Passive House Principles: Renewables

The energy requirements for the Passive House standard (PHIUS) are pretty tight if you compare them against a code built home.  The home must be built to satisfy several key factors which are dependent on climate as per the map below.  The specifications that I am concentrating on are for climate region 6A

1.  Primary Energy Demand of the building can't be any more than (# bedrooms +1)*6200kWh.  Which gives  a total of 24800 kWh.  This seems like a lot but you'll see, its not a much as you may think.

2.  The Total Annual Heating Demand has to be <25.3 kWh/sq. m.  (internal floor area).  For a typical 2000 sq. ft. home this will give a total of about 5000 kWh


3.  The Peak Heating Load has to be less than 13.5 W/sq. m. (internal floor area).  So on the coldest day of the year, if it's not sunny, the heat requirements of a 2000 sq. ft. building will be about 2600 W.  So a 2000 sq. ft. home could he heated with two 40" (1500W) baseboard heaters!

North American standards for passive house can be seen here at the link below along with details about the standard and the energy requirements for passive house designs in different locations.

http://www.phius.org/phius-2015-new-passive-building-standard-summary



The PHIUS standard employs a set of energy conversion factors to calculate the total power used.  The energy used is calculated based on where it comes from or how it is generated.  The idea is to go back to the source of the energy in order to cut down on global warming potential.  For example, our electrical grids in North America are somewhere between 30%-50% efficient in terms of generation.  This means that when we burn oil to create electricity, we loose a significant portion of the energy through burning, thermal generation, transmission lines, etc.  Electricity has a source energy factor of about 3.  So if you use 14 kWh at the meter to heat your daily hot water, you actually use  42 kWh of energy contained in oil to produce that 14 kWh.  Assuming you heat that amount of water each day for 365 days/yr you will use up about 15000 kWh of the Primary Energy allowance for the building.  At least this is my understanding.  For a 2000 sq. ft. home, you will be left with 9800 kWh for heating and appliances.  Good luck!!!! Your appliances can use up to 4500 kWh which scales to 13500 kWh once the energy factor is applied....Your energy budget has been spent!  You have no more energy in your allowance for heating.  Include heating and now the total energy at source is 43500 kWh!!! This is 18700 kWh over the required limit.

So you can see how the energy allowance get chewed up quickly once you take into account the energy factors.  This is where adding renewables come into play or adding a heat pump.  A heat pump is really just a kind of renewable energy.  Electricity is being used, but you are just moving energy from one place to another using a refrigeration cycle.  So let us do the calculation assuming we use a heat pump water heater and a heat pump for heating the house.  We can safely assume the coefficient of performance for the heat pumps are 2.5.  The total energy will be  (assuming the electric energy factor is 3.0)

Energy DHW + Energy Appliances + Energy Heat

= 5000 kWh x 3.0 / 2.5 + 4500 kWh x 3.0 + 5000 kWh x 3.0 / 2.5
=   25500 kWh!! 

So using a heat pump almost gets to the energy limit.  Choosing energy efficient appliances can easily decrease the energy demand by 700 kWh.     In which case, your primary energy demand would be met.  The use of a heat pump really just offsets the penalty for using electricity because the coefficient of performance is similar to the source energy factor.  In any case, the amount of power that you would actually pay for is based on the reading from the meter which would be about 8500 kWh per year.  This equates to a power bill of about $1170.00/year or $97/month if the bill is cost averaged.

Using wood is another alternative.  Imagine heating your home with 0.75 cords of wood per year.  This equates to a 4'x4' pallet of wood that is 4' high and another pallet 2' high.  Wood is a completely renewable resource and is carbon neutral since burning it adds no new carbon to the environment than was already here.  The source energy factor is 1.  Now you just have to find an efficient wood stove.   Most EPA stoves are above 75%.  Calculating the energy required using an efficiency of 75% gives:

= 5000 kWh x 1.0 / 75% + 4500 kWh x 3.0 + 5000 kWh x 1.0 / 75%
=   26833 kWh!! 

So using wood heat gets us close to the limit.  Choosing a more efficient wood stove and some energy efficiency appliances will get us below the 24800 kWh requirement.

Using renewables is important to meeting the energy requirements defined by the PHIUS standard.  Without renewable energy, it becomes much harder to meet the requirements, if not impossible.  Solar panels (PV) can also be used to offset some of the energy requirements using net metering.  Solar panel systems have decreased significantly in cost and expensive battery storage systems would not be required unless you want to live off-grid.  Instead, a system connected to bidirectional meter would used to feed power back to the grid.  The solar potential in Newfoundland is pretty respectable.  Typically a 1 kW panel will produce 1000 kWh of electricity throughout the year.  With a solar tracker, it would produce almost 1400 kWh.  To finish, have a look at some of these links defining the standard in more detail:



http://www.motherearthnews.com/green-homes/home-design/passive-house-zm0z11zphe

This is an add-on style heat pump that can be added to an existing electric tank:

http://water.nyle.com/r-series/

And a new hybrid heat pump water heater,

http://www.rheem.com/product/hybrid-electric-water-heater-professional-prestige-series-hybrid-electric-water-heater


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