Is an 800ltr thermal store worth the hassle?

[Brandon]

The first thing I notice is that the VTC300 valves that you are proposing to use are in the wrong place, they need to be on the return just below your pumps in the drawing, with the bypass to the centre branch, the other point is that the VTC300 only goes up to 3/4" tapping, and therefore unless you are planning to plumb the WBS in 22mm rather than 28mm, you will require a VTC500.

I also suspect that you will find the heat transfer from the indirect coil disappointing.

Do you already have the cylinders that you have drawn, as if not then I would urge you to buy a thermal store (or 2 if you require) with bespoke solar coils, thus allowing you to prioritise the primary store and dump to the secondary in a two store set-up on the controller.

Given that the secondary store would require little in the way of coils (just solar and DHW preheat) it would not be outrageously expensive.

The top of your primary store will do what you are trying to achieve with the hot manifold if you specify the correct tappings in the top of it.

I will think more for you when I get in later, but the wife has just announced that we are expected at friends for dinner!

Hope that that helps.

Brandon.

[beelbeebub]

@ Brandon:

Thanks for the tips:

Are you sure about the VCT units being on the return line.  the manual shows them in two configurations, one of which is essentially my configuration.  The idea is that no water at less than ~70C is allowed into the top of the cylinder, say at startup.  Also if you look I have some switch-able heat dump radiators.  As my stove is biased to water heat, if I want to up my stoves to room output, I divert the output from the boiler stove to the radiators.  This then increases the output to the room (the radiators are next to the stove).  Of course this will cool the water.  To prevent this cooler water from heading to the top of the thermal store the VCT valve will simply switch a portion of the flow back to the boiler so that the net flow through the boiler is low enough to provide water at the right temp.

Good point about the sizing of the valves, but as I'm pumping the stove flow, do I need 28mm pipe?  The overheat condition will be taken care of by a quench coil (besides the system can't thermo syphon as the stove is the same hight as the cylinders and the pipes have to go up and over to get to them.

One of the reasons for using the configuration is that the cylinders can be indirect 1.2m x .45dia copper cylinders.  These are about the cheapest cylinders that it's possible to get, working out about £1 a liter of storage.  It also gets around my problem of not having a tall thin cupboard only a short fat cupboard.

Could I not use the indirect coils as solar coils or are the areas not big enough?  If so I could use the coil in the primary cylinder as the solar coil, to be used for the summer as the primary heating method.

All the above being said, I'm still open to the idea of a tall thin thermal store with a solar and DHW coil, possibly running direct from the gas and WBS, i'll just have to tell the mrs that the airing cupboard's bitten the dust 

Hope the meal went well!

[Brandon]

by putting the valve in the return, you maintain the temperature entering the stove through the return pipe, and therefore have a steady flow temperature (given the usual riders about maintaining the burn of the fire), this way you will get a small volume of water at the right temperature entering your store, and also ensure that the return is maintained at 55^oC or above (presuming that you used a 55^oC valve as back end protection) thus keeping your boiler jacket warm and your fire burning more efficiently.

A normal indirect coil will under perform if used for the solar coil, it will work, but will require higher temperatures to do so, and therefore be less efficient.