radiator query

[dexion]

Untitled

• dexion
• 14 Aug 2009
• 1

thanks for your help on this guys.

on the left and right of the of the pic you will see the vertical pipes which join to the rad. further left than the left side rad feed pipe, there is another underfloor pipe (going down to bottom of the picture) which has travelled the length of the room (dont know where its come from).

between the pipe which connects to the right side of the radiator, and the first joist, there is another pipe going down the picture (parallel to the one discussed above). these two pipes are joined by the pipe which runs horizontally across the picture. i dont understand how any water is pursuaded to flow through the radiator as there is no pressure drop.

i understand the analogies with an electrical circuit and whether the radiators are in parallel or even in seires but the ones in my house simply look like they are shorted out!

 

[D_Hailsham]

Wierd!

The only thing I can suggest is that you trace all the pipework and rad connections from the boiler, draw a diagram and post it here for us to gawk at!

Big task; but you are renovating the house, so there won't be any carpets to lift.

 

[dexion]

OK - half way there!

the upstairs has the rads in series and each rad has a pipe as in the above photo which connects across the inlet / outlet of the rad. the suspicious looking extra pipe on the right side of the photo (heading down on the pic) actually is a tee to feed the rad in the bathroom which is in parallel with the rad in the photo (and also of course in parallel with the shorting pipe across the rad!). other than that the other 4 rads upstairs are all in series. i cant recall whether any of the rooms had colder radiators (which might be expected of the last one in the series chain) but the upstairs was never cold, possibly because of heat rise throughout the house generally.

the furthest downstairs rad from the boiler however was always just luke warm and the room its in (which also has a second large radiator which did get hot) would never get warm enough in winter. i haven't yet taken up the floor boards and this will likely be impossible as its a laminate floor on top of a concrete floor. unfortunately, this particular room is the one which prompted me to look into the whole thing anyway. assumming the downstairs is also series connected what can be done to make this last downstairs rad get hot enough to warm the room?

thanks for the help by the way.

 

[tamz]

One pipe systems work with the water pumping around in a loop (main circuit) to and from the boiler.

The flow and return pipes to the radiators from the main circuit should be minimum of 15mm, kept as short as possible and rise slightly to radiators. Swept tees should be used for branches off main circuit.

The flow of water through the radiators is mainly by gravity circulation and is not effected by pump speed. (This is why they are slow to heat). Turning up the pump speed will not make the radiators heat better.

The radiators will be progressively cooler around the circuit although once up to temperature this should not be too noticable.

If std Trv's are used you will have problems. There is too much restriction on them. Use valves designed for one pipe system use. (All the major manufacturers do them).

If a "balancing" valve is placed on the circuit between radiator tails this is creating a blockage and forcing the water to be pumped through that radiator. This will have an effect on the performance of the rest of the system, more so if that radiator shuts down.
If the pipe between the radiator tails is cut off this will mean that radiator is then part of the main circuit. It will work fine but cannot ever be controlled or turned off.

One pipe systems are fine if they are installed (altered and adapted) properly.

Most problems come about by people altering and adding to them and not understanding the basic principles of how they operate.

 

[dexion]

thanks tamz that all makes sense except the gravity part, what incentive is there for hot water to rise into the radiator and the cold water that's already in the rad to drain out? the hot water in the pipe will be the same temp at both connections to the rad. or is the fractional difference (lets say 0.1 deg C) all thats required to create the flow?

thanks

 

[TicklyT]

The gravity circulation is convection currents within each radiator. Hot water is slightly lighter than cold water, so it rises through the inlet to the top of the radiator, then falls as it cools, eventually reaching the outlet, where it mixes with the hotter water bypassing the radiator. That's why the uphill gradient of the pipes to the rad. is necessary.

Radiators are often connected with the inlet at the top and outlet at the bottom to make the most of this thermosyphon action.

Single pipe systems are still very common in large commercial installations.

Old single pipe heating systems were driven entirely by thermosyphon action, not needing any pump at all, but they needed much larger pipes to achieve adequate flows.