(our bidirectional electricity meter – the first reading is how much power we had purchased from Epcor as of October 18, 2010)

(how many kWh we had sold to Epcor as of October 18)

The concept of a net zero energy building is a brilliant one. For one thing, you can explain it to anyone in one sentence. For another, it sets a non-arbitrary goal. I think that most people have a gut feeling that if every part of the economy gave as much as it took, we would be approaching true sustainability.

From the beginning we have confidently declared that the Mill Creek Net Zero Home would annually generate as much energy as it uses, on a net basis. However, our assertions have been based on computer modeling and rules of thumb. That, and a good dose of optimism.

In fact, I’m not sure that we have a “proven” net zero energy building in Canada yet.

We aim to change that. Our PV modules are all installed now (more on that later), so it’s time to start a year of monitoring. We will only do one year of highly accurate measurement, because to make it a true test we have to abstain from burning waste wood in our wood stove. Since we are loathe to heat with coal-fired electricity  (even if we are offsetting it with solar power), and since the wood stove is such a nice way to heat a house, we only want to go through one winter without wood heat.

So on October 18, 2010, we began our year of monitoring. On that day, our meter readings were as follows:

• bi-directional power meter (total import and export of electricity for the house):
  • import: 4160 kWh
  • export: 2936 kWh
• inverters (cumulative production from each of two PV arrays):
  • fixed modules: 3683 kWh
  • movable modules: 616 kWh

I’m not sure how convincingly this experiment will “prove” that the house has achieved the net zero standard. Even if we do net out, I can’t absolutely prove that we didn’t burn any fires. We will be dismantling the stove so that we can seal the chimney off from letting cold air in. I'll post pictures, but besides that ya'll will have to just trust me!

I read an interesting article recently about how to calculate the size of an on-demand hot water heater.  OK, while not exactly what most people would consider light reading, what I thought was interesting was how much energy it takes to generate something we take for granted.  The article discussed how running a single shower would require the incoming water to absorb energy at a rate of about 75,000 BTUs per hour and that if the tankless water heater was 80% efficient, then the heater would need to have a rated input of 94,000 BTUs per hour.  If you want the ability to run two showers simultaneously, then the numbers double so that the tankless water heater would have a rating of 188,000 BTU.  (For reference, the boiler I have for heating my house and domestic hot water can modulate  read more... »

**EDIT, March 2011 **

The modelling that we did with WATSUN (and upon which this blog post was based) was completely inaccurate. It hasn't been near 100%. In January our tank sits at 20 degrees, and it fluctuates between 25 and 40 during February. Not even close to what the software promised us.

Our solar fraction is probably in the range of 60%-70%.

The Mill Creek NetZero Home (MCNZH) will collect solar energy in three different ways: using passive solar design, using photovoltaic (PV) modules, and using solar hot water (SHW) collectors. The SHW collectors are the ones that heat water - they are the black ones at the top of the above picture.

According to a recent article in Home Power magazine (Oct/Nov 2008, p.40), SHW collector efficiency is 50%-70%. That's pretty good when you consider that the best PV module is about 17% efficient.

I've been contemplating the design of the MCNZH's SHW system for months now. The pieces started to fall into place once the federal government released a crucial tool: The  WATSUN 2008 SHW System Simulator.  read more... »