How to best heat the SLAB ?

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Re: How to best heat the SLAB ?

Postby Warpspeed » Sun Jun 03, 2018 12:36 pm

australsolarier wrote:warpspeed,
ever heard of the heatsink effect?
obviously munter's system is not that much different from the heat sink behind the northern window.

Certainly have.
And the larger it is, the more heat that is required to be added/removed to change its temperature.

Once it cools down, its going to be a lot more expensive to heat back up again (energy wise) than just heating up the air in a room directly.
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Re: How to best heat the SLAB ?

Postby munter » Mon Jun 04, 2018 12:18 pm

Yes – 55 tubes is on the small side. I actually have 1 x 30 plus 2 x 20 tube collector manifolds mounted but can only use 55 of the tubes because of constraints to do with the mounting location. The collector panels are mounted vertically on the northern facing wall of my house. This wall gets great sunlight through winter and is shaded through summer which means I have no issue with excess heat collection through the summer months. It also leaves my roof space clear for PV which produces a valuable output all year round. Our building envelope is reasonably high spec with double glazed timber windows and decent slab insulation (underneath at least – the edges were not done well) so our heat demand isn’t too high.
The reason I only use 55 tubes is that I only fit them in the space between the windows. I don’t want to block the light into the rooms with evacuated tubes as that would be somewhat counter-productive! If I had more wall space I’d really like another 30-40 tubes but I’ve run out of convenient wall space.
Mounting the tubes on the walls has worked out very well. They are out of the way and get a good amount of sun. A little bit of tilt would probably be even better but the convenience of mounting them flat against the wall is quite appealing.
The response rate of the system is very slow. Heat is slow to percolate its way from the hydronic pipe up to the surface. It takes at least a couple of hours for any effect to be noticeable at all. The corollary of this is that it also takes a while to cool down which means that day heat lasts well into the night.
If I had to solve this problem again, I'd probably go with masses of PV and RC AC. The response rate is faster and the panels have better all-season utilisation. At the time, however, solar PV was still very expensive and solar thermal could be had for lower cost because every tom, dick and harry was having a go at importing evacuated tubes from China and most found it tougher to sell them than they thought meaning lower prices as they struggled to move stock. Both those situations are different now.
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Re: How to best heat the SLAB ?

Postby Davo Yarra » Thu Jul 26, 2018 12:43 pm

Hi all,

This is a very interesting and poignant type for me. I hope some of you can help.

I'm in detail design phase of a new build in the Yarra Valley and struggling with how I can make hydronic slab heating work when off-grid. The house has the majority of the passive house design principles (sans perfect winter suns ability to warm the slab as we wanted the aesthetics of verandas all around, however it shall have extremely good insulation and sealing) and is about 260m2 of slab.

I can go on grid if I absolutely have to however due to the distance from the pit ( 350m and 2 Phase only) and the pioneer clause to enter it the cost is huge anyway (cica 25-30k). I will be having solar PV and batteries in one form or another and I'm wondering if simply going bigger with this system is better thantrying to make Solar heating work.

What are the no bullsh1t, real viable options out there that have been tried and tested??

Thanks for your help.

Cheers, Davo
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Re: How to best heat the SLAB ?

Postby Warpspeed » Thu Jul 26, 2018 3:20 pm

it shall have extremely good insulation and sealing) and is about 260m2 of slab.

Then you are looking at heating the whole house 24 hours per day (in winter) to maintain the required comfort level.
Slab heating is not the kind of thing you can get out of bed on a freezing cold morning, switch on the heat and heat the whole slab up in half an hour.
So whatever you use as a heat source to heat up that whole slab is going to be large and expensive no matter what fuels it.

If you are committed to a slab and hydronic heating, use the slab only for minimal background heating, and use something else to very quickly heat up only the occupied rooms if running costs are important.

Its a classic story, people move into a new luxury home with central heating and glory in the comfort of having every room at a constant temperature day or night. Until they receive their first eight hundred dollar gas bill.
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Re: How to best heat the SLAB ?

Postby davidg » Thu Jul 26, 2018 3:32 pm

Davo Yarra wrote:I can go on grid if I absolutely have to however due to the distance from the pit ( 350m and 2 Phase only)


Please don't call SPLIT PHASE or 2 phases of a 3 phase system, 2 phase it isn't, period. We don't supply 2 phase anywhere in Australia from the grid.

2 phase is NO, it is almost certainly SPLIT PHASE. Australia uses a lot of SWER lines in rural locations (Single Wire Earth Return, typically around 19K-22K supply voltage to transformer) to the transformer on a pole, normally rated at 25KVA output and is supposed to be 230/460VAC end to end of the total winding in the transformer, that is the STD it may not be this is reality but it is supposed to be. The output is supplied with via centre tap being used as the NEUTRAL and 2 Actives each of 230VAC to the center tap point these are 180 degrees out phase to each other, this is SPLIT PHASE, to call it 2 phase is totally wrong.

True 2 phase is 90 degrees out of phase to each other or you might have 2 phases (This is not 2 phase either) fed from a 3 phase distribution network. Check Wikipedia for full explanation about 2 phase.

For bigger SWER line supply they sometimes use a double SWER line to the SWER transformer however the output is still classed as SPLIT PHASE or 3 wire single phase, thanks to the way the transformer is wound and the centre tapped.

https://en.wikipedia.org/wiki/Split-pha ... tric_power
..
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Re: How to best heat the SLAB ?

Postby Davo Yarra » Thu Jul 26, 2018 4:21 pm

Roger that davidg, Thanks. I think it’s probably a single phase 3 wire type then. Do you know if it that type would create any issues with implementing an AC coupled hybrid type, on grid solar generation system? Or would it be the same for a normal 1 phase-neutral type supply?
Thanks,
Davo
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Re: How to best heat the SLAB ?

Postby davidg » Thu Jul 26, 2018 10:37 pm

Davo Yarra wrote:I think it’s probably a single phase 3 wire type then.


single phase 3 wire = split phase.

Distributors typically require any power systems to balance across both halves of the transformer.

In fact I'm in the process of doing a Selectronic based design with batteries for a split phase system at the moment, they are one of the few battery inverters that properly support doing split phase on a SWER line supply. At some stage in the future if they want to get off the grid all together it can reconfigured for single phase only or three phase with the addition of equipment, after all it's just money :D , however none of the original equipment and installation is wasted, doing either of these system configuration changes.
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