Hi Andrew,

Last Nov 2008, you mentioned a system of UFH done with 10mm copper under the
floorboards.

Do you have any feeling for how hot the air gets in the inter-joist void,
under the pipes?

Your system would fit *very* well in my house, but I'm wondering how much to
derate the electrical cables by.

I've got the margin to go to about 45C or possibly 50C ambient air temp
absolute max.

I don't imagine the air gets that hot - but as you're heating an entire room
through wood, I'm not certain of that.

Ta muchly in advance.

Tim

Tim S wrote:
Hi Andrew,

Last Nov 2008, you mentioned a system of UFH done with 10mm copper under the
floorboards.

Do you have any feeling for how hot the air gets in the inter-joist void,
under the pipes?

Your system would fit *very* well in my house, but I'm wondering how much to
derate the electrical cables by.

I've got the margin to go to about 45C or possibly 50C ambient air temp
absolute max.

I don't imagine the air gets that hot - but as you're heating an entire room
through wood, I'm not certain of that.

Ta muchly in advance.


It will go as high as you let it.

Normally you limit to around 50C inlet.

However I would say that under wood you can afford to go higher. It wont
catch fire, and it wont normally crack.

As you surmise, the issue is the rate of heat loss into the the
room..with none, the air will be as hot as the water.

A lot depends on what the floor is. Chipboard is far more stable than
real wood.



Tim

"Tim S" wrote in message
...
Hi Andrew,

Last Nov 2008, you mentioned a system of UFH done with 10mm copper under
the
floorboards.

Do you have any feeling for how hot the air gets in the inter-joist void,
under the pipes?

Your system would fit *very* well in my house, but I'm wondering how much
to
derate the electrical cables by.

I've got the margin to go to about 45C or possibly 50C ambient air temp
absolute max.

I don't imagine the air gets that hot - but as you're heating an entire
room
through wood, I'm not certain of that.

Ta muchly in advance.

Tim

My understanding of cables is to derate them to 0% at 70degC. The belief is
that below 70degC PVC won't creep sufficiently and above, it will. You're
going to have to assume that the joists and air around the joists will be
whatever temperature your boiler is set to unless you use a mixer to reduce
temperature.

Floorboards at or above 50degC are going to hurt!!

Fred coughed up some electrons that declared:


My understanding of cables is to derate them to 0% at 70degC. The belief
is
that below 70degC PVC won't creep sufficiently and above, it will. You're
going to have to assume that the joists and air around the joists will be
whatever temperature your boiler is set to unless you use a mixer to
reduce temperature.

I will have a mixer - but it's not necessarily the case that the air will
reach pipe surface temperature, except in a later very close to the pipe.

Calculations based on IEE regs data and other factors limit my design to max
50, preferably 45C ambient (edge case, 2.5mm2 T+E cable, required current
capacity of =20A)

Floorboards at or above 50degC are going to hurt!!

Don't be daft, the *air* below them is at X degrees, where X might be 35,
40, 45 or 50 (the calculation of which is non trivial and certainly beyond
me).

The heat has to transfer through air then wood, where the surface of the
wood is being cooled by losing heat into the room, so it stands to reason
that the air under the floor may be considerably hotter than the upper
surface. But it could be 10 or 20 degrees below pipe temp, especially below
the pipes: In Andrew's scheme, the pipes are about 1" below the floor
surface.

Cables must be 2" below, generally the might be near the mid point, so
3-5" below.

It's all going to be speculation other that a real life observation or a
complicated set of calculations.

Cheers

Tim

On 26 Jan, 18:29, Tim S wrote:
Hi Andrew,

Last Nov 2008, you mentioned a system of UFH done with 10mm copper under the
floorboards.

The relevant BS, BS EN 1264-31998, recommends a maximum floor
temperature of 9 degC above the room temperature, i.e., 29 degC, 33
degC in bathrooms. You could work it out from that.

No-one uses copper for underfloor. PEX is preferable. The Rehau or
Uponor crimp fittings are much preferable to push-fit.

There has been some criticism of 'staple-up' used without radiant
plates in the US trade press; the design heat emissions often aren't
achieved. .

Onetap coughed up some electrons that declared:

On 26 Jan, 18:29, Tim S wrote:
Hi Andrew,

Last Nov 2008, you mentioned a system of UFH done with 10mm copper under
the floorboards.

The relevant BS, BS EN 1264-31998, recommends a maximum floor
temperature of 9 degC above the room temperature, i.e., 29 degC, 33
degC in bathrooms. You could work it out from that.

How?

No-one uses copper for underfloor. PEX is preferable. The Rehau or
Uponor crimp fittings are much preferable to push-fit.

Please see this:

http://groups.google.co.uk/group/uk....c7d25eac4d00fb

On 26 Jan, 20:33, Tim S wrote:

How?

Like U values. Probably try a heat loss type calc where the
temperature differential is the difference between the assumed floor
void temperature and the room temperature. Increase the floor void
temperature until you get the required heat emission to the room.The
BS gives temperature drop through floor construction graphs.

Heat transfer plates would be best, the pipe would be in contact with
the floor, the pipe would have a larger effective area and the
insulation could be close to the pipe.
No-one uses copper for underfloor. PEX is preferable. The Rehau or
Uponor crimp fittings are much preferable to push-fit.

Please see this:

http://groups.google.co.uk/group/uk..../thread/9b6f3f...

Yes, I read it when it was fist posted. Utter bolleaux IMHO.

In article ,
Tim S writes:
Hi Andrew,

Last Nov 2008, you mentioned a system of UFH done with 10mm copper under the
floorboards.

Do you have any feeling for how hot the air gets in the inter-joist void,
under the pipes?

Your system would fit *very* well in my house, but I'm wondering how much to
derate the electrical cables by.

I've got the margin to go to about 45C or possibly 50C ambient air temp
absolute max.

I don't imagine the air gets that hot - but as you're heating an entire room
through wood, I'm not certain of that.

I don't have any way to measure it now -- there's no access under the
floor.

I may be there later in the week -- I'll take an IR thermometer with me
and take some measurements. There was only one wire there, which goes to
the hall light. It was threaded through a mixture of the floor joists
and ceiling supports (bottom of floor joists wasn't level so there were
extra ceiling supports fitted under the joists). What I did do was to
unthread bits of it that looped up and layed it all on the ceiling, so
it's going to be pretty much same temperature as the ceiling, which
should be the coldest part under there.

The home owner is extremely pleased with the scheme, and has commented
on how well it works. The tiled floor doesn't feel hot on the feet, but
if you stop and think for a moment, you would expect it to feel cold,
and it doesn't. I've been curious about what temperature it actually
runs at, so I'll check with the IR thermometer. I didn't know how much
or closely spaced 10mm copper tube I'd need to get the right heat
transfer, and had no time to try it, but it seems to have been pretty
much spot-on.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Onetap coughed up some electrons that declared:

On 26 Jan, 20:33, Tim S wrote:

How?

Like U values. Probably try a heat loss type calc where the
temperature differential is the difference between the assumed floor
void temperature and the room temperature. Increase the floor void
temperature until you get the required heat emission to the room.The
BS gives temperature drop through floor construction graphs.

Ah yes - that might get an approximation - forget the air and just see what
the board lower surface would need to be to get the surface to say 25-30
(which is a reasonable guess for UHF surface temps). I'll have to go and
dig out some U-values for wood.

Heat transfer plates would be best, the pipe would be in contact with
the floor, the pipe would have a larger effective area and the
insulation could be close to the pipe.

Undoubtedly that would be best - would rather nadger access under the floor
though.

No-one uses copper for underfloor. PEX is preferable. The Rehau or
Uponor crimp fittings are much preferable to push-fit.

Please see this:

http://groups.google.co.uk/group/uk..../thread/9b6f3f...

Yes, I read it when it was fist posted. Utter bolleaux IMHO.

Apparently it works?...

Cheers

Tim

Andrew Gabriel coughed up some electrons that declared:


I don't have any way to measure it now -- there's no access under the
floor.

I may be there later in the week -- I'll take an IR thermometer with me
and take some measurements.

I realise my request is a PITA - if there were any indicators between it
being "warm" or "hot" down there, it would be very interesting to know.

I'm short of space for rads upstairs (leaving fan convectors as the next
option), but I do have infinite underfloor space. I'm quite inclined to do
UFH downstairs, so I'll have water available at full temp and reduced
temperature anyway (maybe your system will need higher than normal UFH temp
but less than 80C which is what I may run the thermal store at so I might
need another mixer).

There was only one wire there, which goes to
the hall light.

All my cables are going to be there - my design sheet shows it's the rings
on 2.5mm2 which are the bounding case.

It was threaded through a mixture of the floor joists
and ceiling supports (bottom of floor joists wasn't level so there were
extra ceiling supports fitted under the joists). What I did do was to
unthread bits of it that looped up and layed it all on the ceiling, so
it's going to be pretty much same temperature as the ceiling, which
should be the coldest part under there.

That would help, though I'd not be happy to do that with all my wiring for
obvious reasons. I did think about suspending an inch of wool under the
heating pipes, but it rather destroys one of the obvious benefits of your
design which is it doesn't make access to the underfloor void impossible
(like a plate system would). The other benefit is your system is 30-50
quid's worth of copper tube and elegant simplicity

I guess, I'd take a risk and try it and monitor it closely.

The home owner is extremely pleased with the scheme, and has commented
on how well it works. The tiled floor doesn't feel hot on the feet, but
if you stop and think for a moment, you would expect it to feel cold,
and it doesn't. I've been curious about what temperature it actually
runs at, so I'll check with the IR thermometer. I didn't know how much
or closely spaced 10mm copper tube I'd need to get the right heat
transfer, and had no time to try it, but it seems to have been pretty
much spot-on.


That's nice that it worked just right

Cheers and thanks again,

Tim

In article ,
Tim S writes:
Andrew Gabriel coughed up some electrons that declared:


I don't have any way to measure it now -- there's no access under the
floor.

I may be there later in the week -- I'll take an IR thermometer with me
and take some measurements.

I realise my request is a PITA - if there were any indicators between it
being "warm" or "hot" down there, it would be very interesting to know.

I'm short of space for rads upstairs (leaving fan convectors as the next
option), but I do have infinite underfloor space. I'm quite inclined to do
UFH downstairs, so I'll have water available at full temp and reduced
temperature anyway (maybe your system will need higher than normal UFH temp
but less than 80C which is what I may run the thermal store at so I might
need another mixer).

The system has a condensing boiler, but it's never operated in
condensing mode because it has a user-accessible knob on it, and
the owners just turn it up if they feel cold (not that it changes
the house temperature anyway) and of course never turn it down
again. I've given up explaining what it means to have a condensing
boiler. The radiators are not sized for condensing operation in
any case, so it would probably need turning up during cold spells
(and again, would never get turned down).

I rather suspect that's how most condensing boilers are really
used, other than by a very small minority of users who understand
what they are.

There was only one wire there, which goes to
the hall light.

All my cables are going to be there - my design sheet shows it's the rings
on 2.5mm2 which are the bounding case.

It was threaded through a mixture of the floor joists
and ceiling supports (bottom of floor joists wasn't level so there were
extra ceiling supports fitted under the joists). What I did do was to
unthread bits of it that looped up and layed it all on the ceiling, so
it's going to be pretty much same temperature as the ceiling, which
should be the coldest part under there.

That would help, though I'd not be happy to do that with all my wiring for
obvious reasons. I did think about suspending an inch of wool under the
heating pipes, but it rather destroys one of the obvious benefits of your
design which is it doesn't make access to the underfloor void impossible
(like a plate system would). The other benefit is your system is 30-50
quid's worth of copper tube and elegant simplicity

Yes, indeed. I have got a TRV at one end of the circuit though,
poking out from some boxing. The system relies on not having a heat
spreader and having poor thermal conduction to the floor, rather
than using a mixer to regulate the floor temperature. Now if I was
installing it for me (with a correctly running condensing boiler),
I would probably have had to use a spreader (and hence also a mixer),
as my boiler is normally run at 45C flow, and otherwise there may not
be enough heat transfer (or more pipework would be needed).

I guess, I'd take a risk and try it and monitor it closely.

If you have the luxury of time to try it, I suggest you do so.
I didn't have that luxury. The nearest I got was knowing the
radiator pipes under the floor in a few places did locally
heat it.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

"Tim S" wrote in message
...
Onetap coughed up some electrons that declared:

On 26 Jan, 20:33, Tim S wrote:

How?

Like U values. Probably try a heat loss type calc where the
temperature differential is the difference between the assumed floor
void temperature and the room temperature. Increase the floor void
temperature until you get the required heat emission to the room.The
BS gives temperature drop through floor construction graphs.

Ah yes - that might get an approximation - forget the air and just see
what
the board lower surface would need to be to get the surface to say 25-30
(which is a reasonable guess for UHF surface temps). I'll have to go and
dig out some U-values for wood.

Heat transfer plates would be best, the pipe would be in contact with
the floor, the pipe would have a larger effective area and the
insulation could be close to the pipe.

Undoubtedly that would be best - would rather nadger access under the
floor
though.

No-one uses copper for underfloor. PEX is preferable. The Rehau or
Uponor crimp fittings are much preferable to push-fit.

Please see this:

http://groups.google.co.uk/group/uk..../thread/9b6f3f...

Yes, I read it when it was fist posted. Utter bolleaux IMHO.

Apparently it works?...

But not very efficiently. It needs a spreader plate and a mixer to lower
the return temperature. It appears to be keeping the return temperature to
the boiler up reducing efficiency.