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Old 12-07-13, 05:55 AM   #361
Mikesolar
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That thick stuff must be pretty expensive. Question is.... it there that much value in it?

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Old 12-07-13, 11:59 AM   #362
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Originally Posted by Mikesolar View Post
Just make sure that the reflective bubble material is at least 3/4" below the subfloor or it will have next to no effect. Radiant effect requires an air space for the wavelength of heat to reflect. otherwise it just conducts through.
In the link that michael pointed to, there was the sentence, "The layers of MLI can be arbitrarily close to each other, as long as they are not in thermal contact."

That material was designed for use in space, where, except for conduction thermal radiation is the only mode of heat gain or loss.

The nature of thermal radiation on earth is the same, but heat loss will have the additional mode of convection. Convection depends on the flow of fluids (air can be considered a fluid, since it flows) and fluid flow is inhibited by friction.

So, if the gap between layers, radiant insulation layers that is, is very small, the fluid friction will inhibit convection losses. The larger the space, the lower the fluid friction, the greater the convective losses.

So, the "at least 3/4 inch" idea might have a problem.

Also, regarding wavelengths, check this out:

Quote:
Infrared (IR) light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nanometers (nm) to 1 mm.
So, a long wavelength is 1mm.

If your wavelength idea is correct, you need a maximum space of 1mm to allow the reflective surface to do it's reflecting magic. As your space becomes larger than that, fluid resistance drops, convective currents form... the larger the space, the greater the convection.

I believe I have heard this referred to as "convective pumping".

Best,

-AC

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Old 12-07-13, 12:21 PM   #363
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QUOTE=AC_Hacker michael, I came across an interesting article, discussing, "How Much Insulation Is Enough?"

Good link...thanks. I can easily increase the attic insulation to 50, and I shall. The walls pose a larger problem, but I'm working on the idea of staggered studs and increased fill with fiberglass. I'm also reluctant to go to triple glazing, so I may be stuck with windows with a 3.3 R value. I'm surprised the author doesn't comment on underfloor insulation except re: slabs. Here's a link that speaks to underfloor insulation for framed floors:

BPA - Energy Efficiency | How to Insulate a Floor

In reference to a comment by MikeSolar about maintaining a 3/4" space between reflective insulation surfaces, it seems to me to be too great a space in a wall because convection can circulate up and down in a tall space like that with one heated and one cool surface, but under a floor, convection may prove to be less of an issue as the horizontal space might offer less opportunity for large air movement in a vertical direction, and I believe convection does rely on gravity in most cases.

I wish I had put a quilted reflective foil on top of the subfloor between the wood and concrete, but I was more concerned about trapping water and future degradation of the plywood, so I've opted to place it under the plywood. That should add a little to the R value of insulation. mm
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Old 12-07-13, 01:06 PM   #364
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...I've been schooled in the belief that little heat is dissipated downward in such construction, that it's ceilings first, then windows, walls and finally the floor with the stipulation that there be a thermal break around the edge of the slab (when it's not on grade because there one needs lots of insulation below the slab as well) to prevent heat leaking out the sides. That may be old school...
That's the way I used to think about it, too... as they say, "heat rises".

But it turns out that 'they' were only partially right, and that heat has three modes of transfer:
  • convection
  • conduction
  • radiation

It is only in the case of convection that, "heat rises" is true. It is true that hot air rises, and it is also true that hot water rises. It is gravity that makes this so, because hot air and hot water expand, and become less dense and are displaced by colder fluids of greater density.

But with conduction, it is not true. Otherwise, if you were frying bacon, you would be able to lift the skillet and put your hand on the bottom of it, and it would feel cool. An appeal to common sense is probably sufficient, in this case.

Also, radiation is unaffected by "up-ness". My little electric counter-top broiler/toaster works just fine, radiating heat down to my sizzling pork chops. And in the case of the sun, the source of all life, where is up-ness in that case?

In the case of your radiant floor, the heat from the PEX eventually makes its way to the surfaces of the floor via conduction, which works in all directions. So the top will become a heated radiating surface, and the bottom will also become a heated radiating surface, and the sides, too. If the sides of your floor are in direct contact with the anything, heat will flow into whatever material the sides are made of, etc. So you've seen to that with edge insulation.

The heat that makes it to the upper surface of the floor will radiate out. But it will also heat the air that is in contact with the floor, and it will begin some degree of convective pumping. So in truth, a radiant floor is also a conductive floor, and a convective floor. All three modes are going on simultaneously. But since radiation plays a large part (maybe 30%) it is called a radiant floor.

If you crawl under your house and lay in the dirt on your back and look up at your floor on a cold winter night, and put on some infrared glasses, you will see that the floor is hot, and it is heating by conduction, everything that it touches. You will also see that heat is radiating off of the floor, making your stay in the crawl space dirt a little more bearable. You will also see that air that comes in contact with the floor heats up, but gravity will be in your favor, and convection-heated air will not rise away from the floor (in perfectly still air). But any breeze, or puff, or imbalance in air-heat content will strip away the heat from the bottom of your floor.

So you do need insulation under a radiant floor, unless the space underneath the floor is also heated.

And I think that the minimum R-values still apply...
  • roof/vaulted ceiling insulation is R38
  • exterior walls is R20
  • floors is R30
  • windows R2.86

I mean, you wouldn't tolerate money leaking out from the bottom of your bank account would you?

Best,

-AC
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Old 12-07-13, 01:39 PM   #365
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Michael

Really a nice job!! Nice layout. I like your manifold set-up.

We live in Canada with hydronic floor heating now for a number of years. Of late we had changed from oil fired to solar hot-water with geo-thermal back-up. ( some winters are more geo-thermal with solar back-up "little sun")

The heated floors are the holy grail of heating system. People that come to visit say Wow when their feet hit the floor. During the deep winter (outside temp -10 to -20 Deg. F. ) the floor is maintained at an elevated temperature of 85-88 Deg. F. Its almost therapeutic as it feels so warm. But for the more temperate winter temperatures of 40-0 Deg. F. the floor is maintained at 76-78 Deg. F

I'm not sure what your plan for floor coverings are but we have porceline tiles, wood plank and a big mistake carpet in one room.(going to change eventually)

The tile floors are truly amazing, wood plank OK but wouldn't recommend it. But carpet totally sucks!! A tile floor, if you need a small area rug is OK.

Anyway Great job Michael you'll really enjoy your heated floor.

Oh, one final thing that I had found with the heated floor. Controlling the zones is not so nessisary as the heat is so uniform. I have a thermostat controlling each zone {6}(rooms) A little over-controlled!! One thermostat controlling the main floor is enough and a separate thermostat controlling the garage would be all required. The thermistor is epoxied in the concrete floor as we sense the floors temp and not the air. Use a tube drilled into the concrete or some method that you can change out the thermistor as a thunderstorm that has been close took out some of mine and what a PITA to replace.

Randen
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Old 12-07-13, 05:21 PM   #366
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Quote:
Originally Posted by AC_Hacker View Post
That's the way I used to think about it, too... as they say, "heat rises".

But it turns out that 'they' were only partially right, and that heat has three modes of transfer:
  • convection
  • conduction
  • radiation

It is only in the case of convection that, "heat rises" is true. It is true that hot air rises, and it is also true that hot water rises. It is gravity that makes this so, because hot air and hot water expand, and become less dense and are displaced by colder fluids of greater density.
-AC
'Heat' does not "rise" in any sense of the word. Heat energy flows from a hotter body to a colder body by any or all of the stated means.
In Convection heat transfer, a hot (lighter) fluid may rise within a body of colder (heaver) fluid because of differing fluid mass densities subject to gravitational forces, if physical conditions allow. Why we use glass insulation
in wall and ceiling in spite of the fact that glass has a much higher thermal conductivity than does air. It physically restricts or eliminates the convective heat transfer process, thus a worthwhile trade off.


AC Quote;
So you do need insulation under a radiant floor, unless the space underneath the floor is also heated.

And I think that the minimum R-values still apply...
  • roof/vaulted ceiling insulation is R38
  • exterior walls is R20
  • floors is R30
  • windows R2.86

The R rating of insulation is a measure of conductive resistance. Inasmuch as in the downward direction convection is a negligible problem, an R zero film is sufficient to prevent air movement within the joist space, air being a better conductive resistance than is any insulating bat material.

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Old 12-08-13, 01:48 AM   #367
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...Inasmuch as in the downward direction convection is a negligible problem, an R zero film is sufficient to prevent air movement within the joist space, air being a better conductive resistance than is any insulating bat material...
Please tell us more...

-AC
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Old 12-08-13, 01:03 PM   #368
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Do we agree that there is no gravitational forcing function to cause convection heat transfer in the downward direction beneath a heated floor? By conduction transfer, the warmest, lowest density air is already at the top of the crawl space, the between joist volume. Gravity is holding it there, by displacing the colder air to the bottom of the crawl space. So the heat loss downward is restricted to conduction and radiation phenomena. There is no convection loss downward, in the absence of an externally caused air circulation, such as wind thru open crawl space vents (which is not considerded a natural convection phenomena). I close mine in the winter, and have no conductive nor radiant insulation under my heated floor.

Thus, in the absence of natural convection heat loss in the downward direction, there is a negative value to using a bat type conductive insulation in this area, inasmuch as any bat material will have a higher conductivity than does still air. Bat type, volume insulation is only useful in preventing natural air convection.

When building I decided against the use of radiant, reflective insulation under floor because it is only marginally effective in reflecting this low temperature radiation when new and is rapidly degraded by any accumulation of dust on its upward facing reflective surface. Thus, long term not cost effective.
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Old 12-08-13, 08:44 PM   #369
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Quote:
Originally Posted by AC_Hacker View Post
OK, I looked through the PDF, thanks for the link.
I think there could be someone else on the forum who would be better to answer your question... and I don't know who. Now, if you were building your own heat pump, I could help you out, but divining the intent the factory is just not my specialty. Sorry,-AC
Referring to the original question: can someone explain what the terms "part load" vs. "full load" mean with regard to heat pump performance? I've been reading a PDF from roth-usa.com on their RWT Series Water-to-Water Heat Pumps, and in the performance data under the column titled "capacity," they list values for part and full load. Are they modulating heat pumps, or to what do the terms apply?

Got a reply, and sorry about not being in the correct thread:

Hi Michael,

The Roth RWT heat pumps include a 2-stage compressor. The “Part Load” refers to the compressor operating in the first stage. The “Full Load” refers to the compressor operating in first and second stage. The microprocessor control automatically engages the second stage when the load is greater than the first stage can accommodate.

Please contact me if you have any further questions.

Product Manager
steveg@roth-usa.com

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Old 12-08-13, 10:21 PM   #370
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Originally Posted by berniebenz View Post
there is a negative value to using a bat type conductive insulation in this area, inasmuch as any bat material will have a higher conductivity than does still air. Bat type, volume insulation is only useful in preventing natural air convection.
I believe you're missing the point here. Even though the fiberglass batting does conduct a miniscule amount of heat, it offers a surface for your floor to radiate its heat into. Once the radiated heat is spent on the top surface of the batting, the underlying batting prevents this heat from travelling anywhere. It merely compresses the stratification effect to near the source. At the bottom of the batting, the surface temperature is much closer to ambient, preventing much of the radiant heat from heating the air below.


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