CA1047825A - Apparatus for limiting the outgoing air flow in natural ventilation systems - Google Patents

Abstract

CANADIAN PATENT APPLICATION
OF
OLOV RAGNAR LENNART ERIKSSON
FOR
APPARATUS FOR LIMITING THE OUTGOING AIR FLOW IN NATURAL VENTILA-TION SYSTEMS.

Abstract of the Disclosure This invention relates to a natural ventilation system for buildings and comprises for use at an outlet portion of a venting duct a movable duct closing means and a temperature sensing means which is connected to operate said duct closing means and is mounted to be exposed to prevailing temperature and wind conditions in the atmosphere outside the venting duct as well as to at least a portion of the outgoing air flow in the venting duct to be actuated thereby and accordingly to operate the venting duct closing means, whereby the sensing means will operate so as to a) gradually close the venting duct closing means at increasing wind force, b) gradually open the venting duct closing means at decreasing wind force, c) gradually close the venting duct closing means at increasing flow of outgoing air and increasing outdoor temperature, and d) gradually open the venting duct closing means at increasing flow of outgoing air and increasing outdoor temperature.

Description

~(~47~25 Tllis irlvention relates to an apparatus for limiting the outgoing air flow in natural ventila-tion systems of buildings.
In dwellinys and other premises a not insignificant natural ventilation occurs by the pene~ ation of ou-tdoor air through cracks especially around windows and doors an~ by the exhaust of this air as draught -through outgoing air ducts, usually from kitchens, water-closets and bathrooms. ~ very great percentage of the e~tant housing, int. al. practically all 1~ detached houses, have natural ventilation systems of this type.
When the outdoor temperature is low and in particular if a wind is blowing at the same time, natural ventilation will be strong and result in grea' heat losses, unless the outgoing air ducts have draught limiting devices for counter-acting this increase in natural ventilation, which is unnecessary and uneconomical from the point of view of ventilation. It is certainly true that natural ventilation can be limited in win-ter by manual stepwise or complete shutting of the dampers, if any, in the individual rooms of the dwellings, but this method is impractical and too coarse. It results in either too ample or too meagre a ventilation. The regulation of the dampers can not become economically efficient unless it is continuously adapted int. al. to weather variations that may occur in the course of the day.

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.' ~, .-~, :. , -lV4~825 It is ~rue that it has already been suggested to place in an outgoing air duct a temperature sensing means having a sensitive element whlch by changing ils dimension or configu-ration at temperature variations in the ambient air gradually closes or opens a damper so that the amount of outgoing air can be controlled to some eY~tent. It has also been suggested to place the temperature sensing means at the outlet of the outgoing air duct so that the temperature of the outdoor air will become a factor which may affect the dimensional or con-figurational conditions of the sensitive element and its abi]i-ty to close and open a damper in the outlet.
It has proved, however, that these apparatuses for limiting the amount of outgoing air do not provide any actually energy-saving draught in the natural ventilation system. When the out-door temperature is low and a wind is blowing much more air will be exchanged than at the same low temperature and in calm weather. In dwellings ventilated by natural draught the ventila-tion losses during the cold ~ime of the year are approximately one third of the total heat losses. It is therefore highly de-sirable to be able to limit the amount of outgoing air to the same extent as the wind increases. The prior art temperature sensing means in ventilation systems are temperature sensitive but do not simultaneously record outdoor air velocity changes.
In a cold day with a strong wind blowing the ventilation losses will therefore be unreasonably great in a conventional natural ventilation system even if some of the prior art tem-perature sensing and damper closing apparatuses are utilized -' . , ' ' . . ':
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in the outlet of the outgoing air duct.
It is highly desirable to be able to limit the ventilation in cold weather also for the reason that indoor air humidity would other,lise fall to unsanitarily low values. Present-day low air humidity in dwellings during the heating season is experienced by many people as inconvenient. The unusually great exchange of warm air by cold air highly contributes thereto. After being heated to room temperature the originally cold air will have an uncomfortably low relative humidity. The IG greater the change of air allowed in cold weather the drier the air in the house.
A third weather factor of importance apart from outdoor temperature and wind force, is the intensity of radiation. For instance at heavy solar radiation the indoor temperature will increase in spite of the cold outdoor temperature. It would then be suitable to increase the amount of outgoing air per unit of time. ~Iowever, a prior art type of sensitive element in the outlet of the outgoing air duct, which mainly senses only the cold outdoor air, will not diminish natural draught limitation in the requisite degree, from which follows an un-comfortably high indoor temperature and poor ventilation.
At heavy thermal radiation, "cold radiation", for instance during a cold winter night, increased throttling and reduced ventilation are desirable.
~ pparatuses capable of maintaining, automatically and by volume, the amowlts of incoming air and outgoing air constant ~ ~ -per uni~ of time, are of course conceivable. However, no appa-ratus of simple design and satisfac-tory function has hitherto been developed and proved specifically suited for the large number of ex~ant houses with natural ventilation. The introduc-tion of, for instance, considerably more expensive mechanical ventilation systems, possibly combined with heat recovery units, require much space and the houses into which such systems are installed, must be extremely well-insulated. The air movements necessarily produced by the mechanical ventilation imply highly IG increased risks for heavy leakage and great heat losses.
If the ventilation losses could be better restricted, particularly in very cold weather, it would be possible to make considerable gains in installation and energy production costs.
It is a well-known fact that the installation and energy pro-duction units of a house must be dimensioned for but a few days per year that require specially great heat quantities. By restricting the very high ventilation losses during these days radically the installation and energy production units could be given small dimensions. This would imply lower installation costs for both individuals and society.
A general object of the present invention is to provide a simple mechanical apparatus which senses the temperature, wind force and possibly thermal radiation, "cold radiation", of out-door air and which automatically limits the change of air in a house having natural ventilation to an economically and physio-logically reasonable level irrespective of variations in these parameters.

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1~47825 A special object of the invention is, particularly during the cold time of the year, to keep the change of air in natural ventilation at an acceptable level w:Lth regard to both the temperature variations of the outdoor air and the prevailing wind conditions, and also at an acceptable level when solar radiation is intense and the indoor temperature rises, which is a particularly difficult problem in otherwise cold weather.
More precisely, the object of the invention is automatically to control the amounts of outgoing air according to both in-significant and heavy variations of the outdoor climate, whichmeans both outdoor temperature and wind force but also heat and cold radiation intensity so that a satisfactory as well as an economical ventilation can automatically be maintained also under highly varying circumstances.
It has now surprisingly been found that the object of the invention can be attained with the aid of a simple apparatus in - the outlet duct of a natural ventilation system. The apparatus according to the invention controls, as do prior art temperature - sensitive air flow controlling devices to some extent, the flow of outgoing air in the outlet duct of the system. The appa-ratus according to the invention comprises a damper in the outlet duct, an operating means which is connected to the damper and can be for instance rotary or displaceable and in the form of a shaft, by means of which the damper can be gradually opened and closed, and a temperature sensitive element which is adapted heavily to expand or contract at small temperature changes and is stationarily arranged on the operating means of A

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3~0478~:5 the dam~er i.n order by the action of said operating means to real.ize gradua] closing or opening of the damper by dirnensional or configurational changes of the sensiti~e element at temperature variations.
Particularly characteristic of the apparatus according to the invention is that 1) the sensitive element is located out-side the outlet duct and exposed to the prevailing ou'cdoor . temperature and wind conditions, and 2) the outlet duct has openings which deflect part of the warm outgoing alr towards 1~ the sensitive element. Said part of the warm outgoing air and the prevailing cold wind thus simultaneously influence the sensitive element but to a varying extent owing to the wind force and the temperature and velocity of the outgoing air.
When a strong wind is blowing the temperature effect the wind exerts on the sensitive element will predominate, and when a weak wind is hlowing the effect of the warm outgoing air. With strong, cold winds the damper is closed more than with weak winds of the same temperature since in the first case the part flow of warm outgoing air is not given the opportunity of heat-ing the sensitive element so much as it is capable of doing in the second case. The result will thus be that the heat effect exerted by the warm outgoing air on the sensitive element de-creases at increasing wind force and increases at decreasing wind force, and that the damper is gradually closed at increas-ing wind force and gradually opened at decreasing wind force, or gradually closed at decreasing outgoing air temperature and/or outdoor temperature and gradually opened at increasing outgo~ng - . : . : , .
: , ~ ' ' ~ ' 1()47~;~5 air temperatuxe and/or outdoor temperature.
In a pr~ferred cmbodiment of the apparatus accordiny to the invention the sensitive element is a temperature sensitive bimetal strip in the shape of a sinyl~ helix. The helix is arranged at the outer wall of the out1et duct and exposed to wind and weather. Its one end is fixedly anchored to the wall of the duct and the other end to a shaft which turns a damper disposed in the in~erior of the duct for limiting the outgoing air when the helix is turned by the action of outdoor air and the part flow of outgoing air exiting from holes in the duct in the vicinity of the helix.
In another preferred embodiment of the apparatus accord-ing to the invention the sensitive element is a temperature sen-sitive bimetal strip in the form of a single helix of small diameter, which in turn is shaped into a coil of large diameter so that a double helix sensitive element is obtained. This bimetal construction is of heavily varying dimensions in the axial sense. This feature is exploited in this second preferred embodiment in order, at falling temperature, to displace a shaft with a damper disposed thereon so that the damper is gradually closed. The double helix itself can also function as a shaft, which gives a very simple construction. In that case the sensi-tive element and the control means are united in one and the same movable detail. The double helix shoula suitably be placed in upright position in a housing which is formed with wind openings and in which the double helix can slide vertically as its diameter varies while the housing should be placed coaxially . .

lV4~825 on the ve~rticall~ directed outlet of the outgoing air duct so that the double helix can open and close a damper connected therewith and coaxially arranged in the duct. A part flow of the warm out~oing air is conducted through the housing of the bimetal element while the rest of the outyoin~ air flows away around the housing. At increasing wind force -the part flow of warm outgoing air will have the opportunity to a diminishing extent of keeping the double helix at a temperature deviating from that of the outdoor air, which results in that the double helix gradually expands or contracts depending upon how the he-lical shape of the bimetal strip has been realized, and in that the damper is gradually closed if the outdoor air is cold.
In a further emhodiment of the apparatus according to the invention the sensitive element comprises a stack of washer-shaped bimetal elements. At rather insignificant variations of temperature the stack of bimetal elements will experience heavy length variations in axial direction and pulls or pushes its coaxial axis so that a damper fixedly connected thereto in the outlet duct is gradually closed when the wind increases and/or the temperature of the outdoor air falls.
- In a specifically preferred embodiment of the invention the housing of the bimetal element may be combined with a top wall member for the vertical outlet duct. Said top wall member covers the outlet of the entire outgoing air duct, is preferably slightly sloping and protrudes over the edges of the duct out-let so that the outgoing air will be caused to flow substantially horizontally out of the outlet duct. Such a further improvement - :
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of the apparatus according to the inv~ntion results in an i,n-creased capability of the apparatus to control the amount of outgoing air. With the aid of the sloping top wall member a correction can he made for the heat radiation and "cold radiation", respectively. If the sloping top wal] member moreover is made from a heavily radiation absorbiny/emitting sheet material or provided with a surface coat of this type, said capability is further increased. The pa-^~, of the wind that possibly penetrates beneath the top wall member and flows together with the part 1~ flows of outgoing air upwardly in the housing, is heated and therefore does not cool the l~imetal element to the same extent as ~oes a non-heated air ~luantity, or is coolcd and therefore cools the bimetal element in a greater degree than wind that has not been cooled. An improved effect is thus obtained in cold windy and overcast weather as well as in warm sunny and windy weather. The "cold radiation" towards the sloping sheet metal top wall member cools the warm outgoing air flow and said flow will have a higher temperature effect on the bimetal element than an outgoing air controlling apparatus without such a top wall member. The colder the weather, the greater the inten-sified effect resulting from the reverse radiation ("cold radia-tion"2 which is obtained by the described top wall member since natural ventilation has a tendency of growing exponentially as the outdoor temperature falls and since the combined effect of outgoing air and incoming air on the bimetal element is advan-tageous for draught control.

1~47B~5 ~ mbodiments of the inven-t:loll will be described in more detail hereinbelow with reference to -he accompanying drawinys in which Fig. 1 is a schematic view illustrating the function of the apparatus;
Fig. 2 is an axial section of a particularly preferred embodiment of the apparatus, which includes a temperature sensitive element in the form of a double helix bimetal strip in a housing having a slopiny top wall member at the outlet end 1~ of the housing;
Fig. 3 is a fragmentary cross-sectional view taken on the line III-III in Fig. 2.
Fig. 1 illustrates a natural ventilation system in which the apparatus according to the invention is installed in the outgoing air duct 1 of the system, the outlet end of said duct being designated 2, and in which a damper 3 is provided near the outlet. A temperature sensitive element 5 is arranged on the outer side of the duct 1 outside the damper 3, thus at or in the vicinity of the outlet end 2. The sensitive element 5 is adapted to operate the damper via a shaft 4 connected thereto by rotary or possibly shifting movement in dependence on tempera-ture changes acting upon the element 5. The damper is thus adjustable in the duct 1 for regulating the flow of outgoing air into ambient air. The sensitive element 5 shall thus be adapted to operate the damper 3 for reduction of the cross-sectional area of the duct 1 when the temperature falls, and vice versa.

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The outgoing air 7 flows towardc the clam~er 3 in the duc 1 but before it reaches the damper 3 one or more part flows 7a are deflected ~rom the main flow 7 through one or more openings 6 to actuate the sensitive element 5 thermally. Of the main flow 7 there only rernains the flow 8 which is led into ambient air at the outlet end 2. The wind factor is represented by the arrow 9. The stronger the wind, the more rapidly will the out-going air flow 8 escape as a flow 11 in the wind direction. In windy weather the warm part flows 7a are also affected. The 1~ sensitive element 5 is thus exposed both to wind and t~eather and to the part flow 7a. The stronger the wind, the lesser possibility have the part flows 7a of heating the sensitive element 5. The part flows (or flow) then do not reach the sensitive element to the same extent as in calm weather but are mixed by wind actuation with the outdoor air and are more or less deflected, from which results a lesser actuation of the sensitive element. The arrow 10 represents some of the outgoing part flow. This implies that the stronger the wind in cold weather, the colder the sensitive element 5, and the more will the sensitive element 5 turn or push the connecting element 4 and thus the damper 3 to such positions that the outgoing air will be given a limited possibility of flowing through the outgoing air duct 1. The tendency of an increase of the out-going air flow 7, 8, 11 at increasing wind force in cold weatller ar.d the resulting poor heat economy of the natural ventilation system aréthus corrected or reduced automatically by the appara-tus according to the invention.

~0478Z5i In a preferred embodiment of the apparatus the sensitive element 5 is a temperature sensitive bimetal strip shaped into a single helix. The helix is arranged at the outer wall of the outlet duct 1 and is exposed to wind and weather. One end there-of is fixedly anchGred to the wall of the duct while the other end is rota-tably mounted on a shaft 4. A rotary damper in the duct 1 is operated in dependence of the twist of the helix via said shaft 4 by the action of outdoor air 9 and the part flow 7a of outgoing air exiting in the vicinity of the hellx through the duct openings 6.
Figs. 2 and 3 show a specifically preferred embodiment of the invention, which can be influenced also by heat radiation and "cold radiation". This apparatus includes a temperature sensitive element S in the form of a double helix. The double helix 5 is made from a bimetal strip which has been formed into a single helix of small diameter which in turn has been formed into a single helix of larger diameter, for which reason the term "double helix" for the element 5 is entirely adequate. To wind bimetal strips into such double helic2s is previously known. Depending upon the manner in which the double helix is wound it will expand or alternatively contract when heated.
The embodiment illustrated in Fig. 2 operates on the lastmentioned principle which means that the double helix 5 when cooled closes the damper 3 which in its fully closed position bears against a sealing edge 15.
With the use of a double helix made according to the firstmentioned alternative, that is, of opposite movement with -' ' ~ -,. .. . . . . . .

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regard to the case illustrated, the sealing edge 15 shall be - placed above ~he damper 3 so that the iatter upon closure approaches said sealing edge.
If desired, the sealing edge 15 can be movable so that it can be set into such a position that some ventilation is obtained through the duct also at fully closed damper. The sealing edge r~ also be arranged in another manner for attain-ing this result. At severe cold or when a strong cold wind i 9 blowing the ventilation in normally insulated dwelling-houses is fully satisfactory through existing leaks, for which reason the damper 3 can be fully closed in these circumstances.
The double hel.ix is placed in a housing 16 formed with several ventilation openings 16a at the outlet end of the duct 1 and is fixed at its upper end to the roof 16' of the housing 16 and with its lower L-shaped end portion, which forms a motion transmitting member 4, connected to the damper 3. The double helix thus in an integral piece forms both the temperature sensitive element 5 and a damper operating means 4. A guide sleeve 6a formed with slots or openings 6 is secured to the damper 3 at. the point of fixation of the damper 3 to the end portion 4 of the eIement 5. Said guide sleeve is arranged to slide in a guide 13 in a top wall element 12 which is disposed over the outlet of the duct 1 and is fixed to the duct, forming a supporting means for the housing 16 in which the bimetal helix 5 is placed.
Warm outgoing air 7 flows towards the outlet end 2 of the outgoing air duct 1. The amount of outgoirlg air 7 is determined - . ' ,': : ' ~, .:,- , ~V47825i by the gap between the damper 3 and the sealing edge 15. Part of the warm outgoing air 7 is conducted in the form of part flows 7a through the openings 6 of the guide sleeve 6a (cf.
Fig. 3) and in an upwar~ direction in the housing 16 and there forms a heat addition which toyether with the outdoor air in the housing imparts to the bimetal helix 5 a certain temperature and resulting ïength expansion and to the damper 3 associated with the bime:tal helix 5 a definite position in relation to the sealing edge 15.
I~ A certain temperature condition in the housing 16 results in a definite gap between the damper 3 and the sealing edge 15.
The major portion of the outgoing air flow 7 escapes as flows 8 through this gap and through the main ventilatlon openinys 17 spaced around the outlet end 2 of the duct 1. The part flows 7a successively escape as part flows 10 through the ventilation openings 16a of the housing 16.
By wind influence and by the successive increase of the wind 9 from zero successively changing flow conditions arise, these conditions being exemplified hereinbelow by three phases designated A, B and C. Each of said phases gives an increased and intensified cooling of the bimetal element 5 with resulting ever more decreasing flow of outgoing air.
A. The ~ore the wind increases from zero the lesser possi-bility have the part flows 7a of outgoing air to deliver their heat addition to the bimetal element 5 since said part flows escape ever more early and rapidly as part flows 10 in the dlrec-tion of the wind 9.

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B. At a ~ind force of cercain s-trength some part flows 9a of outdoor air besides penetrate through the main ventilation openings 17 and mix with the part flows 7a of outgoiny air, and depending upon the wind force, said part flovJs 9a wholly or part-ly pass upwardly through the housing 16 in the same way as the earlier part flows 7a of outgoing air alone, in order to acutate the bimetal element 5 therein. ~y the admixture of the cool part ~lows ga of outdoor air in this manner the heat actuation of the bimetal element 5 will be even somewhat lower and as a con-sequence the flow of outgoing air will be reduced as compared to that prevailing in calm weather and in case A above.
C. According as the wind force increases the majority of the warm part flows 7a of outgoing air disappear in ever earlier stages. With very strong winds no warm part flows 7a of outgoing air at all reach the bimetal element 5 but blow away in the direction of the wind 9, escaping directly into ambient air like the flow 11. The result is that the stronger the wind the bi-metal element 5 is cooled to an ever increasing extent and that as a consequence the outflow of outgoing air will be successively reduced, this being the aim contemplated.
The third weather factor, radiation, influences the appa-ratus according to the invention in the following manner.
The influence of radiation may be considered as an intensi-fying effect which is superimposed on earlier temperature and wind influences. The radiation (represented by arrows 18) is directed respectively towards the top wall member 12 and the housing 16 upon influence of solar radiation, and from the top 1~4782S
wall memlber upon influence of "co]d radiation" i.e., heat radia-tion frorn the top wall member, particularly against a dark sky The top wall member 1~ above the duct 1 and the housirg 16 are of such a material and/or so surEace-treated as to be heavily radiation-absorbing or heavily radiation-emitting.
Upon incidence of solar radiation 18 towards the radiation-/ absorbing top ~;all member 12 the part flows 7a of outgoing air and possibly the part flows 9a of outdoor air will receive a heat addition when they pass beneath the slightly sloping top l~ wall member 12 on their way up in the housing 16. This implies a larger heat actuation of the bimetal element 5 with an ensuing increase of flow of outgoing air. Since the housing 1~ also is radiation-absorbing this will entail an additional heating of the bimetal element 5 directly and as a function of the intensity of solar radiation. That the amount of outgoing air per unit of time thus increases with the intensity of the solar radiation 18 is desirable from the viewpoint of ventilation and can be allowed also at a relatively low outdoor temperature, since the room temperature would otherwise be uncomfortably high because of the absorbed solar radiation energy of the building, primarily directly through the windows. The heat amounts absorbed and stored in the walls etc. of the building, which later, in hours of unintensive sun, emit a desired heat addition are not affected by the embodiment of the invention comprising a bimetal element in the form of a double helix. The night following upon a clear sunny day is often clear and cool with intensive "cold radiation"
whereby the double helix will be heavily cooled in a correspond-, , .
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' ~04`78;~5 ing degree since the top wall member 12 and the housing 16 alsoare heavily radia-tion-emitting.
An excess temperature, if any, which has arisen for various reasons in the building implies an increase of the outgoing air flow and temperature as well as higher temperatures of the part flows 7a of outgoing air, which will thus be capahle of heat-\ ing the double helix 5 in a higher degvte, entailing adesired increase of ventilation.
In a further embodiment of the apparatus according to the l~ invention the sensitive element 5 comprises a stack of washer-shaped bimetal elements (not shown), said stack heavily varying in axial length at rather insignificant temperature variations and being adapted to operate a damper or like means in the duct 1 on the same principle as that described with reference to Figs. 2 and 3.
Some further positive effects and system alternatives will now be described.
A thorough sealing of such ordinary paths of heat leakage in buildings as are formed for instance by cracks around windows and doors, is not a sufficient measure to prevent heat losses by natural draught. If the most usual paths of heat leakage are sealed the draught may increase through other leakage paths, and for an efficient saving of energy a satisfactory sealing should be supplemented with a positive control of the ventila-tion systems in conformity with the invention. A well-sealed building equipped with means for natural ventilation and an automatically operating control apparatus according to the '- . . . .
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invention will provide an optimum ecoromical result as the con-trol takes place with due regard to a]l important factors, such as indoor temperature, outdoor temperature, wind force and radia-tion conditions and as the apparatus according to the invention is ine~pensive and can be incorporated without any great costs in ordinary natural ventilation systems.
The invention is applicable also to such prior art systems of mechanical ventilation as are designed for intermittent operation to prevent unnecessary heat losses. In those cases 1~ the mechanical ventilation can be caused to operate only during the periods when considerable ventilation is required. During the intervening periods of natural ventilation the apparatus according to the invention can be utilized also in such a mecha-nical system. During the forced ventilation periods when the ventilators of the mechanical system are in operation the heavy air flow will cause the apparatus according to the invention to open fully. Said apparatus thus automatically adapts itself to the operation of the ventilators of the mechanical system ~nd opens the ventilation duct, and then,that is, during the standstill periods of the ventilators, it controls the ventila-tion duct in the manner described.

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for controlling the flow of air in the venting duct of a natural ventilation system, comprising a movable duct closing means in the venting duct, a motion transmitting device for operating the duct closing means in the duct and for con-trolling the cross-sectional area of the duct, and a temperature sensing means including a sensitive element which is adapted heavily to react to small temperature changes and fixedly con-nected with the motion transmitting device to gradually close or open via said device the duct closing means in the duct in dep-endence on the temperature reactions of the sensitive element, wherein the sensitive element is disposed outside the venting duct so that it is exposed to the prevailing outdoor temperature and wind conditions, and the venting duct has openings for deflecting a part flow of outgoing air into contact with the sensitive element so that both said part flow of outgoing air and said wind of outdoor temperature are allowed to actuate the sensitive element, the arrangement being such that the actuation of the sensitive element by the part flow of outgoing air decreases at increasing wind force and the sensitive element will thus operate so as to a) gradually close the venting duct closing means at increasing wind force, b) gradually open the venting duct closing means at decreasing wind force, c) gradually close the venting duct closing means at increasing flow of outgoing air and decreasing outdoor temperature, and d) gradually open the venting duct closing means at decreasing flow of outgoing air and increasing outdoor tempera-ture.

2. An apparatus as claimed in claim 1, wherein the sensitive element is a single helix of a bimetal strip which is adapted via the motion transmitting device, for instance a shaft, gradually to close or open the duct closing means in the venting duct at varying wind and outdoor temperature conditions outside the venting duct.

3. An apparatus as claimed in claim 1, wherein the sensitive element is in the form of a double helix which consists of a bi-metal strip formed as a single helix from which is formed a helical coil body, and said body is adapted to operate the duct closing means for gradually closing the duct when the wind increases and when the temperature of the outdoor air falls.

4. An apparatus as claimed in claim 1, wherein the sensitive element is a stack of washer-shaped bimetal elements, said stack being adapted to push or pull a motion transmitting device coaxial with the stack so that the duct closing means in the venting duct is gradually closed when the wind increases or when the temperature of the outdoor air falls.

5. An apparatus as claimed in claim 1, for controlling the amount of outgoing air flow according to the temperature, wind and radiation conditions prevailing outdoors, wherein the apparatus comprises a top wall member having a central opening and being coaxial with the venting duct and spaced some distance therefrom, the motion transmitting device and the sensitive element fixedly connected to said device being slidable in said opening coaxially with the venting duct, and a housing accommodating the sensitive element formed with venting slots, said housing being fixedly connected to the top wall member and having a longitudinal axis parallel with the longitudinal axes of the venting duct and the sensitive element and substantially coinciding therewith, the openings of the venting duct being formed by openings in the motion transmitting device, and wherein the top wall member has radiation-absorbing and radiation-emitting surfaces so that part flows of outgoing air and part flows of outdoor air possibly penetrating beneath the top wall member can be mixed, heated or cooled by the radiation and can enter, in greater or lesser amounts depending upon prevailing wind conditions, through the openings of the motion transmitting device flowing in an upward direction in the housing in which the sensitive element is accommodated and which also has radiation-absorbing and radiation-emitting surfaces to actuate the sensitive element thermally.