Heating Loads for the Flatrock Passive House

In the previous post, I presented some numbers from the modelling of my passive house. Although, the loads showed, a maximum of 3.8 kW, that didn't include the thermal gains or the solar gains so infact, the total load will be significantly less.

The PHPP software can only provide static numbers for a whole house and doesn't do any type of room-by-room analysis for heat loads. The PHPP software showed that the total load would be 2.8 kW once internal gains are taken into account. However, in order to ensure heating is distributed uniformly, a more conventional engineering heat load calculation program is used. The table below shows the heat loads required to maintain 20 C inside when its -18 C outside:

Look closely...the numbers are tiny! The upstairs hallway requires 22 W!, The main bath requires 83 W! Even running a 100 W light bulb in that room will be sufficient! However a light bulb is not considered a heat source so we need to explore options for heat sources, a way to distribute the heat and whether or not a couple of zones in the house along with natural air movement is enough to move heat from those zone sources around the home.

The largest heat load is in the kitchen/dining room. At 700 W, this gives, 18.6 W/sq. m.! In the master ensuite, we will require 155 W or 13.8 W/sq. m. These numbers are so small that finding heaters are almost impossible. Where will you find a 100W baseboard? You won't. This is typically why these homes use point source heat rather than huge distribution systems like ducts. Point source heaters, a few in select areas, along with natural stratification is usually enough to distribute heat as long as the HRV/ERV is circulating air.

The average human body radiates 100 W of thermal energy while resting. So two adults sleeping in the master bedroom on the coldest day of the year will heat a room like a 200 W heater. The difference according the load table is about 49.4 W. Unfortunately, sleeping with a light bulb on is not an option. But if it were, it would make a great heat source! It is very unlikely that heating will even be required on most winter nights in the rooms unless the temperature outside is less than -5 C. A body in the rooms will almost be enough to keep it comfortable!

Next step: Determine how to heat the space....Lots of ideas for my next post!

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