I don’t understand where the Minneapolis door can only do 50 or 25 Pa.?
I looked at the DG-700 micro manometer after we talked on the phone about this.
This manometer has many different modes of operation.
One is pressure/pressure.
Two is pressure/flow rate.
Three is pressure/flow rate at 50 Pascal.
Four is pressure/flow rate at 25 Pascal.
Six is pressure/feet per minute.
(I don’t remember what number five is)
From what I can see, option number three and number four are automatic settings that complete the calculations automatically for you, to include controlling fan speed to maintain the 50 or 25 Pascal pressure.
This manometer will automatically calculate air leakage rates that can not reach the target pressure. So if you’re trying to hit 50 Pascal and you can only do 40, the CFM display is the calculated CFM at that reduced pressure.
Selecting option three (at 50 Pascal) must be selected if you want to determine automatically the “can’t reach 50 factor” when you can’t reach the 50 Pascal level. These factors are automatically programmed in the manometer (a different set of factors would be utilized for “can’t reach 25”).
You do not have to drop down to 25 Pascal and do external calculations.
Also, when utilizing the “cruise control” option, setting the manometer to CFM/50 Pascal tells the fan the pressure to maintain.
You should also be able to use option number two which is basically a “manual mode”.
As to subtracting baseline pressures of the building from the tests equations, there is a baseline function that you run with all the door equipment installed, but the fan opening is blocked off 100%. This gives you the natural pressure of the building and the time average to determine this pressure and removes this variance from the automatic calculations in the other automatic manometer modes.
All this has to do with a “one-point test”, where CFM is determined at 50 Pascal.
A second and more accurate test procedure is to perform a “multi-point test”. This test is conducted from as high as a recommended 60 Pa (or more), down to the lowest CFM the fan can calculate. Multiple readings at 5-10 Pascal step reductions are recorded and plotted on a graph or computer software. This provides information as to leakage rates across the potential pressure differentials of the building. There is a potential that you’re building will not leak excessively until it reaches extremely high pressure differentials (which may not be normal conditions for your location). This information can also be utilized to determine where the leakage is actually occurring and when.
I believe that the 75 Pascal criteria may be associated with this “multi-point test”.
There will be no requirement to reach 50 Pa in order to perform the tasks, rather a reference point to attempt to achieve to increase the accuracy of testing.
This is simply a perspective from past HVAC training 30 years ago. I am not trained or certified in today’s standards or equipment.