How best to connect/run cylinder and electric boiler

[silver50]

I needed to change rusty cold tank anyway so have got a 150L Ariston Aquabravo 150L cylinder doing away with cold tank.

I ditched storage heaters and we have fitted a wet CH system. It is a well insulated late 80s 1st floor flat. An energy saving expert felt the wet CH wasn't too bad an option for me giving good controllability and due to the good insulation etc hopefully wouldn't need run excessively.

My problem is really this. I didn't expect this modern immersion heater to ideally need 3 hours to heat fully. I expect in reality it'll provide HW more quickly however running it on E7 overnight it will be on for an uncontrollable long time.

We feel Our E10 option isn't actually all that cheap and the time periods are a bit restrictive. Our plan was going on to a good single tariff which we have in mind at 11p/u.

This flat is for renting out. I am now completely confused about how best to run the cylinder. If it only needed to be on for an hour and half then I'd say fine, just time it to come on early morning and it'd provide enough water for a couple of showers.

I can use my E7 but if the cylinder kicks in at midnight it'll only go off at 3am when fully heated (being on so long will be fairly costly). This would be ok if the peak rate wasn't so high for boosting and running the electric heating.

In reality how long do you think this modern cylinder will take to heat up enough for a couple of showers or a bath? I have also been considering sticking with an electric shower so as all this water heating can be avoided.

Probably my worst fear and surprise is the supposed time this modern cylinder could take to heat up. The unbiased energy saving consultant felt controllability was the key but E7 combined with high peak cost isn't ideal. I have had E10 prices and they're not looking great compared to a good completely flexible flat rate.

Please help! I'm booked for a new single supply meter this coming week as well as needing decisions on connecting up the system, most of which is fitted

Thanks!

 

[flameport]

A 150 litre cylinder with a single immersion heater will take a few hours to heat from cold. The only way to make this quicker is to have a smaller cylinder, or higher power heating element(s).
Makes no difference how modern or old the cylinder is.

If on overnight, it won't be on all the time - the thermostat will switch the element off once the water is heated.

What fuel is used for the CH?

 

[silver50]

It's one of the slim electric boilers for central heating

I was told 150L cylinder which I can see theoretically is about right for a small two bedroom flat with a bath but as I was saying, didn't realise it would take so long. Limited previous experience of immersions made me of the belief an hour or so would heat it

If the cylinder was only on for say one hour, would you be not too badly off for say washing dishes/your wash basin? Does the hot water sort of go to the top of the cylinder...??!!!

 

[muggles]

The heat up time is affected by the amount of power being put into the cylinder. An immersion heater is 3kW, whether it's old or new, so you get the same heat up time as you'd have had with a low-pressure cylinder of the same capacity.

You do, however, have two immersion heaters so why not use both of them to speed up the heating? Also, if you're concerned about it being on for excessively long periods, or at times when the E7 / E10 isn't operating, why not simply fit a timer to the immersion heaters?

You'll use about one third of the capacity of your cylinder per shower, and two thirds of it for a bath, so two showers will be about the same as one bath.

 

[muggles]

Hot water does rise so you can have it on for a shorter period if you only need a bit of hot water, but it'll take a long time to react if demand changes.

Why didn't you get a cylinder that you could connect up to your boiler? It would most likely have heated up in around half an hour to 45 minutes

 

[silver50]

Thanks for replies guys

Up until a few days before the stuff arrived I thought my electric boiler was actually going to heat the tank but no! I do gather since though that it is very very common just have a direct cylinder with the electric boiler. I do appreciate though that water could be heated more quickly if it had been planned like this. The whole electric heating thing and tariffs etc is new to me and has been confusing. Faced with two horrible old storage heaters and a rusting cold tank, we were just doing our best to modernise things.

I'm not sure the energy saving guy really thought enough about my choosing exactly how the cylinder would get heated AND my need to run the electric boiler too. I'm not feeling hugely worried by the running cost of the heating in general (because the flat isn't going to be hard to heat) I'm more concerned about heating water

This has also brought up last minute thoughts on the type of shower. Not sure about mixer or electric. Electric seems a plan if it would save on water heating. A lot of this of course boils down to who will be living in the flat which is something I can't predict when it is for renting!

 

[Madrab]

If you were getting a boiler then an indirect would have been better IMO.

Though now it's direct then a timed controller for each immersion heater.

Horstmann boost controller - http://www.horstmann.co.uk/products/heating-and-hot-water-controls/boost-controls/electrisaver

1 Hour for top element for dishes/ quick hot water etc - 2+ hours for bottom element for baths etc. would be my recommendation if a single cheap tarriff is what you'll be on

 

[silver50]

That looks a useful wee controller

The electric boiler seems best worked from a programmable thermostat. That boost switch I'm assuming you might just use for top element. Any suggestions for actually timing one (or other) element?

Thanks

 

[JohnD]

use the overnight one to fill it using cheap electricity, and only use the peak-rate one if you run out of cheap hot water.

The immersion heater takes very roughly one minute per litre.

 

[Madrab]

I thought you might have gone digging about that site

Hortsmann are the better ones I've found for direct electric water heating control - try this one.

http://www.horstmann.co.uk/products.../electric-water-heating-controls/electronic-7

 

[silver50]

Thanks, no sorry I've not been home as yet, just quick checks back here on mobile.

I actually saw that one the other day when looking at controlling timing on economy 7. I then learned from that company after ringing them that on the old teleswitch you can't actually control when the heating starts/stops on the off peak.

So on single tariff I guess this switch still fine?

 

[Tibbot]

I can't understand the point of electric boilers. Heating primary water takes longer than just heating air. With combustion fuels a central heat source is essential for obvious reasons. With electric, you can have it in any room , why waste time and energy heating primaries to send to rads or an indirect cylinder. Better solution for rental flats is panel heaters (maybe c/w pilot wire & external controls) and a simple thermal store for DHW (immersions seem to last longer in primary water). 2 immersions, Horstamann timer.

 

[Madrab]

The real trouble I think you have here I guess is you have no way of understanding what the energy consumption/habits of your tenants is going to be. All electric heating/hw is never going to be economic unfortunately

E10 is great if there is someone about during the day that can take advantage of the cheaper periods to heat water etc, allows cheaper hot water during the day.

E7 is great if you shower/bath first thing in the morn as the minute you use hot water you are cooling down the water in the cylinder, there is a thermal barrier but during the day, if everyone is out, convection will eventually balance the water temp down a bit by the time they come in at tea time.

Do you have the older meter with the manual tele-switch box that gives you 2 outputs? 1 switches on at E7 times the other is peak or is it an electronic meter with tele-switched tariffs with 1 output??

Your supplier should be able to tell you when your E7 kicks in and set your timer accordingly surely?

 

[silver50]

Again thanks for replies. Yes the older meter with tele switch and two outputs. I am actually meant to be getting a new single meter this week for single tariff

My electrician was first one to say that you cant really time the E7, then a chap at Horstmann explaining that the tele switch just kicks in and starts heating the water as soon as the off peak period starts. I still don't quite understand why a timer can't be incorporated during the off peak but seemingly it can't really.

Yes you're absolutely right that not knowing who may be living at the property doesn't help this

 

[Madrab]

Of course it can be timed, once the E7 side of the electric circuit in the CU is energised by the teleswitch.
It's then exactly like any other circuit, if you have a time switch on that circuit then it switches the power on an off depending on when it's set. Used to have it in my mums old place.