Today felt like the first day of actual construction! After a lot of delay, digging, waiting and watching, today marked the first time I actually put on my boots and climbed down into the hole in the ground to start building our passive house. The first step: installing the ground source loop.
The ground source loop is 600 feet of high density polyethylene pipe installed in a continous loop 18" below our insulated foundation. The loop will eventually be filled with a brine or glycol solution and connected to a heat exchanger in our mechanical room. A small pump in the heat exchanger will move the liquid around the loop, picking up free heat from the ground in winter and free coolth in summer and using it to temper the incoming fresh air in our ventilation system. This gives us all sorts of wonderful benefits:
- the HRV's efficiency will be maximized in even the coldest winters
- no defrost cycle will be required to protect the HRV's core, as the ground source heat will provide enough pre-heat
- the incoming air in the summer will be cooled and dehumidifed
- the size of post-heater for adding the balance of the required heat for the house is minimized
In plainer terms, the ground loop makes heating easier in winter and cooling easier in summer!
The pipe we used is from GeoSmart Energy. It was quite easy to work with, even with the cooler air temperatures this morning. We ran the loops with roughly 2 foot spacing between them. Given the opportunity, an ideal install would likely use greater spacing and a deeper installed depth — to counter this we've installed more length than is propbably required. The spacing and depth are determined in part by the constrictions of our infill site, the size of our footprint, and cost. Going deeper is expensive (not only the digging, but the fill to bring the level back up for the foundation). The original design called for installation 36" below the foundation insulation, but by reducing this to 18" we saved over $4000 in compacted fill and labour. Definitely the right call.
We will be connecting the loop to the Zehnder ComfoFond, which plays very nicely with the ComfoAir 350 we have planned. The two units have been designed to communicate and work together well. I'm happy to stick with one manufacturer for all of the pieces of this heat exchange/ventilation system, which definitely has it's perks when it comes to maintenance and warranty.
I'm looking forward to connecting and filling the loop, but that will have to wait until the mechanical system is installled (which is still months away). Once we do, we will be able to play with the flow rates through the loop to optimize the amount of energy we are able to pull from the ground.
Next up we will be installing the engineered fill and all of the sub-slab plumbing and electrical. We are also looking forward to our first big shipment of insulation from StyroRail on Wednesday!