DE102008023325A1 - Solar plant, particularly solar combination plant for heating drinking water and room heating, comprises model of storage system, which has rectangular shape and is provided in cubical shape during minimum storage - Google Patents

Abstract

Solar plant comprises a model of a storage system, which has a rectangular shape and is provided in cubical shape during minimum storage. The storage walls are provided, which are manufactured from standard insulating materials, such as polyurethane hard foam, for volumes of different requirements and conditions and storage temperatures above 100[deg] C.

Description

Should Heat recovered from solar collectors for drinking water heating, Heating or heating support used, it usually needs to be cached, there is a time difference between demand and availability consists. To solve this problem, Stores with a volume of several hundred liters are up maximum 2500 liters used. The storage medium is water since Water over has a high heat capacity and directly can be used.

solar systems for drinking water heating usually have small storage (up to 500 l), working from spring to but effective in the fall and can easily two-thirds cover the need. However, you can she several days Bad weather periods do not bridge and therefore need and for the winter time a after-heating system.

combisystems usually have larger memory (in the private sector usually up to 1000 l, in the area of multi-family houses is also the use common to several memories of this size), which make it possible solar heat gained over several Days to save and they work effectively for heating support in the transitional periods. The recoverable in the summer months heat can only one small part.

This applies to both Plants for pure domestic water heating as well as for combined plants. The reason is the usual limitation of the storage tank temperature for water storage tanks at 90 ° C up to 95 ° C. If this is achieved, the supply of heat from the collectors is interrupted and further storage is not possible. This interruption in heat dissipation leads to, that the collectors are exposed to high thermal loads. The stagnation temperatures can with flat collectors between 180 to 210 ° C and with tube collectors up to 300 ° C and lead to a faster aging of the collectors and the heat transfer medium. Furthermore, always an automatic emptying of all system parts, which are exposed to these temperatures can be realized. Partially High storage temperatures are also avoided by the Memory during the night over cooled the collectors become. The limitation of the storage temperature thus leads to the ability of tube collectors, Heat over 100 ° C with a to generate relatively good efficiency is not used.

That no memory is used on both types of equipment, all heat recoverable from the collectors absorb and thus increase the amount of useful heat, is due to the high Cost of this store. These are caused, among other things, by that drinking water is taken directly from the storage tanks and thus high hygienic requirements must be met. Another obstacle are limitations in size, the at least for buildings from the existing structure, through stairs, Door and door Window openings, result. These usually allow for small storage volumes. An on-site assembly of multiple parts to accommodate larger volumes reach is not common. That for reasons of space no bigger memory can be used, as few cubic meters Space should actually be available in every basement.

There Water a liquid is the stratification of heat within a water reservoir difficult and is common associated with high temperature losses during heat transfer. Around Solve problems There are many different forms and designs of heat exchangers on the market. Apart from some special forms, the use of water leads always to the highest temperatures in the area of the storage surface can be found (depending on from the loading condition). While memory is usually well isolated, still leads this in that the generally unavoidable heat losses climb.

One general problem of water storage tanks for domestic water supply is that these are harmful to germs (Legionella formation) tend. To an overly strong Therefore, it is useful to avoid multiplication of Legionella the hot water as possible Every day once heated to at least 60 degrees. From a certain memory size this is Provision.

Around the problems of high cost, the overall efficiency of the system negatively affecting low storage volumes, the difficult stratification the heat, the associated problems with heat loss and legionella formation To reduce significantly is the use of isolated to be assembled at the site cuboid Sand storage systems makes sense.

A sand storage system consists of one or more sand stores, as required. Under a sand storage is a cuboid construction to understand their wall material made of stable insulating material and its content (storage medium) is sand. The supply and removal of heat via one or more tube bundles of copper. These have the form of a helix. The schematic structure of a memory can 1 be removed.

description the components of a sand storage system:

1. walls

The walls of the system should consist of pressure- and temperature-resistant, water-repellent insulating materials (for example, rigid polyurethane foam) and form a complete, closed outer shell. Today, these rigid foams are produced by default in large numbers and can be cut into virtually any shape, which makes it possible, in principle, to realize any conceivable shape and size of a cuboid (possibly also of a cube). The thermal conductivity of these rigid foams is very low, which minimizes heat losses. Of course, the losses depend on the wall thickness chosen. This must at least be chosen so that the pressure load can be easily absorbed by the storage material. When assembled on-site, the walls are either glued together or, by means of straps, secured by straps for heavy goods load securing systems, allowing for later trouble-free implementation. In the case of temperature resistance, care must be taken that the material used can withstand temperatures above 100 ° C for a longer period of time. However, this requirement should not be a problem, since these rigid foams are usually designed for continuous loads of 120 ° C and short-term loads up to 250 ° C. In order to remove a possible residual moisture of the sand used as storage material, a hole must be made in the lower area at the level of the bottom plate from which accumulating water can flow ( 2 ).

2. Storage material

When Storage material should be used sand. This one has in comparison to water a lower volumetric heat capacity, which is a disadvantage. The advantage of sand, however, is that there is virtually no limit at the storage temperature and there it is a solid acts, the stratification of heat without big ones Temperature losses possible is. Different types of sand are available inexpensively in the building materials trade. Because sand is a fine bulk material is a transport to every conceivable place of a building without huge Effort possible, of course, assuming appropriate floor / ceiling load capability. In the Choice of material should definitely have a maximum heat capacity and a minimal thermal conductivity be the selection criterion. A low thermal conductivity ensures that the supplied Heat as possible long in the area of the tube bundles remains and is usable.

3. Heat exchanger

• – die Zufuhr von solarer Wärme, denkbar sind natürlich auch andere Quellen wie wassergekühlte Kamine und Öfen, Nah- und Fernwärme
• – die Zufuhr von Wärme aus dem Heizungssystem als Ersatzsystem (Nachheizung)
• – die Entnahme von Wärme für die Brauchwassererwärmung
• – die Entnahme von Warme für die Vorwärmung von Brauchwasser
• – die Entnahme von Wärme für Heizzwecke
• – die Entnahme von Wärme für die Vorwärmung von Heizwasser

The supply and removal of heat should take place via helical tube bundles. These tube bundles should consist of one or more copper cables. Industrially produced copper pipes are available with different pipe diameters and pipe thicknesses (see Table 1). Industrial delivery lengths on wheels are 25 and 50 m. The bending radius is a minimum of six to eight times the tube radius. In order to use storage systems for different functions, it is necessary to use tube bundles of several parallel tubes. Conceivable designs of the tube bundles are 3 refer to. It is assumed that the different tube bundles can be manufactured industrially at low cost, since many companies are involved in the production of components made of copper materials. The essential functions of a tube of a tube bundle are:

• - The supply of solar heat, conceivable, of course, other sources such as water-cooled fireplaces and stoves, local and district heating
• - The supply of heat from the heating system as a replacement system (reheating)
• - The removal of heat for domestic water heating
• - The removal of heat for the preheating of process water
• - The removal of heat for heating purposes
• - The removal of heat for the preheating of heating water

It is also possible to provide one or more tubes of a tube bundle with the same function. So it is conceivable, for example, in a four-bundle, each 2 tubes for the supply and 2 tubes for the Ent use of heat.

Depending on the task of the storage system and more than one tube bundle can be used. For storages having a footprint of about one square meter, two tube bundles are as in FIG 4 meaningful. It would also be conceivable four tube bundles with a small radius. The optimum number of tube bundles and their designs must be chosen very carefully depending on the task.

There for example the surface a 50 m ring, diameter is 22 mm, more than three square meters, is a heat transfer without big ones Temperature loss ensured (see Table 1).

4. Combination options / structure

Since the daily solar heat gain varies a lot over the course of a year, it makes sense to divide it into smaller storage tanks for larger systems. The advantage of this approach is that there is a corresponding isolated storage volume for the amount of heat currently available. In 5 By way of example, a system of three identical and juxtaposed memories is shown. This design means that in times when only the middle memory is operated, this is extremely well isolated on at least two sides. Depending on the amount of heat to be stored then the left or right or both memory can be operated in addition.

If the space available for the storage system is limited, or if the system is operated so that all three stores are frequently in use at the same time, a structure as in 6 make sense. In this construction, the inner walls have the same strength as the outer walls. This reduces the required volume for the system or, for the same volume, increases the space for the actual storage material and thus the storage capacity.

One Assembling systems from smaller sand stores is a course of action which makes it possible uncomplicated changes / extensions make.

5. System description

Out The above-described sand stores, the most diverse Volume and types of tube bundles for heat transfer can have, Is it possible, customized Systems for to put together the most diverse requirements. Hereinafter Two useful systems should be briefly explained.

In 7 is a storage system for the exclusive service water heating shown. The storage is equipped with two tube bundles. The outer is a single bundle (WT2) and the inner one is a triple bundle (WT1). The heat of the collector is supplied to the memory only via WT1. If the temperature at the collector output is higher than the temperature at the lower inlet of the tube bundle by a certain value ΔT (normally 5 to 10 K), the collector circuit pump is started. It is switched off if the temperature at the upper outlet of the tube bundle is higher than the collector temperature minus ΔT. In this way results in a relatively uniform temperature profile from bottom to top. The heat first spreads out around the tube bundle. This ensures that the internal heat exchanger for cold water heating is always in the range of the highest temperatures in the storage tank. With further heat supply, the heat is then transported to the middle and the outer areas of the memory. The inflow of the cold water to be heated always takes place above WT2, because this area of the storage always has at least room temperature after some operating time and is therefore higher than the temperature with which cold water normally enters a building (8-10 ° C). This ensures that the cold water is heated and this part of the store heat is removed. If the store has a high loading temperature, it may be sufficient for the cold water to flow only through WT2. The temperature at the upper outlet of WT2 decides whether the heated cold water is warm enough or needs further heating. If the temperature is too low, the three-way valve must be opened accordingly, so that the preheated cold water additionally flows through WT1. At high temperatures of the storage, it may happen that the hot water for normal use has too high a temperature and must be cooled. This can be done via a mixing valve, which optionally ensures an adjustable useful temperature for the hot water by mixing cold water. If the temperature at the outlet of WT1 is lower than the setpoint temperature, an additional heating must provide for a corresponding heating. For this, a line is provided in WT1. About this can, as is usual with solar systems, a reheating of the memory on the normal Heating system done. As an alternative to afterheating, the passage of the insufficiently heated water through a water heater could also be considered, provided that it is able to heat preheated water to the useful temperature.

In 8th a two-storey system for exclusive heating / heating support is shown. Both memories are identically constructed and have two sets of two (one inner and one outer) for heat transfer. Thus, four heat exchangers are available for the supply of solar heat and removal of heat for heating purposes. These can be used individually, in groups or all at the same time. In total there are 15 different combinations to use for both transmission directions. For the operation of such a two-memory system, a control system (not shown here) is necessary, which guarantees and monitors optimal operation.

Summary

The above description shows that the use of sand storage systems on diverse Way can happen. These systems are available to all conceivable structural and thermal engineering Conditions customizable and can be easily expanded or change. Your installation is likely Under normal conditions always be easily possible. Because all components come from mass production, can be comparatively small Costs are assumed.

By the direct proximity the heat exchanger for the Feeder and for The removal ensures that when solar heat (or Heat from other sources), these without much loss of temperature for use can be provided because of the very good thermal conductivity the copper pipes these and their contents are the first to be heated. Due to the relatively large Volume of the tube bundles There is always a certain amount of warmed up water (see Table 1) and directly available.

There only a relatively small reservoir of fresh water for later use is present in the memory and this also permanently by the high temperatures of heat input is heated, reduces the risk of contamination drastically across from Standard systems.

There the heat with the highest Temperature always inside the memory and not near the memory surface (inside before isolation), the heat losses are limited. Because the storage walls are always rectangular or square, it is also conceivable, vacuum insulation panels to use as part of the insulation. These have very little Space requirements an extremely low thermal conductivity, what the heat losses minimized. However, they provide a special solution, with significantly higher costs connected is.

When high-quality tube collectors serve as a heat source, their full potential, namely to supply heat even in the temperature range above 100 ° C with good efficiency, can be used. A shutdown of the collectors is no longer necessary with proper design of the sand storage system. When using the capability of tube collectors, the volume storage capacity can reach or even surpass that of reservoirs. Pipe diameter outside [mm] Pipe surface [m ² ] Volume pipe thickness = 1 mm length = 50 m [l] Volume pipe thickness = 0.8 mm length = 50 m [l] 12 1.88 3.93 4.25 14 2.20 5.65 6.04 15 2.36 6.64 7.05 18 2.83 10.05 10.56 22 3.46 15.71 16.34 28 4.40 26.55 27,37 35 5.50 42.76 43.81

table 1 The dimensions of commercial Copper pipes for the drinking water and heating construction

Claims (9)

Solar systems for drinking water heating or solar combination systems for domestic hot water heating and space heating with a sand storage system, characterized in that the design of the memory (in the minimum case of memory) of the system cuboid (in special case also cube-shaped) to inexpensively from standard insulating materials (such as polyurethane) Rigid foam) to produce the storage walls for any volume of different requirements and conditions and storage temperatures above 100 ° C. A system according to claim 1, characterized that its cuboid or cube-shaped design the use of so-called vacuum insulation panels, the one extremely low thermal conductivity own, as an outer layer in a sandwich insulation allow. A system according to claim 1, characterized that the material of the memory from the normal building materials available inexpensively Sand, whose property allows heat to be stored at temperatures well above 100 ° C and, since it is a solid, a spatially targeted Storage of heat allows their temperature just below the temperature of the heat source lies. A system according to claim 1, characterized that the heat exchanger in the / the sand storage / s consist of one or more helical tube bundles. The tube bundles Depending on the task, there are one or more copper pipes. The tube bundles should be made of standard lengths for rings (25 or 50 m) are prefabricated with different diameters. It is also possible, several tubes of a bundle for same To use tasks. A system according to claim 1, characterized that only a small amount of that later used as drinking water Heated water will, as the largest part the heat is stored in the sand. Because of this and because of this small amount of water always in the range of high storage temperatures is the danger the bacterial contamination compared to pure water storage significantly reduced. A system according to claim 1, characterized that it consists of several storage units, depending on the offer of heat be loaded and operated and easily to other units added can be. A system according to claim 1, characterized that the chosen one Construction allows tailor made Sizes any To plan volume and assemble easily at the final location. A system according to claim 1, characterized that the use of solid as a storage medium is a stagnation-free Operation of the solar collectors allows what extends their lifespan, because no extreme temperature loads occur and what an automatic cost-causing emptying system of the collector system makes unnecessary. A system according to claim 1, characterized that its construction also allows, in principle, heat from sources other than Collect solar collectors, such as near or district heating.