SYSTEM AND METHOD FOR HEAT RECOVERY

(19)

(11)

EP 4 144 938 A1

(12)	EUROPEAN PATENT APPLICATION
	published in accordance with Art. 153(4) EPC

(43)	Date of publication:
	08.03.2023 Bulletin 2023/10

(21)	Application number: 20828994.2

(22)	Date of filing: 11.12.2020

(51)

International Patent Classification (IPC):

E04H 4/12^(2006.01)

F28D 21/00^(2006.01)

(52)	Cooperative Patent Classification (CPC):
	E04H 4/129

(86)	International application number:
	PCT/ES2020/070783

(87)	International publication number:
	WO 2021/219908 (04.11.2021 Gazette 2021/44)

(84)	Designated Contracting States:
	AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
	Designated Extension States:
	BA ME
	Designated Validation States:
	KH MA MD TN

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Priority:

28.04.2020 ES 202030359

(71)	Applicant: Lago Gutierrez, Santiago
	31013 Berriozar (Navarra) (ES)

(72)	Inventor:
	Lago Gutierrez, Santiago 31013 Berriozar (Navarra) (ES)

(74)	Representative: Maslanka Kubik, Dorota Irena
	C/Vara de Rey 5 TER, 3, Oficina 5 26003 Logroño (La Rioja) 26003 Logroño (La Rioja) (ES)

(54)	SYSTEM AND METHOD FOR HEAT RECOVERY

(57) System and method for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure, comprising a first cylinder (1) with connection ports to the source having a higher pressure and to the heat exchanger (11); a second cylinder (2) with connection ports to the source having a lower pressure and to the heat exchanger (11), and with a rod (3) common to the first cylinder (1); a first volumetric displacement body (4) fixed to the rod (3), generating in the first cylinder (1) two first chambers (6, 6') which are connected in an alternating manner to the source having a higher pressure or to the heat exchanger (11); and a second volumetric displacement body (5) fixed to the rod (3), generating in the second cylinder (2) two second chambers (7, 7').

Description

FIELD OF THE ART

[0001] The present invention relates to a system and a method for heat recovery, with minimum energy consumption, in the storage of liquids which require continuous renewal, as in the case of pools.

STATE OF THE ART

[0002] At present, in certain processes it is necessary to renew fluids in order to maintain their quality. In the case of heated pools, the water to be recycled daily is replaced with cold water from the water system. This amount ranges between 4% and 5% of the total volume of the pool, depending on the applicable regulation and the type of disinfection treatment applied.

[0003] The cold water that is introduced requires being heated to the usage temperature (26 to 27.5°C) from the starting temperature (between 4 and 16°C according to the area and time of year). Depending on the pool, between 20 and 60 m³ have to be heated a day, with a high energy cost that can be easily calculated. If about 28 m³ of water in a semi-olympic pool (25 x 12.5 x 2 m) with an inlet temperature of 9°C are renewed: Q = m · c · (t2-t1) = 28,000 kg x 0.0011619 (KWh/(°C·kg)) x (27-9) °C = 585.6 KWh This is the result without taking into account the heating output, which can be 0.8.

[0004] The installation of a heat exchanger would considerably reduce the energy expenditure of this daily renewal operation, because by circulating the outflowing water with the inflowing water through a heat exchanger, the temperature of the inflowing water could easily be raised up to 23°C. This greatly reduces energy consumption because the thermal difference is considerably lower.

[0005] This very simple and cost-effective operation is currently not performed for several reasons:
Water renewal is an operation that is usually performed manually. This means that an operator opens the drain valve of the pool and in about 10 minutes drains the described amount. It is then filled with water from the water system until reaching the desired level in the pool again. In order to obtain heat recovery in that time, an exchanger capable of handling flow volumes of 126 m³/h, with an exchange power of about 2,050 KW would be needed.

[0006] A standard exchanger of this size is particularly expensive and is not in use most of the day. Therefore, this investment is not appealing.

[0007] The size of the exchanger can be readily reduced by simply increasing the exchange time, that is, reducing the fill and drain speed.

[0008] By performing continuous renewal, i.e., over 24 h a day, the flow volume of the inflowing and outflowing water is reduced to 1.16 m³/h, and the power of the exchanger to 24.4 kW. This exchanger would have an approximate cost of € 800. This solution is more efficient and cost-effective. Nevertheless, for this exchange to be correctly performed it is necessary for the flow volume of inflowing and outflowing water to be considerably the same, otherwise the unwanted overflowing or draining of the pool would occur.

[0009] At this point it should be highlighted that filling is done at a water system pressure and draining is done by gravity. Therefore, the rated water output is entirely different from the rated filling, as pipe diameters and pressures pipes are different. Both rated output and filling must therefore be balanced.

[0010] The systems currently available for performing this balancing are:

Manual setting of the drain and fill valves. It is a very imprecise method that is very open to failures, changes in pressure of the supply system and other instabilities caused by the fouling of the filters. It is the most cost-effective method, but it is not at all recommended since it may give rise to excessive draining or overflowing.
Installation of control systems which may consist of variable volume flow pumps and/or motor-operated valves at the inlet and outlet working in combination with impulse counters and a control in charge balancing out flow volumes. It is a very precise system, but its cost renders its installation unappealing. This system could have an installed cost of € 16,000, in addition to the cost of the power consumption of the system.
Other systems on the heat recovery market are based on water to water heat pumps in which the water added to the pool is heated as it passes through the condenser and the extracted water is cooled upon passage thereof through the evaporator. These systems have a good performance, but their cost and the size necessary for their installation are high. Equipment of this type costs about € 60,000. The problem with balancing out flow volumes in this equipment is also solved by means of complex systems.

[0011] There is also equipment performing a flow volume balancing function, but they are intended for hydraulic power circuits and are not precise enough:

They are generally pumps with gearing that is coupled in pairs through common shafts. This equipment is prepared for working with high pressures in both lines and with lubricating liquids, such as hydraulic oil. Their function is to balance out flow volumes so as to ensure the rhythmic movement of two hydraulic cylinders.
Other equipment consists of auto control valve bodies working in an alternating manner diverting considerably the same flow volumes towards two outlet conduits.

[0012] Both types of equipment suffer from a lack of precision when the circuits with which they are associated have a different pressure.

[0013] Based on the foregoing, the equipment cannot be applied to solve the problem that is being considered.

BRIEF DESCRIPTION OF THE INVENTION

[0014] According to a first aspect, the present invention discloses a system for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure. The system comprises:

a heat exchanger to which both sources are connected; and
pumping equipment, which in turn comprises:
▪ a first cylinder with connection ports to the source having a higher pressure and to the heat exchanger;

▪ a second cylinder with connection ports to the source having a lower pressure and to the heat exchanger, and with a rod common to the first cylinder;

▪ a first volumetric displacement body fixed to the rod, generating in the first cylinder two first chambers which are connected in an alternating manner to the source having a higher pressure or to the heat exchanger; and

▪ a second volumetric displacement body fixed to the rod, generating in the second cylinder two second chambers;

such that the fluid having a higher pressure provides the energy necessary for pumping the fluid having a lower pressure.

[0015] As a result of the particular characteristics of the pumping equipment and its combination with the heat exchanger, the system of the present invention is a simple, compact, low-cost, and reduced energy-consuming system with high volumetric precision, since it can carry out its function without more external energy being provided than what is necessary for supervision functions. The applicant does not know of any solution that is as effective as the one provided by the present invention.

[0016] According to a second aspect, the present invention also provides a method for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure, by means of the system of the present invention. The method comprises the steps of:

a) introducing fluid from the source having a higher pressure into one of the first chambers of the first cylinder, communicating the other one of the first chambers with the heat exchanger;
b) displacing the rod as a result of the energy provided by the fluid having a higher pressure, thereby pumping the fluid having a lower pressure in the second cylinder towards the heat exchanger;
c) circulating the fluid coming from the first cylinder and the fluid coming from the second cylinder through the heat exchanger;
d) displacing the rod in the direction opposite the direction in which it was previously displaced, due to the effect of reversing the operation of the first chambers, thereby pumping the fluid having a lower pressure in the second cylinder towards the heat exchanger;
e) circulating the fluid coming from the first cylinder and the fluid coming from the second cylinder through the heat exchanger;
f) cyclically repeating the previous steps.

[0017] According to a third aspect, the present invention relates to the use of the system for heat recovery according to the present invention in the renewal and treatment of water in pools.

[0018] Throughout the description and the claims the word "comprises" and its variants does not intend to exclude other technical features, additives, components, or steps. Furthermore, the word "comprises" includes the case of "consists of". For those skilled in the art, other objects, advantages and features of the invention will become apparent in part from the description and in part from putting the invention into practice. The following examples are provided by way of illustration and are not intended to be limiting of the present invention. Furthermore, the present invention covers all the possible combinations of particular embodiments herein indicated.

DESCRIPTION OF THE DRAWINGS

[0019] To complement the description being made and for the purpose of helping to better understand the features of the invention, a set of drawings is attached in which the following is depicted in an illustrative and non-limiting manner.

Figure 1 shows a schematic view of an embodiment.

Figure 2 shows a detail of Figure 1.

Figure 3 shows a schematic view of a second embodiment, with a double body valve.

Figure 4 shows a detail of Figure 3.

EMBODIMENTS OF THE INVENTION

[0020] According to a first aspect, the present invention discloses a system for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure.

[0021] As shown in Figures 1, 2, 3, and 4, the system comprises a pumping equipment (23) and a heat exchanger (11) to which the fluid source having a lower pressure and the fluid source having a higher pressure are connected.

[0022] As will be explained below, the pumping equipment (23) continuously displaces the same proportion of fluid from the source having a higher pressure and fluid from the source having a lower pressure, so it is a system with volumetric precision.

[0023] As used herein, the term "volumetric displacement body" is defined as a part moving in an alternating manner inside a cylinder body for displacing a fluid or for receiving movement from the same. For example, a piston, or a membrane, are volumetric displacement bodies.

[0024] The pumping equipment (23) comprises a first cylinder (1) with connection ports to the source having a higher pressure and to the heat exchanger (11). It also comprises a second cylinder (2) with connection ports to the source having a lower pressure and to the heat exchanger (11). Both cylinders (1, 2) have a common rod (3) to which two volumetric displacement bodies (4, 5) are fixed, generating 4 chambers (6, 6', 7, 7'): Namely, a first volumetric displacement body (4) generates in the first cylinder (1) two first chambers (6, 6'), and a second volumetric displacement body (5) generates in the second cylinder (2) two second chambers (7, 7').

[0025] The first chambers (6, 6') of the first cylinder (1) are connected in an alternating manner to the source having a higher pressure or to the heat exchanger (11). While one of the first chambers is connected to the source having a higher pressure, the other one is connected to the heat exchanger and vice versa.

[0026] The pumping equipment (23) utilizes the difference in pressure between fluids to perform pumping. The working fluid coming from the source having a higher pressure, for example water from a supply system (8), enters one of the first chambers (6, 6') of the first cylinder (1) and moves the first volumetric displacement body (4). The movement of the first volumetric displacement body (4) causes an increase in volume of one of the first chambers at the expense of reducing the volume of the other first chamber, which is drained. The movement of the first volumetric displacement body (4) is transmitted by the rod (3) to the second volumetric displacement body (5), and the pumping of the fluid coming from the source having a lower pressure towards the heat exchanger (11) occurs in the second cylinder (2). As described, the fluid having a higher pressure provides the energy necessary for pumping the fluid having a lower pressure.

[0027] According to a particular embodiment, the fluid source having a higher pressure has a lower temperature than the source having a lower pressure. According to an alternative option, it is the fluid source having a lower pressure that has a lower temperature. According to a more particular embodiment, the source having a higher pressure is a supply system (8), and the source having a lower pressure is a basin (9) of a pool. Optionally, the source having a higher pressure can be a pumping system, and the source having a lower pressure can be a tank.

[0028] According to a particular embodiment shown in Figures 1 and 2, the first cylinder (1) has a connection port in each of its first chambers (6, 6'). Each connection port acts in an alternating manner as a suction port or as a discharge port, as a result of the control of a distribution valve (10). While one port acts as a suction port, the other port acts as a discharge port; and subsequently, the suction port becomes a discharge port, and the other port becomes a suction port. With respect to the second cylinder (2), each of its second chambers (7, 7') has a suction port and a discharge port. The distribution valve (10) controls the direction of the fluid in the first cylinder (1), communicating its chambers in an alternating manner with the heat exchanger (11) or with the respective fluid source. In particular, the distribution valve (10) determines at all times to which of the first chambers (6, 6') of the first cylinder (1) the fluid from the source having a higher pressure is diverted and which one is connected to the heat exchanger (11). According to a particular option shown in Figures 1 and 2, the distribution valve (10) is a four-way, two-position valve (4/2 valve).

[0029] According to an alternative embodiment shown in Figures 3 and 4, the arrangement of the connection ports in the first cylinder (1) is the same as in the second cylinder (2). Both cylinders have a connection port in each of their corresponding chambers, acting in an alternating manner as a suction port or as a discharge port, as a result of the control of a distribution valve (10). While one port of a cylinder acts as a suction port, the other port of the same cylinder acts as a discharge port; and subsequently, the suction port becomes a discharge port, and the other port becomes a suction port. In this case, the distribution valve (10) is a double body valve. Each of the bodies of the distribution valve (10) controls the direction of the fluids in one of the cylinders, communicating its corresponding chambers in an alternating manner with the heat exchanger (11) or with the respective fluid source. In particular, a body of the distribution valve (10) determines at all times to which of the first chambers (6, 6') of the first cylinder (1) the fluid from the source having a higher pressure is diverted and which one is connected to the heat exchanger (11); the other body of the distribution valve (10) determines at all times to which of the second chambers (7, 7') of the second cylinder (2) the fluid from the source having a lower pressure is diverted and which one is connected to the heat exchanger (11). According to the particular option shown in Figures 3 and 4, each of the bodies of the distribution valve (10) has a four-way and two-position design (4/2 valve).

[0030] The distribution valve (10) can be programmed by times or controlled by actuation means, such as by control devices for example. According to a particular embodiment, the pumping equipment (23) comprises control devices (12) at the ends-of-travel of the rod (3) which control the distribution valve (10). Optionally, the control devices (12) can be arranged at the ends-of-travel of the volumetric displacement bodies (4, 5).

[0031] The control devices (12) act on the distribution valve (10) such that each time a control device (12) detects the corresponding end-of-travel (or shortly before that if it is more appropriate), the distribution valve (10) alternates the first chamber (6, 6') that is drained and the one that is filled from the source having a higher pressure. This involves the movement of the rod (3) and of the volumetric displacement bodies (4, 5) in the opposite direction. The control devices (12) can be electric, hydraulic, or electronic.

[0032] The fluids discharged from the first cylinder (1) and from the second cylinder (2) are conducted to the heat exchanger (11). In the heat exchanger (11), the heat energy from the fluid having a higher temperature is utilized to increase the temperature of the other fluid. In the figures, the heat exchanger (11) is a parallel flow exchanger, but it can be a counter-flow exchanger without departing from the scope of the present invention as a result.

[0033] According to a particular embodiment shown in the figures, the fluid exiting the heat exchanger (11) coming from the source having a higher pressure and from the first cylinder (1) is diverted to the source having a lower pressure. The fluid exiting the heat exchanger (11) coming from the source having a lower pressure and from the second cylinder (2) is diverted to the outlet of the system, for example to dispose of it in a drain or to send it out for external use.

[0034] The system of the present invention may comprise an inlet valve (24) controlling the fluid inlet into the system and an outlet valve (25) controlling the fluid outlet from the system. The system operates continuously while the inlet valve (24) and outlet valve (25) are open, and stops when at least one of them is closed.

[0035] The regulation of the system (for example the flow volume for renewal of the water of a pool) can be performed by acting on the pressure of the fluid coming from the source having a higher pressure. For example, it may have a pressure regulator (13) or a choke valve.

[0036] As mentioned above, the pumping equipment (23) continuously displaces the same proportion of fluid from the source having a higher pressure and fluid from the source having a lower pressure, so it is a system having volumetric precision. According to a particular embodiment, the first cylinder (1) and the second cylinder (2) have the same dimensions so as to ensure that the displaced volume of fluid from the source having a higher pressure is the same as the displaced volume of fluid from the source having a lower pressure. Since the cylinders have the same dimensions and the displacement of the volumetric displacement bodies (4, 5) also, the volumes of both fluids in each cycle are identical. Accordingly, it is not necessary to monitor the regulation or setting and there is no risk of excessive draining or overflow.

[0037] Optionally, the dimensions of the first cylinder (1) can be different from the dimensions of the second cylinder (2) if a different proportion of fluid having a higher pressure and fluid having a lower pressure is desired. For example, it may be necessary to introduce in the basin (9) of the pool more water than what is extracted so as to compensate for evaporation, overflowing, or other losses. In that case, the cylinders may have different sections. The differences in volume of the volumetric displacement bodies (4, 5), for example based on their thickness, can also be used to modify the proportion.

[0038] According to a particular embodiment, the volumetric displacement bodies (4, 5) are membranes. To ensure precision in the desired proportion, it is necessary for the membranes to be non-stretchable, such as tarp membranes, for example. According to an alternative option, the volumetric displacement bodies (4, 5) are pistons.

[0039] According to an embodiment shown in the figures, the system includes non-return devices (15) to ensure the function of each connection port of the cylinders and that the flow of fluids is performed in the desired directions. The system may also comprise other devices, such as one or more filters (17) to prevent fouling of the heat exchanger (11); one or more pressure gauges (16), and one or more temperature sensors (19) for controlling the correct operation and warning of the possible fouling of the heat exchanger (11); one or more hydropneumatic accumulators (14) for preventing transient excess pressures, for example in the instant that the rod (3) reaches the end-of-travel and the pumping changes direction; one or more flow detectors (18) cutting off the passage of fluid if a flow volume is not detected in some point of the system, to check for leaks, and to prevent flooding or damages in the case of burst pipes; etc.

[0040] Optionally, the system may also comprise one or more electrically operated cut-off valves (20) receiving information from one or more flow detectors (18) and cutting off the passage of fluid if it is detected that it does not reach the desired destination. There can also be arranged a control system (26), controlling the interrelation between corresponding flow detectors (18) and electrically operated cut-off valves (20). The control system (26) may be a mechanical, electric, or electronic system, for example a programmable automaton. Namely, as shown in Figures 1 and 3, the system may comprise:

two flow detectors (18): one in the conduit communicating the heat exchanger (11) with the basin (9) of the pool, and another one in the conduit communicating the heat exchanger (11) with the outlet of the system;
two electrically operated cut-off valves (20): one in the conduit communicating the supply system (8) with the first cylinder (1), and another one in the conduit communicating the basin (9) of the pool with the second cylinder (2);
a control system (26) with which the two flow detectors (18) and the two electrically operated cut-off valves (20) are associated.

[0041] Therefore, if the flow detectors (18) detect that fluid is not reaching the basin (9) of the pool, or that fluid is not exiting the heat exchanger (11) towards the outlet of the system, they send a signal to the control system (26), and the latter actuates the corresponding electrically operated cut-off valves (20), the flow of the supply system (8) and/or the outlet flow of the basin (9) of the pool being stopped.

[0042] The system of the present invention is optimized for low pressures (less than 10 bar). For example, the pressure of the working fluid coming from the supply system (8) is between 2 and 5 bar, and the pressure of the water of the basin (9) of a pool is usually about 0.25 bar (atmospheric pressure plus the hydrostatic pressure corresponding to the height existing between the surface level of the pool and the pump room).

[0043] According to a second aspect, the present invention also provides a method for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure, by means of the system of the present invention. The method comprises the following steps:

a) introducing fluid from the source having a higher pressure into one of the first chambers (6, 6') of the first cylinder (1), and simultaneously communicating the other one of the first chambers (6, 6') with the heat exchanger (11);
b) displacing the rod (3) as a result of the energy provided by the fluid having a higher pressure, thereby pumping the fluid having a lower pressure in the second cylinder (2) towards the heat exchanger (11).
The fluid having a higher pressure, provides the energy necessary for pumping the fluid having a lower pressure. Namely, according to the particular option shown in the figures, the fluid having a higher pressure that has been introduced into one of the first chambers (6, 6') pushes and produces the movement of the first volumetric displacement body (4), and accordingly the movement of the rod (3) and of the second volumetric displacement body (5), with the subsequent pumping of the fluid having a lower pressure;
c) circulating the fluid coming from the first cylinder (1) and the fluid coming from the second cylinder (2) through the heat exchanger (11);
d) displacing the rod (3) in the direction opposite the direction in which it was previously displaced, due to the effect of reversing the fill direction of the first chambers (6, 6'), thereby pumping the fluid having a lower pressure in the second cylinder (2) towards the heat exchanger (11).
To carry out this step, fluid from the source having a higher pressure is introduced in the chamber which was previously in communication with the heat exchanger (11), and simultaneously communicates the chamber in which the fluid from the source having a higher pressure was previously introduced with the heat exchanger (11);
e) circulating the fluid coming from the first cylinder (1) and the fluid coming from the second cylinder (2) through the heat exchanger (11);
f) cyclically repeating the previous steps.

[0044] According to a particular embodiment, the method comprises additional steps c') and e'), after steps c) and e), respectively, of diverting the fluid coming from the first cylinder (1) to the source having a lower pressure, and simultaneously diverting the fluid coming from the second cylinder (2) to the outlet of the system.

[0045] According to a particular embodiment, the changes in direction of the displacement of the rod (3) are carried out by the action of the distribution valve (10), which diverts the fluid from the source having a higher pressure in an alternating manner to either of the first chambers (6, 6') of the first cylinder (1).

[0046] As a result of the particular characteristics of the pumping equipment and its combination with the heat exchanger, the fluid having a higher pressure provides the mechanical energy necessary for pumping the fluid having a lower pressure, and the fluid having a higher temperature provides the heat energy for the increase in temperature of the fluid having a lower temperature, which results in considerable energy savings, which is very useful, for example, in the case of the renewal and treatment of pool water. The system of the present invention is therefore a simple, compact, low-cost, and reduced energy-consuming system with high volumetric precision, since it can carry out its function without more external energy being provided than what is necessary for supervision functions.

[0047] In addition to the application of the present invention in the renewal and treatment of water in pools, it is also applicable in other fields in which fluids are handled, such as in water treatment in general, in the chemical, pharmaceutical, or food industries.

[0048] The applicant does not know of any solution that is as effective as the one provided by the present invention.

[0049] Although the present invention has been described in reference to particular embodiments thereof, those skilled in the art will be able to make amendments and variations to the teachings hereinabove without departing from the scope and the spirit of the present invention as a result.

Claims

1. A system for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure, characterized in that it comprises:

- a heat exchanger (11) to which both sources are connected; and

- pumping equipment (23), which in turn comprises:

• a first cylinder (1) with connection ports to the source having a higher pressure and to the heat exchanger (11);

• a second cylinder (2) with connection ports to the source having a lower pressure and to the heat exchanger (11), and with a rod (3) common to the first cylinder (1);

• a first volumetric displacement body (4) fixed to the rod (3), generating in the first cylinder (1) two first chambers (6, 6') which are connected in an alternating manner to the source having a higher pressure or to the heat exchanger (11); and

• a second volumetric displacement body (5) fixed to the rod (3), generating in the second cylinder (2) two second chambers (7, 7');

such that the fluid having a higher pressure provides the energy necessary for pumping the fluid having a lower pressure.

2. The system according to claim 1, wherein the fluid source having a higher pressure is a supply system (8) at a lower temperature than the fluid source having a lower pressure, which is a basin (9) of a pool.

3. The system according to any of the preceding claims, comprising a distribution valve (10) which diverts the fluid from the source having a higher pressure in an alternating manner to either of the first chambers (6, 6') of the first cylinder (1).

4. The system according to claim 3, wherein the distribution valve (10) is a double body valve, which diverts the fluid from the source having a lower pressure in an alternating manner to either of the second chambers (7, 7') of the second cylinder (2).

5. The system according to either of claims 3 or 4, wherein the pumping equipment (23) comprises control devices (12) at the ends-of-travel of the rod (3), which control the distribution valve (10).

6. The system according to any of the preceding claims, wherein the fluid from the source having a higher pressure is diverted to the source having a lower pressure after the passage thereof through the heat exchanger (11)

7. The system according to any of the preceding claims, wherein the first cylinder (1) and the second cylinder (2) have the same dimensions.

8. The system according to any of the preceding claims, wherein the first volumetric displacement body (4) and the second volumetric displacement body (5) are non-stretchable membranes.

9. The system according to any of the preceding claims, comprising one or more hydropneumatic accumulators (14) for preventing transient excess pressures.

10. The system according to any of the preceding claims, comprising one or more flow detectors (18) cutting off the passage of fluid if they do not detect a flow volume.

11. A method for heat recovery between a fluid source having a lower pressure and a fluid source having a higher pressure, by means of the system defined in any of claims 1 to 10, characterized in that it comprises the steps of:

a) introducing fluid from the source having a higher pressure into one of the first chambers (6, 6') of the first cylinder (1), communicating the other one of the first chambers (6, 6') with the heat exchanger (11);

b) displacing the rod (3) as a result of the energy provided by the fluid having a higher pressure, thereby pumping the fluid having a lower pressure in the second cylinder (2) towards the heat exchanger (11);

c) circulating the fluid coming from the first cylinder (1) and the fluid coming from the second cylinder (2) through the heat exchanger (11);

d) displacing the rod in the direction opposite the direction in which it was previously displaced, due to the effect of reversing the fill direction of the first chambers (6, 6'), thereby pumping the fluid having a lower pressure in the second cylinder (2) towards the heat exchanger (11).

e) circulating the fluid coming from the first cylinder (1) and the fluid coming from the second cylinder (2) through the heat exchanger (11);

f) cyclically repeating the previous steps.

12. The method according to claim 10, comprising additional steps c') and e'), after steps c) and e), respectively, of diverting the fluid coming from the first cylinder (1) to the source having a lower pressure.

13. The method according to any of claims 10 or 11, wherein the changes in direction of the displacement of the rod (3) are carried out by the action of the distribution valve (10), which diverts the fluid from the source having a higher pressure in an alternating manner to either of the first chambers (6, 6') of the first cylinder (1).

14. Use of the system defined in any of claims 1 to 10 in the renewal and treatment of water in pools.

Amended claims under Art. 19.1 PCT