METHOD FOR RECUPERATION OF THERMAL ENERGY FROM A MOTORIZED HEAT PUMP

Abstract

Method of recovering thermal energy from a motorized heat pump (1) comprising a step of: removal of the heat in the condenser (4), removal of the heat in the engine recuperator (11), removal of the heat in the exhaust recuperator (17), restoration of the heat removed in a heat restorer (21) that the heat transfer loop (18) passes through, the method being capable of: determining the power of the combustion in the heat engine (7), determining the refrigeration power available in the evaporator (3), modulating the speed of rotation of the heat engine (7) such that the refrigeration power is numerically superior to the combustion power.

Description

The invention concerns heat pumps and thermo-refrigeration pumps driven by a heat engine, hereinafter called motorized heat pumps and motorized thermo-refrigeration pumps. More particularly, the invention concerns energy efficiency of motorized heat pumps and motorized thermo-refrigeration pumps.

The term thermo-refrigeration pump is used in the industry to designate a heat pump having an arrangement that enables heat and cold to be obtained simultaneously. In other words, heat production is valued as much as the production of cold.

The heat pump is a well-known device. It is used in different applications requiring the production of heat or cold. Thus, heat pumps are found in air-conditioning devices, production of sanitary hot water, or simply in refrigerators.

Generically, a heat pump comprises an evaporator in which the refrigerant absorbs the heat, the refrigerant changes state and passes from the liquid phase to the gaseous phase. The fluid is then compressed in a compressor where its pressure and temperature increase sharply. The refrigerant then passes through a condenser where, as the name indicates, the refrigerant is condensed while yielding up its heat. The refrigerant returns to the evaporator passing first through an expansion valve in which the pressure of the fluid drops. It will be noted that a heat pump on the one hand comprises a low-pressure circuit comprising the evaporator which extends from the expansion valve to the intake of the compressor, and a high pressure circuit comprising the condenser and which extends from the discharge of the compressor to the expansion valve.

The compressor is coupled to an electric motor or heat engine. In the following, we will only be interested in heat pumps for which the compressor requires the use of a heat engine, with no distinction as regards the fuel used to supply it.

The energy efficiency of heat pumps is measured by the coefficient of performance. Said measurement can be calculated by the Carnot method accompanied by a coefficient corresponding to the efficiency of the thermodynamic cycle. Typically, the coefficient of performance of heat pumps falls between 2 and 10. The overall efficiency of transformation of primary energy into electrical energy in an electrical system is known and established by the International Energy Agency. In order for a motorized heat pump to use primary energy as well as a gas fired boiler, a so-called condensing boiler which requires 100% primary energy, a heat pump driven by electric motor must have a coefficient of performance of at least 2.58, which corresponds to the value of the primary energy coefficient for the French electricity system. A motorized heat pump directly uses the primary energy furnished by the fuel and its primary energy coefficient (PEC) can therefore be established.

In a thermo-refrigeration pump, both the cold and the heat are used. Thus, from the point of view of the refrigerant of the heat pump, the cold obtained at the evaporator is used for air conditioning, for example, or for cooling products, and inversely the heat obtained at the condenser is allocated to heating needs.

When the compressor of the heat pump is driven by a heat engine, it is known to recover the heat from its cooling system and its exhaust gases. In order to use the heat, it is advantageous to drive the heat pump compressor directly by the shaft of the heat engine without going through an electric dual conversion.

The British patent published under number GB 652.162 (JAMES HAROLD EVANS) discloses a heat pump driven by a heat engine. The condenser of the heat pump is used to heat the water intended for a building. The water thus heated is mixed with three other sources of water, each respectively heated by a cooling circuit of the compressor, a cooling circuit of the heat engine and by the exhaust gases. Ultimately these four sources of heated water are mixed in a manifold where the temperature of the water thus mixed will vary in proportion to the temperature and volume of the water sources.

This device seems to be a priori complete. However, the uncontrolled mixing of the sources of hot water definitely does not allow the energy efficiency to be optimized. Quite the contrary, since this method only weakens the heating power of the hottest source.

Moreover, the solution presented in said document involves an extremely complex tangle of piping. Furthermore, the heat recovery from the cooling circuits and exhaust gases is also uncontrolled. The benefit (as regards temperature) of the hottest sources is canceled out by the coldest sources.

First, a method is proposed for recuperation of thermal energy from a motorized heat pump equipped with a heat pump in which a refrigerant circulates, comprising:

an evaporator connected to a heat source, a condenser connected to a cold source,

• a compressor,
• an expansion valve,
• a heat engine mechanically coupled to the compressor in order to drive it, the engine comprising an outlet of the exhaust gases produced by the combustion,
• a cooling system for the heat engine, comprising a heat exchanger called engine recuperator,
• a recuperator of heat from the exhaust gases, called exhaust recuperator,
  the motorized heat pump defining at least one heat transfer loop in which a heat transfer fluid circulates intended to remove the heat from the condenser, from the heat engine and from the exhaust gases, wherein the condenser, the engine recuperator and the exhaust recuperator are placed in series, the heat transfer loop passing through the condenser, the engine recuperator and the exhaust recuperator, the method comprising the following steps:
• removal of the heat in the condenser,
• removal of the heat in the engine recuperator,
• removal of the heat in the exhaust recuperator,
• restoration of the heat removed in a heat restorer that the heat transfer loop passes through,
  the motorized heat pump comprising a control unit equipped with a computerized program arranged to:
• determine the power of the combustion in the heat engine,
• determine the refrigeration power available in the evaporator,
• modulate the speed of rotation of the heat engine such that the refrigeration power is numerically superior to the combustion power.

Various additional characteristics can be foreseen, alone or in combination:

• • the method comprises the control of the speed of the heat engine such that the combustion power can be modulated between 30% and 100% of the maximum available combustion power;
  • the combustion power is calculated as a function of the quantity of fuel injected and of the inferior or superior calorific value of the fuel;
  • the method comprises an:
• operation of measuring the temperature of the refrigerant of the heat pump upstream from the evaporator by means of a temperature sensor positioned upstream from the evaporator;
• operation of measuring the pressure of the refrigerant of the heat pump upstream from the evaporator by means of a pressure sensor positioned upstream from the evaporator;
  • the method comprises an:
• operation of measuring the temperature of the refrigerant of the heat pump downstream from the evaporator by means of a temperature sensor positioned downstream from the evaporator;
• operation of measuring the pressure of the refrigerant of the heat pump downstream from the evaporator by means of a pressure sensor positioned downstream from the evaporator;
  • the method comprises an operation of determining the enthalpy upstream and downstream of the evaporator of the refrigerant from data tables for a given refrigerant as a function of the measured pressures and temperatures;
  • the method comprises an operation of calculating the refrigeration power in the evaporator as the product of the mass flow of the refrigerant times the difference in enthalpy of the refrigerant between the upstream and downstream of the evaporator.

Secondly, a motorized heat pump is proposed in which a refrigerant circulates, the motorized heat pump comprising:

• an evaporator connected to a heat source,
• a condenser connected to a cold source,
• a compressor,
• an expansion valve,
• a heat engine mechanically coupled to the compressor in order to drive it, the heat engine comprising an outlet of the exhaust gases produced by the combustion,
• a cooling system for the heat engine, comprising a heat exchanger called engine recuperator,
• a recuperator of heat from the exhaust gases, called exhaust recuperator,
  the motorized heat pump defining at least one heat transfer loop in which a heat transfer fluid circulates intended to remove the heat from the condenser, from the heat engine and from the exhaust gases, wherein the condenser, the engine recuperator and the exhaust recuperator are placed in series, the heat transfer loop passing through the condenser, the engine recuperator and the exhaust recuperator, the motorized heat pump comprising a control unit equipped with a computerized program arranged to execute the method as previously described.

According to one particular embodiment, the motorized heat pump comprises:

• a temperature sensor,
• a pressure sensor, and
• a flow rate sensor,
  the computer program being arranged to execute the method as previously described.

Thirdly, a utilization is proposed of the motorized heat pump as previously described in order to use the energy from waste water from industries or gray waters from housing to heat a heat transfer fluid circulating in a recycling circuit.

Other objects and advantages of the invention will be seen from the following description of an embodiment, provided with reference to the appended drawings in which:

FIG. 1 is a schematic illustration of a motorized heat pump according to a first embodiment;

FIG. 2 is a schematic illustration of a motorized heat pump according to a second embodiment;

FIG. 3 is a schematic illustration of a motorized heat pump according to a third embodiment.

The first part of this description describes the common points of the different embodiments. Each of the FIGS. 1 to 3 represents a motorized heat pump 1 comprising a heat pump 2 equipped with:

• an evaporator 3,
• a condenser 4,
• a compressor 5,
• an expansion valve 6.

The compressor 5 is mechanically coupled to a heat engine 7 supplied by a fuel. A refrigerant circulates in the heat pump 2. The refrigerant is a zeotropic mixture (also known as a temperature glide mixture). The zeotropic mixture comprises several fluids the volatilities of which are different, and as a result the evaporation temperatures thereof are also different.

The heat engine 7 is cooled by means of a cooling system 8 comprising:

• a cooling circuit 9,
• a cooling pump 10,
• a heat exchanger, hereinafter called engine recuperator 11.

A refrigerant, for example brine, circulates in the cooling circuit 9 due to the action of the cooling pump 10. The refrigerant increases in temperature in the heat engine 7, and decreases in temperature in the engine recuperator 11.

The combustion of the fuel in the heat engine 7 generates exhaust gases. The exhaust gases leave through an exhaust duct 12 before entering into an exhaust gas heat exchanger 13.

The heat from the exhaust gases is removed by means of a recuperation loop 14. The recuperation loop 14 is provided with an exhaust fluidic circuit 15 in which a heat transfer fluid circulates. An exhaust pump 16 ensures the circulation of the heat transfer fluid in the exhaust fluidic circuit 15. The exhaust fluidic circuit 15 passes through an exhaust heat recuperator 17 in order to restore the heat acquired in the exhaust gas heat exchanger 13.

The motorized heat pump 1 comprises a heat transfer loop 18 provided with a heat transfer circuit 19 in which a heat transfer fluid circulates. A heat transfer pump 20 ensures the circulation of the heat transfer fluid in the heat transfer circuit 19. The heat transfer loop 18 is arranged in such a way that the heat transfer circuit 19 passes through the condenser 4 of the heat pump 2, the engine recuperator 11, the exhaust recuperator 17 and a heat restorer 21. Thus, the heat transfer loop 18 recycles, in increasing order of temperatures, the heat from the heat engine 7, exhaust gases and from the condenser 4, thanks to the heat transfer loop 18. Said loop restores this heat as a result of the heat restorer 21.

The motorized heat pump 1 exploits waste water from industries or gray water from housing in order to recycle their heat. The gray water enters the motorized heat pump 1 at the evaporator 3 of the heat pump by an evaporator intake 22, at a temperature t₁. The gray water leaves the motorized heat pump 1 through an evaporator outlet 23 at a temperature t₂ that is lower than t₁. In parallel, a heat recycling circuit 24 passes through the heat restorer 21. A heat transfer fluid circulates in said recycling circuit 24, entering the heat restorer 21 by a restorer intake 25 at a temperature t₃. The heat transfer fluid leaves the heat restorer 21 through a restorer outlet 26, at a temperature t₄ that is higher than t₃.

The arrangement set forth above makes it possible to obtain a high Primary Energy Coefficient [French initials CEP] of the motorized heat pump 1.

The following theoretical values are defined:

• the power available at the condenser 4 Q_K=Q₀+W where Q₀ is the power consumption at the evaporator 3 (refrigeration power) and W is the mechanical power of the compressor 5 furnished by the heat engine 7 and transferred to the refrigerant by the compressor 5 in the heat pump 2;
• the coefficient of performance of the heat pump

${\mathrm{COP}}_{\mathrm{PAC}}=\frac{Q_K}{W};$

• the power furnished by the fuel Q_comb=Q_out+W_where Q_out is the thermal power lost by the heat engine 7 at the engine block and at the exhaust;
• the primary energy coefficient of the motorized heat pump 1 with a thermal efficiency equal to 1 (in order to simplify the calculations)

$\mathrm{CEP}=\frac{Q_k+Q_{\mathrm{out}}}{Q_{\mathrm{comb}}};$

• the mechanical efficiency of the heat engine 7;

$R_{\mathrm{méca}}=\frac{W}{Q_{\mathrm{comb}}}$

• the energy recuperation efficiency from the heat engine 7 and from the exhaust gases

$R_{\mathrm{th}}=\frac{Q_{\mathrm{rec}}}{Q_{\mathrm{out}}}$

where Q_rec is the thermal power at the heat engine 7 and at the exhaust.

The primary energy coefficient of the motorized heat pump 1 is written as follows:

$\mathrm{PEC}=\frac{Q_k+Q_{\mathrm{out}}}{Q_{\mathrm{comb}}}$

The numerator and denominator are divided by the compression power W:

$\mathrm{PEC}=\frac{\left(Q_k+Q_{\mathrm{out}}\right)/W}{Q_{\mathrm{comb}}/W}$

This makes it possible to reveal the coefficient of performance of the heat pump 2:

$\mathrm{PEC}=\frac{{\mathrm{COP}}_{\mathrm{PAC}}+Q_{\mathrm{out}}/W}{1/R_{\mathrm{méca}}}$

In accordance with the previously defined values, Q_out=Q_comb−W, which in the previous expression gives:

$\mathrm{PEC}=\frac{{\mathrm{COP}}_{\mathrm{PAC}}+\frac{Q_{\mathrm{comb}}-W}{W}}{1/R_{\mathrm{méca}}}$

According to the definition of mechanical efficiency, we have,

$\mathrm{PEC}=\frac{{\mathrm{COP}}_{\mathrm{PAC}}+\frac{1}{R_{\mathrm{méca}}}-1}{1/R_{\mathrm{méca}}}$ $\mathrm{PEC}=R_{\mathrm{méca}}{\mathrm{COP}}_{\mathrm{PAC}}+1-R_{\mathrm{méca}}$

By adding the thermal efficiency R_th we obtain, in theory, the following equation, hereinafter called equation A:

PEC=R_méca×COP_PAC+R_th×(1−R_méca)

Equation A above indicates that the primary energy coefficient of the motorized heat pump 1 is a function of the coefficient of performance of the heat pump 2, of the mechanical efficiency of the heat engine 7 and of the thermal energy recuperation efficiency.

By taking a primary energy coefficient equal to 1 (which constitutes the minimum low threshold for which it is beneficial to use a motorized heat pump compared to a condensing boiler), and by setting the thermal and mechanical efficiencies respectively to 0.8 and 0.35. A minimum COP_PAC of 2.05 is obtained. This value is lower than the minimum COP when electricity from the French mains is used. Thus, there is a certain interest in using the motorized heat pump rather than a condensing boiler.

The coefficient of performance of the heat pump 2 is a function of the temperature difference between the evaporator 3 and the condenser 4 of the heat pump 2. However, the heat pumps 2 used in industry or in homes are already efficient. Indeed, said heat pumps 2 recover energy from waters the temperature of which varies between 30° C. and 60° C. Said heat pumps 2 then raise the temperature over intervals ranging from 30° C. to 50° C. The coefficient of performance of heat pumps 2 doing such work falls between 4 and 8.

Irrespective of the coefficient of performance of the heat pump, experiments conducted by the applicant have shown that the energy efficiency is better when the refrigeration power at the evaporator 3 is greater than the combustion power available in the heat engine 7.

The applicant examined the theoretical aspect of these observations. The mathematical approach that will now be presented is only an attempt at modeling the phenomenon.

We begin with the expression of the system's coefficient of performance with a thermal efficiency equal to 1 (in order to facilitate the calculations). This makes it possible to express the recuperated power Q_rec as a function of two sources of heat, namely Q_K and Q_comb.

$\mathrm{PEC}=\frac{Q_k+Q_{\mathrm{rec}}}{Q_{\mathrm{comb}}}$

Both sides are multiplied by Q_comb,

Q_comb×PEC=Q_k+Q_rec

Q_comb×PEC=Q₀+W+R_th×Q_out

According to the definition of the power furnished by the fuel,

Q_comb×PEC=Q₀+W+R_th×(Q_comb−W)

Q_comb×(PEC−R_th)=Q₀+W−R_th×W

Q_comb×(PEC−R_th)=Q₀+W×(1−R_th)

With W=R_méca×Q_comb, we have

Q_comb×(PEC−R_th)=Q₀+R_méca×Q_comb×(1−R_th)

Q₀=Q_comb×[PEC−R_th−R_méca×(1−R_th)]

Finally, we obtain the following equation, hereinafter called equation B:

$\frac{Q_0}{Q_{\mathrm{comb}}}=\mathrm{PEC}-R_{\mathrm{th}}-R_{\mathrm{méca}}\left(1-R_{\mathrm{th}}\right)$

It will be noted that equation B establishes the ratio between the two heat sources based only on the primary energy coefficient, the mechanical efficiency of the engine and the efficiency of recuperating heat lost by the engine.

The mathematical equation B enables an important finding to be made about Q₀. By establishing a normal thermal efficiency R_th of 80%, a standard mechanical efficiency for a heat engine R_méca of 35%, and a primary energy coefficient of 1, we have:

$\frac{Q_0}{Q_{\mathrm{comb}}}=1-0.8-0.350.2$ $Q_0=0.13Q_{\mathrm{comb}}$

With a primary energy coefficient equal to that of a gas fired condensing boiler (PEC=1), which it will be recalled recycles 100% of the primary energy that it uses, it will be noted (to obtain the same performance) that the power Q₀ must be equal to at least 13% of Q_comb. It therefore seems possible to obtain a better primary energy coefficient with a motorized heat pump than with a condensing boiler, by ensuring that the power Q₀ is at least more than 13% of Q_comb.

A second finding can be made from the equation B by having the power Q₀ be equal to the power Q_comb with the same efficiency values as before:

PEC=1+0.8+0.35×(1−0.8)=1.87

The primary energy coefficient is already about 1.9, while the power Q₀ is equal to the combustion power Q_comb.

It will therefore be noted that the primary energy coefficient of the motorized heat pump 1 is as much higher as the refrigeration power is higher than the combustion power. In order to act on the combustion power, the power of the heat engine must be variable. The combustion power can then be properly adjusted in order to be sufficiently below the refrigeration power in order to improve the energy performance of the motorized heat pump 1.

The embodiments presented in the figures illustrate an arrangement of the motorized heat pump 1 making it possible to recuperate about 80% of the available energy from the heat engine 7. The available energy from the heat engine 7 corresponds to the recuperated energy by cooling the heat engine 7 and the energy recuperated from the exhaust gases. The mechanical efficiency of the heat engine 7 is at least 0.3, and the coefficient of performance of the heat pump 2 falls between 2 and 10.

In the following, using a specific example the proportions will be illustrated numerically between the power delivered to the condenser Q_K and the thermal powers recuperated from the heat engine when the refrigeration power Q₀ is greater than the combustion power Q_comb. For the calculations, an R_méca of 0.35 and R_th of 0.8 will be used. The PEC of the motorized heat pump 1 is on the order of 2, that is, in practice the necessary primary energy is divided by 2.

By way of example, we will take a temperature t₁ of 30° C., a temperature t₂ of 60° C., a temperature t₃ of 70° C. and a temperature t₄ 120° C. In this configuration the fluid entering the evaporator 3 is at 60° C. and it leaves cooled down to 30° C. In parallel, the heat restorer 21 increases the temperature by a difference of 50° C. The fluid enters at 70° C. and leaves heated to 120° C.

On the basis of the temperatures t₁, t₂, t₃, and t₄ as previously defined, the refrigerant in the heat pump 2 varies between 28° C. and 58° C. to cool the wastewater from 60° C. to 30° C. The average evaporation temperature of the refrigerant in the evaporator 3 is about 43° C.

The recuperated power Q_rec in the heat transfer loop 18 corresponds to the sum of the power available at the condenser 4 Q_K, the refrigeration power in the engine recuperator 11 and hereinafter called Q_ref and the power available in the exhaust recuperator 17 Q_ech expressed as a function of the thermal efficiency R_th. The thermal distribution in the heat transfer loop 18 is therefore established as follows:

Q_rec=Q_K+Q_ref+R_th×Q_ech

with Q_K=Q₀+W, we have

Q_rec=Q₀+W+Q_ref+R_th×Q_ech

and knowing that W=Q_comb×R_méca, we obtain

Q_rec=Q₀+Q_comb×R_méca+Q_ref+R_th×Q_ech

by replacing Q₀ by its expression as a function of Q_comb the result is,

Q_rec=[COP_sys−R_th−R_méca×(1−R_th)]×Q_comb+Q_comb×R_méca+Q_ref+R_th×Q_ech

It is important to note that with a PEC of about 2 (precisely 1.87), a thermal efficiency R_th of 0.8 and a mechanical efficiency of 0.35, the power available at the condenser Q_K is broadly dominant over the others. It corresponds to about 80% of the thermal energy furnished in the heat transfer loop 18. The other two, namely Q_ref and W_ech, will respectively represent 8% and 12%.

The heat transfer loop 18 enables a heating of 50° C. In accordance with the percentages broken down in the preceding paragraph, it can be deduced that the condenser 4 allows a temperature increase of 40° C., from 70° C. to 110° C., the engine recuperator 11 contributes 8% or 4° C., from 110° C. to 114° C., and finally the exhaust recuperator 17 contributes 12%, or 6° C. from 114° C. to 120° C.

The average condensation temperature of the refrigerant of the heat pump 2 is about 92° C., which corresponds to a temperature difference with the evaporator 3 of 39° C. Based on that, the coefficient of performance of the heat pump 2 is determined according to the Carnot method:

${\mathrm{COP}}_{\mathrm{PAC}}=\frac{273+92}{49}=7.45$

However, the efficiency of commercially available compressors is around 0.6. The actual coefficient of performance of the heat pump 2 is therefore:

COP_PAC=7.45×0.6=4.47

By using the formula of the primary energy coefficient of the motorized heat pump 1 in accordance with that of the heat pump, we obtain:

PEC=0.35×4.47+0.8×(1−0.35)=2.08

By using the formulation of recuperated power we have:

Q_rec=[PEC−R_th−R_méca×(1−R_th)]×Q_comb+Q_comb×R_méca+Q_ref+R_th×Q_ech with Q_ech=R_méca×Q_comb

In a heat pump 2 with a compressor 5 driven by a heat engine, the typical distribution of the thermal power as a function of the combustion power Q_comb is as follows: about 35% from mechanical work, 20% from the refrigeration power Q_ref (value measured in continuous operation for a heat engine), 35% from the exhaust and finally 10% from losses by radiation and from the heat transmitted to the engine oil.

Q_rec=1.21·Q_comb+0.35·Q_comb+0.2·Q_comb+0.28·Q_comb

Q_rec=1.56·Q_comb+0.48·Q_comb=2.04·Q_comb

The condenser 4 contributes here 76%, and together the engine recuperator 11 and exhaust recuperator 17 contribute 24% to the total recuperated power.

It is important to note that 23% of the energy available to the condenser 4 is from the mechanical energy of the heat engine 7. The rest is from the evaporator 3 (from the source of cold) in the amount of 77%.

0.77×1.56±2.04=0.589

The evaporator 3 therefore contributes precisely 59% of the total recuperated thermal power which corresponds to Q₀. The remaining power, or 41%, is from the thermal power Q_comb (recuperated from the exhaust gases and from the cooling circuit of the heat engine). This makes it possible to obtain at the recycling circuit 24 a temperature t₄ of 120° C. with an average use at 95° C., and this is from gray waters available in the evaporator at an average temperature of 43° C.

In this way, it was verified that with the parameters provided, namely the temperatures t₁, t₂, t₃, t₄, and the efficiencies R_th and R_méca, as well as the COP_PAC, the valuation of the primary energy is done with a factor of 2 and the power extracted at the cold source is greater than the power provided by the fuel. The different ratios established allow a fine regulation of the motorized heat pump, and make it possible to expect the highest energy efficiencies.

In order to vary the speed of rotation of the heat engine 7 (and of the compressor 5 of the heat pump 2), the motorized heat pump 1 advantageously comprises a computerized control unit (not shown in the figures).

The computerized control unit is equipped with a computer program defining a strategy for controlling the motorized heat pump 1. The strategy can be based on several different factors, one of which can consist of making the power recuperated at the heat transfer loop 18 proportional to the combustion power. The computer program can make the speed of rotation of the heat engine 7 vary so that the combustion power can be modulated between 30% and 100% of the total available combustion power. A rule is deduced therefrom for increasing or decreasing the speed of the heat engine 7 which will affect the speed of the compressor 5 and thus the speed of the refrigeration power. A method based on such a law for controlling the speed of rotation of the heat engine 7 advantageously makes it possible to achieve optimized energy efficiency.

Advantageously, the heat pump 2 is equipped with a temperature sensor and a pressure sensor (not shown in the figures) upstream and downstream of the evaporator 3 in the heat pump 2. Using data tables provided for a given refrigerant, the measured temperatures and pressures enable the enthalpy of the refrigerant to be determined upstream and downstream of the evaporator 3. The heat pump 2 is also equipped with a flow rate sensor to measure the volumetric flow of the refrigerant in the heat pump 2. From the volumetric flow, the control unit calculates the mass flow by multiplying it by the volumetric mass of the refrigerant, which is obviously known at a given temperature. The control unit then accurately determines the refrigeration power available in the evaporator 3 by multiplying the mass flow of refrigerant by the enthalpy difference between the upstream and downstream of the evaporator 3.

The combustion power is determined by multiplying the quantity of fuel injected into the heat engine 7 by the upper or lower calorific value of the fuel.

1^st EMBODIMENT

Represented in FIG. 1 is a motorized heat pump 1 as described previously in the part common to the different embodiments.

In the embodiment illustrated in FIG. 1, the heat transfer loop 18 passes successively through the condenser 4, the engine recuperator 11, the exhaust recuperator 17 and the restorer 21.

The exhaust recuperator 17 is where the temperature is highest. For this reason the exhaust recuperator 17 is positioned at the end of the process, just before the restorer 21. Indeed, the recycling of the heat is better when the heat transfer fluid circulates successively through exchangers for which the temperature is increasing. The inverse would only be pure loss. Through this reasoning, it is advantageous for the engine recuperator 11 and the exhaust recuperator 17 to operate in counter-current form. In that way the coldest heat transfer fluid is in contact with the coldest part of the recuperators 11, 17 and inversely at the end of the course of the heat exchange fluid in the recuperators 11, 17.

2^nd EMBODIMENT

FIG. 2 illustrates a variant of the heat transfer loop 18. The engine recuperator 11 is positioned before the condenser 4. The heat transfer fluid coming from the restorer 21 is therefore first heated before reaching the condenser 4, then the exhaust recuperator 17.

This means that the engine recuperator 11 is at a lower temperature than the condenser 4. Thus, the importance can be seen of an ordered recuperation of the heat in the direction of increasing temperatures for a motorized heat pump.

3^rd EMBODIMENT

In FIG. 3, the heat transfer loop 18 is identical to the first embodiment. The difference is in the fact that a residual exchanger 27 is added in order to capture the residual heat from the exhaust gases at the output of the exhaust exchanger 13. The residual exchanger 27 delivers the heat to a residual recuperator 28 located between the evaporator 3 and the compressor 5 of the heat pump 2. At the outlet of the evaporator 3, the refrigerant is heated at the residual recuperator 28 before being compressed in the compressor 5.

However, this arrangement is only beneficial if the temperature of the exhaust gases in the residual exchanger 27 is higher than the temperature of the refrigerant leaving the evaporator 3.

Claims

1. A method of recovering thermal energy from a motorized heat pump equipped with a heat pump in which a refrigerant circulates, the motorized heat pump comprising: and the motorized heat pump comprising a control unit equipped with a computerized program arranged to:

an evaporator connected to a heat source,

a condenser connected to a cold source,

a compressor,

an expansion valve,

a heat engine mechanically coupled to the compressor in order to drive it, the heat engine comprising an outlet of the exhaust gases produced by the combustion,

a cooling system for the heat engine, comprising a heat exchanger called engine recuperator,

a recuperator of heat from the exhaust gases, called exhaust recuperator, the motorized heat pump defining at least one heat transfer loop in which a heat transfer fluid circulates intended to remove the heat from the condenser, from the heat engine and from the exhaust gases, wherein the condenser, the engine recuperator and the exhaust recuperator are placed in series, the heat transfer loop passing through the condenser, the engine recuperator and the exhaust recuperator, the method comprising the following steps:

removal of the heat in the condenser,

removal of the heat in the engine recuperator,

removal of the heat in the exhaust recuperator,

restoration of the heat removed in a heat restorer that the heat transfer loop passes through,

determine the power of the combustion in the heat engine,

determine the refrigeration power available in the evaporator,

modulate the speed of rotation of the heat engine such that the refrigeration power is numerically superior to the combustion power.

2. The method according to claim 1, comprising the control of the speed of the heat engine such that the combustion power can be modulated between 30% and 100% of the maximum available combustion power.

3. The method according to claim 1, wherein the combustion power is calculated as a function of the quantity of fuel injected and of the inferior or superior calorific value of the fuel.

4. The method according to claim 1, comprising an:

operation of measuring the temperature of the refrigerant of the heat pump upstream from the evaporator by means of a temperature sensor positioned upstream from the evaporator,

operation of measuring the pressure of the refrigerant of the heat pump upstream from the evaporator by means of a pressure sensor positioned upstream from the evaporator.

5. The method according claim 4, wherein the method comprises an:

operation of measuring the temperature of the refrigerant of the heat pump downstream from the evaporator by means of a temperature sensor positioned downstream from the evaporator, operation of measuring the pressure of the refrigerant of the heat pump downstream from the evaporator by means of a pressure sensor positioned downstream from the evaporator.

6. The method according to claim 5, comprising an operation of determining the enthalpy upstream and downstream of the evaporator of the refrigerant from data tables for a given refrigerant as a function of the measured pressures and temperatures.

7. The method according to claim 6, comprising an operation of calculating the refrigeration power in the evaporator as the product of the mass flow of the refrigerant times the difference in enthalpy of the refrigerant between the upstream and downstream of the evaporator.

8. A motorized heat pump equipped with a heat pump in which a refrigerant circulates, comprising:

an evaporator connected to a heat source,

a condenser connected to a cold source,

a compressor,

an expansion valve,

a heat engine mechanically coupled to the compressor in order to drive it, the heat engine comprising an outlet of the exhaust gases produced by the combustion,

a cooling system for the heat engine, comprising a heat exchanger called engine recuperator,

a recuperator of heat from the exhaust gases, called exhaust recuperator, the motorized heat pump defining at least one heat transfer loopin which a heat transfer fluid circulates intended to remove the heat from the condenser, from the engine and from the exhaust gases, wherein the condenser, the engine recuperator and the exhaust recuperator are placed in series, the heat transfer loop passing through the condenser, the engine recuperator and the exhaust recuperator, and the motorized heat pump comprises a control unit equipped with a computerized program arranged to execute the method according to claim 1.

9. The motorized heat pump according to claim 8, comprising: the computerized program being arranged to execute the following method:

a temperature sensor,

a pressure sensor, and

a flow rate sensor,

removal of heat in the condenser,

removal of heat in the engine recuperator,

removal of heat in the exhaust recuperator,

restoration of the heat removed in a heat restorer that the heat transfer loop passes through,

determination of a power of the combustion in the heat engine,

determination of a refrigeration power available in the evaporator,

modulation of a speed of rotation of the heat engine such that the refrigeration power is numerically superior to the combustion power.

10. A utilization of a motorized heat pump according to claim 8, wherein the motorized heat pump exploits the energy from waste waters from industries or gray waters from housing to heat a heat transfer fluid in a recycling circuit.