Monday, March 17, 2014

How Much Energy Did We Use In Our First Year?

About one year ago I cut off 30-inches of my hair and donated the half-pound of hair to Locks of Love, an organization that makes wigs for children.  I've done this a few times before and it makes me feel good.  In the past friends would often ask me, "How's your house project coming along?" and at times it seemed to go on forever.  So at one point I started telling everyone, "You'll know when it's done because I'll cut off my hair and donate them.  If you see me with short hair that means the house is done!"  So I was quite happy when I had this photo taken because it meant the house was done and I didn't need the extra insulation to keep me warm.

Now that we've been living in Midori Haus for one year it's time we share our energy data for the first year of occupancy.  You might recall from my previous post where we compared our energy data for the first 8 months in Midori Haus with the energy data from the slightly smaller condo we used to live in.  We were pleased with the comparison of spring-summer data where our total energy use at Midori Haus proved to be much lower than the smaller condo.  Now that we have the energy data for the winter season it's even better.   Let me show you some graphs.

If you are a PG&E customer, the above graphs will be familiar to you.  You can log into your account at and select the "My Usage" tab to track, compare, and monitor your energy usage.  They do a nice job of comparing your energy usage with similar homes in the area.  Similar homes in the context of Midori Haus is 100 homes with similar square footage (1560 in our case) within half-mile radius that are heated by natural gas.  At Midori Haus we let the sun do the warming most of the time but when the sun is not shining the gas boiler provides make-up heat for the hot water tank and the hot water warms the house.  Since there is not a category for "mostly sun-heated house" we technically fall into the category of "heated by natural gas."

In this past year (March 1, 2013 through February 28, 2014) we used a lot less energy than similar homes.  The total energy use at Midori Haus was 4,334 kWh compared to 19,596 kWh for similar homes.  Our Midori Haus used 2,869 kWh of electricity and a scant 50 therms (this is equivalent to 1,465 kWh) of natural gas while similar homes used 5,118 kWh of electricity and 494 therms (this is equivalent to 14,478 kWh) of natural gas.  To put it in another way, Midori Haus used only 22% of the total energy used by similar homes in the past year. 

By the way, we were comfortable inside and we do not have PV (solar electric) to offset our electricity usage.  We plan to do so in the future but it was important for us to start from the most efficient house before we put in PV.

This next graph is very validating.  We're fortunate to have copies of the energy bills from the prior owner of the house.  The seller was friendly and ordered PG&E to send copies of the past energy bill to us for the years 200 and 2006.  Back then there were 3 elderly occupants in the house and they used gas furnace to heat the house and perhaps some electric space heating too.  Their energy bill from March 2005 through February 2006 is a good basis of comparison with our first year of post-retrofit occupancy at Midori Haus because many things about the house is the same:  same square footage, same foundation, mostly same framing, same floor, same roof, and we kept the original built-in-furniture (dining room buffet) in place.  So the reduction in energy use that you see below represents the performance of the house before (without any insulation or air sealing) and after (super-insulation, extreme airtightness, minimizing thermal bridges, heat recovery ventilator, low energy lighting, and low energy appliances).  

The prior occupant used 21,928 kWh of energy in one year.  Midori Haus used 4,334 kWh of energy in one year.  That is 80% reduction in energy use for the same house!  And Midori Haus stays in a comfortable temperature range year round with good indoor air quality.  Passive House works!

Digging further into gas usage I wanted to see if there is a correlation between rain and gas usage.  So I overlaid the our daily natural gas usage with rainfall.  It's a bit challenging to see the details but you'll notice that the when there is rain (blue column) the natural gas (red column) follows close by.  This confirms that gas boiler turns on if the sun is not shining.  The little blips of gas you see in the summer months represents outdoor barbecue use.  We have natural gas plumbed to the barbecue on the deck.

The source of rain data is from a local weather station that I found on the weather underground site.  The Weather Cat station is located just 2 miles away from Midori Haus so it's a good representative of the outdoor condition for the past year.  Below is a graph of the daily high and low temperature.  What you will see below is that there is always about 10-30 degrees Fahrenheit temperature difference between the daily high and daily low.  Because of this diurnal swing in the temperature we don't need to have air conditioning during the summer because the house will cool off at night if we simply open the windows for an hour or so.  

I now present to you a simple conclusion:  Passive house works.  Up until now we've been telling everyone, "Once we have a house built to Passivhaus standard we will use 80% less energy than similar homes."  Now we can actually show the data where we have used 80% less energy than similar homes.  Don't you want your home to be passive house too?  :)