventilation stack  20  mounted at the top of the room or building. The stack  20  has a first lower opening  40  leading into and providing fluid communication with an interior space  41 . The lower opening  40  has a valve member  42  for selectively varying the size of the first opening. The term ‘size’ can include single dimensional quantities such as length or width of the opening, or it could be a two-dimensional area. The valve member  42  is controlled in this embodiment by an electric stepper motor (not shown), but other devices, such as a fluid thermostat (not shown) directly controlling the member could be provided. The valve member  42  may be a slide valve or any other suitable opening-controller, including an iris-type diaphragm, or a single or multi-blade damper such as is well known in the art. 
     The stack has a second upper opening  30  from the interior space to the outside. The upper opening  30  has a valve member  32  for selectively varying the size of the second opening  30 . The valve member  32  is controlled in this embodiment by an electric stepper motor (not shown), but other devices, such as a fluid thermostat (not shown) directly controlling the member could be provided. The valve member  32  may be a slide valve or any other suitable opening-controller, including an iris-type diaphragm. 
     The passive ventilation stack system operates most efficiently in a room or building in which there is substantially no other source of inlet air into the room or building  10 —for example when any windows and doors are closed. In this manner, the system is not dependent upon exterior wind conditions to admit cooler ventilation air into the stack. When the room or building  10  is occupied with people or computers or other heat sources, the room air warms up and naturally rises into an upper region  50  of the room or building. The warm room air passes through opening  40  into the stack  20  at a controlled flow rate, dependent upon the size of the opening  40 . The room air passes through the stack  20  and through opening  30 , again at a controlled flow rate that is dependent upon the size of the opening  30 . As the opening  30  is substantially the only inlet/outlet of air into and out of the room or building  10 , the room air leaving the stack  20  is replaced by incoming cooler ventilation air. This ventilation air enters the stack  20  through opening  30  at a controlled flow rate dependent upon the size of the opening  30 . Once inside the stack  20 , the ventilation air is able to mix with the warmer room air such that a degree of natural heat exchange takes place between the two streams of air. The ventilation air becomes warmer whilst the room air becomes cooler. The warmed ventilation air then passes through the opening  40  at a controlled flow rate dependent upon the size of the opening  40 , and into the room or building  10  where it falls to occupant level at a temperature that is comfortable to the occupants. 
     A temperature sensor  15  is located in the interior of the room or building  10  in order to measure the room temperature. A second temperature sensor  25  is located in the stack  20  for measurement of the stack temperature. A third temperature sensor  35  is located outside of the stack  20 , close to the upper end thereof, for measurement of the ambient air temperature outside of the room/building. In the present embodiment, a CO 2  sensor  17  is also present in the room or building  10 . The measurements recorded by each of the sensors  15 ,  25 ,  35  and  17  are used as input data into an algorithm for controlling the size of the openings  30  and  40 . The algorithm computes the desired ratio of size of the openings  30  and  40  that will provide a desired stack temperature, measured at temperature sensor  25 , where the desired stack temperature is higher than the external ambient temperature, measured at temperature sensor  35 , but lower than the internal room or building temperature, measured at temperature sensor  15 . 
     The output of the algorithm is used by the electric stepper motor or other controlling device to adjust the valve members  32  and/or  42  independently of each other to automatically produce the desired stack temperature. 
     In an embodiment, the desired stack temperature (T s ) is interpolated using the outside temperature (T e ), and the temperature inside the room to be ventilated (T i ):
 
 T   s   =T   e +( T   i   −T   e )×ƒ( A   2   /A   1 )
 
where A 2  and A 1  are the areas of the second opening  30  and the first opening  40  respectively.
 
     The optimum value of the function ƒ can be empirically determined by the skilled person, depending upon the stack design and the specific geometry of the openings. 
     In the present embodiment, the desired size of the openings  30  and  40  is also a function of the optimum CO 2  level inside the room, measured at sensor  17 . For example, if the sensor  17  detects that there is too high a concentration of CO 2  in the room or building, the openings  30  and  40  can be increased in size whilst maintaining the optimum ratio of size of the two openings. 
     In a second embodiment of the invention, more than one stack may be appropriate as shown in  FIG. 2 . This arrangement can enhance the mixing of ventilation air and room air, providing further control of the temperature of air moving into the room, building or the like  110 . This arrangement may be particularly appropriate where there is a relatively large temperature difference between the atmospheric air temperature and the room temperature. In this embodiment, a second stack  180  is located adjacent to and above a first stack  120 , as shown in  FIG. 2 . However, the two stacks need not be vertically stacked and could be located side by side. A third opening  170  provides fluid communication between an interior space of the first stack  120  and an interior space of the second stack  180 . A third valve member  172  is provided in the opening  170  for selectively varying the size thereof. In addition to temperature sensors  115 ,  125  and  135 , a further temperature sensor  175  in the second interior space of second stack  180  provides an additional input into the algorithm. 
     In a third embodiment of the invention as shown in  FIG. 3 , a large room or building  210  has an elongate stack  220  mounted on top of the room or building, the stack  220  having multiple lower openings  240  in a lower wall  241  of the stack and multiple upper openings  230  in an upper wall  231  of the stack, at spaced locations thereon. A fan (not shown) is optionally employed to assist mixing of the ventilation air with the room air in the stack  220 . Alternatively, one or more splitter plates  255  are optionally employed to assist mixing of the ventilation air and the room air. 
     In a fourth embodiment of the invention shown in  FIGS. 4 and 5 , a stack  320  is located between an upper stack  380  and a lower stack  390 . The stack  320  includes a first opening  330  providing fluid communication between the stack  320  and the upper stack  380 , and a second opening  340  providing fluid communication between the stack  320  and the lower stack  390 . Valve members  332  are located in opening  330  to vary the size thereof. In  FIG. 4 , the valve members are shown as multi-blade dampers, through which air can pass when the blades are open or partially open, although other appropriate types of opening control member can be used. Valve members  342  are located in opening  340  to vary the size thereof. The valve members  332  may comprise two separate valve members  332   a ,  332   b  that are controllable independently of each other or they may be coupled so as to be controllable together to vary the size of the opening  330 . Similarly, the valve members  342  separate valve members  342   a ,  342   b  and may be controllable independently of each other or they may be coupled so as to be controllable together to vary the size of the opening  340 . 
     The upper stack  380  is open to the atmosphere at an opening  370  located at an upper end thereof, and is protected from unwanted ingress of debris, rainwater etc by an exterior hood  385  that is disposed above the stack  380  in spaced relation therewith, so as to allow for the opening  370  to the atmosphere. An optional partition wall  360  may be included in the upper stack  380  so as to at least partially divide the upper stack into first and second flow passages extending substantially from a lower end of the stack  380  to an upper end thereof. 
     The lower stack  390  is open to the room, building or the like to be ventilated. An optional partition wall  365  may be included so as to at least partially divide the lower stack  390  into first and second flow passages extending substantially between the upper end of the lower stack  390  and the room, building or the like to be ventilated. Where the partition walls  360  and/or  365  are partial dividing walls as is described here, a small amount of mixing of the incoming cool air stream and the warmer air exiting the room may take place in the upper stack  380  and/or lower stack  390  respectively. 
       FIG. 5  shows an enlarged detail view of the stack  320 . The stack optionally includes a fan  352  mounted on an inner wall thereof to enhance mixing of the flow streams entering the stack  320  from the upper stack  380  and the lower stack  390 . The orientation of the fan  352  may be variable such that it can be optimised according to operating conditions A further optional fan  354  is disposed towards the upper end of the stack  320 , below or above the valve member  332 , to assist in drawing air downwards from the ambient atmosphere into the stack  320 . A still further optional fan  356  is disposed towards the lower end of stack  320 , configured to draw air upwards from the room into the stack  320  through valve  342 . 
     During use of this embodiment of the invention, the passive stack system can be operated such that cool air from the atmosphere is drawn through the opening  370  into the upper stack  380  as shown by the arrow in  FIG. 4 . The cool air flows downwards into stack  320 . Meanwhile, warm air from the room is drawn upwards by the lower stack  390  into the stack  320 . The cool and warm streams of air meet and mix in the stack  320 , causing a certain amount of natural heat exchange between the two air streams. 
     The heated ventilation air then exits the stack  320  into the lower stack  390 , and hence into the room, building or the like to be ventilated as before, providing the room with naturally heated ventilation air at a temperature that is comfortable for the occupants of the room. 
     The remaining warmer air stream is drawn into the upper stack  380  and to the ambient atmosphere. 
     A further variation of this embodiment is shown in  FIG. 6 . Here, the partition in the upper stack  380  extends all the way up to the exterior hood  385 , such that the first and second passages of the upper stack  380  are completely separated from each other. No mixing of the cooler incoming air stream and the warmer room air stream occurs in the upper stack  380  in this variation. 
     In a yet further embodiment shown in  FIG. 7 , a stack  420  comprises only one opening of variable size  430 , at an upper end thereof. A pair of valve members  432   a ,  432   b  is provided to selectively vary the size of the opening  430 . The opening  430  provides fluid communication between the stack  420  and an upper stack  480 . A lower end of the stack  420  is open to the lower stack  490  with a fixed size opening. The stack is in all other aspects identical to the stack system of the fourth embodiment of the invention and may have a partial or full partition  460 . 
     The valve members  432  may be controllable independently of each other as inflow valve member  432   a  and outflow valve member  432   b  or they may be coupled so as to be controllable together to vary the size of the opening  430 . A controller  446  uses the inputs from a room temperature sensor  415 , stack temperature sensor  425 , external temperature sensor  435  and from a CO 2  sensor  417  to determine how the valve members  432  and the fans  452 ,  454  should be operated. 
     An example of a control algorithm for opening and closing of the valve members will now be described. The skilled man will appreciate that other ways of operating the passive ventilation stack will be possible without departing from the scope of the invention. The example algorithm pertains to the embodiment of  FIG. 7 , but it will be apparent to the skilled person that the algorithm can be adapted for use with each of the embodiments described herein. 
     In the present example, the valve members  432  are coupled to operate as a single valve member. The passive ventilation stack can be user set at a designated switch  444  to one of three different modes of operation as follows:
         a) On, in ‘summer’ mode/‘winter’ mode   b) On, in ‘night cooling’ mode   c) Off       

     When the switch is turned on in summer/winter mode, the outside temperature (T e ) is measured by a temperature sensor  435 . If the measured temperature is above a pre-determined temperature, here 18° C., the passive ventilation stack will operate in ‘summer’ mode. If the measured temperature is below the pre-determined temperature, the passive ventilation stack will operate in ‘winter’ mode. 
     In ‘summer’ mode, the passive ventilation stack operates to provide a predominantly upflow displacement of warm room air to the ambient atmosphere. Input of air into the room in this case occurs through another opening e.g. a window. The optional fans  452  and  454 , if present, are operated in the same rotational direction and the valve members  432  are fully opened. The controller uses the inputs from temperature sensors  415 ,  425 ,  435  and from CO 2  sensor  417  to determine how the valve members  432  and the fans  452 ,  454  should be operated. 
     In the present example, if a CO 2  level of &gt;900 ppm (parts per million) is detected by CO 2  sensor  417 , the fans  452 ,  454  are operated on a slow setting, with the valve members  432  open. If a CO 2  level of &gt;1000 ppm is detected, the fans are operated on a fast setting with the valve members  432  open. 
     Temperature sensor  415  measures the interior room temperature (T i ). If the measured temperature is T i &gt;21° C., the valve members are opened. If the measured temperature is T i &gt;24° C., the fans are turned on at a slow setting and the valve members are opened. If the measured temperature is T i &gt;24° C., the fan speed is set to fast and the valve members are opened. For all other measured temperatures, the valve members  432  are closed and the fans are turned off. The room temperature is checked every 2.5 minutes. The position of the valve members and the fan settings are altered accordingly. 
     In ‘winter’ mode, the passive ventilation stack is operated to provide mixing of the warm and cool airstreams. Substantially all ventilation air is obtained through the stack in this mode, and the room is otherwise substantially sealed from the exterior e.g. windows and doors are closed. Temperature sensor  425  measures the temperature in the stack  420  (T s ). If the stack temperature is measured to be T s &gt;15° C., the valve members  432  are opened almost completely. If 10° C.&lt;T s &lt;15° C., the valve members  432  are opened approximately half way. If T s &lt;10° C., the valve members  432  are opened between the half way and fully closed positions. 
     The optional fans  452 ,  454  can be operated such that they rotate in counter-rotation to each other in this ‘winter’ mixing mode. The controller then uses the input from the CO 2  sensor  417  and from the room temperature sensor  415  to alter the valve member positions and fan speeds as necessary. In the present example, if the CO 2  measurement is &gt;900 ppm, the valve members are opened and the fans  452 ,  454  are run on a slow setting. If the CO 2  measurement is &gt;1000 ppm, the valve members  432  are opened and the fans  452 ,  454  are run on a fast setting. If the room temperature is measured at T i &gt;22° C., the valve members  432  are opened and the fans  452 ,  454  are run on a slow setting. If the room temperature is measured at T i &gt;24° C., the valve members  432  are opened and the fans are run on a fast setting. 
     For all other detected conditions, the valve members are kept closed and the fans are turned off. As with the ‘summer’ mode, the controller checks the inputs every 2.5 minutes. 
     When the switch  444  is set to ‘night cooling’ mode, the controller checks whether the inputs from temperature sensors  435 ,  415  show that the external temperature (T e ) is less than the room temperature (T i ). If the check is found to be true, the ‘night cooling mode’ is initiated. 
     The fans  452 ,  454  are operated in co-rotation and the valve members  432  are fully opened. The controller then checks the inputs from the CO 2  sensor  417  and the room temperature sensor  415  and alters the valve member  432  positions accordingly. In the present example, if the CO 2  measurement is &gt;900, or the room temperature is T i &gt;18° C., the valve members are kept open. If the room temperature is T i &gt;21° C. and/or the CO 2  measurement is &gt;900 and the time is between 3 am and 6 am, the fans  452 ,  454  are turned on and the valve members are open. Otherwise, the valve members  32  are closed. 
     In ‘night cooling’ mode, the above checks may be made every 5 minutes. 
     In the ‘off’ mode, the valve members  432  remain closed and the fans  452 ,  454  turned off. 
     The skilled person in the art will appreciate that there are many ways of programming such an algorithm, and that these are conventional in the art and will not be described here. 
     In each of the embodiments described above, the first and second openings are shown to be located at the top and bottom of the stack. However, one or both the openings could be located on the sides of the stack. The first and second openings need not be vertically displaced, and could be located at the same vertical level as each other. The stack or stacks may be mounted at locations other than the top of the building. 
     The term ‘opening’ will be understood by the skilled person to include an aperture or a conduit, the size of which is or may be variable to control flow rate there through. Where the valve members are single or multi-blade dampers, it will be understood that the size of the ‘opening’ can be varied by opening or closing the single or multiple blades. 
     It will be appreciated by the skilled person that the desired stack temperature depends upon the environment in which the system is operated, and that in practice it may be higher or lower than the desired temperature in the embodiment above. 
     The passive ventilation system may be an integral part of the building design or it may be added later as a retro-fit. 
     Various modifications may be made to the embodiments described without departing from the scope of the invention as defined by the following claims.