VENTILATION PLANT

Abstract: A ventilation plant for recovering heat from the outlet air and preheating the inlet air consists of a valve housing (10) including two fans (15, 16) for controlling the flow of air in two duct pipes (17, 18) connected to the surrounding atmosphere. An accumulator tube (17A, 18A), coupled into these two pipes, comprises a number of loosely inserted rolls (21) of pleated metal foil to achieve a great number of axial ducts communicating (24, 25) with one another at the roll ends. In one position the valve means (26) leads the inlet air through one of the duct pipes and out through an outlet (13) in the valve housing at the same time as the outlet air is led into the other duct pipe and out to the surrounding atomosphere, or vice versa.

Description: VENTILATION PLANT The present invention relates to a ventilation plant of the kind disclosed in the preamble to the appended main claim. This type " of plant is known for example from European Patent Application 0078783. The purpose of the present invention is to provide an uncomplicated ventilation plant which can be assembled from simple and relatively inexpensive components while still maintaining the efficiency of the plant at a sufficiently high level. This purpose is achieved with a plant which according to the invention has the characterizing features disclosed in the appended main claim. The heat exchangers included in the plant are duct heat exchangers representing a type of cyclically regenera- tive heat exchangers in which the heat-storing elements are alternatingly flushed through by the heating and the heated medium. Up to now, heat exchangers have been designed as chamber heat exchangers and not as duct heat exchangers. In the past, the efficiency of the chamber heat exchangers in ventilation plants could only be achieved up to an average temperature efficiency of about 80% without oppressively high costs. In the plant according to the present invention the efficiency can be considerably increased simultaneously as the aggregate can be made less space-requiring and less expensive than the existing products with lower efficiency. The chamber heat exchangers on today's market have limited heat-recovering capacity and are highly efficient only when the outlet air contains a certain excess of energy-carrying humidity, due to the fact that this surplus energy is exploited in the efficiency and that the kinetic energy of the fans is utilized in the form of excess heat. The primary reason for low temperature efficiency in chamber heat exchangers is that the accumulator packages have much too limited surface areas and that the air cannot OMPI therefore effectively be brought into heat-emitting and heat-absorbing contact with the heat-storing elements. With small accumulator surface areas the air speed is forced down in the accumulator portion in order to increase the temperature efficiency. For improving the contact between known accumulators and air, the accumulator plates have been folded to enable the occurrance of turbulent air currents despite low air speed. The low speed of the air contributes to the risk of condensate precipitation and frost formation in the accumulator at low temperatures. In addition, the possibilities of drying up the microcondensate deposited on the accumulator package are limited when dry cold air is heated and capable of taking up this moisture. One reason for having such small accumulator surfaces is the opinion that a greater mass would be required for the accumulators due to the minute-long cycling periods of the valve means in normal operation. The accumulators of the plant according to the invention are characterized in that, instead of a great mass, the accumulator has been given larger heat-absorbing and heat-emitting areas. The accumulators have been designed so as to cause the least possible degree of air turbulence at low speeds in view of the fact that the turbulence will increase with accelerating air speed in tubular ducts. In this way a satisfactory contact between air and accumulator walls is accomplished without artificially trying to create turbulence by purposely restricting the passage of air. Also, the accumulators have been given an elongated shape intended to increase the emission and absorption of heat at higher air speeds. In this way the enlarged accumulator surfaces contribute to the moisture deposit spreading over a larger area insofar this moisture is not ventilated through the accumulator package and out. Moisture deposits dispersed over a larger area as a thin film, or a smaller amount per surface unit in combination with higher air speed, will diminish the drawbacks of moisture deposit and frost formation while simultaneously lowering the costs of the aggregates by a reduced material consumption. When placed in a cold space the elongate aggregates may be affected by the exterior temperature, which may disturbingly influence the function of the aggregate. These disadvantages can be eliminated by providing a pressure, temperature and moisture equalization- in the elongate ' accumulator package. To this end the accumulator package is divided into a plurality of smaller units with intermediate gaps thus creating a passage for enabling an equalization between said divergencies in the accumulator. This measure has also led to a higher efficiency in other respects, particularly when trying to shorten the length of the elongate accumulator. The improved heat recovery has how¬ ever not caused any disturbing pressure drop. As moisture deposits primarily occur at zero and as it is essential to maintain a high air speed when this occurs, the cross- sectional area of the accumulator may be enlarged on the hot side without therefore risking any moisture problems. The portion of the accumulator package facing the heat source may therefore be given a larger cross-sectional area which is then diminished so as to enforce a higher air speed thus preventing disturbances in the form of moisture deposit and frost formation in the colder portions of the aggregate. The moisture will thereby be thrust out along with the air current to a greater extent while simultane¬ ously improving the moisture absorbing capacity when the temperature of the inflowing air is raised. In the novel accumulator construction, each accumu¬ lator element has a length of approx. 0.5 m; the entire accumulator package generally having a total length of 2-3 m. This means that the thermal conductivity resistance of the accumulator metal is so great that any accumulator partition intended to break the cold bridge is negligible and has no practical value. OMPI The essential difference is that with the inventive plant the problem to be solved does not concern the thermal conduction from the ends of the aggregate, but instead the fact that cooling/heating of the accumulator takes place 5. from, the side., which creates a difference between various portions of the transferred air. When the aggregate is placed in a cold attic for example, the temperature is lower in the peripheral ducts of the exchanger package. In order to counteract functional disturbances in the aggre- 0 gate it is therefore necessary to provide temperature, pressure and moisture equlization in the different portions of the accumulator package. According to the invention, this is avoided thus markedly reducing the risk of opera¬ tional disturbances due to moisture deposits followed by 5 frost formation in the colder portions of the package. In heat exchangers of elongate shape and which are disposed in ducts placed in cold spaces such as cold attics, the determining factor is not the axial problems of the accumulator portion but instead the freezing problems 0 occurring at right angles to the duct. These problems have been solved, according to- the invention by dividing the respective accumulator into several units. In a preferred embodiment the desired simplicity is achieved by using standardized cylindrical pipes which can 5 be cut into chosen lengths and connected to pipe bends and other attachments in a simple manner to form the duct system. Two duct pipes are connected at one end to the surrounding atmosphere and at the other end to a simple valve housing which has an inlet for relatively warm outlet 0 air and an outlet for heated inlet air. The valve housing is coordinated with two fans, and by setting a valve means in the valve housing at one or the other position of the valve means, inlet air can be made to flow into one pipe and outlet air to flow out of the other pipe, and vice 5 versa. A straight tube is coupled into each pipe, and because it comprises a number of heat-accumulating bodies it is called the accumulator tube. These accumulator bodies OMPI each consist of a roll made of thin metal plate or foil less than 0.7 mm thick,- preferably aluminium foil having a thickness of approx. 0.1 mm, said metal plate or foil being corrugated or pleated with closely lying folds having a height in the area of 2-10 mm, suitably about 4 mm. This corrugated plate or foil, together with a smooth and thin metal sheet or aluminium foil which is also suitably about 0.1 mm thick, is preferably helically wound into a roll having an outer diameter approximately equal to the inner diameter of the accumulator tube. A number of such rolls are loosely inserted one after the other into the accumu¬ lator tube, and due to their relatively short size the number of rolls can be chosen as required and the accumula¬ tor tube be cut to a length corresponding thereto. The advantage of having several short accumulator rolls of this type instead of one single long roll is that a stop or a gap is obtained at several points along the accumulator body consisting of a number of rolls. Even if the rolls abut against each other end to end, a certain radial leakage will occur resulting in a desirable distribution of pressure, temperature and humidity while simultaneously interrupting the axial thermal conduction in the metal material of the duct walls. The space between the roll ends can also be varied as desired in order to create a larger or smaller distribution chamber between the roll ends. By substituting a long roll of the type in question for a number of short rolls, e.g. three rolls in a performance test, an improved temperature efficienct by about 20 per¬ cent units was recorded at one measurement check. The short accumulator rolls also provide consider¬ able advantages with respect to storage, transport and handling. A suitable embodiment of the inventive plant is schematically illustrated in the accompanying drawing. Fig. 1 shows the plant with two duct pipes including * a coupled-in accumulator tube with a number of loosely inserted accumulator rolls, Fig. 2 shows schematicallv^-* _^ roll insertable into an accumulator tube, Fig. 3 is a schematic perspective view of the valve housing, and Fig. 4 shows a modification of the accumulator tubes. The plant comprises a valve housing 10 with four uni ormly distributed connections 11,12,13,14 of which one connection 11 forms an i let for relatively warm outlet air from a dwelling room or other location and is combined with an induction fan.15. The opposite connection 13 forms an outlet for heated inlet air blown out into the locality in question by means of a fan 16. Two duct pipes 17,18 con¬ sisting of straight cylindrical tubes and bent joints removably attached to the straight tubes are coupled to the two other connections 12,1 . The two duct pipes 17,18 are connected at their outer end portions 19,20 to the ambient atmosphere in a suitable manner (not shown) . The duct pipe 17 comprises an accumulator tube 17A coupled into the pipe, and an accumulator tube 18A is coupled into the pipe 18. The two accumulator tubes contain a number of accumulator rolls 21 performed in accordance with Fig. 2. Each roll 21 consists of a pleated or corrugated thin aluminium foil 22 with a thickness of approx. 0.1 mm and a smooth aluminium foil 23 with a thickness of approx. 0.1 mm. These foils are rolled up into the illustrated roll thereby forming a great number of axial ducts having a large total heating area. The length of the roll is relatively short and suitably between two and three times the diameter of the roll. In the embodiment shown, four rolls 21 are inserted into each accumulator tube 17A and 18A, but the number of rolls can be greater or less owing to the circumstances. As indicated in Fig. 1 the rolls may lie in abutment end to end which however provides a leakage gap 24 between the ends; or the ends may lie more or less spaced apart to form a wider gap 25. In both cases the thermal conduction is interrupted along the total accumulator body formed by the rolls 21 , and simultaneously a radial communication between the axial ducts is obtained at each joint or gap, which results in the desired distribution of pressure, temperature and humidity. In this way the temperature efficiency of the plant is considerably increased in rela¬ tion to an embodiment in which the number of separate rolls has been replaced by one single long roll. The valve housing comprises a valve means 26 which can be set at two different end positions. In the illust- rated position, outlet air is sucked in and blown out through the pipe 18 to the surrounding atmosphere after the outlet air having heated the rolls 21 in the accumulator tube 18A, while at the same time inlet air is sucked in through the pipe 17 and absorbs heat from the rolls 21 in the accumulator tube 17A before the inlet air thus heated is blown out through the outlet 13 and into the room or the like. By resetting the valve means into its opposing end position, the air flow conditions will be reversed. As described above, the structural feature of the plant is extremely simple and can therefore be manufactured at a relatively low cost. The valve housing including the fans has a simple design, and the rolls insertable into the accumulator tube can also be manufactured in a simple and inexpensive way. The tubes and tube joints are standardized products which can be cut to chosen lengths and mounted in desired positions for individual adjustment to existing localities. The modification of the accumulator tubes 17B and 18B, shown in Fig. 4, consists of a tube 27 of larger dia- meter and a tube 28 of smaller diameter, the two tubes each containing a pair of accumulator rolls 29 and 30. Due to the larger diameter of the rolls 29 on the hot side of the tube, the air resistance and pressure drop will be lower in this section of the accumulator tube. When the air is cooled, the water resolved in it is set free and forms a condensate which is led off more effectively by accelerating the air speed, and this is achieved in the constricted section 28 of " the accumulator tube, i.e. in the tube 28 with the rolls 30. This embodiment is preferred when it is desired to avoid in the best way possible the disadvantages which may arise from moisture deposits at low air speeds. With this modification it is possible to reduce the total air resistance and pressure drop'which would otherwise restrict the air flow through the plant and also create a need for fans of larger dimensions. OMPI

Claims: CLAIMS 1. Ventilation plant for the recovery of heat or cold in the outlet air and for preheating the inlet air to dwelling * rooms or- other heated localities such as workrooms, cowsheds, basements, foundations, cold-stores and the like comprising a duct system which includes at least two straight tubes connectible with other tubes or bent tube joints or other couplings for forming the duct system, a valve housing with valve means in combination with one or more fans controlling the flow of relatively warm outlet air through at least one heat-absorbing heat accumulator in one duct pipe of the duct system during the passage of relatively cold inlet air through at least one heat-emitting heat accumulator in the other duct pipe of the duct system for a predetermined period of time, the air flow in the duct system thereafter being exchanged by timed resetting of the valve means, characterized in that each of the duct pipes (17,18) includes at least one removably connected accumu¬ lator tube (18A,17A; 18B,17B) containing two or more accumulator bodies (21,29; 30) inserted into the tube, the total length of the accumulator bodies in each duct pipe exceeding 1 m; that each accumulator body has a cross section adapted to fill up each accumulator tube; that each accumulator body consists of a great number of axial ducts with a cross-sectional area corresponding to diameters of 2-10 mm and which are placed in the folds of a pleated metal foil having a thickness of less than 0.7 mm, prefer¬ ably a pleated 0.1 mm thick aluminium foil, and a flat foil of equal thickness so that, in cross section, the accumu¬ lator will present pleated and flat * foils in alternating layers on top of each other to form grooves between the folds and the flat foils on either side of the pleated foils; that the ends of the accumulator bodies facing each other are more or less spaced in relation to one another for providing a leakage gap thereby equalizing the pressure, temperature and humidity in the air passing throug accumulator; and that said period of time for the valve means at either position lies within the range of 20 to 620 seconds. 2. Ventilation plant as claimed in Claim 1, characterized in that said accumulator tube is assembled from one duct having larger cross-sectional area and one duct having smaller cross-sectional area, the wider end of the accumulator tube being connected to the valve housing (10); and that the larger tube (27) comprises accumulator bodies (29) filling the tube in cross section, whereas the narrow tube (28) comprises accumulator bodies (30) filling this tube in cross section. UREA T _ OMPI ^ 7 - WIPO J !

Inventors: THUNBERG SVANTE, THUNBERG, SVANTE
Applicants: THUNBERG SVANTE, THUNBERG, SVANTE
Application year: 1983
Main classification: F28D17
IPC codes: F24F7, F24F12, F28D20, F28F1