Hi,
I'm hoping to redo my old CH/DHW system. I like the idea of a heat bank; the best place for me would be under a worktop near the wall-mounted boiler in the kitchen.
I've only found one suitable heat bank for this location:
Does anyone know of any other under-the-worktop models it would be worth looking at?
Cheers,
Steve
location:
Mmmm, around £1000 eh!
I feel sure that a certain person will pop up with instructions on how to build your own heat bank with an empty oil drum and the guts from an old boiler for about 25 quid.
One important thing to look at here is that by virtue of the size of an undersink unit, the storage capacity will be quite small. Normally, a heat bank stores water at 80 degrees as opposed to a conventional DHW tank storing it at 60 degrees. The impact of that is that 1.3x the volume of hot water will be produced before the stored energy runs out. So one comparison to make is whether the proposed store is less than 3/4 the capacity of your current cylinder. If it is much less, then tread carefully.
The boiler will begin to reheat the store as you use water. The effect of that will depend on the boiler output. However, once the store is emptied, the rate at which it will be possible to use HW at a given temperature will reduce. You can look up the specs. of equivalent output combi boilers to get an idea of what the final output will be.
Thanks for the suggestions chaps. In response to a couple of your comments:
- I am intending to DIY everything myself except the (gas) boiler. However I'd not considered a DIY heat bank, but it sounds like a possibility if I can get a suitable size and shape of tank that I can properly insulate; I'll definitely consider this.
- The unit would fit under a worktop where there would normally be a cupboard (rather than under the sink) and could easily be a very large tank.
Steve
Consider two combi boilers. Highly cost effective. They can be split to do separate taps and showers, so does not interfere with the others. Also one doing upstairs heating and one downstairs. The can be combined to fill baths quickly.
You don't know what you are on about. The unit the OP was looking at "combines the output" of the boiler "and" the heat bank.
How many baths, showers etc?
On the contrary. You have been reading and swallowing datasheets on web sites again.
That's marketing nonsense. The system will still be limited. With the store fully charged the boiler begins to add heat back once it fires. However, the store will still be losing heat energy at the rate of that required to heat the water minus the rate produced by the boiler.
So for example, if 100kW of heat is required to be transfered to heat the water and then 30kW is supplied from the boiler, the net loss is
70kW. These are typical figures for a practical system. The 30kW will lengthen the time before the store empties, but won't prevent it happening. Once it does, the flow rate for the same water temperature will be only 30% of the original when the store was full.
True, but do compare the volume of the store with that of your existing cylinder before committing yourself.
You are thick.
You are getting thicker.
er...yep.
So if it takes 100kW to fill bath and the boiler can add 30kW of this then only 70kW of heat need be stored making the storage vessel smaller, and small enough top fit under a worktop. This is easy to understand.
He can have a square heat bank.
Not by you. The power output solely determines the rate at which energy can be transfered to the water, and hence the temperature rise for a given flow rate. The issue is for how long will the store be able to supply this rate.
You can't store 70kW of heat. The kW is a measure of power, not of energy.
The contributing effect of the boiler also applies to a conventional cylinder. That may be a little more for a direct heatbank than for an indirect coil cylinder, but it is not correct to suggest that the phenomenon is exclusive to the heatbank. That would be misleading.
It is true, as I said in the first place, that a heat bank can store
30% more energy than a conventional cylinder of equivalent size. Therefore, obviously one can have a store only 3/4 of the size for an equivalent output.My point was that even a full appliance space under a worktop will only accomodate a limited size of store. One should take the capacity of the proposed store, multiply by 4/3 to be able to determine the equivalent size of conventional cylinder that it can replace. Whether that is adequate will depend on the pattern of use.
It's important to point out that while heatbank technology is useful, it is not magic, can't get a two litres from a one litre pot and certainly can't defy physics. Despite what it says in glossy brochures and on web sites.
Matt, I just explained it to you. Your thickness got in the way.
Nope. The heat from the boiler goes directly into the DHW plate heat exchanger in this heat bank. With cylinder the heat build up is slow as it is indirect and heated not at the very top of the cylinder.
Unless a cylinder is heated directly then it will be the same
About right.
Nope. The cylinder stores 30% more energy supplemented by the boiler, say
30kW.
A square vessel even more.
Matt, you need to learn some sums.
Isn't it about time you went to night school and learnt some basics? Far better than wasting your time down the pub.
Please eff off you are a total idiot.
Well this 'idiot' understands the difference between energy and power so I wonder what that makes you? Apart from a pratt, obviously.
BTW, still waiting for that visit from your policemen friends. Or have you conveniently forgotten that episode from your life of fantasy?
Irrelevant. The issue is how long will thre be a supply of energy from the heat bank as a result of what has been stored.
The kW is not a measurement of energy. The cylinder stores 30% more energy. It's irrelevant for comparison purposes to include boiler contribution because that happens with a conventional cylinder as well.
The additional pump, heat exchanger and controls all have to be accomodated.
You mean the kind where kW are a measure of energy?
That would be kind of pointless. Something more approximating a cube would be more useful - it would at least be able to store some water then.
With heat bank the useful hot water from the boiler goes pretty immediately to the taps. Does not happen with a normal cylinder and coil as most heat rises up by convection.
Gosh. He is getting it. Nah he isn't.
kW/hr. Gosh
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.