JPH046357A - Operation method of heat utilizing apparatus using hydrogen-occlusion alloy - Google Patents

Abstract

PURPOSE:To recover the sensible heat at a changeover operation of a heat utilizing apparatus at a high efficiency and in a relative simple way by a method wherein a heat-medium pipes, which supply heating medium from three sorts of heat sources or a thermal load to a hydrogen occlusion alloy tank, is switched first, and then a heat medium return pipe, by which the heat medium is returned to the heat sources or the thermal load after a delayed time period, is switched. CONSTITUTION:Only changeover valves 5, 6, 21 and 22, which are located on heat medium inlet sides, are switched first. That is, heat medium pipes 40 and 50 are switched first. Thereby, the sensible heat of the hydrogen-occlusion alloy tanks 1A and 1B is effectively utilized (sensible heat recovery). 10 - 30 sec after that, changeover valves 7, 8, 23 and 24 on the heat medium outlet sides are switched, so that heat medium pipes 41 and 51 are switched. 30 - 60 sec after the changeover operation of an apparatus is completed, stop valves 33 and 34 are opened to transfer hydrogen. Thus, Hydrogen H2 moves from the hydrogen-occlusion alloy tank 1B to a hydrogen- occlusion alloy tank 17B, and a reverse process, in which hydrogen H2 moves from a hydrogen-occlusion alloy tank 17A to the hydrogen-occlusion alloy tank 1A, takes place.

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a method of operating a heat utilization system using a hydrogen storage alloy, and is particularly suitable for application to heat pumps, heat transport systems, and cooling and cooling systems. .

(b) Conventional technology Hydrogen storage alloys have the property of repeatedly absorbing and releasing large amounts of hydrogen under certain reaction conditions, and at the same time, it is known that considerable reaction heat is generated during this absorption and release. .

Heat utilization systems that utilize this reaction to obtain hot and cold heat have already been proposed, as disclosed in Japanese Patent Application Laid-open No. 56-100276 and Japanese Patent Application Laid-Open No. 58-22854.

However, in these systems using hydrogen storage alloys, in order to enable continuous operation, at least two units are installed in which two hydrogen storage alloy tanks, each containing a hydrogen storage alloy, are connected by hydrogen piping. It is essential to alternately switch and operate the However, during alternating switching operation, the high-temperature heat medium now flows into one hydrogen storage alloy tank, where the low-temperature heat medium had been flowing, and the low-temperature heat medium now flows into the other hydrogen storage alloy tank, where the high-temperature heat medium had been flowing. In this case, the temperature of the hydrogen storage alloy container had to be changed significantly.

Therefore, the necessity of such operations has been a cause of a significant decrease in the thermal efficiency of heat utilization systems using hydrogen storage alloys. In order to improve this, Unexamined Japanese Patent Publication No. 57
As seen in Japanese Patent No. 104063, a structure has been proposed in which each hydrogen storage alloy container of two sets of hydrogen storage alloy tank units exchanges heat.

(c) Problems to be solved by the invention However, the system method shown in the above publication requires large attached equipment, and it is difficult to efficiently recover excess heat from the heat utilization system (sensible heat recovery). It wasn't.

The present invention has been made in view of the above-mentioned problems, and uses a relatively simple method to increase sensible heat recovery during operation switching of heat utilization systems such as heat pumps, heat transport, and cold storage systems that utilize hydrogen storage alloys. The purpose is to provide a highly efficient heat utilization system.

(d) Means for solving the problem The heat utilization system and its operating method according to the present invention are as follows:
In the heat medium piping cutting process for operation switching, the heat medium piping that supplies heat medium from three types of heat sources or heat loads to the hydrogen storage alloy tank is first switched, and then, after a delay time, the heat medium piping is switched from the hydrogen storage alloy tank to the heat source. Alternatively, by switching the heating medium piping that returns the heating medium to the heat load, a sensible heat recovery method is adopted that effectively utilizes the surplus heat in the heat utilization system, and in particular, the heating medium flow rate during sensible heat recovery can be reduced. The flow rate of the heat medium is controlled to be smaller than the flow rate of the heat medium during hydrogen transfer in the heat utilization system.

Preferably, 1 compared to the heat medium flow rate for operation of the heat utilization system.
The purpose is to reduce the flow rate to 73 to 2/3 and increase the heat exchange rate, thereby achieving highly efficient sensible heat recovery.

Furthermore, in addition to the operating method of controlling the heat medium flow rate described above, the temperature of the heat medium supplied to the heat load is sensed, and the operation/stop of the heat medium supply pump to the heat load is controlled based on that temperature, thereby achieving high efficiency heat utilization. system.

(e) Effect The heat medium flow rate when performing sensible heat recovery is set to the optimum heat medium flow rate that enables high-efficiency sensible heat recovery, regardless of the heat medium flow rate during hydrogen transfer in the heat utilization system. sensible heat recovery can be achieved, and a highly efficient heat utilization system can therefore be provided.

(f) Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a conceptual diagram of the configuration of a heat utilization system according to an embodiment of the present invention which can be applied to cold heat generation systems and the like.

In the figure, LA and IB are hydrogen storage alloy tanks containing a hydrogen storage alloy MH [1] with the same characteristics as shown in the equilibrium characteristic diagram described later, and the tanks themselves are made of a pressure-resistant material such as stainless steel. ing. and hydrogen storage alloy MH [
1], AB whose alloy composition is rare earth-Ni based,
Use mold metal. In addition, heat exchangers 2a and 2b are also accommodated in these tanks IA and IB, and these heat exchangers 2a and 2b are
A heat medium is supplied to 2b through heat medium pipes 3 and 4. In each heat medium pipe 3, 4, switching valves 5, 6, 7.8 are provided on the inlet side and outlet side of the heat medium with respect to the heat exchangers 2a, 2b. The heating medium pipes 40 and 41 are arranged so that the heating mediums 9 and 10 circulating between I→VI and ■→■' exchange with each other and flow into the other heat exchangers 2a and 2b by switching 8.
The heating medium path is configured to be switchable. 11 and 12 are the heat medium circulation system ■→ I'
, II→■', a heating medium circulation pump p1. It is p2.

The circulation pump 11 uses a high temperature heat medium 9 of about 130 to 150°C.
The circulation pump 12 is for circulating 20~
This is for circulating the heat medium 10, that is, cooling water, from a cooling source at about 25°C. The above configuration is referred to as system 1.

On the other hand, 17A and 17B are the aforementioned hydrogen storage alloys M)I
[1] are two hydrogen storage alloy tanks each containing a hydrogen storage alloy MH[2] having a characteristic that the equilibrium hydrogen pressure is high at the same temperature. This alloy tank 17A.

17B is also made of stainless steel, and this hydrogen storage alloy MH[2] is also a rare earth-Ni based AB type metal.

Similarly to system I, on the system ■ side where the hydrogen storage alloy tanks 17A and 17B are installed,
Heat exchangers 18a and 18b provided in each tank 17A and 17B
and heat medium pipes 19, 20 that supply heat medium to the respective heat exchangers 18a, 18b, and switching valves 21, 22, 23, 24 provided on the heat medium inlet side and outlet side of the heat medium pipes 19, 20, respectively. , and circulation pumps (P□, P4) 25, 26 that circulate the heat medium between the heat medium circulation systems m-m' and rv-rv'. Also, by switching the switching valves 21, 22, 23.24, the heat medium 27, 30 circulating between m-m' and IV-IV' are exchanged with each other and transferred to other heat exchangers 18a, The heat medium pipes 50, 5 flow into the heat medium pipe 18b.
1, and the heat medium path is switchably formed.

The circulation pump 25 is for circulating a heat medium (cooling water) 27 from a cooling source of about 20 to 25 degrees Celsius, and the circulation pump 26 is for circulating a heat medium 30 that supplies cold heat to a heat load such as a refrigerated warehouse.
It is for circulating.

Then, hydrogen storage alloy tanks IA and IB and hydrogen storage alloy tank 1
7A and 17B are connected by hydrogen pipes 31.32, and an on-off valve 33.34 provided in the middle allows hydrogen to flow back and forth.

With the above configuration, the switching valves 5 and 7 are operated to supply the high temperature heat medium 9 to the heat exchanger 2a, hydrogen is generated in the hydrogen storage alloy tank IA, and the low temperature heat medium (cooling water) 27 is heated. operating the switching valve 21.23 to supply the exchanger 18a;
At the same time, the switching valves 6 and 8 are operated to supply the low temperature heat medium (cooling water) 10 to the heat exchanger 2b.

Further, the switching valves 22 and 24 are operated to supply the heat exchanger 18b with the return heat medium 30 from a heat load such as a refrigerated warehouse. In this state, the on-off valve 3 of the hydrogen pipes 3+, 32
3. Open and close 34.

By the way, each hydrogen storage alloy tank IA, IB, 17A, 1.
Hydrogen storage alloys MH[1] and MH[ accommodated in 7B
2] has the equilibrium characteristics shown in the van't Hoff plot in FIG. That is, the hydrogen storage alloy MH[l] has hydrogen dissociation characteristics shown by the solid line A and hydrogen absorption characteristics shown by the dotted line A' under given temperature conditions. Similarly, the hydrogen storage alloy MH[2] has hydrogen dissociation properties indicated by the solid line openings and hydrogen absorption properties indicated by the openings '. Therefore, with the heating medium piping as described above, the hydrogen storage alloy MH[1] in the hydrogen storage alloy IA through which the I→Bi system high temperature heating medium 9 circulates generates hydrogen H2 with the equilibrium characteristic A. . and.

Since the hydrogen storage alloy MH[2] in the hydrogen storage alloy tank 17^ in which the heating medium 27 of the ■→■' system circulates exhibits an equilibrium characteristic mouth, this hydrogen H2 moves from point A to point 0 in the figure. As shown in the figure, the hydrogen storage alloy MH[
2] absorbs hydrogen and generates heat, and this heat is transferred to the cooling water 2
removed by 7.

On the other hand, the hydrogen storage alloy Ml (El) in the hydrogen storage alloy tank IB through which the cooling water 10 from ■→■' circulates is maintained at a low pressure state where it can absorb hydrogen H2 due to the equilibrium characteristic A'. Furthermore, by opening the valve 34 in the hydrogen pipe 32, the hydrogen storage alloy MH[2] in the hydrogen storage alloy tank 17B can be removed from the hydrogen storage alloy M in the hydrogen storage alloy tank IB.
It is induced by the pressure of H[1] to be in a low pressure state, and at the same time, the hydrogen storage alloy MHE2] lowers in temperature due to its equilibrium characteristic. In this state, hydrogen H
Move from B to hydrogen storage alloy tank IB. Therefore, an endothermic reaction occurs in the hydrogen storage alloy tank 17B, and the heat exchanger 18
The temperature of the heating medium 30 is lowered by b, and cold heat is extracted. Therefore, this cold energy is transferred to the heat load (not shown) of the refrigerated warehouse, etc.
The heat is recovered by the return heat medium 30 from the heat exchanger, and the cold heat is again supplied to a heat load such as a refrigerated warehouse. The above process is referred to as the first process. Note that points A, 0, 8, and D in the above text are assigned to the hydrogen storage alloys MH[1] and MH[2] in the hydrogen storage alloy tanks LA, 17A, IB, and 17B in Figure 1. Alphabet A, C.

This is a substitute corresponding to B and D.

Here, when the hydrogen transfer in both processes is completed, the on-off valve 3
3. Close 34 to stop hydrogen transfer. After that, in order to perform continuous operation, the switching valves 5, 6, 7, 8, 21, 22°2
3, 24, each hydrogen storage alloy IA, 17A
and I.B.

A reverse process (second process) is performed between the tank 17B and the hydrogen storage alloy tank 17A, and cold energy is recovered from the hydrogen storage alloy tank 17A.

That is, this time, the heat medium 30 flows as follows: ■→circulation pump 26→switching valve 22→heat exchanger 18a→switching valve 23→■'.

Cold heat is recovered from the hydrogen storage alloy tank 17A.

By the way, when switching this operation, for example in the I→VI system and the ■→■' system, if the switching valves 5 and 6 on the heat medium inlet side and the switching valves 7 and 8 on the heat medium outlet side are switched at the same time, 1 The following inconveniences occur. That is, upon switching, cooling water at 20 to 25°C flows into the hydrogen storage alloy tank IA, and high temperature heating medium at 130 to 150°C flows into the hydrogen storage alloy tank IB. Since Alloy IA was kept at a high temperature, high-temperature heating medium flows from hydrogen storage alloy tank IA through the route IA → 7 → ■' → ■ → 6 → IA, causing excessive cooling capacity to the cooling source (not shown). request. Similarly, in the hydrogen storage alloy tank IB, immediately after switching, the hydrogen storage alloy IB was kept at a low temperature, so the low temperature heat medium (20 to 25°C) was transferred from the hydrogen storage alloy tank IB to IB → 8 by the switching valve 8. →I′→I, and the heat source (not shown)
requires excessive heating capacity.

In this way, if all the switching valves 5, 6, and 7.8 are switched at the same time, the sensible heat existing in the (-+ I' system, ■→■' system) will adversely affect the system operation.Similarly, Also in the ■→■′ system and the ■→■′ system, the switching valve 21,
Due to the simultaneous switching of hydrogen storage alloy tanks 22, 23, and 24, the sensible heat of each hydrogen storage alloy tank 17A, 17B will adversely affect the operation of the system in the same way as described above.

Therefore, in order to effectively utilize this sensible heat within the system, switching valves 5, 6 and 21.
Only 22 is switched first. Namely.

The heat medium pipe 40.50 is switched first. This way,
For example, the heating medium containing sensible heat (high temperature heating medium) in the hydrogen storage alloy tank IA is I → 11 → 5 → 2b → 8 → ■' → ■ → 10 → 6
→2a→7→■′→■Flows through a closed heat medium path.

An excessive load is not placed on the heat source and the cooling source, and in other words, the sensible heat of the alloy tanks IA and IB is effectively utilized (sensible heat recovery). In this way, the hydrogen storage alloy tank IA.

Heat is received within 18 hours, and sensible heat can be effectively recovered.

By taking such a method, sensible heat is recovered,
After that, by switching the switching valves 7, 8, 23.24 on the heat medium outlet side at intervals of 10 to 30 seconds, the heat medium pipes 41, 51 are also switched, resulting in complete system operation switching. . In addition, hydrogen transfer will begin after 30 to 60 seconds have passed after the complete system operation has been switched, and the hydrogen on-off valve 33.34
Do this by opening up. In this way, hydrogen storage alloy tank IB
Hydrogen H2 moves from the hydrogen storage alloy tank 17B to the hydrogen storage alloy tank 17B, and hydrogen H2 moves from the hydrogen storage alloy tank 17A to the hydrogen storage alloy tank IA.
The reverse process of moving is performed, and the hydrogen storage alloy tank 17A
More cold energy is recovered.

However, the sensible heat recovery system has been completely switched over for 10 days.
Since this is carried out within a short time of ~30 seconds, efficient heat exchange is required.

Therefore, in the present invention, when recovering sensible heat, the flow rate of the heat medium is reduced so that sensible heat can be effectively exchanged with the heat medium from the heat exchanger in each tank. Conventionally, the same amount of heat medium flows during sensible heat recovery as when the system is operating by transferring hydrogen, and it only flows for a short period of about 10 seconds before recovery is complete. However, in the present invention,
The time for flowing the heat medium is also 10 seconds or more (10 to 30 seconds),
A highly efficient sensible heat recovery method is achieved by slowly flowing a small amount of heat medium.

Changes in the flow rate of the heat medium can be handled by adjusting the operating capacity of each pump 11, 12, 25, 26, etc. That is, the present invention is characterized in that the heat medium flow rate during sensible heat recovery for 10 to 30 seconds described above is changed by a smaller amount than the heat medium flow rate when hydrogen transfer is performed.

In this way, the objective is to increase the efficiency of sensible heat recovery during sensible heat recovery, and also to increase the efficiency and output of the refrigeration system. Specifically, in order to optimize the heat medium flow rate during sensible heat recovery, we prototyped a system and investigated the relationship between heat medium flow rate and sensible heat recovery rate.

The prototype cooling and heating system consists of hydrogen storage alloy tanks IA and IB.

16 kg of hydrogen storage alloy MH for each of 17A and 17B
[1] and MH[2] were charged and the operation was performed. In this operation, heating mediums 9, 10, 27 .
The flow rate of No. 30 is 10 fl/win.

First, we tried the conventional sensible heat recovery method using the above prototype cooling and heating system. In other words, the heat medium was flowed at a flow rate of 10 Q/min, which is the same as when the system is operating, and sensible heat recovery was performed by delaying the switching of the valves before and after the hydrogen storage alloy tank as described above. As a result, the delay time is 10 seconds
The maximum sensible heat recovery was achieved at this time, and the sensible heat recovery rate (sensible heat exchange rate) at that time was 50%.

Next, the method of the present invention was tried. That is, the heat medium flow rate was varied only during the period during which sensible heat recovery was performed, and the sensible heat recovery rate was measured. The results are shown in FIG. In addition,
In the figure, the vertical dotted line C indicates the sensible heat recovery rate (50%) when the heat medium flow rate is the same as when the system is operating (10Q/win) and the switching delay time is 10 seconds.

As can be seen from FIG. 3, it was found that the sensible heat recovery rate increased significantly when the flow rate of the heat medium for sensible heat recovery was reduced. On the other hand, if the heat medium flow rate is lowered, highly efficient sensible heat recovery is possible, but in order to recover sensible heat slowly, the delay time for switching the valves before and after the hydrogen storage alloy tank becomes longer, and the heat medium flow rate increases. 5 Q/min is 25~30sec
, lower flow rates require longer times. Therefore, if the heat medium flow rate is significantly reduced, the period during which the movement of hydrogen gas is stopped becomes longer, which reduces the thermal output of the cooling and heating system. Therefore, we investigated the thermal output of the cooling and heating system when changing the heat medium flow rate during sensible heat recovery.

Figure 4 plots the influence of heat medium flow rate on heat output, and from this figure, the heat medium flow rate during normal operation is 10Q.
/m1n(d), the heat medium flow rate during sensible heat recovery is 1
/3 to 2/3 (between E and E).

It was found that this is an operating method that leads to higher efficiency and higher output of the cooling and heating system.

Furthermore, in the present invention, the circulation pump 26 that supplies the heat medium for heat recovery to the heat load is controlled to operate or stop depending on the temperature of the heat recovery heat medium 30, thereby generating temperature-stable heat. It also has the feature of being able to supply a medium.

That is, after achieving highly efficient sensible heat recovery by controlling the heat medium flow rate during sensible heat recovery as described above, in the next process, the hydrogen storage alloy filled with hydrogen storage alloy M) I [2] Cold energy is recovered from the other tank of the alloy tank and supplied to heat loads such as cold storage warehouses, but at the beginning of the process, the hydrogen storage alloy tank is not sufficiently cooled.

Suppose that the operation is switched from the state in which cold energy is extracted from the hydrogen storage alloy tank 1.7B, and the hydrogen storage alloy tank 17A
Assuming that cold energy is extracted from the hydrogen storage alloy tank IA, at the initial stage of switching, the hydrogen storage alloy tank IA is heated by the cooling water 10.
The low pressure and low temperature conditions that allow the absorption of 2 have not yet been achieved. Therefore, hydrogen H2 is not sufficiently transferred from the hydrogen storage alloy tank 17A to the hydrogen storage alloy tank IA through the hydrogen pipe 31, and the temperature of the hydrogen storage alloy tank 17A is not sufficiently lowered, and the heat inside the tank 17A is exchanger 1
The heat medium 30 exiting from 8a remains high in temperature.

Therefore, if the circulation pump 26 is operated even in this situation, warm heat will be supplied to the heat load, and the cooling/heating system will not function sufficiently. Therefore, in this case, the pump 26 that circulates the return heat medium from the heat load is controlled to operate and stop depending on the temperature of the hydrogen storage alloy MH[2], thereby preventing high-temperature heat from flowing into the heat load. Able to drive efficiently. Therefore, H[2
] Temperature detection means 35 for detecting the temperature is arranged in the hydrogen storage alloy tanks 17A and 17B. When the temperature measurement means 35 detects that the heat medium temperature is below a set temperature, the circulation pump 26 is stopped, and when the temperature is higher than that, the circulation pump 26 is continued to operate. By doing so, the sufficiently cooled heat medium 30 can be stably supplied to the heat load, resulting in a high-output cooling/heating system.

In this way, by controlling the flow rate of the heat medium during sensible heat recovery and, if necessary, controlling the operation and stop of the circulation pump for the heat recovery heat medium according to the temperature of the heat recovery heat medium, high heat recovery can be achieved. Able to provide efficient, high output cooling and heating systems. Furthermore, it goes without saying that the above operating method can be applied to heat pump systems and heat transport systems using hydrogen storage alloys in exactly the same way.

(g) Effects of the Invention As described above, the present invention provides that, in a heat utilization system using a hydrogen storage alloy, when recovering sensible heat in the system during alternating operation, the amount of heat medium flowing can be reduced. By making the flow rate of the heat medium smaller than when the system is operating and circulating it slowly, the heat exchange rate can be increased and more efficient sensible heat recovery can be achieved.

In addition, the temperature of the hydrogen storage alloy is measured to control the failure and stoppage of the circulation pump that supplies the heat medium for heat recovery to the heat load, so there is still sufficient cold or heat at the time of operation switching. It is possible to prevent the unused heat medium from flowing into the heat load, and it is possible to stably supply high-quality heat above the usage temperature level.

In this way, by adopting the operating method of the present invention,
High-efficiency and high-output operation are possible in cold-heat system heat pumps and heat transport systems using hydrogen storage alloys, and their industrial value is great.

[Brief explanation of the drawing]

Figure 1 is a system configuration diagram of a cooling/heating system using a hydrogen storage alloy, Figure 2 is a cooling cycle diagram of the cooling/heating system shown in Figure 1 on the van't Hoff diagram, and Figure 3 is a diagram of the cooling system based on the heat medium flow rate. Diagram of experimental measurement results showing changes in sensible heat recovery rate,
FIG. 4 is a diagram showing experimental measurement results showing changes in thermal output depending on the flow rate of the heat medium. LA, IB, 17A, 17B--hydrogen storage alloy tank,
2a, 2b, 1.8a. iab... Heat exchanger, 5, 6, 21, 22... Switching valve on the heat inlet side, 7.8, 23, 24... Switching valve on the heat medium outlet side, 26... To heat load heat medium supply pump, 3o
...heat medium flowing to the heat load. 35... Means for detecting the temperature of the heat medium supplied to the heat load, MH
[1], MH[2]...Hydrogen storage alloy. Agent Patent Attorney Crest 1) Seime ≧ Figure Figure S, V lame tt (//m1n) Figure Mffitt (//min)

Claims (3)

[Claims] (1) first and third hydrogen storage alloy tanks each housing a first hydrogen storage alloy and a heat exchanger to which heat medium from two types of external heat sources having different temperature levels are switchably supplied; The second and fourth hydrogen absorbers each house a heat exchanger to which a heat medium from a third external heat source and a heat recovery heat medium used for heat load are switchably supplied, and a second hydrogen storage alloy. Switching between the hydrogen storage alloy tank, the hydrogen piping to which the first and second and third and fourth hydrogen storage alloy tanks are connected, and the first and third hydrogen storage alloy tanks and the two types of external heat sources, respectively. The first and second hydrogen storage alloy tanks are configured of heat medium piping that connects each other in a switchable manner, and heat medium piping that connects the second and fourth hydrogen storage alloy tanks and the third external heat source and heat load in a switchable manner. The first and second processes in which the directions of hydrogen transfer between the hydrogen storage alloy tanks and between the third and fourth hydrogen storage alloy tanks are opposite to each other are performed alternately, and the switching between these processes is performed using the heat medium. This is done by switching the piping, and at the time of this switching, the heating medium piping on the heating medium inlet side of each hydrogen storage alloy tank is first switched to form a heating medium circulation path for sensible heat recovery, and then, In a heat utilization system that recovers sensible heat within the heat utilization system by switching the heat medium piping on the heat medium outlet side, the flow rate of the heat medium during this sensible heat recovery is used as hydrogen transfer in the heat utilization system. 1. A method of operating a heat utilization system using a hydrogen storage alloy, characterized in that the flow rate of the heat medium is controlled to be smaller than the flow rate of the heat medium. (2) The hydrogen according to claim 1, characterized in that the flow rate of the heat medium during sensible heat recovery is 1/3 to 2/3 of the flow rate of the heat medium during hydrogen transfer in the heat utilization system. How to operate a heat utilization system using storage alloys. (3) A means for detecting the temperature of the hydrogen storage alloy that supplies heat to the heat load is provided, and operation and stop of the heat medium supply pump to the heat load is controlled based on this temperature. A method of operating a heat utilization system using a hydrogen storage alloy.