Thanks for the info.
The whole metrology problem is why I don't chase 100% efficiency.
The goal is to subtract two equal numbers. But, as you approach
that equality, the measurement error in the numbers gets dramatically
worse. And air flow measurement is much worse. 20% error in the
flows is a computational disaster.
My toy HRV has no ducts, so it's nearly impossible for me to get
accurate measurements under true operating conditions.
Current inside/outside differential is only 14F. Makes no sense to
attempt any measurements.
If I understand correctly, you have one symmetrical core of aluminum
and another that alternates coroplastic channels and wide-open
areas. How much difference that makes to the relative air flows
is back pressure and fan dependent. I tweaked mine for zero
inside/outside pressure differential. The fan speeds are significantly
different.
I like the direct measurement approach. Measure what's important
to you. For me, the bottom line is operating cost.
If I had a ducted system like yours, here's what I'd do.
I'd stick a heating element in the plenum inside the box at port4.
I'd poke a 3/4" sense port in ducts 3 and 4 far enough away that
turbulence has stabilized the air temperature.
If you stick a velocity meter in the hole, you'll get a wide range
of velocities depending on how far you stick it in. But if you
go for the peak somewhere in the middle, you should be able
to adjust the fans so that the air speed is equal in ports 3 and 4.
Now, heat up the heating element until the temperatures are
equal at the sense ports in 3 and 4.
The amount of heat necessary to do that is a direct measurement
of what it costs to operate.
To be clear, I don't propose you heat the air. It's just a
temporary measurement technique.
Humidity measurement is another problem area. I have a decent
humidity probe, but the settling time is about an hour. I have to keep
the dew point above 43F or so or I get sinus problems. So my HRV
dumps a lot of water.
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