Sizing a Thermal Store

[amark]

Can anyone explain the theory on sizing a thermal store?

I have an enquiry for a solar compatible thermal store. I know about sizing solar but not thermal stores.

The customer wants to link in a solid fuel stove at a later date and this seems to be the best option.

Any help would be greatly appreciated.

Cheers,

Mark.

 

[carryoncamping]

It's probably long past the moment you needed an answer, but for the benefit of anyone searching in the future here's a reply.

Try this formula:

Energy= Mass x Temperature rise x Specific Heat Capacity of Water

- Mass is volume of thermal store in litres eg. 200 litres
- Temperature rise is the thermal gain of the store, eg. Temperature starts at 20°C and by the end of the day finishes at 45°C so temp rise would be 25°C
- Specific Heat Capacity is a constant, i.e. 4.18 KJ/KG/°C

Plugging that into the equation you get:

Energy (KJ)=200 x 25 x 4.18
=20900KJ convert to KWh by dividing by 3600
5.8KWh

 

[Agile]

Be aware that thermal stores have considerable control problems with multi fuel heat sources.

Their capacity when heated by gas boilers is less than in the past if they are limited to about 70 C to maintain boiler efficiency.

Solar and solid fuel can heat a store to far higher temps and so the use of the stored heat has to be carefully controlled with mixing valves.

Tony

 

[ALEC1]

what you really want is buffer vessel, which performs a similar function


thermal stores rely on very high temperature usually around 80c which solar in the uk will rarely supply....

you are much better off with a twin coil cylinder...or even a triple coil one depending on heat sources...

 

[mysteryman]

Using a thermal store [or buffer vessel] compromises the best possible efficiency of a gas powered heating system, and it is not worth having one for the occasional use of a solid fuel appliance. You can lose more through inefficiency than you gain from solid fuel, even if it is free.

 

[snb]

what you really want is buffer vessel, which performs a similar function


thermal stores rely on very high temperature usually around 80c which solar in the uk will rarely supply....

you are much better off with a twin coil cylinder...or even a triple coil one depending on heat sources...

with your normal understanding of WC i would have thought you would have known more about thermal stores!!

There are a number of thermal stores out there today which are designed to operate at much lower temps. These have come about due to the increased use of heat pumps.

I have fitted a number of these thermal stores but have them connected to oil boilers, solar hot water and woodburners.

They work very well and only require store temp of 55 plus or though 60 plus obviously gives more production.

I also have 2 customers who have solar PV with dedicated out put from their pv controller which is connected to a 2kw element that only works when it is supplied with solar electric.

 

[ALEC1]

well you are talking bout buffer vessels...as in reality the only difference between a thermal store and a buffer temperature is the temperature that the water is stored at to achieve DHW...

somewhere I did read about the difference interns of energy stored, thermal stores store specific heat and buffer vessels store latent heat...but It wasn't that clear in the article...

certainly with manufacturers like gledhill and elsan there is a need to differentiate between the two...

 

[Norcon]

The OP's customer would be better off with an unvented cylinder.

 

[snb]

The OP's customer would be better off with an unvented cylinder.

Would have to disagree.

THe op's customer wants to link a woodburner albeit at a later date.

Main advantage of thermal store or a buffer vessel is that when the customer wants the rads to come on the woodburner often has to be flat out to be able to heat all the rads.

If the rads take the heat out of the buffer vessel or the thermal store it means the woodburner can cope without having to be at max output.