Hot Water Cylinder Questions

mmmmikey

Sorry if these have been answered before but I either can't find what I'm looking for or don't have much confidence in what I have seen on other forums:


1. I have a 210 litre hot water cylinder that's about 25 years old and I'm about to have moved so it could easily be replaced for just the cost of a new cylinder (£200 or so). Does anyone know if there's much difference in the standing heat loss for a 25 year old cylinder with about 30mm of spray foam and a new one with 50mm of foam - i.e. has the efficiency improved much in this time period? It's just a bog standard direct vented cylinder with 2 immersion heaters for E7. Have googled this to death and struggling to get anywhere. A saving of 0.5kWh standing heat loss or more per day would make it worth it.



2. In the real world, what's the life expectancy of a copper cylinder - i.e. if it's 25 years old should I replace it anyway (I'm assuming the old one will be easily recycled)?


3. Would you go copper or stainless steel if you repalced it?



4. Any big advantage in going to the extra expense of a thermal store or unvented cyclinder, other than mains pressure hot water which I'm not bothered about?


5. Any thoughts on whether it's best to connect the iBoost type device to the bottom or top immersion and vice versa for the off-peak E7? (Most of my hot water is heated by surplus solar pv power in the summer, but I'm installing a battery soon so in the shoulder months there will be less spare as it's more cost effective to prioritise the battery)



6. Any clever new technologies I should consider for hot water? (I've pretty much ruled out thermal solar on the grounds of cost, but interested to hear if anyone thinks this is the best thing since sliced bread and worth investigating. Doesn't seem to get much coverage here compared with solar pv - why?)


Not a big saving or money-spinner, but I want to do it right. Thanks in advance for any help that will point me in the right direction, Mike

gefnew

Hi
This might help.
https://www.homebuilding.co.uk/hot-water-storage-the-options/

tacpot12

Going from 30mm to 50mm of insulation will halve the heat lost. This means that if it was worth having 30mm of insulation (what ever that saved you) you would save twice as much with 50mm. As no-one would have an uninsulated cylinder, the saving must be appreciable, so twice the saving is worth having.

A 25 year old cylinder is doing well, so replacing it now would be prudent. You should be able to weigh it at a local scrap dealer. Be prepared to have to show you Driving License or Passport and to only be able to receive the cash into your bank account.

Personally I would go with Stainless steel for longer life.

Having read the article linked to above, I can see no advantage to a thermal store unless you have multiple heat sources.

I would avoid an unvented cylinder if you don't want your hot water at mains pressure.

Sorry, don't know much about E7 or iBoost. This link might be of interest though: https://www.immersun.co.uk/immerSUN-vs-Solar-iBoost/

mmmmikey

Thanks for the replies - that website sums it up nicely. Reflecting on this, I've probably been over-thinking it but always worth checking other opinions, so thank-you. Just the fact that it's 25 years old makes it worth replacing and there doesn't seem to be any compelling reason not to do a simple swap for a new cylinder of the same size. Any energy saving will be a bonus. The techie in me would like to be able to quantify this but as the cylinder seems worth replacing anyway that's only academic. For interest, I think I'll have a go at measuring the standing heat loss for the existing cylinder and then comparing it with the new one. Thanks again, Mike.

pensionpawn

My neighbour also has a Willis system connected to his HW tank and thinks it's the best thing since sliced bread. I have solar and have been mulling over changing my 22 year old tank (also wondering when it is likely to spring a leak) as living in a hard water area the maths suggests that I've lost ~20% of it's capacity to limescale. My IH is driven from a solar divert circuit saving on gas. I've also increased the thermostat to 70c (I would like to go to 80c, however this would mandate a new thermostat) with a thermostatic mixer valve to bring the 70c-80c water down to 42c for distribution to the taps. This effectively increases the capacity of my tank 'at 42c' which is what I need to fill my new 280L 1.8m x 0.8m bath off one full HW tank.

mmmmikey

Thanks - I haven't come across Willis type external immersion heaters before - opens up interesting possibilities for inexpensive boost which I shall mull over.



In the meantime, I've installed energy monitors on my paid for and solar immersion heaters so I can measure the effect of different settings and get a good baseline before I have the new cylinder installed. I'm going to play around with swapping the E7 and solar power sources between the top and bottom heaters and setting different temperatures. In the general scale of things, tuning my water heating is not going to make me rich, but as it now accounts for about 20% of my energy use it's worth looking at - all the little bits here and there add up.


A few of thoughts on your system, based on what I've been looking at over the last few days:


1. You'd probably reduce your standing heat losses by a worthwhile amount by using a bigger cylinder at a lower temperature to get the same effective storage.


2. You'd also save maybe 0.5kWh to 1kWh or so standing heat loss per day by getting a new cylinder with 50mm insulation (assuming you've got 35mm at the moment).


3. You may find a direct cylinder with a horizontally mounted immersion at the bottom better suits your needs (ssuming this isn't what you've got). If you have a "standard" cylinder with a top mounted immersion, even with a long immersion heater you'll probably find the thermostat is cutting out before the water in the bottom of the cylinder is heating, limiting the effective capacity.


Thanks again for the lead on Willis Immersion heaters.

pensionpawn

mmmmikey wrote: »

Thanks - I haven't come across Willis type external immersion heaters before - opens up interesting possibilities for inexpensive boost which I shall mull over.



In the meantime, I've installed energy monitors on my paid for and solar immersion heaters so I can measure the effect of different settings and get a good baseline before I have the new cylinder installed. I'm going to play around with swapping the E7 and solar power sources between the top and bottom heaters and setting different temperatures. In the general scale of things, tuning my water heating is not going to make me rich, but as it now accounts for about 20% of my energy use it's worth looking at - all the little bits here and there add up.


A few of thoughts on your system, based on what I've been looking at over the last few days:


1. You'd probably reduce your standing heat losses by a worthwhile amount by using a bigger cylinder at a lower temperature to get the same effective storage.


2. You'd also save maybe 0.5kWh to 1kWh or so standing heat loss per day by getting a new cylinder with 50mm insulation (assuming you've got 35mm at the moment).


3. You may find a direct cylinder with a horizontally mounted immersion at the bottom better suits your needs (ssuming this isn't what you've got). If you have a "standard" cylinder with a top mounted immersion, even with a long immersion heater you'll probably find the thermostat is cutting out before the water in the bottom of the cylinder is heating, limiting the effective capacity.


Thanks again for the lead on Willis Immersion heaters.

I am thinking of getting a new larger cylinder in a couple of years time, and will investigate the thicker insulation. Running it at a higher temperature isn't really an issue with heat losses as the energy to get it to 80c is free from the sun and would have been exported if not used.

coffeehound

Might as well go for 60 mm insulation if you can find one to suit. Not sure if vented are available with that thickness though. Unvented would give you extra loft space if that were of value plus reduce heat loss further.

The solar vacuum tube systems were not financially sensible when i looked into it some years back, so probably explains why they are not mentioned here much.

pile-o-stone

I'd suggest if you're using solar and expect that the tank temperature might approach 80C that you fit a mixing valve on the hot water outlet to make sure that it doesn't scald anyone.

I'd also look at making sure the hot water pipes are all lagged to prevent heatloss and also remove any risk from touching very hot pipes.

Coastalwatch

Interesting topic for me as I'm planning to install a hot water cylinder in our bungalow. Firstly to reduce our reliance on FF from the combi boiler and secondly to better utilise Solar output. Having experienced the limitations of shower systems accompanying indirect cylinders and pressure variations I'm thinking a direct unvented cylinder would be an improvement. Admitedly it will come at additional cost but hey ho, every improvement does it seems. It maybe sensible to have it controlled for when excess solar is produced, but again another additional layout, circa £200/300! As I'm planning to install a battery at some future time then suspect I can manage without it for now. Installing in the loft gives space to add insulation to the foam jacket they are supplied with to help reduce heat losses further.

I just wondered if anyone had already gone through the above process and advise of any flaws in my thinking or indeed of a particular make/model of tank they would recommend. I have a 200 litre stainless steel model in mind, circa £500!

pensionpawn

pile-o-stone wrote: »

I'd suggest if you're using solar and expect that the tank temperature might approach 80C that you fit a mixing valve on the hot water outlet to make sure that it doesn't scald anyone.

I'd also look at making sure the hot water pipes are all lagged to prevent heatloss and also remove any risk from touching very hot pipes.

Indeed. See post #5.