Most cost effective way to heat 250ltr stored water

[jason61c]

I'm trying to run a few tests to work out the most cost effective way of heating a 250ltr water cylinder. OSO brand cylinder.

Whats peoples opinions? Has anyone tried actually working it out?

Heating the cylinder to 70deg C. Temp sensor is 10 inch from the bottom.

2 on periods 04:00-06:00 17:00-19:00
Constant heat, allowing a 5 degree drop before bringing back to temp
1 period on 04:00-08:00
Constant heat allowing zero drop before bringing back to temp

etc etc.

 

[Newboy]

Are you planing to use any of the hot water or just keep heating it?!

 

[jason61c]

Howdy

It will be used by a 4 person household. 2 adults, 2 young children. Showers AM, shared bath PM(not every day!).

 

[simond]

Since hot water heating only constitutes around 20% of your boiler's annual energy consumption, I could say that you are fiddling while your gas burns.

All thermostats on cylinders have a differential to prevent the scenario of constant heat zero drop, by the way. If I was to say that a modern cylinder may only lose, in terms of wasted energy into the nearby space, around 3Kw a day, you can see why how often it is warmed up is going to have very little influence on the gas (or whatever you are using) consumption.

Space heating, on the other hand, burns shed loads of fuel.

The answer is, of course, zoning. We've been fitting Honeywell Hometronic since 2003, and now their modern virtually identical incarnation, Evohome, has the answer, at a cheaper installation cost.

 

[jason61c]

The house is zoned for heat, upper and lower. All radiators are on thermostats.

We don't have the radiators on from May-Oct so it is a consideration.

 

[Servotech]

I'm trying to run a few tests to work out the most cost effective way of heating a 250ltr water cylinder. OSO brand cylinder.

Whats peoples opinions? Has anyone tried actually working it out?

Heating the cylinder to 70deg C. Temp sensor is 10 inch from the bottom.

2 on periods 04:00-06:00 17:00-19:00
Constant heat, allowing a 5 degree drop before bringing back to temp
1 period on 04:00-08:00
Constant heat allowing zero drop before bringing back to temp

etc etc.

That's a lot of stored H/W there Jason (maybe fitting a smaller cylinder would be the best way to save a few quid).
Out of interest what type of boiler have you got?

 

[simond]

Not running the rads in the summer is normal, so they are still 80% of your gas bill.

Heat loss from your cylinder will be costing you around 20p a day in the summer. Heat loss = Heat required to heat it up again.

 

[JohnD]

There is an efficiency loss if you keep running the boiler for short periods, e.g. to top up the cylinder every time you run a hot tap, beceause you are heating the boiler and pipes. Settjng the timer to heat it before bathtime will be a bit more economical. It is a big cylinder and will probably have enough to last the whole day. If not it can be timed to heat up again before shower time. An hour will be enough.

As said, HW costs are quite small. If you look at the gas meter it might use less than a metre a day in summer.

 

[jason61c]

We do use a lot of hot water and haven't finished expanding yet.

It's heated by an effecta biomass boiler, 35kw. i think one two hour period to 65 deg will work out the best during water only heat times.

 

[simond]

Thats quite refreshing, someone on biomass not trying to use MORE fuel

 

[Agile]

250 li is what I would say is correctly sized for four people, 50 + ( 4 x 50 ) =250.

If reheating with the Biomass then its a good idea to establish long burn times so perhaps a wider differential on the cylinder temperature might be a good idea.

However, its not advisable to heat above 60 C unless you have a blending valve on its output.

Tony

 

[Biggles..]

Why would you want 65 or 70 deg stored water?
Reheating a 250l cylinder from cold is around 35mins, why would you decide you want a 2hour reheat period if your trying to be as efficient as possible.
Current data puts hot water useage at about 35lpp per day, therefore you'll never reheat your cylinder from cold thus the reheat time will be significantly less than the 35mins.
Hot water for showering is generally around the 43-45deg mark, you wouldn't get in a bath of 60 deg water, with a new build requiring a blending valve anyway (agile-you blend at point of use not source!!!)
The body doesn't differentiate the temp difference once water is above 45, all the brain says is that the water is too hot!

60deg, 30mins-45mins burn once a day unless your house is used liked a rugby club changing room, would do your cylinder in summer.

 

[jason61c]

Its got a blending valve fitted, preset to 60deg C.

The trick is to try and tie the heating of the boiler with the water, the boiler has a 180ltr water jacket, as that cools it has to heat up to send 75+deg water around the water coil.

Once winter comes and the heatings on it should cost nothing to heat the water.

 

[Steelmasons]

Once winter comes and the heatings on it should cost nothing to heat the water.

It will use 'x' amount of gas to heat the water , boiler will be on for a longer period when HW/CH is called for....of course you will pay for it...

Some size the boiler for hot water recovery rate which can be as much as 25kw allowing nothing for heating....

 

[Dan Robinson]

Biomass dude