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Discuss UFH Advice required in the Water Underfloor Heating Installations area at PlumbersForums.net

linesrg

Messages
3
Good Evening,

We live in an old stone farmhouse which we are steadily 'improving' as the years go by.

The heating is provided by a CTC GSi 12 GSHP feeding UFH in the kitchen and Dining Room and radiators elsewhere.

The time is fast approaching when the bathroom is due a workover. In common with other farmhouses of this vintage the old pantry is the location of the bathroom and, as a result, it is a relatively small space as the attached plan shows.

My intention is to fit UFH.

The floor will be filled and a concrete sub-base installed overlaid with 200mm of Celotex.

The partition walls to the Utility Room and Lobby are already filled with 50mm Celotex and will be overlaid with a further 20/ 25mm to eliminate cold bridging. The walls against the stone walls will be framed and filled with Celotex and again overlaid with a further layer of Celotex.

The ceiling and 'chimney' to the Velux window will be filled with 50mm Celotex and the horizontal surfaces overlaid with 200mm fibreglass. The framing around the chimney will be infilled and overlaid with 50mm Celotex.

The existing Velux S06 window will be replaced with one of the new GGU 008230 SK06 models.

I need advice on how to maximise the layout of UFH pipework in the space available as I would like to avoid having to install a radiator. We do, however, intend to fit a towel radiator.

I have thermometers in the bathroom and the figures are:-

Radiator inlet - 40.0°C
Radiator outlet - 24.4°C
Room temperature - 20.8°C

The radiator fitted is an Ultraheat 9TS900 which as an output of 3103W at a ∆50.

The mean flow temperature is obviously 40 + 24.4 = 64.4/ 2 = 32.2°C

The room temperature at 20.8°C therefore gives us a ∆ of 11.4°C which is clearly a lot less than a ∆50.

The multiplication factor is 0.136 (derived from manufacturers’ figures) so the actual output of the radiator right now is a mere 422W and the outside temperature is 1°C.

At the end of the improvements less heat will be required than currently.

The question is I have a total floor area of 5.82m2 so allowing for only using 90% of this i.e. 5.24m2 will I be able to generate enough heat?

Regards

Richard




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Ric2013

Plumber
Messages
3,483
My hunch is that since you seem to be going to town with insulation and will also have some level of heat from a towel rail, what you are aiming at may not be especially difficult to achieve.

Best to check with UFH manufacturers as to what the exact output they claim their system provides. 70-100W/sq m is not unusual, but bear in mind you'll be unlikely to be getting that over the entire floor area and will be leaving an unheated area near walls (see manufacturer's installation instructions) and under the bath and WC, for example. Nu-heat is an expensive one, but they have systems that claim better heat output than some of the cheaper firms - but do be sure to shop around and see what else is available.

Some UFH firms sell you the kit with basic information and leave you to muddle out how you want to run and to trim your own pipe to fit from standard coil lengths. Conversely, some suppliers will calculate to the nth degree and sell you the exact lengths of pipe required and specify the flow rate and design the layout for each pipe run.

Make sure the UFH manufacturer is aware your available flow temperature is only 40°C. As a lot of UFH systems tend to work with mixer valves that mix down from a higher temperature flow, you may need to use a slightly different method here, but obviously GSHP and UFH are a good combination. I'm not an expert in UFH, sadly.

Bear in mind that an UFH installation contains a lot of water and, when first switched on, will require a lot of initial heat input in comparison with its rated output, so my only concern is that if the flow to your existing radiator is already the most your system can provide (rather than restricted at the existing radiator valves), it may be necessary to upgrade some of the pipework.
 

linesrg

Messages
3
My hunch is that since you seem to be going to town with insulation and will also have some level of heat from a towel rail, what you are aiming at may not be especially difficult to achieve.

Best to check with UFH manufacturers as to what the exact output they claim their system provides. 70-100W/sq m is not unusual, but bear in mind you'll be unlikely to be getting that over the entire floor area and will be leaving an unheated area near walls (see manufacturer's installation instructions) and under the bath and WC, for example. Nu-heat is an expensive one, but they have systems that claim better heat output than some of the cheaper firms - but do be sure to shop around and see what else is available.

Some UFH firms sell you the kit with basic information and leave you to muddle out how you want to run and to trim your own pipe to fit from standard coil lengths. Conversely, some suppliers will calculate to the nth degree and sell you the exact lengths of pipe required and specify the flow rate and design the layout for each pipe run.

Make sure the UFH manufacturer is aware your available flow temperature is only 40°C. As a lot of UFH systems tend to work with mixer valves that mix down from a higher temperature flow, you may need to use a slightly different method here, but obviously GSHP and UFH are a good combination. I'm not an expert in UFH, sadly.

Bear in mind that an UFH installation contains a lot of water and, when first switched on, will require a lot of initial heat input in comparison with its rated output, so my only concern is that if the flow to your existing radiator is already the most your system can provide (rather than restricted at the existing radiator valves), it may be necessary to upgrade some of the pipework.
@Ric2013 - many thanks for taking the time to reply.

Although my wife wasn't overly keen on the idea we will be fitting a wall mounted W.C. and basin (worst case is the basin would be stand mounted but again on four legs) and the bath will stand on legs thus the entire floor area is available for heating.

When the UFH manifold was installed a way back in 2008 it was fitted with a mixer valve but at that time we had an LPG powered condensing, weather modulating boiler putting water out at 55°C. This has now been removed as we are GSHP powered.

There are the two sets of supply/ return pipes from the GSHP, it was simply bolted on to the existing ground and first floor circuits. Thus they are 22mm. In the case of the ground floor circuit this goes up into the Utility Room 'attic' and then across and down the back of the bath in to the bathroom floor void so the bathroom radiator is actually the first feed. The 22mm pipes then go under the bathroom door in to the void under the Hall floor. They first tee off to the UFH manifold (fitted with a Honeywell DU144 bypass valve) under the stairs, then on to the Hall radiator and then into the Living Room.

I can hear the bypass operating at the moment so there is clearly 'spare' capacity.

The UFH manifold has six outlets. Two are operating the kitchen circuits and two the Dining Room circuits so I have two to play with (the manifold is extendable anyway).

I did send out EM's to a few UFH organisations including Nu-heat so hopefully they'll come back to me.

I'll take advice/ thoughts/ comments from one and all.

I put together a simple Excel spreadsheet with a look-up table this morning so as to monitor the current radiator output.

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Regards

Richard
 

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Ric2013

Plumber
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3,483
I think it's good that you are monitoring the radiator output, though I would suggest you may as well try to calculate the heat losses from your new proposed low energy-refit. But it's good to have a worst case scenario.

Do bear in mind that UFH works rather differently from radiators.
If you go for the spreader plates and suspended wooden floor (not very common now) I can confirm it takes at least half an hour for the floor surface temperature to start to increase and the room obviously can only begin to warm up from that point. Received wisdom is UFH has to run constantly - but sometimes, with spreader plates you can get away with intermittent heat - just. Source: personal experience.

As you will be using the pipes in screed system, it will take longer still to warm up - and to stop giving out heat. I have had a customer who had problems with this as solar gain then tended to overheat his kitchen but I suspect this was due to the UFH overheating as it had been installed incorrectly.
 

linesrg

Messages
3
I think it's good that you are monitoring the radiator output, though I would suggest you may as well try to calculate the heat losses from your new proposed low energy-refit. But it's good to have a worst case scenario.

Do bear in mind that UFH works rather differently from radiators.
If you go for the spreader plates and suspended wooden floor (not very common now) I can confirm it takes at least half an hour for the floor surface temperature to start to increase and the room obviously can only begin to warm up from that point. Received wisdom is UFH has to run constantly - but sometimes, with spreader plates you can get away with intermittent heat - just. Source: personal experience.

As you will be using the pipes in screed system, it will take longer still to warm up - and to stop giving out heat. I have had a customer who had problems with this as solar gain then tended to overheat his kitchen but I suspect this was due to the UFH overheating as it had been installed incorrectly.
@Ric2013,

Our kitchen, UFH pipes in screed, can suffer from solar gain......... I just open the Hall and Utility Room doors.......

The bathroom, is effectively an internal space and faces WSW so only 'sees' the sun late in the day and, at this time of year the sun's altitude isn't high enough to be considered.

Currently looking at Herschel radiant panels and a very whizzo, and expensive passivehaus standard Velux window.

Regards

Richard
 

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