Abstract:
Electrical and thermal energy is generated for at least one load by a combined heat and power plant, wherein the retrieved heat output is increased when a threshold value for a difference between a provided and retrieved heat output is exceeded.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national stage of International Application No. PCT/EP2012/075147, filed Dec. 12, 2012 and claims the benefit thereof. The International Application claims the benefit of German Application No. 102012200889.6 filed on Jan. 23, 2012, both applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    Described below are a method for operating a combined heat and power plant and a combined heat and power plant. 
         [0003]    Combined heat and power plants, which simultaneously provide electrical energy and heat, are becoming increasingly important for supplying energy, firstly because they typically are very efficient and hence have low consumption and emission values, and secondly because they can be used to compensate fluctuations in the feed-in of renewables. 
         [0004]    Combined heat and power plants are usually operated either in a heat-operated or power-operated mode, depending on which demand determines the regulation of the combined heat and power plant. It is known here, in cases where there is a greater demand for electricity than for heat, to temporarily store the excess heat generated in corresponding stores so that the heat and the electricity can be utilized asynchronously. However, the typical sizes of store here enable the combined heat and power plant to operate without a thermal load for only a few hours. If, when a store is full, there is still no thermal load, then such a combined heat and power plant must, as necessary and despite the continuing demand for electricity, adjust its operating mode because of insufficient cooling. When a combined heat and power plant is used in conjunction with electricity networks with a high degree of photovoltaic generation or use of wind power, it can now be the case that particularly high electrical loads are required by the combined heat and power plant without the heat which is generated at the same time being removed. Because of the limited size of the stores, after just a few hours of rain or a few hours of no wind, failure of the combined heat and power plant may therefore occur, so that stand-by power must additionally be maintained which can be used in this eventuality. 
         [0005]    However, this is not advisable from either an operational or economic perspective. 
       SUMMARY 
       [0006]    A method for operating a combined heat and power plant and a combined heat and power plant are described below which enable combined heat and power plants to operate particularly flexibly even when the demand for the thermal energy generated is low. 
         [0007]    In such a method for operating a combined heat and power plant for providing electrical and thermal energy for at least one consumer unit, it is provided that the heat output requested is increased when a threshold value for a difference between provided and requested heat output is exceeded. 
         [0008]    In other words, according to the method, an additional artificial demand for heat is created for the case where the demand for electricity significantly exceeds the current demand for heat. As a result, the load on heat stores which may be used can be relieved so that the electrical energy requested can be reliably provided even for relatively long periods of time without the heat storage capacity of the combined heat and power plant being fully utilized. 
         [0009]    Even when there is a high demand for electricity at the same time as a low requested heat output, the electricity can thus be reliably provided without there being any need for additional stand-by capacity to be activated. 
         [0010]    The method thus enables the power plant to operate particularly economically, in particular in an electrical network with a high number of stochastically fluctuating generators. 
         [0011]    To increase the heat output requested, it is possible to simply dissipate a proportion of the heat output provided, i.e. to discharge it into the environment. For this purpose, a heat exchanger can, for example, be provided which is coupled to the surrounding air and/or to the soil and/or to a water reservoir. The dissipated energy is thus wasted, i.e. is not reclaimed as in the case of a heat store. Specific implementations of this are, for example, a dry or wet recooling, the discharge of heat to stationary or running water or to an opened cooling water circuit, the heated cooling water being disposed of. 
         [0012]    It is moreover possible to increase the amount of heat requested by increasing the heat consumption of the at least one consumer unit. To do this, for example, a set heating temperature for a room, a swimming pool or the like can, be increased, or also the lowering of the nighttime temperature of a heating system can be suspended. The heat consumption is thus increased here via an energy management system, wherein the increase expediently is selected such that a comfort threshold for users is not exceeded despite the rooms, swimming pool, or the like being heated more intensely. 
         [0013]    Furthermore, a further consumer unit can be activated in order to increase the heat consumption. Processes with a high thermal energy requirement, for example heating procedures, cleaning procedures, or the like can therefore, for example, be conducted ahead of schedule, or alternatively rooms which are not per se needed immediately can be heated additionally in order thus to remove the excess heat. 
         [0014]    Described below is a combined heat and power plant for providing electrical and thermal energy for at least one consumer unit which includes a first heat exchanger by which heat can be transferred from a heat source of the combined heat and power plant to a heat distribution network. It is moreover provided that at least one further heat exchanger is thermally coupled to the combined heat and power plant, by which heat can be discharged to the environment when a threshold for a difference between a provided and a requested heat output is exceeded. 
         [0015]    As already described with reference to the method, when there is a high demand for electrical energy and simultaneously a low demand for heat energy, in this way excess generated heat can be dissipated to the environment so that the generation of electrical energy can be continued without the combined heat and power plant overheating owing to the excessively low heat removal. For this purpose, as already described, it is advantageous to couple the further heat exchanger to the surrounding air and/or to the soil and/or to a water reservoir in order to allow even large quantities of heat to be reliably removed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, explained in detail below with reference to the drawing. 
           [0017]    The single FIGURE shows a schematic representation of an exemplary embodiment of a combined heat and power plant. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0019]    A combined heat and power plant  10  simultaneously makes available electrical energy for electrical consumer units  12  and thermal energy for thermal consumer units  14  and therefore has a particularly high degree of efficiency. However, problems can also arise from the fact that the electrical and thermal output of the combined heat and power plant  10  cannot be adjusted independently of each other. For example, if a high electrical output is requested from the combined heat and power plant  10  by the electrical consumer units  12  or via a connected power network  16 , whilst the thermal consumer units  14  require no or only a very low output, then problems can occur with the removal of the quantity of heat generated by the combined heat and power plant  10 . 
         [0020]    Some of the excess heat thus generated can be stored temporarily in stores  18  but if these are overloaded, the combined heat and power plant  10  must be switched off to prevent overheating. In particular when the combined heat and power plant  10  is integrated into a power network  16  with a high number of stochastic generators such as, for example, solar energy or wind power plants, there is however an urgent need for load balancing in the power network  16 . In the case of a combined heat and power plant  10 , additional back-up capacity would then have to be brought onstream, which is not economically advisable. 
         [0021]    In order to avoid this, a heat exchanger  20  is coupled to the heat distribution network  22  of the combined heat and power plant  10 . If the demand for electricity significantly exceeds the demand for heat, then excess generated heat can be dissipated via the heat exchanger  20 . The heat exchanger  20  can thus be coupled, for example, to the surrounding air, to stationary or running water, and to the soil. Opening the cooling water circuit of the combined heat and power plant  10  so that cold fresh water is heated and then disposed of can also contribute to the removal of excess heat. 
         [0022]    The requested quantity of heat can be further managed by controlling the thermal consumer unit  14 . In the event of demand for electricity significantly exceeding the demand for heat, here too additional cooling of the combined heat and power plant  10  can be achieved. A building management system can, for example, slightly increase the room temperature of rooms which are heated by the thermal consumer units  14  in order to ensure additional heat removal. Any heated swimming pools or the like can also be additionally heated up in order to contribute to the removal of heat. 
         [0023]    If the excess heat is generated at night, a nighttime lowered temperature program of the room heating system can be suspended so that the rooms are again heated more intensely and additional heat is also thus removed. Such an energy management system is also possible outside residential premises, for example in commercial operations. Procedures with a high demand for thermal energy, such as heating processes, cleaning processes or the like can, for example, be conducted ahead of schedule so that the excess heat generated is removed. 
         [0024]    As a whole, it is thus possible to prevent the combined heat and power plant  10  from having to be shut down because of overheating, which avoids the need to make available additional back-up capacities in the power network  16  and thus enables economic operation of mixed, small-scale and flexible power networks with a high number of stochastically operating generators. 
         [0025]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).