if you think about it fellas it's a bit like forgetting the spreader tube on the old twin entry valves
pipes get hot rad don't
pipes get hot rad don't
2 metre long rad won't heat up
- Thread starter DIYedboy
- Start date
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TBOE is quite common in commercial properties with steel pipe, and it actually improves the heat output from the radiator.
Certainly shutting the LS valve should improve the circulation, but with the added problem, it will take longer to heat.
Certainly shutting the LS valve should improve the circulation, but with the added problem, it will take longer to heat.
That's putting the cart before the horse. You achieve the correct temperature differential by getting the flow rate right, which you do by getting the differential pressure correct. But as most installers do not carry the necessary kit to measure the flow rates and differential pressure across the radiator, they just look at the end result, i.e. the temperature differential.
It's different in commercial installations where balancing is done by measuring flow rates and differential pressures and installing balancing valves to control the differential pressure in the many branches of the system.
Not strictly correct. It assumes that the flow temperature does not get any lower. A 1000W radiator (at 75/65/20, i.e 10C differential) will produce 1070W at 75/70/20, but only 915W at 70/65/20 (both 5C differential).
The problem then is the flow rate and pipe sizes. The flow rate of a boiler producing 15kW at an 11C differential is approx. 19.5 l/min, which can be easily carried by a 22mm pipe. But if the differential was 5C the flow rate would be 42.9 l/min, which would require a 35mm pipe. Connections to rads would be 22mm. The pressure loss around the system would increase, meaning that the pump would have to be much larger.
The 20C differential of the modern condensing boiler does the exact opposite: smaller pipes required, lower pressure loss and consequently a smaller pump.
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Oh, is it? With the last boiler I installed, there were M.I. specifying a set flow and return temperature, nothing about flowrates through rads, or any of that.
What did the M.I. of the last boiler you installed require, any flowrate or flowspeed in particular?
I wouldn't expect the MI's to say anything about radiator flow rates as the flow rate will depend on the radiator output.
The flow rate through the boiler is not the same as the flow rate through the radiator. A 15kw boiler running with an 11C differential will have a flow rate of 19.5 litres per second. The flow rate through a 1kw rad with an 11C differential will be 1.3 litres/second.
Setting the same differential across a radiator as across the boiler is just a convention. Provided the correct differential is maintained at the boiler, you can use any differential you like at a rad; though the output will vary with differential.
OK! and I promise not to say anything about Tour and Anderssen's Balancing Manual or their Computerised Balancing Instrument.Dave, Just don't mention DRV's and control stations.
Water goes out the boiler, through the rads, back into the boiler. If the water going through the boiler is not the same as that going through the rads, where is it going?
And if you don't expect the M.I. to mention anything about flowrates, what do you expect them to mention? Or rather than expecting, what did the M.I. of the last boiler you installed specify?
The system has nothing in common with the boiler other than it heats the water.
Flow rates, pressure differentials, etc etc are not usually important on a domestic install.
And then along comes the problem rad and no-one knows what to do, other than the obvious and easy way out which is to repipe it BBOE.
Flow rates, pressure differentials, etc etc are not usually important on a domestic install.
And then along comes the problem rad and no-one knows what to do, other than the obvious and easy way out which is to repipe it BBOE.
I think that EVERYONE here except the OP and, rather unusually, D. Hailsham know EXACTLY what needs to be done.
Either BBOE or TBOE !
Tony
But we are talking about a two-pipe system, so all the water does not go through each radiator. Even on a one pipe system, some of the water is diverted to bypass each rad. If it wasn't, shutting off one rad would shut of all rads.
Please don't misquote me.bengasman said:
What I am talking about is all set out in this diagram. The boiler and rad sizes have been selected to make the maths easier.D_Hailsham said:
And the answer to Ben's last question?
That diagram would be easier to assimilate if you quoted the flow rates in litres per minute.
I think that you are making an assumption that the flow rate from a boiler varies. In a few it does, but most are still fixed or stepped pumps.
All boilers vary their power output and the system flow rate is usually constant.
As I said ages ago the flow through a rad is set to provide the temperature differential the boiler requires.
Tony
That diagram would be easier to assimilate if you quoted the flow rates in litres per minute.
I think that you are making an assumption that the flow rate from a boiler varies. In a few it does, but most are still fixed or stepped pumps.
All boilers vary their power output and the system flow rate is usually constant.
As I said ages ago the flow through a rad is set to provide the temperature differential the boiler requires.
Tony
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