EcoRenovator (
-   Solar Heating (
-   -   Attic heat project designed from the bottom up (

Exeric 09-03-13 02:20 PM

Attic heat project designed from the bottom up
I have been working on the attic air heating idea and have done most, but not all, of the construction on it. This is an offshoot from the Using Attic Heat for the House thread:

It uses an open system after all, but where the air enters the vented roof through baffles at the eaves a radiant foil barrier comes down to meet it. This way a thin layer of pretty hot air moves up between the rafters without danger of insulation contamination. Also there is a readily accessible place to change the filter down in the occupied living area. I will be posting pictures soon.

This is a designed from the bottom up system so if if doesn't end up making financial sense here in a moderate climate - California - then it won't make sense anywhere. Having said that, the project is not yet completed, nor have I yet experienced a winter with the system complete, so only time will tell how effective it is. I promise to show you any problems with the system over time and won't keep you hanging if it turns out not to have have been a good idea.

Daox 09-03-13 03:03 PM

Woohoo, can't wait to see this. :)

Exeric 09-03-13 03:25 PM

10 Attachment(s)
Here are some pictures, hopefully in the sequence of construction, so you can get an idea of what's going on. This first picture is of the interior roof that I painted flat black. It shows the 8" roof vents that haven't yet been disabled.

The is a picture of the flashing and turbine used to house the new motorized damper. The lower part of the flashing is 16" wide to accomodate the motor that is on the 12" damper.

This is a picture of the roof damper itself before installation. It is used to close off all attic air from escaping in winter.

Here's the picture of the roof prepared for installing the new damper. You can see the key hole notched out for the motor assembly on the new damper.

Here's the roof damper installed. The remaining 8" vent is blocked off and the beginnings of the white painted boards that the radiant barrier will attach to is installed. This is a hip roof house to it was easy to decide to get all the hot air to come together at the top-middle.

We're finally getting somewhere in this picture. All the white painted boards are attached and you can get a better feeling for what is going on. The round duct in the center board is a backdraft damper. Gravity normally holds it shut. But I plan on installing a whole house attic fan to blow out any hot air that accumulated during summer evenings. So that damper should open when those fans are turned on.

This is the duct that pulls hot air down to the living space. It attaches to the remaining opening in the third white board. It's a 12" duct.

This is where that duct enters the living space. That orange thingy is the motor in a second 12" damper that controls/allows hot air into the living space. It runs right next to my propane fireplace and will be hidden behind a closet door, but still accessible.

This is the filter housing just below that damper, both in that closet area.

All ducts are wrapped in insulation and the reflective foil is installed from inlet soffit right upto and including the white boards at the top.

More later...

Exeric 09-03-13 08:49 PM

2 Attachment(s)
A bit about the building philosophy behind this. From everything I've been reading most people install roof heating systems using the air to either heat some kind of reservoir, usually a crawlspace, or as an one input to the fresh air inlet on a forced air system. The reason is that this kind of attic heating doesn't usually supply a high enough temperature to reliably heat the house directly. Xringer, I think your idea of using attic heat to warm the basement fits into the first category.

I'm taking a bit of an educated gamble here. I have several things going in my favor. One of them is that it is extremely rare for the high temp of the day in winter where I live to be below about 45 degrees. It can get down to 20 degrees at night though. Here are the temperature readings for the house with the roof painted black but no radiant insulation barrier in place.
On the hottest day of the year so far you can see that it was 108F outside temperature in the shade. There was a 26 degree differential temp between that and the 134F temp (lower right in the picture) taken at the interior roof peak. A 26 degree boost ain't much to work with.

Here's a picture of the temps after installing the radiant barrier and insulating the attic ducts.
Here, on another hot day, it is 106F outside in the shade and it is up to 149.9F at the interior roof peak! That's a 43F temperature boost for the attic heat over ambient outside temps. I should add that all these temps were taken with the roof damper open and the living space damper closed. I'm betting that in winter conditions when the positions of those dampers are reversed there won't be much change in the differential temperature.

My reasoning is that the differentiall temps on a sunny day tracks consistently so far at 40 to 45 F, regardless of overall high temps. I been looking at the temps everyday for a month and a half. I also think it might be a reasonable guess that when the roof damper is closed and air is actually being taken into the living area that it won't cool the roof more than having an open roof vent would. Again, more of a hunch. We'll see. I've got tons more work to do on the house, most unrelated to this project.

At any rate, a 40 degree temperature rise on a sunny 40F day still gives me 80 degree air into the house for 2 or three hours a day. If its 50 degrees, overcast and I get only a 20 degree differential temperature then I'm still getting 70F air coming in. So overall I think I may just wiggle through with out having the complexity of having a reservoir system to take the relatively cool air from the attic.

Daox 09-04-13 07:54 AM

Very cool, a 40F differential is pretty good! I like how you were able to boost it with the radiant barrier, very clever. Can't wait to see more.

Exeric 09-04-13 01:35 PM

Daox, thanks for the kind words. I've been wondering how your remote located solar panel project is going. Any updates? I've been busy so I may not have kept up.

Daox 09-04-13 01:53 PM

Sadly no, I've had no opportunity / time to work on it.

MN Renovator 09-05-13 03:26 AM

Attic venting is to remove moisture from the attic and also keeps the attic cool to prevent ice dams once melted snow reaches the eaves. If you aren't in an area that has much snow, which you probably aren't since you said 20 degrees as an overnight low, that might not be a problem but the moisture issue likely is still an issue and could cause serious mold issues in the attic. How are you planning to handle that?

Exeric 09-05-13 11:47 AM

I really don't think moisture is going to be a problem. For one thing, the radiant barriers come in two forms, perforated and unperforated. I'm using the perforated kind and that's what you should use if you want to let the moisture out.

Also, at night the roof will get just as cool as the outside weather because the sun no longer beats down. There's just a lag time before that happens. So there's no reason to keep the attic damper closed during those hours. That should clear out any moisture.

Daox 09-05-13 01:25 PM

I think I get what is going on here, but where are your fan(s) going?

Exeric 09-05-13 02:24 PM

I was waiting for someone to ask that question!

Originally Posted by Daox (Post 31424)
I think I get what is going on here, but where are your fan(s) going?

Daox, it seems appropriate that the first smart cookie to ask it was you. I have thought long and hard about that and have decided the best fan is no fan. I built the ducting to the living space with oversized dimensions and with as minimal a distance as possible just to cut down on air friction. There will probably be less air friction in the duct than there will be in the little filter at the bottom that the air goes through. That means that the only real effective resistance to bringing that air down to the living space will be due to overcoming the stack pressure.

Since this system is bringing warm outside (fresh?) air in winter it makes sense to just use it as makeup air for a bathroom fan. So that's what I plan to do. I think a an 80 or 130 CFM Panasonic bathroom fan should be plenty to overcome the stack pressure and bring that warm air in. The advantage of doing it this way is that you avoid most of the draftiness of only warm, (not hot), air being blown on you from a pwerful fan.

The trick is you have to make the house pretty air tight to do that. Otherwise the house will find some other way than the open duct to get that makep air. I've been spending a LOT of time making the envelope airtight.
I'm also planning on installing a Aldes makeup air vent for those times when I can't, or don't want to, use the attic as a makeup air source.

Daox 09-20-13 12:04 PM

That sounds like it should work if your house is tight enough and your bath fans can pull enough air through. I have two unknown bath fans (recycled), but I'd like to add a 3rd to pull even more air through with my setup.

Exeric 09-21-13 07:31 PM

Hi Daox,
I may have sounded more confident than I was about the adequacy of a bath fan to bring down the air. What I've been thinking about recently is using a 130 cfm Panasonic fan in full ON mode rather than the SLOW mode. The beauty of those fans, besides being efficient, is that they are built to compensate for a somewhat tight house. That is, it will use up to double or triple the power in watts to keep the air moving at the rated CFM when things are tight. I'm hoping that at the full rated 130 cfm, and the ability to compensate for high equivalent wg air friction in the house, that one fan in my relatively small, open plan house will be sufficient.

That also brings up the whole issue of controlling the fan and the duty cycle of the fan. Since I really only want the fresh warm air to come in when the air is actually warm maybe it makes sense to use it on high for a limited amount of time and not at night when the air might be cold. It would depend if you have heat storage. I don't. A lot of the answers to the questions just depend on trial and error. If you plan on going ahead with outsulating your house envelope then it might be worth putting off some of the ripping and tearing until then. You'll then have a good baseline to incrementally increase the airflow as needed.

Exeric 09-24-13 03:30 PM

Update on the bath fan CFM requirements... After googling I found this:

"First, determine the height of the building (H) above grade. Second, arbitrarily select a neutral pressure plane height (Hnpp) above the grade of the building, usually one or two storeys above grade in a multi-level building. In a low building select grade as the neutralpressure plane (npp).
Third, select a given height above (or below) the neutral plane, such as the roof plane. Compute the pressure difference at that plane as follows:

"ΔPs = dig(H-Hnpp)(Ti-To)/To
where ΔPs=stack effect pressure difference (Pa)
and di =density of indoor air, kg/m3
and g=gravitational acceleration, 9.81 m/s2
and H= height of plane above (or below) Npp, m
and Hnpp=height of neutral pressure plane, m
and T=absolute temperature, Kelvin
and i = indoor, o = outdoor

"For a 60-m (197 ft.), 20-storey building with a neutral pressure plane at about the 4th storey or 12 m (40 ft.) from grade, in winter with an outdoor temperature of -20C and an indoortemperature of +20C, the stack effect at the top of the exterior wall (and roof plane) is:

=89 Pa
I calculated the stack effect pressure I would need to overcome by inputing the information from my house. It is 13.5 feet to the top of the roof from the floor in the house, which I'm using as the neutral plane because the floor is where the duct will vent its air. I'm using 4.44 degrees C (40 F) inside air and 29.44 C roof line air (85 F). Those are worst case scenarios with 45 F degree differential temperatures and will cause the most stack pressures that might reasonable have to be overcome after having the house unheated for a time.
Using those inputs:
=18 Pa

Blower door tests are done at 50 Pa. Since I'm going to want to get a blower door test done anyway all I need to do is get that result and convert by 18/50 = .36 My understanding is that a blower door test usually gives the CFM rate within the overall air changes per hour. So when I get that CFM rate I'll multiply it by .36 to get the overall CFM rate of a bathroom fan needed to overcome the 18 Pa stack pressure. I hope I'm getting this right as I'm learning as I go.

Anyone who sees an error let me know. I'm fallible.


Yep, I'm fallible. Used feet instead of meters. It should be
=5.5 Pa

And the correction factor for my house won't be .36 but will be
= .11

Exeric 11-15-13 10:49 PM

2 Attachment(s)
Well, its seems I was looking through rose colored glasses when I estimated that the temp rise in summer of 40-45 degrees would continue into winter. My reasoning was that the lower inclination of the sun was already included in the lower air temperatures in winter so that there would be no reason to double count that in the temperature differential between outside and attic temperatures. So there is a lower temp rise than what is already included in the lower air temperature in winter (technically Fall).

Everyday I've watched the temp rise between outside and attic get lower. I still haven't closed the roof vent because I wanted to see how things change without a lot of variables. Here are some temp rises I've recorded:

Oct 8 - 34 degrees rise, attic high temp 110 degrees
Oct 28 - 31 degrees rise, attic high temp 98.

I was starting to get concerned because on poor solar days it was dropping into a temp rise of the low 20s. I needed to do something before things deteriorated further, which I did. More tomorrow on how I improved things while keeping the roof vent open for comparison purposes.

Exeric 11-17-13 12:14 AM

1 Attachment(s)
Getting back to the problem... attic solar heat has a quality problem, not a quantity problem. That is, there is a huge quantity of roof surface space that the sun radiates onto. There is a lot of solar energy impinging on any roof. But it also has lower temperature than a dedicated solar panel because for various reasons it is not as efficient at capturing energy as a dedicated solar panel. This means that for a given surface area that the sun radiates onto the internal temperature of the air in an attic will be much lower than in a solar hot air panel.

I was realizing that there was a significant amount of heat leaking out on my hip roof that wasn't from leaks in the radiant barrier (besides the open roof vent). I could tell because everytime I went up there midday I'd be sweating, even after the radiant barrier was up. It was a lot less than before the radiant barrier, but it was still about 85 degrees up there even when it was signifiantly colder outside.

The problem isn't equal in all areas so I decided to just fix it at the worst areas. Those are the areas where the heat concentration is the highest.
In a gable roof the greatest heat concentration is right near the ridge. In my hip roof there is a big concentration there, but also along the hip rafters where the regular rafters meet it. One has to allow the air to "slip" past each junction point by dropping the radiant barrier a bit at that point. Every regular rafter that meets the hip rafter must channel hot air from every preceding regular rafter that intersects with the hip rafter. So by the time you get to the highest and last regular rafter junction point all the hot air from the previous lower rafter channels is meeting in that narrow junction point.

Here's a picture I drew that might give anyone a better idea. The areas in the broken lines are the areas of greatest heat concentration. It's a seat of the pants estimate and not a quantitative picture of heat concentration.:p

Exeric 11-17-13 12:31 AM

1 Attachment(s)
So the obvious answer to what I just said is add more insulation at those heat stress points. That's what I did and I used duct board rather than foam board, mostly because it was my preference, even though it is more expensive. Total cost was about 350 bucks for the duct board but its been worth it. The temperature near the roof but below the radiant barrier does not get over about 3 degrees of the rest of the open uninsulated part of the house. My house is under major construction as later photos will show but the one and only advantage is that it pretty much eliminates heated or conditioned air from the living space (except my bedroom) leaking into areas that I don't want and affecting the temperature results. Its basically one big unconditioned space except right above the radiant barrier at the roof.

It seems to have worked. The dramatic spiral in lower heat rises as we approach the winter solstice has been arrested. I'm getting consistant heat rises at or near 30 degrees above outside ambient. I think that's pretty good for having a foot diameter vent wide open at the top of the roof!

That 60 degree temperature reading is in that large unconditioned space. So you can see that even at mid-afternoon while the outside temperature was 63, bedroom temp around 70ish, and roof temperature was 93 degrees, there is surprisingly little leakage of heat from the roof to the unconditioned space. There is no ceiling drywall in the house yet.

iamgeo 11-17-13 08:39 AM

Nice write up.

Exeric 11-17-13 08:05 PM

Thanks Iamgeo. Even with the limited amount of success I've had here I'm still not convinced that an attic solar system will do well in all climates represented on this forum. I think it will probably work and save considerable amounts of energy in places like California, Texas, and most states south of the Mason-Dixon line. But the Pacific Northwest and Alaska... forget about it. In the former there is just too much cloud cover and the latter the sun is just too low in the sky. I think in selective areas north of the Mason-Dixon line it might eventually be a useful way to help heat your house. I think the jury is out. I think you would have to forget about using a direct heating system from the attic in most of those places and just use it as a tie in to a basement, crawlspace, or as a fresh air input to a forced air heating system. :thumbup:

Exeric 11-17-13 09:21 PM

6 Attachment(s)
Here's some pictures of the insulation installation. The ductboards are 2' x 4' in dimension and reflective on the side opposite being seen. They are equivalent of about R-8 (2 inches of fiberglass insulation). I first had to attach 2x2s as extensions to the hip rafters. That allowed an air space between the reflective surface of the ductboard and the foil above it. You can't have a reflective surface touching the surface above or it will directly conduct heat and bypass the radiant insulation properties of the reflective surface. The edges where they touch are insignificant area of the total surface. It can be seen here.

I really couldn't use insulation batts because they flop around too much. But even the duct boards can't be screwed directly, thus the wood strips sandwiching the ductboard against the 2x2s and giving some security.

I then covered all the insulation with foil barrier just to look better. The center section with the backflow damper will remain removable and accessible because behind it is the temperature sensors and damper motor. So I just wrapped the foil around the ductboard next to that section so there won't be damage to the adjoining fiberglass when I have to remove the center section.

Yeah, I know this is all way overkill and taking too long. The only reason I'm even paying so much attention to detail is because, to the best of my knowledge, no one has ever tried using an open system -no air recirculation- and still get high enough temperatures to use that attic air directly. If it works then it will be a first. That's not to say someone somewhere hasn't done it before successfully. Just that I haven't seen it documented anywhere.

Here's the proof of the pudding. Today I got the temp rise back up to 34 degrees with a 98 degree high at the roof. When I close the roof vent I am hoping and expecting to keep that high temp even as the days get colder and shorter. In my climate a 34 degree temperature rise is usable to heat the house. I can't say for other climates.

Daox 11-18-13 10:24 AM

Very nice work. Its really cool to see you work on this and continue to improve the design!

Exeric 11-20-13 06:41 PM

Thanks Daox. It rained all yesterday and the temp rise got to an amazing 4 degrees in the attic! Nothing like rain to keep down the roof temps. Today it was totally overcast and threatening until late afternoon. Yet the attic temp still got to 24 degrees over ambient. No pictures.

I finally closed the motorized roof damper. I bought an optional switch that mounts on the damper so I could monitor the damper position without physically inspecting it. My ohmmeter on the switch contact wiring told me it had closed but since it was the first time operating it I didn't quite trust my reading. So I went up, removed the center insulation and peeked through the backdraft damper. It did indeed close.

So we'll see just how much difference a closed roof vent makes on my system. Here's hoping it's significant.

Daox 11-21-13 07:38 AM

I would imagine that that will make a pretty big difference. I look forward to hearing the results.

Exeric 11-23-13 07:00 PM

3 Attachment(s)
It seems the world is never quite as simple as one anticipates. It's almost like the more I assume something without actually having prior experience the more likely I am to be wrong. You might be guessing about now that closing the roof damper didn't have the dramatically positive results I anticipated. You'd be right.

Here's some results:
11/20/2013 - high roof temp 96 degrees F, temp rise 33 F, very windy day
11/21/2013 - high roof temp 104F, temp rise 32F, windy day
11/22/2013 - high roof temp 101F, temp rise 28F, calm day

I'm slightly embarrassed to admit I was hoping the temp diffs would get into the high 30s with the roof vent closed. Not even close. The biggest positive difference is that when it is very windy the roof temperatures no longer plummets, like they used to. On Sept 20 a 96 degrees F high was a good result because it was so windy that a big rig truck actually blew over on a local highway. Also a 33F temp rise was very good under those circumstances. I'm sure with the vent open I previously would have been lucky for that temp rise to get to 25F from past experience of windy conditions.

What I did not take into consideration is that a closed roof vent works not only on the front end but also the back end. In summer one is into the air conditioning season. The sun is still up greater than 12 hours. So a closed vent in that season will mostly restrict the exit of hot air percolating under the roof.

In winter it can be just the opposite. I've been monitoring the times at which the roof temperatures cools back down to ambient outside air temps. Usually its between 7 and 8 PM. It doesn't require a open vent for this to happen. The roof just radiates heat it has accumulated to the cold night air, regardless. If I had a monitoring system like Xringer does I could show you. Gotta get one one of these days.

For instance the roof got cold soaked on 11/22/2013. At 7 A.M the internal roof temperature was 10 degrees colder than the outside air temperature. Because the roof vent was closed the warmer ambient air temperature could not warm up the roof and evacuate the cold air that accumulated inside during the night. At 9 A.M. even as the roof was warming the air was warming just as fast. So the roof was still 10 degrees colder than outside air temp. Because the days are so short this time of year there really isn't time for that beginning temperature deficit to be overcome as the day heats up. Soooo, the temperature rise in winter with the vent closed at night and early morning will be lower than it otherwise would be, except on a windy day.

Anyway, that's my excuse for now, and I'm sticking to it.:p

Exeric 11-26-13 07:53 PM

Here's the plan
1 Attachment(s)
I've been thinking about how this is all going to work without heat storage. Despite our reputation here it gets cold at night and the unconditioned uninsulated part of the house has already gotten down to 40F degrees in the middle of the night, while the outside temperature is 30F. And that part of the house rarely gets to 60F at any time. So what seems to be happening is that there is about a 20 degree variation in the uninsulated part of the house. On warmer days it goes from about 45F to a high of 65F.

I'm going to be insulating it with dense packed cellulose due to SF and Daox's good advice. It will be equivalent to about 2x6 framing, but without most of the thermal bridging that goes on there. I put 2x2 staggered against the existing 2x4s. If I can get that temperature variation down to 6 degrees F from warm to cold without any heating input during an 18 hour period then this will work. I really do not have the experience to know if the level of insulation I'm putting in will accomplish that. In this climate my house will be hugely better insulated than my neighbors, but nowhere near to Passivhaus standards. If anyone has direct experience with temperature variations in an unconditioned house with my level of insulation (R60 in ceiling, R30 in floor, and spray foam to R10 on the rim joists) I'd be thankful.

In the meantime I'm planning on a 6 degree variation. Here's a picture of the hopeful, but not neccessarily accurate predicted outcome.

Right now on average to good solar days the roof temperature reaches 75F at noon and does not dip below it until 6PM. On those days it is over 90F in the attic for 2 or 3 hours. On cold days it doesn't do as well. For instance today it only reached 84F and the outside high temp was 57F. The coldest day so far. (I know, its not cold) So that's what I'm basing it on. Obviously this is a crude estimate but for now I think it's in the ballpark. I feel very fortunate that I have the attic temperature that I have to work with.

Exeric 11-26-13 11:02 PM

2 Attachment(s)
I don't know what I was thinking when I said a few comments back that the attic and outside temps converged between 7 and 8 PM. They don't. The attic and "unconditioned space temps" converge at that time. The attic temperatures and outside temps usually never converge and the outside temps remain colder than the attic. I was so flummoxed by the lack of a big change with the attic vent being closed I think I was reaching for an explanation. That one day when the temp rise was only 27F seems to have been an aberation.

The day before yesterday I got an attic high of 97 and a outdoor high of 61. A new temp difference record. Here's a pic:

The vent being closed seems to be working on average. You just can't pinpoint when its contributing and when it's not. The long and short of it is that I was getting lost in the weeds while the average temps have improved. Overall the temps and temp rises for the last week have been quite consistantly over 90F and 30F respectively. And even when they fell short on the temp rise a 100F attic high temp is great! What was I worried about?

Today wasn't so good but then we're only 25 days or so from the winter solstice. Here's a pic:

The attic temps are still useable even on a bad day like this. (Rainy weather, forget it). So far things are on track for this plan to work, with or without mild disappointments. Even today it was over 75 degrees F in the attic from 1:00 PM to 5:00 PM. Again, what was I worried about?

jeff5may 11-27-13 06:59 AM

If you insulate the unconditioned room to the levels you posted, the room will hold heat very well. As long as it is not open to the outside, it will in fact float to an average charted temperature like your graph. How much variance from average will depend more on the thermal mass in the room and how heat is supplied to the space. Unless there is lots of solar gain from skylights or windows, outdoor temperature will play a much smaller role in changing the temps from your average.

Exeric 11-27-13 08:21 AM

That's really good to hear. There's not going to be windows or thermal mass used to acquire heat. I'm just using the roof to supply heat. It's beginning to feel like I can quit obsessing about the plan itself and just concentrate now on getting the rest of the house in shape. It could take awhile.:rolleyes:

Exeric 12-06-13 05:37 PM

In the interest of full disclosure
3 Attachment(s)
I probably ought to disclose that I have a significant area of roof for roof heating that is not used as habitable space. This is always an advantage for collecting the rays. I built a large 'L' shaped porch addition to my house in 2011. Here's some pics:

The first is the East side and the second is the South side. I'm thinking of adding some solar PV on the South side at a later date. That will cut into the heating effect somewhat. I have a plan though. I have an attached garage that is disconnected from the rest of the house from the ceiling to the roof. If I go ahead with the solar PV I will build a thermal channel from the garage roof to the house roof above the ceilings. Here's the plan. The top is North. Everything within the dotted line is habitable space and will remain so.

It would give me a little over 3000 watts, which would I think would be plenty since I don't need it for heating. No car charging though.

Exeric 12-06-13 08:54 PM

It's not really authorized by code to have combined attic spaces of homes with attached garages because of the danger of automobile fumes reaching the living space. If I decide I need the combined space with the garage it means any carbon monoxide from a running engine would automatically be pumped into the living space. Soooo, I would only do it because the garage is used for storage only, as most one car garages are around here. Once I convert that attic space then no running internal combustion engines would ever be allowed in there. As is often said, kids, don't do this at home.:eek:

PS. I would only do it if it was found that the removal of roof space for solar electric required it. It might not be needed.

Exeric 12-08-13 07:20 PM

Phase 1: Still just an experiment
1 Attachment(s)
It's easy for me to forget that this is still just an experiment. It's a risky venture in that if it doesn't succeed then it will be a lot of work for nothing. The only thing that makes me OK with that is it will be documented here and the larger society can profit from it, including all of you folks. You'll know better what does not work if this does not work. And you will also know better what roof area per inhabited space and what climate is required if it does work. But failure is only helpful to others when it is documented and publicized enough that others working in any given field know about it. Enough said.

Phase 1 is done - building the heat collecting system and recording the temperatures. With this latest cold snap I now know what to expect in terms of roof temperatures in the very coldest part of winter in this climate. It's been above average temps for most of the winter until the last three days. Three days ago it was 16 degrees below the 54 degree average high for this time of winter and the high never got above 38F. Weather was overcast and the roof temp never got above 50F. Yesterday was a few degrees warmer, clearer, but windy and the roof temp got to 68F. Not quite useable for what I want. Today was the real thing: eight degrees below normal high at 46F but clear and no wind. The roof got to 80F, and it stayed above 75F for 3.5 hours. So today was the threshold day for useability of roof heating for me. So it makes me very happy that a good solar day in the coldest part of winter "might" be useable. So far I've recorded only about 4 or 5 days when there was no useable high temperatures, all when its either too cold, too wet, or a combination of windy and dense overcast. Overcast or windy alone does not seem to preclude useable roof temperatures.

It actually got a little warmer than that 44F shown, but that 80.4F roof temp was the highest reading of the day.

Exeric 12-08-13 07:34 PM

Phase 2: Successful implementation
Phase 2 of this project is quite a ways off in time so don't expect many updates here until later. Phase 2 will require that I am actually able to bring that high temperature air down from the roof and that it does not deplete that renewable resource too much. I think Daox and Xringer both know that the radiation in the attic is a finite resource from their own work. I've compressed that radiation energy into a space much smaller than the entire attic. It has improved the quality of the heat (higher temp) but its hasn't stretched the resource itself. It is still possible that the higher temperature in the confined space up there quickly becomes depleted when it is actually pumped down into the living space. Only the actual bringing down of that air into my space will give indications. Again expect a year or more of other construction until I get to that point.

The other part that needs to be determined is if my plans allow for enough insulation to preserve that radiation resource. I'm not quite as worried about that, but still not sure. The fact is one could build a house like a thermos bottle and you could probably light a candle and have sufficient heat for the winter. It's just not feasible for most folks to build a house like that.

So overall I just want to make sure that everyone knows that I might or might not be breaking new ground here. When you try something new one never knows if it will work. That is the excitement of it and is what has encouraged me in this do far. Things are kind of boring when you only do what others have tried before. Time will tell how this experiment will turn out. If things go against me I'll report that too.

jeff5may 12-08-13 08:32 PM

Good luck renovating the rest of the house. I know it will turn out well, considering the effort and skill you've put into all the projects mentioned in this thread. Take your time and put it together the way you want it. Phase 2 is much less important than the rest of your house.

Exeric 12-09-13 11:52 AM

I'm glad you are able to read between the lines on where 99.9 % of my future work lies.


Daox 01-17-14 03:15 PM

Have you been using this at all? Any other observations?

Exeric 02-26-14 09:03 PM

Hi Daox, I saw your question just now. Better late than never and it's a good excuse for an update. No, I'm not using it this season because there's no insulation in the house yet and all that heat would just disappear into space at night. It's a pity too because I'll probably not see such a good solar thermal heating system as we had this year (drought in California, you know) in decades. Two months from the winter solstice and it has been regularly getting to 110F (43C) just beneath the roof. BTW, an interesting factoid, it seems there is a correlation between west coast drought and midwest and east coast frigid temperatures. The exact same thing happened in 1978 I believe.

Right now I'm just preparing for doing a dense pack of cellulose in the second bedroom, living room, and kitchen. I've put up ceiling drywall in the 2nd bedroom and living room and have yet to do the kitchen ceiling. I've put in 2x2s against the perimeter walls in all three rooms to provide thermal breaks. I've also put up the netting in the bedroom and living room. I just need to put netting up in the kitchen and do the ceiling drywall and then I'll do the perimeter dense pack and put drywall over the walls in all three rooms. I'm not going to do the taping and texturing myself though. Way too tedious for me and others can do it better and faster. I'll gladly pay to have it done. Once I have that done and a few things besides, I'll move into the second bedroom and do the final ripping and tearing on the bathroom and main bedroom.

I've routed a channel in the ceiling with ductboard between the garage and the nearest house hip rafter, but left the firewall in place for now. Once everything is done and the PV panels in place on the south facing roof I'll check if I'm still getting enough heat from the roof. There's a good chance I will because 2/3s of the west facing roof, the bathroom and main bedroom, have yet to have the black paint and radiant barrier put up. If it isn't quite enough then I'll just remove the part of the firewall separating the garage and ductboard channel I just put up. I can cut that out from the garage side so I don't need to trample the insulation.:)

Exeric 02-26-14 09:38 PM

I suppose it might seem weird to add solar PV to a house with a good solar thermal system. Presumably the net metered PV would supply a good ASHP system but unfortunately I got educated late about these things and I had already installed a propane system connected to a built in propane fireplace. So the electrical will be used for general stuff plus AC, not heating. These things happen, that's why I've learned not to be harsh with other people after the fact. As they say, it could happen to you. Luckily weather around here should supply I'm guessing at least 75% of my heating requirements. Besides, who doesn't like the warm glow of a fireplace.:rolleyes:

All times are GMT -5. The time now is 12:41 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
Ad Management by RedTyger