US20120180782A1

US20120180782A1 - Solar apparatus with at least two solar collectors with different exposure

Info

Publication number: US20120180782A1
Application number: US13/384,517
Authority: US
Inventors: Thomas Prachar; Stefan Jedrejcic
Original assignee: VKR Holding AS
Current assignee: VKR Holding AS
Priority date: 2009-07-29
Filing date: 2010-07-07
Publication date: 2012-07-19
Also published as: PL2459936T3; AT508749A1; EP2459936B1; WO2011012411A2; WO2011012411A3; ES2414871T3; EP2459936A2

Abstract

A solar heating system and a method for controlling the system, the system including at least two solar collectors with different exposure, a load, a main supply line which branches into individual supply lines to the solar collectors, and a main return line into which lead individual return lines from the solar collectors, a distribution valve which is arranged at the branch-off of the main supply line to the individual supply lines or at the branch-off of the main return line to the individual return lines, and a pump for conveying a heat transfer medium.

Description

TECHNICAL FIELD

The invention relates to a solar heating system, comprising at least two solar collectors with different exposure, a load, a main supply line which branches into individual supply lines to the solar collectors, and a main return line into which lead individual return lines from the solar collectors, a distribution valve which is arranged at the branch-off of the main supply line to the individual supply lines or at the branch-off of the main return line to the individual return lines, and with a pump for conveying a heat transfer medium.

BRIEF DISCUSSION OF RELATED ART

Several solar collectors switched in series are regarded below as individual solar collectors for reasons of simplicity.
Efforts are principally made in the design of solar heating systems with several solar collectors to arrange them in such a way that the exposure is as positive and similar as possible, as is the case for example in the arrangement with the same orientation on a roof facing to the south. In such a case the heat transfer medium can flow into the solar collectors in parallel or in series without any further measures.
In a number of cases however, such an optimal arrangement is not possible and individual solar collectors have different exposures. The most frequent example of such a situation is the installation of a solar power plant on a building whose roof comprises a roof ridge in the north-south direction. In order to achieve a yield which is distributed as well as possible over the progress of the day, the solar collectors are partly fixed to the roof section on the eastern side and partly to the roof section on the western side. It is obvious that an even flow through the solar collectors will provide a suboptimal result, because during the morning the solar collectors on the western side are not only unable to contribute to the heating of the heat transfer medium but thermal losses can also occur. In the progress of the morning, the solar collectors on the western side are irradiated, but at a more unfavorable angle and constant through-flow will finally lead to the consequence that the heat transfer medium that has been heated to an only very low extent is mixed together with the heat transfer medium from the other collectors, leading to a deterioration in the overall efficiency.
In the afternoon and during the evening on the other hand, the solar collectors on the eastern side are less capable or incapable of contributing to the generation of heat and are therefore a cause for losses.
Other examples of different exposure are also possible such as when individual groups of solar collectors have different hydraulic properties or are shaded off temporarily in different ways.
In order to take such conditions into account it has already been proposed to selectively activate and deactivate the solar collectors, in that the inflow is controlled by a changeover valve. Such earlier solutions have been described for example in JP 2003262405 A or U.S. Pat. No. 4,184,481 A. The temperature of the heat transfer medium fluctuates continuously according to the activation and deactivation of individual flow paths, so that efficient control and optimization of the thermal yield are not possible.
A similar solution has been disclosed in DE 195 33 475 A. In this case too, individual collectors are activated or deactivated according to the temperature.
In order to avoid these disadvantages, solar heating systems are known in which the individual solar collectors or groups of solar collectors are supplied separately from one another by separate feed and discharge lines. Each of the circuits comprises a separate, individually controlled pump in order to take the different exposure into account. Such a solution is not only complex with respect to the equipment, but also shows a number of disadvantages. As a result of this concept, speed-controlled pumps can only be operated for example from a specific minimum throughput, which is approximately 30% depending on the configuration. As a result, solar collectors which are irradiated to a lower level can either only be switched off entirely or be operated with a minimum flow rate. If the solar radiation is insufficient so as to ensure a respective heating of the heat transfer medium at this minimum throughput, the disadvantages as described above will occur. In other words, such a system can only compensate differences in the exposure of individual solar collectors if they are not too large. This problem will be exacerbated when the solar heating system is operated in conjunction with a heat pump, so that the heat transfer medium can also be cooled to very low temperatures depending on the operating state and will then have a very high viscosity. This limits the control range of the pump under certain circumstances to less than 50%.

BRIEF SUMMARY

The invention avoids these disadvantages and provides a solution which offers a simple configuration and optimal efficiency even when solar radiation on the individual solar collectors is relatively high. The invention further provides an improved control method for such installations.
The invention results in the distribution valve being arranged as a mixing valve. A valve with a main connection is generally regarded as a mixing valve from which the through-flow can be divided in a continuously variable way into two branch connections. Such valves are used in heating technology for example to produce a medium with a precisely predetermined temperature by mixing cold medium and hot medium.
Within the scope of the present invention, the individual partial flows on the mixing valve will ideally have the same temperature because only the volume flows can be influenced in a respective manner.
It is important within the scope of the invention that the flow rate of the heat transfer medium through the solar collectors can be controlled by the solar collectors in a wide range from virtually zero to a maximum value which is predetermined by the configuration. As a result, large differences between the individual collectors can be compensated.
One advantage of the present invention over installations with two pumps is also that in the case of a conventional arrangement of the solar heating system with the solar collectors on the roof and the other components in the cellar of a building only two risers are required instead of three, because the mixing valve can be arranged in direct vicinity of the solar collectors. It is principally possible to arrange the distribution valve both in the flow pipe and also in the return pipe; it is preferred however if the distribution valve is arranged on the branch-off of the main supply line to the individual supply lines in direct vicinity of the solar collectors. The thermal load on the distribution valve can be kept at a comparatively low level in this way.
It is especially advantageous if respective first temperature sensors are arranged in the individual return lines or in the solar collectors themselves. It is especially advantageous in this respect if a further temperature sensor is arranged in the main return line. The installation in accordance with the invention will be controlled in its entirety on the one hand, in that the speed of the pump is adjusted to the available heat. On the other hand, the through-flow through the solar collectors will be divided by controlling the mixing valve in such a way that the temperature of the heat transfer medium is as constant as possible downstream of the solar collectors. It is principally possible to perform both controls when the temperature of the heat transfer medium at the collector output is known. Deviations in the control in the mixing valve will have an influence on the control of the pump however, because the total temperature of the heat transfer medium needs to be calculated from the two measured individual temperatures after mixing. This can lead to errors because the individual volume flows are not directly known and conclusions can only be drawn from the respective position of the mixing valve. Moreover, the multiple measurement of the temperature provides improved error control. Moreover, an increased precision in the control of the installation will be achieved when the additional temperature sensors are arranged in the direct vicinity of the loads because the thermal losses in the risers will thereby not lead to any distortions.
A special advantage of the solution in accordance with the invention is also that it is no longer necessary in the configuration of the solar heating system to place special emphasis on the hydraulic arrangement of the solar collectors switched in parallel. It is even possible to interconnect differently large collector fields without any special measures when there are different amounts of space on the eastern and western side. As a result of the solution in accordance with the invention, these differences will automatically be taken into account and compensated, in that the through-flow is adjusted automatically. Even roofs with different inclinations can thereby be provided with solar collectors without any special measures without impairing the efficiency of the installation.
An especially high efficiency can be achieved when the pump is arranged as a speed-controlled pump which is arranged in the main supply line. It is thereby possible to minimize the losses in the pump and to realize an especially fine control.
The invention further relates to a method for controlling a solar heating system with at least two solar collectors of different exposure which are supplied with heat transfer medium via a common pump.
This method provides in accordance with the invention that the temperature of the heat transfer medium downstream of the solar collectors is controlled to a uniform value by dividing the volume flow of the heat transfer medium. In particular, said control is arranged in such a way that a first controller will trigger a mixing valve which divides the through-flow of the heat transfer medium through the solar collectors in order to keep the temperature difference downstream of the solar collectors as low as possible. Such a control is especially simple because both control circuits are decoupled from one another to the highest possible extent and are arranged and can be tested separately from one another. The two controllers are mostly implemented in practice as different software sections in the same control device, but this does not change anything in respect of the logical independence.
An especially high efficiency can be achieved if there is a further control of the pump independent of the control of the temperature difference, which further control is configured to maximize the thermal yield. The total yield of a solar heating system depends substantially on the flow through the solar collectors. A maximum volume flow of the heat transfer medium reduces the temperature of the heat transfer medium on the solar collector and leads to a reduction in the radiation losses; it may no longer be possible during moderate solar radiation to emit the heat in the desired manner to the loads however because the temperature level is too low. In the case of installations with heat pumps, it has to work more and operate under a worse coefficient of performance. By taking these factors into account, a control can be realized which is aimed at maximum thermal yield and which can be arranged in principle on a model of the installation and be provided with a self-learning capability. In addition, efforts can be made to achieve the minimization of power consumption because a low amount of power required for driving the pump will also be considered in modern high-power installations.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be explained below in closer detail by reference to the embodiment shown in the drawing. The drawing shows a circuit diagram of a solar heating system in accordance with the invention.

DETAILED DESCRIPTION

The solar heating system comprises of a first solar collector 1 which is oriented to the west, and a second solar collector 2 which is oriented to the east. The solar collectors 1, 2 are supplied by a common main supply line 3, which branches into two individual return lines 4, 5 which lead to the individual solar collectors 1, 2. Two individual return lines 6, 7 open in an analogous manner into a main return line 8.
The heat transfer medium is conveyed by a speed-controlled pump 9 arranged in the main supply line 3 to the individual solar collectors 1, 2 and is guided through a load 10 which is represented here in general by a heat exchanger. The expression “load” 10 stands here generally for any component which is arranged for utilizing solar heat such as a heating buffer, a device for heating water, the evaporator part of a heat pump or the like.
The temperature of the heat transfer medium is measured by first temperature sensors 11, 12 at the collector output or in the individual return line 6, 7. A further temperature sensor 13 is disposed in the main return line 8 and a still further temperature sensor 14 is provided in the main supply line 3.
These temperature sensors 11, 12, 13, 14 are in connection via various control lines 15 with a control device 16 which triggers the pump 9 and a distribution valve 17 which controls the through-flow in the two individual return lines 4, 5. Said distribution valve 17 is arranged as a mixing valve with a control range from 0% to 100%. The distribution valve 17 is controlled continuously and comprises three-point triggering with 24 V or 230 V.
The present invention allows operating a solar heating system optimally with low effort even when individual solar collectors 1, 2 are supplied differently.

Claims

1. A solar heating system, comprising:

at least two solar collectors with different exposure,

a load,

a main supply line which branches into individual supply lines to the solar collectors,

a main return line into which lead individual return lines from the solar collectors,

a distribution valve which is arranged at a branch-off of the main supply line to the individual supply lines or at the branch-off of the main return line to the individual return lines, and

a pump for conveying a heat transfer medium,

wherein said distribution valve is arranged as a mixing valve.

2. A solar heating system according to claim 1, wherein the distribution valve is arranged at the branch-off of the main supply line to the individual supply lines in the direct vicinity of the solar collectors.

3. A solar heating system according to claim 1 wherein first temperature sensors are respectively arranged in the individual return lines.

4. A solar heating system according to claim 3, wherein a further temperature sensor is arranged in the main return line.

5. A solar heating system according to claim 4, wherein the further temperature sensor is arranged directly close to the load.

6. A solar heating system according to claim 1, wherein the distribution valve has a continuously variable control range of 0% to 100% for each of the branch lines.

7. A solar heating system according to claim 1, wherein the pump is arranged as a speed-controlled pump which is disposed in the main supply line.

8. A solar heating system according to claim 1, wherein the solar collectors are oriented in different directions of the sky.

9. A solar heating system according to claim 1, wherein the solar collectors have different inclinations.

10. A solar heating system according to claim 1, wherein the distribution valve is arranged as a continuously controlled valve.

11. A method for controlling a solar heating system with at least two solar collectors of different exposure which are supplied via a common pump with a heat transfer medium, wherein the temperature of the heat transfer medium is controlled downstream of the solar collectors by dividing the volume flow of the heat transfer medium to a uniform value.

12. A method according to claim 11, wherein first controller triggers a mixing valve which divides the through-flow of the heat transfer medium through the solar collectors in order to keep the temperature difference downstream of the solar collectors as low as possible.

13. A method according to claim 11, wherein a further control of the pump occurs independently of the control of the temperature difference, which further control is configured for maximizing the thermal yield and/or for minimizing power consumption.

14. A method according to claim 13, wherein the further control is performed by setting a speed of the pump.