On Wed, 19 May 2004 14:37:20 +0100, in uk.d-i-y "IMM" strung together this:
< snip tripe by IMM >
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.
Basically, if you understand the principles, it is simple.
Keep it heated exactly the same way (i.e. via the indirect coil and immersion). No need to fiddle there, really, if the cylinder is already adequetly warmed by the existing boiler. You do need to ensure you have a cylinder thermostat and you need to bump up the temperature a bit (i.e. 75C) and ensure boiler flow temperature is higher still (i.e. 82C).
Then you can use the hot water outlet at the top, pass it through the heat exchanger, then the pump and back into the old cold feed at the bottom. No need for extra flanges, etc.
The mains cold water goes through a flow switch and then through the other channel of the heat exchanger. The flow switch controls the pump directly. After this, the hot water (and cold mains feed) go through a thermostatic mixing valve to get fixed temperature water (i.e. 55-60C), which then goes into the old hot water pipework.
You can make the filling tank much smaller and bring it just above the cylinder and out of the loft, if you prefer. I'd recommend making it manual fill rather than a ball valve as this reduces the ability of the system to flood the house during a leak. You could still use a ballvalve, but put a manual lever valve just before to cut off the automatic operation when full.
Don't forget to take advantage of the fact that the cylinder can now contain corrosion inhibitor.
Don't bother to connect the boiler circuit directly to the cylinder rather than through the coil. There are distinct disadvantages, such as increased complexity of the conversion, not being allowed sealed pressurised operation (required for many modern boilers), and increased leakage/drainage/inhibitor requirements that aren't usually outweighed by the advantages (which are basically down to being able to install multiple heat sources, such as solar or multiple boilers/ranges).
Parts:
22mm TMV3 thermostatic mixing valve.
Pump.
Flow switch.
Plate exchanger (100kW min).
Sundry joints, pipework and electrical connections.
Have a look on the Potterton website at the manuals for the Powermax HE boiler. This is the most efficient domestic boiler in the SEDBUK list. The non-condensing version is marketed under the Range name, probably not for much longer though.
The Powermax boiler has an integral heat-store/water cylinder which contains primary heating water. The combi version has a flat-plate heat exchanger, and a second pump, instead of the more usual and less reliable diaphragm diverter valve. The mains water passes through a BPHE and is heated by primary water pumped from the heat-store by the second pump. The first (heating) pump stops whilst the second pump is running. A similar strategy should be feasible for your system.
You'd need a mini-expansion vessel on the DHWS and you'd need a much bigger expansion vessel to accomodate the expansion of the additional HTG primary water in the heat store.
SWEP make BPHEs, fairly cheap I recall, but I don't know if they do one to suit. Otherwise salvage some from the local combi graveyard/dump. Descale and find suitable fittings.
It's very irritating how every other previous post is pasted at the top of every new post on the group. Why don't people delete all previous stuff? Sorry if anyone else has mentioned any of the above, I can't be bothered to plough through all the previous posts.
On 19 May 2004 15:58:59 -0700, in uk.d-i-y snipped-for-privacy@hotmail.com (Aidan) strung together this:
It's also irritating how people don't put their replies in the right place, and cut all previous text from the reply. I haven't a clue whether you are meant to be replying to Christian or Rob, and which bit of which post you're meant to be replying to. In future, if you just snip the unrequired text from the post and reply in the correct place I'm sure we'll get along fine.
Not by my reading of it - 90.5/90.6%. The most efficient gas boiler at
91.3% is the Baxi Potterton Promax 15 HE which is a wall-hung balanced flue condensing boiler
formatting link
the disclaimer from the SEDBUK website:
"Boiler efficiency tests are subject to a degree of measurement uncertainty. Consequently small differences in the efficiency values calculated from them are not significant and should not be relied on when comparing boilers. Statistical analysis suggests that if two boilers have SEDBUK values 3 percentage points apart then there is 95% confidence that the boiler with the higher value is more efficient."
It's very irritating how every other previous post is pasted at the
The Potterton Powermax incorporates an unvented cylinder full of fresh water. The older Range (IMI) Powermax incorporates a thermal store. Two very different approaches.
I would not do this as the existing coil is most certainly not big enough to take all the boilers output.
This is madness. Have the same F&E tanks fill the cylinder and the CH and have an intermediate coil to heat the cylinder?
What complexity?
If you are havinbg an F&E tank, you may as well get a boioer that can operate as an open system. Many state-of-the-art boilers can do both sealed and open.
How can you tell? Even DPS's indirect products are based on standard indirect cylinders. How would you know if the existing system is rapid recovery or not? Even if not, then all it would mean is a longer recovery time, just as before. The recovery performance will be no worse.
I said nothing about merging the boiler primary circuit and the heat bank water. Indeed, I propose the opposite, having separate systems with no connection other than thermally through the indirect exchanger coil. Radiator circuits do work much better pressurised even if the boiler allows open vented. They are easier to fill, with fewer airlocks, no pumping over and are typically manual fill to avoid house wrecking incidents.
Well, the additional tappings required in the cylinder, basically. The method I have proposed requires no modification to the cylinder itself. No requirement for additional Essex flanges or replacement Surrey types. This makes the entire conversion much simpler.
As stated before, besides limiting boiler choice, open vented radiator primary circuits are a PITA.
With shared water, you might have 200L+ in your primary circuit, instead of
30L, depending on the size of your cylinder/radiators. This has repercussions when it comes to refilling, or if the system leaks. Obviously, you might fit isolation valves to mitigate the effect of a draindown by keeping the cylinder full. This doesn't solve all the problems, though, such as system leakage consequences and keeping compatible inhibitors.
You misunderstand. I listed multiple heat sources as the main advantage of combining the primary circuit and heat bank water. A bit like a 150L Dunsley Neutraliser. You can always mix and match by having a modern condensing boiler on an indirect coil, whilst pumping genuine heat bank water round a range or solar panels.
Yes, I stand corrected. The Promax is now top, the Powermax is relegated to No. 46. I think the Powermax used to be top when I last looked at the SEDBUK site, or did I misread Promax as Powermax? We may never care.
Still, it's a very efficient boiler and there are some relevant lessons to be learned from it's design; there's no point in re-inventing an arrangement that some smart person has already figured out.
I had been replying to the person who wanted to construct a heat-bank system. If I had bothered to plough through all the posts, the re-posted posts, the re-posted re-posted posts and the "click here to read the rest of this message (246 lines)", then I would have posted my comments in the most appropriate place. Sadly, I didn't.
You have to be careful if you have the incoming mains feed permanently immersed in the heat store, as you then have an unvented system where you need to handle the expansion of the water, albeit a somewhat smaller volume that a conventional unvented cylinder. If you look at the offerings on the market with internal heat exchangers, they all have some form of expansion vessel (internal or external) and check valves.
With an external heat exchange circuit, there is no need to account for expansion, as heat is only applied while there is flow in the circuit.
There are a number of manufacturers of brazed plate heat exchangers of this type, including Alfa Laval. (link for data sheet:)
The expansion vessels are mainly to prevent a clunk when turning off a tap quickly. Check valves are not mandatory. Expansion can be via the cold mains pipe; expanding backwards.
DPS were selling a 14 plate one for around £30-40, last time I dealt with them. It may have changed since then.
It is highly unlikely his cylinder will not even comply with Part L.
Best have it connected directly. It is simple. Many cylinder have a 3/4" shower takeoff on te side. This can be used for the flow and a Surrey flange for the cold feed. It is simple to do, by only extending pipe a few feet to top and bottom of the cylinder.
All you do is fit two Surrey flanges which are simple to do, and extend pipe a few foot up and down to them. Simple!!!!
You could clean out the now unused coil and use this as a pre-heat and used only when low flows are draw-off, like a basin. The pump and plate heat exchanger only come in when high flows are required. This is known a thermal store hybrid, prevent excessive pump operation.
You know little of heating to come out with that.
You answered your own reservations. Use isolation valves to drain down the parts of the system that require draining.
Actually it is the agreed convention of this group. I post to other groups as well and keep having to remember which group prefers which style. Top posting is actually prefered in some places.
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