Hi I have been reading the excellent threads concerning heat banks on here. I would like to move my HW tank into the roof space as part of the upgrade to a heat bank. However space is somewhat limited. Would configurations such as
Thanks for your speedy replies
More info. What DHW needs: showers, baths, etc? Heating? Other constraints? You intent to build your own heat bank?
OK - this is an idea - not based on practical experience.
Paralleling both cylinders sounds like a lot of extra pipework
What about putting the cylinders in series as far as the boiler goes?
So boiler hot feed enters near the top of the first cylinder, exits from the normal boiler return point of the first cylinder, then feeds into the entry point near the top of the second cylinder and finally returns to the boiler from the lower exit point from the second cylinder.
Hot water PHE is hooked to the first cylinder, and central heating circuit(s) to the second cylinder. That may reduce hot water depletion by space heating.
It might also be possible to configure valves so that an extra return pipe from the first cylinder goes back directly to the boiler - for summer use, when switched to "hw only".
Stats would be required on each cylinder, either able to call for heat in winter, and reconfigurable for summer so that only the 1st is active.
Is the above scheme workable?
Yep.
Points:
May as well keep them separate, one doing DHW, one CH (a CH buffer), with DHW priority. Hot water depletion by space heating can be prevented by a CH pump interlock - DHW priority. That is the CH does not extract heat from the cylinder while DHW is called and cylinder is below temperature. There again the rads are in themselves a thermal store and the heat in them can be usefully used to provide DHW. A good sized direct boiler will recover the cylinder quickly. The great thing about using a heat bank/thermal store is that a directly coupled boiler can be any size and will not cycle, with full flow through the heat exchanger at all times.
DHW needs are 1 bath + 2 showers, CH is for 4 bed house. I was thinking about leaving the CH directly fed from the boiler, as it will be difficult to retrofit the CH to run from the heat bank. Also want to enable a solar option in the future as have a sw facing roof.
Yes looking to make my own heat bank with the external heat exchanger as I'm worried about the all in one commercial solutions furring up in our hard water area.
Thanks all for the help
What sort of boiler? New boiler? Existing boiler?
The diagram is for the CH off the heat bank. The left hand side of the cylinder is what you need. As you are doing a DHW only heat bank, I would have a one 140/150 litre "direct" cylinder heated via 100kW plate heat exchanger. This isolates the boiler (which can be sealed) from the cylinder and will take all its output. The F&E tank will only heat the cyoidner in which its water always stays only in the cylinder - no sludge can accumulate. Using a Keston Qudos boiler CH is modulating and DHW priority is ramping the DHW temp to maximum temperaure for a quick cylidner re-heat. This means, that when the cylinders heat partially depletes and the stats switch in the boiler, the boiler and cylinder combine to give DHW, thus extending the cylinders size.
So, a:
- Qudos boiler,
- 150 litre cylinder
- two 100kW plate heat exchangers
- two pumps
- cylinder stat (the Quodos stat/sensor)
- blending valve
- flow switch
- Surrey flange (if a shower connection on cylinder not needed)
- Magnaclean filter for CH return.
- two check valves
- enough full bore isolating valves
- a 3-way "diverting" valve for the boiler (DHW or CH)
Over to you....
What sort of boiler? New boiler? Existing boiler?
The diagram is for the CH off the heat bank. The left hand side of the cylinder is what you need. As you are doing a DHW only heat bank, I would have a one 140/150 litre "direct" cylinder heated via 100kW plate heat exchanger. This isolates the boiler (which can be sealed) from the cylinder and will take all its output. The F&E tank will only heat the cyoidner in which its water always stays only in the cylinder - no sludge can accumulate. Using a Keston Qudos boiler CH is modulating and DHW priority is ramping the DHW temp to maximum temperaure for a quick cylidner re-heat. This means, that when the cylinders heat partially depletes and the stats switch in the boiler, the boiler and cylinder combine to give DHW, thus extending the cylinders size.
So, a:
- Qudos boiler,
- 150 litre cylinder
- two 100kW plate heat exchangers
- two pumps
- cylinder stat (the Quodos stat/sensor)
- DHW blending valve
- flow switch
- Surrey flange (if a shower connection on cylinder not needed)
- Magnaclean filter for CH return.
- two check valves
- enough full bore isolating valves
- a 3-way "diverting" valve for the boiler (DHW or CH)
- a blending valve (on the cylinder side of the boiler plate heat exchanger to ensure only full temp water enters the cylinder).
Over to you....
Hi boiler is existing (Vokera Mynute 28SE which is 28kW) Y connected sealed primary. I'm not sure I follow your thinking on using a direct cylinder with a PHE to isolate the boiler, why do this rather than just use an indirect cylinder?
I started looking at two tanks as most web sites say I need 200 to
250L tank size for the size of house (its been extended). Which I cannot fit into the existing space (which has a tank that is around 160L and seems to work fine - but we don't use the bath very often). Do you think I could get away with a single indirect tank of 160L with a fast coil and always have the boiler heat available?
An indirect cylinder would need a fast recovery coil to take all the boilers output. 28kW is a whack and few coils will take all that. These are not cheap. Then you would use two. Double expense. Using a plate heat exchanger, which is far more efficient than a coil, and will take all the boilers output, means you can combine the heat output of the boiler and the cylinder, which means you only need one direct cylinder of 150 litres. It is cheaper and far more efficient and you will never run out of hot water as when the cylinder is depleted you run off the boilers output - like a combi.
Do you intend to keep the existing cylinder? In a hard water area if it is oldish, it is best to get rid. If OK, you will get away with it using a plate heat X that puts the boilers heat right at the top of the cylinder where it is needed.
It will not be any more expensive having a direct cylinder, plate heat X and pump, than a fast recovery coil cylinder.
I would have a 3-way "diverter" valve, the boiler set to maximum for fast re-heat and a pipe stat, wired though the room stat circuit, on the CH flow pipe to set the rads temperature. So when DHW full temp and when CH onto the pipe stat. This boiler is not a condesning boiler and must be run at 80C anyhow.
Hi Thanks for your help, I have drawn it up to help me understand. Please could you let me know of any errors
One cause for concern is the max temp that the solar panels might achieve, (say if the system is unused for a few days in the summer) could you suggest how to protect from this.
Markt
PS Screwfix have a 140L indirect cylinder which is a 20 minute re-heat for =A3180 does this change the economics of using the PHE+Pump on a direct cylinder?
Sorry link did not work, try this one
buffers heat from the boiler be reversed. Thinking was to change the 3 port Y valve to something more complex (two single valves, with a complex control circuit) to allow heat from the thermal store through the HPE and into the CH. Boiler pump and PHE pump both turned on. Triggered by an Over temp stat on the heatbank. Its not failsafe - would this matter?
Markt
Have high limit temperature stats on the solar cylinder "and" DHW heat bank - I assume they are fitted as per drawing - set to 95C. When above 95C the DHW pump runs to act as a shunt pump mixing the water in the two cylinders. The DHW heating from the boiler is switched out when the shunt pump runs - over 95C in any of the cylinders.
The heat from the solar cylinder will naturally rise into the heat bank, although slowly as most heat will be rising via one pipe. Having water at
96C in the heat bank will do no harm as DHW is blended down.Using the heat bank as a heat dump for the solar cylinder should be fine in a UK climate. If both cylinders do get over 100C water will expand into the F&E tank. If this does occur (climate change) the fit a radiator (bathroom) off the heat bank and pump that to dissipate heat.
Is is only Part L. It will do 20 mins if 80C water is run through and at the correct flow through the coil. It is not quick recovery and will not take
28kW. Fine for a solar cylinder. The plate will ensure the full output of the boiler will go to the heat bank and the outputs of the heat bank and boiler will combine to give a larger DHW output and make the boiler cast as a combi (never run out of DHW) when the heat bank is depleted of heat.Have a zone valve on the return to the solar panel, as in winter heat from the solar cylinder will drop to the panel and you will be heating the sky.
will be no condensing in the boiler and only hot, not warm, water enters the heat bank. This makes fast recovery and ensure the boiler and heat bank combines outputs.
Have a larger expansion vessel on the solar side. 16 litres, may be cheaper to have two 8 litres.
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