New cylinder or improve insulation on excisting tank

Macker · 04-02-2024 5:21pm #1

hi , since going smart meter I intend to heat my water overnight I currently have a copper cylinder with a basic lagging jacket ,should i replace that and buy a new modern cylinder that will keep the water hot most of the day or spend mone y on an upto date lagging jacket,we are not big users of hot water ,just bathroom and kitchen sink.

Sleeper12 · 04-02-2024 5:50pm

With a factory insulated cylinder you can't tell if the water is hot or cold by touching the cylinder itself. This shows how well it is insulated. With an old cylinder you will always know how hot it is now matter how many lagging jackets you have on it. Bottom line is factory insulated cylinder is far better at keeping the water warm compared to lagged cylinder.

The real thing you need to decide is how long will it take for you to save enough on the new cylinder before it pays for itself. I'd hazard a guess you would pay €600/€700 for a new cylinder supplied & fitted

It's worth putting foam insulation on at hot pipes coming out of the cylinder too

Macker · 05-02-2024 11:15am

https://www.boards.ie/discussion/comment/121720910#Comment_121720910

cheers for that , I will be using solar to heat water when the sun comes out so Id probably be a long time getting 700 euro back ,I think Ill invest in better insulation including the pipes as you suggested

Sleeper12 · 05-02-2024 11:22am

It's worth remembering that you don't get "free" hot water from PV solar panels. Many people fall into this train of thought. If your energy provider will buy electricity from you for 20c per unit then the water isn't free. It's costing you 20c per unit.

I get a lot of calls from people wanting to remove the A energy rated electric shower using 3 to 5 litres of water per minute and install a power shower using 14 litres of water per because they believe the water is heated for free. In most cases it's better value to sell the electricity and use the electric shower.

Having said all that the power shower is a more pleasant way to shower

Macker · 05-02-2024 11:31am

https://www.boards.ie/discussion/comment/121723535#Comment_121723535

I realise that but using an EDDI to top up hot water during the day afer heating a full tank over night might be worth while

stiophan · 06-02-2024 12:43am

You may want to check if the cylinder is the correct one for a Solar PV. Most Solar PVs have a specialised hot water cylinder designed for heat pumps or constant solar heating. You're also presuming your hot water needs in winter will be met by solar (outside heating the house power demand). Unless your sleep patterns correspond to your smart tariff then you need a timer to run the immersion during x tariff time. Lagging every hot water pipe you can find is good ideas no matter what heating system you have.

con747 · 06-02-2024 2:07am

https://www.boards.ie/discussion/comment/121727498#Comment_121727498

Can you clarify what you mean by this? "Most Solar PVs have a specialised hot water cylinder designed for heat pumps or constant solar heating." I was under the impression any hot water cylinder with an immersion can be heated by an Eddi which only heats the water when there is excess PV.

06-02-2024 7:53am

https://www.boards.ie/discussion/comment/121723535#Comment_121723535

While Id say it's correct you don't get free hot water from pv panels (via an immersion), because the owner has paid upfront for a pv system and possibly for hardware to divert, eventually they pay off if you are using the hardware for what it is intended, as the alternative is buying from the grid indefinitely which is typically expensive (aside from EV/reduced rate hours which many solar pv owners will advocate utilising, because you then have a multiplier/offset for any sold units by buying cheaper at off peak hours). After a system is paid off any power produced is as close to free after that can be. While selling your electricity might get you 20c/kwh for each unit, using it instead spares the pv owner from buying at 36c/kwh or possibly more, which they will be paying for to heat water or run an electric shower. In the example figures it would cost them 16c more per kwh to import any electricity after selling to the grid, a Hot Water store or battery is an excellent way to store and utilise solar PV, I don't get why anyone who advocates selling units to the grid in lieu of utilising themselves because it will cost them more to buy it back at times it is needed, and then use it in an "A rated" shower.

Regarding being A rated, I think the use of "A rated" is disingenuous on the manufacturers part to say the least, I wondered was the A rating their own energy label applied by manufacturers (which I think Ive seen something about on packaging), although I did find some information referring to it for an electric shower suggesting 483kwh/annum, breaking that down 483/365days is 1.32kwh/day (for all showers) 1.32kwh/9kw is 0.14hours or 8 minutes & 49 seconds. That makes it appear energy ratings are per a very specific amount of use, because there is no way a whole family is getting all showers in that time (assuming even only one per day in all instances)

The majority of people I have read about that have solar pv advocate having a pumped electric shower of some form because that uses less electricity while running and using stored hot water from PV. While some people do advocate selling to the grid, there is only a limited allowance before a person starts getting hit for tax, which I think will become more refined at getting from the consumer/pv producer in the future.

While Im sure your advice about electric showers is a sincere personal opinion, I consider it to be wrong and to be bad advice, because by my calculation, it requires specific circumstances to work out (looks to be a 1.47 person household at best), the well established manufacturer I got the 483kwh/annum is clearly under specific circumstances, because if you turn that into a 3,4,5 person household, electrical consumption starts to increase substantially, so it has to be use dependent. it is no way comparable to how much energy a fridge might consume per annum which isnt as affected by the number of people using it.

imo it looks to be misrepresenting how much power a shower of that type consumes by labelling it as "A rated". I have solar pv and during the winter I have used an EV rate overnight with an eddi solar diverter (the op or others could use just a timed immersion), I only have a factory insulated (hard foam) copper cylinder (in place when I got here) and the water is piping hot since having solar pv which covered my HW needs in the last summer, I could only change to a smart tariff approaching the winter, so started to avail of an EV tariff to heat water over the winter. One very noticeable thing since getting solar was the immediate drop in power consumed by the pumped electric shower (via an app graph) compared to using a pumped shower in another shower since and a considerable drop in costs.

Some people will advocate selling electricity to the grid, I only advocate doing so after someone has consumed all they need first because it costs them a substantial percentage more to buy back anything they require afterwards. If the OP goes looking for an opinion from a solar pv forum elsewhere, Id say the majority will suggest swapping out the likes of a 9kw pumped electric shower for a pump or a pumped shower (no heating element) if they can get a HW supply to it. A standard copper cylinder thats factory insulated is likely to cost them less than a more modern one, I found oil heating poor at heating water compared to pv.

06-02-2024 8:23am

The difference in performance between a factory lagged cylinder and a jacket lagged home job is massive. Fibre glass takes at least 4-6 inches of lagging to match the foam of a factory foamed unit, few people have the space and shoving it into a smaller gap just doesn't do it. I recently upgraded to a kingspan stainless steel cylinder and I am frankly amazed at how good it is. I am going to be adding a smart relay and temp sensors to allow it to be integrated into our smart home for overnight heating - and this will prepare the ground for us to add PV in the new year. Priority will be internal consumption, battery and immersion before a single unit goes back to the grid. I don't think there is a single plan out there where they pay more than the night rate kWh charge so the more you can use internally the quicker your payback.

Another thing to consider is that kingspan stainless tank is highly optimized, it's coil is right at the bottom of the tank which means it heats right to the bottom. It also has a baffle for the cold inlet which means it never mixes hot and cold so your water stays at a more useful temp for longer. I have never seen a single coil copper that ever effectively heats the bottom third of the tank which means they are a third wasted space.

You can usually pick up very clean second hand cylinders for about a third of the price of new so it doesn't have to be a huge up front investment, always budget and extra €200 for brass and copper fittings on the switch over, and that if you can do the plumbing yourself. I got mine for €150.00

My advice is don't scrimp on the cylinder, get a good second hand kingspan and fit it yourself.

Sleeper12 · 06-02-2024 8:41am

https://www.boards.ie/discussion/comment/121727728#Comment_121727728

This is the rabbit hole people go down.

Whatever your utility company is willing to pay you for electricity, 20 or 25c per unit is what it costs you to heat you water for "free". The fact that you chose not to sell it is costing you 20 or 25c.

A five minute power shower costing needs around 30 to 60 minutes of electricity at 3kw. A five minute electric shower uses 5 minutes of electricity at 9kw. It is far cheaper to use an electric shower compared to the "free" hot water you get from solar.

06-02-2024 8:51am

https://www.boards.ie/discussion/comment/121727795#Comment_121727795

Most of that draw will be from the grid at one of the higher kWh unit rates since few people shower at the night rate time of day. With a tank you also have hot water when you actually need it. Also very few people actually avail of a five minuit shower.

Sleeper12 · 06-02-2024 9:04am

https://www.boards.ie/discussion/comment/121727822#Comment_121727822

This is my point the electric shower still works out cheaper than the "free" water.

I'm happy to take €1000 and upwards to install a power shower to avail of all the "free" water they get but I always break it down and explain that the free costs more than the electric shower. I also point out that the power uses 4 to 6 times the amount of treated water and this isn't exactly the green thing to do

06-02-2024 9:17am

https://www.boards.ie/discussion/comment/121727858#Comment_121727858

No one is really advocating a power shower here, if you fit a power shower then you have no thought for economy.

Ours is a gravity fed shower and a single standard sized tank will easily do two showers and have third of a tank left over for washing. One heating cycle will provide all our hot water for the day.

On top of this the user experience of a pumped electric shower is horrible - they are horribly noisy and they tend to have a very short in service life before either the element or the pump burns out. We have one and for these reasons alone I can't see us ever using it.

Sleeper12 · 06-02-2024 9:26am

https://www.boards.ie/discussion/comment/121727894#Comment_121727894

More than 99% of the country have a power shower or electric shower. It's actually less than 1% rely on gravity alone without a pump. So the point I am making is for the vast majority of homes in Ireland. The 99% rather than the 1% of Irish homes. Electric shower is cheaper to run than the "free" water power shower.

The point is pv owners convince themselves that the water is free but the very fact that the electricity used to heat it costs them whatever their energy provider is willing to pay for it. In some cases it could be better value to sell it to energy provider during the day & buy it back at a cheaper rate at night or even get it for free at the weekend on some tariff

06-02-2024 9:32am

https://www.boards.ie/discussion/comment/121727795#Comment_121727795

It isnt costing you 20 or 25cent by exporting, it is more likely saving you another 11 or 15cent per kwh that you aren't consuming by importing, your logic is export for 20/25cent but buy it back at 36/38cent is a loss of 11+cents, because that is what you will be doing with a 9-9.5kw shower because no domestic solar pv system can produce that much and is unlikely to be by battery either. There is also a limit on how much you can export before tax becomes applicable, so then all export is worth about 50% of what you exported, which is more likely if a person is focused on exporting. A 6.5 minute pumped electric shower is going to consume 1kwh of power ( a 4 people household per billing cycle will cost them about €92 or 552/annum). Rather than importing that electricity, you consume what you produce, a power shower I have using HW from a cylinder heated by solar consumes instantaneously a few hundred watthours at most.

It is not far cheaper to use a 9-9.5kw pumped electric shower than using hot water heated by solar ( I never said it was free, but it does pay itself off eventually), in fact, the more a 9-9.5kw pumped electric shower is used, the more the cost increases, whereas the more a solar heated cylinder is used using a pumped shower that consumes less power, the more benefit it is (to the limit of the HW cylinder capacity).

One consideration you havent mentioned is, importing power means you are taxed on that (thats how it is). By not importing and consuming as much of solar production as possible means your tax portion of your bill is substantially reduced too. My bill which overlapped with my solar installation aside from dropping in usage/cost due to reduced import, had a substantial reduction in the cost of the useless (to me) cost of the tax.

I could see the graph and figure of my usage when the 9.5kw shower was still in use when I had my app up and running that came with a car charger, but before my Solar PV installation was in place, compared to after the solar pv install, the amount of imported consumption dropped dramatically, you can see it on a day to day basis both graphed and in numbers for how much imported power is used.

The other thing is, how water in a cylinder can be used for other things besides showers. Electricty for 9.5kw showers is typically not at off peak rates. Even your example of 30-60minutes at 3kw is 1.5-3kwh (cost per bill can be as low as €15) and still have potential excess for export. 4 persons showering for 6-6.5 minutes is 4kwh (cost €1.60, per bill about €95).

There is no rabbit hole, its is absolutely cheaper to use solar excess to heat water and then pump it with what a solar panel or battery can manage day in day out than indefinitely import 4kw per example which is likely to be fairly typical (2+2).

Exporting gets you less in return if you have to then buy back electricity by importing at a higher price, rather than storing and consuming at a lower level by using a different device that doesnt consume as much power because it doesn't have to heat (thats where the cost is, instant heating costs because it consumes so much power). Any cylinder that is pre-insulated will be an improvement on one that is lagged with a jacket, even an ordinary copper cylinder thats factory insulated. The only reason Id change my cylinder for a more modern type is if I was getting a heat pump.

Calahonda52 · 06-02-2024 9:43am

https://www.boards.ie/discussion/2058334645/new-cylinder-or-improve-insulation-on-excisting-tank

The fundamental question here is in the last line: not big users, so if you are heating 200 or so litres of water every night, regardless of how well insulated the tank is and not using the hot water then its a waste.

Under sink heaters and electric showers.

By way of example, in my house here, the pipe run from DHW cylinder to kitchen is 2.8 litres before I get 60 degree water.

Do that once a day is equal to 60 kwhs per annum,. enough to drive 320 kms in my Leaf.

Storing/using excess energy in water is a poor choice, batteries a better option with more choice.

The other problem is that the concept of " unlimited free hot water" encourages waste of a scarce resource.

Keep well

06-02-2024 10:23am

An immersion tank is just more versatile than any of the instant heat alternatives. It's also very likely to work out cheaper since the cost of instant heaters, cabling and electrican fees will be substantial.

Most of the water heating in the winter is a byproduct of heating the house. Minimal additional cost.

You can optimise your water heating by choosing the time of day to use it rather than been at the whim of whatever daytime tariff you are on, and domestice solar will never keep ahead of instant heaters so you are always going to be drawing from the grid whenever the hot tap is on. Heat at peak times and that could be 50c a kWh.

There is always hot water available for washing and bathing. Think about that - no more baths if you dump the immersion.

DublinDilbert · 06-02-2024 7:58pm

I fitted two lagging jackets to a bare copper cylinder and the second jacket has made a big difference. Hot-press is no longer getting hot and with the second jacket I was able to go right over the top of the cylinder. I have more or less doubled the jacket up for the top 1/2 of the cylinder so it is more like 3 lagging jackets. Lagging jackets are cheap in the likes of screwfix.

Macker · 07-02-2024 1:38am

Thanks for all the answers folks ,can I throw a spanner in the works and say that Ive been heating water using gas because we run the gas central heating a couple of times a day ,in summer the gas may not be used at all unless I close all rads and run it for an hour before we need hot water

07-02-2024 9:51am

You really would benefit from a cylinder upgrade. A good cylinder can hold hot water all day and makes running an immersion for an hour a day a viable option.

New cylinder or improve insulation on excisting tank

Comments