System for controlling automatically the setting of a damper in a ventilation duct

The invention relates to a control system for adjusting the setting of a damper (9) in a ventilation duct (8) and maintaining a substantially constant pressure at a selected region in the ventilation duct, the system comprising a cylinder (1) having a vertical cylinder axis and housing a readily movable, pressure-responsive device (2), which together with the cylinder defines a pressure space. The pressure space (22) communicates with the ventilation duct at the aforementioned selected region, and drive means (11, 12) are provided for adjusting the damper setting in response to the position of the pressure-responsive device, so as to maintain a constant pressure. The inventive system is characterized in that the pressure-sensitive device (2) has a mass which corresponds to a selected pressure at the aforementioned region in the duct and is intended to balance the pressure force acting on the device.

The present invention relates to a system intended for controlling 
automatically the setting of a damper in a ventilation duct. 
Control systems of this general kind have not found wide use in the 
ventilation field, mainly because they are particularly imprecise and thus 
have a poor control function, unless made prohibitively expensive. 
Consequently, the systems used today are mainly systems which incorporate 
manually adjusted dampers, and in which the dampers are set to positions 
in which the calculated and desired pressure drop is obtained. One problem 
encountered with such systems is that subsequent to ascertaining that the 
air flow to a particular location or room is correct, or at least lies 
within acceptable tolerance limits, a subsequent adjustment to the damper 
function in a ventilation duct which serves a different location or room 
will result in a change in the damper setting of the first mentioned 
location. This manual adjustment of the dampers of each individual 
location or room is therefore particularly time consuming and, in 
practice, it is extremely seldom that the air flow to each separate 
location or room has the desired value. 
The undesirable air vents or openings which are found in buildings between 
the various locations, rooms, etc., therein and between the different 
floors of the building also constitute a problem when using ventilation 
systems which incorporate manually adjustable dampers, not least because 
of the energy losses that are experienced and because e.g., smoke is able 
to spread freely throughout the building in the event of a fire. 
Attempts have been made to control the damper setting automatically, by 
utilizing the pressure drop across the damper blade in order to establish 
a constant air flow, wherewith springs and counterweights are used in 
co-action with the damper blade to this end. The forces which act on the 
damper blade in response to a pressure drop across the blade are, however, 
generally too small to adjust the damper setting satisfactorily. 
The object of the present invention is therefore to provide a damper 
control system which will overcome the problems experienced with known 
systems of this kind, and which despite being of simple construction will 
afford a particularly accurate control function and which is able to adapt 
readily to the ventilation requirements of each particular location or 
room served by the system. These objects are realized by a damper control 
system which has the characteristic features set forth in the following 
claims.

The illustrative embodiment of FIG. 1 includes a control cylinder or 
float-chamber 1 in which a float device, or pressure-responsive device, 
generally referenced 2, is intended to move freely in the direction of the 
vertical axis of the cylinder. The float device, which moves freely in the 
cylinder, comprises two cylindrical parts 2' and 2" which are spaced 
axially, at a given distance apart. The upper float part 2" of the float 
device 2 has provided therein at least one fluid out flow port, in the 
illustrated case two ports referenced 3 and 4, each of which communicates 
with an annular space 5 defined between the mutually opposing surfaces of 
respective float parts 2' and 2". Provided in the wall of the control 
cylinder 1 is a first aperture 6 and a second aperture 7 which can be 
placed in communication with the flow channels formed by the space 5 and 
the ports 3 and 4, in a manner hereinafter described. It will be seen from 
FIG. 1 that the first aperture 6 is spaced axially from the second 
aperture 7, the distance between said apertures being a pre-determined 
distance. The float device 2 has a mass which corresponds to the pressure 
desired in an outlet channel or duct 8 which leads, e.g., to a selected 
office or office location. 
The duct 8 has arranged therein a damper 9 which is intended to regulate or 
control the flow of air entering the illustrated duct from a main 
air-supply duct (not shown), this main duct supplying air to a plurality 
of ventilation ducts 8, each of which serves a respective office or office 
location, with the aid of a fan or blower (not shown), wherein the 
pressure in the main supply duct is held constant or at least 
substantially constant. In the illustrated state of the control system, 
the damper 9 is only slightly open, such that the flow of air to the duct 
8 will correspond to the amount of air desired, i.e. such that the 
pressure prevailing in the duct 8 is the pressure desired. The illustrated 
duct 8 also has arranged therein a damper control means 10 which, in the 
case of the illustrated embodiment, comprises a cylindrical housing 11 and 
an air-impermeable piston or diaphragm 12 which is housed in the housing 
11 and which seals, or essentially seals, against the inner wall surface 
of the cylindrical housing 11 and which is securely mounted on a hollow 
shaft 15 which extends through both end walls 13 and 14 of the housing 11, 
said housing being shown in a shortened view. The damper 9 is carried on 
one end of the hollow shaft 15, i.e. the left end in FIG. 1, and will abut 
a seating 16 when the shaft 15 is moved to the left to its fullest extent. 
The interior of the hollow shaft 15 communicates with the duct part 
located to the left of the damper 9, i.e. with the main air-supply duct. 
The hollow shaft 15 has provided therein ventilation apertures which are 
located on respective sides of the air-impermeable piston 12, such as the 
illustrated apertures 17, so as to establish mutually the same pressure in 
the cylinder spaces or chambers on either side of the piston 12 when the 
system is in a balanced state, as hereinafter described, this cylinder 
pressure being, of course, equal to the pressure prevailing to the left of 
a damper in FIG. 1 The left-hand chamber 18 defined by the piston 12 and 
the cylinder 11 communicates with the aperture 6 in the cylinder 1, via a 
pipe 19, whereas the right-hand chamber of the damper control means 10 
communicates with the aperture 7 in the cylinder 1 via a pipe 21. The 
bottom cylinder space 22 defined between the mutually opposing surfaces of 
the lower float part 2' and the cylinder bottom is connected to the duct 8 
through a pipe 23, and the pressure acting on the two major surfaces of 
the "weighted" float device which face towards the space 22 will therefore 
correspond to the pressure in the duct 8. 
FIG. 1 illustrates the ventilation system in a state of balance, i.e. the 
pressure in the duct 8 and therewith the volume of air flowing into the 
ventilated location per unit of time correspond to desired values. As 
before-mentioned, this pressure is, in turn, contingent on the mass of the 
float device 2. The pressure prevailing in the duct 8, which is the 
desired pressure, is transmitted through the pipe 23 to the bottom space 
22 of the cylinder 1, and acts on the bottom surface of the float part 2' 
with a force which is determined by said pressure and by the surface area 
of said float part, and which consequently holds the float device 2 
suspended on a cushion of air. As illustrated in FIG. 1, in the balanced 
state of the system the aperture 6 is held partially closed by the plunger 
part 2" and the aperture 7 is also held partially closed by the plunger 
2', i.e. the air which is fed to the interior of the hollow shaft 15 from 
the main air-supply duct and which flows into the chambers 17 and 18 is 
passed to the surroundings through the pipes 19 and 21, the annular space 
5 and the outlet ports 3 and 4, and consequently the pressure that 
prevails on either side of the piston 12 will be standard atmospheric 
pressure, provided that the piston 12 and the damper 9 remain in their 
illustrated set positions. 
If the pressure in the main supply duct (not shown) should fall, i.e. on 
the left of the damper 9 in FIG. 1, the pressure on the right-hand side of 
the damper will, of course, also fall. Consequently, the pressure in the 
cylindrical bottom space 22 of the cylinder 1 will also fall and therewith 
exert a smaller force on the float device 2, which will subsequently be 
lowered in the cylinder 1. As the float device 2 is lowered in the 
cylinder 1, the outlet aperture 6 is closed fully and the left-hand 
chamber 18 in the cylindrical housing 11 will no longer be ventilated, 
wherewith the pressure in the chamber rises. Since this lowering of the 
float device 2 will simultaneously expose the whole of the outlet aperture 
7 located axially beneath the aperture 6, the right-hand chamber 17 will 
be ventilated to the surroundings and the piston 12 and the damper 9 
carried thereby will be moved to the right in FIG. 1. As a result of the 
subsequent increase in free space between the damper 9 and the seating 16, 
the volume of air which flows into the duct 8 will also increase and cause 
the pressure to rise in the duct part located to the right of the damper 
9, as seen in the Figure. This increase in pressure is transmitted to the 
bottom space 22 in the cylinder 1, through the pipe 23, therewith lifting 
the float device 2. As the float device rises, it will partially uncover 
the opening 6, therewith establishing equilibrium between the pressure 
prevailing on both sides of the piston 12, whereupon movement of the 
damper ceases. The system has thus been brought to a new state of 
equilibrium or balance, and the pressure prevailing in the duct 8 is again 
the pressure desired, despite the lower pressure in the main air-supply 
duct. It will be understood that the pressure in the duct 8 may also fall, 
for instance as a result of opening a window in the location served by 
said duct. The system will also be restored, in this case, to a state of 
equilibrium, however, in the same manner as that just described. 
Should the "buoyancy pressure" in the bottom space 22 increase, i.e. the 
pressure in the duct 8 increases above a desired value, the float device 2 
will be lifted in the cylinder 1 and the float part 2' will begin to close 
the aperture 7. When this aperture is closed completely, or at least 
throttled to an extent such that no air flows through the pipe 21 or such 
that the air flow in said pipe is significantly smaller than the unimpeded 
air flow in the pipe 19, the pressure in the left-hand chamber 18 in the 
cylinder 11 will be lower than the pressure in the right-hand chamber 20 
and the piston 12 will be moved to the left in FIG. 1, wherewith the 
damper 9 will move closer to its seating 16 and subsequently reduce the 
amount of air that can flow into the duct 8. The pressure will thus fall 
in the duct 8 and the float device will subsequently be lowered in the 
cylinder 1 and begin to close the aperture 6 progressively, while exposing 
the aperture 7, until the desired equilibrium or balanced state is 
achieved. 
In order to ensure that the damper 9 will close when the fan or blower 
associated with the main air-supply system is stopped automatically, e.g. 
in the event of a fire, a thrust spring may be arranged between the damper 
9 and the housing 11. When the pressure ceases in response to the fan 
being switched off, or rendered inoperative in some other way, and the 
pressure in the duct thus falls to atmospheric or ambient pressure, the 
spring will urge the damper 9 against its seating 16. 
Although not shown in FIG. 1, the float device 2 is preferably provided 
with a metal screw which forms a taring weight, so that with the aid of an 
appropriate screw the float device can be given a total mass which 
corresponds to the desired pressure for the duct to be controlled or 
regulated. Obviously, other kinds of taring weights can be used. 
The described system can also be used to design a so-called variable air 
volume system, which implies that the air supplied to a room or some other 
location from a so-called hygiene-air flow can be increased to a cooling 
air flow. A cooling air flow is required when a room becomes overheated 
due, for instance, to the presence of a large number of people therein. 
This cooling function of the system can be achieved, for instance, by the 
provision of an electromagnet 24 which is controlled by a room thermostat 
25. In this case, the float device 2 is provided with a ferromagnetic body 
which, when the electromagnet 25 is energised by the thermostat 25, draws 
the float device 2 upwards to a terminal position in which the damper 9 is 
practically closed and in which a suitable air flow is engendered from an 
hygienic aspect. The thermostat 25 is set to a desired maximum 
temperature, and when this temperature is reached the thermostat will 
break the current to the electromagnet 24 and the float device 2 will 
begin the function and set the system to the pressure determined by the 
mass of the float device 2, so that a maximum air flow is introduced into 
the room. 
FIG. 2 illustrates schematically and in section a float device 2 whose mass 
can be varied by means of an exchangeable taring screw 26. In this case, 
the throughflow channels 5-3 of the FIG. 1 embodiment are formed by a bore 
27 which is ventilated through a passageway 28, whereas the throughflow 
channels 5-4 of the FIG. 1 embodiment are formed by a bore 29 and a 
passageway 30. As distinct from the float device of the FIG. 1 embodiment, 
the float device illustrated in FIG. 2 requires the provision of guide 
means to prevent rotation of the device about its vertical axis. Rotation 
of the float device may result in blockaging of the apertures 6 and 7 in 
FIG. 1. 
FIG. 3 illustrates an embodiment in which the damper-driving motor 11, 12, 
18, 20 of the FIG. 1 embodiment is replaced with an electric motor 33 
which is controlled via pressure switches 31 and 32. The motor 33 is 
connected to the rotational shaft 35 of a damper by means of a suitable 
transmission arrangement or shaft 34, indicated in broken lines, and is 
intended to rotate the damper 9' in the duct 8 for the purpose of 
adjusting the flow of air through said duct. 
The control system of the FIG. 3 embodiment is, in principle, identical 
with the control system illustrated in FIG. 1, and thus includes a float 
device 2 which exhibits an annular space 5 and moves vertically in a 
cylinder 1. As with the aforedescribed embodiment, the pressure in the 
duct 8 downstream of the damper 9' is transmitted to the bottom surface of 
the float device 2, via a pipe 23, and control pressure is transmitted, 
via the aforedescribed pipe 19, to a pressure-control switch 31, which 
when activated closes an electric circuit to the motor 3 and causes said 
motor to rotate the damper 9' anticlockwise from the position illustrated 
in FIG. 3, therewith to reduce the flow of air through the duct 8 and also 
to reduce the pressure downstream of the damper 9', and permit the float 
device 2 to sink in the cylinder 1 and close-off the pipe 19. If the 
pressure in the duct 8 downstream of the damper 9', as seen in the 
direction of air flow, falls to a value beneath the value determined by 
the mass of the float device 2, the float device will sink to a lowest 
level and the orifice of pipe 21 in the cylinder wall will be exposed at 
the same time as the orifice of pipe 19 will be covered, wherewith the 
pressure-responsive switch 32 is activated and starts the motor 33 in the 
damper opening direction, i.e. the damper 9' is swung clockwise around its 
axle 35 until the duct pressure downstream of the damper 9' has been 
re-set to the value determined by the mass of the float device 2. The 
drive pressure delivered to the two switches 31 and 32 is obtained via a 
pipe 36, which delivers air to the annular space 5 at a pressure 
corresponding to the air pressure upstream of the damper 9' as seen in the 
direction of air flow. It will be understood, however, that this drive air 
can also be taken out downstream of the damper 9'. 
As will be understood, the friction between the float device 2 and the wall 
of the cylinder 1 shall be as small as possible, although the float device 
should seal sufficiently against the cylinder wall to prevent the 
pressure-indicating air supplied through the pipe 23 from disturbing the 
air flow through, for instance, the pipe 36. It may therefore be suitable 
to enclose the bottom space or pressure chamber 22 in a bellows-like 
device 37 or the like which is sealingly connected to the bottom surface 
of the lower float part and to the bottom of the cylinder 1, and which is 
made of an extremely thin rubber material or the like which will not 
appreciably affect the mass of the float device 2 or engender forces which 
will influence movement of said float device in the cylinder 1. 
FIG. 4 illustrates a modified damper control system which includes a 
cylinder or float housing 1 which has a pressure-responsive device or 
float 38 arranged therein. The float device 38 comprises, for instance, a 
sheet of plastics material or metal and is connected sealingly to the 
inner wall surface of the cylinder 1, by means of an essentially 
frictionless and lightweight bellows structure or diaphragm 39, and is 
able to move essentially frictionless within the cylinder and without 
being hindered in its movements by the diaphragm 39. The float device 38, 
which is disc-shaped in the case of the illustrated embodiment, has fitted 
thereto an exchangeable central rod or taring device 40 which together 
with the disc 38 determines the mass of the float device. Thus, the disc 
38 and the diaphragm 39 form therebeneath an air-tight pressure chamber or 
bottom space 22 which communicates, via the aforedescribed pipe 23, with 
the duct 8 at a point downstream of the damper 9" as seen in the direction 
of air flow. The pressure prevailing in the duct downstream of the damper 
9" will therewith also prevail in the bottom space 22 of cylinder 1 and, 
when the float device is in a state of equilibrium it will take a 
determined position. In this equilibrium state, the mass of the float 
device, including the tare 40, balances the upwardly directed force 
determined by the pressure prevailing in the bottom space 22 and the 
active area, i.e. the pressure-receiving surface, of the disc 38. When, 
for instance, the duct pressure downstream of the damper 9" increases, the 
upwardly directed force will exceed the downwardly acting force, 
determined by the mass of the disc and the taring device, and the float 
device will rise in the cylinder 1. An electronic sensor 42 is intended to 
sense the upward movement of the rod or the taring device 40, and also the 
magnitude of said movement, by reading off, e.g., a scale 41 on the rod 
40, and sends, in response to said reading, control signals to the 
electric motor 33, which may, e.g., have the form of a stepping motor. As 
previously described with reference to FIG. 3, the motor 33 in this case 
will rotate the damper 9" in an anticlockwise direction in FIG. 4, so as 
to reduce the duct pressure downstream of the damper 9" and permit the 
float device to adopt the position determined by the mass of said device 
and, of course, also its pressure-receiving surface. Since the mass of the 
float device is changed when the taring device 40 is changed, whereas the 
pressure-receiving surface of the disc 38 remains unchanged, each taring 
device or rod 40 can be labeled with the pressure it affords. This sensing 
of the movement of the float device, or the pressure-responsive body, can 
also be applied to the float device 2 of the FIG. 1 embodiment. 
The described damper control system can also be used in conjunction with 
subpressure systems. FIG. 5 illustrates one such system, intended to 
measure the subpressure relative to atmospheric pressure in an evacuation 
duct. Those components found in the FIG. 1 embodiment have been identified 
with the same reference marks in FIG. 5. 
The cylinder 1 of the FIG. 4 embodiment has a bottom, perforated surface or 
net 43, the sole purpose of which is to prevent the float device 2 from 
falling from the cylinder 1 should the subpressure generated by an 
evacuation fan 44 in the duct 8 disappear because the fan 44 stops, 
whereupon the pressure in the duct 8 will be equal to atmospheric 
pressure. The duct 8, with the aid of the fan 44, withdraws consumed air 
from a room or some other location lying to the left of the Figure. The 
damper 9 co-acts with its seating 16 and is carried by a hollow shaft 15 
having openings 17 on both sides of a piston 12. In this case, the shaft 
15 is open towards the fan 44, and consequently when air is drawn through 
the duct 8 by the fan, a region of subpressure is created relative to 
atmosphere. This subpressure is transmitted through the pipe 23 to the 
space or chamber defined between the float 2 and the closed end of the 
cylinder 1. The subpressure creates a lifting force on the float device, 
the magnitude of which force depends on the magnitude of the float surface 
facing the space 22. When this lifting force corresponds to the mass of 
the float device 2, the float device will be held suspended or floating in 
the cylinder. Should the subpressure diminish, i.e. approach atmospheric 
pressure, the float device 2 will fall in the cylinder 1 and in doing so 
open the pipe 19 leading to the space 22 and to the interior of the 
housing 11, at the same time as the pipe 21 is open or is opened towards 
the housing 11. The pipe 21, which communicates with atmosphere through 
the ports 3, thus imparts to the chamber 20 to the right of the piston 12 
a pressure (atmospheric pressure) which is higher than the pressure 
prevailing in the chamber 17 on the left of the piston 12, and therewith 
the damper 9 will be closed still further and the duct pressure will fall, 
whereupon the float device is drawn upwards to its position in which the 
system is again in balance. 
If, on the other hand, the subpressure should increase above the value 
determined by the mass of the float device 2, the float device 2 will be 
drawn upwards and close the pipe 21 and open the pipe 19, this latter pipe 
therewith being placed in communication with atmosphere through the ports 
3. The pressure in the chamber 17 is therewith brought to atmospheric 
pressure, whereas the pressure in the chamber 26 is brought to the 
subpressure value prevailing in the duct 8. As a result, the damper 9 will 
be moved to the right in FIG. 5, such as to reduce the subpressure in the 
duct 8 and cause the float device to return towards a balanced position, 
or to return fully to a balanced position. It will be understood that a 
subpressure control system according to FIG. 5 can also be used to 
activate other types of drive arrangements, for example those drive 
arrangements described with reference to FIGS. 3 and 4. 
It may also be convenient to provide a damping spring between the float 
device and the cylinder, as indicated at 45 in FIG. 5, therewith 
preventing the float device from striking the bottom of the cylinder 1 in 
the event of abrupt changes in pressure. This spring will preferably not 
exert any tension or pressure on the float when the device is in its 
balanced position, its floating position, although a certain degree of 
influence on the float device can be tolerated, the mass of the float 
device preferably being corrected to a corresponding degree.