Which hot water tank to buy

pinnks

I am not at this point yet but have been thinking about when, rather than whether, I need to change my 200l (ish) tank and immersion. My guess is that at 31 years of age it will be fine today and dead 10 minutes later...


I have an immerSUN so 1 or 2 immersions with 1 bottom mounted seems sensible but after that which brand, copper v steel and probably other things I have not thought of.


We don't need more hot water than the tank currently gives us with only 2 in the house for 95% of the time but would it be more efficient to go large or less so and similar questions.

Anyone any experience/thoughts?

zeupater

pinnks wrote: »

I am not at this point yet but have been thinking about when, rather than whether, I need to change my 200l (ish) tank and immersion. My guess is that at 31 years of age it will be fine today and dead 10 minutes later...


I have an immerSUN so 1 or 2 immersions with 1 bottom mounted seems sensible but after that which brand, copper v steel and probably other things I have not thought of.


We don't need more hot water than the tank currently gives us with only 2 in the house for 95% of the time but would it be more efficient to go large or less so and similar questions.

Anyone any experience/thoughts?

Hi

It's a trade off really, large means that you'll have a better buffer against a number of consecutive dull days, but then again, you need more energy to charge the system up which becomes an issue in the winter ....

We're slightly different in that the output of our solar thermal is dedicated to DHW so we don't need to worry about sizing the cylinder to our excess generation so storage volume is relatively high for what we use ... the added advantage in winter is that we can use the GCH to heat the top of the tank when necessary using a longer boiler/heating cycle to increase system efficiency ... effectively the solar thermal provides most of the energy to warm the water & the GCH raises the temperature to MrsZ's "strip the skin off you back" preference for shower temperatures .... even in deepest winter the log burner usually provides most of our space heating, so the boiler might only be used for 30minutes every three days-or-so just for DHW with no problems at all ...

If you're happy with the storage volume at the moment relative to the pv generation then it would make sense to not play around with the balance too much ... maybe look at ~220/250litres if you really want a little more buffer, but don't push it too high ...

Copper vs SS ?? ... well there plenty of information to suggest that copper provides a more sterile environment, which is good if you're operating at <50C for regular periods, but then again, SS should theoretically have a longer service life (quality vs quality) ... having said that, I know someone who had two large SS thermal stores fail within a short time .... like most people, we've got copper .....

A really important consideration is the cylinder design and level of insulation ... you'll probably be better off with a tall/slim unit than short/fat (if you've got room) as it'll encourage better stratification ..... solar spec insulation (thicker) would reduce the loss of the heat you've collected, especially in winter when there's not much excess generation to waste ...

Just ramblings, but hope it's useful ...
Z

pinnks

Thanks Z.


Mrs. Pinnks has showers in common with Mrs. Z. Must be a gender thing...


Good thoughts on copper and sterility. Hadn't thought of that one. And if the copper lasts as long as the current one, I doubt I'll care any more, if I'm still around - lol


So, gets me thinking, tall, 250l or so, copper, well-insulated of course with two immersion's. Plus, by the sound of it a log burner, haha.


Any brand suggestions, or are they much of a muchness?

zeupater

pinnks wrote: »

Thanks Z.


Mrs. Pinnks has showers in common with Mrs. Z. Must be a gender thing...


Good thoughts on copper and sterility. Hadn't thought of that one. And if the copper lasts as long as the current one, I doubt I'll care any more, if I'm still around - lol


So, gets me thinking, tall, 250l or so, copper, well-insulated of course with two immersion's. Plus, by the sound of it a log burner, haha.


Any brand suggestions, or are they much of a muchness?

Hi

Hadn't noticed the size of the install you have in your signature ... I'd hazard a guess that you're still exporting a decent proportion even with proportional diversion in place, so pushing the cylinder volume up a little shouldn't really be an issue - do you currently monitor diverted energy against total generation and have a view of what is still being exported ? .... increasing the volume by 25% doesn't mean that you'll divert 25% more energy, realistically, as long as usage remains a constant, the logical difference should be confined to cylinder heat-loss which in the case of solar-spec insulated cylinders is really low, especially when compared to your existing 31year old unit (my guess - bare copper & jacket ?) ...

Anyway, concerning makes ... I've read it all, buy this make, but that ... all I know is that a good plumber once told me that as long as they were BS standard cylinders sold at the same grade, then there not much real difference between anything and to just stay clear of anything being pushed which was rated below grade 3 or didn't suit your pressure requirements ... We followed this advice when our latest solar thermal went on the roof of this house ... Ours is a Newark, which seems to be highly rated for their solar range and supposed longevity and was the natural choice of our selected installer, but they were just as happy to use Albion (etc) if we had a preference ....

HTH
Z

pinnks

Diversion v generation is of course very seasonal with solar. But if we can divert between 2 and 3 kWh then we have hot water a-plenty. Today we generated 25kWh and diverted 3; exported 14. That is typical for this time of year. In the middle winter we will squeeze 1.5+ kWh into the immersion on all but the very darkest days. So, quite a bit of spare generation on most "normal" days for at least 9 months a year.

Current tank is not quite just copper - about 25mm of now quite tired insulation and a newly fitted jacket, which has helped.

Ours is a vented system, so no pressure issues.

Anyway, some good thoughts to set me on a reading spree - a quick look at the Newark website looks interesting and informative - had not heard of them before. The E7 cylinder looks to be what I'd I think, to use boiler and 2 immersion's.


Thanks for the info...

pinnks

Newark website is quite informative. I imagine one would want to use what they describe as Economy 7 cylinders, not to move onto E7 tariff but because they have a bottom mounted immersion and boiler coil. Whether one would want a second immersion is a good question but presumably alternating between the two would assist circulation/mixing in the tank.

zeupater

Hi

Standard practice for a solar thermal install is to have twin coils ... the solar coil (larger with fins to increase heat exchange rate at low DeltaT) at the bottom of the cylinder and a standard GCH coil around half-way-up ... the idea is that when 'purchased' energy from GCH is essential, you're not heating the entire water column in order to have hot water at the top ... if we didn't have solar thermal but had GCH and two immersions, I'd be tempted to look for a single (middle) GCH coil and look for a way to control the priority of the two immersions .... probably set priority to heat with top immersion until it reaches temperature then heat using the bottom one ... will your proportional diversion handle this ??

Make sense ??

HTH
Z

pinnks

Interesting and, yes, makes sense. I guess your thinking about setting the top immersion first is because you would get the most usable hot water from the available sun and only heat the whole tank once the top has reached temp. I had not thought about doing that but it does make best use of the available free energy.


From the drawings on the Newark website it looks as though the coil is near the bottom which might make sense if the "only" time you use the GCH is when you're unlikely to get enough sun for the diverter anyway, hmm... On the other hand, they also do bespoke work, so they (other firms are also available) might make up something like you suggest?


The Immersun can set priorities, heat one or other element first and then the other, or equal times for each. Can't remember but I think you can also set the times for "equal" too, so 15 minutes each, or 20 or 30 etc.


Good job I am doing the thinking before the panic of a busted tank sets in...

silverwhistle

On a related subject, I have an iboost feeding a tank with a blue foam integral jacket (the little detail is because I just checked!). This is, in summer, nicely warm and the copper pipe issueing from it is likewise. Would an additional jacket over the top be worthwhile? Even if my tank is 'HOT' according to the iboost and I use no hot water it needs a fair bit of to[p up the following morning (no, I haven't done a calculation:-). This obviously isn't an issue at the moment but during the shoulder months might be: any opinions?

zeupater

silverwhistle wrote: »

On a related subject, I have an iboost feeding a tank with a blue foam integral jacket (the little detail is because I just checked!). This is, in summer, nicely warm and the copper pipe issueing from it is likewise. Would an additional jacket over the top be worthwhile? Even if my tank is 'HOT' according to the iboost and I use no hot water it needs a fair bit of to[p up the following morning (no, I haven't done a calculation:-). This obviously isn't an issue at the moment but during the shoulder months might be: any opinions?

Hi

Before we changed cylinders in this house we had a standard bare copper one with a pretty thin jacket ... as part of our early efficiency measures we simply fitted a second, much thicker, jacket over the top to double-up .... it made a noticeable difference on the standing heat-loss and paid for itself quite quickly, well within a year ....

HTH
Z

lstar337

zeupater wrote: »

Hi

Before we changed cylinders in this house we had a standard bare copper one with a pretty thin jacket ... as part of our early efficiency measures we simply fitted a second, much thicker, jacket over the top to double-up .... it made a noticeable difference on the standing heat-loss and paid for itself quite quickly, well within a year ....

HTH
Z

And when I used to have an E7 system with a bare copper tank and thin jacket, I wrapped an old duvet around it and saw instant savings. I later doubled it up, cut it to shape and stitched along all the edges to make it safer/more pretty.



A bit of free money saving. :money: