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High Velocity Variability
I recently had installed two high velocity air conditioning systems, one for the first floor and basement and the other for the second floor. I noticed some variability in the velocity of the air flow coming from the outlets so I bought a wind meter and measured the velocities of all the outlets.
My measurement technique was to stand the meter off the outlet with a 3/4" block and take a measurement. My objective was to measure the air flow velocity as close as possible to the outlet while impeding the flow as little as possible. I used a 3/4" block instead of holding the meter freehand to improve repeatability. While these measurement may not be valid absolute velocity measurements, I think they are valid relative velocity measurements that can be use to compare one outlet to the next.
The downstairs and basement system is a 2 1/2 ton Spacepak unit with 15 outlets. The maximum velocity was 7.2 meters/sec, the minimum was 4.1, the average was 5.3 and the standard deviation 1.0. The slowest outlet had 57% of the velocity of the fastest.
The upstairs system is a 2 ton Unico unit with 12 outlets. The maximum velocity was 8.6 m/s, the minimum was 5.5, the average 7.0 and the standard deviation 1.2. The slowest outlet had 64% of the velocity of the fastest.
In comparing the upstairs and downstairs systems, the upstairs system has velocities about 1.5 m/s faster than the downstairs system.
Does any of this matter? I am concerned about these variations and the difference between the upstairs and downstairs systems, but in the middle of the summer all I care about is if the system meets its design spec of 75 degrees inside at 95 outside. I live in a relatively well insulated three bedroom colonial near Boston.