We now can make some statements about the performance of our new Tirga measurement. I'll call this "fan" vs the original "shield".
Shield was deployed at ehs. First, I have to remove a bias of +1C from tc.5m to make T.2m and tc.5m agree with the heat flux. I then find that Tirga is generally within 1C of both T.2m and tc.5m. Some days and nights (presumably clear skies), Tirga.5m agrees closer to T.2m than to tc.5m. This makes sense, because the radiation error would act to raise daytime temps and lower nighttime temps, which is the same effect as measuring closer to the surface. Generally, the magnitude of this radiation error was about 0.5C.
Fan was deployed at bao. No tc adjustment was needed. At this site, large differences between 2m and 5m are seen – typically 5C at night. When the fan was running, differences from tc are typically within 1C. When the fan wasn't running (may 19 16:30 – apr 29 17:30), daytime Tirga was typically 4C higher than tc. Presumably, this is the internal EC100 box temperature heating up.
Considering all of the above and using data only with the fan working, nighttime Tirga.5m-tc.5m differences are about the same between fan and shield – typically within 0.5C. Daytime Tirga.5m-tc.5m has shield on the order of 70% of fan – say 0.9 vs 1.3C. Thus, after all this work, fan still is worse than shield 
. Perhaps we need a double-shield inside the EC100?
3 Comments
Steve Oncley AUTHOR
A bit of an update using peak values:
Unaspirated shield: -1.6C -> 2.6C (mostly in the form of sharp peaks); 90% within -1C -> 1.5C
Our mod, single tube:-4C -> +2C; 90% within -1.5C -> 1.5C
Our mod, double tube: -1.5C -> 1.3C; 90% within -1C -> 1C
Thus, our mod using double tube is better, but not by a large margin. Why is unaspirated this good??
Suggested future work:
Steve Oncley AUTHOR
I decided that a better metric was the standard deviation of the temperature difference, Tirga-tc. The results are:
9 Mar - 19 Mar: ehs (factory unaspirated shield): 0.45 degC
9 Mar - 19 Mar: bao (our mod, single shield): 0.59 degC
29 Apr - 26 Jun: bao (our mod, double shield): 0.58 degC
So...the unaspirated shield still wins! (and our double didn't help a huge amount). The double shield period had a bit more sun (240 W/m2) and thus we would have seen better results in March (195 W/m2). Nevertheless, it amazes us that the unaspirated does this well.
We plan to monitor the unaspirated shield with a thermistor during the current CentNet TRH shield tests.
Steve Oncley AUTHOR
Just powered up the bao EC150 in the lab and measured the flow rate using Steve S.'s hand-held device. I got 2.9 m/s from the outlet and (approximately) 1.6 m/s in the core of the inlet. For an outlet diameter of 22mm, the outlet flow would be 66 lpm, which is pretty close to the manufacturer's spec of 60 lpm! Thus, this fan seems to be working just fine (after 2 months of field use).
BTW, this is EC150 SN#1276.