water cylinder question is this feasible

[stillrandom]

Hi,

I have an oil fired aga which provides all the hot water in our house, we also have an old oil fired boiler which provides only the central heating via a large bore single pipe system.

All very old stuff and in need of replacement.

I want to start with the central heating so I'm intending to put UFH upstairs only.

Rather than feed the UFH directly from the boiler I want to feed it from a new hot water cylinder.

The idea being that the aga would be the primary heating coil in the cylinder with a secondary coil which would call the boiler under certain circumstances, as a third heat source there should be immersion heaters to increase water temperature overnight using economy 7.

Is this feasible from a hot water cylinder and if so does anyone know a manufacturer that can provide one?


Cheers

Andy

 

[Softus]

I have an oil fired aga which provides all the hot water in our house, we also have an old oil fired boiler which provides only the central heating via a large bore single pipe system.

All very old stuff and in need of replacement.

What are the existing problems that you think a new system will solve?

I want to start with the central heating so I'm intending to put UFH upstairs only.

Rather than feed the UFH directly from the boiler I want to feed it from a new hot water cylinder.

In that case you need a heat store. You also need a blending valve and manifold for the u/f heating.

The idea being that the aga would be the primary heating coil in the cylinder with a secondary coil which would call the boiler under certain circumstances

Don't understand your banter there. You want two heat sources to provide heat to the heat store? Why?

as a third heat source there should be immersion heaters to increase water temperature overnight using economy 7.

That's a feasible optional extra.

Is this feasible from a hot water cylinder and if so does anyone know a manufacturer that can provide one?

Pretty much all of them I would expect. Take your pick and provide a drawing for them to quote against.

 

[BigBurner]

You need a thermal store. This is ideal for what you are doing. See:
http://www.heatweb.com for explanation.

Many makers make them, not just DPS. Range, Albion. Copperform, Newark, McDonald Engineering, etc.

Many will make one to suit.

 

[Softus]

You need a thermal store. This is ideal for what you are doing.

But why is he doing it?

See: http://www.heatweb.com for explanation.

FFS Water Systems, won't you ever stop peddling that site?

 

[stillrandom]

Hi,

Thanks all for the responses.

As to why I'm doing it, the oil fired boiler runs just the large bore single pipe system.
The end of this system's useful life has come and gone, to replace the boiler I have also to replace the central heating, so rather than just get another costly to buy and costly to run oil fired boiler running inefficient radiators I want to increase my options.
In my opinion (and please educate me here) by putting in UFH in the upstairs of the house (too expensive to do that downstairs at the moment) and running it through the hot water tank/heat store I take the boiler out of the equation. So that a later date I can either replace the aga with a more flexible range cooker alternative or put in ground source heating.

By having more than one heat source for the cylinder I can ensure that there is always hot water, the aga is gravity fed and whilst it currently provides all our hot water requirements it would be useful to have an "on demand" heat source for occasions when the aga can't cope.

I can't afford to do everything at once so UFH and new tank/heat bank this year, new range next year and then decide if I need any other heat sources after that.

I have the option to put solar in to provide hot water during the summer if this was an option I could incorporate into the cylinder.

 

[Agile]

I dont understand why you particularly want UFH upstairs or at all.

I hope you know that it has a long time constant and you have to predict your requirements an hour or two beforehand.

Perhaps your circumstances are very stable and you always do the same thing at the same time every day. I choose what and when I do things totally unpredictably.

Tony

 

[stillrandom]

Hi Tony,

I want UFH for a number of reasons,
a) you need less real heat to acheive a comfortable environment (eg 17deg at floor level rather than 20 deg from rads)
b) I have to disrupt the house either to replace a single pipe system with a dual pipe system and new rads or with UFH given the disruption I would rather have the flexibility of UFH
c) with the new thermostats available you can "call" the UFH based on exterior temperatures to ensure optimum temp at the correct time
d) by zoning each room we can ensure it only heats up when we want it to, and we have regular heat requirements in specific rooms so this is essential
e) UFH heating at foot level is healthier than convection heating and as I work from home this is a major benefit for me.

Cheers

Andy

 

[stillrandom]

I have spoken to advanced appliances and a very helpful man there suggested a 210 litre thermal store with a heat exchanger for the UFH. He has suggested direct connection for the Aga and a coil for the boiler.

I have read a number of the discussions about the various merits of these over other systems and can see that some strongly held opinions have been expressed on both sides.

But given my situation of an Aga which is not being replaced in the short term and an existing old oil fired boiler which is categorically not being replaced by any type of oil fired boiler, will this technology provide me with UFH and hot water for 1 bath / 2 showers /etc and if so what are the potential pit falls, will for instance putting in a water softener (something I'm going to do anyway because we have very hard water) remove the possibility of limescale build up in the hot water coil and boiler coil.

 

[Softus]

I have spoken to advanced appliances and a very helpful man there suggested a 210 litre thermal store with a heat exchanger for the UFH. He has suggested direct connection for the Aga and a coil for the boiler.

That's a plausible configuration.

I have read a number of the discussions about the various merits of these over other systems and can see that some strongly held opinions have been expressed on both sides.

Unfortunately, the 'sides' were formed on a personal basis, not a technical one, because one particular member (who now posts under a different user name and who appears now to be heavily sedated) made personal and idiotic comments aimed at anyone who didn't agree with him. In fact, even at the people who did.

Anyway, if you're intending to have dual heat sources into one cylinder then your only other practical choice is two coils, and it sounds like you'll be already having a second one to sink the solar-produced heat.

But given my situation of an Aga which is not being replaced in the short term and an existing old oil fired boiler which is categorically not being replaced by any type of oil fired boiler, will this technology provide me with UFH and hot water for 1 bath / 2 showers /etc

It would be worth working out the room sizes, and the heat losses, and the power requirements, rather than having a stab in the dark. The u/f manufacturer should be able to tell you the dissipation per unit area or per unit length of pipe.

and if so what are the potential pit falls

The biggest two are:

1. Insufficient insulation underneath the u/f pipework.
You might struggle with this one, so some heat will be lost downwards.

2. Wrong water temperature through the u/f zone(s).
You need to blend the water from the heat source with what's already circulating in order to keep the temperature down. There are now abundant kits on the market that include the correct electronics, valves, and manifold.

will for instance putting in a water softener (something I'm going to do anyway because we have very hard water) remove the possibility of limescale build up in the hot water coil and boiler coil.

No, because that water is in a closed circuit (or two, or three).

However, if you go with the plate heat exchanger to take the heat from the heat store then the secondary side will scale up very nicely.

IMHO the replacement cost/effort of a heat exchanger doesn't alone justify the investment cost, and the running costs, and the maintenance and servicing costs, of a water softener. (If you put good quality gate valves to isolate the HEX on the primary side then a swap would take 10 minutes, if you yawned a lot while you were doing it.)

If the other benefits of a softener are important to you, then you might be able to justify one.

 

[stillrandom]

Hi Softus,

Advanced Appliances suggested (At the moment) that there is one coil for the boiler, one coil for the hot water and the aga is heating directly into the store, I haven't confused them with adding in a solar coil yet.

The UFH requirement has been sized at 5.3 KW and would have a water volume of just under 40 litres, when it's installed we're going to fill the cavity below with insulation.

The current spec I've had from the UFH (Wavin) allows for their mixing block.

The softener would be nice to reduce the limescale all over the glass and shower walls so I'm going to be doing that anyway, but the area of concern I had with the thermal store was the talk of sludge and coils furring up, the aga gets the water temperature up high so is this going to present any problems like that?

 

[Softus]

Advanced Appliances suggested (At the moment) that there is one coil for the boiler, one coil for the hot water and the aga is heating directly into the store, I haven't confused them with adding in a solar coil yet.

I predict that confusion, rather than lack of it, will result from keeping it a secret.

The UFH requirement has been sized at 5.3 KW and would have a water volume of just under 40 litres, when it's installed we're going to fill the cavity below with insulation.

OK. Does that cover the whole of the upstairs zone(s)?

The current spec I've had from the UFH (Wavin) allows for their mixing block.

That's good to hear.

The softener would be nice to reduce the limescale all over the glass and shower walls so I'm going to be doing that anyway, but the area of concern I had with the thermal store was the talk of sludge and coils furring up

A water softener won't stop the tendency for the system to corrode. In fact, the salt content will increase it. By all means feed softened water through the secondary coil, or secondary side of a heat exchanger, but don't fill the heating system with it. For the latter use a chemical dose of proprietary corrosion inhibitor. Two examples of well-known brands are Fernox and Sentinel.

the aga gets the water temperature up high so is this going to present any problems like that?

Yes - if you heat hard water to above 65°C then it will tend to deposit scale on the hot surfaces.

 

[stillrandom]

Hi Softus,

Well I think that covers it, (the UFH is sized for the whole of the upstairs), I'll talk to AA about what my options are for adding in solar, and then it's just a question of finding a plumber happy to plumb it all in.

If anybody has any other information that they think I should take into consideration then please feel free to voice it.

Regards

Andy

 

[RigidRaider]

Yes - how old is the Aga? Heating water with an Aga is dreadfully inefficient and the Aga boilers don't last forever. As the cost of oil increases (I heard $250 a barrel by 2009 on BBC R4 just now) that Aga hot water is going to become more and more expensive. Are you sure the Aga boiler isn't already leaking? Get the engineer to check it at your next summer service, a small leak will not show up but the insides of the Aga cabinet will be rusting. Simply removing the black top cover, the fibreglass insulation and a couple of buckets of the vermiculite stuffing will soon tell you; this is not a difficult job, the hardest part is unscrewing the four chromed flat bolts then when replacing the top, lining the long studs up with the holes.

 

[Softus]

Blimey!

It's The Aga Can't.