Wednesday, August 2, 2017

Passive House Standards Met

Passive House Standards Met
It has been just over 1 year since we moved into the house. I finally have about 1 years worth of data (minus cooling for this year). Here is where we stand:

One really nice thing about PH International is the simplicity of the standard. I don't mean it is simple to achieve, but it is simple to explain.
1) Airtightness under 0.6 ACH50
2) Heating Demand - 4.75 kBTU/sf/yr
3) Cooling Demand - 5.39 kBTU/sy/yr
4) Primary Energy - 38.0 kBTU/sf/yr
5) Thermal Comfort / Thermal Bridge Free design - Blog post to come!

So lets do some unit conversions, since my house is totally electric - so my calculations are in kWh:

  • Heating Demand - 1.39 kWh/sf/yr
  • Cooling Demand -  1.58 kWh/sf/yr - I'm told this is to account for dehumidification being energy intensive. 
  • Primary Energy - 11.1 kWh/sf/yr
Lets see how we did - Our PHPP model shows 2930 sqft

1) Airtightness: My previous blog posts shows how we met this standard comfortably

2) Heating Demand: I installed 2 electric meters measuring my 2 air source heat pumps that I read monthly, so I can accurately measure my electrical consumption for Heating and Air Conditioning.

  • The top meter measures the Water Heater electrical consumption (installed on 2/1/2017)
  • The bottom left measures the 2nd floor minisplit heat pump (installed on 10/25/2016)
  • The bottom right measures the 1st floor minisplit heat pump (installed on 10/25/2016)
I should note, we had not used the minisplits for heating until after the meters were installed.

My electrical use dedicated to heating over the 2016-2017 winter was: 1730 kWh

1730/2930 =
0.59 kWh/sf/yr or 2.02 kBTU/sf/yr

The 2016/2017 winter had 5593 Heating Degree Days - our 30 year average is about 6380. So our winter was about 12% warmer than normal, but we are less than 1/2 of the PH limit of 4.75 kBTU/sf/yr

3) Cooling Demand: We are not done with cooling for this summer yet (it is early august). But we can interpolate a little bit. So far for the summer of 2017 we have used 187 kWh

0.06 kWh/sf/yr or 0.22 kBTU/sf/yr

As long as I don't use 4,400kWh the rest of the summer I will be under the limit (remember I've only used 187 so far this summer)

4) Primary Energy: Now that I have a full year's worth of electric bill I can do this calculation. The primary energy portion of the Passive House accounts for grid losses (The assumption is the grid is 38% efficient). We moved into the house in July 2016, so August 2016 was our 1st full month of utility bills. This number includes all of the heating, cooling, water heating, ventilation, cooking, plug loads, etc. 
 Here is our Monthly breakout of usage:
August 2016             685 kWh -  $85.53
September 2016       573 kWh -  $75.15
October 2016           452 kWh -  $63.80
November 2016       622 kWh -  $73.63
December 2016       968 kWh - $103.94
January 2017         1232 kWh - $142.60
February 2017         957 kWh - $121.58
March 2017             848 kWh - $93.68
April 2017               633 kWh - $79.51
May 2017                418 kWh - $65.79
June 2017                474 kWh - $66.36
July 2017                 537 kWh - $75.48
Total                      8399 kWh - $1,047.05

2.6 x (8399/2930)= 
7.45 kWh/sf/yr or 19.37 kBTU/sf/yr

Again, we are FAR under the limit of 38.0 kBTU/sf/yr.

I do have a meter on the water heater and ventilation system but I installed it in late January, so I don't really have meaningful data yet. But this is what I have so far:

The Water Heater Electrical usage so far has been:
February 2017    136 kWh - $14.86
March 2017        166 kWh - $15.01
April 2017          113 kWh - $11.16
May 2017           104 kWh - $12.14
June 2017             86 kWh -   $8.96
July 2017             69 kWh -    $7.51
Total                   674 kWh - $69.64

The Ventilation System Electrical usage so far has been:
February 2017    38 kWh - $4.15
March 2017        42 kWh - $3.80
April 2017          34 kWh - $3.36
May 2017           32 kWh - $3.74
June 2017           42 kWh - $4.37
July 2017            46 kWh - $5.01
Total                  234 kWh - $24.43

Lets take a look at how my electrical bill breaks out for 2017:

(This is only from January on, so the heating number may seem misleading since it is only for half of the winter)
The 2 things that stand out to me are:
1) The $17 per month service charge certainly adds up fast!
2) I am surprised at how little the ventilation system costs to run considering it is the only piece of equipment in the house that runs 24/7 (roughly $4 per month to operate - and that includes the Comfofond ground loop!)

I hopefully will have some news on the Certification front soon! Passive House Academy is working on it! 


  1. Interesting that your water heating is less than your space heating. There is a lot of talk of water heating being the big bill in a Passive House.

  2. I agree, I did install a hot water circulating loop (pump is not monitored by the water heater meter) and drain water heat exchanger - so those are certainly helping, but I was pleasantly surprised how well the Sanden did over the winter.

  3. Matthew, Thanks so much for sharing - this is priceless information!

  4. Hey Matthew - congrats on a great passive house and thanks for all of the monitoring numbers. I was surprised to see your heating demand come in at half the PHI standard. The difference may be the COP for your heat pumps - 1 kW of electrical consumption (measured) could be 2-3 kW of heat supplied to your house depending on outdoor temperature. I'm thinking about this on my own house calculation and would appreciate your thoughts