Abstract:
A method and a related device for providing heat for heating buildings and optionally for heating tap water via a solar collector, in which the solar collector is filled and permeated with a thermal carrier medium in the event of incident solar radiation, in order to heat the thermal carrier medium, and in which the solar collector is otherwise emptied, the thermal carrier medium being collected in a storage reservoir.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a method for providing heat for heating buildings and optionally for heating tap water via a solar collector, in which the solar collector is filled and permeated with a thermal carrier medium in the case of solar radiation, in order to heat the thermal carrier medium, and in which the solar collector is otherwise emptied, the thermal carrier medium being collected in a storage reservoir, and the thermal carrier medium being kept under elevated pressure in the storage reservoir and in the solar collector. 
       BRIEF DESCRIPTION OF RELATED ART 
       [0002]    The standard construction of solar plants comprises a thermal carrier medium being conducted through the solar collector in a closed circuit. Since the solar collector always remains filled, it is necessary to take corresponding technical precautions to ensure reliable operation, such as antifreeze agents, compensating reservoirs, and the like. In specific applications, however, a simplification of this construction is desirable to achieve particular robustness and cost-efficiency. For this reason, solar plants have been developed in which the solar collector is only flooded with thermal carrier medium during operation and otherwise is emptied. Such a plant is disclosed in DE 20 20 6564 U. In such a plant, the thermal carrier medium is removed from a storage reservoir and pumped through the solar collector for heating when appropriate heat is available. If the pump is stationary, the solar collector empties, so that no danger of freezing exists even without antifreeze agent. In addition, in the event of an already fully loaded storage, overheating or vaporization of the liquid can be prevented, whereby the danger of stagnation can be avoided. 
         [0003]    The given solution has the disadvantage that at least one heat exchanger is required for the usage of the heat in a building heating system, and losses of thermal carrier medium due to vaporization can occur in the event of strong solar radiation and low consumption. In addition, corrosion can occur due to the absorption of oxygen from the air. 
         [0004]    In addition, U.S. Pat. No. 4,269,167 A discloses a closed system made of solar collector, compensating reservoir, and heat exchanger. The vaporization and oxygen problems can be reduced by a possible pressure application, however, the disadvantage of the lack of efficiency and the required expenditure still exists. 
       BRIEF SUMMARY 
       [0005]    The invention intends to avoid these disadvantages and to specify a solution, which is simple, cost-effective, robust, and efficient at the same time. Robust not only means insensitivity in the mechanical sense, but rather also non-problematic control behavior. Efficient primarily means a high efficiency and a good utilization of the available heat. 
         [0006]    According to the invention, the method is characterized in that the storage reservoir is partially filled with thermal carrier medium and partially filled with gas in all operating states, and the thermal carrier medium is removed directly from the storage reservoir for heating the building. In addition, tap water can be heated. 
         [0007]    The fact that the entire system is always kept under pressure, whereby multiple goals are achieved simultaneously, is essential to the present invention. 
         [0008]    Through the solution according to the invention, the pressurized thermal carrier medium can be used directly for building heating, so that any heat exchanger in the heating system can be avoided. A heat exchanger typically means a temperature loss of approximately 3 K to 5 K, which results in a corresponding loss in efficiency. However, in the solution according to the invention, the necessity of installing typical compensating reservoirs is also dispensed with simultaneously, since the storage reservoir itself serves as the compensating reservoir. By increasing the boiling point of the thermal carrier medium, it can be heated to higher temperatures in the solar collector. The thermal carrier medium typically primarily comprises water, which boils at 100° C. under normal pressure. Temperatures of 120° to 140° can certainly be permitted using the solution according to the invention. No losses of thermal carrier medium occur as a result of the closed system. 
         [0009]    It is particularly advantageous in this context if a temperature stratification is maintained in the storage reservoir. In this way, the total energy efficiency can particularly be increased, since typically energy can be used at a lower temperature level even in the event of low incident solar radiation. 
         [0010]    A particularly simple construction is achieved if the thermal carrier medium has a free surface in the storage reservoir. Membranes or the like are not necessary for separating air and thermal carrier medium. 
         [0011]    According to one variant of the invention, multiple solar collectors and/or storage reservoirs can be connected in parallel. In this way, it is not only possible to increase the total performance, but rather also to take an East-West orientation of the solar collectors into consideration, if this is necessary because of structural conditions. 
         [0012]    According to a particularly preferred embodiment variant of the invention, it is provided that tap water is heated in that it is conducted through a heat exchanger in the storage reservoir. In this way, a solar system which is used both for heating and also for hot water preparation can be prepared using simple means. The temperature stratification of the thermal carrier medium in the storage reservoir can be utilized optimally by a spiral tube heat exchanger, which extends in the vertical direction over a substantial part of the storage reservoir. 
         [0013]    In the simplest case, air is used as the gas, systems having nitrogen filling also being advisable. The pressure in the system is typically set to a value between 2 bar and 5 bar. 
         [0014]    Furthermore, the present invention relates to a device for performing the above method for providing heat for heating buildings and optionally for heating tap water, having a solar collector, a storage reservoir, and a heating system, the solar collector being provided with an apparatus for operational emptying. 
         [0015]    According to the invention, it is provided that the system made of solar collector, storage reservoir, and heating system is implemented as a closed system fillable under pressure using a single thermal carrier medium, and the storage reservoir is fillable with gas in addition to the thermal carrier medium. Such a system is simple, efficient, and robust. 
         [0016]    It is particularly favorable if the device according to the invention is implemented so that a supply line to the solar collector is provided, which originates from the lower area of the storage reservoir and in which a delivery pump is provided, and a return line is provided, which opens into an upper area of the storage reservoir, which is located above a maximum fill limit for the thermal carrier medium. In this way, the ventilation of the solar collector can be performed easily by turning off the delivery pump, if it is implemented so that it can have flow through it opposite to the delivery direction. It is important that the solar collector is arranged sufficiently far above the storage reservoir. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention is explained in greater detail hereafter on the basis of the exemplary embodiments shown in the figures. 
           [0018]      FIG. 1  schematically shows a device according to the invention, 
           [0019]      FIG. 2  shows an alternative embodiment variant. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The device according to the invention from  FIG. 1  comprises a solar collector  1  and a storage reservoir  2 , as well as a heating system  3  for a building (not shown in greater detail). The heating system  3  can be a system made of radiators, or a floor or wall heater, in a way known per se. The heating of the thermal carrier medium can be performed directly by a heat pump or another appliance, for example, however, the thermal carrier medium can also be heated in the storage reservoir  2  via a heat exchanger or an electrical heating rod. The storage reservoir  2  is connected via a supply line  4  having a delivery pump  5  to the solar collector  1 . A return line  6 , which opens into the storage reservoir  2 , is attached to the top side of the solar collector  1 . In order to achieve a corresponding temperature stratification, the return line  6  continues in a stratification pipe  7 , which has a plurality of backflow openings  7   a  arranged vertically one over another. 
         [0021]    To ensure a reliable backflow of the thermal carrier medium as needed, the solar collector  1  is arranged above the storage reservoir  2  by a height h. 
         [0022]    The heating system comprises a heating line system  9  having a heating pump  8 , which is connected directly to the storage reservoir  2  and correspondingly has the same thermal carrier medium flowing through it as the solar collector  1 . 
         [0023]    Furthermore, a spiral tube heat exchanger  10  for the hot water preparation is provided in the storage reservoir  2 , which extends vertically in a way known per se over a substantial section of the storage reservoir  2 . 
         [0024]    The storage reservoir  2  has an upper section  12  in which a gas, for example, air is provided. The area  13  is filled with thermal carrier medium, which has a free surface  11 . It is essential that the return line  6  or the stratification pipe  7  has an opening which is located above a maximum fill level for the storage reservoir  2 . 
         [0025]    The operation of the device according to the invention is explained hereafter. In the event of corresponding incident solar radiation, the delivery pump  5  is put into operation and the solar collector  1  is filled with thermal carrier medium, which flows back via the return line  6  into the storage reservoir  2 . As long as the backflowing thermal carrier medium has a higher temperature than the thermal carrier medium present in the storage reservoir  2 , the thermal carrier medium returned from the solar collector  2  will flow out at the highest point of the stratification pipe  7  and therefore generate a temperature stratification in the storage reservoir  2 . However, if the temperature of the backflowing thermal carrier medium is between the temperature in the lower section of the storage reservoir  2  and the temperature of the thermal carrier medium in the top section of the storage reservoir  2 , the thermal carrier medium will primarily flow out between these areas. The storage reservoir  2  is therefore essentially charged from top to bottom while maintaining the temperature stratification. 
         [0026]    An air space is implemented in the upper area  12  of the storage reservoir  2 , in that air is present under a pressure of approximately 3 bar, the volume of this air space being greater than the volume of the solar collector  1  and the relevant line sections  4  to or  6  from the solar collector  1 , respectively. If the delivery pump  5  is turned off, the thermal carrier medium flows opposite to the delivery direction of the delivery pump  5  back into the storage reservoir  2  and air is suctioned out of the upper section  12  of the storage reservoir  2  into the solar collector  1  via the return line  6 . The liquid level  11  in the storage reservoir  2  thus rises and the air space is reduced. The system is operated so that a minimal air space remains in the storage reservoir  2  in any case, however. The danger of freezing at correspondingly low temperatures is entirely avoided by the complete emptying of the solar collector  1 . 
         [0027]    The air space  12  in the storage reservoir  2  simultaneously also serves as a compensating space for the heating system  3 , which is kept at a matching pressure level in this way. 
         [0028]    Since the system is closed per se, the system pressure is dependent on the temperature of the thermal carrier medium, of course. Because of the relatively large-dimensioned air space, however, these variations are slight and are in a range of a few tenths of a bar in the normal case. 
         [0029]    In the variant of  FIG. 2 , two solar systems A and B are connected in parallel to a feed line  14  and a return line  15  of a heating system (not shown in greater detail). These systems A and B each comprise a solar collector  1  having a shared storage reservoir  2 , as well as a delivery pump  5  in the supply line  4 . The two solar systems A and B can be operated independently of one another in this way. It is also possible to provide a separate storage reservoir  2  for each of the solar collectors  1 . 
         [0030]    In the case of heating systems having a large intrinsic storage capacity, such as floor heaters, the storage reservoirs  2  may be implemented relatively small, in the extreme case so that in operation, i.e., with flooded solar collector  1 , only a minimal quantity of thermal carrier medium is present in the storage reservoir  2 . 
         [0031]    The system according to the invention is very robust, since temperatures of 120° C. and more can also be permitted in the solar collector. However, even in the event of an excess of incident solar radiation and a simultaneous lack of consumption, overheating can easily be avoided by simply turning off the delivery pump  5 , since a further heat supply into the system is suppressed in this way.