Sunday, May 24, 2009

Nothing like a good foundation

(Jeremy) A busy week indeed. The foundation was excavated, footings and drain lines were installed and Superior Walls delivered and installed the precast foundation. All that was done Monday and Tuesday! From there we ran into a snag of needing a lot more fill to backfill around the foundation than originally estimated. Fortunately our new neighbor, Troy, was quick to point out a huge mound of fill he needed removed from his property and voila, problem solved (oh, and an additional $3500 for the excavator to supply the machinery and equipment). We're getting very familiar with change orders from the GC!
So on Wednesday he started breaking up the fill and bringing it to the site. We decided to have them install a layer of gravel inside the foundation over the dirt to prevent any capillary action into the 3" of rigid insulation above. The insulation was then installed over the entire area inside the foundation - two layers of 1.5" rigid foam insulation (EPS - Encapsulated Polystyrene), with the joints staggered for better thermal barrier. We also had them install an additional two inches of insulation against the inside of the foundation walls. This was in addition to the 1" of rigid insulation that was installed in the factory. So what are we doing with all this insulation inside our foundation? We're creating a huge heat sink under the house. This "earthbox" as we're referring to it, is 3' of sand directly under the slab. On Friday, they brought in the sand and put 18" of it into our foundation walls (on top of the insulation) and compacted it well. On Saturday, Karann and I spent a good part of the day laying down 1200 linear feet of radiant tubing (7/8" PEX). We read the installation manual from Radiant Floor Company and designed the three 400 foot loops the night before. We were surprised how easy it was (although hard on the backs and knees). Monday, our heating contractor will pressure test the system and on Tuesday the building inspector will inspect everything allowing the excavator to install and compact the remaining 18" of sand. The first major component of our home complete.


Jamie Wolf said...

I appreciate your effort to construct a low energy building but am concerned about the engineering of your "earthbed".

Could you post a description of how the mechanical system was designed, what the buildings design loads are and how the system was sized, and most significantly, how you imagine controlling temperature with all that mass?

As my friend a veteran solar designer Mark Kelley says - this could be a "dog that bites"!

Jeremy and Karann said...

Hi Jamie:
I'll work on trying to post additional information on the mechanicals and controls for the system. I'm trying not to get ahead of myself by posting only information on what we are installing or working on currently. In several weeks we'll be working on installing the solar and heating systems so stay tuned. I'll also try to send you some info through your website. A biting dog?? That's an odd analogy. I guess I look at my project from a different point of view as your friend Mark. People who are willing to take risks and try new things can teach others and bring positive change, even when setbacks or failures occur.

Jamie Wolf said...

What I am talking about is your ability to control temperature with that much mass - a lesson learned by the solar pioneers (Mark being one). The dog that bites reference is to the loveable pooch who every now and then nips.

Your "earthbed" is likely to produce internal temperatures that, due to charging by the sun or overcharging due to control "lags", will flywheel up into the 80's and stay there for a very long time as you wait for it to slowly discharge all that heat energy, and you will have no way, short of opening all the windows, to turn that "radiator" down.

I just wanted to know if you were aware of this and how you thought your control system(thermostat) was going to deal with what is in effect an effort like turning a cruise ship - it happens very slowly and requires adept anticipation.

Jeremy and Karann said...

Sorry, it's taken me so long to answer...obviously we've had our hands full.
We have given much thought over the past year to the controls of the system, in particular, the earthbox and here are our thoughts and how we arrived at the decisions we made. First, tanks are expensive, have limited life cycles, and are inefficient methods for storing the copious amounts of hot water produced during a sunny day. The first solar design/quote I received from a solar company contained 2-huge storage tanks and was over $25K for just the solar portion (panels, tanks, and associated components). It seemed expensive and wasteful to me. Thats when we started researching the earthbox idea. Our earthbox is approx 3' deep and 1500 square feet in area. Thats a huge thermal mass to absorb energy. It is designed not to exceed 80 degrees in temp. When all hot water demands are met (domestic hot water, and radiant heating if needed) then hot water is then sent to the earthbox in the foundation. Walking on the cold concrete floors, even this summer in the house, was mildly unpleasant. As far as opening windows...that's exactly what the house is designed for. In a traditionally heated home, opening windows is taboo, but in a solar home it is perfectly acceptable. After all the heat is FREE. Nobody is going to yell at me for wasting heat!! If it gets warm, we have automatic window openers in our cupola for drawing warm air out of the house. Additionally, we are placing the solar panels in an array on the ground, so if we need to, we can shade or cover a portion. I understand your concerns regarding the "cruise ship" effect, but I also see great advantage in this. In winter, when we have numerous cloudy days in a row, our slab and earthbox will take a long time to cool down, hopefully, limiting the use of the backup propane system. I see a glass half full.
When we get our system operational, I'll post some schematics of the controls for people who are interested, like yourself.