High Velocity Variability

JohnG_3

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.



Thanks.

Techman

Variables

Sure it matters.Type of main trunk duct layout, length of each take off, the use of restrictor plates,and a few others affect the proper air flow. But ,if,you are comfortable,that is what counts.