FR2956190A1 - Method for regulating thermal installation in dwelling and domestic water heating device, involves allowing pump to operate in three different levels of thermal power, where third power level is reached by pump when compressors function - Google Patents

Abstract

The method involves allowing a heat pump (3) to operate in three different levels of thermal power. The first power level is reached by the pump when a first compressor (9) comprises lower swept volume functions and a second compressor (10) is stopped. A second power level is reached by the pump when the second compressor comprises a highest swept volume functions and the first compressor is stopped. A third power level is reached by the pump when the first and the second compressors function. An independent claim is also included for a thermal installation comprising a setting unit.

Description

Power stage heat pump

The present invention relates to a method of regulating a heat pump, as well as to a thermal installation comprising such a heat pump. The present invention relates in particular to the heating installations of a building, as well as the heating devices of the sanitary water. The principle of operation of a heat pump allows it to transfer calories from a cold environment to a warmer environment, that is to say contrary to the natural diffusion of heat. For example, a heat pump takes heat from the outside air of a building, to transfer it to the indoor air or to a hydraulic circuit for heating the building. The energy transfer between the two media is effected by the change of state, gas / liquid and liquid / gas, of a fluid, called refrigerant. These changes of state generally take place in a heat exchanger, which is a device designed to facilitate the heat exchange between the refrigerant and the medium to be heated or cooled. Typically, a heat pump (PAC) comprises a closed refrigerant circuit, which passes successively through the following elements: - an evaporator, which is the heat exchanger between the refrigerant and a heat source. This source is for example the air outside a building heated by the CAP. The refrigerant passes from the liquid state to the gaseous state by drawing heat at the source. a compressor: actuated by a motor, it raises the pressure and the temperature of the gaseous refrigerant by compressing it; a condenser, which is the heat exchanger between the refrigerant and a medium to be heated. The refrigerant passes to the liquid state by transferring heat to the medium to be heated. an expander: it reduces the pressure and the temperature of the refrigerant in the liquid phase. It is known that a heat pump as a heating means allows the thermal plant to achieve good performance coefficients. The coefficient of performance is the ratio between the thermal power delivered and the electrical power absorbed.

However, the thermal power delivered by the heat pump and the coefficient of performance increase with the temperature of the heat source. More precisely, they increase as the difference between the temperature of the source and that of the medium to be heated decreases, this medium being, for example, heating water.

Consequently, if the heat source of the heat pump is the outside air, the thermal power delivered by the condenser decreases in cold weather. Conversely, the heating needs of a building, especially a home, tend to increase in cold weather, due to greater heat losses.

When a heat pump provides most of the heating capacity of a domestic thermal installation, its compressor is classically sized according to a minimum outside temperature, called base temperature. This temperature depends on the geographical area concerned. It is for example -7 ° C. The power of the compressor must be able to meet the heating needs of the building when the outside air is at the base temperature. In mid-season, when the outside temperature is above 0 ° C, the compressor is oversized in relation to the heating needs of the building. The heat pump is operated cyclically, passing through short successive on / off phases. Such cyclic operation is a source of loss of efficiency for a heat pump. In fact, the transient phases of start-up at each start reduce the coefficient of performance.

In addition, the over-sizing of the compressor imposes a low evaporation temperature of the refrigerant in the evaporator. If this temperature is below 0 ° C, it favors the accumulation of frost on the surface of the evaporator, which decreases the efficiency of the heat pump.

Finally the compressor motor generates unnecessary noise pollution.

It would therefore be advantageous to make a heat pump that makes it possible to work at different compressor powers, depending on the temperature of the heat source and / or the heating requirements of the building. A solution to this problem is described in CA2312175.

It consists of an air / air heat pump equipped with two compressors arranged in parallel. One of said compressors is of low volume. It operates alone when the outside temperature is above a threshold. The other compressor is larger in volume. It operates alone when the outside temperature falls below this threshold.

Such a device allows to use the largest compressor in case of cold outside temperature. The heat pump therefore has two power levels, depending on the temperature of the heat source. In order to improve the efficiency of the thermal installation, however, it is advantageous to have a third power level allowing continuous operation of the heat pump over longer periods. For example, a low power level can be used for mid-season heating, an intermediate level for most of the winter and a higher level for particularly cold conditions. The present invention makes it possible to obtain at lower cost an installation that can operate at three different power levels. An object of the present invention is in fact a method for regulating a thermal installation of a building, said installation comprising a heat pump, said heat pump comprising a refrigerant circuit passing in particular by the following elements: an evaporator in contact with the air outside the building; a condenser in contact with a heating water circuit; two compressors installed in parallel, a ratio of the swept volumes volumes of said two compressors being between 1.25 and 2.5; said method enabling the operation of the heat pump at at least three different thermal power levels, a first power level being achieved when a first compressor of lower volume swept volume operates, the second compressor being stopped, a second power level being reached when the second highest swept volume flow compressor operates, the first compressor being off, a third power level being reached when the first and second compressor are operating. The swept volume flow is understood as the product of the swept volume of the compressor by the rotational speed of its motor. The power of the compressor is related to its swept volume flow. The ratio of the swept volumes volumes of the two compressors is chosen so as to obtain an intermediate power level sufficiently far from the lowest level and the highest level. Indeed, two levels too close limit the practical interest of the invention.

A preferential ratio between the swept volumes volumes of the two compressors is between 1.30 and 1.80. According to one embodiment of the invention, the method comprises the following steps: a temperature Text outside the building is measured; then the value Text is compared to two values (TI, T2) of reference with T2 <T1; then, if Text? T1, then only the first power level is allowed; if T2 <Text <T1, then only the first and second power levels are allowed; if Text <T2, then the three power levels are allowed. Thus, the colder the outside air, the higher the power can be used to meet the heating needs of the building. According to another embodiment of the invention, the method comprises the following steps: a temperature (Text) external to the building is measured; then a temperature (Te) of heating water setpoint is determined according to Text; then a temperature (water) of heating water is measured; then an operating power level of the heat pump is determined according to an increasing function of (Tc to water). Thus, the more the heating water cools down through the heating circuit, the higher the power can be used to meet the heating requirements of the building. Preferably, Tc is determined according to a decreasing function of Text. In fact, the heating needs of a building generally increase as the outside temperature decreases. Preferably, when a power level is determined as described above, the transition to this level is carried out in stages, that is to say that the heat pump passes successively by each power level between the level of origin and the level determined. More preferably, when a bearing lower than the determined level makes it possible to reach the desired water temperature quickly enough, the increase in power of the heat pump is limited to the level corresponding to said bearing, in order to increase the efficiency of the the thermal installation. Typically, a heat pump using air as a heat source comprises a fan which ensures the passage of an outside air flow through the evaporator. The optimum flow rate for this fan depends on the amount of heat that the refrigerant can absorb. This amount is a function of the flow rate of said evaporated fluid in the exchanger, therefore the power of the compressor or compressors.

However, the fan of the evaporator can generate an unpleasant noise for the neighborhood. It is therefore preferable not to operate said fan above an optimum speed. Accordingly, in a preferred form of the invention, the rotational speed of the fan is an increasing function of the total power of the compressor (s) in operation. The invention also relates to a thermal installation provided with means for implementing a method as described above. The compressor housings contain a reserve of lubricating oil. This oil is miscible with most refrigerants. Part of the compressor oil is therefore entrained in the fluid circuit. When the latter is in the vapor state, the oil moves in the form of a film along the walls of the circuit. With the circuit forming a loop, an oil flow returns to the compressor as another oil flow is driven out of the housing. When the heat pump is equipped with two different compressors connected in parallel, the oil return can be more favorable towards one of the two compressors rather than towards the other. One of the compressors may therefore be in default of lubricating oil.

Consequently, according to a preferred form of the invention, the heat pump is equipped with a means of balancing the return of lubricating oil between the two compressors. According to another preferred form of the invention, the heat pump is equipped with a lubricating oil transfer means between the casings of the two compressors. According to a preferred form of the invention, the heat pump uses a low-temperature refrigerant during compression, for example propane (R290).

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented as an indication and in no way limitative of the invention. The figures show: FIG. 1: a schematic view of a thermal installation according to one embodiment of the invention; - Figure 2: a schematic view of a control device of an installation as shown in Figure 1; FIG. 3: a graph representing a law of variation in a method according to one embodiment of the invention; - Figure 4: a graph representing another variation law in a method according to one embodiment of the invention; - Figure 5: a detailed view of a thermal installation according to one embodiment of the invention; Figure 1 shows a schematic view of a thermal installation according to one embodiment of the invention. The thermal installation 1 provides the heating requirements of a building 2. The installation 1 is equipped with a heat pump 3. Said heat pump 3 comprises a refrigerant circuit 4, which passes in particular through a condenser 5. The condenser 5 is for example a heat exchanger connected to a hydraulic circuit 51 for heating. The hydraulic circuit 51 serves to heat the building 2.

The refrigerant circuit 4 then passes through an expander 6, then an evaporator 7. Said evaporator 7 is in contact with the air outside the building 2. According to a preferred embodiment of the invention, the evaporator 7 comprises a fan 8 which ensures the passage of a flow of air through said evaporator 7.

The circuit 4 then passes through two compressors (9, 10) arranged in parallel. These are fixed speed compressors. A first compressor 9 has a swept volume flow rate lower than that of the second compressor 10. According to the invention, the ratio of flow rates swept between the second compressor 10 and the first compressor 9 is between 1.25 and 2.5. According to a preferred embodiment of the invention, this ratio is between 1.30 and 1.80. The operation of the heat pump 3 is managed by a regulating device 11. This device 11 is in particular connected to a thermal probe 12 located outside the building 2. Preferably, the probe 12 is located near the air inlet of the evaporator 7. Furthermore, the device 11 is connected to each of the compressors (9, 10). Figure 2 shows a schematic view of the regulating device 11. Said device 11 comprises in particular a microprocessor 13, a data memory 14, a program memory 15 and at least one communication bus 16. By an input interface 17, the device 11 is in particular connected to the thermal probe 12.

Through an output interface 18, the operation of the heat pump 3, in particular compressors (9, 10), is controlled by a program 19 which executes the steps of a method according to an embodiment of the invention. the invention. According to a first embodiment of the invention, the program 19 executes the following steps: firstly, the program 19 interrogates the thermal probe 12, which communicates a value Text of the outside temperature to the building 2; then the value Text is compared to two values (TI, T2) stored in the data memory. T2 is less than TI. For example, TI = 5 ° C and T2 = -3 ° C are chosen.

If Text is greater than or equal to TI, we are in a temperature zone where the heat pump 3 achieves good performance coefficients. Moreover, at this temperature Text, the heating requirements of the building 2 are relatively moderate. The first level of power of the heat pump 3, the lowest level, is sufficient to provide these heating needs, while ensuring operation of the heat pump 3 by cycles on / off long duration. Consequently, if Text is greater than or equal to TI, the program 19 authorizes the operation of the first compressor 9 and prohibits the operation of the second compressor 10. If Text is smaller than TI but greater than or equal to T2, the heating requirements are higher than in the previous case. It is therefore preferable to use a higher power level. Accordingly, if Text is smaller than TI but greater than or equal to 10 T2, program 19 allows operation of first compressor 9 alone or second compressor 10 alone, and prohibits operation of both compressors (9, 10) in parallel. If Text is less than T2, we are in particularly cold weather conditions. It is necessary to use the maximum power level that can be delivered by the heat pump 3. Consequently, if Text is less than T2, the program 19 authorizes the operation of the compressors 9 and 10, alone or in parallel. According to another embodiment of the invention, the program 19 does not preclude a mode of operation in parallel at certain temperatures. The power level used is determined by the control method of the heating system. For example, according to another embodiment of the invention, the program 19 performs the following steps: firstly, the program 19 interrogates the thermal probe 12, which communicates a value Text of the outside temperature to the building 2. Program 19 then determines a temperature Tc of heating water setpoint according to Text. A law of variation of Tc as a function of Text is stored in the memory 14 of data. In general, it is a decreasing law. Indeed, the colder the outside temperature, the more the building 2 undergoes thermal losses. A higher temperature of heating water is necessary to compensate for these losses. An example law of variation of Tc as a function of Text is shown in FIG. 3. The value Text is compared with two values (T3, T4) stored in the memory 14 of data. T4 is less than T3. If Text is less than 35 T4, the setpoint temperature Tc is equal to a value Tc1. If Text is greater than or equal to T3, the setpoint temperature Tc is equal to a value Tc2, less than Tc1. If Text is in the interval [T4, T3 [, Tc varies linearly between Tc1 and Tc2. Then, the program 19 interrogates a thermal probe 52 in contact with the heating water. The probe 52 (FIG. 1) is preferably placed in the hydraulic circuit 51, at the inlet of the exchanger 5. The probe 52 communicates to the device 11 a water value of the water temperature at the inlet of the exchanger 5. The program 19 then determines a power level of the heat pump as a function of the difference (Tc-Teau). A law for varying the power level of the heat pump 3 as a function of (Tc - water) is stored in the data memory 14. For example, if (Tc û Teau) is less than 0, the heat pump 3 is stopped; if (Tc-water) is greater than or equal to 0 and less than a differential DI, the heat pump 3 operates at its first power level, that is to say that only the first compressor 9 is running; if (Tc-water) is within a range [DI, D2 [with D2> D1, the heat pump 3 operates at its second power level, i.e. only the second compressor 10 is on ; if (Tc-water) is greater than or equal to D2, the heat pump 3 operates at its third power level. The two compressors (9,10) then operate in parallel. Another example of a law for varying the power level of the heat pump 3 as a function of water is shown in FIG. 4. This variation law allows a hysteresis operation. A hysteresis H defines a water temperature difference between the triggering and stopping of the same power level. A differential D3 defines the difference in water temperature between the triggering of two successive power levels. This same differential D3 applies between the stopping of two successive power levels.

For example, if the water temperature is greater than or equal to Tc, the power level is at zero, the compressors 9 and 10 are at a standstill. If the water decreases and is in the range Tc-H, Tc], the power level remains at zero. If the water decreases and is in the range [Tc-H-D3, Tc-H], the first power level is turned on, i.e. the compressor 9 is operating. If the water decreases and is in the range Tc-H-2 D3, Tc-H-D3], the second power level is turned on, i.e. the compressor 10 is operating. If the water decreases and is less than or equal to (Tc-H-2 D3), the third power level is turned on, i.e. the compressors 9 and 10 operate in parallel.

At this point, if the water begins to rise and is less than (Tc-2D3) the power level is maintained, i.e. the compressors 9 and 10 operate. If water increases and is in the range [Tc-2D3, Tc-D3 [, the heat pump 3 goes to the second power level. If water increases and is in the range [Tc-D3, Tc [, heat pump 3 goes to the first power level. According to a preferred embodiment of the invention, the transition from one power level to another takes place in a staircase; for example, to go from a zero power level (the two compressors 9 and 10 being stopped) to the third power level, the heat pump performs a first level at the first power level, then a second level at second power level before reaching the third power level. Each bearing is subjected to a minimum operating time to avoid the on / off beats of the compressors (9, 10) of the heat pump 3.

When the heat pump is in the power up phase, it is possible to take advantage of these stages to evaluate the rate of heating of the heating water. If said speed is greater than a certain threshold, it means that the current power level is sufficient to meet the heating requirements of the building 2.

Accordingly, preferably, the method described above then comprises the following steps: a power level lower than the level determined in the previous step is engaged; then a change in the temperature of the water of heating water as a function of time is measured; then, if a heating water heating rate is higher than a threshold speed, then switching to a higher power level is prohibited. These additional steps are of interest for example when the building 2 has thermal inputs such as solar radiation through windows, or a heat generating activity (significant human presence, electrical appliances in operation ...) to 2. Such thermal inputs reduce the heating requirements of the building 2. For example, the temperature Text is considered to be less than T2. The program 19 will therefore determine a high setpoint temperature Tc for the heating water. Depending on the deviation (Tc-water), the program 19 then determines a power level for the heat pump 3. For example, early in the morning, a low water temperature may be present in the absence of sunshine or activity in building 2. Program 19 therefore determines that the third power level is required.

Following this determination, the program 19 first applies the first power level, that is to say that the first compressor 9 operates alone. Several water measurements are made at different time intervals, so as to calculate a calf velocity for heating the heating water. For example, the program performs three water measurements at ten-minute intervals and calculates a mean calf rate. If the building 2 has at this time heat inputs other than the heat pump 3, the calf speed can be high. The program 19 compares calf with a threshold speed vm; n, stored in the memory 14 of data. If calf is greater than vm; n, it is considered that the first power level is sufficient to meet the heating requirements of building 2. Program 19 then prohibits the switch to a higher power level. If calf is less than or equal to vm; n, program 19 may allow the transition to the second power level and repeat the previous steps. According to a preferred embodiment of the invention, the device 11 (Figure 1) is connected to the fan 8 via the interface 18 output. The greater the total power of the compressor (s) (9, 10) during operation, the higher the flow of refrigerant arriving in the evaporator 7. Consequently, the greater the total power, the more the fluid is able to absorb calories in the evaporator 7. In order to optimize the efficiency of the evaporator 7, the air blown by the fan 8 must provide the maximum amount of heat that can be absorbed by the refrigerant. It is therefore wise to choose the speed of rotation of the fan 8 in relation to the total power of the compressor or compressors (9, 10) in operation. Preferably, the program 19 provides that, when only the first compressor 9 is in operation, the fan 8 rotates at a first speed vi. When only the second compressor 10 is in operation, the fan 8 rotates at a second speed v2 with v2> v1. When the two compressors (9, 10) are in operation, the fan 8 rotates at a third speed V3 with v3> v2.

When Text is greater than TI, for example in mid-season, the fan 8 therefore rotates at a moderate speed vl. The noise generated by the fan 8 is less important than in very cold weather, where the fan rotates at a high speed v3. The evaporator 7 and the fan 8 can be installed near a garden. It is therefore advantageous to limit the noise nuisance associated with the fan 8, especially when the mild temperatures favor the presence of people outside the building 2. FIG. 5 represents a detailed view of a thermal installation according to one embodiment of the invention. In particular, a sectional view of two compressors (9, 10), equipping a heating installation 1 as shown in FIG. 1. In the example of FIG. 5, the compressors (9, 10) are spiro compressors. hermetic (scroll) hermetic, with fixed rotational speed. This type of compressor is known from the state of the art. The compressor 10 has a refrigerant inlet 20, which opens into a compartment 30, close to a motor 21 having a vertical axis of rotation. Through a shaft 22, the motor is coupled to an assembly 23 located above said motor. The assembly 23 comprises two intercalated spirals. Under the action of the motor 21, one of the spirals moves eccentrically without turning, relative to the other spiral which remains fixed. The relative displacement of the two spirals traps and compresses pockets of refrigerant in the vapor state. The compressed fluid is discharged into an upper compartment 24 of the compressor 10, to an outlet 29 connected to the refrigerant circuit. The fluid pressure in the compartment 24 is therefore greater than the pressure in the compartment 30 located around the engine 21. The compressor 9 operates according to the same principle as the compressor 10.

The compressors (9, 10) have different powers, more precisely different swept volumes volumes. It is considered that the motors 21 of the compressors 9 and 10 have the same speed of rotation. The smaller compressor 9 has a swept volume VI. The largest compressor 10 has a swept volume V2. The ratio V2 / V1 is between 1.25 and 2.5, preferably between 1.30 and 1.80. The shaft 22 is hollow. Its lower end takes lubricating oil from a web 26 at the bottom of the housing 27 of the compressor 10. The oil rises in the hollow of the shaft by centrifugal force and is distributed to the areas requiring lubrication.

Part of the lubricating oil is entrained by the refrigerant vapor at the outlets (28, 29) of the compressors (9, 10). A certain oil flow circulates in a loop in the refrigerant circuit of the heat pump equipped with said compressors (9,10). In inputs (31, 20) of the compressors (9, 10), the refrigerant is essentially in the form of steam. The oil is driven by the flow velocity of said vapors; it progresses in the form of a wall film and possibly a net at the bottom of the horizontal tube. The compressors (9, 10) are connected in parallel in the heat pump system. More precisely, upstream of said compressors, the fluid circuit 32 splits into two branches (33, 34). The branch 33 is connected to the inlet 31 of the smaller compressor 9, the branch 34 is connected to the inlet 20 of the largest compressor 10. When the two compressors (9, 10) are in operation, the oil return is favored towards the branch in which the flow velocity is the highest. If the two branches (33, 34) have an identical section, the fluid flows more rapidly to the compressor 10, which has the highest swept volume V2. One way of ensuring a distribution of the oil flow proportional to the rate of steam sucked by each compressor is to maintain a substantially identical flow rate in each inlet branch (33,34). Consequently, preferably, a passage section 35 of the suction tube 33 of the compressor 9 is smaller than a section 36 of the suction tube 34 of the compressor 10. The ratio of the sections 35/36 is substantially identical to the ratio of the scanned volumes V ~ / V2. Preferably, upstream of the two branches (33, 34), the tube 32 forming the fluid circuit is in a vertical position for a better distribution of the oil film on its inner wall. Preferably, a section of the tube 32 is chosen so as to ensure a flow rate substantially identical to the speed in the branches (33, 34). According to another preferred form of the invention, the compressors (9, 10) may comprise an oil transfer means between their housings.

This transfer means may be associated with means for regulating the oil return to inputs (20, 31) of said compressors, as described above. In the example shown in Figure 5, a balancing tube 37 ensures the transfer of oil from one compressor to another, by the principle of communicating vessels. The tube 37 is positioned horizontally and the height of the taps (38, 39) of said tube on the compressor housings (9, 10) is chosen as a function of the oil levels in said compressors. If the fluid pressure above the oil ply 26 is different in the two compressors (9, 10), a difference in oil levels can be established between the two crankcases to compensate for this pressure difference.

Such a difference in levels disturbs the transfer of oil by the tube 37. Preferably, the compressors (9, 10) are provided with a pressure equalization means between their compartments (40, 30) located around the engines. . This means balances the pressures when the two compressors are in operation.

In the example shown in FIG. 5, the pressures in the compartments (40, 30) are substantially equal if the pressure drops due to the flow of the gases sucked into each of the branches (33, 34) are equivalent. This result is obtained in particular when the following conditions are met: - the ratio of the sections 35/36 of the branches (33, 34) is substantially identical to the ratio of the scanned volumes VI / V2, - the geometry of the tubes (33, 34) is identical in terms of length, number of elbows and radii of curvature, - the connections of the tubes 33 and 34 on the collector 32 are symmetrical and of similar shape. Preferably, the compressors (9, 10) are equipped with a crankcase heater, which maintains the oil temperature above the condensing temperature of the refrigerant at the pressure of the crankcase. This heating resistor is engaged when the compressor is stopped. Such a device is intended to prevent the migration of refrigerant in the oil. Indeed, such a migration of refrigerant in the oil is not desirable because it disrupts the equilibration of oil sump, by changing the apparent oil level. Moreover, this migration decreases the lubricating properties of the oil and alters the life of the compressor. According to a preferred form of the invention, the heat pump 3 uses a refrigerant with low heating during compression, for example propane (R290). When connected to a heating circuit 51 supplying, for example, radiators, the heat pump 3 must supply its power at a sufficient temperature level, for example 65 ° C. on the coldest days, to allow the diffusion of heat into the heat pump. atmosphere of the building to heat. The large temperature difference between the heating water and the outside air results in a high compression ratio at the heat pump 3 and its compressor or compressors (9, 10). With hydrofluorocarbon type refrigerants, for example R410A or R407C, the heating of the fluid during compression is very important and would result in unacceptable discharge temperatures for the longevity of the compressors (9, 10). The compressors using these fluids must then be equipped with an internal cooling device which complicates the circuit of the heat pump. The use of a low-temperature refrigerant, such as the R290, simplifies the design of the heat pump.

According to a preferred form of the invention, the spiro-orbital compressors (9, 10) shown in FIG. 5 are optimized for compression ratios greater than 5.

Claims (1)

CLAIMS1.- A method for regulating a thermal installation (1) of a building (2), said installation comprising a heat pump (3), said heat pump comprising a refrigerant circuit (4) passing in particular by means of following elements: - an evaporator (7) in contact with the air outside the building; a condenser (5) in contact with a heating water circuit; two compressors (9, 10) installed in parallel, a ratio of the swept volume flows of said two compressors being between 1.25 and 2.5; said method enabling the operation of the heat pump (3) at at least three different thermal power levels, - a first power level being reached when a first compressor (9) of lower swept volume flow is operating, the second compressor (10) being stationary; a second power level being reached when the second highest swept volume flow compressor (10) operates, the first compressor (9) being at a standstill; - A third power level is reached when the first (9) and the second compressor (10) operate. 2. A process according to claim 1, comprising the following steps: a temperature (Text) outside the building is measured; the value (Text) is compared with two reference values (TI, T2) with T2 <T1; - if Text? T1, then only the first power level is allowed; if T2 <Text <T1, then only the first and second power levels are allowed; if Text <T2, then the three power levels are allowed. 3. A process according to claim 1 or claim 2, comprising the following steps: a temperature (Text) outside the building is measured; a temperature (Te) of the heating water setpoint is determined as a function of Text; a temperature (water) of heating water is measured; - An operating power level of the heat pump (3) is determined according to an increasing function of (Tc-Teau). 4. The method of claim 3, further comprising the following steps: a power level lower than the level determined in the previous step is engaged; an evolution of the temperature (water) of heating water as a function of time is measured; - if a heating water velocity (calf) is higher than a threshold velocity (vmin), then the change to a higher power level is prohibited. 20 5.- Method according to one of the preceding claims, such that a fan (8) ensures the passage of an external air flow through the heat exchanger, the rotational speed of said fan being an increasing function of the flow rate total swept volume of the compressor (s) in operation. 25 6.- Thermal installation (1) of a building (2) provided with means (11, 19) for implementing a method according to one of claims 1 to 5. 7. Installation according to claim 6, such that the heat pump (3) comprises means (35, 36) for balancing the lubricating oil return between the two compressors (9, 10). 8.- Installation according to claim 7, as upstream of the compressors (9, 10), the refrigerant circuit (32) is divided into two branches (33, 34), each connected to an inlet (20, 31) of a compressor, a section (35) of the branch (33) connected to the compressor (9) of lower volume swept volume being lower than a section (36) connected to the compressor (10) higher volume swept volume . 9.- Installation according to one of claims 6 to 8, such that the heat pump comprises means (37) for transferring lubricating oil between the housings of the two compressors. 10.- Installation according to claim 9, such that the transfer means is a horizontal tube (37), connecting the housings (27) of the compressors (9, 10).