Technical Aspects of Thermal Stores


Evidently, to make a thermal store work successfully we have to make sure the heat is stored well without getting lost, and the heat is well available for further use.

The first point has to do with thermal insulation. According to the main laws of thermodynamics, every difference of temperature will tend towards zero in the course of time, i.e. every closed system will tend towards a uniform temperature distribution. So, a  perfect insulation is physically impossible. The only thing we can influence is the time the system will take to achieve this uniform temperature distribution, i.e. the time it will take for the heat to escape from the thermal store. If it takes considerably longer for the heat to leak from the store than for us to make use of it for heating the house or taking a hot bath, our system is running successfully. If it is the other way around, we will end up in a cool house or a lukewarm bathtub wondering where all the heat is going.
Our thermal stores go with a thick (100 mm) soft PU-foam insulation. It is put and fixed around the thermal store only when the final position for installation has been reached.

The second point is somewhat more intricate.
Let’s consider two identical thermal stores, one with a uniform temperature of 40° C from top to bottom, the other with one half at 60° C and the other half at 20° C (the hot water being in the upper half and the cold water in the lower half). Evidently both contain exactly the same thermal energy, but with the second one we can heat a house or produce very hot water for the bath tub, whereas the first one is almost useless for an ordinary heating system (except if you have a good underfloor heating system).
So the temperature distribution within the thermal store or the way it is charged and discharged plays an important part in its successful application.
For maximum efficiency there should be a clear cut temperature division between the hot and the cold water zones, or as you say a good thermal layering or thermal stratification.
There are many “ingenious” and mostly very expensive gadgets of rather doubtful usefulness on the market with the purpose of securing a good thermal layering.
In an average heating system, however, the most important points are the intensity and direction of flux within the store:
If the hot water gushes in at high speed right into the middle of the thermal store, you can be sure of maximum turbulence, of a real “good” stir and as a result of a tank full of lukewarm water.
If, on the other hand, the store is charged slowly and carefully with the incoming water being kept in a restricted part of the tank (e.g. in a layer near the surface or in a tubular part near the center) until it has reached the layer corresponding to its temperature, the thermal layers will be quite precisely defined.

It is possible to put these two aspects into practice without much difficulty - and without high costs - using simple deflector plates or tubes in the inside of the store and a good hydraulic scheme of installation.

If the connections for the incoming (hot) and outgoing (cold) water are equipped with an extended tube each leading right into the (upper and lower) vault of the store, the water gets pumped into this vault from where it can quietly disperse over the whole diameter of the store and find its place according to its temperature, thus producing a good thermal layering.

These tubes and deflector plates at each connection are standard in our thermal stores.

In addition we can offer more sophisticated solutions, like e.g.

For a good stratification it is important that not too much water come into the store at too high a velocity. Therefore we don’t recommend schemes where all the hot water produced by the boiler is first pumped into the store from where it is taken out again into the heating circuit of the house. It is better to take away the hot water needed for the house from the incoming water BEFORE it reaches the thermal store. In this way only the surplus water goes into the store - a much smaller quantity. Thus we spare the store a good deal of the turbulence otherwise incurred.

Another important help is the Laddomat 21, a time-proven effective unit for charging a store and boosting the return temperature for the boiler. It charges the store at a high and even temperature and with low flow thus ensuring optimal thermal layering.
Actually it even has a third purpose which is very useful: As soon as the pump stops (in case of a blackout or when the boiler has burnt down) an automatic valve opens and allows self-circulation of the hot water in the boiler into the thermal store.

Laddomat 21

Now let’s have a look at the prices.

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