Passive House Principles: Renewables
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.
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)
This is an add-on style heat pump that can be added to an existing electric tank:
And a new hybrid heat pump water heater,