Is BIGGER any better? :)

[PeedOftec]

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Hot water storage, is it better to store LOADS of hot water in a well insulated tank and keep the temperature topped up, or produce the hot water on demand, as and when required?

If the latter then I guess it means you could do away with a storage tank all together and use one of those boiler thingys that heats the water as it goes through it. Downside of this is that you need to be able to utilise "instant heat source" at the flick of a switch. (oil, gas, electric.) Obviously solar (or wood stove) cannot be utilised with ths system, or can it?

So... if you want to use solar (or wood stove) then you need some way of storing the collected energy (heat), and I would guess that would be in the form of a "hot water cylinder", "heatbank", "solar store", call it what you will.

In order to OPTIMISE the storage then the "cylinder" (I'll call it that from now), will have to be sized accordingly. I supposed it would be pointless having a 5 gallon cylinder (don't know of anyone who makes one as small! LOL) as A) the solar panel would have to be relatively small otherwise it would just boil up with a modest amount of sunlight and B) it would store enough heat/volume of hot water to just about wash the pots and no more...

On the other hand... if the solar panels were connected up to a massive 20,000 gallon "cylinder" the heat produced would be "lost" in the 20,000 gallons unless there were acres of solar panels. (Bit like pouring a kettle of boiling water in a lake!, the heat is there but dispersed throughout the lake.)

The compromise would be balancing the stored water size (cylinder size) to the hot water usage, (number of showers, baths, basins, washing machines, dish washers etc) and lifestyle, (is everybody out all day with a mad rush for showers/washing early morning and evenings or can folk get a bath/ shower throughout the day allowing recovery of the cylinder?)), balancing this with solar panel size.

In my mind I think the water usage and lifestyle primarily dictates the cylinder size, this needs matching to the solar panels and if there is no room for the required panels then the cylinder needs re-sizing accordingly? If the tank was too big then the required temperature would not be attained, too small and it may boil up. Does that sound logical?

How do I size the cylinder? Does anybody want a stab at working it out for me please? There is LOADS of roof space for panels albeit facing south/southeast. And the wood stove is rated at 20Kw but would have a relatively short firing time, ie it wouldn't be on all day, just evenings potentially.

I am looking for guidance in determining the size of the cylinder please......

Cheers guys.
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[Diyisfun]

The size of the storage tank, I THINK should depend on the amount of water you use & the cost of heating it.
If you dont use a lot & want it on demand, then it should be instant heater.
If you use a lot & can heat it cheap using solar then you need a big tank, no point having solar with a small tank.

 

[PeedOftec]

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If you dont use a lot & want it on demand, then it should be instant heater..

If cost came into it then the above yes, otherwise you colud throw lots of money at a small solar system maybe? I'm not sure of the whys and wherefores, pros and cons of either way of doing it.
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[JohnD]

I don't understand what you've got in mind

Are you intending to use a wood-burning stove or something as (one of) the sources of heat for the hot water?

Are you intending to use Solar as (one of) the sources of heat for the hot water?

Are you intending to use gas or electricity or anything else as (one of) the sources of heat for the hot water?

How much hot water do you expect to use (a) in a typical day (b) in a maximum day?

Are you just using it for washing, or do you have a swimming pool, greenhouse, conservatory or something?

Is it just an ordinary house a with a few people in it? Do you mostly have baths or showers?

Have you got a lot of money, and do you want to spend a heap of it on things that will not generate a financial return, and will save you less than you could earn as interest on your savings?

Are you interested in building something yourself? Are you competent at plumbing and wiring?

 

[PeedOftec]

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I don't understand what you've got in mind

Are you intending to use a wood-burning stove or something as (one of) the sources of heat for the hot water?

Yes.

Are you intending to use Solar as (one of) the sources of heat for the hot water?

Yes.

Are you intending to use gas or electricity or anything else as (one of) the sources of heat for the hot water?

Electric with immersion heater and standard oil boiler.

How much hot water do you expect to use (a) in a typical day (b) in a maximum day?

Good question.... there are six adults (well 2 adults and 4 teenagers!). Could be more with guests. It's a mad rush in the morning for washes/showers. Washing machine on, may be dishwasher and the same in the evening so peak requirement first thing and last thing in the day, virtually nothing through the day. There will be 2 x sinks, 4 x basins, 1 x bath, 1 x power shower (18l/min), 1 x normal shower, 1 x dishwasher, 1 x washing machine in the house so peak usage could be high. How much water?? Have a guess??

Are you just using it for washing, or do you have a swimming pool, greenhouse, conservatory or something?

Just for washing, no pool, no greenhouse, no conservatory, no UFH.

Is it just an ordinary house a with a few people in it? Do you mostly have baths or showers?

See above... it's a bungalow. "ordinary" house?.... no it's a mad house!! LOL. Could be baths and showers going at the same time.

Have you got a lot of money, and do you want to spend a heap of it on things that will not generate a financial return, and will save you less than you could earn as interest on your savings?

No bottomless pit of money! I want to future-proof the energy usage, not being dependant on one source. May go ASHP or GSHP too at some point.

Are you interested in building something yourself? Are you competent at plumbing and wiring?

Yes, I would have a crack at something myself but would rather have an expert oversee the work....

Ta.
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[JohnD]

well, as you want to use Solar and the wood-burner, you're going to have some kind of storage. AFAIK it is worth having a large store, so it will get hot on sunny days and not run out if you have a cold cloudy day.

you can add an electric or gas heater to these as well; either to top up the single cylinder, or have a solar store feeding the final cylinder.

some boilers have the ability to integrate themselves with Solar. I know Viessman do on their larger boilers. If you want to, you can have a Combi boiler feeding one or more showers, but also heating a cylinder as if it was a System or Conventional boiler (lots of people forget this, as they like to put a combi in as a quick and easy job and not install a cylinder)

 

[mickyg]

you'll probably be better off with a thermal store not a hot water cylinder, and yes it wants to be pretty big. Hard to say how big without knowing exactly what your using to heat it, what draw offs etc... sounds all a little bit pie in the sky at the moment!