One pipe system

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Hi, I have an installed a new radiator on a one pipe system, It is directly above the bypass and doesn’t have any bends. The inlet side pipe is red hot yet the outlet is approx 30% cooler. The radiator also feel cooler on the outlet side. I have checked for air and the pressure is 2 bar.
lock shield fully open and trv on inlet side. Any thoughts would be great.
Thanks
 

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The other radiator I have is exactly the same set up and is working ok.
 
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The inlet side pipe is red hot yet the outlet is approx. 30% cooler.
That sounds normal to me for a one pipe system. The pump circulates water around the one pipe loop, but the pressure it exerts on the radiator inlet and outlet connections is pretty much identical (as they are sitting atop the same pipe) therefore the pump doesn't actually push much water through the radiator, and instead it relies on natural gravity circulation of hot water rising cool water falling. It's a slow process compared to water being pumped through the radiator so the water remains in the radiator longer and looses more heat. The bigger the radiator (ie the higher the output) the greater the difference between flow and return temperatures, which sounds like what you are seeing.

To assist the process with a one pipe systems sometimes they have higher inlets. Although I doubt that would be possible or desirable in your case.

abc.jpg



As has been said, because they are designed for two pipe systems some TRV's and radiators are require the pressure that a two pipe system provides, and so they don't work too well on one pipe systems due to the lack of differential pressure. But from my experience of one pipe systems, the temperature drop you are seeing is fairly typical.

As the loop progresses around the property the cold water from the earlier radiators is deposited back into the one pipe feed to the others so as a result they are cooler, it may be that your other radiator that gets hotter is earlier in the loop.

Also, in one of your photos, the pipe looks to be flattened where it passes through a narrow slit. I'm sure it's an optical illusion, but if it is squashed that won't help.


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Good morning - I have a one pipe system and taught myself quite a bit about it including facing problems with adding a new radiator

Can I ask
  1. What size pipework do you have in the system and to the radiators
  2. What boiler do you have
  3. What size pump do you have
  4. Is it an open vented heating and hot water I assume
 
That sounds normal to me for a one pipe system. The pump circulates water around the one pipe loop, but the pressure it exerts on the radiator inlet and outlet connections is pretty much identical (as they are sitting atop the same pipe) therefore the pump doesn't actually push much water through the radiator, and instead it relies on natural gravity circulation of hot water rising cool water falling. It's a slow process compared to water being pumped through the radiator so the water remains in the radiator longer and looses more heat. The bigger the radiator (ie the higher the output) the greater the difference between flow and return temperatures, which sounds like what you are seeing.

To assist the process with a one pipe systems sometimes they have higher inlets. Although I doubt that would be possible or desirable in your case.

View attachment 328369


As has been said, because they are designed for two pipe systems some TRV's and radiators are require the pressure that a two pipe system provides, and so they don't work too well on one pipe systems due to the lack of differential pressure. But from my experience of one pipe systems, the temperature drop you are seeing is fairly typical.

As the loop progresses around the property the cold water from the earlier radiators is deposited back into the one pipe feed to the others so as a result they are cooler, it may be that your other radiator that gets hotter is earlier in the loop.

Also, in one of your photos, the pipe looks to be flattened where it passes through a narrow slit. I'm sure it's an optical illusion, but if it is squashed that won't help.


View attachment 328368
What therefore can you suggest for the addition of a new radiator onto the system ? Turn up pump speed ?
 
It could be tried, but as the pressure would increase by the same amount on both the radiator inlet and outlet, I can't see that it would offer much, if any improvement on the circulation of water through the radiator itself. However, increasing the pump speed would mean more water was flowing through the one pipe loop and increase the temperature at the end of it. Assuming that it's presently significantly lower than the start. Much depends on the demand on the rest of the loop. Obviously there would be less temperature drop with 5 small single radiators, more drop with 7 bigger ones.

A possible downside with a condensing boiler is that the return water to the boiler will be hotter and if so, its efficiency will be less. A properly designed one pipe system would take the temperature drop around the loop in to account and increase the size of the radiators relating to their location on the loop to suit.

I have a one pipe system and taught myself quite a bit about it including facing problems with adding a new radiator

Is your experience of the % temperature drop across the flow and return pipes of your larger double radiators similar to that of the OP?
 

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