IT201800009760A1 - System and method for heating a fluid using a heat pump and a boiler - Google Patents

Description

"System and method for heating a fluid using a heat pump and a boiler"

"System and method to heat a fluid via a heat pump and a boiler"

DESCRIPTION

TECHNICAL FIELD

The present invention refers to a regulation system and method for heating a fluid, preferably for users in the residential sector, of sports facilities such as gyms and swimming pools, of campsites and other structures in which the heating of a preferably closed environment is necessary. and the use of domestic hot water.

STATE OF THE ART

The generation of heat for residential use and building structures requires a compromise between flexibility of user-selectable parameters and energy efficiency.

PURPOSE AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system and a method capable of optimizing the simultaneous use of the heat pump and the boiler for heating domestic hot water.

The object of the present invention is achieved by means of a system for heating a fluid comprising:

- At least one heat pump having a condenser;

- At least one boiler;

- An accumulator of the carrier fluid;

- A supply branch of the accumulator connected in parallel to the condenser and to the boiler to bring a heated vector fluid into the accumulator;

- An electronic control unit to control the simultaneous operation of the heat pump and the boiler;

in which the control unit modifies an inlet temperature to the condenser and a quantity of heat generated by the boiler on the basis of the temperature of the external environment, a pre-defined quantity of heat of the fluid for a user of the fluid heated by the system and of a mathematical model of system efficiency, so that the difference between the amount of heat generated by the heat pump and the pre-defined amount of heat is generated by the boiler.

The present invention refers to the coordinated use of at least one boiler, at least one heat pump and at least one heat accumulator, preferably sensorized for controlling the vertical thermal gradient. The hydraulic circuits for using the heated fluid and connected to the accumulator may be different from those shown in the figures. Furthermore, efficiency is achieved since the inlet temperature to the condenser decreases when the outside temperature decreases, for example in winter and / or at night, in order to keep the COP of the heat pump high. Furthermore, the boiler is adjusted to supply the quantity of heat missing to satisfy the pre-defined heat request by the user / user, which the heat pump is unable to supply completely due to the decrease in the inlet temperature. capacitor. Preferably, the regulation of the boiler provides for the heating of the fluid to a temperature higher than that to which the fluid leaving the heat pump is heated.

According to a preferred embodiment of the present invention, the accumulator is configured to be connected to a space heating circuit and the control unit is programmed so that the pre-defined amount of heat of the fluid is the amount of heat required for space heating via the space heating circuit.

According to this embodiment, the combined exploitation of the boiler and the heat pump is applied to the generation of heat for space heating and the pre-defined quantity of heat is that necessary to guarantee a pre-defined temperature inside the heated rooms. It is also possible to associate additional thermal utilities to the system, such as domestic hot water. In this case it is possible that the heat for the domestic hot water is supplied through a different boiler control strategy from the one indicated above. For example, the heat for domestic hot water is generated exclusively via the boiler. The object of the present invention is also achieved by means of the method of claim 9, applicable both to plants or systems for heating a fluid entirely to be made and to plants already existing and integrated with the components necessary to carry out the control.

Further objects and advantages of the present invention will become more evident from the detailed description which follows.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will be described hereinafter by means of some preferred embodiments, provided by way of non-limiting example, with reference to the attached drawings. These drawings illustrate different aspects and examples of the present invention and, where appropriate, similar structures, components, materials and / or elements in different figures are indicated by similar reference numerals.

FIG. 1 is a diagram of a fluid heating system according to the present invention;

FIG. 2 is a diagram illustrating the cost of the thermal kWh with reference to a fuel boiler (Enea with horizontal solid section) and to a heat pump combined with the boiler (solid line with a succession of wavy and horizontal sections). The cost of the thermal kWh of the heat pump that exceeds that of the boiler is shown;

FIG. 3 is a diagram illustrating the cost of the thermal kWh in which the boiler curve is shown with a continuous horizontal line, with an interrupted waving line the curve of the heat pump at maximum load and relatively low COP, with a continuous waving line the curve of the heat pump. heat with low load and relatively high COP and with a continuous line often an optimal curve obtained through the joint operation of the boiler and the heat pump; And

FIG. 4 illustrates a visualization map of a mathematical model of efficiency implemented in the control of the system of figure 1.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates, as a whole, a system for the generation of domestic hot water 1 comprising at least one boiler 2, preferably but not exclusively fueled, at least one heat pump; in the figure there are a first and a second heat pump 3, 4, a technical accumulator 5 for a heat-carrying technical fluid, for example water possibly with additives, and a technical circuit 6 to fluidically connect the boiler 2, the heat pumps 3, 4 and the technical accumulator 5. According to the embodiment in figure 1, moreover, the system comprises a sanitary accumulator 7 for hot water, a heat exchanger 8 connected in thermal exchange with the thermal carrier fluid through the technical circuit 6 and a sanitary circuit 9 to connect the accumulator together 7, the heat exchanger and, through inlet 10 and outlet 11 connections, a domestic hot water user system as both domestic and utility toilets. sports facilities or gyms, and for recreational facilities such as swimming pools, whirlpools or recreational stations with artificial pools of heated water. More generally, all uses can be considered for which the maximum temperature of the hot water leaving the sanitary circuit 8 does not exceed 70 °.

Furthermore, according to a variant of the present invention illustrated in Figure 1, the system comprises a branch branch 12 for withdrawing the heat-carrying technical fluid from the accumulator 5 and conveying it to a space heating system, such as a floor heating system, a system using fan coils or a system using radiators. Preferably, this circuit picks up and returns flow rate of heat-carrying technical fluid to the technical accumulator 5.

Moreover, advantageously, the heat pumps 3, 4 comprise respective electric motors to drive the respective compressors and these motors can be electrically connected, according to a variant embodiment, to a photovoltaic system for the generation of electric energy (not shown).

In figure 1 the technical circuit 6 is a closed circuit and the sanitary circuit 9 is open through the connections 10, 11 towards the sanitary hot water user. The two circuits are fluidically separated so that the heat transfer fluid does not contaminate the domestic hot water through the heat exchanger 8.

The system also comprises an electronic control unit 15 connected to temperature sensors and electronic control boards for the electric motors and the boiler 2 to manage operation in an optimized way. For this purpose, the control unit 15 is programmed taking into account the temperature stratification inside the technical accumulator 5 which comprises a head input 16 connected to the boiler 2, a head output 17 connected to an input of the exchanger 8, at least one intermediate inlet 18 connected to the heat pump 3, 4 to receive heat transfer fluid heated by a condenser (not shown) of the heat pump, at least one intermediate outlet 19 to draw heat transfer fluid from the technical accumulator 5 in the direction of boiler 2; and at least one bottom outlet 20 for drawing heat transfer fluid from the technical accumulator 5 in the direction of the condenser of the heat pump 3, 4.

In the present description and in the claims, the term intermediate inlet / outlet is to be understood as arranged at any vertical height between the head and bottom inlets / outlets. According to the non-limiting embodiment of Figure 1, the vertical height of the intermediate inlet 18 and of the intermediate outlet 19 is approximately in correspondence with the center line of the technical accumulator 5.

In a situation of particular interest, both the boiler 2 and the heat pump 3, 4 transfer heat to the heat transfer fluid directed towards the technical storage tank 5, for example to satisfy a pre-defined heat demand of the space heating system . In particular, the boiler 2 and the heat pump 3, 4 are configured so that a temperature of the heat transfer fluid leaving the boiler 2 is higher than the temperature of the heat transfer fluid leaving the heat pump 3, 4. Consequently, the circuit technical 6 includes high temperature branches arranged to connect the output of the boiler 2 to the inlet of the exchanger 8 and to the head inlet 16 and medium temperature branches to connect respectively the output of the heat pump 3, 4 to the boiler 2 and at the intermediate entrance 18; the outlet of the exchanger 8 to the boiler 2 and / or to the technical accumulator 5, the intermediate outlet 19 to the boiler 2 respectively; and low temperature branches to connect the bottom outlet 20 to the inlet of the heat pump 3, 4 and the return circuit of the space heating system to the bottom of the technical storage tank 5.

According to the embodiment of Figure 1, the low temperature and medium temperature branches for connecting the heat pump 3, 4 to the technical storage tank 5 are in heat exchange with the condenser of the heat pump 3, 4 by means of a heat exchanger. heat 21, 22 preferably configured so that the heat transfer fluid of the technical circuit 6 does not mix with a technical fluid of the heat pump 3, 4.

Figure 2 illustrates the trends in the cost of thermal kWh during a numerical simulation, for heat pump - PDC and condensing boiler. With an ON-OFF control strategy, the electronic control unit 15 limits itself to identifying, with a predetermined frequency, the minimum value between the two cost curves and will automatically switch off and / on and automatically the most efficient heat generator.

Conveniently integrating the boiler 2 and the heat pump 3, 4 means, on the other hand, finding the correct mix in order to produce a synergistic interaction effect: in practice, when the heat pump 3, 4 has some 'coefficient of performace '- Very low COP which would make its operation not economically convenient, boiler 2 will take over not to cover all the thermal load (as would happen according to an ON-OFF logic) but only to integrate a fraction of the total thermal power producing the effect to lighten the thermal load of the heat pump 3, 4, allowing the latter to work in energetically more convenient conditions, i.e. at higher COP. Consequently, if the energy mixes are rationally weighed, operating costs are obtained that are lower than the thermal kWh values of boiler 2 and heat pump 3, 4 if considered individually: this is the meaning of synergistic integration of the two different heat sources for the heat transfer fluid. The above is shown in a qualitative manner in figure 3 in which the curve of the boiler 2 is represented in a continuous horizontal line, with an interrupted section undulating the curve of the heat pump PDC 3, 4 at maximum load, with a continuous section undulating the curve of the pump PDC 3, 4 with reduced load and continuous line often an optimal curve obtained through the joint operation of the boiler 2 and the heat pump 3, 4.

It should be noted that the COP decreases significantly with the decrease in the external temperature of the environment, to which the heat pump 3, 4 transfers heat. In order to maintain high COPs even at low external temperatures, it is necessary to intervene on a control of the maximum temperature T2 of the heat pump cycle 3, 4, i.e. the inlet temperature to the heat pump condenser. In fact, it has been verified that by lowering the maximum temperature T2 in proportion to the external temperature, it is possible to guarantee high COP.

However, this is not the only effect we have on the performance of the heat pump 3, 4 as the maximum temperature T2 decreases; in fact, observing the trends of the thermal power as a function of the external ambient temperature, it is observed that these decrease significantly as the maximum temperature T2 decreases.

Therefore, the reduction of the maximum temperature T2 maintains high COP but requires the integration of thermal power by the boiler 2.

When boiler 2 takes over, the electronic control unit 15 applies a mathematical model based on an optimization function which weighs the contributions of boiler 2 and heat pump 3, 4.

In the case of boiler 2 we have:

assuming a methane cost of about 0.8 (referring to today's average <v>

tariffs for primary energy) and a lower calorific value Hi of 35.8 MJ / nm <A> 3 and an efficiency of the boiler 2 of 1.06, we have a total cost of the thermal kWh for the boiler of approximately:

data in line with what can be found on the net.

In the particular case of the heat pump 3, 4, the relative contribution in the case of integration with a photovoltaic system (not shown) is:

In which we note the dependence on: cost of electricity (€ / (kWh of electricity)),

load conditions i.e. the thermal power transferred by the heat pump 3, 4 through the

condenser (Q _pdc), and environmental conditions (temperature and solar radiation)

which directly affect the COP and the production of generated electrical power

from the photovoltaic system (P_PV).

In a first form, the full optimization function is:

Where Xpdc represents the share of heat supplied by the heat pump 3, 4 compared

to the total heat output required by the user:

In the example of figure 1, the total thermal power in the denominator is the thermal power for space heating through the circuit 12. According to a non-limiting embodiment, the heating of the domestic hot water storage tank 7 is managed by including the power required by the latter in the total heat output, or is managed independently by means of an appropriate control of the boiler 2 only by the control unit 15.

It is clear that the choice of the maximum temperature T2, in order to minimize costs, cannot depend solely on the value of the external temperature: we therefore proceed to the solution of a constrained optimization problem, that is, to maximize the benefit (in this case the economic savings) within a set of constraints that are represented by the boundary conditions.

Specifically, it is a question of finding the minimum of the optimization function as a function of the decision variable T2.

In visual terms, through the minimization of the optimization function, the map illustrated in figure 4 is obtained which, depending on the external temperature present and appropriately detected by means of a temperature sensor, is sectioned becoming a curve on a plane of abscissa T2 and ordinate € / kWhT and minimized with respect to the target variable T2.

The optimization function can express, instead of the cost per thermal kWh, the emission of carbon dioxide as follows, always providing for the optional contribution of the electrical power generated by the photovoltaic system:

In both cases, since the optimization functions are calculated in numerous conditions of external temperature and T2 temperature, the thermal power transferred to the vector fluid by the heat pump and the COP are stored as maps and are characteristic quantities of each specification. heat pump 3, 4.

According to the preferred embodiment of the invention illustrated in Figure 1, the sanitary accumulator 7 is sensorized to control the vertical thermal gradient of the sanitary hot water by means of the electronic control unit 15. Preferably, the electronic control unit 15 is programmed in an energy saving function to select a bottom, intermediate or head inlet, connected fluidically to the exchanger 8, so that the domestic hot water circulates in a volumetric portion of the accumulator 7 and another volumetric portion of the accumulator 7 is substantially in fluidic rest. In particular, the volumetric portion subject to circulation of the domestic hot water has a maximum temperature higher than the maximum temperature of the volumetric portion in fluidic rest, i.e. it is placed at the top. In this way, an energy saving is obtained with respect to the operating condition in which the whole accumulator 7 has a substantially homogeneous temperature, i.e. a substantially zero temperature gradient. This energy saving function is particularly suitable when the user does not require the maximum flow rate of domestic hot water.

Finally, it is clear that it is possible to make changes or variants to the system as described and illustrated above without thereby departing from the scope of protection as defined by the attached claims.

For example, it is possible that the accumulator connected to the boiler 2 and to the heat pump 3, 4 is filled with domestic hot water. This involves the absence of a connection with a space heating circuit or the presence of a closed circuit connected to the technical accumulator 5 comprising a heat exchanger configured so that the heat carrier fluid of the technical accumulator 5, 7 transfers heat to a further heat transfer fluid of the space heating system. Furthermore, the boiler 2 can be connected by means of an exchanger to the medium and / or high temperature circuits so that the heat carrier fluid of the technical accumulator 5 and a heat carrier fluid circulating between the boiler 2 and this heat exchanger do not mix. The sanitary accumulator 7 can be sensorized by means of at least two temperature sensors S spaced vertically to allow the control of the vertical thermal gradient but other methods of measuring the vertical thermal gradient and / or a greater number of temperature sensors are possible.

Circuits 6 and 9 comprise suitable recirculation pumps, deviation valves and taps connected to the control unit 15 to manage the flows of the fluid and of the domestic hot water.

Claims (9)

CLAIMS 1. A system for heating a fluid comprising: - at least one heat pump (3, 4) having a condenser; - At least one boiler (2); - An accumulator (5) of the carrier fluid; - A power supply branch (6) of the accumulator (5) connected in parallel to the condenser and the boiler (2) to bring a heated vector fluid into the accumulator (5); - An electronic control unit (15) to control the simultaneous operation of the heat pump (3, 4) and the boiler (2); in which the control unit (15) is programmed to modify an inlet temperature (T2) to the condenser and a quantity of heat generated by the boiler (2) based on the temperature of the external environment, of a pre-defined quantity of heat of the fluid for a user of the fluid heated by the system and a mathematical model of the efficiency of the system, so that the difference between the amount of heat generated by the heat pump (3, 4) and the pre-defined amount of heat is generated by the boiler (2). 2. System according to claim 1, in which the mathematical model of the efficiency of the system provides for the decrease in the temperature (T2) of the inlet as the temperature of the external environment decreases. System according to claim 2, wherein the mathematical model of efficiency of the system is a weighted average of a first representative member of the boiler (2) and of a second member relating to the heat pump (3, 4). System according to any one of the preceding claims, in which the efficiency function is representative of the hourly cost of the thermal kWh or of the production of carbon dioxide during the operation of the boiler (2) and of the heat pump (3, 4). System according to any one of the preceding claims, in which the heat pump (3, 4) is powered at least partially by a photovoltaic system and the efficiency function is: In which: € / (kWh electricity): is the cost of the electricity kWh; Q _̇pdc: is the thermal power transferred by the heat pump 3, 4; COP: is the 'coefficient of performance' of the heat pump 3, 4; P_PV: is the electrical power generated by the photovoltaic system for powering the heat pump 3, 4; € / (thermal kWh): is the cost of the thermal kWh of boiler 2; is the share of heat supplied by the heat pump 3, 4 compared to the total heat output required by the system user. System according to any one of the preceding claims, wherein the accumulator (5) is configured to be connected to a space heating circuit and the control unit (15) is programmed so that the amount of heat pre-sets defined of the fluid is the amount of heat required for space heating via the space heating circuit. System according to claim 6, wherein the boiler (2) is connected to the accumulator (5) to receive the fluid from a first subvolume and the heat pump (3, 4) is connected to the accumulator to receive the fluid from a second subvolume; where the first sub-volume is greater than the second sub-volume; and comprising a branch branch (12) connected to both the first and second sub-volume and configured to be connected to the space heating circuit. System according to one of claims 6 or 7, comprising a further accumulator (7) for domestic hot water, a heat exchanger (8) for transferring heat between the fluid and domestic hot water and an open circuit (9) for connect the further accumulator (7) and the heat exchanger (8) to a domestic hot water user. 9. Method of controlling a system for heating a fluid comprising an accumulator (5) for a fluid heated by a boiler (2) and a heat pump (3, 4) in parallel, comprising the steps of: - Detect an inlet temperature (T2) of a heat pump condenser (3, 4); - Detect an operating temperature of a boiler (2); - Detect a temperature of an external environment to which the heat pump (3, 4) transfers heat; - Modify the inlet temperature (T2) and a quantity of heat generated by the boiler (2) on the basis of the temperature of the external environment, a pre-defined quantity of heat of the fluid for a user of the fluid heated by the system and a mathematical model of system efficiency, so that the difference between the amount of heat generated by the heat pump (3, 4) and the pre-defined amount of heat is generated by the boiler (2).