Gravity flow circuit sapping heat from Cylinder?

Raiser

Hi Folks,

Have a Stanley Erin Boiler model with a Gravity flow and all seems to be working well - I did howerver notice that its flow/return circuit is constantly hot weeks after the Stove has last been in use and it seems apparent that the system is working in reverse and now sapping heat from Cylinder?

Its a triple coil cylinder and heated by solar means as of now (ie. summer) and also condensing boiler otherwise. I have noticed that its losing a good bit of water heat overnight and so on.

I hate the idea of getting the water temp up to 65 degrees or whatever and then having some of this heat constantly dissapate into my hotpress, attic, walls and floors 24 hours a day 7 days a week.

I have lagged all the 1" copper myself to minimise loss - Whats the best way to lag the brass joints etc? Something like an insulating wrap or tape would seem to be the way to go.

Plumber tells me that this circuit cannot be tampered with but surely there is a simple solution to a simple detail such as this?

Any help or advice appreciated

kscobie

i have seen an 1" flap type non return valve fitted on the return pipe after the cylinder, but this is against the building regs.

Raiser

Thanks for that kscobie - I'd be interested in hearing opinions on firing a non return valve into this particular system - pros and cons and whether there is a good solid reason not in terms or performance/safety or whatever

- As is its 1" copper with a saftey valve fitted near stove side (piped outside into dead space behind & below a path) so would be curious as to whether there is a crafty solution that would work here and let my cylinder retain its heat....

yoshytoshy

Raiser ,don't use a non return valve. The flap type can stick closed if there is any dirt.
I had to fix this problem for someone before ,basically the cylinder was on the same floor as the back boiler and the return was chased into the floor across to the cylinder. Managed to sort it out ,without a non return valve.

heinbloed

The installation of a non-return valve is a 'must' in ST systems, the cold ST panel would use-up all stored thermal energy from the storage cylinder otherwise. Unless the cylinder is stored higher than the collector.

If this effect (the trade calls it "thermo-syphoning") starts the hot water rises in the system and the cold water falls. A circulation starts to begin and will only end when all points of the system have reached the same temperature. Are cooled down.

As you have described the situation (post a drawing, some pictures) the installer isn't worth his money.

Another point could be a circulation pump set on overrun, working 24h/day.

Otherwise it's surely thermo-syphoning.

Raiser

heinbloed you're on the money.....As far as I understand it, the situation is that that system will run in reverse until the built up heat in my cylinder is radiated wastefully into my attic and odd dark places and only cease once I'm having cold showers

Interestingly enough you also mention a circulating pump on permanently which wasn't the case at all previously...... until today when the Sparks followed the Plumber and fitted a pipe stat and must have wired it ar$eways as the pump now runs permanently regardless of where the thermo dial is set.

- Finally I did open MS Paint to sketch up the plumbing of this but gave up as it looked like crap - and anyhow its totally standard stuff as far as I am aware - 1 inch copper to attic,over 12-15 metres or so,drops to cylinder and return is concreted into floors.

I think I just need to add in a non-return correctly somewhere in the mix - But where?

heinbloed

The non-return valve is usually fitted between thermal source and thermal 'waster'.

So if the warm water thermosyphons from the storage cylinder up to the ST collector and cools down there and consequently returns to the storage cylinder the 'thermal emptying' of the storage tank has to be stopped at the leak: at the hottest point, at the pipe between the hot thermal storage and the cold ST collector. The nearer to the tank the better.
And this is done at point of the highest difference of temperature: the top of the cylinder.

There are two types of non-return valves:

The first type is the bog standard type, a valve which will be activated only if the pump kicks in. This is the type of non-return valve which the poster Yoshytoshy probably had in mind when being afraid to recommend this for a ST installation.
And then there is the gravity non-return valve.

The first one, the non-return valve used for normal pumped,central heating systems can be used in principle for both issues: ST and central heating. But it depends on the parameters, so I extend the excursion :

For ST installations on their own (where the thermal storage tank is directly connected to the solar collector) the solar gravity valve is rcommended - in standard household situations. High temperature installations like ST industrial installations are a different issue. High rise and extra wide-pipe diameter installations are a different issue as well.

But when we look at the standard ST storage situation we would opt for a standard ST gravity valve. This gravity valve has nearly no resistance to the flow once the pump is turned on.

But a normal (closed looped central heating) non-return valve would 'consume' flow energy, the pump would have to work harder to transport the same amount of water since this 'normal' valve would put a resistane into the plumbing system, it works - even when open - like a break to the volume transported (liter/minute), it would reduce the flow. No problem for a CH circulation pump, it has enough power to overcome this obstacle.

Not so the smaller A-rated, sophysticated, intelligent, (and so on) solar pump ...

The ST gravity valve ads less resistance to the flow volume of the circulated water compared to a CH non-return valve.
It has to be of a different material quality as well:the high-temperature type since the temperature and pressure in ST systems can get much higher than in normal domestic central heating systems. And the glycol can be corrosive, decay certain materials used normally in CH systems.

I summarise:

A ST suitable gravity valve (temperature resistant AND glycol resistant) has to be installed between the hottest and coldest point (DeltaT Kelvin).

Many plumbing shops have these ST gravity valves ready available. Contact the ST specialised traders if you can't find one.



Now, we haven't analysed the complexicity of your thermal drainage, the thermosyphon effect.
There might be other thermal leaks.
The connection between the thermal storage tank and the ST collector we will treat with the gravity valve.
But there might be also a thermosyphon effect between the other system's components, for example between the hopper or feeder tank (in case your plumbing system is a non-pressurised, open system!) and the thermal storage, be it the tank or the pipes running in the rooms......

Here we can again choose between gravity valve and normal, pressure operated valve. Depending on the difference of height between the plumbing system and the hopper and feeder tank ( the 'head') we can opt for a cheap gravity valve (a non-solar type) and a standard central heating pressure operated valve.....

Install the gravity valve between storage tank and solar collector first.

This will certainly stop the very most of thermal losses.There will still be some thermal losses because of thermal cunductivity of the materials but these can't be avoided. Unless the pipes are separated.

About the DeltaT Kelvin: what you observe now in summertime will get worse in winter time. The higher the temperature difference is the faster the water will move, thermosyphoning.
Think about a hot air ballon: the more it is heated up the faster it rises. The colder the air is the less fuel is needed to make it float.

So check your pipes now and then, esp. in winter time. If the gravity valve doesn't help the temperature difference might be to high. But in a standard household situation (two storeys, flat collectors and about 10 meters beween tank and collector) it should do the trick. That is what these solar gravity valves are designed for.

Read the instruction label anyhow, the shop asistant might be able to explain the limits and details of the particular make.

About the thermal losses via the hopper and feeder tank: this is not realy my speciality, but the same principles aply.
If possible avoid the unpressurised plumbing system, avoid tanks and pipes running unnecessarily in cold rooms. Try to keep the piping lengths short, the whole system plain and simple.

Make drawings in a sketch book. No matter how bad they seem to look , it's your second memory. Note materials, makes of valves and sensors and the like. It will save a lot of climbing and dismanteling in case future problems arise. Keep the leafelets which come with materials as reference.

And ask your plumber/installer if he had put the non-return valves in or not. He might have done so and they failed because of sludging-up, being in the wrong place or chosen for the wrong purpose.

Raiser are you having problems with heat loss via your solar installation? Or is it simply your circuit between the cylinder and boiler?

heinbloed

http://shop.solardirect.com/product_info.php?products_id=340

(US product, check thread sizes and temperature stability!)





For vertical installations (<220C):

http://asotec.de/shop/Solartechnik/Regler-Pumpstationen-Ventile/Muffenrueckschlagventil-3-4IG-aufstellbare-metall-Schwkbr-::3924.html

For horizontal installations (<220C):

http://asotec.de/shop/Solartechnik/Regler-Pumpstationen-Ventile/Muffenrueckschlagventil-SOLAR-1IG-nicht-aufstellbar::3923.html

Raiser

*Edit - Started this reply ages ago and got called away - Thanks again Folks!*

Heinbloed thanks for all of that, I really appreciate the time, effort and thoroughness - Need to reread it and digest the finer points before commenting - Lots of it is new to me etc.

gary71 wrote: »

Raiser are you having problems with heat loss via your solar installation? Or is it simply your circuit between the cylinder and boiler?

Good question - Am unsure now, but certainly I first posted specifically on the circuit between the Stove Boiler and Hot water cylinder - That was because I noticed the heat in Hotpress and that the 1" copper was very hot days after the Stove had died (was only lit for a test run!)

Starting to wonder if heat is being 'syphoned' off in all directions now!!!

- Although to keep the hysteria levels in check, the heat retention in the cylinder was reasonable prior to the Stove flow/return circuit going into perpetual motion...

As a related point - if you have a triple coil cylinder there is some amount of pipework and blanks coming off it from all angles, providing a means for heat to slowly escape, you can then read how how much exactly via the Solar LCD temp display the next morning or whatever.

- Whats a proper/recommended way of DIY insulating it? Would like to apply foam/lagging/whatever to every bit of metal I can feel heat coming of this weekend......

heinbloed

Contact the insulation material suppliers on how to use their materials at bends, joints and junctions.

Some pictures here from a German DIY chain:

http://www.hornbach.de/cms/de/de/bauen/projekte_bauen/energiesparenspecial/projekte_9/heiztechnik_1/projektanleitung_15/projektanleitung_16.html

After insulating with insulants the joinst must be glued with sticky tape to avoid movement. Usually an aluminia-vapour covered plastic tape. Looks like aluminia but is plastic with a very thin aluminia cover.
Available where they sell aluminia backed mineral wool.
Stay away from the pure Aluminia foil tape, it sticks well in the beginning but loses its stickyness soon.

See for such a failure example the ceiling in the IKEA car park (Dublin) where the insulation bats (Fooltherm from Queenspan) come down.
There the aluminia tape doesn't hold the boards anymore after only 3 years, moisture has taken it's toll on the glue. Total failure, the foam boards shrunken, warped and the tape falling off.
Moisture got behind the insulation, condensed at the coldest points, the alu-tape. And by-by to ammortisation of the insulation works, to the entire energy concept.....

So use the flexible plastic tape for taping the joints, it will go with the movement of the insulant. And check if this tape is suitable for damp or wet conditions.

If insulating the standard central heating pipes a foam based insulant might be ok (for example Armaflex). But with the solar pipes use a mineral fibre material (for example Isover).
The foam is not suitable for high temperatures or damp conditions.

Outside, over the mineral insulant at the ST collector, a protective coverage has to be installed, usually UV stabilised PVC pipes and bends.

Again only a German link from me, sorry:

http://www.hood.de/auction/36960758/rohrisolierung-daemmung-pvc-bogen-15-20.htm

Ask at the plumbing shop for detailed material and workmanship recommendations. In writing, from the manufacturer, bad practice is absolute normal here in Ireland when looking at ST insulation jobs on our roofs. The shop steward might not know any better than what his clients fiddle every day. So insist on written instructions from the manufacturer of the insulants.

Raiser

Hmmm - heinbloed this thermo syphoning is happening on gravity circuit to Stove only - What would you rec. specifically for that?

- I had assumed that the pumping station for the Solar system would control backflow on that circuit?

heinbloed

Raiser asks:

...this thermo syphoning is happening on gravity circuit to Stove only - What would you rec. specifically for that?

There seems to be a fault with plumbing installation in this case. Or a wrong concept.
A boiler ( a heating device preparing circulated hot water is called a boiler according to EN standards!) transporting thermal energy via the plumbing system is doing it's job.
It is doing what it is designed to do.

So I'm not sure if I understand the question, Raiser.
Post some drawings, pictures with dimensions [height differences ('heads'), temperatures meassured] - if possible.

And ask the installer anyway, he/she should know how to run the system.

CBYR1983

heinbloed wrote: »

Contact the insulation material suppliers on how to use their materials at bends, joints and junctions.

Some pictures here from a German DIY chain:

http://www.hornbach.de/cms/de/de/bauen/projekte_bauen/energiesparenspecial/projekte_9/heiztechnik_1/projektanleitung_15/projektanleitung_16.html

After insulating with insulants the joinst must be glued with sticky tape to avoid movement. Usually an aluminia-vapour covered plastic tape. Looks like aluminia but is plastic with a very thin aluminia cover.
Available where they sell aluminia backed mineral wool.
Stay away from the pure Aluminia foil tape, it sticks well in the beginning but loses its stickyness soon.

See for such a failure example the ceiling in the IKEA car park (Dublin) where the insulation bats (Fooltherm from Queenspan) come down.
There the aluminia tape doesn't hold the boards anymore after only 3 years, moisture has taken it's toll on the glue. Total failure, the foam boards shrunken, warped and the tape falling off.
Moisture got behind the insulation, condensed at the coldest points, the alu-tape. And by-by to ammortisation of the insulation works, to the entire energy concept.....

So use the flexible plastic tape for taping the joints, it will go with the movement of the insulant. And check if this tape is suitable for damp or wet conditions.

If insulating the standard central heating pipes a foam based insulant might be ok (for example Armaflex). But with the solar pipes use a mineral fibre material (for example Isover).
The foam is not suitable for high temperatures or damp conditions.

Outside, over the mineral insulant at the ST collector, a protective coverage has to be installed, usually UV stabilised PVC pipes and bends.

Again only a German link from me, sorry:

http://www.hood.de/auction/36960758/rohrisolierung-daemmung-pvc-bogen-15-20.htm

Ask at the plumbing shop for detailed material and workmanship recommendations. In writing, from the manufacturer, bad practice is absolute normal here in Ireland when looking at ST insulation jobs on our roofs. The shop steward might not know any better than what his clients fiddle every day. So insist on written instructions from the manufacturer of the insulants.

Not wishing to go off topic but noticed IKEA car park myself recently - makes me worry about any foam backed board dry lining I've done! Very poor performance.

Bruthal

heinbloed wrote: »

The installation of a non-return valve is a 'must' in ST systems, the cold ST panel would use-up all stored thermal energy from the storage cylinder otherwise. Unless the cylinder is stored higher than the collector.

If the solar heating coil is below the gas boiler heating coil in the hot water cylinder, how will the solar one now thermo syphon the heat from the tank to the panel on the roof? Is the solar heated coil not normally the bottom coil in the cylinder for this reason?

heinbloed

If the solar heating coil is below the gas boiler heating coil in the hot water cylinder, how will the solar one now thermo syphon the heat from the tank to the panel on the roof? Is the solar heated coil not normally the bottom coil in the cylinder for this reason?

As long as there is a temperature difference on a vertical piping the hot will raise and the cold will fall.

The ST heatexchanger in the storage cylinder can be placed at the bottom of the cylinder (here:a two-coil cylinder), but this is to save on fuel other than ST (oil, gas etc.) and to increase the thermal storage capacity.

If the bottom of this tank has 20 degrees Celsius for example and the outside temperature drops below this value (that's every night!) the STcollector will 'empty' the thermal storage. Until both temperatures are the same.