The Numbers Are In! 7300 kWh per year!

The numbers are in!  And there are lots of them! and they're all good!  The first round of energy modelling has been completed.  Based on the model and the orientation of the house on the lot, the energy usage looks great.  There are too many numbers to talk about so I'll focus on the important numbers.  The PHPP software used to model the home is quite complex.  The data entry is exhaustive and it contains information from the transparency of windows to the air change rate related to the wind blowing on the building (based on the weather data)!

First lets look at the total energy balances:

The BLUE columns show the energy lost by the building and the RED columns show energy gained by the building based on our climate.  Windows typically drain energy from a building in the winter.  However, if oriented properly the winter solar gains can offset the loss through the windows.  In our model, the south windows gain slightly more energy than the total lost through all the windows in the envelope!  This is a great start!  In the summer, the south facing windows gains quite a bit more than is lost but ventilation alone takes care of much of the heat.  The main windows causing this are on the main level since there is no shade structure.  The model shows that added solar screens to the outside of the building cuts this by 60% since they decrease the solar irradiance by about 50%.

Now lets look at loads:
Loads are the instantaneous use or gain of energy.  Here it's shown in BTU/hr but we typically use power in kW to represent this.  The Winter balance is on the coldest day of the year.  The summer balance is on the warmest day of the year.

What does all of this mean?  Well lets decipher the balances and try to put this in perspective.  First I want to talk about Demand or total yearly energy usage for heating.   I'll use kWh to represent this rather then the BTU convention used in the diagrams.  Look below at the plot.  Summing up the red bars (in BTU and converting to kW) in the plot gives a total energy usage of 17kWh/sq. m. for heating during the whole year.

How does this compare to a code built home?  A typical code build home uses about 70 kWh/sq. m.!  So the model estimates a 75% savings in heating cost alone!!!

How about the load on the coldest day of the year?  In the load bar plot above, the total heat used by the building is about 13000 BTU/hr or 3.8 kW!!!  This is amazingly small for a house that's 2176 sq. ft.  In fact, the heating load per square meter was determined to be about 13 W/sq.m.!!  Most code built homes are about 5-10 times this number!

If electricity were used for everything in the building, the total yearly electricity usage would be about 12400 kWh including heating, appliances, hot water, etc.  At todays rates, the cost averaged bill will be about $100/month.  Using a heat pump and a heat pump hot water heater, this drops to 10300 kWh or $83 per month.  A typical code built house of the same size would use almost 24000 or about $195 per month!!!  At our current rate, the savings would be about (24000 kWh-10300 kWh)*$.0972/kWh = $1330 per year and the total monthly electricity bill would be $1001 per year...not too shabby!  HST hasn't been included here.

One of the principles of passive house is adding renewable energy to further decrease the total energy usage.  Do you think that you could be on the grid and minimize energy usage below this while still living comfortably?  You betcha!!!  Using a unique approach, we have further minimized our electrical consumption by another 3000 kWh!  Our total estimated electrical energy usage will be around 7300 kWh.  If all goes as planned...and it will, our estimated monthly electricity bill will be $86.30! This includes the HST tax and the monthly service fee.    Compared to a code built home, the bill would be $245.67.  That's a savings of 65%.  I'm pleased.

With a total energy savings of about 65% and the heating requirement that's 75% less than a code built home of the same size, The Flatrock Passive House is on the road to be the most energy efficient detached home in Newfoundland!


  1. David,
    You may achieve being the most energy efficient, but at present for my cottage 260.00 for heat for a heat for 1000 sq ft. It is one level about 1700 sq ft. It was just 650 sq ft, but with building on all 4 sides, and a mini-split it was remarkable, and used good upgrade methods, including solar gain. Some of the new area is not yet heated , but needs little additional heat, so I am heating constantly 1000 instead of 1700. You have the advantage of two level, which almost allows free heat upstairs , as heat rises.
    As to peak electrical load you say 3.8 kw under worse winter condition.For a R2000 house twice your size we use 3.7 kw peak for heating 4000 sq ft at -17C, which includes the garage. Excluding the garage it would be about 3 kw.
    We find, for the R2000, outdoor temperature must go to about-10C before heat is needed upstairs. Bedroom door kept slightly open at night allows suffficient heat for sleeping.
    I find we get little sun and need to take advantage of what we do get. With one room,at my cottage (not R2000) with both south and west glass, we obtain 83F in winter if the sun is out all day, which is seldom. In the summer, I have patio door to open and let the breeze go through, very effective to cool, and cool with the heatpump just occasionally.....more to dehumidify on humid days. Are you using triple pane glass. Triple pane patio doors would be a great asset for my cottage,,,,,,I see they use them in Germany.....not aware if they use them in Noeth America yet.
    Winston Adams

  2. that 3.8 kw includes solar gains and internal gains. total load is more like 2.8 kW and in my latest post, Writesoft software has determined the load to be 2.4 kw. Ultimately, I think that load doesn't matter as much as total demand since you are paying for kWh, not kW. The house has been optimized for solar gains in order to achieve this. We will be using a triple glazed window with high SGHC made by kohl tech (kohler in nova scotia), have super spacers and has all the necessary data to be used for passive house planning (a certified window according to PHIUS). As for patio doors, since they are fairly leaky we'll be using standard doors with large glazings.

    The passive house model ensures total energy saving over all seasons including over heating in the summer. using simple trellis and some solar screen we have been able to decrease the over heating in the home significantly. In fact using an add on heat pump (nyle ro series) inside the thermal envelope and ducting it from one side of the home to the other, we'll gain enough cool air and dehumidification by sinking internal heat (sensible and latent) to the hot water tank that adding a mini split won't make much sense for us....but I am going to add in the necessary avenues to add a ductless unit just in case.

  3. My experience with Kohler windows ....some 12 years ago.......they ahd such a tint that they allowed very little solar gain amd reduced the light some 30 percent. As my wife has a vision problem, I oversized the glass area some , but it was so dark and no heat gain that I could not use them, and I switched to ACAN. They were not triple galze. Trust yours are suitable.
    You have plenty of glass on the south it seems.
    Should your north bedroom window go the the west, and the west be lower elevation I wonder.
    I used 4 ft overhang on the south which gives ggod shade in summer but allow heat in the winter.
    Will you use attic space for anything....... what is the attic height
    I will comment more later on peak demand.
    Winston Logy Bay, now at Bishop`s Cove cottage.

  4. These windows are certified for use in PHIUS homes. and their solar heat gain coefficients and transparency have been verified by third party raters. My architect and engineer are currently using these in homes in other parts of atlantic canada. All bedrooms are on the south of the house so there are no north windows in any bedrooms. The overhang on the eave will effectively shade the second floor windows but we are adding a trellis structure above the windows to ensure. I will be adding an exterior mesh shad to the windows in summer which, in the model, has proven to take care of most overheating events by decreasing solar irradiance by 65%.. My attic space will have about 36" of cellulose but then it's dead space. The attic space in my garage will be for storage.

  5. You show about 800 watts of window solar gain in winter. This week on a sunny day I observed the gain on the R2000 house via the energy monitor. With about 1.7 kw heating load at about 0C , it dropped midday to about 1.2 kw for about 3 hours, so about .5 kw reduction . But as this is heatpump load with a COP of about 2.5, this means a 1.25kw of solar gain. If electric baseboard, the load without heatpump would be about 4.25. For 24 hrs, if no other heat source, this would be about 102kwh. With heat pump it was a reduction of 28 percent. A solar gain of 1.25 kwh for 3 hrs is 3,75 kwh and perhaps another 2.75 gain over the other sunny hours for say 6.5 kwh total solar gain for the day. But over 24 hrs this is only about 6.3 percent. Yet the load on each of 3 units was about 600 watts each, but the south unit dropped for a while to just 100 watt solar was close to heating the full south side, 2 floors, about 1800 sq ft.
    Now this was a sunny day, and we are lucky to see one or two such days a week, and it can go to 2-3 weeks straight in spring sometimes without sun. I estimate on a cloudy day the gain is about 400 to 450 watts with baseboard heaters for a few hours, about 2kwh saving, less than a third of a sunny day.
    Now this house has more north glass and just double pane, as compared to yours. But in winter , on average, I think the R2000 may see only 2-3 percent benefit from solar gain.
    If so, is it optimistic that you might attain 18 percent.

  6. Keep in mind that PHPP is a static energy balance. It doesn't say a whole lot about demands over hourly or daily time spans but gives averages based on the granularity of the climate data.There are ways to do this but people have found that, on average, its not necessary. The PHPP software also includes components to model thermal mass of the building. My first floor is concrete. that's it. and it will soak up heat much more than wood, carpet, etc. This is included in the model. In addition, heat loss is massively impacted by air infiltration. For R2000 the infiltration rate needs to be at most 1.5 ACH at 50 Pa. If the home is small, 1.5 ACH is small, if the home is large then 1.5 ACH is a lot of infiltration. This is why the PHIUS standard now measures air changes based on gross envelope area and not volume. In any case for smaller homes i.e. 2000 sf total, the ACH will work out to be about 0.6 ACH50. This is more than two times less than R2000. Although some thermal efficiency is gained from insulation, a lot of the energy efficiency comes from the tightness standard. Based on real world experience from by architect their homes are able to perform within 10% of the calculated numbers. The devil is in the details though. Seemingly minor deviations from the plan can lead to huge energy consequences. Thats why I am the general contractor. This house has to meet the air tightness criteria before the walls are closed in with insulation. I am expecting my solar gains to be within the tolerances defined by the model as long as the air tightness criteria is met and the insulation is installed perfectly.

  7. I read that the PHPP is being tweeked for different countries due to different climates. It is a German model originally. So I wouldn`t be surprised if Nfld will need its own treek, similar to us having a different time half an hour!
    I am not sure if solar gain is affected by RH, and I think it may. I have not monitored that, but I have the impression that solar gain is much more on what is dry sunny days.......any thoughts on that David. If so, if may seriously impact the solar gain we get here, and the cause of future tweek. I did monitor attic temperatures for a full year about 8 years ago, but did not correlate with RH.
    Our R2000 must have been well constructed, as wind conditions seems to have little effect in the heatpump mode. RH has some 4 or 5 times bigger effect it seems......and who would expect that.
    And the devil is in more than the details, as to calculations and minor changes....the devil may be more so in the contractor and quality workmanship. In being your own general contractor you can solve that problem and limit the devil in his activity. What is your usual line of work and you are technically knowledgeable.

  8. Hi winston, just saw this comment.

    originally PHPP was used only in germany. the climate there is fairly moderate. translating their standard to a north american climate made no sense: There are 8 climate zones here ranging from tropical to arctic. Their climate sits in the middle. the standard is very socialist in nature. it assumes that any one single doesn't need any more than the base energies defined int he standard. and those numbers germany. in alaska it lead to builders needing walls 21" thick (! this is just not cost effective given diminishing returns on insulation....even then Im not sure that they can pass the standard as they have to go to extremes to store solar in the summer...for the winter in massive storage tanks!

    The newffoundlnad model is actually underling going tweeking as we speak. there are some minor issues with respect to the total yearly demand is my understanding and they have estimated it to be a little too high. As for solar gains, I agree that there are many environmental factors which will affect it. Unfortunately I am at the hands of the model and can only place trust based on previously built houses.

    As for construction. I am the GC. I have a strategy in place to dealing with education, training, and weekly updates as well as some other tricks up my sleeve including being on site as much as possible for the most important air sealing details. Ill control the devil as much as I can to stay true to the model. issues that come up will involve my passive house designer/architect to ensure we are still within the specs of the model if changes need to be made. I plan on this being a build with a lot of communication.

    I am a physicist by profession. I work as a radiation oncology medical physicist but my interests go far beyond this. I just wish i could sleep less than the 5 hours/day that I currently get...maybe then I could explore a few more interest!. Building has interested me since I completed my PhD. I have been through many renovations, one total house build. I would say that the next build will be my last move...but I do have a bug for building....and headaches!



  9. David
    Trying to get my head around your statement that the performance will be 5-10 times that of a code built house.
    You show a heating requirement onthe coldest day of 13 watts per sq meter= 1.2 watts per sq ft
    Now for our R2000, recently measures for -17C using 3.7 kw at night, and this would equate to about 10 kw if baseboard heaters were used. This is a 4000 sq ft house including a heated garage.So with baseboard it would be 2.5 watts per sq ft, which is about double what your passive will need, which is 1.2 watts per sq ft.
    Now since we use minisplits we are getting 0.925 watts per sq ft.
    Now you reduce the electricity use to need less than 1.2 by wood heat for space and hot water and optimised construction etc.
    But is suggests our R2000 is very good construction, and it is south facing for the main windows, but still twice the heating load as yours. I do know that a R2000 next door to that one of a different style and maybe a different contractor has much higher heating costs.
    But regardless your heating needs is at least half that of a standard R2000, and I would expect much less than half many of them.........does this sound right.
    By the way.......will you use waste water heat recovery from your shower, dishwasher, washer ....
    can be done from upstair locations only as you have no basement.


  10. Your R2000 is better than code. R2000 is performance based. if you meet the blower door test requirements its guaranteed that your house will use close to the loads modelled using hot2000. style will drastically affect energy. every corner doubles up energy loss for the most part. adding bump outs etc. are extremently inefficient. using purely electric, a passive house uses about 1/2 that of a R2000 home. This is mainly due to infiltration. The passive house criteria requires 0.6ACH50, the R2000 requires 1.5ACH50. When I talk performance I am only talking about heating requirements. right now, the model is showing about 3200 kWh per year for heating. In our climate the savings works out to be about 75-80 percent less. R2000 is about 50% less. The german standard is 10 W/m2 but the northamerican standard for NL works out to be about 13 or so. in germany, the passive house heating is about 10% that of a code built home. I agree, that who ever built your R2000 got the details right. taking the ratio of heating requirements for the passive house to your R2000 gives a ratio of 0.48 which is consistent with what people are seeing, i.e. that heating a passive house is about 50% less than R2000. This seems to be consistent with your numbers i believe unless I am interpreting them wrong.

    So by using wood, its no different than using a heat pump in the sense that I am still heating using the same amount of energy, Im really just changing up the source of the energy to have less dependency on the grid and upside is less dependency on the grid.

    I have looked at waste water recovery. I am considering it but the real way to do it would be using some sort of waste water tank that transfers heat from the water to another heating holding tank using some sort of heat pump. I don't think this exists. The passive DWHR units like power pipe have a fairly long payback. their longest most efficient unit is about $1000 and I think the payback for our family was something like 3-4 years from what I remember. I was down this road quite a bit. I am thinking that a more effective method is conservation in this case. Maybe concentrate on the biggest energy user in my showering. It guzzles water. Using less may be a better option with almost immediate payback...take a look at this shower: It saves 70 percent of the water used during showering and at about 500 you could put one in each bathroom for the price of the DWHR. based on a a couple of online calculators, I estimated that 1 nebia shower between two people would pay for itself far quicker than the power pipe in our household by using less water. there are also a couple of other shower heads on the market like that uses a venturi to inject air to increase the water surface area. they can use up to 70% less also. the price is more like 169 and it fits on a standard thread...the payback is about one year...and then perpetual. I still have to think further on this one.

  11. Hi David,

    Heard your piece on VOCM and thought this was interesting. I'm wondering if you can provide contact information for the provider of the training course you attended in Halifax.

    Thanks, Andrew

  12. Hi Andrew,

    Natalie Leonard is her name. her company is its best to contact her through the site. As for building a home here, your choices are quite limited. Hence the reason why I did the builders course and we (my father and I) have created Evolution Homes to oversee and guide construction of my own house. If this house goes OK we will move forward with construction of another home next year. We will be providing general contracting, consulting and site visits to help the passive house movement in NL. At least thats the plan.


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