Hi All, new member with question about Water Heating

[jjwb]

Hi Guys,

General questions about the best way to heat water in a small cottage with two people.

 

I am looking for the best way i.e. cheapest, to heat water in our small cottage with just myself and my Wife and only three hot water taps. Should we heat a Hot Water Tank or would an instantaneous water heater be a better option. We are electric only no oil or gas.

Many thanks.

[Conor]

Welcome.

 

I lived in an electric only apartment for a year with a work colleague, it had a small 100l well insulated tank that was heated on overnight economy 7 tariff. Did the job and I don't think it cost very much at all.

[SteamyTea]

As a combination of installation costs and running costs, a basic vented cylinder and E7 heating is probably the easiest as it can be self installed.

If it comes to running costs, a small ASHP may work better as it will usually have a CoP of 3, so even at full daytime electric costs it is cheaper than resistance heating on E7 (about 7p/ kWh as opposed to about 10p/kWh).

 

You may find that an exhaust air heat pump could work for you if the rest of the building does not cost too much to heat (how is that heated), and it needs mechanical ventilation to keep the humidity down.

 

It is really a matter of sitting down, finding the prices of different equipment and doing he sums.

 

Long term I do not think that E7/10 will be a good financial option and will probably be phased out when variable tariffs come into play more.

[MikeSharp01]

10 hours ago, SteamyTea said:

Long term I do not think that E7/10 will be a good financial option and will probably be phased out when variable tariffs come into play more.

+1 to that in a sense. In reality there is no real timescale for full variable tariffs, second by second, and it cannot come in until our big electricity consumer devices can be controlled / control themselves to work with it. IE Turn off / down and on against the instantaneous price of the juice. A crude version of these tariffs are called Time Of Use (TOU) tariffs and you can read a bit of the speculation around them here: https://energysavingtrust.org.uk/time-use-tariffs-all-you-need-know/ where they say a household could save £5 (Yes Five)  a year without changing lifestyle. Good old Octopus Energy have got quite close 30 minute slots, updated daily - so you do the operation planning of the washing machine, dishwasher, water heater etc and, according to their blurb, you can actually get paid for using electricity at some points in the day - do your bit to keep the grid balanced.

 

 

 

[Nickfromwales]

Dependant on your consumption of hot water, a 180L UVC ( un-vented cylinder ) will give balanced high-flow hot and cold water supplies to all mixer outlets. Relatively cheap to buy, requires a G3 registered fitter to install, and ongoing annual G3 inspections, but will be very efficient, quiet, and will require no bulky, noisy cold water storage tanks which you need if you go for a "cheaper" vented cylinder. With vented you may also need a pump to get a decent shower /fill the bath quickly.

If you change to Octopus Go! tariff then you can heat the cylinder once a day, overnight, at 5p/kWh. You may need an occasional midday top-up depending on your bathing / hot water patterns.

An UVC is simple, efficient and reliable, with few moving parts. If you go for a stainless cylinder, and keep the G3 up to date, you will get a lifetime warranty from Telford. Speak to Trevor@cylinders2go and mention the forum for favourable prices.

Instantaneous water heaters are the anti-christ. You can go for a decent electric shower, but the bigger the kW rating, the more dependant they become on the cold supply being dedicated solely to the shower times. Flush a loo whilst using these and watch the thing shut down. The most reliable / least erratic electric showers are around 7.5-8.5kW but will never ever come close to the showering performance of a balanced hot water feed from an UVC. You would still need an electric multi-point heater to service sinks / basins even if you go for an electric shower, so cost will soon start to spiral, as well as that becoming a more expensive install, and far more points of faliure.

With stored hot water you can choose to cherry pick low cost pockets of electricity, but with instantaneous, you're Donald Ducked.     

[SteamyTea]

1 hour ago, MikeSharp01 said:

+1 to that in a sense. In reality there is no real timescale for full variable tariffs, second by second, and it cannot come in until our big electricity consumer devices can be controlled / control themselves to work with it

I was chatting to someone that runs a data centre that collects usage data for the National Grid.

He was enthusing about 15 minute blocks.  Personally I don't think we will, or need, to go that low.  So will probably stay with the half hour slots that are currently used.  This gives time for capacity to come on line (hot and spinning reserves) and also minor over generation can be easily controlled by switching off RE generation (you don't just pull the plug on a 5 MW turbine or solar farm).

The other things is that local storage and automation may make much of this balancing unnecessary, it will happen behind the scenes by the DNOs, as it is done now.

Much of it does depends on how our Nuclear generation program pans out long term.  With 15 to 20% of our generation currently covered by this, it still plays a very important part.  We know from Frances example that a large country can run with very high fraction of nuclear (~70%).  They have the advantage that they can off load to nearby countries (including the UK), but that off loading could be changed to storage.

For the foreseeable I think gas will be doing the bulk of the work, regardless of the governments ambitions to have ever home powered by wind and solar.

Adding capacity is easy, removing it is not.

I also don't hold out much hope for carbon capture and storage, even if we can reduce to 100g/kWh.  Last year Q1 generation was ~75 TWh.  That is still 7.5 million tonnes to collect and storage.  Landfill, for just our household rubbish, for 2018 was 24.4 million tonnes for the year, so 6.1 million tonnes a quarter, a similar amount.  We currently recycle about 45% of that.

We could say that carbon capture is similar to recycling in that it needs collecting, sorting, processing and transportation, before the actual end use is realised.  So about 2.7 million tonnes a quarter is a useful amount.  I cannot find a reliable figure for the percentage captured by CCS, but it will not be 100%, probably 50 to 60%, then add in the extra energy needed for the process, there is little to be gained from it.  Either way, it is a mammoth task.

So that leaves us back to the path we are taking, which is nuclear and RE generation.

As we increase the capacity of these, we have to pay upfront, with nuclear being a huge amount before it starts earning, and RE a lesser amount (because it is smaller scale and distributed).  If you look at the capacity factor of the technologies, nuclear is around 90%, offshore wind around 40% and solar is just about pushing 20% now.  That leaves a big gap which needs to be filled with either demand management or storage.  This does depend on the percentage share that each technology contributes to both our total energy requirements and out peak and trough needs.

We can probably up the total amount of nuclear to French levels, maybe a bit more, which would leave 20% for wind and solar.  I am not sure if this is realistically financially or socially.

So I think we could probably have around 30% capacity covered by nuclear (probably fit that onto existing sites) and a lot more solar, which is cheap and easy to deploy (but socially unacceptable), and about 1 TWh of storage, or about 35 kWh/home.  If Vehicle to Grid technology becomes a reality, then 35 kWh is not a large amount, most EVs will have double that, but only use a quarter of their capacity on a normal daily basis.

Edited May 14, 2021 by SteamyTea

[Nickfromwales]

 

[MikeSharp01]

6 minutes ago, Nickfromwales said:

 

@SteamyTea posts do that sometimes but you would struggle to argue with the basic analysis even if it has roamed a bit from the thread - interesting all the same. 

[SteamyTea]

2 minutes ago, MikeSharp01 said:

@SteamyTea posts do that sometimes but you would struggle to argue with the basic analysis even if it has roamed a bit from the thread - interesting all the same. 

Basically saying that it is hard to predict future energy prices, but you can know, almost to the penny, what an installation will cost.

Over the last 30 years, domestic energy prices have been about 5% of mean household wages.  This has been a developed world trend.

[Nickfromwales]

Easy to conclude then, that stored hot water would be better all round, vs instantaneous, and maybe an argument still exists to oversize the UVC to harvest enough cheap rate energy to get through a typical 24hrs on a 'single charge'. 

[SteamyTea]

9 hours ago, Nickfromwales said:

Easy to conclude then, that stored hot water would be better all round, vs instantaneous, and maybe an argument still exists to oversize the UVC to harvest enough cheap rate energy to get through a typical 24hrs on a 'single charge'. 

Which also means you can have a smaller capacity boiler/HP.

Take my E7 DHW system, it has a 3 kW element and a 200lt cylinder.  Total Cost for parts about £400.

[Nickfromwales]

12 hours ago, SteamyTea said:

Which also means you can have a smaller capacity boiler/HP.

Take my E7 DHW system, it has a 3 kW element and a 200lt cylinder.  Total Cost for parts about £400.

Plus a noisy pump for a half decent shower, a much larger ( 50 gal ) with cold water storage tank ( and space for ), plus all the pipework in between the two tanks and having two separate hot and cold systems ( one gravity one pumped ) etc.
£400? Nope.