Thermal stores are being used more and more widely - especially in biomass heating systems. In Germany e. g. recent legislation even stipulates a minimum store volume for any manual or automatic biomass boiler. Why?
Before getting into any details, let us define our terminology:
When talking about “Thermal Stores” or “Buffer Tanks” or “Accumulator Tanks” we mean a reserve tank made of steel, which contains heating water (not drinking water), the same dirty water that circulates in your radiators and in your boiler. The drinking water is stored and heated in a “Hot Water Cylinder”.
Now, what does a thermal store look like?
This is a picture with insulation.
Let’s take a look at the naked tank:
Now let’s cut it open to see what’s inside:
There can be heat exchangers (coils) inside, up to three - or none at all.
The lower heat exchanger is made of ordinary steel. Its purpose is to get the heat from solar panels into the thermal store. In a more refined version an additional heat exchanger in the upper part allows to differentiate where the solar hot water releases its heat first. Alternatively it can be used for a heat pump.
The central heat exchanger is made of corrugated stainless steel. Its purpose is to provide clean hot water. When connected to a water supply (the mains), drinking water flows through this stainless steel heat exchanger and when it leaves the store it has got hot.
This heat exchanger can also be made of copper:
Now again some terminology:
A store without any heat exchanger is called “TS” (from Thermal Store). A store with one heat exchanger (in the lower part) for solar panels is called “STS”. A store with two heat exchangers for solar panels is called “S2TS”. A store with a heat exchanger for domestic hot water is called “HWTS”. A store with one heat exchanger for solar panels and a heat exchanger for domestic hot water is called “HWSTS” And finally a store with all 3 heat exchangers is called “HWS2TS”.
There is still one more kind: a thermal store with a domestic hot water cylinder inside. We call this one “CTS”.
So, now let’s see what the purpose of such thermal stores is.