DE3117019A1 - IN PARTICULAR, COMPRESSION REFRIGERATOR WITH SOLUTION CIRCUIT DETERMINED FOR OPERATION AS A HEAT PUMP - Google Patents

Description

BOSCH-SIEMENS HAUSGERÄTE GMBH 3 Munich 80, 23.0-Ί.1931 Stuttgart Hochstrasse 17

TZP 81/412 Wi / ant

Compression refrigeration machine intended in particular for operation as a heat pump with solution cycle

The invention "relates to a compression refrigeration machine with a solution circuit, which is intended in particular for operation as a heat pump . ■■ slauf, with a degasser, from which the poor solution in the solution cycle is conveyed by means of a solvent pump via a temperature changer into a resorber, where it is removed from the degasser by a compressor sucked in and compressed refrigerant-rich vapor is absorbed and from there returns to the degasser as a rich solution via the temperature changer.

According to a proposal by E. Altenkirch, absorption chillers are referred to as compression chillers with a solution cycle, which are also equipped with a compressor. Among other things, in issues 10, 11 and 12/1950 of the magazine "Refrigeration" described by Altenkirch compression refrigeration machine with solution cycle has compared to the usual

TZP 81/412

compression chillers have the advantage of noticeable energy savings. This is particularly important when it comes to their use the case as a heat pump. However, since it is technically more complicated than a normal compression refrigeration machine, has the compression refrigeration machine with a solution cycle has not achieved any practical significance until today.

The invention is based on the object of compression refrigeration machines of the type described at the beginning and by further reducing the energy consumption the disadvantage of the machine-technically more complicated structure compared to normal Compensate for compression chillers and thus enable their use on a broad basis.

This object is achieved according to the invention in that a connecting line between the connected to the degasser Lines for the poor and rich solution partial flows of these solutions can be converted into one another.

The connecting line arranged according to the invention and the The resulting transferability of partial flows into one another allows flexible adaptation to different ones Temperature ranges of heating medium and cooling medium and thus contributes to a considerable increase in efficiency and the economy of such a compression refrigeration machine at.

The invention makes use of the knowledge that in heating technology there is always material flows (water or air) in one Temperature band Δ T are to be heated up or cooled down. Because of the sliding temperatures, the Carnot process with its constant temperatures is not the ideal comparison process to strive for but rather the Lorenz process, which in the inner

compared to the Carnot trial
Behavior / a higher theoretical energy saving

- TZP 81/412

* ·: - ·: 17019

speaks, the larger the temperature band is. It was found that in your for the sowing / as a heat pump extremely important external behavior the Lorenz process is even more favorable and thus causes an additional energy saving.

A construction has proven to be a particularly favorable arrangement for solving the object on which the invention is based result, according to which a connecting line is arranged behind the degasser, through which a feedback of a Partial flow of the poor solution takes place in the rich solution flowing back to the degasser.

A particularly advantageous embodiment of the object

even
According to the invention, the connection line is connected on the one hand to the line for the poor solution between the solvent pump and the temperature changer and on the other hand to the line for the rich solution between the temperature changer and the degasser. The inventive Rückspei solution of a branched off between the solvent pump and the temperature changer partial flow downstream of the temperature changer makes it possible to adjust the temperature range of the heating medium as precisely as desired to the different temperature range of the refrigerant.

According to a further advantageous configuration of the invention it is provided that a control valve in the connecting line is through which the feed back of the partial flow according to the respective operating state of the compression refrigeration machine takes place with the solution cycle.

Further, in the claims characterized advantageous features of the invention are in the following description in Relation to an example of a compression refrigeration machine shown in simplified form in the drawing as a circuit diagram explained with the solution cycle as well as corresponding diagrams and tables. Show it:

TZP 81/4 12

1 shows a simplified circuit diagram of a compression refrigeration machine with solution cycle,

2 shows a schematic pressure-temperature diagram (lg ρ: l / T) of a solvent-refrigerant mixture,

Fig. 3 'schematically shows the temperature profile in the inner or external process (heating medium and refrigerant) over the heat exchanger length L of the compression refrigeration machine with solution cycle,

4 shows the coefficient of performance of a Carnot process £ _ or Lorenz process £ _T , depending on external process conditions,

5 shows the coefficient of performance of the compression refrigeration machine with solution cycle depending on the partial flow rate or the suction pressure ρ and

6 shows the ratio of the volumetric heating capacities of a compression refrigeration machine with a solution cycle that of a normal compression refrigeration machine with a single substance refrigerant as a function of the suction pressure ρ.

A compression refrigeration machine with a solution circuit shown in principle in FIG. 1 essentially has a degasser E, a solvent pump P, a temperature changer T, a resorber R, a throttle element X and a compressor V according to the Ig ρ - T diagram according to FIG. 2, the compressor V sucks refrigerant-rich vapor (for example NH from the solvent H ₃ O) from the state from the degasser E

'TZP Sl /' iLÜ

(l) from. The solution degassed from state (?) To (J) in one Temperature range to which the temperatures of the secondary refrigerant (For example air) can be adjusted by countercurrent flow. The poor solution is raised by the pump P.

brought a higher pressure ρ and demanded into the resorber R, where it is preheated in the temperature changer T. In the resorber R, it meets the compressed refrigerant gas m from the state (2) coming from the compressor V and resorbs this in the temperature range when the state changes from (6) to (5). Here, the heat of absorption Q is transferred to the heating medium to be heated (eg water) flowing in countercurrent. _{The solution m r} , which has thus been enriched to the state (J), finally flows through the temperature changer T and the throttle element X back to the degasser E, where it can again absorb the heat Q of absorption.

When using the illustrated and described compression refrigeration machine With the solution cycle as a heat pump, considerable energy savings can be achieved due to the fact achieve that in heating technology, material flows (water or air) are always heated or cooled in a temperature band ΔΤ are. Because of the sliding temperatures, the Carnot process with its constant is not the ideal comparison process To aim for temperatures, but rather the Lorenz process.

That the Lorenz process promises a higher theoretical energy saving, the larger the temperature band, the greater the temperature range, has already been proven earlier (cf. "Rational use of energy in refrigeration systems" H. Lotz, Congress Expoclima 76, p. 57 / B5) . As will be shown in the following, the Lorenz process leads to further energy savings in the important external behavior.

O TZP 81/412

The heat output coefficient C _{n of} the Carnot process can be represented with the designation from FIG. 3

and the coefficient of performance £ _ of the Lorenz process under the Requirement 4 T., = T - T = a + b »T and the" local "

^€ LX = WA ^T ws ^TO:

with the abbreviations:

b = 1 -Δ Τ

a = (1 - b) * (T _w2 +/- _w -4T _w ) - (T _s2

T = ^ T, equation (2a) is simplified to:

O W

l _L -

The values plotted in FIG. 4 for £ ~ and £ _T over the increasing temperature difference ^ in the condenser "or evaporator (or the k'A value derived from it, based on the k» A value "at y = 1 K the heat exchanger) show that the Lorenz process gives significantly better values than the Carnot process, especially at smaller temperature differences below 4 K (or relative "k« A values above 0.3). The higher the temperature band T, the higher these values is.

With the compression refrigeration machine described with the Altenkirch solution cycle, it was already possible to implement such a Lorenz process. This machine, however, had the problem that the improvement shown in Fig. 4 was only fully achieved if the temperature bands / \ T in the resorber and in the degasser are the same, i.e. the heating medium is heated by the same amount as the coolant is cooled . Such a state is, however, quite rare; these states are usually different, which means that the possible energy savings are significantly reduced.

This deficiency is now modified in accordance with that described here ten compression refrigeration machine with solution cycle according to Altenkirch fixed as follows:

By feeding back a partial stream m downstream of the degasser E, it is possible to create any temperature band of the refrigerant that differs _{from the temperature band ^ T 1 of the heating medium}

to each other " ^s

exactly / adapt by changing the subset in. otherwise also ^x

This is a real advantage over the compression refrigeration machine with non-azeotropic refrigerants, where the temperature bands in the condenser and evaporator are known only depend on the filling concentration and are therefore rigid and have approximately the same values.

With the help of heat and quantity balances and the prerequisite that in the temperature changer T with full heat exchange t- = t "can be achieved and in the degasser E or in the resorber R the temperature difference ff * is kept constant by suitable countercurrent flow over the heat exchanger length and the energy consumption of the solution pump is negligible, the following results for the coefficient of performance with the designation from Fig. 1:

_KHL - * V h - ts ^ U-

h h

The concentrations γ and £ _{r are} determined by the initially freely selectable pressure ρ and the temperature t _Λ - / ß *

sets, while the enthalpy h- by the temperature t. +

^ a wi

is determined. The one to be set according to the equation (Ji)

TZP 81/412 partial flow f determines the concentration of the rich solution

. is determined by ρ and t _o - J ^

Furthermore, the enthalpy h ₀ after compression is initially the isentropic coefficient and c as the spec. Heat capacity

pm

tat of the gas mixture as well as V. as the quality level "based on isentropic compression:

fc-f

All of the following calculations for the compression refrigeration _{machine with a solution circuit have been made for the solvent-refrigerant mixture NBL / H o} 0, since, due to the predominant use in absorption systems, an operation in the compression refrigeration machine with a solvent circuit also makes sense. However, other mixtures are also conceivable, but they would have to be examined more closely with regard to the special requirements of the compression refrigeration machine with a solution cycle.

For comparison, the table below shows various heat output coefficients and a heat exchanger temperature difference registered by IK and 5K. The outer Conditions "Heizraediumerwärmung von 45 C around 1OK und.Kälteträger räb cooling from 5 ° C around 5K" were chosen because they a represent frequently encountered operating conditions

™ TZP 81/412

-Sf-

and these and a T d ( the partial flow control clearly show.

different temperature bands AT and a T have the advantage

The heat output numbers of the comparison processes according to Carnot £ ~ and Lorenz £ ,. are determined using equations (l) and (2j. The practical values for the compression refrigeration machine with R 22 and with the non-azeotropic refrigerant mixture of R 22 / R 114 resulted from measured values for the

according to Jacob (5)
inner behavior /. The coefficient of performance for the compression

for the proposed part of electricity laying sion chiller with solvent was / with the equation

(3) calculated.

The table clearly shows that because of the flexible adaptation through partial flow control of the compression refrigeration machine Solution cycle to the different temperature bands of heating medium and refrigerant the compression refrigeration machine with Solution cycle to achieve significantly higher thermal coefficients permitted as a compression refrigeration machine with non-azeotropic refrigerants, with an adapted temperature band in. at least one heat exchanger (δ T = 10 K at £ * = 0.79) · At poor adaptation of the compression refrigeration machine with non-azeotropic refrigerants to the outer temperature bands (here e.g. at .4 T = 16.5 K with "£ = 0.56, which is the maximum £ for

7 even

mean inner behavior), this / lies with the values

Compression c 'tc' machine
the / with Einstoff ikäl terai L ^ l. The single-component compression refrigeration machine with R 22 naturally has the lowest values, especially in the case of large-scale heat exchangers (ie small temperature differences ν).

In Fig. 5 is the heat output, s number of the compression refrigeration

In the version described here, the machine with the solution cycle fin is plotted as a function of the partial flow f according to equation ^ 4 ^ and the suction pressure ρ. Of the

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TZP 81/412 f?

upper section of the p _ifi . T'zel ^^ E ^ * v'Jm partial flow f - O an increases steadily until the maximum value f is reached. l) ie «or hai. a con / .outiatlon in the circuit? 3 ⁼ f 3 max ^so " ^{llUii (} |} calibration ('i; resulting in the saturation declaration in point © (p _lg . i), determined by the Pressure ρ and the temperature t +, V In the lower section of FIG. 5 it can be seen that with ^f max ^{as a} parameter, the heat output _{coefficients have} an optimum depending on the suction pressure Pq, which is at relatively low pressures. These maximum values are shown in the table registered.

A recalculation shows that it is permissible to neglect the solvent pump output to determine ζ- ^ , since it only achieves about 0.25% of the compressor output even with a pump efficiency of 25%.

The partial flow branch "m" indicated by dash-dotted lines in FIG. 1, in which, in contrast to the partial flow branch "m", part of the rich solution coming from the temperature changer T is fed into the line from the degasser E for the poor solution, as a further possibility has, moreover, relatively high irreversible mixing losses and is therefore less favorable than the control "m" shown in FIG. 1 with solid lines. It results in heat output figures which, for example, for the calculated case according to the table, at J ^ = 5 K, are only about S5% of those for the partial flow control "m".

_{The partial flow branch "m y} " shown in FIG. 1 by dash-dotted lines results in relatively high irreversible mixing losses and is therefore less favorable than the control "m" shown in FIG. 1 with solid lines. It results in coefficients of heat output which, for example, for the calculated case according to the table at .J ^ = 5 K, are only about 85% of those for the partial current control "πι _χ ". The relatively low suction pressures are characteristic of the compression refrigeration machine with a solution cycle. As shown in Fig. 6, this has a low volumetric

Heiz] eistuns; q _{x /} in relation to the compression chiller ^.

^ ^v with one component refrigerant- --- *

result. In Fig. 6 the ratio ν of the volume-

thermal output of the compression refrigeration machine with solution cycle to that of the R 22 - one-material - compression

$ 1

TZP

sioas chiller IUr two different HE temperature differences referenced. The volumetric heating power increases sharply with increasing suction pressure. These relatively low volumetric heating capacities affect However, the size of the heat exchanger is not decisive, since liquid solutions circulate here and the degassing or degassing. Resorption processes with the large volumes of circulating gas and because of the availability of pressure gradients the compression can be carried out inexpensively, i.e. with a relatively small heat exchange surface. Is influenced in the only the size of the compressor is essential.

Under these conditions it is particularly advantageous for flow compressors such as screw compressors, which are insensitive to a possibly wet gas mixture.

The compression refrigeration machine described and shown with a solution cycle is made possible by the exact setting of the variable partial flow m on different temperature bands in the degasser / resorber, that at any time at the maximum coefficient of performance can be worked. Microprocessors, which control the various operating states, can be used as control organs to control the partial flow m can process so that always worked with the optimal partial flow portion f can be.

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Tabel

it ^:

- Heating medium heating from t,, * = 45 to t.

= 55 ⁰ C

Cooling medium cooling from t .. = 5 to t _g2 = OC avg. Temperature difference in the heat exchangers ΛΛ. = " ⁷ L = 1 D3W. 5 λ

= 10 K) = 5 K)

Quality grade> p. based on the isentropic compression power, for the KKM with R 22 and with NA R 22 / R 114 according to measurements from [5] and for the calculation of the KML ip _is = 0.726

WT temperature difference jj . K 1 . 5 Carnot - heat output coefficient En
Lorenz - Viärm achievement number £ τ 5.96
6.55 5.54
5.71 Heat output coefficients of:
- KKM with R 22 according to [5]
- KKM with NA R 22 / R 114
according to [5] for £ = 0.79 (δT = 10 K)
u " I = 0.56 (ΔΤ = 16.5 K)
- KIiL after this work for maximum
ρ according to 3 picture 5 - 3.36
3.61
3.29
4.22 3.12
3.20
3.11
3.77

KKM = compression refrigeration machine

KFiL = compression refrigeration machine with solution cycle NA = liichtazeo-cropes Kalteraittelgeraisch

Γ 5I "contribution to the Yerwendun ^ non-azeotropic dual-component refrigerants in V.'ärmepumpen ", R. W. Jakobs, dissertation University of Hanover 1980

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Claims (6)

TZP oil / Ί12 Expectations / 1.J Compression refrigeration machine designed especially for operation as a heat pump with a solution cycle, with a Degasser, from the poor solution in the solvent circuit by means of a solvent pump via a temperature changer is conveyed into a resorber, where it is sucked in by a compressor from the degasser and condensed refrigerant-rich vapor is absorbed and from there as a rich solution via the temperature changer into the Degasser returns, characterized in that connected to the degasser (E) via a connecting line between the Lines for the poor and rich solution partial flows of these solutions can be converted into one another. 2. Compression refrigeration machine according to claim 1, characterized in that a connecting line is arranged behind the degasser (E) through which a return of a partial stream (m) of the poor solution (7) into the rich solution ( ^{2) flowing back to the degasser (E)} ^ a) takes place. 3. Compression refrigeration machine according to claim 1 or 2, characterized in that the connecting line on the one hand the line for the poor solution (7) between the solvent pump (P) and the temperature changer (T) and on the other hand connected to the rich solution line (3a) between the temperature changer (T) and the degasser (E) is. 4. Compression refrigeration machine according to claim 1, 2 or 3, characterized characterized in that there is a control valve in the connecting line through which the partial flow is fed back (m) according to the respective operating state of the compression refrigeration machine takes place with the solution cycle. TZP 81/412 - 2 - 5. Compression refrigeration machine according to claim 1, characterized in that that behind the degasser (E) a connecting line is arranged through which a partial flow can be fed back (m) the rich solution (4a) into the poor solution (7a) coming from the degasser (E) takes place before the solvent pump (P). 6. Compression refrigeration machine according to one of the preceding claims, characterized in that the compressor (V) as Flow compressor, preferably as a screw compressor is trained.