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Author Topic: Sanity check Please? Conservatory PV 24v underfloor heating, Winter is coming.  (Read 5333 times)
clockmanFR
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« on: September 15, 2013, 12:07:32 PM »

Sanity check?  Conservatory, PV 24v underfloor heating.

Forum members /Bright Sparks please help!.

Sometime ago  I discussed  using 24v under floor heating in the conservatory, using a 1kw of 250w PV panels charging 300ah gel batteries, and the concrete slab acting as a thermal store.  No mains voltage anywhere near the garden shed and conservatory.

Primary use was for lighting, and my shed, but liked the idea suggested of a cost effective system using 12v car heated rugs, suitably amended and imbedded into a concrete screed.

So heres a pic of a 12v matt suitably ready.

1. Wire in series for 24v.?

2, Possibly use 4off 12v matts  as each is only 55w.?

3, Looks like they have 2 thermal cutout/fuses, these will need to be disconnected and somehow used as a safety/temp switch actually on the concrete surface, or shall I fit a temp sensor and probe ?, 24v hmm.

5, Not sure how long the concrete slab 6m by 2.5m by 200mm thick will take to get hot using these wire elements,? Or is the thermal  cutout/fuses for the element protection to stop it getting to hot and melting?

6, The conservatory is warm in day time with any light, so need system working for a few hours in the night. So will probably use a timer.
 
7, I have a 24v LVD,  (low voltage disconnect) switch set at 24.50v to protect the batteries. (Marts mini micro cycles).

Suggestions or observations please.


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« Last Edit: September 15, 2013, 06:15:40 PM by clockmanFR » Logged

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A.L.
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« Reply #1 on: September 15, 2013, 12:32:01 PM »

Sanity check?  Conservatory, PV 24v underfloor heating.

1. Wire in series for 24v.?

2, Possibly use 4off 12v matts  as each is only 55w.?

5, Not sure how long the concrete slab 6m by 2.5m by 200mm thick will take to get hot using these wire elements,? Or is the thermal  cutout/fuses for the element protection to stop it getting to hot and melting?

Suggestions or observations please.


- Assuming they are just resistance elements wiring in series will be O.K.

- So only 220Watts total output? - The thermal mass of the slab is around 1.8Kwh/C, so it would take 8hrs to heat it by 1C but the matts will only be a fraction of the area, but if 1/10 the area temperature rise would still be at worst 10C locally in 8hrs and in reality considerably less
« Last Edit: September 15, 2013, 12:51:45 PM by A.L. » Logged
knighty
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« Reply #2 on: September 15, 2013, 12:57:11 PM »

can you not just buy the right type of wire for resistance heating ?

I know bit freezers need under floor heating (under the insulation) to stop the cold getting down and freezing the ground (over years) - they just use normal copper wire, powered through a transformer to drop the voltage down (no idea what voltage I'm afraid)

if you can find out what kind of wire you need, and what length, it should be pretty easy to zig zag it around under the floor ?



EDIT: it might be easier to run at 12v instead ?  easier to power your lights etc.. and the heating should be easier too ? - 12v vs 24v isn't a bit deal if you're only powering lights etc.. ?
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clockmanFR
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« Reply #3 on: September 15, 2013, 01:10:41 PM »

Thanks A.L.

So looks like a rise in the local area of 10 C best after 8hrs, will not probably effect the wire element one tot.

So at first I will remove the thermal cutout/fuses and keep an eye on the temp conditions.

Hi Knighty, yes there are loads of element wires available, and I use them in all my buildings here. Low voltage types are not so easy, and I thought of just modifying the 12v car blanket type was a little less hassle and not so much experimentation.

As regards zig zagging, its flipping hell  faint when the element wire is slightly ridged. This car blanket has been made with a sort of geo textile and the wire woven on. So will glue lined shrink fit all joints and just cement screed the geo textile as it is, with cement underneath and then skim cement on top.
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clockmanFR
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« Reply #4 on: September 15, 2013, 01:18:50 PM »

Hi Knighty, just seen your edit.

24v just means that my cables do not have to be so chunky, and besides I now have all the 24v low watt bulbs, and I have a spare 1.5kw 24v Inverter.

Hmmm! could move into my shed, Huh especially when the Mrs complains about her chillie plants getting chilly.   hysteria Huh
« Last Edit: September 15, 2013, 01:27:48 PM by clockmanFR » Logged

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Tiff
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« Reply #5 on: September 15, 2013, 02:05:15 PM »

Clockman - very interesting idea that may just solve a similar problem we have.

We have a tiled floor that gets painfully cold in winter, would love to have some underfloor heating just to take the chill off. Ripping up and relaying the tiles is not something I want to spend either the time or money on. Its only a section of around 1-2 sq metres that needs heating.

Some of the grouting is not that great, so I'm thinking I could remove the grout insert the wires between the tiles and then re-grout.

Can I ask how thick the cables are and how long they are?

I would just add protection for short circuit, with only a few hundred watts output I can't imagine there ever being a problem with overheating when embedded in a floor.
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skyewright
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« Reply #6 on: September 15, 2013, 02:33:05 PM »

6, The conservatory is warm in day time with any light, so need system working for a few hours in the night. So will probably use a timer.
Lateral thought...

Have you considered black drums of water as a diurnal heat store / temp stabiliser?

http://aes.missouri.edu/bradford/education/solar-greenhouse/solar-greenhouse.php

N.B. Most of the US is further South than we often appreciate, so their solar ideas don't always translate...
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David
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« Reply #7 on: September 15, 2013, 02:55:49 PM »

Me and my mate sparky pool have installed quite a few electric UFH systems running from the mains. To be honest even 2kW systems are only good for taking the chill off the floor. Space heating though is another matter especially if there is not sufficient insulation under the screed. If it is just about taking the chill off the floor it might work.

Desp
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clockmanFR
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« Reply #8 on: September 15, 2013, 06:14:33 PM »

Hi Tiff,  wire diameter is 2 mm, length in total about 13 meters per 12v 55w blanket.

Skyewright, might consider sealed/vented drums of water that is heated as a thermal store, say in a poly tunnel where a concrete base is not practical.

Hi Desp my hot mate,
All our buildings here have underfloor heating matts, from 300w to 3500w, but all take about 6 hours to come up to temp. And this is our main source of heating but then we are very well insulated to passive house standards. And most UFH matts are switchable into the AC side of our dumping power generation.
Desp I only fit the 220vac 200w per sq meter area type.   
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« Reply #9 on: September 15, 2013, 06:59:39 PM »

Hi Mr CM,

absolutely given high levels of insulation and 200W/m2 you will be toasty, I didn't pick that up from your OP, I was also referring to Tiffs post at the same time, think that if he doesn't have much insulation then all he will achieve is warming up the ground a little bit.

ATB

Desp

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knighty
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« Reply #10 on: September 15, 2013, 07:13:16 PM »

oops, I thought you were planning a 48v system not a 24v system... no idea where I got that from

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clockmanFR
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« Reply #11 on: September 15, 2013, 07:19:44 PM »

No probs knighty, Our main 65kwh system is yes, 48v.

But this is a cheap separate and independent 24v 7.2kwh jobby.
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« Reply #12 on: September 15, 2013, 08:27:58 PM »

Hi Mr CM,

absolutely given high levels of insulation and 200W/m2 you will be toasty, I didn't pick that up from your OP, I was also referring to Tiffs post at the same time, think that if he doesn't have much insulation then all he will achieve is warming up the ground a little bit.

ATB

Desp



One half of the floor is an extension which is very well insulated with celotex, the other half only has very thin insulation. The floor is conctrete block and beam with screed on top and seems to get cold quickly in the winter, I put this down to limited insulation and low thermal mass. Just looking to try and take the chill off and make it more comfy on the feet in the winter months. Also only looking to heat a few key areas where you tend to stand for long periods.

clockman - thanks for the details, very useful.

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