house building question

[bow-tie]

...as for insulating value of soil, it is a huge advantage. But only if done right so you don't have the issues many others have spoken of...

As for passive solar, south facing windows, as you already mentioned, with enough thermal mass to absorb the heat from the sun during the day. It will then release that heat at night. Just so you have the right amount of thermal mass, it is very comfortable and lowers both cooling costs and heating costs...

In my estimation, over 90%+ of houses built in Iowa include basements, so I would like to think what I want to do isn't a great departure from the standard building protocol performed in this area. In my eyes, the greatest departure from the norm would be an absence of an 'upstairs'. The basement would be the living quarter, with a standard pitched roof covered in steel instead of shingles. In 2008, we put steel on the house have now, and I would do it again if given the choice.

What intrigues me about this design is the possible efficiency of building into the earth. When it's hotter than billy blazes here in July/August, our current basement is cool (but humid). However, in the winter, it's very cold. I would guess these characteristics (humidity / cold in winter) are based on how the basement was constructed, i.e., with inadequate interior/exterior basement insulation. The way I figure it, if I can control the humidity, and the lack of heat in the winter (hence the south facing windows and thermal mass), we'd be good to go. I would likely use a good roof overhang to keep the July/August sun out of the windows, plus shades/curtains and some strategically placed shade trees.

Geothermal sounds awesome, but it scares me a bit. It's so expensive and I don't know of anyone, around my area at least, who has had it long enough to say it was a good investment. There seems to be so many things that could go wrong. But a local contractor has been installing a boatload of them. My buddy is putting it in his house currently. I would like to keep it low tech, to some degree, if possible. But I want to stay open minded.

Zathras - thanks for the heads up on the I-joists. I need to look into those.

p.s. - you guys KICK A$$ with all of your feedback. It's very appreciated. Keep it comin'.

 

[samclem]

What intrigues me about this design is the possible efficiency of building into the earth. When it's hotter than billy blazes here in July/August, our current basement is cool (but humid). However, in the winter, it's very cold. I would guess these characteristics (humidity / cold in winter) are based on how the basement was constructed, i.e., with inadequate interior/exterior basement insulation. The way I figure it, if I can control the humidity, and the lack of heat in the winter (hence the south facing windows and thermal mass), we'd be good to go.

Assuming you can keep the groundwater out, the humidity in summer is going to be the toughest thing to beat. The physics is cut and dried: If the ambient air is 90 deg F and 40% RH (actually kinda dry in the midwest during summer), then that air will be at 75% RH when cooled to 70 deg F in your basement home. 70% RH is where mold problems begin. If you're counting on the earth coupling to cool the air, then you can't insulate the walls very much, so they'll be cooler still (water will begin to condense out of this same packet of air at 62 deg F) You can't fix this problem with more fresh air--the more you bring in, the more condensation you'll get. Yes, you could address this with mechanical dehumidification, but that costs money, adds complexity, and adds heat to the air. You might as well use air conditioning (and enjoy windows, light, and the above-ground world).
One of the good things about "standard" air conditioning is that it lowers the air temp a lot as the air crosses the expansion coil. This allows the RH to be very high and water to be removed at one convenient location (rather than over all your interior walls). Bottom line: If you are depending on the building's walls for cooling in the summer, you need to find a way to deal with moisture. If the building is in a desert, no problem. Anywhere else--problem.

 

[Free To Canoe]

I wonder if the humidity is a problem for those people that bought old missle silos and are living in them. I seen them on TV programs a couple of times.

 

[samclem]

Again, as long as it is built correctly, earth tubes work wonderfully. The have been in use in Europe for ages.

Oh, I'm sure they can be made to work in some situations.

As I understand it, in Europe, it is fairly standard in new houses to simply wrap the tubing around the outside of the foundation of the house.

Building codes and the building inspectors who enforce them are very conservative. In most of the country, the whole reason they ask us to dig a foundation to a certain depth is to get it below the depth the soil freezes (based on historical data for each area). This is to prevent the building from heaving, cracking, and making smaller buildings from bigger ones. I can imagine the reception I'd get when I tell the building inspector of my plan to deliberately introduce subfreezing air all around the depth of my foundation during the winter.
Yes, we could make it work. Perhaps with a soil temperature measurement system or use of another source of makeup air in the winter. But that was a major point of the tubes, right?

In the summer the environment in those dark, warm tubes is going to be at 80%+ all the time if they are installed in a place with typical US summer humidity. We can include a condensate pump (complexity) or a gravel dry well at the lowest point to let the liquid water out, but it's still going to be at 80% or more RH in those warm, dark tubes. Maybe we're counting on excluding nutrients to preclude mold growth, but mold grows very well on cave walls under these same conditions, eating only the organic stuff that blows in. We'll be "feeding" it air (and pollen, dust, and anything else that will get past any filters) at 40 CFM. And what emerges from the dank, wet pipe is the nice "fresh" air I am deliberately introducing into my home to displace the pollutants.

But, I'm sure it can be made to work, in the right circumstances. If it does work, it will require careful engineering based on local conditions. I agree with the not-so-rosy evaluation provided by the US EERE at the link you provided.

Moreover, dehumidification, another equally important aspect of cooling, is difficult to achieve with earth cooling. Mechanical dehumidifiers will most likely be necessary. The dark and humid atmosphere of the cooling tubes may be a breeding ground for odor-producing molds and fungi. Furthermore, condensation or ground water seepage may accumulate in the tubes and encourage the growth of bacteria. Good construction and drainage could eliminate some of these problems.
Insects and rodents may enter the tubes of an open-loop system. You should install a sturdy grille and insect screen at the tube inlet to deter potential intruders.
Economics
Earth cooling tube systems can be very expensive. Considering current electric power rates and the cost of materials and labor, it is unlikely that an earth cooling tube installation can be justified on economic grounds alone.

 

[harley]

Geothermal sounds awesome, but it scares me a bit. It's so expensive and I don't know of anyone, around my area at least, who has had it long enough to say it was a good investment. There seems to be so many things that could go wrong. But a local contractor has been installing a boatload of them. My buddy is putting it in his house currently. I would like to keep it low tech, to some degree, if possible. But I want to stay open minded.

I'll add a positive review on geothermal. We're heading into our 5th year in the house using it, and our electric bills are approximately half of what our neighbors using regualr heat pump technology are paying. Pretty much equivalent homes. If anything, ours is larger than most of theirs. We haven't had any significant problems yet (knock on wood). As far as low tech, geothermal isn't any more high tech than heat pump tech, it just uses a loop for liquid heat collection/dispersal instead of ambient air. In our case we were building new, and since we were already drilling a well the cost of going geothermal was not that much higher than a regular system, maybe a third higher. At the time we were looking at a 7-10 year payback, but with rising energy and electric costs I think it's more like 5-7 years now. Hopefully we're nearly there. I'd recommend a closer look.

 

[ERD50]

Here is a manufacturer's site with some details: REHAU AG + Co - AWADUKT Thermo - Air-ground heat exchanger system

You might also like this site: Passive Cooling Techniques

But overall it seems a pretty good review of pros and cons with links to a number of sources.

Thanks for the links, I skimmed them and it appears to me the cons greatly outweigh the pros. I see references to UV air treatment to prevent mold, and 300-400 Watts continuous to run the circulation fan. That gave COP numbers that seem far less efficient than a heat pump. What's the point?

Can you really make a case for these? I didn't see it.


To the OP, I'm going to second the input of others - avoid anything too unique, unless you are doing it as a 'hobby' and don't care about resale value. A bunch of unfamiliar 'systems' are going to scare 99% of buyers away.

On the positive side, like some others, I think you can go a long, long way to reduce energy needs with careful application of some of the more conventional designs. Lots of insulation (can be achieved many ways - thick I-Beam walls sound good to me, I'd also look into ICF or SIP), even careful placement of overhangs to limit unwanted solar heating, and get some solar gain, even if you don't go full 'passive solar' (which I would also look into). And outdoor shade screens to limit the sun hitting windows that can't be shaded otherwise - stop the heat before it gets in.

I'm also interested in air exchangers, which you probably need in a very well insulated, tight house. These give you controlled 'leakage' of air - the outgoing air heats/cools the incoming air, reducing waste. These things seem expensive though, but probably necessary for a tight house.

If I were designing a house, I'd consider a vestibule of sorts (could be a small or large enclosed porch) for each entry. This could really cut down on leakage from doors, esp if people open only one door at a time to enter & leave. We added a 3-season room on the back of the house where we had sliding patio doors - those doors were always cold and drafty, now they are comfortable as the 3-season room 'tempers' the cold and there is no wind. Big difference. Not cost effective as a retrofit for energy savings, but if you work it into the design, I'd do it. Many homes have the laundry room between the garage entry and the main house - that's a good example. You don't need that laundry room to be heated/cooled to the same degree as the living spaces, so it makes a nice 'buffer zone' (essentially, another level of insulation).

I think some pretty basic things will give a good bang for the buck. I'd expect to hit diminishing returns (and negative returns) pretty quickly after that.


-ERD50

 

[REWahoo]

To the OP, I'm going to second the input of others - avoid anything too unique, unless you are doing it as a 'hobby' and don't care about resale value. A bunch of unfamiliar 'systems' are going to scare 99% of buyers away.

+1

One of our neighbors in our rural subdivision didn't like his well water so he spent upwards of $20K on a DIY rainwater collection system. This includes piping, pumps, filtration systems, and two 8,000 gallon holding tanks all enclosed in a small barn.

They have been trying to sell their house for more than two and a half years and have been unsuccessful even thought they have lowered the price three times to a point well below replacement cost. It seems that potential buyers don't want to deal with unfamiliar technology - especially when it appears to have highly questionable utility: Nine more years of Texas drought possible

 

[bow-tie]

...I'm also interested in air exchangers, which you probably need in a very well insulated, tight house. These give you controlled 'leakage' of air - the outgoing air heats/cools the incoming air, reducing waste. These things seem expensive though, but probably necessary for a tight house...

If I were designing a house, I'd consider a vestibule of sorts...

-ERD50

ERD50,

The air exchanger you are talking about, is it similar to an energy recovery ventilator? I read about the ERV from the link provided by Zathras about the house build by the NDSU students. I have never heard of ERVs and wonder how long they have been around and if they are a proven technology.

I also like the idea of vestibule for an additional buffer.

 

[jayc]

My idea is to essentially build a basement and put a roof on it. People have been digging basements for generations, so we hopefully wouldn't run into any unique water issues (of course, you are never guaranteed).
Humidity does seem like a big consideration.

Does your current house have basement? Move the family down there for a few months and try it. I bet you will change your mind for all the reasons already listed. Build a stick house with good insulation. Use geothermal.

I was the general contractor on the house I currently live in. The best way to control costs is you buy and control all materials. Don't build a berm house, log house, round house, or weird house because as already mentioned, you limit your resale audience.

 

[travelover]

......... Build a stick house with good insulation. Use geothermal............

This is what I suggested back in post #9, but I'll add anecdotal evidence.

When I was building houses with Habitat for Humanity we sealed them carefully and used 2x6 walls, which were fully insulated. Once the houses were closed in, but before the HVAC was installed, we heated the whole house very comfortably with a couple of 5000 btu electric heaters in mid winter. If you took this a step forward and installed even more insulation, tighter sealing, better windows and orientation for maximum winter solar gain, you could end up with a normal looking house with very low energy needs. I believe that some Scandinavian countries have taken the lead on tweaking the details for passive design.

 

[ERD50]

ERD50,

The air exchanger you are talking about, is it similar to an energy recovery ventilator? I read about the ERV from the link provided by Zathras about the house build by the NDSU students. I have never heard of ERVs and wonder how long they have been around and if they are a proven technology.

I also like the idea of vestibule for an additional buffer.

Yes, that's what I'm talking about, but I don't really know much about the them. Just that they act as a heat exchanger so the fresh air drawn in is heated/cooled by exhaust air from the house. This way, some of the energy is recovered, rather than just escaping.

Sounds good, but I haven't come across numbers to tell me how much this saves/costs (energy to run the fan offset by energy recovery).

-ERD50

 

[jayc]

This is what I suggested back in post #9, but I'll add anecdotal evidence.

When I was building houses with Habitat for Humanity we sealed them carefully and used 2x6 walls, which were fully insulated. passive .

Insulation was one task that I planned to do myself, but the insulation companies could actually buy in bulk and install for less than I could buy it. Plus they did it all in 2 days and knew where to seal. Also in hind site this was good because there was an inspection that I probably would not have passed the first time. I also passed on the liability of putting a foot through the ceiling.

I used brick, but regret not going to 2x6. I opted for 9 foot walls. They made 2x4 9' precut but I would need 2x6 10'.