Refrigeration – Reversible – i.e. – heat pump – With cooling apparatus other than gas compressor
Reexamination Certificate
1999-11-30
2001-10-23
Buiz, Michael (Department: 3744)
Refrigeration
Reversible, i.e., heat pump
With cooling apparatus other than gas compressor
C062S476000
Reexamination Certificate
active
06305181
ABSTRACT:
This invention relates to a double-acting apparatus for heating as a heat pump and, respectively, for cooling a fluid, in particular air. The object of the invention is to solve the problems arising in currently known double-acting machines when they are to be used as heat pumps for environmental heating.
Currently available apparatus use water as the refrigerant and a LiBr/H
2
O solution as the absorbing liquid. Known double-stage machines consist of an evaporator, an absorber, two generators and two condensers connected together in accordance with a scheme well known to the expert of the art. The heat has to be yielded by the condenser at low temperature and by the absorber, the heat produced in the absorber being at a relatively low temperature of between 32 and 42° C. and consequently unusable for heating.
The patents EP-B-470432 and U.S Pat. No.3,483,710 describe double-acting absorption systems having two interacting but non-communicating circuits, in which there are two separate stages, namely the first and second stage, each consisting of an evaporator, an absorber, a generator and a condenser, wherein the first stage receives heat via the evaporator from an external fluid, for example from icy water originating from an air treatment plant, and simultaneously yields heat via the absorber to the evaporator of the second stage, which in its turn yields the heat of its absorber to the outside environment. The dilute solutions from the absorbers are fed to respective generators, the generator of the second stage being heated by an external energy source, whereas the generator of the first stage is heated by the steam produced in the second stage, and in this manner operates as a high temperature condenser, whereas the steam produced in the generator of the first stage is condensed by heat transfer against an external fluid, generally air. The concentrated solutions and the condensed refrigerants return to the respective apparatus from which they originate. The main object of the two cited patents is to provide absorption machines which can be cooled by air even in tropical zones, so avoiding the use of evaporation towers which make absorption machines difficult to use especially on a small scale, and hinder their acceptance. Moreover as they are provided with an evaporator, an absorber, a generator and a condenser for each stage, such apparatus can operate as heat pumps, yielding energy from the second stage absorber and from the first stage condenser at temperatures suitable for winter heating. The apparatus described in the cited patents have however a serious drawback in that as the two devices interact but are separate, rigid control has to be provided in order to be able to ensure that the system heat balance, which requires that the input enthalpies are always equal to the output enthalpies, is satisfied under all situations. Separating the two stages prevents such apparatus being able to undergo auto-regulation as difficult temperature control of the condensed refrigerant entering the evaporators is required to be able to ensure that the heat balance is satisfied.
A further heat pump is that illustrated in U.S Pat. No. 4,475,361, which describes an apparatus schematically similar to that of the present invention and able to operate as a heat pump to provide heat at a temperature suitable for environmental heating purposes. However, according to that patent, the temperature at the low pressure evaporator is about 0° C. (as indicated in column 9, line 14, point “F”), even though the evaporator contains a small quantity of LiBr used as antifreeze, this practice being already known to the expert of the art and widely used in commercially available absorption machines. The temperature usable in the evaporator limits the operation of the heat pump of the said patent, to a temperature of about 10° C. less than the external air or fluid from which heat is to be recovered, this value being too high because it totally prevents the use of the apparatus as a heat pump when the external temperature is less than 10° C. This drawback also applies to the other two aforesaid patents.
The object of the present invention is to provide a heat pump able to operate with an external temperature of down to 0° C. or even less.
The heat pump of this invention uses in the low pressure evaporator a mixture of low freezing point, preferably LiBr/H
2
O having a freezing point sufficiently low to allow evaporation at a temperature of about −10° C., so enabling heat to be recovered from the external air or from the fluid from which heat is to be recovered, down to an air or fluid temperature of 0° C. or less, while still achieving a temperature at the second stage absorber such as to be usable for environmental heating. The concentration of LiBr or of substances having the same function within the evaporator is that necessary to obtain the aforesaid freezing point, consequently its influence on the evaporator temperature is modest and merely of the order of 2-3° C., which virtually has no influence on machine efficiency.
Moreover in U.S Pat. No. 4,475,361 (as indicated in its
FIG. 2
a
and as expressly stated in claim
1
), the concentrated solution originating from the generators feeds in series firstly the high-temperature absorber G and then the low-temperature absorber E. It follows that the entire dilute solution is fed to the generators, so creating considerable problems. For example, to achieve a good coefficient of performance (C.O.P.) the minimum possible solution for concentration must be fed to the generators, so increasing to a maximum the concentration difference between the dilute solution entering and the concentrated solution leaving, whereas in the absorbers, to achieve effective heat transfer between the absorbent solution and the cooling fluid flowing within the heat exchanger tubes, it is advisable for the solution throughput to be relatively high, in particular using spray nozzles, as stated in the said patent. It should also be noted that the aforementioned drawback is further aggravated in the case of machine operation with partial load. In such a case, as indicated in
FIG. 2
a
, the throughput of the pump
42
which feeds the generators is reduced by the valve
70
, with the result that the concentrated solution returning to the absorbers decreases, this decrease also causing a variation in the pressure drop and spray angle of the nozzles, so making it difficult to ensure that all the absorbent solution comes into contact with the tubes through which the cooling liquid flows. That solution part which is not cooled cannot absorb the steam from the evaporator, so resulting in a loss in machine efficiency.
The U.S Pat. No. 3,556,200 describes a heating and cooling system comprising one generator (
10
), one condenser (
11
) and also two absorbers (
13
,
14
) and two evaporators (
16
,
17
) operating at different pressure levels: a siphon tube (
37
) connects the two absorbers, and a siphon tube (
78
) connects the two evaporators. Like in U.S Pat. No.4,475,361 the entire dilute solution coming from the two absorbers is fed to the generator (
10
), thus suffering of the same drawbacks pointed out for such patent. It is to be noted that the two absorbers (
13
,
14
) are serially connected with the consequence that the concentrations of the liquids fed to each absorber are different, so that the temperature difference between the high pressure absorber (
14
) and the respective evaporator (
17
) is lower than that existing between the low pressure absorber (
13
) and its evaporator (
16
): the consequence is that cooling of absorber (
14
) is more difficult than it would be should the concentration of the liquid in it be same as in the absorber (
13
).
In the heat pump according to the present invention, the dilute solution originating from the absorbers is mixed and partly fed to the generators. The remainder is recycled by a pump after being mixed with the concentrated solution originating from the generators, forming an absorbent solution which is again fed to the abs
Buiz Michael
Jones Melvin
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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