Terra-Dome Earth Shelter Build

[patrick_g]

Back in 1990 through 1994, I was a Production Engineer for Quintron Corporation in Chantilly Virginia. All we did was design and build flight simulators for DOD. We did P3s, T37, T38, T1A and T400.

The machine I was trained on and was my entire USAF job was old when I got there and about 7-8 years ago I saw the exact model and variant in an air museum in Fayetteville Arkansas. The retired bird col who was the volunteer docent told me they had some engineers look at it and were told it couldn't be fixed. My translation of that is they were digital types and had no clue.

The LInk C-11 was almost all analog computers made with tube type power supplies and servo amps, chock full of shaped card potentiometers, selsyns, autosyns and other variants of synchronous transmitters and receivers, rate servos, position servos and on and on. Interesting technology but not something recent EE grads have much of a clue about. Only a couple years prior to visiting that air museum I had tossed out my personal schematics marked up with colored pencil when in tech school on that model. Bad timing.

I witnessed a de-installation of electronic and computer equipment at Minot AFB. When I first arrived the SAGE (Semi Automatic Ground Environment) system was being de-installed. The system's computers were comprised of a jillion tubes and hefty tube rectifier type power supplies. The SAGE bld was three stories with a full basement and a backup electric generating station. The diesels of the generators were big enough you could climb in a valve and ride up and down the cylinder standing on the piston to inspect for PM. There were huge chiller towers for the A/C system that had to remove the heat of all those tubes. The smaller plenums were big enough for two or three guys to walk abreast with full standing head room.

When I arrived guys were chopping bundles of coax cables into 5 ft lengths to be light enough to carry out to a dumpster to be sold for scrap.

The Minot SAGE facility was deactivated after less than two years of operation, in May 1963, never being operational.but waws used for a Manual Control Center (MCC). The facility was then renamed the PRIDE Building ("Professional Results in Daily Effort") after ADC's and SAC's alternate motto of the 1960s and 1970s, and became a large office building housing many different organizations. The USAF tried to make much of the bld into office spaces but throttling down the A/C was not easy and summers in the SAGE bld were almost indistinguishable from winters outside for the office rats. This was good for the training devices section as all our trainers and sims for the various combat aircrew positions needed a lot of cooling so we were comfortable.

This three story including basement complex was near miss A-bomb proof and had no windows. It was replaced with a system built into a couple semi-trailers (aren't transistors just marvy poo?).

BIG bucks to build and never went operational and de-installed 3 years later.. your Government at work.

Now to some on-topic stuff... I was told that the typical earth sheltered home (cast concrete construction) takes 2-3 or more years to really get rid of all the excess moisture from the concrete and that running a dehumidifier during that time is recommended. What is your take on this considering your 10-15 years newer with your information/involvement?

Pat

 

[SamWalton]

Now to some on-topic stuff... I was told that the typical earth sheltered home (cast concrete construction) takes 2-3 or more years to really get rid of all the excess moisture from the concrete and that running a dehumidifier during that time is recommended. What is your take on this considering your 10-15 years newer with your information/involvement?

Pat

I am sure you can add and remove moisture from concrete indefinitely. The trick is to get it to a good moisture level and seal it, preferably from both sides. Our concrete had been very dry and I opened the windows while a storm front was coming through and the concrete pulled the humidity from the air within minutes and then began to sweat. I don't think this will change until we seal the surfaces.

 

[sajurcaju]

I am sure you can add and remove moisture from concrete indefinitely. The trick is to get it to a good moisture level and seal it, preferably from both sides. Our concrete had been very dry and I opened the windows while a storm front was coming through and the concrete pulled the humidity from the air within minutes and then began to sweat. I don't think this will change until we seal the surfaces.

I don't think sealing will change that. Sounds like condensation--the concrete was cool enough to be below dew point when the storm came in.

Steve

 

[patrick_g]

I don't think sealing will change that. Sounds like condensation--the concrete was cool enough to be below dew point when the storm came in.

Steve

Not to gang up on Sam but that is my take also. My garage floor slab (not insulated) does that where under certain conditions the temp of the surface is below the dew point.

Pat

 

[carpolisher]

Earth sheltered houses are tightly sealed which can cause high humidity in winter. Our TD averages 68% RH with a dehumidifier running 24/7. I am in the process of installing an HRV and getting the air handler operational to correct this.

Bob

 

[sajurcaju]

Earth sheltered houses are tightly sealed which can cause high humidity in winter. Our TD averages 68% RH with a dehumidifier running 24/7. I am in the process of installing an HRV and getting the air handler operational to correct this.

Bob

Hi Bob,
The heated area of our earth sheltered house is about 1900 square feet. We have two HRV ventilators. One at each end of the house--no way to do it with one unit due to ducting issues. This winter I'm running both at their lowest continuous setting, which it looks like gives about 40cfm each. We are running about 40% RH with no other dehumidification. We have radiant in-floor heat. This is a much more comfortable humidity level than in our previous forced air heat home.

The end of January I found a problem with the units. I was working near one and realized my hair was getting wet. Above me was the insulated flex connection between the HRV and outside air. The center tube of the flex duct was cinched to the HRV as it should be, the insulating sleeve just loosely ended up at the unit with no cinch. House air was infiltrating into the insulation (from the loose end), getting cold and dropping it's moisture--inside the insulation. The flex had a dip (low spot) where the moisture gathered, and froze into a hard lump (well, a ring). This was how my hair got wet, from condensation on the outside of the flex.

I'm doing several things to mitigate (in process):
1. Cinch outer insulation sheath on top of cinch for inner pipe to minimize infiltration.
2. I may tape the end as well, depending how it goes together.
3. I'm adding a 4x4' hot air solar panel on the roof for each inlet. The idea isn't so much to add heat to the house, the idea is to preheat the airstream above dew point for inside air. If I get it above 40 degrees, that should eliminate the problem. This only works during the daytime, so I will also run the HRV's on a timer.
4. Not that I like belt and suspenders or anything.

We had a problem last summer with humidity condensing in one bathroom, despite the HRV's. The house was just finished last summer, so we may get less humidity this year with the concrete better cured.

Steve
Maine

 

[carpolisher]

Hi Tom,

Your results are encouraging. Sealing the insulated duct should stop the condensation. Tempering the incoming air is a good idea and should limit the
defrost cycle on the HRV. The tubes around the wall are for this purpose.

Bob

 

[carpolisher]

Sorry I meant Steve

 

[SamWalton]

If you didn't install a high quality vapor barrier on top of a deep bed of crushed stone, completely taped and sealed around pipes and other protrusions like stated below you may have moisture issues related to the below.

Our home will require a few months of HVAC operation to get the moisture content of our concrete to the correct level before we acid stain and seal the slab but after that our moisture problems in the floor will cease. I will use a flexible sealer on the gaps between the wall and slab to prevent any water from penetrating. Remember we went crazy with or 15 mil Stego barrier and tapped everywhere and our barrier went up the wall.

Sub-Slab Vapor Retarders
The importance of these materials has risen with the need to reduce moisture intrusion into building envelopes. Numerous companies are producing excellent products that offer measured permeability ratings below 0.1 U.S. perms. High quality vapor retarders are designed with tear and puncture resistant characteristics to ensure durability on a construction site. Typically they come with installation instructions that include methods of sealing around pipes and other protrusions that will necessarily penetrate the membrane. All of the earth has some amount of free moisture and construction processes often require adding moisture at a building site to achieve necessary compaction and stability. Regardless of source or causation the best means of preventing soil borne moisture from entering a concrete slab is through the employment of an effective sub-slab vapor retarding membrane.

For slabs placed on-grade with no vapor retarder, everything changes with regard to moisture. Without a vapor retarder, the concrete is subject to moisture intrusion from sources below the slab. The soil, sub grade and sub base will maintain 100% humidity even under dry weather conditions and provide an infinite source of moisture that can move through the slab. Moisture moves through the concrete as liquid water or water vapor. High levels of water vapor can accumulate to the point of saturation and condense into liquid water. Capillary action can draw liquid water through the fine soil and into the concrete. Capillary breaks of crushed stone are placed below the slab to stop the capillary rise of liquid water but they will not stop the free movement of moisture vapor. The availability of moisture vapor from below the slab is not influenced by the depth of the water table. Other sources of moisture that can find their way under the slab and eventually move upward through the concrete include rainfall, broken pipes, landscape irrigation, snow banking or runoff from inadequately designed gutters and own spouts. Although rare, if the slab is below the water table, hydrostatic pressure can play a role in moisture failure.

 

[dave1949]

If you didn't install a high quality vapor barrier on top of a deep bed of crushed stone, completely taped and sealed around pipes and other protrusions like stated below .....................

Good post Sam. I am enjoying watching your project, nice to see it coming together.
Dave.