—”By the way in case you didn’t know, flow varies directly with speed.... it’s a 1 to 1 relationship. If your fan speeds up 20%, the flow goes up by 20%. However, the power goes up by the cube of the speed. Thus if the fan speed increases by 20%, the power increases by 73%.”
Good stuff, thank you, I see in the study linked below, they use FAN RPM to determine CFM.
I painted a white dot on the fan but holding a steady aim is not easy, I might have to put a couple of screws in the wall for this one. Also, I have readings from the tach where there is no paint dot???
I acquired a nice selection of cardboard and a working plan...
I shaped a box to fit the front of the head unit and was taping it in place and noticed the unit pulling slightly from the wall???
PROBABLY NOT GOOD.
Pulling down gently on the front of the unit distorts the wall bracket ...
Everything except the bracket is plastic, the unit weighs about 20 pounds, I easily hung it singlehanded. Not made for additional attachments.
And I wanted a long strait trunkline...
Well, I could add a few trapeze hangers?
Looking around I found Figure 13 Flow test setup, on page 13 from:
https://www.nrel.gov/docs/fy11osti/49881.pdf
I have always heard using flex duct is not good for flow.
...Moving on to my floor mount unit with a large flat return grille to attempt a few measurements and compare three different anemometers, a friend loaned me #3.
The grille is dived into six horizontal elements, so one high, one low, and a dozen samples should work.
The meters were surprisingly consistent with each other, the hot wire had a flyer or two; probably from how I held it?
My son-in-law the HVAC guy said “Hold the meter center and multiply by 0.9 “ of what the meter shows in CFM for the opening size.
Doing a second flow survey the numbers dropped and the air cooled???
DEFROST CYCLE; that and a few more variables make hard(or close) numbers difficult to find if not constantly logging input and output. The outside coil will frost up, limiting flow, and the system used compressor heat and maybe steals a bit from the house to defrost.
And the temperature is dropping to minus seven tonight, a good time to be watching what the heat pump does. Typically we have 5 subzero days each year, we had 3 over Christmas... about over.
Looking around the few solutions that come up are expensive and/or junk.
Scope, time, cost-—PICK TWO!
And I’m Cheap Charlie #10
Also, I have readings from the tach where there is no paint dot???...... White paint dots don’t always work… you should be using a strip of proper tachometer ‘reflective tape’. It’s cheap and readily available. The other problem is that when you put it on a location where other blades pass by the laser, it’s possible to get false readings. Is there someplace you can put the reflective tape where it doesn’t also cross the other blades. Can you get access to the end panels of the impeller or a rotational part of the motor.?
Pulling down gently on the front of the unit distorts the wall bracket ..... My goodness, that’s not much of a factor of safety, is it?
I have always heard using flex duct is not good for flow..... No kidding. I looked at the pictures and it does not look like a good set up at all. The idea is to test and not change the conditions by adding any system resistance. It’s always better to test on the inlet side of a unit due to the fact there is less turbulence than after the unit. However, that can be a problem if there isn’t any available space.
Doing a second flow survey the numbers dropped and the air cooled???....... Yup… not easily to test a moving target.