Simon

My soil temperature experiment has been running for over 2 years.  It has been a long time since I saw anything new in the data, so I am not too worried about it any more, but I figured that every years temperature profile is different, so I might as well let the experiment keep on running until I build…

Last time I downloaded the data, I noticed that there was one bad sensor, but I was busy and since I didn’t really need the data, I didn’t worry about it.

Several of the wires had been damaged, probably by little teeth…  This white wire is the biggest sensor on the station and includes air temp and relative humidity.

Prepping for this next winter, I went out to the property today to change the batteries and download the data.  I also replace the burlap skirt that I had over the wires.  I remembered that one of the sensors had given bad data last time, so I took a careful look at the wires and found that two had be severed and a couple more were chewed partway thru.

Could this have been prevented?  Possibly.  In some of the pics, you can see what is left of the original burlap that I had used to protect the cords.  It had been worn away by the environment (sun and weather), and I had been too slow to replace it.  Had I replaced it sooner, I might have prevented whoever was chewing on the wires from having access.  “Stitch in time saves nine.”

I downloaded the data and took a closer look…  Things were a bit strange (as the charts will show), so I decided to try the number-one IT trick “turn it off and turn it on again”.   I changed the batteries and rebooted the data logger.

The black wire was for the 7.5 ft deep control temp.  Behind it, a bit more out of focus, you can see another black wire that was nicked…

Back at home this afternoon, I see that the data showed the 7.5ft deep control temperature probe (black wire) failed on June 6th, 2013 at around 5:30 PM.  Instead of turning off and not giving any data, the sensor showed ridiculous numbers in the -90°C range.

In the middle of the night on September 6th, three months later, the air temperature and RH data (the white wire) went horribly wrong.   Suddenly air temps appeared to drop from 12°C down to -91°C and relative humidity went from 93.9% to a nonsensical, but consistent, value of “1”.  I don’t know why, but the air temperature fluctuated, so I guess some electrons were getting thru.

This chart shows the sudden drop in the air temperature data, along with subsequent fluctuations.

The data started getting strange lately…

Then something else strange happened… Shown as a blue vertical spike in the previous chart   Not sure what, but on Oct 10th, the data suddenly went crazy…  Perhaps the data logger hiccuped?  Or the battery failed for a moment?  Or maybe a deer peed on the station?  I probably will never know, but this next chart shows the raw data around that time.

Raw data from my sensors showing the strange hiccup…

The data goes crazy for about 8 readings, but then things seem to reset.  After the reset, everything seems to have shifted down a bit…  The strangest thing is that the 7.5 ft deep temperature sensor and the air temperature and RH sensors started making sense again (see columns H, L and M, before and after the hiccup). I can’t think why the data would start making sense with the wire still cut… perhaps there was data in the cache and it is showing me samples from a previous year?  Anyway, when I saw this, I was glad I had reset the system while I was out there today…  Hopefully things will look better next time I download the data.

This next chart shows all the temperature sensors, but I removed the 8 really bad readings from the above chart…  You can still see the sudden shift on October 5th, as well as how long the 7.5 ft deep gauge was misbehaving…  You can also see that everything returned to “normal”, but shifted downward a bit.

Fortunately, I had already determined that there was hardly any difference between the dry and control temperatures at 7.5 ft deep, so I won’t miss that sensor too much…  But I will need to get out there and repair the other sensor when I get a chance and see if the probes appear to be trustworthy again after their reset.

Build status

Well, it is October.  If it started construction now, it would soon be winter and the weather may be too cold for strong concrete.  This may interrupt construction.  Since the terms of my construction mortgage motivate me to complete the task in 12 months, I think we are at the point where I need to decide not to build this year.

The fact that I am not really ready to start construction now anyway just makes the decision to wait for spring even easier.  I am obstructed by crazy bids and some of my own missing tasks.

One crazy bid was for heating.  I had already got 2 bids for geothermal and radiant floor heating.  The lower of which came to about $20k after a 30% federal tax rebate.  I knew that these were expensive systems, and also required a lot of excavation and hundreds of feet of ground tubes to collect the energy from the earth.  They are 4 or 5 times more efficient than electric-resistance systems, but many people claim that the initial cost is so high that the savings never pay off the initial investment.  Mean while, I had seen a sleek/simple system using an “Electro mini boiler“.

This is the same idea as an on-demand water heater, but with a lot more BTUs.  It is heated with simple electrical resistance, which can be expensive.  However, if I went with natural gas, I would need to run gas lines, etc.  When it is not in use, it doesn’t use any electricity (unlike something with a hotwater tank or a pilot light).  It also gains efficiency from the radiant floor distribution and can help to store/redistribute my passive solar gain.  I could even add a heat exchanger connected to my solar hot water tank, so it should be pretty good overall.

The Electro system would have the same radiant floor as the geothermal system, but would replace the expensive geothermal heat-exchanger hardware with a simple $1200 unit that I could bolt to the wall and hook up easily (one inlet, one outlet and plug it in to a 240 socket) without any excavation, etc.   I found a distributor/installer in my area and asked for a quote.  After 4 weeks, I managed to meet with the guy.  We went thru everything and then he told me that it would cost 550$ for a proper design/bid.  I told him I thought that was fair for a detailed design, but I just wanted some rough budget numbers for now.   A couple weeks, and several pestering emails and phone calls later and I got the “rough” bid…  $50,000!  No details.  Wow.  I told him I didn’t think that could be right and asked him what it included.  He checked the numbers and got back to me a week later with a bid for $29,500.  Again, no details, just a single number. I asked twice more for details and eventually got them.  His quote covered similar components to the geothermal quote (except he didn’t tell me the size of the mini-boiler).

The other company I asked for a quote on this sort of system has yet to get back to me after several emails and calls.  Since I have endless patience, I will call again this next week.

And the fence guy from a few weeks ago…  The original guy I spoke with is “no longer with them”, so my request got passed to someone else. I have called him twice, still no quote.  It really should take 5 minutes.  Maybe next time I will just stay on the phone until he does it.

Anyway, I have quotes for almost everything, but if I take them at their face value, the house is un-affordable.  We will need to find better quotes and/or do more of the job ourselves to make this work.  I had planned on making the rib forms and doing the ceilings, closets and stairwell shroud, but now I am looking at doing more of the rebar work, steel stud work, etc.

I also have not made some of the detail designs for things like the elliptical arch forms… so I will try to take care of that over the next few months and be ready to build in the spring.  It should also be easier to get quotes over the winter when the contractors are hungrier.

Visit

As you know, I had found out about an earth sheltered home going up last year and visited a couple times to help out and learn what I can.  They got their occupancy in mid summer this year after 13 straight months of construction.  I called Scott to ask him how it had gone and if he would recommend the shotcrete guy he had worked with…  He invited my family out for dinner instead. There were some scheduling hiccups, but we eventually got out there this past weekend.  The visit actually happened just as I was getting depressed about the quotes I had got, so it provided encouragement just when I needed it.

Duct mounted heater

Scott and I talked about the stages I had missed, from the waterproofing to final details like plaster and concrete stain. They also showed me a nice slide presentation they had put together.

The heating system was tiny.  He used a small inline ducted heater (I think it was only 1000W).  The system just fits into the duct system and plugs into a regular 110 volt outlet.  These units are meant for adding a little incremental heat to rooms at the ends of long duct runs, certainly not intended to heat a whole home.   Scott worked out (mathematically) that his passive solar house doesn’t need a heater at all, so he expects this little heater is all bonus.  I will call him in winter to see if it has worked out as planned.  He did show me his calculation (prediction) graphed along with his actual measurements.  So far, the house looks to be performing perfectly, but he has not gone thru a winter yet.  Personally, I would feel comfortable with a bit more heating capacity (calculation insurance), but if Scott needs a bigger furnace, he has the room to add it later.

Update: I called Scott on the first day of spring to ask how his little inline duct heater worked out…  Keep in mind that this was the coldest winter we have had in over 100 years.  He said the earth around his home (Scott did not use an umbrella) is already 10 degrees warmer then in the fall.  He thinks he is on track for a 3 year ramp up to a stable room temperature.  He said the little duct mounted heater did not have enough pressure (axial fan) to blow air properly through the ducts, so he used electric heaters during the day (powered by his large solar array) and a small propane heater on the coldest nights.

When I told him about my trouble getting reasonable bids, Scott seemed to recognize the problem.  At one point, he talked about trying to find a general contractor, but quickly realizing that they were all going to make the project un-affordable.   He ended up following the same tactic for a number of the trades.  When bids came in much higher than they should be (based on the cost of materials and skill/labor required), he took on the jobs himself.

This is what is know as FUD.  Fear, Uncertainty and Doubt combine to increase the cost of a bid in order to cover the contractors risk.  One way around this is to pay the contractors “time and materials”.  This puts all the risk on the homeowner if it turns out to be a harder job than expected.  But there is an old GC saying that says, “if you want a job to cost more and take longer, pay by the hour…”  For “risky” earth sheltered construction, I suggest a balance.  Pay “time and materials” on straight forward jobs where the person will steadily move to completion (shotcrete work is driven by the speed of the concrete pump), or where their reputation is important enough to their livelihood that you can trust them to work quickly.  Get a “fixed bid” when you don’t have as much trust and/or expect they could expertly “fiddle around” for hours (fancy stone work).   Even with “time and materials” deal, you will still need a best guess on the cost to budget, but the contractor will be more comfortable guessing reasonably if you can’t hold them to it.

For the water proofing, Scott decided against the expensive bentonite system that Formworks wanted to include with their kit.  Instead he planned to use a rubber membrane sprayed directly on the concrete.  This is the “blue stuff” often used inside concrete swimming pools.  The quote he got for the work was in the $50,000 range, aka un-affordable.  He found he could buy a top-of-the-line sprayer and all the waterproofing liquid he would need for a small fraction of that…  So he did it himself.  He mentioned that his straight extension ladder could not properly reach certain parts of the large (50ft diameter) domes, so he got the sides and the tops, but had to leave a strip between (at the shoulders of the domes) until after he had back-filled half way up and had better access.  He also put a layer of that drain board that quickly guides any water down to the perimeter drains.

Any waterproofing applied directly to the concrete can fail if the concrete cracks (although the rubber membrane can span small cracks).  It also doesn’t shield the soil near the house.  My plan calls for using an underground umbrella made of at least 3 layers of plastic sandwiching rigid insulation that should keep the house, plus many tons of dirt around it, dry and warm.   If the plastic is punctured, the water should run along the underside and continue away from the house…

Scott hired some young men (high school/college) to help with some of the tedious tasks, such as tying rebar.  I asked how that went and he said that they were affordable and hard working, but you had to be on site all the time to tell them what to do every little step of the way.  I definitely think this might be an affordable way for me to power thru several of the tedious but “low skill” tasks on my build.

His garage is wider than mine (in a 40ft wide dome), but only had two doors.  I am wondering about my plan to fit 3 doors in my 30 ft wide Quonset hut.  The doors will fit, but it may be really tight in there.  I may decide to go with 2.

He showed me his temporary saftey rail made of barrels filled with sand and connected by ropes.  This was enough to keep anyone from falling off the roof by accident and satisfied the inspectors.

Another interesting aspect of Scotts home was his solar electric system.  He said he was “not a survivalist, but” his house is set a long way back from the road and the cost of running electricity out there (included 4 poles, etc.) was going to be high.  He crunched the numbers and decided to set up his own solar system instead.  I forget all the numbers, but his array is quite large and should be more than enough, even during our cloudy Michigan winters.  He will have tons of extra electricity during the sunny summers.  He expects the pay back (if electricity prices don’t go up at all) should be about 20 years.

Mean while, my wife was talking with Scotts wife about topics such as “resolving conflict” (I wonder why that came up ;^) or nosy visitors sneaking on to the property.  Apparently the answer to the first question was “divide and conquer”.  Apparently they both had to compromise on some details.  The answer to the second was that they have had nosy guests sneak all the way back there and look around.  That can be a real problem with so many things to steal and places to hurt yourself on the job site.  They put up some serious looking “NO TRESPASSING” signs and have not had many troubles since.

We chatted for about 4 hours while walking around, having burgers, etc.   A very pleasant evening.

Eye Candy

And now the part most people tell me they prefer.  The eye candy.

If you want to sign a petition to save Charlies earth sheltered house (due to be torn down at the end of October 2013, for not getting permits before hand), check out this link.