Help for a newbie ..Thermal store or twin coil in attic?

[Patrick_newbie]

Hi All

Firstly I have been reading through the forum and found some useful stuff but I cant quite put all the info together due to lack of knowledge so anyone that can shed some light I would be most grateful...

My situation:

5 bed 1930's house , cavity wall insulated, attic insultated , Suspended wooden floor about to be insulated on ground floor, Valliant system boiler with cold water tank in loft , Hot water copper cylinder in first floor bathroom airing cupboard. And their is also a shower room in use a fair amount as well.

What I am trying to achieve :
Move the hot water cylinder out of the bathroom and into the attic...to free up much needed space...mobility issues
Effecient heating system boiler, I dont really have the cash to go crazy , so I need to do this in stages..like add the solar later if possible. and I also want it to be as simple as possible..keep the system boiler.

Solar Water Panel heating .

Manifold style plumbing to wall hung radiators. Manifold plumbing to sinks etc ..purely because no joints and individual isolatable runs of pipework.


My questions:
1, It seems possible with good load bearing support to put  a cylinder / thermal store in the attic, judging from other posts....is this a sensible thing to do? I realise the cold water tank needs to be raised above the cylinder. I do really need the space in the bathroom but if the heating doesnt work afterwards ..thats worse:)

2, What should I put in the attic? A thermal store / A vented twin coil cylinder ? ...Should I can I go for a horizontal cylinder arrangement?
Any advice greatly appreciated.

Patrick

[Brandon]

a thermal store would negate the need for the cold water tank.  UVC would be the other option.

[brackwell]

1) No reason why not but you do need to understand the structural problems. My tank i positioned over a T joint of the walls.

2) my tank in the loft suffers from air caused i believe by warming the cold water which then releases the entrapped air.  My feeder tank is above the height of the tank of course.   Anybody know what to do about this?
   One way is to use a thermal store but with higher temps required and only being able to use say 60% the effective volume of water,this is not my choice but does have the advantage of mains pressure showers etc.
  Horizontal cylinders are for people who do not have the space.

   Ken

[wookey]

A tank is the loft is a bad idea if you are trying to be efficient (and it does seem you are trying to do that). The loft is poutside the thermal envelope so it's a lot like putting your hot-water tank outside. Unless it's got 60cm insulation all the way round it'll be losing a lot of heat.

(here's a good post on the optimum amount of insulation for a hot water tank - it's cost-effective up to at least 30cm: http://www.iwilltry.org/b/projects/super-insulate-your-hot-water-tank/ )

Horizontal tanks don't stratify well (at all?) so you usually lose efficiency that way as well.

So, yes you can do this if you really can't find space somewhere inside the house (sure you can't steal a corner of a bedroom/cupboard or something instead? - I'm planing to use the end of the hall).

If you do do this then go absolutely crazy on the insulation: build a big hut over the tank and completely fill it with insulation, removing the insulation below it.

Thermal stores have the advantage of being more flexible than a cyclinder and they remove corrosion issues so you can use cheaper materials than copper. But I've never seen a horizontal thermal store. It's possible I guess. Newark cyclinders can make anything you ask for.

Whatever you do make sure you put in the solar coil for later.

[Iain]

Hi Patrick

I had a similar problem with the cylinder.
I ended up with a 180ltr unvented(ultrasteel) Has been an excellent answer to my problem. I addressed the insulation by boxing in the cylinder with solid insulation. If I were to do it again all I would change would be to increase the thickness of the insulation of the box for the cllinder. It is all a compromise but we needed the space and the cylinder in the loft works really well. It is just above the bathroom(above the bath/shower, so the hot water is there with less than 1/2 ltr run off.

http://www.navitron.org.uk/forum/index.php/topic,1572.0.html

http://www.navitron.org.uk/forum/index.php/topic,5923.msg60209.html#msg60209

Iain

[Patrick_newbie]

Thanks all for your responses so far. I appreciate it.

Unfortunatly there is nowhere else for this cylinder to go. the house layout is particularly inflexible at that location.

Wookey, your right, I am trying to be effecient as far as is practical. I just see the insulation as the bare minumum to do, not to waste energy and money.  

I have the space for a vertical tank in the attic so will forget the idea of a horizontal one.

As far as the thermal enevelope goes ..understood ...funny enough I was thinking along the same lines ...so thats a definite approach and bizarrly had got a qoute from Newar cylinders this morning for a solar twin coil cylinder.

Iain thank you ..just saw your post will read right now! ...When you say unvented ..is that a thermal store? or is that one of the unvented cylinders that has a lot of safety regulation around it ? ..Can you tell I am new at this !

Can I ask a dumb question...The way I understand it the thermal store is just a body of hot water kept ina cylinder at temperature with a heat exchanger inducing the heat from the thermal store into mains water via some blending valve for temp control ...hope thats somewhat right... whereas a twin coil cylinder stores the actual hot water you will use.

How can you do away with the cold water tank with a thermal store ? Is it because the mains is pressurising the Thermal store system rather than the head pressure from the tank ?

And what is more effecient ? and can I put in shower pumps with a thermal store ?..I read some where it said you get mains pressure showers with a thermal store ..how can I tell if that mains pressure  will be remotley like a power shower ?

Patrick
 

[Iain]

Hi Patrick

Iain thank you ..just saw your post will read right now! ...When you say unvented ..is that a thermal store? or is that one of the unvented cylinders that has a lot of safety regulation around it ? ..Can you tell I am new at this ! Smiley

It is an unvented cylinder and should be fitted by a suitably qualified (G3) person. A lot of people dislike them and keep saying they explode!( I haven't seen any reports of that happening yet though!!) (no doubt someone will post the link to the Mythbusters video, yet again) Have been fitted in Europe for years and have plenty of safety features. It suited my situation spot on. It is just another option to look at. It fitted in my loft with 2" to spare which just allowed the extra insulation.
Iain

[Patrick_newbie]

Thanks Iain , I will definatley take a look , at this stage all options are open . I cant see that if its proven technology that it is that dangerous , G3 qualified ..okay I am off to google that ...what about maintenance / planning / regs etc ..did you have any issues ? I will try to find out the pros and cons and formulate a decent question later :

Patrick

[Iain]

Hi Patrick
Maintenance once per year. Basically checking the safety reliefs are operating and working pressures are OK. Most info in the link below. Mine was the Copperform Ultrasteel, can't find it now so I think the names/companies have all changed. Identical to the link below

http://www.google.co.uk/url?sa=t&rct=j&q=g3%20checks%20on%20unvented%20ultrasteel&source=web&cd=1&sqi=2&ved=0CB0QFjAA&url=http%3A%2F%2Fwww.albionwaterheaters.com%2Fpdfs%2Ftechnical%2Fultrasteel.pdf&ei=UqwET6CZOsygOqbWuJgB&usg=AFQjCNHgjPuEj_TAvF3ORBaPo1WOuHx4DQ&cad=rja

Mine is the 180ltr twin coil
Iain

[JohnS]

Patrick

In the vast majority of cases hot water systems have two seperate water circuits.  (There are some called Fortic, or something similar, which might combine them.  I have never bothered to understand them but use the word vast to play homage to the pedants on the forum.)  Also, I am going to ignore combis.  I am assuming you know what they are and don't want one.  Excellent choice for all but small flats, IMHO.

First there is the water which goes through the boiler. It can either be pressurised or open.  If it is open, it has a small header tank.  It it is pressurised, it has an expansion vessel coloured red.  If it is open, air can get into the water and cause corrosion.  A good design minimises this.

Then there is the water that goes to the hot taps.  In a conventional system, it is stored in a cylinder.  It to can be either open and fed from a storage tank in the loft or at mains pressure fed directly from the mains.  Usually with a reducing valve to guard against very high pressure mains.  Sometimes does not work with low pressure mains. 

If fed directly from the mains, it is called an Unvented Cylinder (UVC) and must be installed by a G3 qualified person.  Gassafe (the new 'Corgi') list all qualified heating engineers and includes whether they are G3 certified or not.  The annual check only adds 10 or 15 minutes max to the annual boiler service.  It is not a deal breaker, whatever the luddites say.  The Rolls Royce of unvented cylinders are Sadia Megaflos.  Been around for donkey's years and totally reliable.  I have one.

Thermal stores work slightly differently.  The hot water that comes out of the taps is not stored.  Instead it is heated, as it is used, by the thermal store.  It either passes through a coil in the store or is heated by a heat exchanger through which hot water from the store is circulated.  Heat exchangers need a seperate/additional pump to for this circulation.  The consensus is that they are marginally more efficient at extracting heat from the store.

The store is heated by the boiler.  This can either be by a coil like a conventional cylinder or by directly pumping the water in the store through the boiler.  Advantages of the coil are that there is a small circuit of water passing through the boil which 'never' gets contaminated with anything else and can be pressurised.

If pumping all the water through the boiler, again it can be either pressurised or open with a header tank.  The latter is far more common.  If pressuised, a large expansion vessel is need.  A typical pressurised heating system is under 100 lites water volume.  A typical cylinder is 200-300 litres, so an expansion vessel 3 or 4 times bigger is needed.

The 'holy grail' of a through the boiler system is to lay a layer of hot water at the top of the cylinder as the water is pumped in and to take a layer of cold water out from the bottom.  The new layer is at the temperature you want to heat the water to.  As it gets replaced by a further layer, the boundary between hot and cold water moves down the cylinder until the hot water is being fed back into the boiler and the thermostats switch the boiler off.  Water goes through the boiler just once.  You need to balance the pump speed with the boiler power and to avoid to much turbulence and mxing of the layers.

With a store, there will be another pump to take water from the store, pump it round the rads and return it lower down the store.  The outlet from the store will be near the middle of the store to allow a big chunk of water above it to be used to heat the hot water.

The terms thermal store and heat bank can be used interchageably but might have once distinguished either using a coil or heat exchanger for the hot water or using a coil or pumping throught he boiler to heat the store.

Some store, especially Gledhills when badly installed and/or maintained have got the reputation of being sludge buckets filling up with sludge.  A well designed system, properly dosed with Fernox or equivalent should avoid this.

Hope this helps.

John

[desperate]

Hallo Patrick,

one problem you will almost certainly have if you put a vented hot water cylinder in the loft is air being drawn down the hot water pipes resulting in a "gluggy" flow of hot water at the taps. I would guess that you will build a raised platform for the cold water cistern(tank) and site the hot cylinder below this, yes? If so unless you have a really high roof in your loft, the height difference between the water level in the cistern and the point at which the hot feed to the taps tees off the open vent is only going to be a metre at the most. When you open the bath tap the level in the open vent will drop from its static level (the same as the level in the cistern) and as soon as it drops to the tee off point air will go down the feed pipe to the taps.

If you think about the cold feed from the cistern to the hot cylinder and the open vent pipe/ hot feed pipework, you have a huge great U tube with the feed pipe to the taps at the top of one arm, when you open a hot tap water will drop down in the open vent, this creates a pressure difference that gets the cold water flowing from the cistern down to the hot cylinder and through it and then on up to the open vent and feed pipework. The cold feed to the hot water cylinder is very nearly always a lot longer than the open vent to the tee off point and will take a while longer to get moving. This is why cylinders in lofts often cause problems with air entrapment in the hot water. One way to minimise the problem is to plumb the cold feed to the cylinder in 28mm or even 35mm pipe and use the biggest fittings you can.

Sorry to bang on a bit, but I get asked this quite a lot in my working life so I thunk it may be of some help.

Desperate

[Philip R]

If you want to go solar later on, use a twin coil hot water cylinder not a thermal store.

I say this because if you use a condensing boiler, specify a cylinder with a large heat exchange coil, look down inside, a minimum of 8 turns of 22mm coil or one of those fitted with the microbore tube nest like the albion supercyl. Then your condensing boiler will have its primary cct running at a closer temperature differential to the warming water within the cylinder and thus maximise efficiency.

Use a thermal store, then one needs to maintain high store temp to gobtain hot tap water. This operating regime forfeits many benefits of a condensing boiler, and thus consign yourself to reduced boiler efficiency.

Mounting hot tank floors away from the load requires long dead legs, large bodies of cold water, often wasted before hot water emerges from tap. Also more reheating of lost water required. Could use secondary circulation, more plumbing and insulation required.

Could you use much smaller cylinders on each floor?
PhilipR

[wookey]

philipR, the temp diff between a HWC and  thermal store should be no more than 4-5C for a given output temp. The important thing in condensing boilers is the water return temp. If heating the tank to 60C the water return temp should still be around 40C which is just fine for condensing. In favour of the thermal store is the option to use it as a buffer tank and thus make significant savings on reduced boiler cycling if the house is reasonably well-insulated.

So I'm not convinced that an HWC will use more energy than a thermal store. It is a complicated set of tradoffs, I agree.

Desp is right about the hot-water air-entrainment. Good reason to use a mains-pressure tank or a thermal store. Yes mains-pressure water is at least as good as a power-shower (and the water company pay for the pumping energy). You can check beforehand by fitting a pressure guage to find out what your mains pressure is.

I can't see any point worrying about the G3 stuff. Same as I don't worry much about having my boiler serviced. It's not hard - do it yourself and be sure it's done properly. It's only the British that even have unvented cyclinders - everywhere else in Europe has been using them for decades, and they don't bother with annual checks.

[micko]

I like a mains pressure cylinder, no safety problems unless it is plumbed in wrong as with any cylinder. As stated before your main concern should be that you loft can take it, 200kgs is quite a lot and it needs to be sitting on something strong, mine is above an internal wall.

If you go down this line you have to ensure you have enough cold water flow and pressure to feed it, this is the most important thing to find out.. If you do your hot water will come out of the shower or tap at the same rate as your cold does now.