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Author Topic: UFH calculations  (Read 4050 times)
titan
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« Reply #15 on: March 01, 2012, 09:21:32 AM »

Some nice manifolds here  http://www.pulsardirect.co.uk/heating/underfloor/manifoldsacc/1-in-x-2-port-manifold-euroconus-mxf.html  in that same section are all the other bits you need. For your workshop I would  suggest it be an idea to keep it simple, UFH is very slow to respond so sophisticated controls are not required. The simplest solution would be to use a basic manifold with lockshields on flow and return then balance the loop flows on the return lockshields using an infra red thermometer to check the return temperatures. You could then have one room trv on the main supply to the manifold.
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wookey
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« Reply #16 on: March 01, 2012, 10:23:52 PM »

Hmm, those are very cheap in comparison to the 200 quid everyone else wants.

But the thing is this manifold isn't just going to do the workshop (floating floor 13m2), it's also going to do the extension (screeded floor 27m2) and (eventually) the kitchen and lounge, both retrofit floating floor (probably) 10m2 and 32m2 respectively. I was going to have a spare way in case I even wanted to do the hall too, or the bathroom. So that's a 6-way jobbie.

UFH people are telling me that floating floor and screeded floor can't be on  the same manifold because they need very different flow temps. I don't want two more pumps and manifolds and reckon that by proper design (pipe spacing +flow rate control) - I can get the two floor types to run off one manifold and one pump. Ideally I'd just have one pump for the whole damn things, but I'm not sure that's practical unless I get rid of all the radiators.

There is a not-quite finished drawing here:
http://wookware.org/extension/builders/pdf-drawings/UFHplan.pdf
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Wookey
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« Reply #17 on: March 02, 2012, 12:49:33 PM »

Wookey said :-
UFH people are telling me that floating floor and screeded floor can't be on  the same manifold because they need very different flow temps. I don't want two more pumps and manifolds and reckon that by proper design (pipe spacing +flow rate control) - I can get the two floor types to run off one manifold and one pump. Ideally I'd just have one pump for the whole damn things, but I'm not sure that's practical unless I get rid of all the radiators.



Hmm, well they would, they have IMHO overcomplicated UFH to sell loads of expensive gizmos, I think that control of flowrates/spacings would give you enough leeway to run both off one manifold/pump. Even combining rads and UFH is doable I reckon, how about a remote sensor TRV to monitor the floor temp and adjust the flow accordingly, maybe provide a roomstat as well to monitor air temp,and operate a 2 port valve, what else do you need?
Some "designers" have said to me that you will end up with the floor too hot, but in practise that doesn't happen, only if the stats were over-ridden and the system on for an extended period would the floor overheat, and even then if the flow rate is suitably restricted by say a gate valve, it will reach equilibrium at an acceptable level.

 2 port valves, remote sensing TRVs, roomstats, and standard plumbing fittings are all that is needed methinks.

Desp
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djh
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« Reply #18 on: March 02, 2012, 01:51:53 PM »

Just occaisionally. Which may in practice only keep my feet warm, but I'm hoping that a large radiative surface will help if 'feel' adequately warm - we'll see.

Perhaps a fan-blown radiator/coil hung from the ceiling would be easier and/or better-matched to usage?
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rt29781
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« Reply #19 on: March 02, 2012, 03:06:46 PM »

Perhaps a fan-blown radiator/coil hung from the ceiling would be easier and/or better-matched to usage?

We have reversible air to air heat pumps and they heat the head but leave the feet freezing,  Real bad idea.  We then fitted UFH and it is bliss.
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Nowt currently, Aberdeen.....well actually very well insulated extension with passive solar that seems to heat the house....
djh
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« Reply #20 on: March 02, 2012, 03:23:47 PM »

We have reversible air to air heat pumps and they heat the head but leave the feet freezing,  Real bad idea.  We then fitted UFH and it is bliss.

Workshop? Or sitting about in a house?
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rt29781
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« Reply #21 on: March 02, 2012, 04:03:02 PM »

Workshop? Or sitting about in a house?

House, although not sure why it matters feet still cold without UFH.
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Nowt currently, Aberdeen.....well actually very well insulated extension with passive solar that seems to heat the house....
gb484
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« Reply #22 on: March 02, 2012, 06:07:29 PM »

I used manifolds similar to the Pulsar ones when I did my UFH. They were bought as a kit of bits and included butterfly valves and bottle air vents on supply and return. As I didn't want to install all the circuits at the same time, I installed isolation valves on all supply and return connections; they can be used to turn off circuits when purging air out of individual loops and as a crude method of adjusting flow if necessary. There's no need to spend hundreds of pounds. Antares sell a TRV type device for regulating temp if needed, and they have the brass/stainless manifolds too. 
PS: I also used basic Pulsar-style manifolds and plastic pipe for distribution of DHW throughout the house.
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pb
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« Reply #23 on: March 02, 2012, 10:16:16 PM »

UFH people are telling me that floating floor and screeded floor can't be on  the same manifold because they need very different flow temps. I don't want two more pumps and manifolds and reckon that by proper design (pipe spacing +flow rate control) - I can get the two floor types to run off one manifold and one pump. Ideally I'd just have one pump for the whole damn things, but I'm not sure that's practical unless I get rid of all the radiators.

The problem they're worried about doesn't seem to be average energy input (which, as you say, you could control by spacing or flow rate), it's more to do with point temperatures in the screed.  Concrete has quite a high rate of thermal expansion and the prevailing wisdom seems to be that running the screeded part of the UFH at a flow temperature of much more than 35C risks cracking the screed through differential movement.  And, if you run your floating floor at 35C, the R-value is probably high enough that you wouldn't get enough heat transfer even with zero spacing between pipe runs.

That said, I know people who are piping 70C water from the radiator circuit straight through their screeded UFH with no obvious ill effects.
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JohnS
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« Reply #24 on: March 02, 2012, 11:19:31 PM »

I recall that when there were discussions on international standards or specs for UFH, the Koreans objected because they traditionally ran their UFH at higher temperatures and did not want to be ruled out of supplying UFH to China.   One of the issues was that if the flow temperature is too high, the floor could be too hot in local areas and cause injuries.  I cannot recall the outcome of the discussions. 

John
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« Reply #25 on: April 03, 2012, 04:40:19 PM »

I've now done a spreadsheet implementing (part of) BS1264-2 UFH calculations (which are really quite fiddly).

It only does floating floors so far - I'll add screeded floors soon.

It's quite interesting to twiddle floor thickness, flow temp, temp drop, pipe spacing, floor conductivity, pipe conductivity, ali plate thickness and see what actually makes a difference to W/m2.

What is the normal thickness of ali plates? I guessed 0.5mm?
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Wookey
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