Home made Heat Bank

I have read the Home made Heat Bank thread (and the faq on DIY Heat stores plus a few other threads) from start to finish with great interest.

As it wont let me post a reply to the group on the original thread, I'll reluctantly have to start a new thread.

I am in a similar situation needing more pressure for showers particularly, but for the DHW in general. I currently have a bog std vented primary feeding CH and indirect DHW tank via pump motorised 3 way valve. I'm happy enough with the CH - its the DHW that's the problem. I dislike the energy useage of a 3bar shower pump c 850watts for a Stuart Taylor pump I saw, so would like to make use of the pressure there for free in the water mains. I have a friend with a very nice but very expensive Pandora Heat Bank - there's absolutely no way I want to shell out that sort of money!!

On the whole, thanks due to a number of contributors I am reasonably clear on what is required. I have a specific queries before I take the plunge next week:

1] So, adding 2 Essex flanges gives 4 connections to the main body of the tank (coil connections now unconnected and treating the tank as a direct) Where should the flow and return to the boiler be connected and where should the flow and return to the PHE be located?

2] And related... is the positioning of the Essex flanges on the tank critical/is there a good spot ie a certain distance from the top/ bottom to locate them?

Now for the heat exchange circuit...

3] Are there any concrete recommendations for the capacity of the PHE? eg is 100kW regarded as a minimum for DHW at mains pressure ad flow? I see gea-ecobraze PHEs are recommended, so will probably go for one of these. Is there any heat output (kW) stats for the gea- ecobraze PHEs? ...are they not quoted as this would depend on the rate of primary flow.... mmmm...??

4] What rating does the pump need to be? I know the water needs to go round fast for the PHE to get enough throughput. But it's only shifting a tiny volume of water (if it's all juxtaposed to the tank), so presumably a "high geared" design is required - if there is such a thing - big impeller, but not hugely powerful motor?? Is a standard CH pump not overkill for this job? Basically I want to avoid using more electricity on the pumping than I have to, so want to get this "tuned" right.

5] I get a bit nervous (plumbing is fine and electrics yep thats fine too, but electronics - not especially my forte) with talk of triacs and making up the electrics for this from components. I understand why the flow switch cannot directly switch the pump. Are there any suitable relay circuits available off the shelf to operate a pump off a flow switch? If so any suggestions of make and model again would be really useful.

6] On the circuit diagram on

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is an MOV - what is that please? Also 2 refs to 100R?

7] There is a "TMV" displayed in
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looks like it's blending hot and cold water is it a thermostatic valve? If so are these mechanical or electronically controlled. If electronically controlled, what is required for the controller? Presumably this is required so the hot water is always the same temp regardless of flow rate (within reason!) I guess they must have to react very quickly unlike a radiator TRV for example.

8] Also referred to in

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an in-line 'Y' strainer. Presumably servicable to stop crud going into the PHE and clogging it up?

9] Finally on the subject of the CH, I gather to get heat bank temps for the DHW I'll prob have to turn the boiler up and therefore make the rads hotter. Apart from the issue of potentially burnt little fingers (what is the optimum/recomended temp for rads anyway?? Is there one??) this should just mean that the rooms heat up quicker and the TRVs shut down the flow sooner. This should mean the boiler works harder for a shorter period of time before its own thermostat shuts it off, which is better isn't it? Or perhaps that's not adequately taking into account the return temp potentially being too high for effective condensation? Isn't it a bit swings and roundabouts this one?

Cheers

Mike

Reply to
Mike Holmes
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there is an MOV - what is that please? Also 2 refs to 100R?

MOV = Metal Oxide Varistor - basically a spike suppressor. It has a high resistance at 240V, but the resistance then falls as the applied voltage rises. Its effect is to short out spikes of high voltage that you may typically get when switching inductive loads (which can generate big back voltages (or reverse EMF if you prefer).

100R simply means a 100 ohm resistor. 100K would be 100K ohm, 2K2 would be 2.2K or 2200 ohms. Its all to do with writing values in a way that means you don't need to use the decimal point which can get lost on spec sheets. Helps Cut down errors.

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It looks like it's blending hot and cold water is it a thermostatic

It is: TMV = Thermostatic Mixing Valve. See

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part no: 12163

Mechanical - wax capsule etc

Yup, see

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part number 7533

Is your boiler a condensing one?

With a condensing boiler, lower return temps give more efficiency. On a conventional boiler that is not true. (in fact lower return tempts might help promote condensing which is not a good thing on a conventional boiler where higher temps will prolong the life of the HE.

Reply to
John Rumm

I'm in a similar position to the OP, trying to get my head around the details of a heatbank design.

Mine will differ slightly in that it will be built from scratch and I really need a mains pressure CH circuit (difficult pipe routings), whilst sticking with the unpressurised boiler/tank circuit.

To do this, is it simply a case of duplicating the DHW/PHE circuit? (With an expansion vessel on the CH side) How should the pipework be split off for this duplicate circuit?

What would the control system look like? Would the boiler simply be controlled by a tank thermostat, so it's function in life is simply to maintain tank temp? Would the CH circuit have TRV's on rads every location except one main rad, and then a room thermostat to cut the pump(s) on that circuit?

Finally, this diagram

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't show an expansion vessel on the DHW circuit - does it need one, or does it rely on the fact that a tap must be open before any significant mains pressure water is heated?

Reply to
dom

Cold water (potable and under pressure) is presented at / into one side of a heat exchanger - When a 'hot' tap is opened water flows through the pipe and is observed by a flow-detector; this detection enables a pump which pumps water into the 'other' side of the heat exchanger (think, a twin-tube car radiator). (Now) Hot water at the tank's temperature is blended with cold water via a wax-cartridge thermostatic mixer valve to produce 'Hot' water at your pre-set temperature. Effectively. there's no 'Hot' water until you open a tap. The 'hot' water is off the 'cold' mains- only the energy required to bring incoming mains at (say) ten degrees is extracted from the tank to heat it up to (say) fifty-five degrees. The 'rest' of the energy remains available for use in the tank. [There's owt for nowt and you'll need to have your boiler replace the energy sometime.]

Reply to
Brian Sharrock

Thanks for all the specific info John.

Boiler is a Worcester Greenstar 24Ri, about a year old - so yes it's a good condensing boiler

Mike

Reply to
Mike Holmes

The easiest way to explain this is that if you had an expansion vessel (assuming you're just meanign a normal vented F&E tank) your house would flood horribly :-( The DHW is directly connected to the mains via the PHE. Open a hot tap or any other point in the circuit and you'll get mains pressure and flow.

HTH

Mike

Reply to
Mike Holmes

Now I think on a bit more, my mind ventures onto controls.

I seem to recall reading something about having 2 tank-stats on the tank in this kind of setup... is that correct. I'm thinking that would be ideal - one stat set at 80degC, one stat set at something much lower eg 45degC, to provide max and min temps for the store. The theory being that the boiler would fire up when the store got below

45deg and burn on full until 80deg then cut out. I'm assuming this would be more efficient than even a modern condensing boiler that can modulate down, as it would remove boiler cycling phenomenon altogether. The big question for me is, is this possible? And more to the point is it feasible for me with my modest electronics skills!

I'm thinking a simpler alternative might be to time how long it takes for the boiler to heat the tank to 80deg on an average day (ie average hot water useage and therefore initial tank temperature). Once I have this info I could just tune the timer clock for the DHW programmer (which I already have)

Mike

Reply to
Mike Holmes

I can only attempt to answer you by comparison with 'my' Pandora unit.

The heatbank accepts heated 'fluid' from the boiler which flows in at the top. The working fluid is pumped back down to the boiler controlled by a wax-cylinder mixing valve. This working fluid temperature is selected by the 'thermostat' mixing valve; the duration of the circulating pump is set by the 'timer'. The thermo mixing valve accepts a 'Hot' input from the top of the heatbank and a 'Colder' flow from the bottom of the heatbank. In other words, the fluid is circulated all the time the 'timer' is 'ON' and is maintained at the setting on the wax-cylinder mixing valve. This fluid is available for circulating through the CH system -where it will relinquish heat - when the fluid flows back into the heatbank then back to the boiler to regain heat energy. The boiler should 'switch off' when the 'demand heat' line is dis-abled .

The controls seem premised on marinating the HeatBanks working fluid at a constant temperature, and the boiler supplying heat into the working fluid only when necessary.

In practise, I find that switching the boiler on for thirty odd minutes is sufficient to provide all day hot water for two/three baths/showers and all the kitchen sink requirements. Worst case - no heat in the tank - the hot fluid , for DWW and CH usage, is taken off the top of the heat tank and will apply the energy from the boiler directly to the taps and radiators. It's only then that the 'heat' sinks down through the heatbank to the bottom - they call it stratification.

Reply to
Brian Sharrock

I wouldn't have thought that'd be a significant consideration in the big picture, since it'd only be running for some tens of minutes a day and the power that it uses would be dwarfed by the energy used to heat the water it's pumping. However if you want to go the DIY heat bank route ..

Oh and I think it's Stuart Turner, not Taylor.

I'd be inclined not to bother with the Essex flanges and just connect the boiler flow (after the 3-port valve) and return to the top and bottom connections of the HW cylinder, Teed with the connections to the heat exchanger and pump.

Mine was 50kW which runs cold at full flow into the bath. I haven't done calculations or measurements to check but I think this is because the heat exchanger can't cope at that flow rate, so 100kW would be better. I think that's what DPS use and they ought to know!

I just use a standard Grundfos (clone) 15-50.

If you want to avoid all electronics you can get a flow switch capable of driving the pump directly as a part from DPS. (You can buy a PHE from them too.)

Reply to
John Stumbles

Use a 100kW plate heat ex. Use a flow switch not electronics as in the Stumble Wiki sketch. Use the top and bottom ports of the cylinder - maybe using a Surrey flange. If buying a new cylinder then use a direct cylinder with a Maganclean filter on the return to the boiler from the rads - this eliminates sludge build up in the cylinder. For a totally sludge free system use a direct cylinder using a 100kW plate heat ex to heat the cylinder - these work out cheaper than a coil and far, far more efficient in re-heat than a coil and return a low temp for condensing. The new Glow Worm stored water combis use a plate to heat the cylinder rather than an internal coil as they re-heat far quicker and give lower return temperatures for condensing. There will also be a higher cylinder water capacity without the coil.

Reply to
Doctor Drivel

All you need is a cheap £5 relay from Maplin. Only electrical. Look at DPS's web site they give the wiring diagram. The larger the cylinder the less storage temperature. You may get away with 70 to 75C. Set the bottom stat to say 80C and top to say 50 to 60C. The bigger the boiler, the faster the re-heat, and the lower the storage temperature.

You may have to live with it and set to suit. Some have winter and summer settings - lower storage temps in the summer.

Reply to
Doctor Drivel

You mean pressurised CH circuit?

Use a plate Heat Exchanger and pump to heat the low pressure direct cylinder. That is a DHW plate and a plate to heat the cylinder.

Have the CH off the heat bank, have TRVs on all rads and use a Grunfoss Alpha pump or the Wilo equiv in S/fix.

The boiler then only maintains the cylinder temperature - a simple task for the boiler.

Do you want to heat the CH from the heat bank cylinder too? Best to and use a Magnaclean filter on the CH rads return to the cylinder.

Reply to
Doctor Drivel

Sorry to be thick, but I don't follow your answer.

Yes, I wan't pressurised CH. So boiler and cylinder are directly connected to each other (and nothing else) and run at low pressure, but CH is seperated from the cylinder by a heat exchanger and is pressurised by a filling-loop?

Is the basic setup as follows?:

Direct connection between boiler and cylinder (unpressurised) with circulation pump. Cylinder to heat-exchanger number 1 and heat-exchanger to CH (pressurised on CH side) (pumps on both sides of PHE). Cylinder to heat-exchanger number 2 and heat-exchanger to DHW (pump on cylinder side of PHE)

Or did you mean a heat exchanger between boiler and cylinder?

As far as the control system goes, I follow the explaination of high and low tank thermostats.

Does the rest of the system go as follows?:

The time clock controls the boiler and pump between boiler and cylinder. (Does this pump run continuously when timer says "on", or only when boiler is firing plus a bit of overun?). The switch on the time clock for heating&hotwater/hotwater only controls whether pump(s) in CH circuit are also active. (Do these run continuously when timer says "on"?) TRV's on every rad, no room thermostat, and presumably a bypass on the circuit somewhere? No motorised valves anywhere.

Apologies if my questions ask again, what has already been explained.

Reply to
dom

Bzzz. No. They cannot be "directly" connect as one high and one low pressure. CH at 1 bar, cylidner at 0 1 bar.

By a heat exchnager? So not "directly" connected. Use a plate heat exchanger as the exchanger and pump to heat the cylinder.

I'll explain below.

Yep.

  1. A pressurised CH system using a 3-way "diverter" valve, not a "mid-position" valve.
  2. Use a direct cylinder, with an F&E tank top up.
  3. To heat the cylinder have a plate heat exchanger (pref 100kW) and a normal CH pump, pumping water from the cylinder into the plate. When calling for DHW the normal boiler pump is on, as is the plate pump. The heat transfer is exceptionally high (the best you can get without being direct), giving low return temps for condensing.
  4. Have a 100kW plate for the DHW and normal CH pump too, as per normal heat banks with a non-return valve after the pump and activated by a flow switch.
  5. Have two cylinder stats to prevent boiler cycling.

Then a low pressure cylinder and a high pressure CH circuit with low return temps. This is heating the rads directly from the boiler. You can have the CH off the cylinder too. Best to do this but a larger cylinder is needed. Best a direct one again and heat via a plate. Got it?

Reply to
Doctor Drivel

Farnell will supply the flow switch

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Farnell number:

1006771 22mm compression joints.

Flow Switch, makers site: The FS06

Reply to
Doctor Drivel

Well there's a bit more to it. I'll be running 2 showers, so will need a multi-installation pump and I also have a 1800x800 bath which takes years to fill on the std DHW and I even get bored waiting for the kitchen sink to fill sometimes - seems there would be many benefits to having a higher pressure DHW system. I can't afford a Pandora or similar BUT I can build a DIY Heat Bank system for prob about the same money as a pump, which will only benefit the showers in the house.

Yep, you're right. I shall have to fire my secretary!! ;-)

I read in another thread somewhere that if you set it up like this you'd have one of 2 situations depending how it was set up exactly.

1] If the boiler primary inlet onto the tank was effectively the PHE circuit outlet, then if boiler was heating the bank and there was demand for DHW at the same time (hot tap on), then the tank itself would be effectively out of the loop, the boiler primary flow effectively preferentially going through the PHE/pump arm of the circuit, fllow being restored through the tank once the DHW demand (tap off) had passed. 2] If the inlets and outlets to the tank for the boiler primary and the PHE circuits were tee'd together, then they'd be in opposition and cause turbulence at the tee both trying to force water against the other at the common inlet and water being forced into the tank.

Which is the best scenario?? Neither seems ideal. What of the dynamics inside the tank in the latter?

How much power does this pump use? Isn't it overkill to have a CH pump driving such a small circuit?

Thanks

Reply to
Mike Holmes

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