Thursday, January 11, 2018

2017 Utility Data

2017 Energy Data


To meet International Passive House (PHI) Standards the house must be built to the following performance criteria:

  • 4.75 kBTU/sf/yr - Heating Demand (or 3.17 BTU/hr/sf Heat Load)
  • 5.39 kBTU/sf/yr - Cooling Demand
  • 38.0 kBTU/sf/yr - Primary Energy (2.6 Source Energy Factor)
  • Thermal Bridge Free
  • Airtightness below 0.6 ACH50

To meet Passive House US (PHIUS) Standards the house must be built to the following performance criteria - this is based on Climate Zone 5 (Rochester International Airport)

  • 6.0 kBTU/sf/yr - Heating Demand
  • 2.2 kBTU/sf/yr - Cooling Demand
  • 6200 kWh/per person/yr - Primary Energy (3.16 Source Energy Factor)
  • Thermal Bridge Free
  • Airtightness below 0.05 CFM50/sf envelope area
* Keep in mind the way both standards measure sqft is different
** Watch our for UNITS! kBTU and kWh

To keep this post relatively short, we will only focus on the 1st 3. I suppose you'll just have to trust me that we are still below the airtightness and we are thermal bridge free.

I have compiled all of the energy data from 2017. Here is a quick break down of the different components I have been metering over the past 12 months:

Over the past year, my total electric usage - according to my bill was 8129 kWh - $1050.63
Here is the Breakdown, based on my meter readings:


*** I estimated the electric use for the water heater or ventilation system for January 2017 because I didn't install my meters on those components until Feb 1, 2017

Here are some comments on the utility data breakdown:

  • My largest single expense was the $17/month Service Charge
  • My Average monthly bill is $87.55
  • The 10 year average HDD for Rochester, NY is 6265
  • 2017 had 5766 Heating Degree Days - so it was a "warm" winter.



Okay this is all great, but low utility bills are objective. After all, this barn used 100% less energy than me last year:
(This is also a case when a single pane window is more efficient than a wall)

This is where comfort comes into play. Now here is Western NY I have done plenty of Energy Audits and people will go to some pretty extreme lengths to keep their heating bills as low as possible. I have heard the following quotes more than once:

"We turn the thermostat back to 55 F at night"
"We only set the thermostat to 64 F during the day"
"We don't heat the upstairs"
"We don't heat the basement"
"We don't heat the extra bedrooms"
"We burned 9 cords of wood last winter"

I've heard them all.

Well, obviously we have done none of that, and we have kept the whole house warm (or cool) all year.

I downloaded the weather data from my NETATMO weather station (Its a really cool device that can give you more data than you'll ever care to analyze).

I took a look at every day last year and took the high and the low temperatures - both indoor and outdoor. Then I averaged the high temperatures over the course of each month and I averaged the low temperatures for each month and made this graph:
The Blue Line is the Outdoor Average Maximum temperature for each month
The Red Line is the Outdoor Average Minimum temperature for each month
The Green Line is the Indoor Average Maximum temperature for each month
The Purple Line is the Indoor Average Minimum temperature for each month.

Basically the Outdoor Temperature was between the Blue and Red Line most of if not all of the year.
On the same note, the Indoor Temperature was between the Green and Purple line most of the year.

Here is some interesting notes:
  • We maintained the indoor temperature between 70-72 degrees for most of the year (Close to 80% of the time)
  • The highest recorded indoor temperature was 79 F - this is because we had a 72 F day on Feb 24th. I was NOT going to turn on the A/C is February. 
  • The lowest recorded indoor temperature was 64 F - this was because I left too many windows open overnight to achieve some passive cooling in September.
  • There have been a few times it has been colder than 30 F outside and we have had to open windows to cool off. This does mess with the Relative Humidity a little bit. On Christmas Day 2017 we had to open windows to cool down the house with company over. We were at 75 F inside.
  • In the summer the heat pumps only ran in the "dehumidify" mode (where they try to maintain 60% RH), and we only turned them to A/C with a set temperature when we were gone for a week for vacation.
  • I will be doing a ERV vs. HRV post in the future so I don't want to go into too much detail, but we have swapped to the ERV core for the winter to help maintain RH. From January-March we struggled to keep the RH around 30-35%. So far this winter we are in the 40-45% range - even with the bomb cyclone dropping temps here to around 0 F for a few days. 
  • For 80 % of the year we are in the 40-60% RH. The other 20% is due to opening windows for passive cooling in the shoulder months - when it gets down to 55 F at night and 90% RH. Then heats up to 80 F during the day at 60% RH. I am not good enough with Excel to show you a graph of that. 
Okay, Back to the Utility Data:
Now to take a closer look at how we used our Energy compared to the PHI and PHIUS Standard: The number on top of the Bar Graph is the Passive House Limit. The number in the blue is the 2017 energy use for RPH.

One quick note on the primary energy from PHIUS. It is calculated as 6200 kWh per person per year divided by 3.16 (losses in the grid). The number of "persons" is based on number of bedrooms +1 (just like RESNET). We have 3 bedrooms and an office without a closet. For purposes of this calculation included the office as a bedroom. Amazingly, that closet matters! We currently have 5 people living in the house, so I figured it was okay. I know neither standard is perfect but seems silly that the difference between certification and not is whether or not you build a closet in a room.

Thanks for taking the time to read, and if I messed up any of my calculation I'm sure someone will tell me. 

I'll be working on a post for HRV's VS ERV's and my experience with both shortly.


7 comments:

  1. Sounds great. Congratulations.

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  2. Great to see the data, Matt - important work!

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  4. Awesome house, Matt. And your 0.15 ACH @ 50 Pa airtightness is certainly paying off nicely. Bomb cyclones and all. Best, Tad

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    1. Thanks Tad,
      I am going to be putting together some "savings" data as well as various IAQ data in different rooms of the house. Should be interesting. Hoping to have something to present at the next Passive House Conference

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