DIYbanter - UFH Running Costs

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UFH Running Costs

Have any of you estimated and/or measured the running costs of under-floor
heating in a way which enables you to suggest a methodology to use?

We are converting a built-in garage into a kitchen, and are considering
using UFH - either wet or electric.

On the face of it, electric would be a lot more expensive to run, since the
price of on-peak electricity is still three times that of gas. However, you
then have to consider efficiency. With electricity, all the consumed energy
ends up where you want it. With gas, my boiler is at best 75% efficient and
I suspect that it's considerably less efficient than that when running at a
low output - like when the *only* thing it's heating is the kitchen floor.
[Perceived wisdom seems to suggest that UFH needs to be on either 24 x 7 or,
at least, for longer than the radiators in order to allow for the thermal
inertia]. Even so, it seems likely that more than 1/3 of the heat generated
by burning gas would end up in the floor - so it should *still* be cheaper
to run than an electric system.

What effect does UFH have on heatloss calculations? On the face of it, the
delta-T between the floor and the soil below is roughly twice as great with
UFH as it is with a 'conventional' heating system - so presumably the losses
through the floor (everthing else being equal) are roughly doubled, so that
the overall room heatloss is a bit higher. I say "a bit" because the loss
through the insulated floor is - according to my calculations - only about
6% of the total, so doubling it would add another 6%. Is this a reasonable
assumption?

Whilst it's easy enough to calculate the steady state heatloss under defined
conditions (e.g. ambient temp of -3 degC), estimating the total annual
energy requirement is not so straight-forward. I will describe the rationale
which I have followed thus far, and would welcome any constructive comments
as to its reasonableness.

I use gas for CH in cold weather, and for HW throughout the year, but not
for cooking. I know how much gas I use in a year and how much in the summer
months when just used for HW. I can thus estimate the annual use for HW and
deduct it from the total in order to calculate the annual use for heating.
If I assume a figure for boiler efficiency, I can calculate the kWh/annum
which actually gets to the radiators. If I divide that by the house heatloss
in kW under the defined conditions, I can calculate the *effective* number
of hours per year for which the system is running at its rated capacity. [Of
course, in reality, it's running for much longer than this - at a lower
capacity for most of the time - but this gives a basis for comparison].

Extrapolating this for the 'new' room, if I work out the room heatloss under
the same defined conditions and multiply it by the effective hours figure
obtained above, I get a figure for the likely annual heat input to the room.
For an electric system, this is the number of kWh required and for a wet
system the figure needs to be divided by the boiler efficiency to work out
the number of kWh of gas consumed. In both cases, the figures are fairly
horrific! Are there any fundamental flaws with this approach?
--
Cheers,
Roger
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UFH Running Costs

"Roger Mills" wrote in message
...
Have any of you estimated and/or measured the running costs of under-floor
heating in a way which enables you to suggest a methodology to use?

We are converting a built-in garage into a kitchen, and are considering
using UFH - either wet or electric.

Look at a Myson kickspace heater for a kitchen.

UFH Running Costs

On Tue, 13 Jan 2009 19:36:59 +0000, Doctor Drivel wrote:

"Roger Mills" wrote in message
...
Have any of you estimated and/or measured the running costs of under-floor
heating in a way which enables you to suggest a methodology to use?

We are converting a built-in garage into a kitchen, and are considering
using UFH - either wet or electric.

Look at a Myson kickspace heater for a kitchen.

=========================================
And the 12V model for safety in the bathroom:

http://tinyurl.com/9mgs2r

http://www.heatandplumb.com/acatalog..._600H_12v.html

Cic.

--
==========================================
Using Ubuntu Linux
Windows shown the door
==========================================

UFH Running Costs

Roger Mills coughed up some electrons that declared:

Have any of you estimated and/or measured the running costs of under-floor
heating in a way which enables you to suggest a methodology to use?

Hi Roger,

http://www.dionic.net/Alveston/UFH-everywhere.xls

(Done in OpenOfficeCalc - probably OK in Excel)

Is the best estimate I could manage, with data on the U-Value of concrete on
earth from

http://www.celotex.co.uk/Other-Resou...lue-Calculator

I wanted to see how much worse (and how much cost of gas I'd waste) by
having wet UFH on a bit of insulation vs normal heating and no insulation
which is how the house is now.

You'll need to change B6 if your permiter/area value is different - use the
celotex calculator set to 12mm floor celotex and you'll see that B6 has a
back-calculation to remove the U-Value component of the celotex leaving the
floor.

It's rough, undocumented and the Ground Temp is over a range because I don;t
know what to assume - so I thought I'd study the likely range and see how
far the heat losses ranges.

It might even be all wrong, but I'd be interested if anyone can fix this.

Cheers

Tim

UFH Running Costs

Roger Mills wrote:
Have any of you estimated and/or measured the running costs of under-floor
heating in a way which enables you to suggest a methodology to use?

We are converting a built-in garage into a kitchen, and are considering
using UFH - either wet or electric.

Dont use electric fo serious heating.

On the face of it, electric would be a lot more expensive to run, since the
price of on-peak electricity is still three times that of gas. However, you
then have to consider efficiency. With electricity, all the consumed energy
ends up where you want it. With gas, my boiler is at best 75% efficient and
I suspect that it's considerably less efficient than that when running at a
low output - like when the *only* thing it's heating is the kitchen floor.
[Perceived wisdom seems to suggest that UFH needs to be on either 24 x 7 or,
at least, for longer than the radiators in order to allow for the thermal
inertia]. Even so, it seems likely that more than 1/3 of the heat generated
by burning gas would end up in the floor - so it should *still* be cheaper
to run than an electric system.

Correct. Plus electricity costs more. heta pumps are a different matter,
but thats a wet system.

I think the breakeven with oil is at around the 25p a liter level.

What effect does UFH have on heatloss calculations? On the face of it, the
delta-T between the floor and the soil below is roughly twice as great with
UFH as it is with a 'conventional' heating system - so presumably the losses
through the floor (everthing else being equal) are roughly doubled, so that
the overall room heatloss is a bit higher. I say "a bit" because the loss
through the insulated floor is - according to my calculations - only about
6% of the total, so doubling it would add another 6%. Is this a reasonable
assumption?

Its a bit hard to say. I cant actually offer real figures, but this
last spell of cold I simply let mine run 24x7 and I noticed that the
floor never got as hot as it did when I was running it timed. Since it
never had the '4 hour burn' to get it warm. My gut feeling is I used
LESS oil on 24x7 for that reason. Cooler floor=less heatloss.

Whilst it's easy enough to calculate the steady state heatloss under defined
conditions (e.g. ambient temp of -3 degC), estimating the total annual
energy requirement is not so straight-forward. I will describe the rationale
which I have followed thus far, and would welcome any constructive comments
as to its reasonableness.

I use gas for CH in cold weather, and for HW throughout the year, but not
for cooking. I know how much gas I use in a year and how much in the summer
months when just used for HW. I can thus estimate the annual use for HW and
deduct it from the total in order to calculate the annual use for heating.
If I assume a figure for boiler efficiency, I can calculate the kWh/annum
which actually gets to the radiators. If I divide that by the house heatloss
in kW under the defined conditions, I can calculate the *effective* number
of hours per year for which the system is running at its rated capacity. [Of
course, in reality, it's running for much longer than this - at a lower
capacity for most of the time - but this gives a basis for comparison].

Extrapolating this for the 'new' room, if I work out the room heatloss under
the same defined conditions and multiply it by the effective hours figure
obtained above, I get a figure for the likely annual heat input to the room.
For an electric system, this is the number of kWh required and for a wet
system the figure needs to be divided by the boiler efficiency to work out
the number of kWh of gas consumed. In both cases, the figures are fairly
horrific! Are there any fundamental flaws with this approach?

No, but it seems long winded. Average UK temps are between 9C (Scotland)
and 11C (south west) IIRC. Just take the heatloss and that level on a
24x7 basis for your sort of 18C type internals.

I can tell you one ting tho, UFH done proper is no less efficient than
any other system, although an in screed system with a large mass is
something iu cannot modulate quickly, BUT it can work at more efficient
boiler outlet temps.

If you are talking conservatories though, forget it: the floor output
simply isn't enough to cope with all the glass heatloss.

UFH Running Costs

On 14 Jan, 02:25, The Natural Philosopher wrote:
Roger Mills wrote:
Have any of you estimated and/or measured the running costs of under-floor
heating in a way which enables you to suggest a methodology to use?

We are converting a built-in garage into a kitchen, and are considering
using UFH - either wet or electric.

Dont use electric fo serious heating.

On the face of it, electric would be a lot more expensive to run, since the
price of on-peak electricity is still three times that of gas. However, you
then have to consider efficiency. With electricity, all the consumed energy
ends up where you want it. With gas, my boiler is at best 75% efficient and
I suspect that it's considerably less efficient than that when running at a
low output - like when the *only* thing it's heating is the kitchen floor.
[Perceived wisdom seems to suggest that UFH needs to be on either 24 x 7 or,
at least, for longer than the radiators in order to allow for the thermal
inertia]. Even so, it seems likely that more than 1/3 of the heat generated
by burning gas would end up in the floor - so it should *still* be cheaper
to run than an electric system.

Correct. Plus electricity costs more. heta pumps are a different matter,
but thats a wet system.

I think the breakeven with oil is at around the 25p a liter level.

What effect does UFH have on heatloss calculations? On the face of it, the
delta-T between the floor and the soil below is roughly twice as great with
UFH as it is with a 'conventional' heating system - so presumably the losses
through the floor (everthing else being equal) are roughly doubled, so that
the overall room heatloss is a bit higher. I say "a bit" because the loss
through the insulated floor is - according to my calculations - only about
6% of the total, so doubling it would add another 6%. Is this a reasonable
assumption?

Its a bit hard to say. *I cant actually offer *real figures, but this
last spell of cold I simply let mine run 24x7 and I noticed that the
floor never got as hot as it did when I was running it timed. Since it
never had the '4 hour burn' to get it warm. My gut feeling is I used
LESS oil on 24x7 for that reason. Cooler floor=less heatloss.

Whilst it's easy enough to calculate the steady state heatloss under defined
conditions (e.g. ambient temp of -3 degC), estimating the total annual
energy requirement is not so straight-forward. I will describe the rationale
which I have followed thus far, and would welcome any constructive comments
as to its reasonableness.

I use gas for CH in cold weather, and for HW throughout the year, but not
for cooking. I know how much gas I use in a year and how much in the summer
months when just used for HW. I can thus estimate the annual use for HW and
deduct it from the total in order to calculate the annual use for heating.
If I assume a figure for boiler efficiency, I can calculate the kWh/annum
which actually gets to the radiators. If I divide that by the house heatloss
in kW under the defined conditions, I can calculate the *effective* number
of hours per year for which the system is running at its rated capacity.. [Of
course, in reality, it's running for much longer than this - at a lower
capacity for most of the time - but this gives a basis for comparison].

Extrapolating this for the 'new' room, if I work out the room heatloss under
the same defined conditions and multiply it by the effective hours figure
obtained above, I get a figure for the likely annual heat input to the room.
For an electric system, this is the number of kWh required and for a wet
system the figure needs to be divided by the boiler efficiency to work out
the number of kWh of gas consumed. In both cases, the figures are fairly
horrific! Are there any fundamental flaws with this approach?

No, but it seems long winded. Average UK temps are between 9C (Scotland)
and 11C (south west) IIRC. Just take the heatloss and that level on a
24x7 basis for your sort of 18C type internals.

I can tell you one ting tho, UFH done proper is no less efficient than
any other system, although an in screed system with a large mass is
something iu cannot modulate quickly, BUT it can work at more efficient
boiler outlet temps.

If you are talking conservatories though, forget it: the floor output
simply isn't enough to cope with all the glass heatloss.

Interesting post
I have installed wet UFH and as you state the thermal mass and slow
heat up is a perceived problem but only by SWIMBO!
If I were you I would use a buffer to ensure the boiler did not keep
switching on and off and large diameter pipes at close centres to
speed up heating
If it is not too late I would put as much inuslation as I could
underneath to minimse heat loss to the soil under and keep the output
temp as low as practicable.
I use a heat pump but if you are on gas (LPG or natural?) you are at
risk in the long term and it would be sensible to have a further coil
in your buffer for a wood burner! That is what I have done (in fact my
buffer is in direct line with the Heat Pump and has two other sources
going into it - a primary flow and return from a boiler (due to be
backburning wood but currently LPG) and DC and AC immersions one for
true emergencies when there is only elec and the heat pump is off
(anti frost) and one for a wind generator.
Chris

UFH Running Costs