Radiator installed below single pipe circuit - will it work?

[john37]

Hello

Does anyone know if a radiator/towel rail will work on a single pipe system if it is installed below the pipe work? I.e. if the pipe work is higher than the top of the radiator.

 

[erj]

sorry it wont work hot water rises that's the only way a one pipe system work

 

[john37]

Thanks erj, I guessed so.

The single pipe loop runs in the suspended ceiling. Will it work if I extend the loop down to pass below the towel rail and connect the towel rail to it using short vertical tails?

 

[erj]

yes

 

[newcastle phill]

Is the system fully pumped

 

[erj]

I have never seen a fully pumped one pipe system

 

[newcastle phill]

They exist lol.

 

[stevetheplumber]

dont think ive seen an unpumped one on domestic other than partial heating in bungalows

 

[newcastle phill]

If the systems pumped it will work to some degree

 

[john37]

I'll explain the system we are installing, grateful for any help.

In a new conversion we are plumbing 6 bathrooms and 2 kitchens with DHW on a secondary return loop pumped on the return by a small Grundfos Comfort circulating pump (UP-15-14BA PM(80) - 97916757). The pipe from the unvented DHW cylinder is 28mm, reducing to 22mm and finally 15mm for the final return to the pump after the last tap off.

Half way through the install we decided to add towel rails in each of the first and second floor bathrooms running off the DHW circuit. There are no radiators in the property, only UFH. I'm proposing to use JIS Ashdown 520 stainless steel towel rails. These are rated at 733W off a normal radiator circuit (delta T 60 deg C)...I reckon we might get about half that output from a DHW loop at 55 deg C (delta T 35 deg), which will be fine for the ensuites to supplement the UFH, and with the advantage that they will work whenever the hot water circuit is on, throughout the year.

One problem is that two of the towel rails are below the DHW loop and so no heat can enter them because there is no convection. One possible solution might be to cut into the DHW loop and extend it so it runs underneath the valves of both these towel rails. Erj helpfully suggests this should work in principle. Is there any other solution without running a separate circuit for the towel rails?

Other potential problems:

1. I'm hoping to use JIS Streamline TRVs for the towel rails. Could these work on a DHW loop?

2. The Grundfos circulation pump has a max head of 1.4m and max flow rate of 0.6m3/hr. It works fine to keep the DHW loop hot at the moment but that's without the towel rails installed. I guess it may be too small. The maximum total heat output of the 6 towel rails at 55 deg C average temperature would be approx 2,250W (6 x 375W). Does anyone have a link or details of the calculations for pump sizing?

 

[chris watkins]

You are opening a big expensive can of worms with this one.

Why do you need to supplement the UFH ? if it is just to warm / dry the towel then this could be done using the electrical option heaters.

Have you checked to see if the Ashdown 520 stainless steel towel rails are suitable if heated by secondary hot water rather than primary (heating) water? just because they are s/steel will not make them immune from scale, are you in a hard water area ?

Comfort auto adapt pump will not be big enough & with it controlling its own stop starts may not be what you want with the heating of the rails.

Pump what need to be sized to suit the installed index circuit.

Do you have just one secondary loop or does it branch to each floor or area ?

 

[john37]

Thanks for your reply, Chris. My responses to your points:

We need to supplement the UFH because much of the floor areas in the ensuites will be taken up with shower trays, sanitary ware/units. Also we need to dry towels because there may be one or two people in each bedroom serviced by its ensuite.

Good point about scale, I'll check with JIS. Their towel rails are guaranteed for 25 years
but they won't be any more immune to scale than the rest of the fittings fed by the DHW loop. We will have a "scale buster" type of conditioner on the cold water supply, and probably a second one after the circulating pump before the hot water returns to the cylinder, but who knows how well these water scale inhibitors work? We are in a hard water area, Thames Water. The temperature will be much lower than a radiator circuit which should help, but of course we can't add inhibitor. If we hold max temp to about 60 deg maybe not too much of the problem (?), no worse than a combi secondary anyway, I guess.

The Comfort pump I would use in its temperature control mode, not Autoadapt. It would therefore be on whenever the DHW temperature in the loop drops below the target temp (50 deg?). The pipes of the loop are being insulated with 30mm thick phenolic foam (conductivity 0.025 W/(m.K)). At 60 deg C I estimate the heat loss at less than 6kWhr per day, even including the towel rail loop extensions and tails.

Not sure what you mean by "Pump what need to be sized to suit the installed index circuit" please can you explain?

There is only one secondary loop.

 

[erj]

John empty you message box so I can send you a message you ERJ

 

[john37]

Thanks erj, done. Sorry I thought I had emptied it. John

 

[chris watkins]

Thanks for your reply, Chris. My responses to your points:

We need to supplement the UFH because much of the floor areas in the ensuites will be taken up with shower trays, sanitary ware/units. Also we need to dry towels because there may be one or two people in each bedroom serviced by its ensuite.
You shouldn't need to if UFH is designed & used correctly as the whole thermal mass of the floor will be heated by the rooms around it, with warm air being drawn in from adjacent rooms when the extract is on.
Towel drying via electric elements in the rails, why not?

Good point about scale, I'll check with JIS. Their towel rails are guaranteed for 25 years
but they won't be any more immune to scale than the rest of the fittings fed by the DHW loop. We will have a "scale buster" type of conditioner on the cold water supply, and probably a second one after the circulating pump before the hot water returns to the cylinder, but who knows how well these water scale inhibitors work? We are in a hard water area, Thames Water. The temperature will be much lower than a radiator circuit which should help, but of course we can't add inhibitor. If we hold max temp to about 60 deg maybe not too much of the problem (?), no worse than a combi secondary anyway, I guess.
None of the water conditioner work, it is not so much the scale but the oxygenated water that will be a problem depending on the grade of s/steel used it can still be effected but it is the accumulation of air in them that would see them stop working unless they are fully vented.

The Comfort pump I would use in its temperature control mode, not Autoadapt. It would therefore be on whenever the DHW temperature in the loop drops below the target temp (50 deg?). The pipes of the loop are being insulated with 30mm thick phenolic foam (conductivity 0.025 W/(m.K)). At 60 deg C I estimate the heat loss at less than 6kWhr per day, even including the towel rail loop extensions and tails.
That seems very low for the losses from the rails as well, your hot water will need to be no all day to make these up & stop the system dropping below 60 - 65 flow / 55 return.

Not sure what you mean by "Pump what need to be sized to suit the installed index circuit" please can you explain?
What I meant is that the circulator would need to be sized correctly as it will now need to over come the frictional resistants from the towel rails & pipework as well as supplying the correct amount of water as this will be carrying the heat now needed.
There is only one secondary loop.

Sorry for the delay in getting back to you been away for a couple of days.