Todd,
I take it your house is on the icf frost wall and 4" xps you commented about earlier?
I dont recall ever reading about your house before, could you share some details, wall/roof makeup, is it a rectangle with long wall facing south? Monopitch with tall wall facing south? Im just curious as to what is working instead of reading about concepts.
Thanks

Posted By kach22i on 02 Dec 2017 02:16 PM
To the people actually living with concrete slab floors, and some passive solar design helping out, would you attempt a ground floor slab without hydronic radiant slab heating?

My latest notes on my schematic design has a lot of south facing windows under an overhang (insulating shades at night), well insulated concrete slab, open plan with gas fireplace and blower, Master Bedroom and other zones with split mini Heat/A/C eliminating duct-work and creating several "zones".

I am worried that eliminating the hydronic radiant slab heating system of my earlier concept is going to create some MRT issues.

Also concerned that just blowing hot air into the great room (open plan w/kitchen and dining) isn't going to get the heat up under the glass where it belongs. Maybe I can duct under slab the gas fireplace hot air to vents under the windows? Is there such a thing?

Maybe some supplemental mini type heating system for just the windows that go down to the slab?

Yes, I think the combination of HR floor heating and mini splits would be the right approach for your situation. Adding PEX tub to a concrete slab you are already pouring is pretty cheap insurance to ensure comfort. I would even dare say that anyone who pours an interior slab without insulation under it and PEX tube embedded in it has made a foolish mistake.

Posted By sailawayrb on 02 Dec 2017 03:57 PM

... I would even dare say that anyone who pours an interior slab without insulation under it and PEX tube embedded in it has made a foolish mistake.

That depends on where you live.  If you live in an area where deep earth temperature >65F and in a cooling dominated climate, coupling the slab to the earth can lower your overall energy bills.  I do think slab perimeter insulation is a good idea to reduce winter heat losses there.  And if you live in an all electric home (no natural gas available) then there isn't much advantage to run pex in the slab if you don't have an economical way to heat the water (I don't consider electric boilers economical when highly efficient air source heat pumps are available) plus you would generally need two systems for hydronic heating plus one for cooling/dehumidification.

As Arkie says, slab on grade is SOP in the south. I lived 20 years in Texas with ceramic tile over concrete SLAB. It was a definite plus with in the cooling season, and a nonfactor in winter. Bear in mind that soil temps under slabs from the center out will experience a thermal lag measured in months so that the slab is warming through the fall and cooling through the spring.

Guesswork isn't advisable with passive solar. I used UCLA's HEED modeling software and weather data from Harrisburg 50 miles away to see what happens through the year, and Sketchup with Google Earth to see how the sun lights the interior. Cloud cover is the killer here; Some Decembers we see Santa Claus more often than the sun. In Colorado or Arizona, where insolation is predictable, backup can be forced air, wood stove or whatever. At that point though, sizing glass and the thermal mass takes a sharp pencil. My job was easier. Pour enough concrete that overheating isn't possible and insulate it well enough to be sort of responsive.

Greentree, It's a Wright inspired shotgun house, 72 feet long and 18 feet wide through the living area, with a great room occupying 45 feet of that length, a den and bath occupying 12 feet and a 23-wide attached garage as the remainder. The upstairs is 33x18 with two bedrooms and a bath. Wright from the '30s until his death in 1959 designed several hundred "Usonian" homes he meant to be haute architecture for the masses. They live on as the rancher or ranch-style. I wanted stucco and I wasn't putting it over wood. I settled on AAC for walls as more DIYable than ICF, for R10 before mass effect. The attic is R60. The house is super tight, to the point that I bought a conventional dehumidifier because the mini wasn't getting it done on cooling and was freezing us on dehu. My goal was not energy efficiency. More like, how can I live in this thing?

I fully agree, in a cooling dominated climate you are better coupling a slab to the earth. My comment should have stated “...anyone who pours an interior slab in a heat dominated climate without insulation under it and PEX tube embedded in it has made a foolish mistake...” Having an unheated slab can be uncomfortable and just using HR to raise the temperature to 65F can significantly increase comfort.

Posted By kach22i on 02 Dec 2017 02:16 PM
To the people actually living with concrete slab floors, and some passive solar design helping out, would you attempt a ground floor slab without hydronic radiant slab heating?

My latest notes on my schematic design has a lot of south facing windows under an overhang (insulating shades at night), well insulated concrete slab, open plan with gas fireplace and blower, Master Bedroom and other zones with split mini Heat/A/C eliminating duct-work and creating several "zones".

I am worried that eliminating the hydronic radiant slab heating system of my earlier concept is going to create some MRT issues.

Also concerned that just blowing hot air into the great room (open plan w/kitchen and dining) isn't going to get the heat up under the glass where it belongs. Maybe I can duct under slab the gas fireplace hot air to vents under the windows? Is there such a thing?

Maybe some supplemental mini type heating system for just the windows that go down to the slab?

So here is our experience after one year in a primarily Heating climate (approx. 7000 HDD) Min outside temp -24 max 100 We have a 5 inch slab on grade throughout over R10, Foundation is insulated r10 outside and r5 inside at perimeter of slab. Passive solar windows on south side. One minisplit in Master bedroom, second in great room is mainly backup to Fireplace rated at 10K to 30K BTU. Floors are comfortable to bare feet year round. Average 65 to 68 in winter where not exposed to sun. Can climb as high as 80 in good sun. The most comfortable house we have ever been in. the only place the floor feels cold is in an outside corner that has windows close to the corner, in the coldest temps. I had considered putting PEX in the floor but didn't. In retrospect it would have been wasted money.

I would still recommend putting in the couple hundred dollars worth of PEX, even if you don’t initially hook it up. Some day you or a future owner might want the comfort that HR affords and do away with often unsightly looking and drafty mini splits. It would be very expensive to create a HR emitter in the future without this provision.

Posting a couple of articles touching on the topic of thermal mass. Interesting to note the second article section on high mass walls getting by with lower R-Values. http://www.crsi.org/index.cfm/benefits/sustainability https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation


EDIT:

Found another article on passive solar related to mass, swinging me the other way?

Forget the thermal mass


A link from that article...............

All about thermal mass

Posted By sailawayrb on 04 Dec 2017 03:01 PM
I would still recommend putting in the couple hundred dollars worth of PEX, even if you don’t initially hook it up. Some day you or a future owner might want the comfort that HR affords and do away with often unsightly looking and drafty mini splits. It would be very expensive to create a HR emitter in the future without this provision.

I realize you install and promote In floor heat, but you are making claims that are just not True. First, minisplits are not drafty. I have three and you never feel them. and second, it is well known that Passive solar and in floor heat are not compatible. In fact, if you build a passive solar home in Oregon and it has in floor heat, it is automatically rejected for solar energy tax credits.

My imagination may not be an accurate computer simulation, but I imagine having a way to transfer excess heat from one part of a slab, to another colder part via PEX tubing hydronic flow is an advantage.

The warm slab of course being heated by the sun. The cold part of the slab on the north side of the house. Might not be true if zones not interconnected though.

kach22i, the issue you might have in this and any passive solar room is the temp rise. To be able to move heat around you need a delta T before it will do anything. That delta T might be ten degrees depending on what is in the room and how the sun gets to the floor to be able to absorb the heat.

I have an empty 500 sqft passive solar room right now with a radiant heated floors (bare 1-1/2 concrete) R30 walls and the room temp on sunny days jumps up 7 degrees and stays there the whole day. At peak sun the whole floor is covered in sunlight. There is a 15' tall wall of windows that have .69 SHRC glass in them (http://www.cardinalcorp.com/products/coated-glass/loe-180-glass/)

I am not sure how much heat I am moving around but I do keep the floor pumps on continuously.

Very interesting newbostonconstruction.

If my understanding of what you wrote is correct; a hydronic system can only absorb heat and re-passage it if the slab is hotter than the hydronic fluid.

Meaning you would have to run cold fluid in order to suck the heat out of the slab.

In addition, by the time there is enough useful energy to draw out of the slab, the air temperature would have gotten a bit out of control, meaning the room could be uncomfortably warm from the sun.

In concept what I've described is a primitive active solar collector, yes?

Meaning instead of solar hot water panels on the roof heating fluid on the roof and being pumped down into a hot water tank, one is using window wall glass to heat a mass (the slab) then transfer that heat out of the room via fluid in the slab PEX tubing.

In short, you are living inside of a solar panel.

If this is the case, would it not be more efficient to take the mass of the slab out of the equation, and just have a floor composed of all tubing?

Imagine rectangular tubing you can walk on, a glass or translucent plastic floor in which hydronic fluid is flowing and removing excess heat to be used elsewhere in the home.

Maybe a metal floor in contact with tubing makes more sense, and you could fry eggs on it too while you are at it.....................oh my.

Not all ideas are good ideas, just exploring goofy ideas to understand the concept fully, and the concept is not fully developed.

However, it's fair to say that if there is any temperature difference between slab and hydronic fluid, there will be a transfer of energy.

You can put in heat or take away heat depending on the temperature of the slab and the hydronic fluid.

And I seem to recall reading some thread titles about cooling a home in hot climates with in slab hydronic systems. I did not click on them, but it planted a seed of curiosity - not my climate though.

> I am not sure how much heat I am moving around but I do keep the floor pumps on continuously.

If it's a separate zone, you should measure it. There seems to be a real lack of detail data on passive solar homes.

If you really want to move heat around, a water to water heat pump will do it. In theory, with low mass radiators, you could maintain zero temperature rise in the sunny room (ie, remove all the heat before it raised the air temperature).

Posted By jonr on 22 Dec 2017 02:10 PM
> I am not sure how much heat I am moving around but I do keep the floor pumps on continuously.

If it's a separate zone, you should measure it. There seems to be a real lack of detail data on passive solar homes.

If you really want to move heat around, a water to water heat pump will do it. In theory, with low mass radiators, you could maintain zero temperature rise in the sunny room (ie, remove all the heat before it raised the air temperature).

Lots of Internet search hits using the term "Low Mass Radiators" also called "Low Surface Temperature Radiators".

New term for me but have seen them many times, just didn't know they had their own name.

Posted By whirnot on 21 Dec 2017 04:22 AM

Posted By sailawayrb on 04 Dec 2017 03:01 PM
I would still recommend putting in the couple hundred dollars worth of PEX, even if you don’t initially hook it up. Some day you or a future owner might want the comfort that HR affords and do away with often unsightly looking and drafty mini splits. It would be very expensive to create a HR emitter in the future without this provision.

I realize you install and promote In floor heat, but you are making claims that are just not True. First, minisplits are not drafty. I have three and you never feel them. and second, it is well known that Passive solar and in floor heat are not compatible. In fact, if you build a passive solar home in Oregon and it has in floor heat, it is automatically rejected for solar energy tax credits.

We have mini splits in our Maui home and I find them to be both drafty and noisy. But mostly, I find them to be very intrusive and ugly. Of course, this is just my subjective opinion and they make good sense in Maui. We always recommend mini splits in lieu of doing HR floor heating with anything other than a concrete slab emitter, especially if you need AC. However, AC is not required in OR because of our diurnal climate that enables ICF to perform above R60 during the Summer and provides a nighttime cooling option not often available in other locations. Opening windows or running a whole house attic fan during nighttime will reduce the temperature of the interior thermal mass sufficiently so that with all the windows then closed during the daytime the indoor temperature will never exceed 70F even during our several heat wave days of 115F.

Yes, I am very familiar with the flawed OR passive solar tax credit application. It incorrectly derates HR heated floors for passive solar application. We had ASHRAE write them a letter several years ago to clarify and correct this which they indicated they would eventually do. However, government agencies don’t always move very fast and this tax credit will end this year before they made the clarification/correction. Even so, we still received deviations of this HR heated floor derate for many clients.

Passive solar and HR heated floors are not incompatible if designed correctly, but most companies don't know how to accomplish it or don't want to get involved with it as some engineering is required. The most simple way of accomplishing this is to zone the passive solar heated areas separately from the other areas and not call for heat in these areas based on slab and/or air temperature. The better but more complicated way of accomplishing this is to extract the excess heat absorbed by the passive solar heated slab and move it back to the boiler return line for use in other heating zones that are calling for heat. The temperature of a concrete slab doesn’t affect how much heat that it can subsequently absorb. The slab just keeps getting warmer and it can overheat the room if something isn’t done about it. Anyhow, we have been successfully doing this for over 10 years now and it works very well. In fact, passive solar and HR floor heating design integration is what we specialize in...that, and water project integration (i.e., water rights, hydro power, hydraulic ram pumps), which is why our company logo looks the way it does...

Again, one needs to accomplish an integrated design that fully considers passive solar design, thermal mass design and HVAC design for the given location to achieve great results.

Good Morning All I live in Zone 7 in Northern Maine and have a ICF house footer to rafter with Hydronic in slab and under joist for 1st floor, I am heating 1600 SQ feet of living space and only use 320 gallons of heating oil per year to include my hot water.. Yes my house will increase 2-3 degrees above set point sometimes when the sun shines into my house. 100 percent windows on front facing west. I see only a positive for my "THERMAL MASS" In addition I have floor sensors installed and this time of year where it is 10 at night and 45 and sunny in the day i just bump down the floor sensor 1 0r 2 degrees, no biggy for me. just my 2 cents. In addition I use a window 12k AC unit in the summer and it cools my whole house

Buildnewb:

I find it kind of fishy when you start a thread and use dramatic language like, "a very, very bad thing"

All the studies show that thermal mass is never a "very, very bad thing". Like Sailawayrb said, it can have a neutral effect but never is it really a horrible thing like you put it.

I also find it fishy when scientific studies and performance calculators are shown, you say nothing.

I have a feeling that you are here to push some type of product you sell and maybe ICF was your competitor so best to knock off your competition by trying to slander them. Just my hunch.

Thermal mass through simple solid matter is one thing - the mass gives off or absorbs heat only when it changes its temperature, so that mass of itself assures some undesirable temperature swing. Thermal mass through phase change materials (PCM) is a far different animal, but I see so little discussion on this site. PCM is an integral part of home and commercial design in Europe - what's up with the US? Does anyone have experience with PCM in residential construction? Any US manufacturers?