In a sealed central heating system, the pipes leave the boiler i
22mm......at which stage do you reduce the pipes down to 15mm??Please help, no one seems to know the answer and its getting very col in our house!
Wil
-- Will
The top whack heat carrying capacity for 15mm is about 6kW. So you can only use that where the total load on it is that or less... (and since you ought to be designing for lower flow/return temps to get the best results from condensing boilers it would make sense to be a little more conservative.
A generally "safe" rule of thumb would be to run a backbone feed and return in 22mm, and then string each rad between the backbone pipes in
15mm.
Don't forget that in a new design, the normal thing for a condensing boiler design should be to work on the basis of 70 degree flow and 50 return. This means that pipe sizes don't need to be as great as for
82/70 from a conventional boiler.Radiators need to be larger, of course, to exploit this behaviour.
Agreed, although it's wise to use the application note from the Copper Development Association web site.
In Scandinavia it is 60 - 40.
au contraire, it means your pipework needs to be bigger.
NT
Technically you are mistaken. Its the temperature drop between the flow and return that determine the energy delivered. As the drop is 20C (rather than 12C) the pipe is delivering more energy for the same flow.
Rule of thumb is three radiator on 15mm. As with all rules of thumb apply common sense and dead reckoning beforehand and if all else fails do calculations.
Nope.
Energy transfer is directly proportional to mass (of water in this case) multiplied by temperature rise or fall multiplied by specific heat.
Since the temperature fall is 20 degrees (sometimes even more) rather than 12, for the same amount of energy transfer, the mass of water is less, the flow is less and therefore potentially the pipes can be of smaller diameter or if of the same diameter have a greater heat carrying capacity.
Sometimes people confuse the issue of lower temperature implying lower heat output from the radiators. This would be true if the original radiators having adequate output for a mean-water-to-air-temperature of 55 degrees (i.e. 82/70) were used. In this case, when it's cold, the boiler would of course modulate up to create these temperatures in order to satisfy the room thermostat or TRVs. However, if the radiators are part of a new design and are sized to suit the lower MWTA of around 40 degrees, the flow will indeed be lower.
So 10 kW for the 15mm pipe limit _provided_ the radiators are installed to an 70C/50C spec. Sow we are perhaps looking at 5 radiators for the rule of thumb. However since you will be installing all new you are going to have to do some calcs anyway so you'll know what's needed.
Also keep an eye on possible future developments so if a loft conversion might be possible bear that in mind.
Possibly, although wet systems with a boiler are much less common in domestic use that electric heating.
For example in Sweden:
The most common are district heating in the case of multi-dwelling buildings in urban areas.
For individual dwellings, the main forms of heat are electricity, oil and biomass and to some extent heatpumps.
Natural gas is not big in Sweden or Norway (in terms of use) although is more so in Denmark.
Denmark is 60 - 40. The Russian natural gas pipeline will stop in Sweden, so it may be common there in years to come.
It is in the south and up the west coast as far as Goteborg where there is a supply brought in from Denmark, but not on the east side.
I could imagine industrial use and perhaps as a fuel for district heating stations if the price remains reasonable, but AFAIK, there is not any notable gas distribution infrastructure in mid-Sweden as far as domestic premises are concerned.
Outside Scandinavia in Finland, there is more substantial use of natural gas (although again not for domestic use) and this comes almost entirely from Russia.
There is also the Mid Nordic gas pipeline project, under discussion, which is intended to distribute natural gas from the Norwegian fields across north central Sweden and into Finland.
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