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Earth Tube and House Performance

Part of this project was to monitor the performance of the building envelope and of the earth tube/air source heat pump combo. NRCan team members have installed sensors in various places allowing this monitoring. This will continue for a few years. We could not yet monitor the energy use of the Minotair as it is wired into the breaker not a plug.  I will see what we can do after the solar install.

Earth Tube air intake – notice sensor mounted on side

The NRCan guys are monitoring the earth tube performance.  We can see there is still water/humidity in the earth tube.  At some point I need to put a camera again down there to see what it looks like in the summer months.  Here are some of the graphs.  So you understand, I have the following thermostat program:

2230-0700: 18C

0700-1900: 22 C

1900-2230: 20 C

I have inside humidity set for 45%. For the past week, here is data:

Air coming into the earth tube from outside
Air coming out of earth tube into the Minotair
Temperature inside the house

Air velocity in the earth tube:

Where 1 = 250 cfm and 0.4 = 135 cfm

For reference here is the outside Temp and RH:

So it is keeping the house cool but the test will come later in the summer. At them moment I am getting about a 10 C degree drop from this system.

The other NRC guys are monitoring the wall panels which are dry – not issues.  The data is boring as it is pretty constant. I have attached it. The wood and dense wood fibre insulation is dry.

Temperature inside the wall
Relative Humidity in the wall
Moisture inside the wall in g/kg

The wall assemblies are dry as they vary between 5-10 g per kg so as dry as can be.

The earth tube will need to be replaced at some point – the tube material is definitely the wrong one – after some research I have been told this material should be replaced with something more water tight and stronger.  In the meantime let’s see what happens over the first year. I think the idea is right but the implementation needs some work.

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