DE3519694A1 - Dew point cooler - Google Patents

Description

The invention relates to a dew point cooler for cooling an air flow, the cooler having a heat exchanger with the following Share has:

a) a package of vertically arranged tubes, on the outside of which primary air is to be cooled with heat exchange strokes along;

b) Means for passing through pre-cooled secondary air through the inside of the tubes;

c) Means for introducing water into these tubes from the top and for forming a water film on the inner wall of the tubes;

d) means for removing the humidified secondary air and

e) Means for introducing at least part of the cooled primary air into a room to be cooled.

A similar dew point cooler is known per se from US Pat. No. 4,023. This patent suggests a space by air conditioning (to cool) that primary air from the atmosphere is cooled in this way and into the room concerned is conducted and that at the same time a stream of secondary air

(which has almost the desired temperature) with evaporation of water is passed through the heat exchanger, so that the primary air flow is cooled.

A similar principle, but in a slightly different construction, is shown in US Pat. Nos. 1,986,529, 2 107 280, 2 174 060, DE-OS 24 32 308 and the Dutch Patent Application No. 77 11 149 disclosed.

These known devices differ slightly from one another in the construction of the heat exchanger used (Tube package or plates as heat exchange surface) and in the way in which the water evaporates in the secondary flow lets (a mist of water droplets, a water-retaining wall surface, alternating supply of water to two Halves of heat exchange plates or continuous spraying of water).

In each of these known methods, the secondary stream is humidified and below the temperature by evaporation of water of the primary stream cooled. Due to the resulting temperature difference, the secondary current is in the Able to absorb heat from the primary current, which is thereby cooled. As a result of this heat absorption, the secondary current again unsaturated with water vapor, so that a further amount of water can be evaporated and another amount of heat can be consumed by the primary current, etc.

As a result of the cooling of the primary stream, the temperature of the primary stream falls, while the absolute humidity of it Air flow (in grams per kilogram of air) remains constant.

Since, as a result of the heat flow resistance, the exchange of sensible heat between the primary and the secondary Air flows require a temperature difference between these two flows, and there is this temperature difference

is brought about by humidifying the secondary air flow, which in a preferred embodiment of the invention is a partial flow of the primary flow and then has an inlet temperature which is equal to the outlet temperature of the primary air flow the initial temperature of the primary airflow that can be reached is much higher than the dew point the air in the primary flow. Only in the ideal case can the outflow temperature of the primary current must be equal to the dew point. This gives rise to the name "dew point cooler".

This method of air cooling is cheaper than using the more common mechanical cooling unit because this requires a lot more energy.

Some of the aforementioned publications also mention that the cooled air can be given a lower water content by having some or all of the cooled Primary flows coming from the heat exchanger are given a subsequent cooling treatment with a mechanical cooling device can be so that part of the water vapor condenses will. This combined cooling can then be used with success when the atmospheric air has a higher absolute Has moisture content than is desired in the cooled air. In this case, a remarkable saving can be made can also be achieved, since in fact the mechanical refrigeration machine only has to be used when necessary is to reduce the absolute water content. In all other cases only the much cheaper dew point cooler will be used used.

Despite these clear and great advantages, such a dew point cooler is to the knowledge of the applicant has not been used in practice in either a small or a large version.

A reason for this was never given. It is clear, however, that a dew point cooler can only be used if a very efficient heat exchanger is used, and this can only be achieved with a large heat exchange surface are in view of the relatively small temperature differences between the air currents that are necessarily must occur.

In all cases in which this is reported in the literature, the proposed heat exchanger turns out to be such that it an effective surface area on the side of the primary flow whose size does not depend significantly on the effective surface area on the side of the secondary flow deviates. Under these circumstances, the volume of the heat exchanger becomes prohibitively large in most cases.

In addition, practice shows that it is extremely difficult, if not downright impossible, to produce a secondary current, which is saturated with water vapor. Such a stream naturally has the lowest secondary temperature.

The object of the invention is to create a dew point cooler with which a the best possible cooling can be achieved.

This object is achieved with a dew point cooler of the type explained in more detail with the invention in that the means mentioned at the beginning under c) are suitable for periodically supplying water, and that the tubes on their outside, that comes into contact with the primary air, are provided with elements and that the ratio of the outer surfaces to the inner surfaces of the pipes provided with the elements is greater than 3: 1.

Surprisingly, it has been found that the aim set by the combination of these measures is achieved according to the invention can be.

The invention will now be described in more detail with reference to the accompanying drawings using examples. It shows:

Fig. 1 shows an embodiment of a dew point cooler according to of the invention in a vertical cross-section,

2 is a diagram illustrating the use of dew point coolers as part of an air conditioning system,

3 is a diagram showing the use of a dew point cooler as part of another air conditioning system represents

4a shows a tubular plate, as it is preferably used in the invention, in plan,

FIG. 4b shows a part of the tubular plate shown in FIG. 4a in cross section, which also shows an embodiment of the collar shows how it is used with the invention and which indicates the manner in which the collars fit together,

5 shows the heat exchanger as used in a preferred embodiment of the invention, in an exploded perspective view,

6a shows a water distributor as used in a preferred embodiment according to the invention is, in a side view and partially in section,

6b shows the water distributor according to FIG. 6a in a cross section along line VIb-VIb of FIG. 6a,

6c shows the water distributor according to FIG. 6a in a top view,

Figure 7a

and 7b water supply devices as can be used in the invention, in a vertical position Cut,

Fig. 8a,

8b and 8c another water supply device, which is used in

of the invention is useful, and

Fig. 9

to 11 still other devices for supplying water in connection with a water collection and distribution device, as useful in this invention.

Fig. 1 shows a vertical cross section of a dew point cooler, in which several sections of vertically arranged Tube packages are designated by 3. The primary flow 1 enters these sections on the left-hand side and flows through them one after the other in the horizontal direction. The (wet) secondary stream enters the device at the top right corner, then flows downward through the tubes of the rightmost section, as indicated by the arrows 2 is, and then successively through the tubes of the other sections, whereupon this secondary flow the device at the top left corner.

The water to be evaporated is from containers 4 (Fig. 1), which are located under the pipe package sections, with pumps 5 to Devices 16 raised, from where the water on the upper

most pipe plates 7 is passed, which are provided with an upstanding edge. The water wilds with them on these tube plates Water distributors 13 distributed over the pipes in such a way that the inner wall of each pipe of a section with a Water layer is covered, along which the secondary air flow flows upwards or downwards with evaporation of water, whereby the heat required for evaporation is cem primary current is withdrawn, which flows around the outer wall of the tubes and the ribbed plates connected to them. Which did not evaporate Part of the water runs back into the container 4.

The origin of the primary current depends on the way in which the dew point cooler is integrated into the air conditioning system. In a simple embodiment, the primary current can be from Consist of air that is drawn in from the outside, the air being cooled in the heat exchanger and then by the right Page of Fig. 1 is passed into the room to be cooled.

To maintain the desired temperature in this room, a part of the air present in the room, for example 10% per hour, is continuously withdrawn and used as Secondary current 2 used. During the passage of the various sections 3 water is evaporated in these, wherein at the same time this secondary flow absorbs heat from the primary flow with the result that the temperature of the secondary flow is increased while the primary stream is cooled. It is this substantial rise in temperature that makes it possible makes that more and more water gets into the secondary flow, so that finally a very humid air flow at the left end with a temperature that is higher than the temperature of the room to be cooled. This very damp Air can no longer be used for the present cooling process. However, it is extremely important that in the refrigerated Primary flow, the amount of water vapor has not changed during its passage through the heat exchanger.

Good heat exchange requires that the heat first pass from the (dry) primary stream to the (usually metallic) wall. The amount of heat transferred is then directly proportional to the product α, · F, where F, the transfer area and α, the heat transfer coefficient. When this heat has penetrated the partition, the same amount of heat must pass from this wall to the (wet) secondary flow, and the amount of heat transferred is then ^a 2 * ^F 2 directly proportional, where again F "is the heat transfer area and cc- is the heat transfer coefficient.

It is known from "Leidenfrost, W .: Analysis of Evoporative Cooling and Enhancement of Condensers Efficiency and Coefficient of Performance, Heat and Stoftransmission \ 2_ (1979), pp. 5 2 3" that when heat is transferred from one wall to one Air flow in the presence of a film of evaporation water on this wall the heat transfer coefficient is a multiple of the heat transfer coefficient that applies to the convective heat transfer on the same wall. Leidenfrost gives a smallest ratio of 3 for the case of saturated air and a ratio of> 5 for the case of unsaturated air.

Apart from the difference in convective heat transfer in streams within pipes and in streams around which (finned) pipes flow, it would flow out of the The above-mentioned reasons may be necessary in a dew point cooler according to the invention, a heat exchanger of the initially explained in more detail To be used in which the ratio between the dry outer surface and the wet inner surface is greater than 3: 1.

A condition here is that the heat exchange surface is on the side of the secondary air flow always with a: thin layer of water should be covered.

Since the ratio a "/ a, depends on the nature of the imported Depending on primary air, the goal for F, / F "will be to approach α ^ / α,. The ratio between the size of the outer surface and the size of the inner surface of the tubes is preferably between 5: 1 and 10: 1.

Since the effective size of the outer surface can be used for the outer surface, this can be calculated using published Calculate formulas for pipe structures with elements.

All of the above publications on dew point coolers agree that they describe a ratio of F _{1 / F 9} that is less than or not significantly different from 1: 1. It is believed that this is why none of these proposals have found practical applications.

If a heat exchanger is designed in which the area ratio F ₁ / F _{0 is} about 6, the result is that for the same capacity, the volume need only be a third to a quarter of the volume of a heat exchanger in which F 1 = F ₂ is.

To make the necessary difference in the heat exchange surfaces to manufacture, it is possible, analogous to known construction methods, to start with tubes on which fins or ribs are mounted, whereupon these finned tubes are combined to form larger units, for example to Rxppenrohrbatterien. Known heat exchangers of this type are usually used for remarkable pressure differences between two of their heat exchanging gas flows constructed. In the case of a dew point cooler, however, the pressure difference is at most a few mbar, and this enables a very light construction.

The most common method of building back tube batteries is the following:

x> - 3519594 1Ί

In metal plates, for example aluminum plates, with a thickness of 0.2 mm to 1.0 mm, preferably 0.25 mm, are Punched out holes, most of which are also provided with a collar. The rib plates are then placed on tube cores pushed, and these tubes are expanded mechanically or hydraulically to clamp the fins onto the tubes. These Ribbed tubes are then secured in conventional tube sheets.

This construction can also be used in the present case.

However, the heat exchanger is preferably constructed from several plates in which a field of openings is arranged, each of which has a collar which fits into an opening in an adjacent panel. The panels are on top of each other stacked to form a package in which the interconnected collars form a multitude of tubes passing through the remaining part of the plates are connected to each other, which represent the ribs or fins.

The openings in the collar can effectively have a diameter of 20mm to 40mm and the collar height can be up to 4mm 7 mm.

For structural reasons, the holes usually have a round shape. A diameter of 30 mm and a collar height of 6 mm has been found to be very effective.

When the collar is suitably shaped, each collar can be integrated into the underlying ones for about half its length Tubes are inserted, as shown in Figs. 4a and 4b. The core tubes and the combination are then unnecessary tubes and fins can be made at a remarkably lower cost and in a much more compact shape will. In the following the word "pipe" or "tube"

-μ-

be understood to include a pipe made up of such partially nested collar is made. If the collars are pushed into each other with only a little pressure a simple but still tight construction can be achieved in which the various pipe sections are in have a sufficiently close surface contact.

The tubes, regardless of how they are designed, must be provided with a thin layer of water on the inside can be, and this layer of water should cover the entire pipe wall if possible and one as much as possible have uniform thickness. In addition, all pipes should of course be moistened to the same degree. The water supply system should therefore be against a level fluctuation or disturbance of the water level on the top of the uppermost tube plate must be insensitive.

The above-mentioned US Pat. No. 2,107,280 suggests using plate-like exchangers which are on the wet side with are provided with a cloth or a covering. The patent mentions that better results can be obtained if that Water is not supplied continuously, but periodically. A construction as described in this patent has the disadvantage that the plate surface with a racial Cloth is covered which, although it can be kept uniformly wet, has an even greater resistance to heat transfer opposed to a film of water applied directly to the metal.

In a preferred embodiment of the dew point cooler after According to the invention, means are provided with which part of the cooled primary air can be used as secondary air.

It is also possible to have means for humidifying the secondary air flow before it is fed to the second side of the tubes. Appropriate means enable immediate

direct evaporation of water in the stream. Examples of this are a wet mat or a water veil.

More specifically, the humidifying means are present at the "turning point", i.e. in the secondary stream after the cooled one Air was split into a primary flow and a secondary flow.

It has been found, and this is another feature of the invention, that the distribution of water can be effectively achieved by placing on top of each vertical Pipe a water distributor is arranged (Fig. 6a, 6b, 6c), which consists of two short, concentric pipe parts 30, 32, of which the inner pipe part 30 protrudes into the pipe, where it is clamped in a sealing manner, while the outer pipe part is supported on the uppermost tube plate and is provided at its lower edge with one or more openings 33, which extend up to an annular slot 31 between the two pipe parts, of which the inner pipe part 30 with a plurality of recesses 34 is provided, which are arranged at a distance from one another on its circumference, which the annular Connect slot 30 with the interior of the tube and are arranged at a certain distance above the dew plate. These Openings 34 distribute the supplied along the circumference of the pipe Water. The gas flowing through the tube can then escape or enter through the inner tube part. Preferably a funnel-shaped part 35 is provided on the upper edge of the inner tube. This water distributor according to the invention have the advantage of a very low pressure drop.

As can be seen from Fig. 1, one or more containers 4 for Water to be evaporated is provided in which non-evaporated water is collected and from which water is transferred to the upper tube plate 7 is routed, on which the water distributor 13 is

3519894

are supported. This tubular plate is provided with a raised edge.

Although Fig. 1 shows an embodiment with four tube package sections shows, it is obvious that it is also possible to use any other number of tube package sections and that the primary stream 1 and the secondary stream 2 can also be passed through such further sections to meet the requirements to meet. If the pipe package consists of several sections 3, 3, successively from the secondary flow are traversed, it is useful if each section has its own collecting container 4, because the sections belong to different temperatures of the secondary current. The water level in the tanks can be known in Way to be kept constant. The primary stream 1 is then passed between the plates around the outside of the tubes.

In order to periodically supply the water to the uppermost tube plate, i.e. at the right time and in the right amount and in the correct intervals, different devices can be used.

The simplest option is a pump that is switched on and off in a known manner. Such switching devices are however, subject to incorrect switching. The above-mentioned US Pat. No. 2,107,280 describes a device with a double tilting trough. This device works satisfactorily, but has the disadvantage that it has moving parts so that it is subject to wear and cracks and does not work reliably for very long periods of time.

According to the invention, the preferred device is a self-starting one Lifting system.

The principle of such a system is shown in FIGS. 7a and 7b. The container R is for example with the help a pump that pumps water from the container 4 under the pipes in question, continuously filled with water. As soon the water in the container has reached level 1, the siphon H begins to act as a simple overflow. The lifter is, however, provided with a ski jump D, which the water flowing over the bottom of the jack H against the top of the siphon, which closes the air volume above the ski jump. As a result of the proportionate high water velocity, the pressure in the nozzle on the ski jump is reduced and as a result the air is drawn down from the top of the lifter. As a result, the siphon is quickly filled with water and reached the situation shown in Fig. 7b. From this moment on, the siphon quickly fills up completely, after which the Water drainage through the siphon quickly reached its maximum. This drainage continues until the container R is emptied to level 2, so that air can enter again at the left end of the siphon and the supply of water to the tubes is interrupted. In this way, an amount of water determined by the size of the container R can be in be fed at regular intervals.

Tests have shown that in some cases the siphon time was too long, so the exact relationship between the Siphon time and the working period could not be reached.

As stated above, there is actually a ski jump in the lift D present. This causes the air to be removed so that the lifter starts quickly and easily; but at the same time the dam or ski jump D in the outlet may form an obstacle after the jack has started to work, so that the dam interferes with the flow of the outflowing water.

For this reason, in a further, preferred embodiment the invention next to or above the (small) described lifter B (Fig. 8a, 8b and 9) a second, larger Mounted siphon A, which opens into water or in the outlet of which a water seal is provided, as shown in Fig. 8a and 8b is shown. The vertex of the larger lifter is slightly higher than the vertex of the small lifter, so that the small jack B is self-starting, but the larger jack is not.

The bigger lifter doesn't have a ski jump. The small lifter starts in the manner described in more detail above, but emptied now, in addition to itself, also the larger jack mounted next to it or above it, over one or more Connecting lines, for example the connecting lines V shown in Fig. 8c so that the larger jack is also started quickly. Due to the large outlet cross-section, in which there is no obstacle in the form of a ski jump is the discharge capacity of the lifter A. so large that a short emptying period is achieved.

In summary, there is the essence of the combination described of a large main siphon A with a small auxiliary siphon B in it, that the small siphon is essentially to it serves to set itself in motion first and then the big jack. The drainage of water through the small siphon is of minor importance here. On the other hand, the large jack is designed so that it is possible to use a to remove large amounts of water in a limited period of time.

Discharging water in a short period of time is important because it is necessary to periodically remove such a large amount of water to pour into the (wet) tubes of the heat exchanger that the entire inner wall made wet in all tubes at the same time to form the desired water film.

ZO

Air flow is normal during the humidification period not possible for a short time in the pipes with heat exchange to a secondary flow. Only then can normal heat exchange take place be continued. Due to this periodic water supply, not only is the water film maintained, but at the same time any dust and debris are removed from the tube wall.

So that the water can be distributed as evenly as possible over the pipes, the water is not directly into the Poured tubes, but e.g. on an upper tube plate 7, which is provided with a raised edge (see Fig. 1). The water flows from the tube plate between the various water distributors 13 and rises in the space between the inner pipe part and the outer pipe part of the water distributor. Due to the flow resistance in the gap each pipe can only hold a limited amount of water, which is along the circumference of each pipe through the openings 3 4 is distributed (Fig. 6). When each pipe has taken in the desired amount of water, the water level has on the pipe plate removed to below the edge of the openings 34 so that no more water is fed to the pipes, until the next amount of water is added.

In practice, the size of the small lifter is selected so that it is operated by the amount of water supplied while the large lifter is dimensioned so that the container is emptied within 10 seconds and preferably in about 5 seconds will.

As a result of the high speed of the water outlet from the large siphon, the water rises in practice at a point that is from the position of the siphon outlet above the tube plate depends on where the water finds its way over the tube plate. This increase leads to the fact that the rows of pipes arranged in the immediate vicinity receive an overdose of water

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while more distant rows of tubes receive too little water. The water has been found to be effective to collect from the lifter in a trough 10 (Fig. 10), which is provided with a narrow outlet opening 11, the below Water flows along one edge of the tube plate 12.

When the main siphon (FIG. 9) has started to run, it will first fill the trough 10 up to the overflow edge 13 (Fig. 10). When this ridge has been reached, the water begins to flow over this ridge and becomes over the whole Distributed along the length of the tubular plate. Since the outlet 11 is very narrow, the initial supply of water from the main siphon however is very large, the water rises to a higher water level in the trough, which is due to an increase in pressure in the overflowing Water is accompanied. This pushes the air present in the head of the overflow down and leaves the overflow act like a full-winged siphon. This has the consequence that in addition to an even distribution of the excess water the intermittent effect of the main siphon is reinforced over the entire length of the tubular plate.

The last part of the described combination of the water container with the main and auxiliary siphon on the one hand Side and the water collection trough with a slot-shaped outlet the other hand is that all of the affected tubes are completely moistened within three to four seconds are.

The dimensions of an auxiliary jack determine the minimum amount of flow water required to keep the jack in action to put. The volume of the container can then be determined in connection with the desired return time.

Also with regard to the water collection trough, the lifting activity is above a given (very short) flow rate in Gear set. In practice, this flow rate is

sings of the water collection drug, as used in dew point coolers becomes so large that it is impossible to use just one water collection trough as a constant water metering device with more accurate WMreturn time, outflow period and exact outflow quantity to use.

For larger systems with a proportionally larger addition of water, the connected main and auxiliary lifters in their above-described combination of a water reservoir with interconnected main and auxiliary lifters and the water collection trough to be replaced by a (vertical) overflow line, which extends up to the most necessary Extends water level in the reservoir and is covered, for example, with a diving bell so that water in the Overflow line can enter under the edge of the cap (Fig. 11). The overflow line must be in the water collecting trough form a liquid seal. The reservoir is filled with a continuous stream of water. From the moment in which the water flows out of the reservoir through the overflow line, the water collecting trough becomes the same Water flow filled, and the water level rises both in the collecting trough and in the outlet of the overflow line.

As soon as the collecting trough has started its lifting activity, the water level in the collecting trough drops and at the same time the water level in the outlet of the overflow line. As a result of this lowering of the level, the amount in the overflow line and in the cap is reduced Air pushed down. Since the pressure in this air space is constant, the water is drawn up and into the cap as a result, the overflow line begins to function as a siphon. The residual air present in the overflow line is then also pushed out so that the reservoir is emptied with the full siphoning power until air at the lower end the line enters the overflow line.

The best results will be with the combination described above then achieved when the water collection trough so sized is that the water flow withdrawn from the collecting trough by the lifter is either equal to that of the overflow line acting as a lifter supplied water flow or a little larger, so that the two jacks terminate their activity almost simultaneously.

In large air conditioning systems, the room load is covered by recirculating air into the room, which air is in a or several central air handling units are cooled, while the required fresh outside air is either in separate ones Conditioned treatment devices and then into the main return system introduced or directly with the one just returned Air is mixed.

If these fresh air treatment devices with a cooler according to the present invention, a so-called dew point cooler, are equipped and provided with mechanical after-cooling, it is possible to use the return air treatment devices without to train mechanical cooling and to cover the main room load fully with a dew point cooler according to the invention.

Accordingly, the present invention also relates to a room air conditioning system having a first part in which the The temperature and the water content of the outside air are brought to a desired value and then the air treated in this way is guided into the said space and which has a second part in which air circulates in the space and its Temperature is returned to the desired value, with the greater part of the circulating air being returned and a smaller part of it is discharged, this system being characterized in that in said first part Outside air cooled in a dew point cooler according to the invention and, if necessary, then the temperature and / or the Moisture content of this air to the desired values

is reduced by mechanical cooling and that in the second part the cooling with a dew point cooler after the Invention, as indicated above, is carried out. Such a system is shown in FIG.

The invention also relates to a room air conditioning system, which has a part in which the temperature and the water content an air mixture present in the room and outside air can be adjusted to desired values, the greater part the mixture is returned and a smaller part of it is discharged, the system being characterized in that a part of the cooling process carried out in said part using a dew point cooler of the type explained in more detail above whereupon, if necessary, the temperature and the water content of the air continue in a manner known per se be reduced.

The following example gives an insight into the energy savings that can be achieved with these two embodiments, in which the two types of related air conditioning systems are compared with a device that is only mechanical Served cooling.

example

We assume an office room with a heat generation (room load) of 100 kW, a return air volume of 30,000 m / h and a minimal amount of fresh air
Return air is to be conditioned.

30,000 m / h and a minimum amount of fresh air of 15% of the

Based on the comfort diagrams taken from the literature (Recknagel, Pocket book for heating and air conditioning, Oldenburg Verlag, Munich 1974) is the desired room condition in the office 25 ° C / 45%. The quality of the outside air (fresh air) is assumed to be 30 ° C / 50%.

It is assumed that no water vapor is generated in the office room becomes (absolute moisture content χ = constant). The amount of return air is 30,000 m / h = 36,000 kg / h; the The mass flow (air flow) is therefore 10 kg / sec.

The heat generation is 100 kW (= space load). The increase the enthalpy is = 10 kJ / kg; this corresponds to a temperature increase of 10 ° C. It follows that the inlet temperature the room air must be 15 ° C.

Method 1; Mechanical cooling only (for comparison)

The fresh air and the return air are mixed before passing through the cooling device. As a result, the mix persists from 85% room air with the condition 25 ° C / 45% and from 15% fresh outside air with the condition 30 ° C / 50%. Of the The heat content of the mixture is h = 51 kJ / kg. The condition of admission is 15 ° C / 85% with an enthalpy of h = 38 kJ / kg. The decrease in enthalpy due to cooling is 13 kJ / kg. The mass flow of the mixture m = 10 kg / s. The required cooling capacity is then q, = m (Äh) = 130 kW.

Method 2: dew point cooling of the main load and

combined dew point / mechanical cooling of the fresh air (Fig. 2)

Based on experiments with a test arrangement of the dew point cooler it has been found that it is possible to reduce airflow from the associated wet bulb temperature to a temperature of less than 1.5 ° C. From these test values it follows that in this example the space load is completely due to dew point cooling can be covered. The decrease in enthalpy is 10 kJ / kg. It is also known that through appropriate adaptation of the volume flow ratio between primary air and secondary air is the difference between the inlet temperature the primary air and the outlet temperature of the saturated secondary air can also be kept at 1.5 ° C. The increase

the enthalpy of the secondary air is then 70-38 = 32 kJ / kg, so that the flow ratio must be 3.2 or that of the secondary air current in the main dew point cooler ■ = - ^ χ 36 000 = 10 800 kg / h amounts to.

This amount must be supplied to the system as fresh air. This fresh (outside) air with the original condition of 30 ° C / 50% is also cooled down to 21 ° C / 85% by dew point cooling and then mechanically Chilled to the condition 15 ° C / 85%.

The decrease in enthalpy during this mechanical cooling treatment is h - h = 56 - 38 = 18 kJ / kg, the mass flow of this fresh air m = 10,800 kg / h = 3 kg / sec. The cooling capacity q ₂ = m (Ah) = 3x18 = 54 kW. Expressed as a percentage of the cooling capacity required in method 1

54
one comes to γ ~ x 100% = 41.5%.

The statistical data for the situation in the Netherlands show that the same absolute moisture content occurs for 27 hours in the year as in the example described above. 22 hours of this, the condition 21 ° C / 85% can be achieved by dew point cooling. This means that the calculated cooling capacity of 54 kW is only required for 22 hours a year and that, with the exception of 14 additional hours, it is always sufficient to use less energy for the rest. It is therefore meaningful to ^{introduce the expression "cooling degree hours 11"} here. This expression is defined as the product of the number of hours in which a certain amount of air must be cooled in order to achieve a given condition and the temperature range in centigrades through which such cooling takes place. This cooling degree hour is a measure of the amount of energy that is required for such cooling.

With the aid of the statistical data mentioned above, it can be calculated in the above manner that the air conditioning of the Office space in our example requires 3,720 cooling degree hours per year using method 2.

In the above-mentioned publication, Recknagel specifies for the cooling method 1 8,175 cooling degree hours per year. In method 1, the number of cooling degree hours is 15% of 36 000 kg / h = 5 400 kg / h applicable, while the remaining 30 600 kg / h through 10 ° C for a period of about 3.5 months in the cooling season during office hours (8 a.m. to 6 p.m.) need to be cooled. In method 2, the calculated number of cooling degree hours only leads to 10 800 kg / h.

As a result, the cooling energies Q1 and Q- used in the two methods per year have the following relationship to each other:

p_2 3 720 χ 10 800 ,,

Q ₁ 8 175 χ 5 400 + 10 150 χ 30 600 ^Ufii

This means an energy saving of 89% in the cooling process, as suggested by the present invention.

Note: This example does not take into account the fact that outdoor conditions that are not as extreme as 30 ° C / 50% do so more often occur than this value, the cooling requirements in the room are lower. In the tables given by Recknagel these influences are taken into account.

In summary, it can be stated that in the case of the above Whipped cooling method 2

1. the cooling capacity to be installed to 40% of the cooling capacity of a fully mechanical Cooling can be reduced,

2. the number of full load hours of this reduced cooling system in the Netherlands in the worst case is only 40 hours per year and

3. An energy saving of almost 90% is achieved.

Method 3: Combined dew point / mechanical cooling

a mixture of return air and fresh air (Fig. 3)

Of course, it is also possible to first run a mixture of room air and fresh air through a dew point cooler and then mechanically cooling the mixture. The dew point cooling principle requires that the mixture now consists of about 70% There must be room air and about 30% fresh outside air. The enthalpy of the mixture is h = 53 kJ / kg. Cooling on one Temperature that is 1.5 ° C above the assigned damp temperature means cooling to 17 ° C (with a Enthalpy of h = 44 kJ / kg). The decrease in enthalpy is then 9 kJ / kg.

On the basis of the final temperature to be achieved of 25 ° C (that is 1.5 ° C below the temperature of the mixture) the increase in the enthalpy of the secondary air flow 76 - 44 = 32 kJ / kg.

The volume flow ratio between the primary air flow and the secondary air flow must be: m / m "= 32/9, so that m" = 0.28 m

III L · Δ * ItI

(consequently the mixing ratio of 70% - 30% turns out to be correct). The difference between m _m and m ₂ is the amount of return air and from here = 36,000 kg / h, so that

m - m ~ = (1 - 0.28) m = 36,000, from which it follows: m λ m

m = 50,000 kg / h and

m ₂ = 14,000 kg / h.

As a result of the dew point cooling treatment, the mixture of room air and fresh air reaches the condition 17 ° C / 85%. To the To generate an inlet condition of 15 ° C / 85%, this amount of air (36,000 kg / h or 10 kg / sec) is then mechanically chilled. The decrease in enthalpy is 44 - 38 = 6 kJ / kg. The mechanical cooling capacity then becomes:

q ₃ = 10χ 6 = 60 kW.

Expressed as a percentage of the cooling capacity according to method 1, this means:

60 130

100% = 46%

As with method 2, this example results in 1 * 852 Calculated cooling degree hours that apply to 36,000 kg / h of air. The required mechanical cooling energy on an annual basis Q., in relation to method 1, is the following:

- ^ - = 1,852 χ 36,000

8 175 χ 5 400 + 10 150 χ 30 600

_n , _q

With this method, too, the energy savings are considerable (more than 80%). In relation to the procedure with method 3, the energy savings are a little less spectacular, that's true, but on the other hand there are Method 3 saves a remarkable amount of capital because there is no separate fresh air dew point cooler is.

Finally, it can be observed that when using dew point coolers it should be taken into account that the energy required for transport is somewhat higher, firstly because in addition to the usable air, a quantity of air is sucked in

must be used as secondary stream after cooling and secondly because the pressure losses in the heat exchanger described are higher than those in conventional cooling systems.

The construction of the cooling device according to the invention is particularly suitable for use as a recuperator or air preheater in winter time. The fresh air supplied flows around the pipes, while the used room air flows through the pipes flows through. If necessary, condensation water can flow downwards along the inner circumferential wall of the pipes and collected in the collecting trough provided. In addition, the humidifier makes it possible that the pipes are washed regularly to remove any adhering dust.

In air preheating mode, the ratio between the two air currents in principle = 1. Thanks to the magnification of the Surface with the help of the fins on the dry side of the heat exchanger becomes the heat transfer coefficient, which is for the pipe surface area is calculated, mainly from the heat transfer coefficient determined on the wet side (inner pipe surface) and is numerically approximately equal to this Coefficients. Together with the large proportion of tubes in the heat exchanger this leads to a high overall heat transfer, so that the efficiency of the heat exchanger is 80% to 90% can.

BATH ORIGINAL

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Claims (10)

519694 claims: 1. Dew point cooler for cooling a stream of air, the one Has heat exchanger with the following parts: a) a package of vertically arranged tubes that undergo heat exchange from the primary air to be cooled are flowed around on their outside; b) means for guiding precooled secondary air through the interior of the tubes; c) Means for introducing water from above into these pipes and for forming a water film the inner wall of the tubes; d) means for removing the humidified secondary air and e) Means for introducing at least a portion of the cooled primary air into one to be cooled Space, characterized in that the means mentioned under c) are suitable for periodically supplying water, and that the Tubes on their outside that are in contact with the primary air comes, are provided with elements, the ratio between the outer surface and the inner The surface of the pipes provided with the elements is greater than 3: 1. 2. dew point cooler according to claim 1, characterized in that the ratio between the outer surface and the inner surface area of the tubes is between 5: 1 and 10: 1. 3. dew point cooler according to claim 1 or 2, characterized in that the heat exchanger has a plurality of horizontal plates has, in which a series of openings is arranged, each of which has a collar that into a Opening of an adjacent plate fits, and that the plates are plugged together and form a package in which the collars together form several tubes or tubes connected by the remaining part of the panels that serve as ribs. 4. Dew point cooler according to one of claims 1 to 3, with a periodically operating water supply device, characterized characterized in that the water supply device has a water tank, which is actually in operation is continuously filled, and that a self-starting siphon is provided for the contents of the water tank periodically emptied. 5. dew point cooler according to one of claims 1 to 4, characterized in that the container is provided with two lifters the first of which is a self-starting lifter that takes the air out of the second, outer one when starting Sucks out the lifter and thereby actuates the second lifter. 6. dew point cooler according to one of claims 1 to 4, characterized characterized in that an elongated container is arranged below the outlet of the lifter and that this container is provided on one side with a lifter, the inlet and outlet of which are along a side surface of the upper Extend tube plate across the tube plate transversely to the direction of flow of the secondary air. 7. Water distributor for a dew point cooler according to one of claims 1 to 6, characterized in that the water distributor has two concentric tube parts, the inner one of which extends into or surrounds a tube and can be sealingly attached to this and of which the outer pipe part is supported on a pipe plate can be and is provided at its lower edge with one or more openings, which are in the annular Gap between the two tubes extend into it, and that the inner tube part has one or more openings which are arranged at a distance from one another on its circumference and the annular gap with the interior connect the pipe, 8. dew point cooler according to one of claims 1 to 6, characterized through a water distributor according to claim 7. 9. Room air conditioner, which has a first part in which brought the temperature and water content of outside air to a desired value and the air thus treated is passed into the room to be cooled, and which has a second part in which the existing in the room Air circulates and its temperature is returned to the desired value, with the greater part of the circulating Air is recirculated and a smaller part of it is discharged, characterized in that in the first part outside air with a dew point cooler after one of the Claims 1 to 6 or 8 cooled and, if necessary, the temperature and / or the moisture content of these pre-cooled air is then reduced to the desired value by mechanical cooling, and that in the second Part of the cooling process is carried out with the aid of a dew point cooler according to one of claims 1 to 6 or 8. 10. Air conditioning system for a room, which has e ± Bn part, in which the temperature and the water content of a mixture of air and outside air present in the room can be adjusted to a desired value, with the greater part of the mixture being recycled and a smaller part Part of it is discharged, characterized in that at least part of the cooling process is carried out in this part of the device carried out with the help of a dew point cooler according to one of claims 1 to 6 and 8 and then, if necessary, the temperature and the water content of the air can be further reduced in a manner known per se.