Hot Water Cylinder Questions

mmmmikey

Yes, the expansion vessel and external plumbing are in addition to the diameter stated.



If you put it in the loft, you'd have to think carefully about strengthening the floor as it's an awful lot of weight in a small footprint when full. Also, check the dimensions, I don't think it would go between my ceiling joists. Quite big and unwieldy to manhandle, and a fair weight even when empty. So all in all, I'd be quite wary about the loft idea (for a retrofit), but not saying it couldn't be done.



As far as capacity is concerned, suspect I may have oversized mine, although that was intentional as I wanted the thermal storage capacity for solar electrcity to even out peaks and troughs in the shoulder months. Also, you really need some access to the top for servicing, so if having the 210l version means you can only just squeeze it in height wise, that needs some careful thought.

Coastalwatch

Thanks for the advice, it's much appreciated. Headroom in the loft is an issue, as I can barely stand up straight and I'm only 5' 6" in old money. I think it's going to be a squeeze depth ways in the airing cupboard, as internally it measures 1000mm x 600mm max(which the door opens from) but that would be my preference if I can juggle the pipework to suit!

mmmmikey

....my cupboard is 900 x 595 and it fit's in there (just) with the immersion heater bosses protuding into the space between the back of the door and the opening to the cupboard (i.e. the thickness of the walls less a bit) if that makes sense. I'll take a picture later and see if I can work out how to put it somewhere and post a link.

zeupater

Coastalwatch wrote: »

Thanks mmmmikey and Z, looks like I'll be heading in that direction then. Just have to decide whether to fit one in the "old" immersion cupboard or up in the loft. I suspect the 160 litre version will have to suffice as the 210 litre appears too large for either the cupboard or fitting through the loft hatch.
I'd rather keep any heat loss within usable living space as opposed to the atmosphere, so guess the cupboard may end up as it's final resting place!

I assume the expansion vessel to be in addition to the diameter of the unit stated on the data sheet!

Hi

There were a couple of reasons we stayed away from a thermal store, but in terms of the current discussion, the minimisation of gas consumption during the winter months was important.

Effectively a thermal store needs to be kept hot enough to transfer heat to the mains water feed ... the configuration & number of heat exchange coils within the heat-bank setup can be quite complex, but generally as the store content cools, so does the DHW temperature which can be available at the tap, therefore requiring the whole store to be recharged to operating temperature ... with a column of water in a large cylinder, as cold water enters at the bottom & hot water exits at the top a thermal boundary layer gradually moves upwards - water in the lower 3/4 of the tank could be ~10C, but the top 1/4 could be 60C ready for delivery, however, with the average temperature being ~22C the exchange transfer efficiency in a heat-bank with the same capacity & thermal charge would be low, resulting in tap temperatures which would likely be of no use to anyone.

In the deep of winter our solar thermal system does little other than pre-heat the water below the variable thermal boundary and the gas duty is reduced by only heating the upper portion of the cylinder, thus resetting the position of the stratified thermal boundary ... having less energy stored in the cylinder reduces the newly charged standing loss & having access to usable temperature for longer decreases the frequency at which non-renewable energy top-ups are required ....

Just something to consider ....

HTH
Z

Coastalwatch

mmmmikey wrote: »

....my cupboard is 900 x 595 and it fit's in there (just) with the immersion heater bosses protuding into the space between the back of the door and the opening to the cupboard (i.e. the thickness of the walls less a bit) if that makes sense. I'll take a picture later and see if I can work out how to put it somewhere and post a link.

Thanks, it makes perfect sense as to the back of the door on our cupboard, the 600, plus a bit comes to 650mm so hopefully sufficient to accommodate any further necessary protrusions!

A picture would be great as it would assist in which orientation is best to set it at. In case you've any problems posting it on here I'll drop you a pm with my email address. Thanks again.

Coastalwatch

zeupater wrote: »

Hi

There were a couple of reasons we stayed away from a thermal store, but in terms of the current discussion, the minimisation of gas consumption during the winter months was important.

Effectively a thermal store needs to be kept hot enough to transfer heat to the mains water feed ... the configuration & number of heat exchange coils within the heat-bank setup can be quite complex, but generally as the store content cools, so does the DHW temperature which can be available at the tap, therefore requiring the whole store to be recharged to operating temperature ... with a column of water in a large cylinder, as cold water enters at the bottom & hot water exits at the top a thermal boundary layer gradually moves upwards - water in the lower 3/4 of the tank could be ~10C, but the top 1/4 could be 60C ready for delivery, however, with the average temperature being ~22C the exchange transfer efficiency in a heat-bank with the same capacity & thermal charge would be low, resulting in tap temperatures which would likely be of no use to anyone.

In the deep of winter our solar thermal system does little other than pre-heat the water below the variable thermal boundary and the gas duty is reduced by only heating the upper portion of the cylinder, thus resetting the position of the stratified thermal boundary ... having less energy stored in the cylinder reduces the newly charged standing loss & having access to usable temperature for longer decreases the frequency at which non-renewable energy top-ups are required ....

Just something to consider ....

HTH
Z

Thanks Z and much appreciated too. I have to confess that even with our PV array here there will be precious surplus energy in the depth of winter - Mid Nov to mid Feb. Last Dec we averaged 7.6kWh's/day ranging between 0.6 and 17kWh's(Do we need a battery!). Either we shall have to bite the bullet and grudgingly pay to import from the grid or switch the system over to the gas fired combi boiler which we shall have the option of doing. Neither being ideal I must confess.

Eventually we intend going all electric but just need to make a few compromises between now and that eventual outcome.

With thanks to all for the imput received on here the thermal store does appear to offer us the simplest installation, albeit at perhaps a premium cost. But it has the benefits of very limited servicing, it utilises mains water and pressure to drive it, thus erdicating the risk of infection compared to other systems requiring a header tank.
I guess time and future government renewable policies(if any) will tell if we've made a good choice.

mmmmikey

Hi again - have emailed photos.


Managed to install it in one (long!) day, with limited plumbing experience, but including tidying up the shower plumbing and putting in pipes in readiness for rainwater harvesting, which is a few projects further down the list.


Only (minor) thing that went wrong was overfilling the header tank. From the factory, the float valve was set too high. Didn't overflow, but brought cold level up to just below overflow, and had to empty with sponge and bucket. The header tank (which you can't see with the top on because it's inside the casing) is much narrower than the main cylinder, so the level rises quickly as the water gets hot and expands. You don't have much to play with as it's also fairly shallow.


So if I was doing it again, I'd fill it so you've only got 1cm or so in the header tank when cold, and then re-check after it's heated up to bring it to the level in the instructions.


Any questions, just ask...

pile-o-stone

zeupater wrote: »

Effectively a thermal store needs to be kept hot enough to transfer heat to the mains water feed ... the configuration & number of heat exchange coils within the heat-bank setup can be quite complex, but generally as the store content cools, so does the DHW temperature which can be available at the tap, therefore requiring the whole store to be recharged to operating temperature

This is why we went with a plate heat exchange rather than internal coil with our thermal store. The plate is more efficient and the feed is taken from the very top of the tank rather than having a pipe curling up the inside of the cylinder from the bottom to the top. The feed in from the gas boiler is close by at the top of the cylinder, so even if the water in there is cold, it soon feeds hot water through from the gas boiler.

It is also better in hard water areas as the plate heat exchange can be easily/cheaply replaced if it clogs with limescale, whereas an internal coil will just get thicker and thicker with limescale, effectively insulating it from the water, and it cannot be replaced without pain.

mmmmikey

So many choices

I opted for the internal coil on the grounds of simplicity & cost, and not worrying about limescale because I've installed a water softener (which I was going to do at some stage anyway). Capacity and re-heat times aren't issues for me because I've sized (over sized?) the cylinder accordingly.

Time will tell, I guess. 3 weeks isn't a long time, but very pleased so far.

Solarchaser

Hi guys, I'm just dipping my toe into hot water storage.
I never really considered it before, but my new batteries are now full before midday, and so alot of excess solar is going to the grid.

I'm in a soft water area, so no issues with limescale.

In my head, it makes sense to run the supply for hot water through a coil based thermal store, because even in the dead of winter, the thermal store is likely to be above the 4C my cold water comes in at, and so even when the solar isn't actively heating the store, it will still be taking the chill off it?
And then when heated if I use a trv type mixer then I should have instant warm water best case, and less gas use of the combi worst case?

I've took all the various links from this thread I'll now go and investigate, but I guess I'm asking if if missed something obvious?

Also what would you think (ballpark) it will cost to do this, including buying an iboost type thing, tank, heaters etc... assuming I'll do plumbing etc myself