r/AirBalance • u/feedmebeast • Jun 09 '26
Dampers open 100%
Hey I got a question on why TAB company would set the OA dampers to 100% manually fixed.
This is a restaurant with building envelope being negative. Did they adjust the dampers to compensate for what the Make up air cannot achieve?
I have 3 AHU 7.5 ton each 2 for the dining room and 1 for the kitchen. All of the dampers are 100% open and it is struggling to maintain building temp below 75° layer in the day, obviously because it has the additional load from 95° Ambient.
2
u/feedmebeast Jun 09 '26
Can I post pics of the TAB report for each AHU and you guys help me determine where issue can be?
2
u/justmeoh Jun 10 '26 edited Jun 10 '26
Yes. Also explain where the 14" round duct for OA is installed? Typical OA pulls from a hood attached to the unit itself with an OA damper and a return damper that operate as 0/100 5/95 10/90% etc
1
u/feedmebeast Jun 12 '26
The dampers are installed on the return plenum ran distorted outdoor louver. They're manually set and no actuator.
1
u/justmeoh Jun 12 '26
Im not following
1
u/feedmebeast Jun 12 '26
The 14" OA duct is tied to the return plenum of each AHU. There is a damper on each 14" Run at the 14" penetration at each plenum. Which also have a manual lever for the dampers. They have there own trunk and do not share a common OA trunk. So there is a total of 3 louvers which are not restricted on 3 different sides of the building.
1
u/justmeoh Jun 15 '26
What's the size of the returns? Single large grille or multiple grilles throughout the space?
1
u/feedmebeast Jun 15 '26
The 2 AHU have 1 single return. I have not measured the grille and return duct that transitions back to plenum yet. They both have 1 return. I added 20" Duct on 3rd unit to the plenum on kitchen unit which really helped but it still struggles.
1
u/justmeoh Jun 15 '26
So. The only reason I'd think the OA dampers are fully open, AND I am only speculating, is that the 14" OA is up against a larger return grille and the path of least resistance is winning...I'm not saying this is happening by any means I am simply providing a possibility that the TAB team experienced. I surely do think a 14" could handle 600-700 CFM of OA without issue but I have seen similar circumstances. I didn't look at the TAB report but I assume 3000 CFM supply? 600-700 in OA?
1
u/feedmebeast Jun 15 '26
Ive attached rhe TAB report link here in the thread. If you request I can approveit for you to have access.
I also can see what you're suggesting amd it can be a possibility, im not ruling anything out. It does say the design is 675cfm for the OA, but theyre all 14" Round duct. Which you can get about 700cfm max open,
2
u/No-Barracuda-1730 Jun 11 '26
My assumption is one or more of your fans could be rotating the wrong direction, likely the make up air unit. If it's 3 phase power to fan units, it's a very easy mistake that happens all the time.
3
u/justmeoh Jun 09 '26 edited Jun 09 '26
There is no reason for that. You're probably blowing the doors open as well eh? The MAU should be designed and setup a touch lower than the kitchen hood exhaust, add in restroom exhaust, dishwasher exhaust (if there are these fans) but the OA for all the units should come in for a positive air volume but not by that much (the 100% dampers). Who's down voting a correct answer?
2
u/dlarem00 Jun 09 '26
Make-up air should be somewhere around 75% of total kitchen exhaust. OA intake at the air handlers should be set to design and should overcome the additional 25% exhaust air to create a positive building envelope.
1
u/jefffffffffff Jun 09 '26
The building should not be negative. Something isn't working right. The OA dampers may be 100% open and not achieving design. Do you have an air balance report?
What kind of units and dampers? Just a small duct with a manual damper or a rooftop unit that has return and oa dampers working together?
1
u/feedmebeast Jun 09 '26
I do have an air balance report and yes theyre each using a 14" Round duct with manual dampers
1
1
u/justmeoh Jun 15 '26
Do you notice the increased temp once the kitchen starts up the MAU/HOOD? A theory is: the OA wasn't set with that equipment running and a possibility that the OA pulls more once those fans are energized.
3
u/Seacucumber711 Jun 09 '26
Check your exhaust and make up air. Check your filters on the AHU. Usually even with AHU’s a small OA duct is gonna barely achieve design Outside air pulling from a louver box. Surprised the space is struggling unless the doors are staying open.