Patent Application
20110101119
The present invention relates to a heating system for a property, including a thermal interconnection between a thermal heat generator, in particular a conventional heating system, and a plurality of heat consumers for simultaneous production of heat and electricity, the thermal interconnection being controlled by a control unit, one of the heat consumers including a conversion system based on a thermodynamic cycle, in particular a water vapor or an ORC or Kalina process, and provided for the conversion of thermodynamic energy into electrical energy, and the condensation heat occurring in the thermodynamic cycle being transferred to further heat consumers.
As regards the following description, reference is made to the attached “List of terms used and their meanings” and the “List of abbreviations”.
The brochure “Kurzinfo: Lion® Powerblock” (as at October 2007) of OTAG Vertriebs GmbH & Co. KG, Olsberg, Germany (http://www.otag.de/download/071007_Lion_Kurzinfo—2007_D.pdf) presents a heating system for residential properties according to the prior art. Essential components of this system are a gas burner, a steam-based thermodynamic circuit consisting of a tube evaporator and a heat exchanger for condensation of the water vapor and for transferring the condensation heat to the heating circuit. The steam pressure energy generated is first converted into linear kinetic energy by means of a double free-piston uniflow steam engine and then into electric power with the aid of a linear generator coupled thereto. The supply of steam into the working chamber of the free piston is controlled mechanically by way of slide valves which are firmly connected with the piston rod and, depending on the piston position and piston velocity, open and close the inlet for a specific time that can not be controlled further. As a result of this, the piston path in which the inlet is open is always fixed and is therefore optimally designed for one working pressure only. The lower working pressures occurring, e.g., during start-up or switch-off can therefore not be optimally exploited since this requires a relatively longer opening of the inlet to ensure a full utilization of the expansion chamber.
After the piston has performed its expansion work, it travels over an opening in the cylinder wall which serves as an outlet for the expanded water vapor until such time as the piston closes the opening again in its return movement, which, for one thing, results in that compression work is to be performed on the steam remaining in the cylinder in order to push the piston to its initial position again. This compression work is carried out by the contradirectional working cycle of the double free piston, accompanied by the losses in the energy conversion which inevitably appear in the process. For another thing, the piston is unable to perform the maximum possible expansion work since at the moment when the piston travels over the outlet opening, an overpressure must still be present in the working chamber for the remaining water vapor to flow into the condensation chamber at all, something which leads to further conversion losses.
A further drawback of this known mini CHP (combined heat and power) unit results from the use of water as the medium for the thermodynamic cycle since water will only condense at 100° C. at normal pressure. But since the domestic heat consumers often require only distinctly lower temperature levels, such as, e.g., in the operation of a floor heating system with a flow temperature of 50° C. max., the maximum possible efficiency of electric power generation, which is based on the spread between vaporization temperature and condensation temperature, is not exhausted thereby. While a cycle using water vapor as the medium and involving condensation temperatures of below 100° C. is also conceivable, the negative pressure resulting therefrom is difficult to maintain in the long run due to leakages that can be hardly avoided for technical reasons.
For a more economic way to generate electricity by means of a mini CHP unit, the following characteristics would additionally be worthwhile:
The current state of the art relating to heating systems with a simultaneous thermal heat production and an electricity production based on a thermodynamic process is characterized by the following features:
E
Heiz(t)+ESp OUT(t)=EWW(t)+EHW(t)+ETHDY(t)+ESp IN(t)
P
Heiz(t)=PTHDY(t)+PSp IN(t)
Generally, the following boundary conditions and requirements are to be taken into account for an economic electricity generation by a thermodynamic process by means of a mini CHP unit:
Furthermore, the problem has to be solved of how the various heat generators, heat accumulators and heat consumers can be thermally coupled to each other in the most favorable way.
According to the invention, provision is made in a heating system of the type initially mentioned that the heating system is operable in at least one of two modes of operation, wherein in the first mode of operation the heat generated is supplied to the thermodynamic cycle for producing electricity and the residual heat resulting from the thermodynamic cycle is used for heating, and in the second mode of operation electricity is produced independently of the heating demand in that a heat sink absorbs the condensation heat of the thermodynamic process. Advantageous and expedient configurations of the heating system according to the invention will be apparent from the dependent claims.
The invention is primarily geared to a heating system for residential properties, which is used to heat the rooms of a property and/or the domestic service water of the property (heat consumers). For the first time, a system is proposed in which a conventional heating system is combined with a thermodynamic circuit, for instance with an ORC circuit (Organic Rankine Cycle) “on a small scale” (i.e. not in industrial plant engineering or power plant construction) to provide in this way an efficient option for generating electrical power. Until now, ORC installations have been rarely made use of in the low load range since the efficiency of conventional ORC installations in this range is generally considered to be too low.
The invention provides a heating system which avoids the above-mentioned disadvantages of the prior art by one or more preferred measures and meets the additional requirements. These preferred measures relate both to improvements in the basic system structure and improvements in respect of a demand-oriented efficiency- and cost-optimized design of each individual component, and also to an optimized overall system structure resulting from the additional requirements. A special overall system consisting of a combination of the advantageous measures listed below leads to a preferred technical realization of the heating system which, based on the thermodynamic system design, results in a maximum energy efficiency in the conversion of thermodynamic to electrical energy:
Generally, the thermal coupling according to the invention, of a heat sink provided at the property, configured as, e.g., an air moisture heat exchanger, a geothermal collector, a geothermal probe, a body of water, an air cooling system or a cold reservoir, allows an additional mode of operation in which electricity can also be produced at a time when there is no heating demand, by the heat sink absorbing the condensation heat of the thermodynamic cycle. By the thermal coupling of a heat sink provided at the property to the thermodynamic cycle, a maximum temperature spread is reached between the temperature level of the medium prior to expansion (TTHDY-In) and the temperature level of a heat sink (TWs) provided at the property.
The theoretically possible Carnot efficiency in the conversion of the thermal energy thus results from the formula:
ηCARNOT=1−TWs/TTHDY-In
Especially advantageous with respect to the maximum possible Carnot efficiency is the use of a special high temperature heating system, in particular a biomass combustion plant configured in this way, such as, e.g., a wooden pellets heating system allowing medium outlet temperatures TH Out of above the boiling point of water, in particular with outlet temperatures of greater than 300° C.
In order to be able to exploit the high outlet temperatures of the high temperature heating system, a thermodynamic circuit medium (e.g., thermal oils) suitable for this temperature range and having a critical temperature above the outlet temperature of the high temperature heating system is required.
The generation of electricity with the aid of the thermodynamic cycle is effected in that the working medium, preferably a cooling agent having a low boiling point, is vaporized, a high pressure being produced by the vaporization. This pressure can be extracted as mechanical kinetic energy in the form of volume change work during the expansion of the gas and be converted into electrical energy in the process.
Preferred is a medium which is suitable for the thermodynamic cycle, e.g. thermal oils, or an ORC medium which is specially developed for this application and which, in addition to the good heat transfer characteristics required, also distinguishes itself in that no negative pressure relative to the ambient pressure arises in the medium in the required low condensation temperature range since the efficiency of the thermodynamic cycle is reduced by an ingress of air during negative pressure conditions, which is difficult to avoid in the long term for technical reasons. Furthermore, the superheating of the vaporized gas required prior to expansion should be as small as possible since the energy added during superheating does not increase the energy yield of the thermodynamic cycle.
The control unit manages the energy distribution and, based on periodically determined measured data, adjusts an equilibrium between thermal energy generation and thermal energy demand according to the formula
E
Heiz(t)=EWW(t)+EHW(t)+ETHDY(t)+ERest(t).
According to a special embodiment of the invention, a valve-controlled piston engine is provided which can be used for separately and variable setting the inlet and outlets periods of each working cycle. For one thing, this results in that under the given conditions, each expansion proceeds under optimum pressure conditions. For another thing, based on the inlet period the inlet volume is controlled and thus the outlet pressure of the medium after expansion has been effected, which in turn allows the temperature of the medium after the expansion of the thermodynamic cycle to be able to be variably adjusted to maximum temperature required at the moment of conversion, of one of the heat consumers. Ideally, the condensation of the medium then also takes place at this temperature level. Therefore the maximum possible portion—under the given circumstances—out of the thermal energy available is used for electricity generation. The equilibrium between the thermal energy generation and thermal energy demand is periodically determined and adjusted by the control unit here preferably according to following formula:
E
Heiz(t)=EWW(t)+EHW(t)+ETHDY(t)
A further improvement in the energy utilization is achieved by a thermally coupled heat accumulator in which the thermal heat produced by the heating system can be temporarily accumulated and be passed on to at least one heat consumer offset in time. Owing to this thermal interconnection, the heating system always only needs to be put into operation for a short time for heating purposes. Furthermore, as will be described below, the heat accumulator also allows the solar energy to be utilized both for heating purposes and for solar electricity generation. The heat accumulator preferably is a heat accumulator of an additive configuration having different temperature levels (stratified storage tank), in which a heat exchange takes place both in the flow line and in the return flow in each case at a selectable, best possible temperature level available in the heat accumulator. In addition to the extensively used buffer vessels, other types of accumulator are also conceivable, such as, e.g., space-saving latent heat accumulators with an accumulator medium which performs a phase change, preferably from solid to liquid, in the required accumulator temperature range, or a thermochemical heat accumulator. The equilibrium between thermal energy generation and thermal energy demand is periodically determined and adjusted here by the control unit preferably according to the following formula:
E
Heiz(t)+ESp OUT(t)=EWW(t)+EHW(t)+ETHDY(t)+ESp IN(t)
Based on data from sensors for detecting process-influencing parameters, the control unit automatically adjusts the most favorable operation at and for each particular point in time by changes in the process control variables (such as, e.g., flow velocity of the circuits, etc.). On the basis of sensor data, each heat exchange between individual components of the heating system is adjusted by a closed-loop control of the heat flows occurring, such that the transfer of the thermal energy of the respectively warmer medium to the respectively colder medium is as effective and complete as possible. The control unit can also include information from an electricity supplier of the property into the process of controlling the heating system to allow a production of electricity in particularly profitable periods of time.
The equilibrium between thermal energy generation and thermal energy demand is periodically determined and adjusted by the control unit preferably according to the following formula:
E
Heiz(t)+ESp OUT(t)=EWW(t)+EHW(t)+ETHDY(t)+ESp IN(t)+ERest(t)
By means of sensors for detecting process-influencing parameters, the control unit independently sets one or more of the modes of operation characterized below:
In connection with the temperatures indicated above, an ideal situation without losses in the thermal transmission is assumed in which the control unit adjusts the operation at the respectively most favorable temperature spreads.
One difficulty in the technical realization of the thermal equilibrium between thermal energy generation and thermal energy demand in a plurality of modes of operation is constituted by the required load distribution between the individual components, which need to have a power throughput dependent on the mode of operation and on the condensation temperature. The following must always apply:
P
Heiz(t)+PSp OUT(t)=PWW(t)+PHW(t)+PTHDY(t)+PSp IN(t)+PWs(t)
The generator side of the equation can always be equalized for all modes of operation by the use of a heating system which is controllable in terms of the power PHeiz(t) and which generates a constantly high output temperature TH Out at a constant thermal transfer efficiency, independently of the power required. The consumer side of the equation can always be equalized by a variable power throughput of the thermodynamic conversion system PTHDY(t), which, however, additionally requires a closed-loop control for the condensation temperature. An additional option resides in regulating the heat accumulator input power PSp IN(t).
The technical realization of a heating system having a controllable heating power PHeiz(t) at the required high output temperatures TH Out>300° C. is difficult. It is therefore of advantage if the heating system can be operated at a constant heating power PHeiz, irrespectively of the mode of operation, by the required load distribution being effected either by means of the variable accumulator inflow PSp IN(t) or by means of an adjustable power throughput PTHDY(t) of the thermodynamic conversion system.
The dynamic load distribution required has the following effect on the relevant modes of operation:
The thermal equilibrium of this mode of operation reads as follows:
E
Heiz(t)+ESp OUT(t)=ETHDY(t)+EHW(t)+ESp IN(t)+EWW(t)
The heat accumulator absorbs the condensation heat of the thermodynamic process and, at the same time, the heat consumers are supplied from the heat accumulator. Thus the following applies:
E
Sp OUT(t)=EWW(t)+EHW(t)
E
Heiz(t)=ETHDY(t)+ESp IN(t)
E
Sp IN(t)=EHeiz(t)−ETHDY(t)
On the power level this means:
P
Sp IN(t)=PHeiz(t)−PTHDY(t)
At a constant heating power:
P
Heiz(t)=PHeiz=constant
While this mode of operation is active, the power throughput PTHDY(t) of the of the thermodynamic conversion system is constant:
PTHDY-Heizk at TKond=THeizk RL
This results in a constant accumulator inflow:
P
Sp IN
=P
Heiz
−P
THDY-Heizk
An equalization of the inconstant energy consumption of the heat consumers is effected by means of the heat accumulator filling level. The operating mode is active until the heat accumulator filling level has exceeded an upper limit, and becomes active again as soon as the filling level has fallen below a lower limit.
No regulation by means of the accumulator inflow takes place here. The thermal equilibrium of this mode of operation reads as follows:
E
Heiz(t)=ETHDY(t)+ERest(t)
and, hence:
P
THDY(t)=PHeiz−PWs(t)
When the temperature level TWs is sufficiently low, a constant cooling capacity PWs can be taken from the heat sink. Thus, the following applies:
P
THDY(t)=PTHDY=constant at TKond=TWs
While this mode of operation is active, the power throughput PTHDY(t) of the thermodynamic conversion system is constant:
P
THDY-Stromp
=P
Heiz
−P
Ws
When it is intended to operate the heating system at an equally high heating power PHeiz irrespectively of the mode of operation, this means:
PHeiz-Stromp=PHeiz-Heizk=PHeiz-Heiz Solar=PHeiz-Solar
This results in a separate power level for PTHDY for each mode of operation:
Mode of operation (a) PTHDY-Heizk=PHeiz−PSp IN
Mode of operation (b) PTHDY-Stromp=PHeiz−PWs
Due to the lower temperature of the heat sink, PTHDY-Stromp is higher than PTHDY-Heizk. When the temperature levels of TWs and THeizk RL are unequal, the following applies:
PTHDY-Stromp≠PTHDY-Heizk
One option to realize a heating system with only two modes of operation, (a) and (b), and a constant conversion power PTHDY and a constant heating power PHeiz is obtained when the temperature level of the heat sink equals the return temperature of the radiators THeizk RL.
When TKond=THeizk RL=TWs
then PHeiz=PTHDY-Stromp=PTHDY-Heizk applies.
The maximum Carnot efficiency reduced thereby for this system thus results from:
ηCARNOT=1−THeizk RL/THeiz
A further option to realize a heating system having a constant heating power PHeiz is obtained when the outlet pressure constantly corresponds to the temperature level of the heat sink TWs. The mode of operation (a), which, as a result, is no longer applicable, must therefore be replaced by a mode of operation in which the heating system 2 produces thermal energy exclusively for use as thermal heat and for WW heating, with the appropriate heat circuits needing to be integrated for this purpose, of course. While this requires a conversion system having a variable conversion power PTHDY(t), an advantage of this application resides in that the conversion system only needs to implement a constant ratio of the inlet pressure to the outlet pressure and the power can be controlled by means of the repetition frequency fcyc. Realization is possible using a turbine or a uniflow steam engine, for example.
The maximum Carnot efficiency of this application results from the following formula:
ηCARNOT=1−THeizk RL/THeiz
A preferred option for producing electricity is a linear conversion system for converting thermodynamic energy into electrical energy, which is coupled to the thermodynamic cycle and includes one or more pressure cylinders, a linear generator, and a filter and rectifier unit. The linear conversion system provides for a piston/cylinder unit which is coupled to the thermodynamic cycle and specifically matched therewith, for initially converting the thermodynamic energy into kinetic energy from which electrical energy is then produced by means of a linear generator that is likewise specifically matched with this application, and the electrical energy is converted by means of a grid-based frequency converter into an AC voltage suitable for being fed to the grid. A suitable pressure cylinder/linear generator arrangement distinguishes itself by a high overall conversion efficiency, low prime costs, quiet operation as well as by a long service life as there are no transverse or rotational forces.
A special aspect of the conversion system consists in that by means of a valve-controlled piston engine, the inlet and outlet times of each working cycle can be adjusted separately and variably. This results, for one thing, in that under the given conditions, each expansion proceeds under optimum pressure conditions. For another thing, based on the inlet time the inlet volume is controlled and, hence, the outlet pressure of the medium after the expansion is completed, which in turn allows the temperature of the medium after the expansion of the thermodynamic cycle to be variably adapted to the temperature required at a maximum at the moment of conversion, of one of the heat consumers. Ideally, the condensation of the medium likewise takes place at this temperature level. As a result, the highest possible amount—under the given circumstances—of the thermal energy available is used for generating electricity.
To prevent the piston from striking against the cylinder head or cover, it is possible, in principle, to limit the piston stroke in that the piston rod is coupled to an idling crankshaft, for example.
A further possibility of avoiding a hard strike consists in that the expansion stroke available is not completely utilized for decompression and the remaining piston travel is realized by way of a magnet snapping. Here, the induction force that guides the piston up to the stop is adjusted such that only small forces act upon impact, thus allowing long-lasting operation.
In a thermodynamic pressure cylinder conversion system having a variable conversion power PTHDY(t), the conversion power is obtained from the product of the number of working cycles (stroke1 and stroke2) and the work performed by one piston stroke WTHDY and the cycle frequency fCyc:
P
THDY(t)=2*WTHDY*fCyc(t)
The work WTHDY performed is a function of the constant cylinder dimensions and the variable parameters:
W
THDY=(t)(TVaporizVEinl,TKond)
At constant, high TVaporiz and in conversion systems having a constant inlet volume per stroke VEinl, the outlet pressure of the medium can not be closed-loop controlled. This means that in these systems only one condensation temperature level is possible for all modes of operation:
WTHDY=constant
The conversion power PTHDY(t) in this thermodynamic pressure cylinder conversion system can be varied by changes in the cycle frequency:
P
THDY(t)=2*WTHDY*fCyc(t)
One possibility of making the cycle frequency fcyc to be variable consists in varying the expansion velocity and, hence, the expansion duration tExp of a piston stroke by making the induction force Find to be variable through electrically variable parameters of the linear generator.
The cycle frequency fcyc is dependent on the expansion duration tExp. When a working cycle is immediately (without dead time) followed by the contradirectional working cycle, then the following applies:
f
cyc=1/(2*tExp)
The expansion duration tExp is dependent on the stroke length, which however is constant, and on the expansion velocity of the piston, which, in turn, is the result of the equilibrium of forces between the mechanical thrust Fstroke of the pressure cylinder during expansion and the opposed induction force FInd of the linear generator.
t
Exp
=f(FInd)
and, hence: fCyc(t)=f(FInd)
An electrically adjustable parameter of the linear generator is the coil inductance, which can be varied, for example, through an electrically selectable wiring of coil pairs.
Another way of configuring the induction force FInd of the linear generator to be variable consists in a closed-loop control of the load current of the inverter by the input resistance of the inverter, for example. The special advantage of this configuration resides in that this interface, for example in the form of a semiconductor junction, allows a very rapid and precise closed-loop control of the induction force FInd also during the expansion phase. This, in turn, results in that the combination of pressure cylinder and linear generator can be optimized in the design of the dimensions since this allows an optimum operation to be realized under the limiting factors of maximum acceleration and maximum piston velocity. The highest power throughput is produced when the piston is initially constantly accelerated at maximum acceleration during expansion. Once the maximum permissible velocity of the piston is reached, the piston is moved at this maximum velocity until it is necessary to decelerate the piston again at a negative and constant maximum acceleration.
In this way, it is possible to provide a heating system having a variable conversion power PTHDY(t) for all modes of operation; however, since it is not possible to adjust the outlet pressure, the following applies here, too:
Tkond=THeizk RL=TWs
The technical implementation of such a conversion system, such as, for example, a pressure cylinder, a uniflow steam engine, or a Corliss engine, is effected by means of a periodic valve timing. Each individual inlet valve and outlet valve is opened and closed periodically at the cycle frequency fCyc for a time period as determined by the valve timing settings, as illustrated in
tEinl1=tEinl2=constant
t
Cyc
=t
Ausl1
+t
Ausl2
f
Cyc=1/tCyc
t
Exp=1/(2*fcyc)
All of the valves are synchronized in time in that in its expansion phase, the pressure cylinder periodically changes the valve position by the mechanical motion of the pressure cylinder or a synchronized motion derived therefrom, such as a rotary motion, and in this way directly mechanically controls the closed periods of each individual valve. The open periods for each valve are defined by the dimensions of a piston valve, for example, which opens and closes a valve by a linear motion. One example of a linear design of a periodically operating conversion system having a double-acting pressure cylinder is the known steam engine by James Watt.
A rotary type of this periodic pressure cylinder conversion system includes separate rotary valves which are opened and closed synchronously with the cycle frequency fCyc for defined periods of time as illustrated in
In order to realize a dynamic closed-loop control of the outlet pressure of the medium and, thus, of the condensation temperature TKond, the inlet volume per stroke VEinl needs to be adjustable, which is possible by way of a variable open period of the inlet valves tEinl. Ideally, the inlet valves are externally controlled, i.e. a control unit sets the inlet volume VEinl(t) by means of the inlet period tEinl such that the desired pressure of the medium is reached over the full piston stroke upon completion of the expansion. The condensation temperature of the medium is thereby set such that it corresponds to the maximum required temperature of the heat consumers coupled.
Preferably, inlet valves that can be electrically driven are employed for this purpose. In principle, the valve can also be driven pneumatically or hydraulically. Further conceivable is a solution in which the inlet valves are realized with a piston valve which opens and closes the inlet valves by its linear motion, the linear motion of the piston valve being externally controlled, i.e. not being derived from the motion of the pressure cylinder. A controlled linear motion of the piston valve can be realized using a linear motor, for example.
One way of implementation is constituted by the valve-controlled double-acting pressure cylinder illustrated in
Since it is always the full piston stroke that is used for expansion, a direct interrelation exists between the inlet period tEinl and the desired condensation temperature TKond, i.e. for each adjustable condensation temperature TKond there exists a corresponding inlet period tEinl and thus a constant value for the work performed by a piston stroke WTHDY. As a result, the following applies:
W
THDY
=f(TKond)
This means that the inlet period tEinl can not be made use of for controlling work performed by a piston stroke WTHDY. The inlet period tEinl can be exclusively used for adjusting the outlet pressure of the medium after the expansion. The conversion power PTHDY(t) in a thermodynamic pressure cylinder conversion system can therefore be exclusively varied by varying the cycle frequency. The conversion power PTHDY results from the product of the number of working cycles (stroke 1 and stroke 2) and the work performed by one piston stroke WTHDY and the cycle frequency fCyc:
P
THDY(t)=2*WTHDY(TKond)*fCyc(t)
This principle is, of course, also applicable when using two contradirectional pressure cylinders, as are made use of in conventional free piston systems, with one working chamber always remaining unutilized and only one pressure cylinder carrying out the working cycle at a time alternately, while the other one is currently in the outlet phase.
Based on a conversion system implemented in this way, the cycle frequency fCyc thus controls the conversion power PTHDY, while the condensation temperature TKond is adjusted on the basis of the inlet period tEinl.
The following results from this for the different modes of operation:
Mode of operation (a) PTHDY-Heizk=2*WTHDY-Heizk*fCyc-Heizk=PHeiz−PSp IN
It is, however, technically complicated to configure the induction force of a linear generator to be adjustable in order to use it for regulating the conversion power. A further advantage of the valve-controlled double-acting pressure cylinder consists in that it is not necessary to immediately start with the execution of the next working cycle once a working cycle has been executed. By a variable dead time ttot inserted between execution of the working cycles, the repetition frequency and thus the conversion power PTHDY can be controlled. The cycle frequency fCyc is dependent on the expansion duration tExp and the dead time ttot:
f
cyc=1/(2*(tExp+ttot))
For the required capacity (power) adaptation, the control unit determines the appropriate cycle frequency fCyc in the different modes of operation:
f
Cyc
=P
THDY/2*WTHDY
Here, the control unit waits between execution of one working cycle and execution of the contradirectional working cycle until half the period duration TCyc has elapsed. A power-modulated valve control takes place here, as illustrated in
In the process, the outlet valves are alternately opened and closed after half the period duration TCyc, that is, synchronously with the cycle frequency fCyc. It is therefore feasible to design the outlet valves to be externally controlled, such as, e.g., by electrically drivable valves, and also by a control derived from the linear motion of the pressure cylinder, such as, e.g., by means of a rotary valve control that is synchronous with the piston position.
Basically, however, a generation of electricity is also possible using a valve-controlled rotational conversion system coupled to the thermodynamic cycle, such as a compressed air motor specially matched therewith, in which the linear piston movement is first converted to rotational energy by means of a crankshaft, the rotational energy then being converted to electrical energy by means of a generator likewise specially adapted to this application.
A further preferred option is offered by the use of a rotary piston machine, in particular a DiPietro engine as such, in which the inlet volume per working cycle can be likewise controlled. An RMT generator, primarily designed for wind power plants, presents itself for use as a rotational generator. Both components distinguish themselves by a high efficiency in conversion as well as by very low start-up and switch-off losses in the required capacity range, even at low rotational speeds.
The electrical voltage produced in the generator in all of the systems described may, of course, also be used for other purposes. Instead of generating a line voltage, it is possible to generate battery charging voltages using a suitable converter, e.g. for lithium ion batteries for electric vehicles, or voltages suitable to be used for obtaining hydrogen through electrolysis. The kinetic energy produced by the conversion system may also be used for other purposes, e.g. for cooling indoor air by means of a refrigerating machine.
In a combustion plant involving output temperatures of TH Out>300° C., it is technically difficult to reach the low waste gas temperatures required for an efficient operation. A marked improvement according to the invention in the efficiency of the combustion system is achieved by the thermal interconnection of a waste gas heat recovery system in a function as a separate heat generator for the thermal heat energy ERück(t) recovered having the temperature level TRück.
The equilibrium between thermal energy generation and thermal energy demand is periodically determined and adjusted here by the control unit preferably according to the following formula:
E
Heiz(t)+ESp OUT(t)+ERück(t)=EWW(t)+EHWETHDY(t)+ESP IN(t)+ERest(t)
For one thing, the waste gas residual heat can be made use of for meeting the heating and WW demand, the following applying:
E
Rück(t)=EWW(t)+EHW(t)
Therefore, a further improvement in accordance with the invention is the use of the waste gas residual heat for producing electricity in the thermodynamic cycle, that is, in the modes of operation (a) and (b), the following applying:
E
THDY(t)=ERück(t)+EHeiz(t)
By a thermal coupling of thermal solar collectors either directly to a heat consumer or preferably to the heat accumulator, the annual heating costs may be reduced. The equilibrium between thermal energy generation and thermal energy demand is periodically determined and adjusted here by the control unit preferably according to the following formula:
E
Heiz(t)+EsSol(t)+ESp OUT(t)+ERück(t)=EWW(t)+EHWETHDY(t)+ESp IN(t)+ERest(t)
An optimum energy utilization is obtained by a thermal interconnection, according to the invention, of the individual components of the heating system, which ensures that each heat generator is in a heat exchanging relationship with each heat consumer, the heat accumulator, or with any other heat generator, with provision being preferably made for a contradirectional heat transfer when different heat transfer media are involved, and preferably for an exchange of medium when identical heat transfer media are involved.
Furthermore, the heating system according to the invention may be selectively operated in a plurality of modes of operation. In a first mode of operation, the heat generated or accumulated by one or more heat generators is used for heating or for filling the heat accumulators. In a second mode of operation, the heat generated is supplied to the thermodynamic cycle for the production of electricity, the residual heat arising from the thermodynamic cycle being transferred to the heat sink. In a third mode of operation, the heat generated is supplied to the thermodynamic cycle for the production of electricity, the residual heat arising from the thermodynamic cycle being used for heating or for filling the heat accumulators. On the basis of predefined criteria, the control unit automatically determines in which one of the modes of operation the heating system is operated and, to this end, can optionally obtain information from an electricity supplier of the property to allow a production of electricity in especially profitable periods of time.
This heating system is able to effectively exploit solar energy, both for the production of electricity and for obtaining thermal heat, by further raising the low temperature level prevailing in the heat accumulator or in the solar collector, which must only be higher than the temperature of the heat sink (TWs), by the remaining temperature range up to a consumption-dependent target temperature.
Further advantages arise in that, in one mode of operation of the heating system, in particular during the night or in winter, the solar collectors are made use of as a heat sink which absorbs the residual heat of the thermodynamic cycle. A multistage solar collector structure is of advantage here, which includes a series connection of different types of collectors consisting, on the one hand, of cost-effective collectors having a lower thermal insulation and, on the other hand, of higher-quality collectors having a high thermal insulation. For the purpose of energy optimization, it is further of advantage in some modes of operation that the individual collector types can also be bypassed, i.e. the solar medium does not flow through them. Based on predefined criteria, such as, e.g., the outside temperature, the control unit here determines whether the solar medium flows through only one of the collector types or through both in series.
In addition, radiators or a floor heating system provided in the property may be utilized as a permanent heat sink for the thermodynamic cycle, even when there is no heating demand. A special radiator in the laundry room, which is heated with residual heat whenever the latter develops during the exclusive production of electricity, could at the same time be utilized for laundry drying, for example.
As a rule, a solar-assisted heating system shows an inverse ratio between the availability of solar primary energy and the heating demand, i.e. while a large amount of primary energy is available in summer, there is hardly any or only little heating demand, whereas the opposite applies in winter. The invention makes use of exactly this inverse ratio, to the effect that the surplus of primary energy is converted into electrical energy. Due to a multiple dual use of the resources of the components which are already present in the solar-assisted heating system, of the solar collectors, heat accumulators, heating system and radiators, only the prime costs of the conversion system plus worthwhile add-ons such as additional collector surfaces and additional accumulator volume have to be incurred for solar electricity production. A high overall system utilization of the cost-intensive collector surface is advantageously achieved as there is no excess supply of solar heat energy in summer any more and in winter the solar supply is utilized via the heating system.
Due to the weak points as initially described of the circuit media currently available, the system presented so far, which is based on a thermodynamic process for electricity generation, is however not able to cover the desirable high temperature range which is given, on the one hand, by the high flash point of a heating system (>1000° C.) and, on the other hand, by the ambient temperature (<0° C.) of theoretically available temperature potentials.
A marked improvement according to the invention is therefore constituted by the combination of two thermodynamic cycles (partial processes) for successive temperature ranges, each partial process being a separate independent thermodynamic process and each partial process having a conversion system of its own for the conversion of pressure to electrical energy, and the condensation heat of the partial process for the higher temperature range being used as vaporization heat for the partial process of the lower temperature range by means of an interconnection via a heat exchanger. For example, a steam, butyl benzene, propyl benzene, ethyl benzene, toluene or OMTS cycle may be used for the temperature range of from 300 to 150° C. and an ORC cycle using the R245fa medium may be used for the low temperature range of from 150 to 15° C. The resultant addition of the temperature ranges results in a theoretical Carnot efficiency of 50% in this example.
The equilibrium between thermal energy generation and thermal energy demand is periodically determined and adjusted here by the control unit preferably according to the following formula:
E
Heiz(t)+ESol(t)+ESp OUT(t)=EWW(t)+EHW(t)+ETHDY1(t)+ETHDY2(t)+ESp IN(t)+ERest(t)
A further improvement according to the invention appears if the necessary capacity compensation between the partial processes occurs in that the control unit controls the transition temperature between the condensation of the medium of the first partial process and the vaporization of the medium of the second partial process and the capacity ratio of the two partial processes and adjusts it in accordance with the requirements.
A further aspect according to the invention is a cost-effective coupling of individual components of the two conversion systems for the conversion of pressure into electrical energy, so that it is not required to provide all individual components twice, by means of a mechanical coupling of the conversion systems which is configured such that the mechanical forces add, so that only one generator and one grid-based frequency converter are required, each of which transfers the sum of the energy of the partial processes.
A further possible cost-effective coupling of individual components of the two conversion systems for the conversion of pressure into electrical energy, so that it is not necessary to provide all individual components twice, can be implemented by means of an electrical coupling of the generator outputs; as a result, only one grid-based frequency converter is required, which transfers the sum of the energy of the partial processes.
In principle, it is also possible to couple the pressure cylinders of the two conversion systems for the partial processes by means of a crankshaft, the generation of electricity being effected by way of a rotational generator.
Of particular advantage here is the coupling of a waste gas heat recovery system and a thermal solar plant to the low temperature circuit of the two-stage thermodynamic process. The energy supply ETHDY is effected here in two stages at different temperature levels. In the low temperature stage (stage 2), the thermal energy ERück recovered is made use of for heating or partial vaporization of the thermodynamic medium up to the temperature level TRück, the following applying:
E
THDY2(t)=Esol(t)+ERück(t)+ERest1(t)
This means that owing to the different temperature levels, the amount of energy for conversion into electrical energy ETHDY-stage2 and thus ETHDY additively increases by the value of the waste gas heat ERück(t) recovered and the solar energy ESol(t).
In the first stage of the thermodynamic process, the thermal energy EHeiz recovered is made use of only for residual vaporization of the thermodynamic medium from the temperature level TRück up to the temperature level THeiz, the following applying:
E
THDY1(t)=EHeiz(t)−ERest1(t)
By means of sensors for detecting process-influencing parameters, the control unit independently sets one or more of the modes of operation characterized below:
In connection with the temperatures indicated above, an ideal situation without losses in the thermal transmission is assumed in which the control unit adjusts the operation at the respectively most favorable temperature spreads.
It is possible, of course, to establish further modes of operation from the above tables by combining several modes of operation or by omitting a generating unit, accumulator or consumer in some modes of operation; these further modes of operation, however, shall not be discussed in further detail here.
How the heating system is operated depends on the current situation. As a rule, the production of heat energy is more efficient than the production of electricity. But when selecting the operating mode, the control unit also takes into account, inter alia, the supply of primary energy, the (predicted) demand for heat energy, the time-dependent degree of utilization of the heat accumulator, and the ratio between the income for electrical power fed and the effective heating costs. The control unit provides for an energy management for a situation-based distribution of energy in consideration of determined and predicted process-influencing parameters.
According to one aspect of the invention, provision is also made for a sequence of different modes of operation which, owing to the resultant high and constant utilization of the heating system accompanied by a simultaneous effective production of electricity, is advantageous whenever the heating and WW energy demand is lower than the maximum heating capacity of the heating system installed. In accordance with such a sequence of modes of operation, alternately the first the mode of operation (a), “Heating, WW and production of electricity”, is active until such time as the heat accumulator is filled sufficiently, and then, after this condition is met, parallelly the modes of operation (b), “Exclusive production of electricity from thermal heat”, and (e), “Solar heating and WW by means of heat accumulator”, until such time as the amount of heat accumulated in the heat accumulator falls below a lower threshold.
To be able to operate the system in all modes of operation, the power throughput PTHDY1(t) and PTHDY2(t) of the conversion systems 116 and 118 must be adjustable for each mode of operation, the following applying to each relevant mode of operation:
PHeiz=PTHDY1
P
THDY2
=P
Rück
+P
Rest1
PHeiz=PTHDY1
P
THDY2
=P
Rück
+P
Rest1
PHeiz=PTHDY1
P
THDY2
=P
SP Out
+P
Rück
+P
Rest1
Since the condensation temperature of the second stage TKond2 is different in the various operating modes, it is advantageous to provide the second stage with a conversion system which has an outlet pressure that can be regulated, such as, for example, the valve-controlled linear generator described above or a DiPietro engine.
Since the condensation temperature of the first stage TKond2 is constant in the various operating modes, it is advantageous to provide the first stage with a conversion system without an outlet pressure that can be regulated, such as, for example, a uniflow steam engine or a turbine.
Based on a modified configuration (see
The mode of operation (a) modified thereby is characterized by the following features:
Further general increases in efficiency for all system structures presented are obtained, for one thing, based on the fact that internal heat exchangers (regenerators) are provided for the thermodynamic cycle.
For another thing, it is often difficult in hot summer nights to reach cooling temperatures below the desirable 15° C. One cost-effective solution is constituted here by a sprinkler system which cools down solar collectors additionally, inter alia by the evaporative heat loss produced in the process. This sprinkler system should, of course, be activated by the control unit only when, all in all, cost benefits are expected to result thereby.
It is furthermore conceivable that the conversion system for the high temperature circuit 402 is realized by means of a Stirling engine since Stirling engines are designed for higher temperatures. It would be theoretically possible in this way to produce electrical energy at a high overall efficiency with burner circuit temperatures of >500° C.
Further details of the invention will be apparent from the following description with reference to the accompanying drawings, in which:
According to
The system illustrated in
The expanding working medium flows through the first line 601 into the first working chamber 603 of the pressure cylinder 600. To this end, the control unit 609 opens the port 605 and closes the port 606. At the same time, the control unit 609 closes the port 608 of the second line and opens the port 607. This results in a force Fstroke being exerted on the piston 608, causing the piston 608 to move to the right (according to the illustration in the Figure), accompanied by a performance of work. This process, which terminates after one stroke of the piston 608, constitutes a “normal” working cycle of the pressure cylinder.
In the contradirectional working cycle, the control unit 609 closes the open ports 606, 607 and opens the closed ports 605, 608, so that an oppositely directed piston force −Fstroke and a movement of the piston 608 to the left are produced. It depends on the current position of the piston 26 which one of the two working cycles (normal or contradirectional) is carried out.
The volume (inlet volume) flowing into the working chambers 603 and 604, respectively, is controlled by means of the control unit 609. Upon an evaluation of sensor data 610, the start and duration of the inflow process are determined automatically, and the pressure and, hence, the temperature of the medium after the expansion are adjusted thereby such that this temperature corresponds to the maximum required temperature of the heat consumers coupled. That is, the inlet volume is a function of the medium pressure available on the input side and the pressure desired on the output side during condensation, which allows a very efficient energy conversion.
As already mentioned, the control/closed-loop control of the individual circuit processes and of the linear generator is performed taking process-influencing parameters into consideration (thermal energy supply, thermal heating demand, pressure and temperature of the working medium, the heat accumulators, and the surroundings, etc.), which are provided by a large number of suitable sensors 610 (pressure, temperature sensors, etc.)
This principle is, of course, also applicable when using two contradirectional pressure cylinders, as are made use of in conventional free piston systems; in this case, the working chamber 304 remains unutilized and only one pressure cylinder carries out the working cycle at a time alternately while the other one is in the outlet phase.
The invention has been described with reference to several exemplary embodiments. It is, of course, apparent to a person skilled in the art that modifications may be made without leaving the idea of the invention. In addition, the exemplary embodiments illustrated are of a sketch-like nature. Any missing details are not relevant to the essence of the invention, but may be added by a person skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 008 832.3 | Feb 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/001023 | 2/13/2009 | WO | 00 | 10/13/2010 |
