Any plumbers / heating engineers in here?

[berendd]

Ok so sizing the boiler is fairly simple calc (volume of rooms, insulation, windows, room type, local weather conditions plus some, temp needed) but how do I size the thermal store so I can do one burn (with refills if needed during the evening so that in the morning it will release enough heat to warm the house back up?

The more I look the more questions seem to apear.

Justme

you'll need a certain amount of power for heating, say 8kW continuously

let's say your stove does 24kW so you can store 16kW's of it... you can than have it going 33% of the time...

33% of the time you will have to have the fire going, let's say you do this 8hrs a day to heat the house for 24hrs..

you'll need a buffer of 16kW*8hrs=128kWh's

now you will have to decide for you buffer temperature which is depending on the feed temperature.. let's say 70 degrees here and let's say 40 degrees when it's empty

you'll have 30degrees temperature difference to store heat in..

given E=M*C*T1-T2
M=E/(C*dT)

where E=energy=128KWh=128*3600=460800kJ
M=mass
C=specific heat: 4,2 kJ/degree*kg (for water)

so M=(128*3600)/(4,2*30)= 3 657kg's of water so around 3 cubic meters


you could include heat loss in this, but since your storage is likely to be in your basement or at least in the house, the lost heat will be added to the house...

change the values above to realistic values for your situation..

 

[rtbcomp]

why a couple?

No particular reason, would depend on size and output of boiler, but you wouldn't want to risk a closed TRV with the fire burning and the pump off.

as opposed to a fused spur? gosh thats forward thinking

I don't know whether or not the socket was on the ring main or a spur, doesn't matter really for practical purposes as long as the fuse in the plug is appropiate.

 

[Haze]

No particular reason, would depend on size and output of boiler, but you wouldn't want to risk a closed TRV with the fire burning and the pump off.

most houses will have one radiator to act as a bypass, i see no reason for adding another.

 

[Justme]

most houses will have one radiator to act as a bypass, i see no reason for adding another.

So if the boiler is going full wack (30 KW in my case) one rad can keep it to a safe level? NO. On a normal system if the power goes of so does the boiler. The one rad is just incase the boiler/stat calls for heat when all the TRV,s are closed to stop cavitation of the pump & over heating of the boiler. On a wood boiler the heat does not stop with the power so it can over heat if the pump stops if you dont have enough of a heat sink.


Justme

 

[Justme]

Hi berendd,

Thanks for that.

DOnt realy know where to start with changing those numbers as my situation is far removed from that example.
My calcs (using online calcs but they are designed for standard boilers) say I need about 30kw of heat (current oil boiler is 120,000 btu which copes easily & does not come on much of for very long once warm). So we have been looking at 30kw wood boilers. We have the heating on for about 20 mins in the morning & 30-40 mins at night. Toped up with the room wood fire which heats a lot of the house & the rayburn cooker which also gives out heat.

Justme

We currently (in winter time) have the heat on for about 20 mins morning & night but topped up with the wood room fire for a few hours.

 

[Haze]

So if the boiler is going full wack (30 KW in my case) one rad can keep it to a safe level? NO. On a normal system if the power goes of so does the boiler. The one rad is just incase the boiler/stat calls for heat when all the TRV,s are closed to stop cavitation of the pump & over heating of the boiler. On a wood boiler the heat does not stop with the power so it can over heat if the pump stops if you dont have enough of a heat sink.


Justme

ah yes of course, im not thinking of overheat :S

 

[Justme]

ah yes of course, im not thinking of overheat :S

Thats the big danger with wood fired. Once its lit you are commited. Ok you can shut the air dampers down etc but its still going to burn.

Justme

 

[berendd]

you could try and fit a water buffer in the attic fire up the buffer and pump it from there to the rads..

dunno what kind of house you live but you will need a fairly solid construction..

 

[berendd]

any news on the question?

 

[Justme]

I am still looking at all the options./ Dont want to spend £2k ish to find it dont work.

 

[syborg]

i do a bit of plumbing and boiler inspections now and again.

id say 10 feet is about right, there is a ratio for height and pressure.aint got a clue what it is without making phonecalls,lol
id say imagine a header tank in ya loft.
or your heating system expansion tank.

im sure the pressures wont be too much different for oil or gas boilers.

hope this helps,

syborg.