Home made heatbank system

On 18 May 2004 14:28:16 -0700, in uk.d-i-y snipped-for-privacy@lineone.net (Rob Graham) strung together this:

Just a word of advice, if IMM suggested it, it's probably a madcap idea, and if it involves plastic pipe it'll leak, and if he built one himself it probably blew up while he was trying to shower his overly-ample frame. I've no doubt the concept might work but listen to other peoples advice on construction methods.

Wasn't around here then, but if the intention was to get heat out of a standard hot water tank via the coil usually used to heat the water, forget it. On most tanks the transfer rate is poor so peak hot water flow rate is low and as the coil doesn't go anywhere near the hottest water at the top of the tank so you need to keep the tank at a very high temperature just to get the water warm.

Conversely if the suggestion wasn't this, my apologies to IMM.

No - you use an external heat exchanger and circulating pump between the hot outlet at the top and the cold inlet at the bottom. The other side of the heat exchanger is rising main straight to hot taps or shower mixer valve and transfer rates can be several tens of kilowatts, so a good shower !! - going to do the same myself ! Nick

hot outlet at the

shower !! - going to

I think there are some pictures on the DPS web site (google ...) Basically you'll need a flow sensor switch which turns on a pump (like CH pump, but should be non-corrodible rotor) when water flows in the DHW pipework (i.e. someone turns a hot tap on) and pumps water from the hw cylinder through the plate heat exchanger.

Another homebrew way to do it (which I haven't tried either) would be to have a tank of primary hot water (i.e. heated directly by the boiler) with a coil of perhaps 20m of 10mm dia tube immersed in it which carries mains water to the taps, getting heated directly as it goes (i.e. that's your heat exchanger). You'd have to have the tank at the top of your system, at the same level as your f&e tank (implying an open-vented system).

DPS also sell the complete thing as an assembled entity.

You can buy the stainless steel heat exchanger separately as well. I bought one from them made by a Swedish company, GEA Ecobraze for an application where I wanted to have a second heating circuit totally isolated from the first.

These heat exchangers are extremely good and have a massive surface area between the primary and secondary sides. The result is that they can easily transfer 100-200kW in a unit about the size of a brick. Cost is about £80.

.andy

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"Rob Graham" wrote | Searching through the archive found IMM's suggestion of a year ago | (6/5/2003) of using an ordinary DHW tank, etc.

Well, duh, that was /last/ year's solution. It's been superceded by two combi boilers. Do try and keep up at the back.

Owain

I did a "cylinder conversion" a couple of months ago. I got heat exchanger, pump, flow and mixing valve and a few other parts from

- as spare parts - and very good service. I didn't want to take out my hotwater cylinder and replace it with their "pandora" heatbank - so I just replumbed the cylinder so that the original hotwater output goes to the heat exchanger - thats the only change needed as the CH, diverter valves and boiler side is left untouched. (I could post a photo of the outcome)

It works a treat - although some of the original british made tabs in the house had to be replaced with continental tabs that can handle the pressure - also the ballcocks in the cisterns needs upgrading.

It was great to chop off the multitude of pipes going into the loft as well as chuck out the noise shower pump - and bin the water tank on the loft making room for the loft conversion. Taking a tranquil shower in the morning is worth all the plumbing.

I was told though that we needed a 22 mm mains feed and I only have 15 mm - but being with thames water a high pressure on their water mains removes that problem

go for it - good luck

cheers lars

Please. the man is requesting serious information. He doesn't need a clown interjecting.

Many quick recovery cylinders are suitable.

So why have you?

.andy

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Yes. I have. Work a treat.

Draw this out.

Take a normal cylinder:

- Fit a Surrey flange on the draw-off tapping (at the top)

- Fit a Surrey flange on the cold feed tapping (at the bottom)

- Take the boiler flow to the port on the Surrey flange that is not protruding immersed in the water.

- Take the boiler return to the port on the Surrey flange that is protruding in the water.

- From the remaining port on the draw-off take a pipe to the plate heat exchanger.

- Insert an auto air vent into this pipe above the cylinder.

- Insert an anti vacuum valve also into this pipe above the cylinder, as near to the cylinder as possible.

- From the remaining port on the cold feed take a pipe to the other side of the plate heat exchanger.

- Take the cold mains into the plate heat excahnger and out of it to the taps. Try and keep it 22mm.

- in the cold main (on the cold side) fit a flow switch.

- After the plate heat exchanger fit a blending valve on the hot draw-off.

The now new heat bank will be filled via the heating system. No zone valves are needed. Ensure that the cylinder can vent and has no zone valve in the pipe.

If you already have tappings on the side of the cylinder use these for the boiler flow and return instead of the Surrey flanges.

Fit two cylinder thermostats on the side of the cylinder to eliminate boiler cycling. The flow and return to the cylinder can be the existing flow and return pipes feeding the internal indirect coil. Make sure you put in enough inhibitor.

What wisdom have you imparted? Err, err...... none at all.

Actually I did comment on the efficacy of GEA heat exchangers - having actually used one.....

.andy

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Which Surrey flange? You should clarify.

Which flange?

Isn't there a pump missing? How do you circulate the primary water from the cylinder through the heat exchanger?

Where does the vent connect? Presumably to the top of the cylinder, but now venting into the heating F/E tank? Provided that the existing vent is in place and there is a vent valve on top of the cylinder, an extra vent pipe shouldn't be needed..

If there are no zone valves or a diverter valve, how is the heatbank prevented from overheating and kept separate from the heating?

Connected how?

Are you suggesting an indirect cylinder i.e. heating water, heatbank water separate?

If so, the cylinder needs supply and vent arrangement from another small FE tank or equivalent. Otherwise the indirect coil is redundant.

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This is not a complete solution. There are numerous missing pieces to the description and a general lack of clarity.

While the idea may be interesting in principle, you have spoiled it by not describing it in enough detail to make it usable.

.andy

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Given that you are unable to document the proposed solution adequately enough to make it useful, the only conclusion that one can come to is to

.andy

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