Energy Modeling, Energy Plus software

I'm using EnergyPlus software to model the thermal situation of our earthship. After reading all kinds of posts in Facebook groups and web pages, I thought I needed various things: heat exchangers, insulation under the whole floor. Ulaanbaatar, Mongolia is under spotty permafrost. It's just below freezing 5-15m down all the time. However, even 2m down on open exposed soil, the winter soil temp is only about -4C. Today I was running the Ground Temperature Calculator again. Several things were quite obvious. With a slab and no insulation, the center of the slab is actually warmer than with insulation, because even with a regular house the house can access the mass under the center of the house. However, the perimeter areas of the slab are much colder. 2m Vertical insulation is the default setting on that program, and that works quite well, because it contains a lot of mass for the living space. The downside of that is you need a backhoe to dig out a 2m deep trench and manage the edge of the slab. Possible, but more expensive. Surprisingly covering the entire floor with an insulated slab did not perform the best. Then 2m of horizontal insulation in from the edges was OK for having a warm temp near the perimeter, but the living space was a little colder (less than 1C). I tried to model just 1m of horizontal insulation under the 3rd greenhouse, but extending 2m horizontally out to the south and sides. That worked great, because it maximized the mass under the living space and 2nd greenhouse. I thought for our climate that it's too cold to go without floor insulation, but the tire U's with living space glass are collecting a lot of heat like solar ovens with thermal buffer zones around them and lots of mass in the floor. The 3rd greenhouse will go below freezing here, but the 2nd greenhouse low temp is about +17C. This is a fabulous tool. I found some researchers who modeled a vol. 2/3 south facing earthship with south facing roof and one thermal zone. I modified their file for the current v.7.2. They confirmed that the tool modeled reality. 

We're still waiting to sell our old apartment. Hopefully the sale comes soon so we can start building this summer.