METHOD OF OPERATING AN ABSORPTION HEAT PUMP OR REFRIGERATOR, AND AN ABSORPTION HEAT PUMP OR REFRIGERATOR

Abstract: A method of operating an absorption heat pump or refrigerator consisting at least of a refrigerant circuit and a refrigerant-containing solution circuit, with a generator for evaporating refrigerant from the solution with the supply of relatively high-temperature heat, a condenser for condensing refrigerant and giving up heat at an intermediate temperature level, an evaporator for evaporating refrigerant with the absorption of heat from a relatively cold heat source, a heat exchanger for transferring heat from the liquid passing out of the condenser to the refrigerant vapour and liquid coming from the evaporator, an absorber for absorbing refrigerant vapour into the solution with the giving-up of heat at an intermediate temperature level, and means for circulating the solution or maintaining the pressure, wherein the delivery of refrigerant is regulated in such a manner that the temperature differentialΔt w between the liquid entering the heat exchanger on the condenser side and the liquid and vapour leaving the heat exchanger on the absorber side substantially coincides with the temperature differential Δt k between the liquid passing out of the heat exchanger on the evaporator side and the liquid and vapour entering the heat exchanger on the evaporator side. This four-temperature control system is very effective and results in an increase of the power of the apparatus. The invention further relates to an apparatus constructed to fulfill the above operating conditions.

Description: The invention relates to a method of operating an absorption heat pump or refrigerator, consisting at least of a refrigerant circuit and a refrigerant-con­ taining solution circuit, with a generator for evapor­ ating refrigerant from the solution with the supply of relatively high-temperature heat, a condenser for con­ densing refrigerant and giving up heat at an intermedi­ ate temperature level, an evaporator for evaporating re­ frigerant with the absorption of heat from a relatively cold heat source, a heat exchanger for transferring heat from the liquid passing out of the condenser to the refrigerant vapour and liquid coming from the evaporator, an absorber for absorbing refrigerant vapour into the solution with the giving-up of heat at an intermediate temperature level, and means for circulating the solution or maintaining the pressure. A method of this kind is known from Plank, R., "Handbuch der Kaltetechnik" (1959), Part VII, particu­ larly pages 10 to 19. In the apparatus described there a heat exchanger, also referred to as an after-cooler, afterevaporator, or liquid cooler, can be included, in which condensate coming from the condenser is cooled by heating vapour and evaporating any entrained liquid. The action of this heat exchanger is described on page 13 and on pages 182 to 188 in the work referred to above. In an apparatus of the type first described above it is desired to achieve optimising regulation of the refrigerant delivery (D exp ) via a throttle means to the evaporator in order to increase the power of the apparatus. In the case of a heat pump this power is the power output for a constant generator power, and in the case of a refriger­ ator the evaporator power (refrigerating power) for a constant generator power. It has now been found that this power of the apparatus can be increased by applying a method of the type first described above, which is characterized in that the delivery of refrigerant is regulated in such a manner that the temperature differential Δ tw between the liquid entering the heat exchanger on the condenser side (t₁) and the liquid and vapour leaving the heat exchanger on the absorber side (t₄) substantially coincides with the temperature differential = t k between the liquid passing out of the heat exchanger on the evaporator side (t₂) and the liquid and vapour entering the heat exchanger on the evaporator side (t₃). This regulation will be referred to hereinbelow as four-temperature control. According to the four-­ temperature control of the method of the invention the heat ratio of the heat pump, that is to say the quotient of the power output and the power supplied to the gener­ ator, or the refrigeration factor of the refrigerator, that is to say the quotient of the power received in the evaporator and the power supplied to the generator, is substantially increased, particularly if the temperature of one or more of the heat sources and/or the (various) output temperatures vary considerably. For this purpose the delivery of refrigerant is regulated in such a manner that the difference (ΔΔ t) between Δ t w (= t₁ - t₄) and Δ t k (= t₂ - t₃) preferably amounts to about 0, and in particular at most amounts to plus or minus 10 K. In the present description the expression "heat source" is to be understood to mean any medium from which heat can be taken, for example air, earth, water (either flowing or still), foodstuffs. In order to enable the heat pump or refrigerator to work in a stable manner, the delivery of refrigerant is preferably also regulated on the basis of the dif­ ference (Δ t) between the temperature (t b ) of the heat source and the temperature (t o ) of the evaporator. It is preferable to apply the four-temperature control in cascade with regulation on the basis of t b - t o , so that the desired value of the latter is optimized. When the heat source is air and the evaporator temperature is lower than 0°C, it is advantageous for the moment of the commencement of the thawing of the frost accumulating on the evaporator also to be determined on the basis of Δ t or ΔΔ t, as the case may be. The invention also relates to an absoprtion heat pump or refrigerator which consists at least of a re­ frigerant circuit and a refrigerant-containing solution circuit, with a generator for evaporating refrigerant from the solution with the supply of heat at a relatively high temperature, a condenser for condensing refrigerant and giving up heat at an intermediate temperature level, an evaporator for evaporating refrigerant with the absorption of heat from a relatively cold heat source, a heat exchanger for transferring heat from the liquid passing out of the condenser to the refrigerant vapour and liquid coming from the evaporator, an absorber for absorbing refrigerant vapour into the solution with the giving-up of heat at an intermediate temperature level, and means for circulating the solution or maintaining the pressure, which heat pump or refrigerator is characterized in that at the inlets and outlets respectively of the heat exchanger there are disposed, in or on the four pipes or members connected thereto, temperature sensors which are connected via a regulating means to a regulable valve (throttle means), whereby the supply of the refrigerant to the evaporator is controlled. The invention further relates to an apparatus of the abovedescribed type, in which there are disposed both at the site of the heat source and in the evaporator, or close thereto, temperature sensors which are connected via a regulating means to the regulable valve controlling the supply to the evaporator. This regulation with the aid of temperature sensors at the site of the heat source and in or near the evaporator is preferably connected in cascade with the regulation with the aid of four tempera­ ture sensors at the site of the inlets and outlets of the heat exchanger, the latter regulation optimizing the desired value of the former. For an effective action of the four-temperature control according to the invention it is desirable for the liquid side of the heat exchanger to be continuously completely filled with liquid. The invention is explained more fully below with reference to the accompanying drawings. Figure 1 shows schematically a continuously acting absorption heat pump which can be operated in accordance with the invention. The components are as far far as possible set out in a p-T diagram, which clearly shows where the pressure or temperature is relatively high or low. In a generator 1 refrigerant is driven out of the solution of refrigerant and solvent by the supply of heat Qg. The generator 1 may be provided with a rectifier (2) in which the refrigerant vapour is freed from at last a part of the likewise evaporated solvent and the heat Q T released is discharged. The refrigerant vapour is passed via a pipe 3 to a condenser 4, in which the vapour con­ denses and the heat Q C is discharged. The liquid coming from the condenser 4 is passed via a pipe 5 to a heat ex­ changer 6, and the cooled liquid leaves the heat ex­ changer 6 via a pipe 7. The heat exchanger 6 is also known as an afterevaporator, liquid cooler, or after­ cooler. In the pipe 7 a throttle means 8 for an evap­ orator 9 is disposed. The refrigerant liquid at least partly evaporates in the evaporator 9 and takes up heat from the heat source (Q o ). The liquid-vapour mixture leaves the evaporator 9 via a pipe 10 and passes into the heat exchanger 6, which is connected by a pipe 11 to an absorber 12. In this absorber the refrigerant is ab­ sorbed, with the giving-up of heat Q a , into the solution, which is supplied via a pipe 15 from the generator 1. A throttle means 16 is disposed in the pipe 15. With the aid of a solution pump 13 the solution is passed via a pipe 14 to the generator 1. Figure 2 shows on a larger scale a part of the apparatus shown in Figure 1. In this Figure, Δt k and Δt w represent the differences between t₂ and t₃ and between t₁ and t₄ respectively. ΔΔ t is the difference between Δ t w and Δ t k , and surprisingly is an extremely suitable signal for optimum regulation of the evaporator. Figures 3a and 3b are block diagrams of the regu­ lation procedures which can be applied in accordance with the invention. The symbols used here, insofar as they have not previously been explained, have the following meanings: r value adjusted. c difference between value measured and value ad­ justed. The apparatus according to the invention can be operated with pairs of substances customarily used in apparatus of this kind, for example ammonia and water. The refrigerant need not be completely pure and may still contain a small amount of solvent. According to the present invention the evaporator used is a continuous-­ flow evaporator, for example a coil evaporator, from which any unevaporated refrigerant is entrained by the current of vapour. The application of the principle according to the invention is not restricted to the apparatus shown in Figure 1, and it can be applied in an absorption heat pump or absorption refrigerator of any type.

Claims: 1. Method of operating an absorption heat pump or refrigerator, consisting at least of a refrigerant cir­ cuit and a refrigerant-containing solution circuit, with a generator for evaporating refrigerant from the solution with the supply of relatively high-temperature heat, a condenser for condensing refrigerant and giving up heat at an intermediate temperature level, an evaporator for evaporating refrigerant with the absorption of heat from a relatively cold heat source, a heat exchanger for trans­ ferring heat from the liquid passing out of the condenser to the refrigerant vapour and liquid coming from the evaporator, an absorber for absorbing refrigerant vapour into the solution with the giving-up of heat at an inter­ mediate temperature level, and means for circulating the solution or maintaining the pressure, characterized in that the delivery of refrigerant is regulated in such a manner that the temperature differential Δ tw between the liquid entering the heat exchanger on the condenser side (t₁) and the liquid and vapour leaving the heat exchanger on the absorber side (t₄) substantially coincides with the temperature differential Δ tk between the liquid passing out of the heat exchanger on the evaporator side (t₂) and the liquid and vapour entering the heat exchanger on the evaporator side (t₃). 2. Method according to Claim 1, characterized in that the delivery of refrigerant is regulated in such a manner that the difference (ΔΔ t) between t₁ - t₄ and t₂ - t₃ amounts to approximately 0 and at most to plus or minus 10 K. 3. Method according to Claim 1 or 2, characterized in that the regulation of the delivery of refrigerant is also made dependent on the difference (Δ t) between the tempera­ ture of the heat source (tb) and that of the evaporator (to). 4. Method according to Claims 1 to 3, characterized in that the moment of the commencement of the thawing is adjusted on the basis of Δ t (= tb-to) or ΔΔ t (=t₁ - t₄) - (t₂ - t₃) = Δ tw -Δtk). 5. Method according to Claims 1 to 4, characterized in that the liquid side of the heat exchanger is kept continuously completely filled with liquid. 6. Absorption heat pump or refrigerator which con­ sists at least of a refrigerant circuit and a refriger­ ant-containing solution circuit, with a generator for evaporating refrigerant from the solution with the supply of heat at a relatively high temperature, a condenser for condensing refrigerant and giving up heat at an inter­ mediate temperature level, an evaporator for evaporating refrigerant with the absorption of heat from a relatively cold heat source, a heat exchanger for transferring heat from the liquid passing out of the condenser to the refrigerant vapour and liquid coming from the evaporator, an absorber for absorbing refrigerant vapour into the solution with the giving-up of heat at an intermediate temperature level, and means for circulating the solution or maintaining the pressure, characterized in that at the inlets and outlets respectively of the heat exchanger there are disposed, in or on the four pipes or members connected thereto, temperature sensors which are connected via a regulating means to a regulable valve, whereby the supply of the refrigerant to the evaporator is con­ trolled. 7. Apparatus according to Claim 6, characterized in that there are disposed both at the site of the heat source and in the evaporator, or close thereto, temperature sensors which are connected via a regulating means to the valve (8) which regulates the supply to the evaporator. 8. Apparatus according to Claim 6 or 7, character­ ized in that the regulation by means of temperature sensors at the site of the heat source and in or near the evaporator is connected in cascade with the regulation by means of four temperature sensors in or on the pipes or the members connected thereto in the heat exchanger.

Inventors: GELDERLOOS, POUWEL JELTE
Applicants: NEDERLANDSE ORGANISATIE VOOR TOEGEPAST-NATUURWETENSCHAPPELIJK ONDERZOEK TNO
Application year: 1986
Main classification: F25B49
IPC codes: F25B15, F25B41