DE2416294A1 - Heat recovery between exhaust and make-up streams - consists of several independent heat transfer circuits - Google Patents

Abstract

The system can apply to fresh air and extract ventilation or to other processes requiring heat exchange between leaving and entering streams. A series of heat exchangers is placed in the entering fluid stream and a second series of heat exchangers is placed in the leaving fluid stream. Each exchanger of the first set is connected to one exchanger of the second set by vapour and liquid lines through which a heat transfer medium circulates. The medium condenses in the heat exchanger in the intering stream and evaporates in the heat exchanger in the leaving stream. Each heat transfer circuit operates on a smaller temperature difference than the overall difference and thus the total efficiency is increased.

Description

The invention relates to a device for heat recovery, E.g. from exhaust air to heat fresh air or from exhaust gases for domestic water heating, whereby the heat of the outflowing, warmer medium is transferred to the inflowing, colder medium using the principle of the condensation-evaporation cycle a third medium is released.

Heat exchangers or heat exchangers are devices for transmission the thermal energy from a warmer to a colder medium either with continuous or with periodic Heat flow. A heat recovery system is now based on that Heat exchange between an outflowing warm medium and an incoming cold medium. A well-known example is

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the heating of the heating air in a car by means of the outflowing hot exhaust gases. Other common applications are e.g. the heat exchange between combustion air and exhaust gases through recuperators, i.e. heat exchangers with continuous heat flow, or the heat exchange between fresh air and exhaust air in ventilated buildings by means of a rotating regenerator, that is a periodic heat exchanger. Apart from the principle of indirect heat exchange via the counter-current principle Apparatus and the heat exchange via alternately flowed through regenerators are also known heat exchange elements, so-called heat pipes, in which inside a pipe one vaporizing at one end and one at the other end of the tube condensing medium circulates to carry the heat through the pipe. Finally, there are still simple heat exchangers known which built into the two inflow and outflow streams and which are via a liquid circuit with a pump are interconnected, the heat within the liquid circuit from one heat exchanger to the other is transported.

These known systems have advantages and disadvantages which make them unusable for one or the other purpose.

The most essential task of a heat recovery system is a high efficiency with the lowest possible energy consumption. This means that the warm, flowing medium is the heat should be largely withdrawn until the outflow temperature of the outflowing medium is more or less equal to the inflow temperature of the inflowing medium is. In this respect, the regenerative working systems come first. Your most significant The disadvantage is that the medium flowing in and out is at one point must flow in the immediate vicinity, e.g. must flow in In a building, the supply and exhaust air ducts converge at one point, while it would be better if the supply and exhaust air would be on

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in places that are far apart, e.g. on the roof and in the basement.

Another disadvantage is that the inflowing and the outflowing medium with the same surfaces one after the other comes into contact and thus impurities, dust, odors or bacteria are transferred from the exhaust air into the supply air can · recuperators using the countercurrent principle avoid the last · mentioned disadvantage, but also the first disadvantage is present and in addition, because of the supply and discharge of the medium in countercurrent, large, space-consuming "heads" at the Ends of such apparatus are necessary.

The high degree of efficiency can be understood from the fact that both in the recuperator with the countercurrent principle and in the regenerator is run with a sliding temperature, theoretically (with an infinitely large exchanger surface and low flow velocity) the temperature of the outflow is equal to that of the inflowing medium could be. In the case of a device with numerous, arranged one behind the other in the direction of flow heat pipes, a similar effect is achieved as with the recuperator or with the regenerator, since each individual heat pipe in the opposite « current is arranged so that a maximum heat exchange is achieved. However, there is also the disadvantage that the incoming and outgoing medium must be brought together.

If the merging is not possible or too costly, it is known to use a separate one through which liquid flows To use a heat exchanger system in which a second medium of such an amount must be circulated that the water values both media are the same size. At temperatures below 0 ° C (fresh air - heat exchanger - exhaust air), for example, a glycol / wa8ser mixture had to be used to maintain the

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ijbertragungskreislaufes requires high pump powers.

The invention is therefore based on the object of providing a device for heat recovery of the type mentioned at the beginning create in which the merging of the two media streams is not necessary and with a separate recording of the two media streams at any point, even at several Set, is achieved without the need for high pumping capacities.

The solution to this problem is that according to the invention a The outflowing, warmer medium flows through a plurality of heat exchanger spaces (evaporator, heat sources) one after the other a plurality of heat exchanger spaces (condensers, heat sinks) flowed through one after the other by the inflowing, colder medium are arranged spatially separated from one another, with an evaporator and a condenser being part of a known condensation-evaporation circuit, which are connected in stages one behind the other.

The invention makes an extension of the Carnot cycle, the so-called Lorenz process, usable. The Lorenz process generally consists of several strung together Carnot cycle processes. For example, connecting a large number of heat pipes in series is a Lorenz process.

The device according to the invention has over the known Heat exchangers have the advantage that they achieve at least the same or better efficiency than a regenerator or a recuperator, but with the invention Device no merging of the two media streams that are to be heated or cooled takes place, i.e. a Durohmixing of the two streams and the associated ones, at the beginning

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mentioned disadvantages are no longer possible. Furthermore, the device of the invention required for the! Condensations "Verdampfungekreisläufe principle no pump _$ if the capacitor, namely, the heated heat exchanger is arranged above the evaporator, so that the condensate can flow freely latter. There is, however, the possibility of providing a condensate pump, whereby various individual circuits can also be operated with one pump.

If only one condensation evaporation circuit was used, so Since the evaporation and the condensation take place at the same temperature, an efficiency of at most 5056 would be achievable. But there will be more such cycles in the media flow installed one behind the other, an adjustment to the sliding medium temperature is achieved, with three separate ones Circuits practically efficiencies in the order of magnitude that can be achieved by regenerative heat exchangers

To direct the condensate from the condenser to the evaporator is with the appropriate position of the two parts, the static inlet height of a condenser leading through the evaporator is sufficient. However, if the altitude is reversed, an additional condensate pump is required, but this is much less Requires drive energy, as a liquid pump, here too there is the possibility of various individual circuits with a supply single pump.

In terms of process, it can be said that for the first time according to the principle of the Lorenz process from exhaust air to heat fresh air or was made possible from flue gases for domestic water heating, between a warmer and a colder medium several condensation-evaporation circuits to switch in stage, with the warmer medium spatially completely separated from the colder medium is.

Furthermore, the inlet and outlet lines for the colder or warmer medium can also be spatially separated from each other,

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In a preferred embodiment of the invention, a fan is arranged in the steam line of one or more condensation-evaporation circuits to increase the pressure within the condenser. In this way it is achieved in an advantageous manner that the losses (which are always present in the actual cycle) are compensated, since every cycle and thus also the practical Lorenz process has an irreversible component. The pressure increase by means of a fan means that work is added to the vaporous medium of the condensation-evaporation cycle, but this work only corresponds to a very small fraction, e.g. 1/20 to 1/50 of the additionally recoverable amount of heat. By switching on a fan it is achieved in an advantageous manner that the condensation takes place at a slightly higher pressure level (and thus temperature level) than the evaporation. As a result, an exchange efficiency of 100 % or even more can be achieved with this low additional energy requirement. This means that the outflow temperature of the outflowing medium is lower than the inflow temperature of the inflowing medium. Theoretically, such a circuit has the characteristics of a heat pump, although with the peculiarity that, in contrast to the generally known systems of this type, a large number of individual circuits are built in one after the other with a relatively slight increase in pressure in the media flows to be exchanged, so that instead of the usual heat pumps Compressors simple blowers can be used. It is of course possible here to arrange the heat exchangers in any number at different points.

There is a particular advantage of the device according to the invention in that the individual heat exchangers or heat exchanger spaces are designed as desired, depending on the task to be mastered could be. In this respect, the subject matter of the present invention opens up a variety of possible applications, which the Leave the individual design of the respective heat exchanger system remain.

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As a heat-transferring, evaporating and condensing medium come within the condensation-evaporation circuits the halogenated hydrocarbons, depending on the temperature, e.g. R 113 for temperatures around -35 ° C to + 12o ° C,

R 12 by -5o ° C to + 8o ° C,

Octocyclobutane (CVFg) for temperatures above 100 ° C to 2oo ° C in question, but also inorganic substances such as HgO, SO ₂ , NH «·

Examples of the invention are shown in the drawing and described below. It shows:

Fig · la, b the principle of a counterflow heat exchanger and the

Temperature curve of the inflowing and outflowing medium,

Fig »lc, d a regeneration heat exchanger and the temperature curve of the inflowing and outflowing medium,

2a and b show a separate heat exchanger with liquid as Transmission medium and the temperature profile of the inflowing and outflowing medium and the transmission medium,

3 shows an arrangement according to the invention of three separate ones Condensation cycles,

the temperature profile for the arrangement according to FIG. 3 »a basic arrangement for full utilization the "assisted" Lorenz process with a single Condensation cycle,

the temperature profile for the arrangement according to FIG. 5i an example according to the invention, consisting of three separate condensation circuits for full utilization of the "supported ¹¹ Lorenz process the temperature profile for the arrangement according to FIG. 7 »and a schematic representation of a fresh air / exhaust air heat recovery system according to Figures 7 and 8, Consists of three separate condensation circuits with fans in their steam lines.

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For a better understanding, the conditions in heat exchangers of the state of the art are again based on FIGS. nik explained.

Fig. La shows a counterflow heat exchanger with a heat exchanger shear space 1 for the inflowing, warmer medium and a heat exchanger space 2 for the outflowing, colder medium. The temperatures here are based on the inlet temperatures in the heat exchanger space. The reference symbol 3 denotes the inflowing medium, and the reference symbol k denotes the outflowing medium. Its heat transfer surface 5 serves to exchange the heat. Fig. Ib shows the temperature profile of the arrangement shown in Fig. La. The temperature of the inflowing medium 3 falls during the heat exchange from point A to point B. At the same time, the temperature of the outflowing medium rises from point C to point D.

1c and d show the relationships in a rotating regenerative heat exchanger 8. Again, the reference numerals 3 and k denote the inflowing and the outflowing medium, respectively. This regenerative heat exchanger works on the countercurrent principle. Fig. Id shows the temperature profile of the inflowing and outflowing medium.

2a, a circuit 6 with a liquid transfer medium is connected between a heat exchanger space for the inflowing medium 3 and a heat exchanger space 2 for the outflowing medium k , the transfer medium being circulated within the circuit 6 by a circulating pump 7. When exchanging heat there is ζ. Β the inflowing medium 3 from its heat within the heat exchanger space 1 to the circulating medium of the circuit 6, which transports the heat to the heat exchanger space 2 and thus to the outflowing medium k.

The temperature curves of both the incoming and outgoing Medium and the circulating medium are shown in Fig. 2b. the

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The temperature of medium 3 drops from point A to point B, while the temperature of medium h increases from point C to point D. At the same time, the temperature of the transfer medium rises within the heat exchanger space lvora point B ¹ to point A ¹ , in order then to ^{fall again within the heat exchanger space 2 from point D 1} to point C ^r .

A first example of a device according to the invention for heat recovery is shown in FIG. 3. Three heat exchange spaces 1, 1 * and 1 * 'for the inflowing medium 3 and three heat exchanger spaces 2, 2' and 2 * ' for the outflowing medium h are connected in series in such a way that the inflowing or the outflowing medium 3t ^ all heat exchanger spaces 1, 1 * and 1 ** or «2, 2 * and 2 * 'flows through one after the other. The heat exchanger spaces 1, 2; l ^f , 2 * and 1 * *, 2 '* each form the transfer spaces for a closed condensation-evaporation circuit. The heat exchanger rooms

1, 1 * and 1 * 'are therefore condensers, the heat exchanger spaces

2, 2 * and 2 * 'evaporators. The steam lines are denoted by the reference symbols 9t 9 * and 9 * '»the liquid lines are denoted by the reference symbols Io, Io * and Io".

The temperature conditions occurring in such an arrangement are shown in Fig. H. The reference numerals 17 »18 and 19 denote the condensation evaporation circuits,

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consisting of the condenser-evaporator pairs 1 and 2, 1 * and 2 and 1 · 'and 2 "".

When flowing into the evaporator 2 ″, the temperature of the outflowing medium k gives off heat to the transfer medium of the condensation-evaporation circuit 19 and falls from point A * 'to point B ¹ '. Thereafter, the outflowing medium k flows through the evaporator 2 'and falls from a temperature A ¹ = B ¹¹ to a temperature B ¹ . The medium k then flows through the third evaporator 2 and falls from a temperature AsB ¹ to a temperature B in the process. At this temperature B, the outflowing medium h now flows into the open. At the same time, the inflowing medium 3 flows into the first condenser 1 and increases its temperature from point C to point D. After flowing through the third condenser 1 ″, the temperature of the inflowing medium 3 has the vert D ″. The temperature of the inflowing or outflowing medium was thus increased or decreased in steps. In between, closed condensation-evaporation circuits are connected for heat transport, each of which represents a complete cycle process. The reference numerals 11 "11 'and II ¹ " denote practically the same condensation and evaporation temperature of the transmission medium. With such full utilization of Lorens-Prosessös of FIG "3 is a recovery of the heat of the effluent van ca · 12 ^ can be reached ·

5 shows a simple condensation circuit, again with a condenser 1 and an evaporator 2 of the circuit, which additionally has a steam blower 12. In Fig. 6, the effect of this steam blower 12 is explained. The steam fan increases the pressure in the condenser, which means that the condensation and evaporation temperatures differ. The condensation temperature is now at the level 13 "the evaporation temperature at the lower level 1". This is

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It is possible to raise the temperature of the condensation-evaporation circuit by approximately lo ° C and a pressure difference of approximately 0.25 atm. Switching on a steam blower means nothing more than adding work to the gas in the condensation-evaporation circuit, this work being equivalent to a very specific amount of heat. Hit a single supercharged condensation cycle can be a Heat recovery of approximately $ 55 can be achieved.

7 shows a further example of a device according to the invention, consisting of three condensation-evaporation circuits, a steam fan 12, 12 ', 12 " ^{being switched on in each of the steam lines 9, 9 1, <? ·'.} This full utilization by the "supported" Lorenz process results in a recovery of the heat of the outflowing medium ■ k of approx. 9o #. If several stages are connected in series, it is even possible to achieve an efficiency of over Io0 $, which means that the outflow temperature of the outflowing medium is lower than the inflow temperature of the inflowing medium. The limit, however, is where the additional energy consumption of the steam fan achieves the energy gain by cooling the outflowing medium.

FIG. 9 shows a schematic illustration of a fresh air / exhaust air heat recovery system according to FIG. 7 within a large building 23. On the roof of the building 23 there is a condenser chain consisting of the condensers 1, I ¹ and 1 ″ through which the inflowing medium 3 flows one after the other. The medium has an inflow temperature of -lo ° C. In the first condenser the medium warms up to 0 ° C, in the second to + lo ° C and in the third to + 2o ° C and is heated to this temperature (or above) by means of a supply air fan blown into the building, which is indicated by the arrows.

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The fresh air is heated further inside the building, so that the medium now flowing off in front of the evaporator battery, consisting of the individual evaporators 2, 2 * and 2 ^{11, has} a temperature of 26 ° C. 2 in the first evaporator ¹ 'cools the effluent to 16 C., the second at 6 ° C and finally in the third, the medium on -k ° C cooled, and is blown by an exhaust fan 16 to the outside. " The capacitors 1, 1 *, and I ^11, and the evaporator 2, 2 * and 2 ^'1 are each part of a closed condensation · evaporation cycle shown in Fig. 7 · In ^the steam pipes are steam blowers 12, 12 · and 12' installed ·.

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Claims (1)

Patent claims 1.) Device for heat recovery e.g. from exhaust air for heating from fresh air or from exhaust gases for domestic water heating, whereby the heat of the outflowing, warmer medium to the inflowing, colder medium using the principle of the condensation-evaporation cycle of a Heat-transferring medium is given off, characterized in that, that a plurality of heat exchanger spaces (evaporator, Heat sources) flowed through one after the other by the outflowing, warmer medium and a plurality of heat exchanger spaces (Condensers, heat sinks) one after the other, the inflowing, colder medium flows through them, spatially separated from one another are arranged, with an evaporator and a condenser being part of a known condensation-evaporation circuit that are connected one behind the other in stages. 2 »Device according to claim 1, characterized in that the inlet and outlet lines for the colder or warmer medium are also spatially separated from one another. 3. Device according to claim 1 or 2, characterized in that that in the steam line one or more condensation-evaporation circuits a fan is arranged to increase the pressure inside the condenser. 509842/0234