Continuing from the previous post ….
To realistically simulate different load driven flow conditions,
our procedure planned to incrementally raise the discharge
temperature set point. This would reduce the cooling effect
available from the supply air and the terminal units would have to
open and provide more flow in order to maintain set point, all
other things being equal. We discovered that it took a while
for the system to react to this change and elected to modify our
procedure to speed things along. Specifically, we took
advantage of the empty meeting spaces and adjusted their set points
down into the low 60’s (F) to cause the terminal units to drive to
full cooling. This simulated the effect we desired and had a
much faster response time.
Its not unusual to discover that you need to make a change in
your test plan once you are out in the field, but when it happens,
its good to take a few minutes to think it through and mark up you
procedure to make sure that there won’t be unanticipated problems
down the road.
The following pictures are the portion of our test form were we
documented our data and calculated additional information based on
our measurements and will give you a feel for the details of our
procedure. Note that we cycled the kitchen exhaust fan on and
off under two limiting operating conditions (minimum load and
maximum load) to assess if it had an impact on minimum outdoor
air flow. We also stepped the dampers open and then back
closed under the same two conditions to assess the impact of play
in the linkage system and other hysteresis generating factors.
Return To Normal
Taking a few minutes to make sure any adjustments you made to
the system for the purposes of testing have been removed and that
the system is functioning normally is always a good idea, no matter
how tempted you are to head home at the end of a long day. In
our case, we verified that all of our manual over-rides were
released and then monitored the operation of the system for about
45 minutes to make sure everything appeared to be
normal. While we were monitoring the system, we started to
analyze our data and look at our results.
TaDa – The Results (Finally!)
The graph below depicts the over-all results of our test.
They are surprising in that the dampers appear to be fairly linear
despite the fact that the rules of thumb would say that they are
oversized. They also document that the missing blade seals
result in significant leakage in both the minimum outdoor air mode
as well as the 100% outdoor air mode.
In a couple of days, I’ll start another post and take a closer
look at our results and their implications in terms of performance
and energy consumption.