THERMAL STORES

[webmaster]

These are open vented (so OK for DIY install) hot water cylinders, not unlike a domestic hot water cylinder. The big difference is the internal heat transfer tubing, and the way the hot water take off occurs.

In a conventional DHW tank, the transfer coil is connected to the boiler, and the boiler is also connected to the central heating pipe feed and return. The hot water is run off from the DHW cylinder, being replaced by the cold water cistern, and this is heated by the transfer coil. The coil has to transfer all the boiler heat and this is the weak point, resulting in long warm up times and long recovery periods.

The Thermal Store differs in that the boiler is connected directly to the cylinder, circulating the whole cylinder contents. This direct transfer means faster response (mass of hot water = thermal store).

The transfer coils are typically much larger in surface area than in typical DHW tanks and are 10's of metres long, coiled up and usually finned. There are two of these transfer coils. The one at the lower part of the tank which feeds the heating system and is typically set to be around 40 degrees C. The upper transfer loop has one end connected to the incoming mains water supply, and its other end is the domestic hot water feed.

The upper part of the tank is set to run at around 75 degrees C, the large store of hot water in the tank allowing you to run the cold water through the coil at 5 or more gallons per minute. So you get mains pressure hot water, which is one big benefit of this system.

The other big benefit is that there is a large thermal mass of hot water in the cylinder. This means that the boiler can run for a long efficient burn, rather than the repeated small cycles that are inherent with a traditional coil connection.

Thermal stores can be used with any wet heating system, and are mandatory in some Under-floor heating systems: the store provides the thermal mass at a LOW temperature that makes it ideal for use with such a system. Otherwise, the small volume of water in the UFH pipes would cause repeated cycling of the boiler. The temperature differential in the taller cylinder with a lower and upper thermostat also means they can be used effectively with condensing boilers, which otherwise present a problem for under floor heating.

ASCII diagram:

Thermal Store

--------- blender valve Hot water take offs

| |________X_____________|________|_______|______

-------| | | |

| | | | return

| |________|_____O<______________________________| loop

Boiler | | | pump * optional

Loop | | |

| | mains water feed

| |

| |----------------

| | Underfloor heating loop

--O<--| |--------O<-----

pump | | pump
---------


(The above will only look correct if your browser/mail package is set for a non-proportional font, e.g. Courier.)

There is a picture of the authors thermal store at: http://uk.groups.yahoo.com/group/UK_Selfbuild/files/Rick%27s%20selfBuild/Thermal%20Store.JPG


Regards, Webmaster
_________________
Regards, Webmaster