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Old 02-23-15, 04:44 PM   #511
Mikesolar
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P.S. here is a link to a new Passive House project in my area that is the most modest I have yet seen(though I am sure still has a non modest price) but in my mind going the right direction. They call it a "retrofit" but it is a full rebuild and only retro fit to the lot site, TE Studio - Residential Passive House Design Experts.
Haha, I like some of the home designs he has done but "she who must be obeyed" wants victorian........bummer.

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Old 02-23-15, 08:26 PM   #512
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We therefore have a condition that the paper does not talk about (unless I missed it) which is what to do during part load, run at full and open a window?
I hope not!

In my well insulated current house (4 pane windows, R35 walls, R50 ceilings) the radiant tile floors never feel warm to bare feet, even when it's 0*F outside.

My answer: wear slippers, I know it's hard to take such an inconvenience!

A/C from everything that I have read, it don't make sense to pump with turbulent flow
that is > 8fps.

The increase in pumping energy is too much vs. gain in heat transfer into concrete.

Also water noise in fittings & flow balancing valves + possible erosion in copper fittings increases.
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Old 02-23-15, 11:24 PM   #513
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But the question is......do you need it? A typical 1/2" tube on 8" spacing with 110F water can give 50 btu/ft2. I'll bet Drakes home won't need more than 10-15btu max. There is no need to try to get the most heat out of a tube when it will only make your feet uncomfortable.
There's a very different way to look at this...

If you make the radiant surface as efficient as possible (closer tubes, larger diameter, turbulent flow, increased volumetric flow, better thermal conduction, etc) you can satisfy your heating requirements with lower temperature (lower exergy) water.

This equates to substantial gains in efficiency, especially if you are using a heat pump. In fact, with a heat pump, linear reductions in feed temperature will result in exponential increases in heat pump efficiency.

With fossil fuels, I think that linear decreases in required feed temp will result in linear increases in efficiency. Still a good thing.

This low temperature heating thing is really phenomenal... who would have guessed that you can use cold air to make your house warm... or cold dirt, or cold water.

And unlike fossil fuels, of which there is an ultimately vanishing supply, there is a vast amount of cold air, and cold dirt, and cold water... the supply is unimaginably large.

Low-Exergy (AKA: low delta-T) techniques really do open up completely new opportunities.

-AC
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Old 02-24-15, 09:37 AM   #514
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By far the biggest challenge to me is developing control of a well designed hydronic radiant system. So many variable ways to use hydronic, hi-temp/low-temp, hi-mass/low-mass, on-demand heat/storage, and combinations thereof. Can't see one control method fitting every situation so customizing seems to be the goal. And some may be as low tech as some fresh air. Or just putting on a sweater for awhile till floor catches up. Constant comfort is a hard thing to provide efficiently as possible in a variable world.
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Old 02-24-15, 10:47 AM   #515
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By far the biggest challenge to me is developing control of a well designed hydronic radiant system. So many variable ways to use hydronic, hi-temp/low-temp, hi-mass/low-mass, on-demand heat/storage, and combinations thereof. Can't see one control method fitting every situation so customizing seems to be the goal. And some may be as low tech as some fresh air. Or just putting on a sweater for awhile till floor catches up. Constant comfort is a hard thing to provide efficiently as possible in a variable world.
If you are concerned with fluctuations in your house, and you seem to be, and you think that you will experience these fluctuation with a large radiant slab, maybe you should change directions and go with low-mass heating rather than high-mass heating.

The Magazine article you linked to before, which is all about renewable-sourced radiant heating, features all low-mass solutions. Heat is stored in a suitable buffer tank, and is released to the interior as required. This and the low-mass radiators he is featuring, all have thermostatic control on each radiator.

What is your ZIP code?

* * *

I jist made a guess that your ZIP CODE would put you somewhere near the MPLS-St.Paul International airport.


Here's a graph of last years temperature data. Looks like you have a lot of temperature swings over the year, especially during heating season.

If you're not interested in investing in serious dense-pack insulation (=> 12" thick walls). Maybe you should forget high-mass heating, and go with an overall lower efficiency, low-mass system that is able to anticipate and track ambient temperature fluctuations.

-AC
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Old 02-24-15, 05:18 PM   #516
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With R45-50 walls my main concern will be controlling overheating, not under, most of the time. With a lag time measured in days, it will be hard to predict heat need days out even with a reset valve. MN winter temps can and do swing 30 above to 30 below and back. Fortunately I have a large 3 season space to bleed off extra heat if needed. The goal is to try to not over heat if possible. Large solar gain capacity will also add to the challenge. Luckily my wife would love it 90 inside in winter. I'm outside most of the time anyway,lol.
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Old 02-26-15, 09:22 AM   #517
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With R45-50 walls my main concern will be controlling overheating, not under, most of the time. With a lag time measured in days...
OK Drake, I think I have found the answer to coping with the thermal lag of your heating slab...


You need a Veskimo Personal Cooling Vest. This is no joke, it is a real product.

I think it will work in reverse, for warming also.

Problem Solved!

-AC
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Old 02-26-15, 03:11 PM   #518
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Nice product, now if it could come with a self contained boiler my wife finally be able to be happy in MN in the winter. As for keeping my cool I have a retreat called an "ice fishing" house that sits on up to 3' of frozen lake which I plan to spend a lot more of my MN wintertime in once I get this build done. Also like my unheated basement shop as well. Seriously because I am incorporating so much passive solar potential and want to control to make use of off peak elec rates I will have a strip or two of standard elec baseboard for quick demand supplemental heat if in working to control to the minimum hydronic heat input leaves me on the cold side. Part of the maximizing of the energy of our homes is a comparable lifestyle and interaction with the structure. Low tech takes more interaction(another log in the fire or manual thermal blinds on windows) or hi tech for automation, to each there own. I must be getting old because more and more I'm wishing for the good 'old tech things that worked long enough to at least pay for them.
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Old 02-26-15, 05:25 PM   #519
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As for control of the slab, I would just use a slab sensor in a neutral area to trigger the heat source. Don't worry about night setbacks or fancy controls. Have lots of pumpkin or apple pie for extra energy and sneak out the ice fishing hut with some beer (or kahlua and coffee).

That passivehous i am doing will be based on outdoor temp + a neutral area air temp overide due to all the window area.
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Old 02-26-15, 05:55 PM   #520
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I know my space will even be greatly affected by just the day or two a week we bulk cook/bake with oven/stove as opposed to the remaining microwave leftover days.

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