Underfloor heating pump and blending help

[Tadge]

Hi all, you help is needed. Call me stupid if I'm missing something obvious. Regarding underfloor heating pump and blending assemblies. I have a few questions.

I'm replacing my entire sytem with grant oil boiler and pressurised indirect solar cylinder, there will be mainly radiators but the kitchen 6m x 6m (as I am putting a new screed floor down ant it will be covered in tiles) will have UFH wet system.

Q1, if I want the UFH to run only when the heating is on, why cant it run off the boiler pump, through a stat controlled 2 port valve and onto a mixer valve (or temp control valve) and then to the underfloor pipe? Why do I need another pump, is this not to run the UFH independant of the boiler?

Q2, If I do need the pump, why do I have to use an expensive pre assembled kit? They seem expensive for what they are £300 ish for a cheap one. Can I not make on up myself out of the relevant parts, mixing valve (temp control valve), pump and 2 port valve controlling the outlet to the manifold?

Q3, In my small bathroom the plumber recommended using a temp control valve such as the danfoss one and fit this in the return of the UFH, the room is 3x3m. Ant problems with this?

I am just trying to use the same components but putting them together myself so its cheaper, why are the pre made ones so expensive? If I have to use a pre made one, can anyone recommend a good quality one at a reasonable price?

Thanks for the help in advance

 

[Norcon]

Q1, if I want the UFH to run only when the heating is on, why cant it run off the boiler pump, through a stat controlled 2 port valve and onto a mixer valve (or temp control valve) and then to the underfloor pipe? Why do I need another pump, is this not to run the UFH independant of the boiler?

The 3 port mixing blender need's positive pressure on the hot port which will be supplied by the boiler pump.
The by-pass valve ideally should be sited close to the blender.
The extra pump is needed on the mixed outlet.

Q2, If I do need the pump, why do I have to use an expensive pre assembled kit? They seem expensive for what they are £300 ish for a cheap one. Can I not make on up myself out of the relevant parts, mixing valve (temp control valve), pump and 2 port valve controlling the outlet to the manifold?

Yes you can make them up separate.

Q3, In my small bathroom the plumber recommended using a temp control valve such as the danfoss one and fit this in the return of the UFH, the room is 3x3m. Ant problems with this?

Probably the FJVR which will be fed direct from the boiler. You need a double meander loop layout for this valve.
If your room thermostat switches the boiler off then the uf section may not be up to temperature. (assuming it does not have a separate zone)
I' ve never fitted this particular valve tbh so cannot say for sure how it will perform but can see no other problems other than boiler cycling if you zone it separately.
You could probably zone it along with the 6m X 6m section if piping practalities allow and might offer better performance.
It would be advisable to fit an inline strainer on the hot port to the blender to protect the valve seat.
Same applies to the FJVR.

 

[Tadge]

thanks, obviously I now have more questions.

[Yes you can make them up separate]



What would be the components I need and what order do they connect in?

[If your room thermostat switches the boiler off then the uf section may not be up to temperature. (assuming it does not have a separate zone)
]

Is this not just the same as a room with a radiator and a TRV? The boiler switching off before the rooms are up to temp. I wasnt planning on having a stat to control the boiler. The 6x6 room would have one to operate the UFH actuator and the other rooms in the house will have TRV's. The towel radiator in the bathroom will have no TRV creating the open loop/bypass. I'm going for a grant oil boiler and I assumed this would fire until the heating return temp reached a certain level and then this would switch the boiler off. I had a Vaillant combi and thats how this operated.

The small bathroom UFH I was told to run a flow and return in 22mm to rads and T off this to the UFV and the return would have the FJVR valve fitted. Is this wrong?

Thanks for your help

 

[Norcon]

Page 6 might be helpful..............
http://www.rehau.co.uk/files/V268_Intelligent_Controls_Manual_UK.pdf

The manifold should have a temperature guage on the flow and ideally a HLS fitted also. ( see page 22)

You should have at least 2 zones. Upstairs/downstairs or living/sleeping.
The fjvr senses the water temperature unlike a trv which senses air temperature so very different and should be fitted as per the instructions.
Also the fjvr may likely be fitted to a loop buried in a cement screed which will slow down room target temperature response time which is why the boiler cutting off on a separate stat controlling radiators is not a good idea.

 

[Tadge]

thats excellent. do you think its worth the bother making my own control station up or buying a factory one? Its for 1 room of 6 x 6 only so seems expensive, may be worth the outlay for a whole house but for 1 room?

Thanks

 

[Norcon]

Yes it's worth the bother IMO.
Wirsbo's small area pack for up to 38sq/m will set you back nearly £1000.
You should be able to source the necessary components for between £500 and £700.