I googled to see if I could find something for you. I found Bristish Home Stores and a reference to the British saddleback pig......

So I'll explain as well as I can. A conventional hot water cylinder (HWC) starts off full of cold water. Assuming it is not heated by elec immersion, it is heated by the fact that a coil (a heat exchanger) full of the same hot (80 deg C) mucky water as your radiators passes through it. A thermal store works the opposite way round. The cylinder is full of mucky rad water, VERY hot, and 2 heat exchangers pass thro' it, one for the C Htg and one for the hot water. They pull heat out of the cylinder to heat the house and the water. This allows you to have mains pressure HW, if you have a very efficient heat exchanger. If the thermal store is the same size (c 100 litre) as a conventional HWC, it'll need its heat topping up pretty often. But it could be 200 lt, or 500 lt, or, as in the case of CAT's old ISHS (inter-seasonal heat store) 100,000 litres!!!

Try that for a start.

Nick

Thats really interesting. Sorry if these are silly questions - I'm completely new to this.
I've heard people talk about a Megaflow cylinder - is this product a thermal store ? What I struggle to grasp is how cold water at mains pressure can be heated quickly enough to satisfy demand for say, filling up the bath. Presumably there is a store of some hot (clean water) stored in the cylinder also ?
Also, surely it takes more energy to heat this mass of water as opposed to the traditional cylinder/coil arrangement ?

They are also known as accumolator tanks, here are a copule of link where you can learn more (Heatweb/DPS in particular is very good)

http://www.heatweb.com/
http://www.accumulatortanks.co.uk/

I have a thermal store which I purchased from Chelmer (http://www.chelmerheating.co.uk/). One of the main benefits is that it acts as a big thermal buffer, with the idea that the boiler then does a few long efficient burns, rather than cycling on and off frequently. I assume this also has some benefits in the lifetime of boiler, pump and control valves. However, add in installation costs and you are probably looking at ~GBP 2k, so installation is probably an act of faith rather than economic rigour, even in a large house.

I installed a 250l DPS thermal store with an 18Kw gas condensing boiler in my 4 bed house 5 years ago.

Plumbers then were very wary - had to go to one with commercial experience and even then had to 'hold their hand' and check the work.

It works well, boiler doesn't short cycle and condenses all the time.

FLow 75C, return 55C

lots of hot water. no motorised valves to go wrong.

remember to size rads for lower temp and make sure the structure can support the weight (with controls, expansion tank etc. mine weighs about 300kg with a 500mm diameter footprint.

If I could cange anything now, I'd have a coil (or 2) added for later addition of solar hot water or wood stove input.

Hope that helps

I've recently fitted a DPS thermal store and a pellet boiler. The DPS store comes ready assembled with pushfit connections and you can configure it for UFH, solar etc. It also has a blender valves on the boiler return and for the domestic hot water which stops scalding hot taps. The electrical connections between store and boiler processor took a bit of sorting, but DPS managed that with sending an extra relay. It all works a treat, so far. In my research I found that local plumbers and plumbers merchants didn't know what I was talking about. Its not your usual diy, but at the moment the alternatives are much more expensive. I'm quite happy to share my experiences.

kebabman,

Yes, you can feed solar hot water at the top. In fact it's a good solution to improve the layering in the tank. See this picture http://www.solgruppen.se/bilder/4ssoltank.jpg

As you can see you require a 3-port motorised valve to be controlled by the solar controller (the Resol DeltaSol ES can do this for example). You can also achive this by using a PHE and a 3-port motorised valve. Or if you don't want to use a motorised valve you could use one of these http://www.acaso.se/english/produktblad/TERMOVAR%20AF%20(EN)%200305.pdf.

I found that a number of local plumbers knew about stores (both mains pressure and vented) - I guess it depends on where you are.

S.

We're planning to link our existing Stanley super 80 (or a new Esse W23) central heating cooker, together with a new central heating woodburning stove (StratfordTF90b?) to a new thermal/heat store to provide all heat for the 20 radiators in our house and all our domestic hot water (plus retaining nice warm kitchen and current cooking possibilities).
We also hope to add solar hot water to the thermal/heat store for summer domestic hot water when we don't want to light cooker or stove. If so am I right in believing that existing hot water tank becomes redundant as all domestic hot water heated via heat exchangers within heat store?
Has anyone got any advice regarding how to calculate the size of thermal/heat store needed, and how near to either cooker or stove heat store needs to be?
If solar entry is at top of thermal store, I understand we’ll get hot water in summer but will radiators be cooler in winter? If solar entry is at bottom of a big store will we just get lukewarm water in summer?
Is a heat store sufficient for safe containment of all hot water from proposed sources (I'm imagining, from what I've read from various sources that we'd need a store with capacity of up to 2500 litres) without needing emergency outlet such as current gravity fed radiators, for example?
Also, any advice on the best value heat stores out there? Any problems to look out for?

Scotch

My central heating runs directly off my DPS store with no problems, I also specified an grundfos alpha pump (auto variable speed pump) to help ensure that the return temperature from the central heating is low (ie flow from boiler is 75 deg C, so return from CH should be slightly below 55 deg C to help the boiler return be 55 deg C (ideal for condensing gas boiler). Lots of tweaking of rad valves to get that one right (do it when house is cold but store is hot).

Then all I had to do was adjust the blender on the boiler return to get 55 deg at the boiler ( 2 people and an electronic thermocouple meter).

Except that the plate heat exchanger for the hot water needs the store to be HOT (my store at 73-75 is about as low as you want to go). The lower the store temp, the lower the flow rate for a given temperature. Also the energy stored is a function of the temperature and volume of water stored, so higher temp = smaller store, lower temperature = bigger store.

Evidently the Alpha Pro pumps are even more efficient than the alpha I have.

Mike

You're right - If the pump doesn't slow down and the rads close on trvs then less heat loss on the circuit and as you rightly say higher return temp. the boiler primary return can only be as cold as the CH return. To get the magic 20 degree drop between the boiler flow and return you need to make sure that the return from the rads is pretty cool - I've reduced the speed slightly on my alpha pump to assist with this (slower round the circuit = more time in the rads to loose the heat).

In my eyes a long lower output burn is better than several short higher output burns for the boiler. The things which give a condensing boiler efficiency are two fold

1. return has to be below 55 deg C else the boiler won't condense and
2. Difference between flow and return temp should be 20 deg C

If the boiler is modulating down, then that's not a problem - my boiler drops to about 1/2power after 20 mins or so of running.
To help the boiler run for longer rather than short cycling, I've set the upper stat to a few degrees lower than the lower stat (in my case 65 on the top stat and 72 ish on the bottom one. The boiler won't fire until both stats are below the set temp. therefore making sure there's a fair amount of water to heat (DPS told me that one). Bottom stat dictates the store temperature, top one says minimum store temp before boiler starts. I've got at TP7000 programmable room stat with a simple (non learning) optimum start to cut down on boiler time on warmer mornings. It also has a 'cron' function that reduces the overheat when the requested room temp is reached.

I did think about putting a jacket round mine (after all 40mm is not loads of foam around the cylinder) but mine is in one of my kids bedrooms so I recon most of the heat loss goes to heating that room. In your case I'd definitely consider boxing it in and insulating the box. I did cut a circle of 50mm polyurethane foam and put it between the top lid and the expansion tank lid.

Matthew