FR2565337A1 - DEW POINT REFRIGERANT - Google Patents

Abstract

THE REFRIGERANT IS OUTSTANDING IN THE FACT THAT THE MEANS FOR INTRODUCING WATER INTO THE TUBES FROM ABOVE AND FOR FORMING A FILM OF WATER ON THE INTERIOR WALL OF THE TUBES ARE SUITABLE FOR PROVIDING PERIODICALLY AND IN THAT , ON THE OUTER PART IN CONTACT WITH THE PRIMARY AIR, THE TUBES ARE PROVIDED WITH ELEMENTS, AND IN THAT THE RELATIONSHIP BETWEEN THE EXTERNAL SURFACE AND THE INTERIOR SURFACE OF THE TUBES PROVIDED WITH ELEMENTS IS SUPERIOR A3: 1.

Description

-1-

Dew point refrigerant.

  This invention relates to a dew point refrigerant for cooling an air stream, said refrigerant comprising a heat exchanger with a) a battery of vertical tubes arranged to let the primary air to cool along the outside of the tubes with heat exchange; b) means for passing the precooled secondary air through the interior of said tubes; c) means for introducing water into said tubes from above and for forming a film of water on the inner wall of the tubes; d) means for evacuating the humidified secondary air; and e) means for passing at least part of the air

  primary cooled in a space to be cooled.

  A similar dew point refrigerant is known per se from US Pat. No. 4,023,949. In this patent, it is proposed to condition the air (cool) of a space by cooling the primary atmospheric air in this way and by leading it to the space concerned, and at the same time passing a secondary air stream (already having approximately the desired temperature) through the heat exchanger with water evaporation, so that the primary air stream either cooled. -2- A similar principle, but of a slightly different construction, is disclosed in U.S. patents 1,986,529; 2,107,280; 2,174,060; in the german patent

  2,432,308 and in the Netherlands Patent Application 7,711,149.

  These principles differ slightly from each other in the construction of the heat exchanger used (tube bundle or plates as heat exchange surface), and in the way in which the evaporation of water is produced. in the secondary stream (a mist of water droplets, a wall surface retaining water, alternatively by supplying water to two halves of the heat exchange plates, or by

  applying continuous watering).

  In each of these methods, the secondary circuit is humidified and cooled to a temperature lower than that of the primary current by evaporation of the water. Due to the resulting temperature difference, the secondary current is capable of receiving heat from the primary current, which is thus cooled. As a result of this heat absorption, the secondary current is no longer saturated with water vapor, so that a new quantity of water can be evaporated and a new quantity of heat can be absorbed from the primary current, etc. As a result of the cooling of the primary stream, the temperature of the primary stream decreases, while the absolute humidity of this air stream (in grams per kilo of air) remains constant. -3- Since, as a result of resistance to heat flow, tangible heat transfer between the primary air stream and the secondary air stream requires a temperature difference between the two streams, and as this difference temperature is obtained by humidifying the secondary air stream which, in a preferred embodiment of the invention, is a partial stream of the primary stream and has an inlet temperature equal to the outlet temperature of the air stream primary, the outlet temperature of the primary air stream that can be obtained is most often higher than the dew point of the air in the primary stream. It is only in an ideal case that the outlet temperature of the primary air can be equal to its dew point. This is at

  the origin of the name "dew point refrigerant".

  This method of air cooling is cheaper than that using more mechanical refrigerant.

  current, because the latter consumes much more energy.

  Some of these publications further state that the water content of the cooled air can be reduced by subjecting some or all of the stream of cooled primary air exiting the heat exchanger to subsequent cooling using a mechanical refrigerant, in order to condense part of the water vapor. This cooling

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  Combined can be advantageously used when the atmospheric air has a higher absolute humidity than is desirable in the cooled air. In this case, too, there is a significant saving, since the mechanical coolant need only be used when necessary to lower the absolute water content. In all other cases, only dew point refrigerant is used.

much cheaper.

  Despite these important and obvious advantages, such a dew point refrigerant, to the knowledge of the applicants, has never been used in practice, whether on a small or

on a large scale.

  We never gave a reason for that. It is obvious, however, that a dew point refrigerant can only be chosen when the heat exchanger used is very efficient and, given the relatively small temperature differences between the air streams, which must necessarily be

  production, this is achieved only with a large exchange surface.

  In all the cases reported in the publications, the proposed heat exchanger has an effective surface on the side of the primary current which does not differ essentially in dimensions

  of the effective area on the side of the secondary current.

  In these circumstances, the volume of the heat exchanger

  heat will in most cases be far too high.

  Furthermore, it has been found in practice to be extremely difficult, if not impossible, to produce a secondary current saturated with water vapor. Such a current has of course the

  lowest secondary temperature.

  An object of the present invention is to provide a dew point refrigerant with which a

  optimal cooling using a compact construction.

  For this purpose, the dew point refrigerant defined in the introductory paragraph of this is characterized, according to the invention, in that the means referred to in paragraph c) are adapted to supply water periodically and that, on the outer side coming into contact with the primary air, the tubes are provided with elements, and that the ratio between the outer surface and the inner surface of the tubes

  fitted with elements is higher than 3: 1.

  It was surprisingly found that, given the combination of the measures taken according to the present invention, these

objectives were achieved.

  These and other features will emerge

  of the description which follows and, to fix the subject of the invention,

  without however limiting it, in the accompanying drawings, FIG. 1 is a vertical cross section of an embodiment of the dew point refrigerant according to the present invention; -6- Fig. 2 is a diagram illustrating the use of dew point refrigerants forming part of an air conditioning installation; Fig. 3 is a diagram showing the use of a dew point refrigerant forming part of another air conditioning installation; Fig. 4a shows a plan view of a tubular plate as it is preferably used according to the present invention; Fig.4b is a cross-sectional view of part of a tubular plate as shown in fig. 4a, also showing a shape of a collar as used according to the present invention, and indicates the manner in which the collars fit into each other .; Fig. 5 is an exploded view of the heat exchanger used in a preferred embodiment of the present invention; Fig.6a shows a water dispenser as used in a preferred embodiment of the present invention, in partial section; Fig.6b shows a cross-sectional view of the water dispenser, considered along line IIIb-IIIb of fig. 6a Fig.6c shows a top view of the water dispenser illustrated in fig. 6a; -7- Figs. 7a and 7b show a water supply means as it can be used according to the invention; Figs. 8a, 8b and 8c show a variant of water supply as it can be used according to the present invention, and FIGS. 9 to 11 show yet another means of water supply used in combination with a water collecting device and water distributor such that

  can be used according to the present invention.

  Figure 1 is a vertical sectional view of a dew point refrigerant. On it, a plurality of sections of vertical tubes are designated by the reference 3. The primary current 1 enters these sections on the left and passes through them successively in the horizontal direction. The secondary current (wet) enters the device in the upper right corner, then flows down through the tubes of the section located on the far right, as indicated by the arrows 2, then passes successively through the tubes of the other sections, after which this current leaves the device in

the upper left corner.

  The water to be evaporated is lifted from the containers 4 (fig. 1) situated below the sections, by means of pumps 5, towards the devices 16, after which the water passes through the tubular plates 7 situated at the upper end , plates provided -8- with a vertical rim. On these tubular plates, the water is distributed over the tubes by water distributors 13, in such a way that the interior wall of each tube of a section is covered with a layer of water along which passes the secondary air flow (up or down) with water evaporation, the necessary heat of evaporation being removed from the primary current in contact with the outer wall of the tubes and the fin plates. The non-evaporated part of

  the water is returned to the containers 4.

  The origin of the primary current depends on how the dew point refrigerant is included in the

air conditioning system.

  In a simple embodiment, the primary stream can be composed of the air taken from outside, which is then cooled in the heat exchanger, and transferred

  in a space to cool on the right side of fig. 1.

  To maintain the desired temperature in this space, part of the air present in the space, for example% per hour, is continuously evacuated and used as a secondary current 2. During the passage through the different sections 3, the water evaporates, and at the same time this secondary current absorbs the heat of the primary current, and it follows that the temperature of the secondary current increases as the primary current is cooled. It is this significant increase in temperature which allows the evaporation of an increasing amount of water in the secondary stream, so that ultimately a stream of highly humidified air s' escapes on the left side, at a temperature higher than the temperature in the space to be cooled. This highly humidified air is not able to be

  used in this cooling process.

  It is very important, however, that in the cooled primary stream the amount of water vapor is not changed as it passes through the heat exchanger. Good heat exchange requires that heat is first transferred from the primary (dry) current to the wall (usually metallic). The amount of heat transferred is then directly proportional to the product l1F1, where F1 is the heat transmission area and A1 the transmission coefficient. When this amount of heat has passed through the material of the separation wall, the same amount of heat must be transferred from this wall to the secondary current (wet), and the amount of heat transferred is then directly proportional to (2F2, o , again, F2 is the heat transmission surface and a2 the transmission coefficient - 10- We know from Leidenfrost, W. Analysis of the cooling with evaporation and increase in the efficiency of the capacitors and the efficiency coefficient, transmission of heat and matter 12 (1979), pages 5 to 23, that in the case of the transmission of heat from a wall to a current of air, in the presence of a film of water which evaporates on this wall , the coefficient of heat transmission is a multiple of the coefficient of heat transmission which occurs by transfer with convection on the same wall. Leidenfrost describes a minimum ratio of 3 in the case of saturated air, and more than 5

in the case of unsaturated air.

  Aside from the difference in convective heat transfer in the flows inside tubes and in the flows around tubes (with fins), it would be necessary, on the basis of the above, to use a heat exchanger heat in a dew point refrigerant according to the present invention, of the type referred to in the introductory paragraph of this document, in which the ratio between the dry exterior surface and the wet interior surface is

greater than 3: 1.

  One condition for this is that the heat exchange surface on the side of the secondary air stream is always

  covered with a thin layer of water.

  As the ratio C2 / e1 depends on the state of the primary air on arrival, the aim will be to ensure that -11- F1 / F2 get closer to î2 / 1 'The value of the ratio between the surface outer and inner surface of the tubes will be located

preferably between 5: 1 and 10: 1.

  As the external surface value, the effective external surface can be used which can be calculated using the published formulas for the construction of tubes

fitted with elements.

  All of the above publications regarding dew point refrigerants agree that an F1 / F2 ratio little or not at all different from 1: 1 is described. This is probably the reason why none of these proposals

  has only led to practical applications.

  When we study a heat exchanger in which F1 / F2 is of the order of 6, we note that, for an equal capacity, it is enough that the volume is from 1/3 to 1/4 of the volume of a

exchanger in which F1 = F2.

  To produce the necessary difference in the exchange surface, it is possible, in a manner analogous to that of known construction methods, to start with tubes on which fins have been mounted, after which these fin tubes are combined to form larger units, for example fin batteries. Known exchangers of this type are usually constructed to give considerable pressure differences between the two streams of heat exchange gas. In a dew point refrigerant, this

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  -12- pressure difference is at most only a few mbar and

  this allows for a very light construction.

  The usual method of construction of fin batteries is as follows: In metal plates, for example aluminum plates with a thickness of 0.2 to 1.0 mm, holes of 0.25 mm are punched out by example, which most often have a collar. The fin plates are then placed on inner tubes, and these tubes are mechanically or hydraulically expanded, so as to fix the fins on the tubes. These tubes fitted with fins are then mounted on

  conventional tubular plates.

  This construction can also be used in

the present case.

  However, the heat exchanger preferably consists of a plurality of plates having a row of openings, each opening having a flange connection inside an opening of an adjacent plate, the plates being stacked with so as to form a package in which the collars together constitute a plurality of tubes interconnected by the rest of the plates serving as fins. The openings in the flanges can actually have a diameter of 20 to 40 mm, and the height of the

  flanges can be 4 to 7 mm.

  -13- For construction reasons, the shape of the holes is most often round. It was found that a diameter of 30 mm

  and a 6 mm flange height were very effective.

  When the flange is properly formed, each flange can be placed in the underlying tubes over about half their height, as shown in Figures 4a and 4b. The inner tubes are then no longer necessary and the combination of tubes and fins can be produced at a much lower cost and in a more compact form. In the text which follows, the word tube should be interpreted as being a "tube" constituted by such collars partially mounted one inside the other. When the flanges can be slid into each other by applying only low pressure, a simple but robust construction can be obtained, in which the different sections of tubes are in contact with sufficient sealing of a

surface on the other.

  The tubes, whatever their design, must allow to receive inside a thin layer of water, this layer should if possible cover the entire wall of the

  tube and to be as regular as possible in thickness.

  In addition, all tubes must naturally be wetted to the same degree. The water supply system must therefore not be sensitive to a misalignment or to a disturbance of the water level at the top of the tube plate located

at the upper end.

  The above U.S. Patent 2,107,280 proposes to use

  plate heat exchangers covered with fabric on the wet side.

  He mentioned that better results are obtained if water is not supplied continuously, but periodically. A construction such as that described in this patent has the disadvantage that the surface of the plates is covered with a wet cloth which, although it can be wet uniformly, nevertheless offers greater resistance to heat flow than

  does a film of water applied directly to the metal.

  In a preferred embodiment of the dew point refrigerant according to the present invention, means are provided for using part of the cooled primary air.

like secondary air.

  It is also possible to use means for humidifying the secondary air stream before it is supplied to the secondary side of the tubes. Appropriate means ensure the direct evaporation of water in the stream. Of

  examples are a wet carpet or a curtain of water.

  More particularly, the humidification means are present at the "reversal point", that is to say in the secondary current, once the cooled air has been subdivided

  in primary current and secondary current.

  It has been found, and this is another characteristic -15- of the invention, that the distribution of water can be done effectively by placing a water distributor at the top of each vertical tube (FIGS. 6a - 6b - 6c), consisting of two concentric short tubular parts (30, 32), the inner part 30 of which extends inside or around the tube, where it is tightly fixed, while the outer part is supported on the tubular plate located at the highest part and has on its lower rim one or more openings 33 extending in the annular space 31 formed between the two tube parts, the internal part 30 being provided with a plurality openings 34 spaced around its circumference, communicating the annular space 30 with the interior of the tube, and spaced at a certain distance above the dew plate. These openings 34 distribute the water supplied along the circumference of the tube. The gas flow through the tube can then escape or enter through the inner tube portion. It is preferable to plan a part 35

  funnel-shaped at the top of the inner tube.

  These water distributors according to the invention have the advantage

very low pressure drop.

  As shown in FIG. 1, as in the known dew point refrigerants, one or more containers 4 for the water to be evaporated are provided below the tube bundle 12, in which the non-evaporated water is collected. , and from which water is supplied to the plate

  upper tubular 7 supporting the water distributors 13.

  This tubular plate is provided with a vertical rim.

  Although Figure i shows a concrete embodiment with 4 sections of tubes, it is obvious that it is also possible to use any number of sections, and that the primary current 1 and the secondary current 2 can pass through. a number of different sections as required. When the tube bundle is made up of a plurality of sections, 3, 3, successively crossed by the secondary stream 2, it is useful for each section to have its own container 4, because the sections correspond to different temperatures of the secondary stream. The level in the tanks can be kept constant in a conventional manner. The primary current 1 is then passed between the plates to

the outside of the tubes.

  So that water periodically feeds the upper tube plate, that is to say during the correct period, with a correct quantity of water, at the correct frequencies, we

  can use different devices.

  The simplest possibility is a pump started and stopped in a known manner. Such switching systems are, however, likely to fail. The aforementioned U.S. Patent 2,107,280 describes an apparatus with a double tilting trough. This system works satisfactorily, but has the disadvantage of having moving parts, so that it is subject to wear and does not work.

  reliably for long periods of time.

  According to the present invention, the preferred system is a self-starting siphon system.

  The principle of such a system is given in Figure 7.

  The tank R is filled with a continuous water supply, for example by means of a pump which supplies the water from a container 4 placed below the tubes concerned. As soon as the water in the tank reaches level 1, the siphon H starts

  initially to function as an overflow only.

  However, the siphon is provided with a rebound dam D, which causes the water flowing from the bottom of the siphon H to flow against the upper part of the siphon, thereby closing the volume of air located above it. above the bouncing dam. Due to the relatively high speed of the water, the pressure of the jet on the rebounding dam decreases and, consequently, the air escapes from the upper part of the siphon. As a result, the siphon quickly fills with water to reach the situation shown in Figure 7b. From this moment, the siphon fills quickly and completely, after which the discharge of water through the siphon increases rapidly to reach its maximum. This discharge lasts until the tank R is emptied to level 2, so that the air can again enter the left side of the siphon, and the water supply to the

tubes is stopped.

  In this way, an amount of water determined by the dimensions of the tank R can be supplied at regular intervals. Experiments have shown that in some cases the siphoning time was too long, so that the correct ratio between the siphoning time and the

cycle period.

  Indeed, as indicated above, there is in the siphon a rebound dam D. This has the effect of expelling air, so that the siphon starts quickly and easily, but at the same time the dam D can form a obstacle to the exit, after starting the siphon, so that it obstructs

the flow of effluent water.

  For this reason, in a preferred embodiment of the invention, there is mounted next to the small siphon B or above it (see FIGS. 8a, 8b and 9), a second larger siphon A, the outlet is in the water, or in which a water lock is provided at the outlet, as shown in Figure 8. The large siphon has a slightly higher top than the top of the small siphon, so that the small siphon B is at

  self-priming, while the big one is not.

  -19- The large siphon does not have a rebounding dam. The small siphon starts as described above, but, in addition, ensures the evacuation of the large siphon mounted next to it, or above it, by one or more passages, for example, the passages V shown in Figure 8c, so that the large siphon starts as quickly. Due to the large outlet diameter without a rebounding dam which would present an obstacle, the discharge capacity of siphon A is such that we reach

a short discharge period.

  In summary, the essential characteristics of the described combination of a large (main) siphon A with a small siphon B (auxiliary) are that the small siphon is used primarily to start first and then to start the large siphon . The discharge of water through the small siphon is of secondary importance. The large siphon, on the other hand, is designed to allow the discharge of a large amount

  water for a limited period.

  The discharge of water for a short period is important, because it is necessary to periodically pour such a large amount of water into the (wet) tubes of the heat exchanger, that in all the tubes the whole wall is wet in

  same time to form the desired water film.

  -20- During the humidification period, the normal air flow in the tubes with heat exchange with a secondary current is not possible for a short time; it is only after a normal heat exchange can continue. Due to the periodic water supply, not only the film of water is maintained, but at the same time all

  dust and deposits are removed from the wall of the tube.

  So that the water can be distributed over the tubes as regularly as possible, the water is not poured directly into the tubes, but for example onto an upper tubular plate 7 provided with a vertical edge (see FIG. 1). From the tubular plate, the water flows between the various water distributors 13 and rises in the space formed between the internal part and the external part of the tube of the water distributors. Due to the resistance to flow in this space, each tube can receive only a limited amount of water which is distributed along the circumference of each tube through the openings 34 (see Figure 6). taken the desired amount of water, the water level on the tube plate decreased and fell below the edge of the openings 34, so that there is no more water admitted into the tubes until 'at the next water supply. -21- In practice, the dimensions of the small siphon will be chosen so that it is activated by the applied water supply, and the large siphon so that the tank is emptied in less than 10 seconds, and preferably in About 5 seconds. Due to the high speed of water exit from the large siphon, there will in practice be an excess of water at a point (depending on the position of the siphon outlet above the tube plate), and c This is why the water will find its way above the tube plate. The result of excess water is that the rows of tubes in the immediate vicinity will receive excess water, while the rows of tubes further away will receive too little. It was found that it was good to collect the water from the siphon in a trough (10, FIG. 10) provided with a narrow outlet orifice 11 below the water along a

edge of the tube plate 12.

  When the main siphon (figure 9) has started, it will fill the trough 10 in the first case (figure 10) up to the overflow 13. When the level of the overflow has been reached, the water begins to overflow and is distributed over the entire length of the tube plate. As the outlet 11 is very narrow, while the instantaneous supply of water by the main siphon is very important, the water will rise to a higher level in the trough, a phenomenon which is accompanied by an increase in the thrust on overflowing water. This causes the air present at the head of the overflow to be discharged downwards, so that the overflow will function as a perfect siphon. The result is that, in addition to a regular distribution of the outlet water along the length of the tube plate, the intermittent effect of the main siphon is reinforced. The final result of the described combination of a water tank fitted with a main siphon and an auxiliary siphon on the one hand and the water collecting trough with split outlet on the other hand , is that all the tubes in question are

  perfectly humidified in 3 to 4 seconds.

  The dimensions of an auxiliary siphon determine the minimum water flow required to activate the siphon. The volume of the tank is then determined according to the

desired cycle period.

  With regard to the water collecting trough, the siphon is actuated above a given (instantaneous) flow. In practice, with the dimensions of the water collecting trough as it is used in dew point refrigerants, this flow is of such a size that it is impossible to use a collecting trough. water as a stable water metering device with the appropriate cycle period, the period

  outlet and the correct amount of effluent.

  -23- For large installations with a proportionately larger water dosage, the main and auxiliary siphons coupled in the above described combination of a tank with coupled main and auxiliary siphons and the water collecting trough, can be replaced by an overflow pipe (vertical) extending to the highest level necessary in the tank and are covered (for example by a bell) so that water can enter the overflow pipe - full below the rim of the bell (see Figure 11). The overflow pipe should form a water lock in the water collecting trough. The tank is filled with a continuous stream of water. As soon as the water passes from the tank into the overflow pipe, the water collecting trough is filled with the same stream of water, and the water level increases both in

  the collecting trough and at the outlet of the overflow pipe.

  As soon as the collecting trough has started its siphon action, the water level in the collecting trough decreases, and

  at the same time the level decreases at the outlet of the overflow pipe.

  As a result of this drop in level, the air present in the overflow pipe and in the bell moves downward. As the pressure in this volume of air is constant, the water is brought back into the bell, after which the overflow pipe -24- starts to function as a siphon. The rest of the air in the overflow pipe is then discharged, so that the tank empties with the full capacity of the siphon until the air enters the overflow pipe at the bottom edge of the pipe. The best results are obtained with the combination described above when the dimensions of the water collecting trough are such that the current of water discharged by the siphon of the collecting trough is equal to the water current supplied by the siphon overflow pipe is slightly larger so that the two siphons finish their

  operating at about the same time.

  In large air conditioning systems, the space charge is covered by recycling the air in space, air which is cooled in one or more air handling units, while fresh outside air required is either packaged in separate processors and then transferred to the main recycling system, or

  mixed directly with recycled air.

  With these fresh air treatment devices mounted with a refrigerant in accordance with the present invention (dew point refrigerant) in combination with a complementary mechanical cooling system, it is possible to design air treatment devices. recirculation air without mechanical cooling and fully cover the main space charge by means of a dew point refrigerant

according to the present invention.

  The present invention also relates to an air conditioning apparatus for a space, apparatus comprising a first section in which the temperature and the water content of the outside air are adjusted to the desired value, and the air thus treated is transferred into said space, a second section in which the air present in the space is recycled, and the temperature readjusted to the desired value, the major part of the recycling air being brought back, and a minor part of it ci being discharged, the apparatus being characterized in that, in said first part, the outside air is cooled in a dew point cooler in accordance with the present invention and, if necessary, the temperature and / or the rate are reduced humidity of said air to the desired values by mechanical cooling, and in a second part, the cooling operation is carried out with a refrigerant

  dew point according to the invention as indicated above.

  Such a system is illustrated in Figure 2.

  The invention also relates to an air conditioning apparatus for a space, apparatus comprising a section in which the temperature and the water content of a mixture of air present in said space and outside air are adjusted to the desired values, the major part of the mixture being recycled and a minor part of it being discharged, said apparatus being characterized in that part of the cooling process in said section is carried out using a point-point refrigerant dew of the type defined above, after which, if necessary, the temperature and the water content of the air

  are reduced to a lower value in a known manner.

  An overview of the energy savings to be achieved with these two embodiments is given in the following example, in which the two types of air conditioning apparatus in question are compared with an apparatus using a

  mechanical cooling only.

EXAMPLE

  We start from an office space to be subjected to air conditioning with heat production (space load) of 100 kW, a quantity of recirculating air of 000 m / h and a minimum quantity of fresh air of 15% of the air

recycling.

  Based on the comfort diagrams taken from the publications (Recknagel, Taschenbuch fur Heizung und Klimatechnik, Oldenburg Verlag, Munich 1974), the desired office space conditions are 25 C / 45%. The state of the outside air (= fresh air) is assumed to be 30 C / 50% -27- It is assumed that no water vapor is produced in the space reserved for the office (humidity level absolute x = constant). The recycling air flow is 30,000 m 3 / h, i.e.

  36,000 kg / h; the mass flow is therefore 10 kg / second.

  The heat production is 100 kW (space charge). Increase in enthalpy = 10 kJ / kg; this corresponds to an increase in temperature of 10 C. As a result, the air inlet temperature of the enclosure must

be 15 C.

  Method 1: mechanical cooling only (comparatively) The fresh air and the recycled air are mixed before passing through the cooling unit. Consequently, the mixture consists of 85% of air from the enclosure at 25 C / 45% and 15% of fresh outside air at 30 C / 50%. The enthalpy of the mixture is hM = 51 kJ / kg. The air condition at the inlet is 15oC / 85% with an enthalpy of h = 38 kJ / kg. The decrease in enthalpy by cooling is 13 kJ / kg. The mass flow rate of the mixture m m is 10 kg / second. The cooling capacity required

is then of q1 = mm (ah) = 130 kW.

  Method 2: Cooling by dew point refrigerant of the main charge and combined cooling of fresh air by dew point refrigerant and mechanical refrigerant (Figure 2) Based on the experiments carried out with a test device of the refrigerant dew point, it was found that it was possible to cool an air stream to a temperature below 1.50C of the corresponding temperature

  measured with a wet tank thermometer.

  It follows from these data that, in this example, the charge of the enclosure can be entirely covered by cooling by dew point refrigerant. The decrease in enthalpy is 10 kJ / kg. We also know that if we properly adjust the ratio of mass flow rates between primary air and secondary air, the difference between the inlet temperature of the primary air and the outlet air temperature

  saturated secondary can also be kept at 1.5 C.

  The enthalpy increase of the secondary air is then - 38 = 32 kJ / kg, so that the ratio of the mass flows must be 3.2, that is to say that the air flow secondary in the main dew point refrigerant is 1 x 36,000 = 10,800 kg / h. 3.2 This quantity must be supplied to the circuit in the form of fresh air. This fresh air (outside) initially at 30 C / 50% is also cooled by a dew point refrigerant until 21 C / 85% is obtained and is then cooled.

mechanically at 15 C / 85%.

  The decrease in enthalpy during this mechanical cooling is hC hI = 56 - 38 = 18 kJ / kg, the mass flow rate of this fresh air is m = 10,800 kg / h -29- = 3 kg / second. The cooling capacity q2 = mv (h) = 3 x 18 = 54 kW. Expressed in percentages of cooling capacity required according to method 1, this gives 54

x 100% = 41.5%.

  Statistical data on the situation in the Netherlands shows that, every year, for 27 hours, we have the

  same absolute humidity as in the example above.

  For 22 hours of this time, 210 C / 85% can be obtained by cooling with dew point refrigerant. This means that the calculated 54 kW of cooling capacity is required for 22 hours each year only and that, with the exception of 14 additional hours, the rest is sufficient

to use less energy.

  It is therefore significant to introduce the term "cooling in degrees per hour" here. This term is defined as the product of the number of hours during which a certain quantity of air must be cooled to reach a given situation and a range of temperatures in centigrade over which such cooling takes place. It is a measure of the amount of energy required for such cooling. Using the statistical data above, it can be calculated in the above manner that the conditioning of the office enclosure, in our example, by method 2, requires

  3,720 degrees / hour of cooling per year.

  -30- Recknagel, in its publication cited above, specifies, for cooling method 1, an amount of 8,175 degrees / hour of cooling per year. In method 1, the number of degrees / hour of cooling is applicable to 15% of 36,000 kg / h = 5,400 kg / h, while the rest, i.e. 600 kg / h, must be cooled by 10 C for one approximately 3.5 months during the cooling season, during office hours (8 am to 6 pm). This total number of coolings (about 1000) corresponds well to the figure 10 found in Figure 10 for air temperatures above C. This number is 1015, so that the number of degrees / hour of cooling is 10 150. In Method 2, the calculated number of cooling degrees / hour applies to

800 kg / h only.

  Consequently, the cooling energies Q1 and Q2 to be used in the two methods per year have the following ratio between them: Q 3 720 x 10 800 -: z - = O, 11 Q1 8 175 x 5 400 + 10 150 x 30 600 0.11 This means an energy saving of 89% in the method of

  proposed cooling according to this invention.

  Note: this example does not take into account that with outside atmospheric conditions not as extreme as C / 50%, which occur more frequently, the cooling requirements of the enclosure will be lower. In the tables

  given by Recknagel, these influences have been taken into account.

  -31- In summary, we can say that, in the cooling method 2 proposed here: 1. The cooling capacity to be installed can be reduced to around 40% of that which is obtained in the case of fully cooling mechanical, 2. The number of hours at full load of this reduced cooling installation is, at worst, in the Netherlands, hours per year,

  3. Energy savings of almost 90% are achieved.

  Method 3: combined cooling by dew point refrigerant and mechanical refrigerant of a mixture of recycled air and fresh air (Figure 3) Naturally, it is also possible to have a mixture of air first enclosure and fresh air that is passed through a dew point cooler, after which this mixture is mechanically cooled. The principle of cooling by dew point refrigerant implies that the mixture must be composed of approximately 70% of the air of

  the enclosure and about 30% of the fresh outside air.

  The enthalpy of the mixture is h = 53 kJ / kg. Cooling to a temperature of 1.5 C above the corresponding temperature measured with the wet tank thermometer means

  cooling to 17 C (with an enthalpy h = 44 kJ / kg).

  The decrease in enthalpy is then 9 kJ / kg.

  On the basis of the final temperature of 250C to -32- obtain, (i.e. 1.5 C below the temperature of the mixture), the increase in enthalpy of the secondary air stream

is 76 - 44 = 32 kJ / kg.

  The ratio of mass flow rates between the primary and secondary air streams must be ni mm / m2 = 32/9, so that mni2 = 0.28 mm (as a result, the mixing ratio of 70% / 30% s turns out to be correct). The difference between mmni and m2 is the amount of recirculated air and, therefore, is equal to 36,000 kg / h, so that mm- m2 = (1-0,28) mmni = 36,000, hence it follows that

  we have nim = 50,000 kg / h and m2 = 14,000 kg / h (see Figure 12).

  Following cooling by dew point refrigerant, the mixture of enclosure air and fresh air reaches the condition of 17 C / 85%. To produce the inlet condition of 15 C / 85%, this quantity of air (36,000 kg / h or 10 kg / second) is then mechanically cooled. The resulting enthalpy decrease is 44 - 38 = 6 kJ / kg. The mechanical cooling capacity then becomes:

q3 = 10. 6 = 60 kW.

  The cooling capacity expressed in percentages, in method 1, is as follows:

60. 100% = 46%

  In the same way as in Method 2, in this example, 1,852 degrees / hour of cooling were calculated, applying to 36,000 kg / h of air. The mechanical cooling energy required on an annual basis Q3 is related to -33- that obtained with method 1 as follows Q3 1 852 x 36 000 019 - = 8 175 x 5 400 + 10 150 x 30 600 Q1 In this method also, the energy saving is considerable (more than 80%). Compared to method 2, the energy saving in method 3 is a little less spectacular, it is true, but on the other hand, method 3 makes it possible to realize considerable savings in capital investment, because it n there is no separate point refrigerant

dew for fresh air.

  Finally, we observe that, when dew point refrigerants are used, it must be taken into account that the energy required for transport is a little higher, firstly because in addition to the useful air , it is necessary to suck in an amount of air to be used after cooling as a secondary stream, and secondly because the pressure drops in the heat exchanger described are higher than those

  we have in conventional refrigerants.

  The construction of the cooling device according to the present invention is extremely suitable for use as a recuperator in winter. The fresh air supplied circulates around the tubes, while the air from the spent enclosure passes through them. In this way, if necessary, the condensed water can descend along the inner circumference of the tubes.

  and be collected in the planned collecting trough.

  In addition, the humidification device allows regular washing of the tubes to remove adhering dust.

on these.

  When working in recovery, the mass ratio between the two air flows is in principle equal to 1. Due to the increase in surface area by means of the fins on the dry side of the heat exchanger, the transmission coefficient heat, calculated on the surface of the tubes, is mainly determined by the heat transfer coefficient of the wet side (= interior surface) and numerically is approximately equal to this. With the large participation of the heat exchanger tubes, this leads to a high total heat transfer, so that the efficiency of the exchanger

can reach 80 to 90%.

-35-

Claims (11)

  1. Dew point refrigerant for cooling an air stream, said refrigerant comprising a heat exchanger provided with a) a bundle of vertical tubes arranged so as to allow the passage of primary air to cool along the outside of said heat exchange tubes; b) means for passing the precooled secondary air through the interior of said tubes; c) means for introducing water into said tubes from above and for forming a film of water on the inner wall of the tubes; d) means for discharging the humidified secondary air; and e) means for passing at least part of the cooled primary air through an enclosure to be cooled, characterized in that the means mentioned in c) are adapted to supply water periodically, and in that, on the outer side, in contact with the primary air, the tubes are provided with elements, and in that the ratio between the outer surface and the inner surface of the tubes provided with elements is greater at 3: 1.   2. Dew point refrigerant according to claim 1, characterized in that the ratio between the external surface and -36-   the inner surface of the tubes is from 5: 1 to 10: 1.   3. dew point refrigerant according to claim 1 or 2, characterized in that the heat exchanger comprises a plurality of horizontal plates provided with a row of openings, each opening comprising a flange connection fitting in a opening of a neighboring plate, the plates being stacked so as to form a bundle, in which the collars jointly constitute a plurality of tubes in   communication by the rest of the plates, serving as fins.   4. Dew point refrigerant according to the claims   1 to 3, having a water supply with periodic operation, characterized in that the water supply comprises a water tank which, in operation, is filled practically continuously, and a self-priming siphon   for periodic discharge of the contents of the tank.   5. Dew point refrigerant according to claim 4, characterized in that the reservoir is provided with two siphons, the first of which is self-priming, and by the fact that, when priming occurs, this siphon sucks air from the second siphon   larger, thus activating the second siphon.   6. Dew point refrigerant according to claim 4, characterized by an elongated container placed below the outlet of the siphon, said container being provided on one side with a siphon whose inlet and outlet extend along d '' a lateral surface of the upper tube plate transversely to the air flow direction -37-   secondary above said tubular plate.   7. Water dispenser suitable for a dew point refrigerant which is the subject of any of the   Claims 1 to 6, characterized in that it comprises two   concentric tubular elements, the inner tubular element being able to extend inside or around a tube, and being able to be fixed thereon in a leaktight manner, the external element being able to be supported on a tubular plate, and being provided at its lower edge with one or more openings extending in the annular space formed between the two tubes, the inner tube having an opening or a plurality of openings spaced around its circumference, connecting the annular space with inside the tube.   8. Dew point refrigerant which is the subject of one   any of claims 1 to 6, and further comprising a   water dispenser according to claim 7.   9. Installation of air conditioning for an enclosure, said installation comprising a first section in which the temperature and the water content of the outside air are adjusted to the desired value, the air thus treated passing into the enclosure to be cooled, and a second section in which the air present in said enclosure is circulated and the temperature of which is adjusted to the desired value, the major part of the air in circulation being recycled, and a minor part of that -this being evacuated, -38- characterized in that, in said first section, the outside air is cooled in a dew point refrigerant   forming the subject of any one of claims 1 to 6 or 8   and, if necessary, the temperature and / or the humidity of this precooled air is then reduced to the desired value by mechanical cooling, the cooling process in the second section being carried out by a point cooler   dew that is the subject of any of claims 1 to 6 or 8.   10. Air conditioning installation for an enclosure, said installation comprising a section in which the temperature and the water content of a mixture of air present in said enclosure and of the outside air are adjusted to a desired value, the major part of said mixture being recycled, and a minor part of it being discharged, characterized in that, in said section, at least part of the cooling process is carried out by a dew point refrigerant which is the subject any one   claims 1 to 6 and 8, after which, if necessary,   reduces the temperature and the water content of the air in a known manner. 11. Dew point refrigerant substantially as described herein with reference to the accompanying drawings, as well as the example given.