Dunsley Neutralizer ????

[bell]

Hi, Does anyone know what's inside one of these?

It's a bit of kit to link up two boiler systems. My dad's doing a self build and he's going to need one but is curious as to how they work.

Thanks x

[IMM]

nothing. it is empty, just a neutral point.

He needs one? On a selfbuild he is better off using a thermal store/heat bank, which also acts as a neutral point and gives a hell of a lot more,like mains pressure hot water, than the Dunsley.

[EricP]

Google for it, there's quite a bit, including diagrams. Might help you.

[Rick Dipper]

There is NOTING inside them.

I had one, I was not overly impressed with it, in fact I have now taken it out.

Rick

[IMM]

Give me his scheme and I will suggest, if better of course, an alternative.

[Christian McArdle]

It is effectively a direct heat bank which is too small for useful storage. Basically just a can with lots of pipes coming out of it. Nothing magical about it at all, but just a simple elegant solution.

Any heat sources pump (or gravity feed) into the can. Any heat sinks pump (or gravity feed) from the can. Simple and effective. It enables several heat sinks or sources to be used simultaneously without each appliance interfering with the other's pumped or gravity circulation.

For a new system, you might want to consider a direct heatbank instead. This is the same thing, but with a huge tank, rather than a little can, allowing for useful storage, which reduces short cycling inefficiency. Then your solid fuel appliance and gas/oil boiler can both power radiators and even provide lashings of mains pressure hot water through a plate heat exchanger. You can also have a hybrid system with an additional indirect coil, which allows sealed pressurised operation on the oil/gas boiler.

You lose a little in efficiency from a condensing boiler, as the flow temperature has to be higher, but gain on eliminating short cycling and using otherwise wasted heat from a solid fuel appliance (or hydronic solar, or any other heat sources you install).

Christian.

[Christian McArdle]

What did you replace it with?

Christian.

[Rob Graham]

No point in describing it any further - it's all been said, apart from the fact that in the system I'm using it works spendidly. I've an oil fired boiler pumping into it and a log stove gravity feed into it. Trying to remember the output configuration without diving into a folder - the cylinder has to be gravity fed but is shut of with a fail safe valve when the CH pump is on. A bit of home grown electronics controls the system such that the oil burner is shut down if the log stove is hot.

Plumbing it in is an keen-amateur job - no self respecting plumber would take it on unless the customer had deeeeep pockets. In a confined space it looks very neat but plumbing wise a 'challenge'.

I'm assuming that of the two heat sources the OP has, one needs to be gravity run as I have. I would be interested to know how the heatbank arrangement can be configured for this; I'm in the market for a design for such a set-up as I need to overcome low pressure in the HW system and am not a fan of pumps. I've been following the various threads on the subject but have had difficulty understanding some of the piping diagrams that have been posted.

Having said all that I went to visit a friend the other day who lives in a stately pile where he has built a system of 2 domestic gas boilers working in some astonishing configuration involving homemade heat exchangers, etc; the pipework would do the boiler room of small steam ship a run for it's money.

Rob

Rob

[Rick Dipper]

I had mine configured with 2 boilers, gas & wood.

I replaced it with some simple electronice, when the wood fire is hot the gas boiler switches off, and all the zone valves open. When the wood fire is cold, the zone value closes it off.

So the two flows from the boliers are simply joined together, and the hot water feeds into the heating circuits. Only one bolier ever operates at a time.

I found problems with then Dunsley were :-

A pain in the butt to fit into a reasonably small space. A pain in the butt to fitt, if you got a leek, you had to take half the plumbing apart to get a spanner anywhere neer. Totally impossible to insulate

I am not a profesionall plumber, maybe I would have been happier if sombody else had done the thing, so I could not critisie my own work.

Rick

[Dave Liquorice]

What is the state of the zone valves without power? Is the gas boiler isolated when the wood fire is hot or does hot water circulate through it?

[Christian McArdle]

The problem is that in an electrical or zone valve failure, the system may explode. Are you sure that in the event of valve or electrical failure that:

(a) There is a direct unvalved vent path from both appliances to the outside. (b) There is a direct unvalved water feed path from the header tank to the appliances that doesn't share with the vent path. (c) For any solid fuel appliances, there is a direct unvalved flow path from flow to return to dump unwanted heat.

Christian.

[Christian McArdle]

The heatbank is just a huge Dunsley Neutraliser. It is plumbed in the same way. The only differences are additions.

(1) A pumped plate heat exchanger loop to provide mains pressure hot water. (2) An indirect coil to allow modern sealed pressurised boilers to be used. Gravity fed (or circulated) appliances go directly to the heatbank, not through the indirect coil. (3) An immersion heater (or 2) for electrical backup.

Christian.

[Rob Graham]

Thanks for that Christian - that makes it all nicely fall into place though I'm not sure whther I'm confused or not by the 'sealed pressurised boiler' bit. The oil burner I have is some 12 years old - is that modern - there is no vent from it.

Rob

[Christian McArdle]

Sounds like it, if there is really no vent. That can use the indirect coil. Is there a pressure gauge? Do you refill the boiler using a tap, manually referring to the pressure gauge, or is it filled through a little tank in the loft?

Christian.