Humidity control in casual dining restaurant, beach location
Humidity control in casual dining restaurant, beach location
(OP)
In troubleshooting a reported condensation issue in a local restaurant (Myrtle Beach, SC), built less than 1 year ago, I find the following:
- condensation at table tops in dining room, heavy enough to warp/split new wood tables (mainly in summer), and keep salt shakers caked up
- untempered fresh air intakes on (3) RTU's in dining room; total tonnage 21 tons with estimated fresh air at least 2000 CFM, over 1500 CFM thru 1 7.5 ton unit (too much!); total AH flow ~ 8400 CFM
- untempered fresh air intakes on (2) RTU's in kitchen; total tonnage 12 tons with estimated fresh air at least 1100 CFM; AH flow ~ 4800 CFM
- approx. 600 CFM differential between kitchen hood exhaust and dedicated makeup air (MUA ~ 90% of exhaust, total exhaust ~ 5300 CFM)
The client's kitchen hood supplier recommends a DX makeup air conditioning system, but I don;t think the dining room condensation is being caused by kitchen makeup air differentials. I lean towards:
a) balancing dining room units fresh air to distribute OA load
b) install ERV's to temper OA
c) reduce OA flow (my calcs show abt. 1700 CFM required)
d) in lieu of a dedicated MUA DX system, bring in more OA thru the kitchen RTU's and condition there.
This is all preliminary, and I appreciate any other opinions about this kind of situation...the owner wants to avoid spending unnecessary money.
Other data:
Dining room area ~ 2200 SF
Kitchen area ~ 1600 SF
Hood size - 22' x 4.5 '
Occupancy ~ 180 patrons, ~ 20 staff
Thanks for your insights!
- condensation at table tops in dining room, heavy enough to warp/split new wood tables (mainly in summer), and keep salt shakers caked up
- untempered fresh air intakes on (3) RTU's in dining room; total tonnage 21 tons with estimated fresh air at least 2000 CFM, over 1500 CFM thru 1 7.5 ton unit (too much!); total AH flow ~ 8400 CFM
- untempered fresh air intakes on (2) RTU's in kitchen; total tonnage 12 tons with estimated fresh air at least 1100 CFM; AH flow ~ 4800 CFM
- approx. 600 CFM differential between kitchen hood exhaust and dedicated makeup air (MUA ~ 90% of exhaust, total exhaust ~ 5300 CFM)
The client's kitchen hood supplier recommends a DX makeup air conditioning system, but I don;t think the dining room condensation is being caused by kitchen makeup air differentials. I lean towards:
a) balancing dining room units fresh air to distribute OA load
b) install ERV's to temper OA
c) reduce OA flow (my calcs show abt. 1700 CFM required)
d) in lieu of a dedicated MUA DX system, bring in more OA thru the kitchen RTU's and condition there.
This is all preliminary, and I appreciate any other opinions about this kind of situation...the owner wants to avoid spending unnecessary money.
Other data:
Dining room area ~ 2200 SF
Kitchen area ~ 1600 SF
Hood size - 22' x 4.5 '
Occupancy ~ 180 patrons, ~ 20 staff
Thanks for your insights!





RE: Humidity control in casual dining restaurant, beach location
RE: Humidity control in casual dining restaurant, beach location
What would lead to stratification of colder, moister air at the table level? The supply air is all from diffusers spread around the 10 ft high ceiling.
Thanks,
JLL
RE: Humidity control in casual dining restaurant, beach location
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
RE: Humidity control in casual dining restaurant, beach location
RE: Humidity control in casual dining restaurant, beach location
> A/C during the day?
> Circulating OA during the night?
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
RE: Humidity control in casual dining restaurant, beach location
A/C runs during day, and is cut back during evening hours (this is a breakfast/lunch only, closes at 2 PM. OA is drawn directly into RTU's at "economizer" interface, only no economizer, just a filter and damper. OA can infiltrate when blower is off, as the duct work allows direct communication with OA intake.
That's all I know right now...
RE: Humidity control in casual dining restaurant, beach location
RE: Humidity control in casual dining restaurant, beach location
I believe you have a fixable issue given the information you have provided. I also think it is can be achieved for very little cost to the owner - mostly just an O.A. balancing issue as I see it.
I calculate O.A. requirement per ASHRAE 60.1 to be roughly 1,750 CFM for the Dining area. 60.1 does list "Kitchen" specifically for O.A. so I would calculate based on 5 CFM per person and 0.06 CFM per SF for roughly 200 CFM.
Obviously by the numbers you listed from observed O.A. installed, infiltration into the space causing condensation is not a factor. So the problem with condensation probably arises from a combination of short cycling of the units combined with the large O.A. values.
Here is what I would suggest:
- Adjust the Dining area 3 RTU's to deliver a total of 1,750 CFM required.
- Adjust 2 Kitchen RTU's to deliver the 200 CFM required.
- Many thermostats presently have inputs/outputs that can control auxiliary equipment such as dampers. I would suggest that the thermostats be capable of closing the O.A. dampers completely on night set back.
- Verify or provide transfer path between Dining and Kitchen to make-up exhausted air by the kitchen hood. This way the kitchen remains negative not allowing kitchen cooking odors into the dining space.
- My guess would be the RTU's serving the dining area are manually set two position type. Suggest to the owner these be replaced with modulating type interfaced with a space mounted carbon dioxide sensor to modulate them based on air quality. Set the minimums on all three combined to be no less than 600 CFM to keep the space positive and allow for kitchen make-up.
Just my first blush opinion Hope it helps.
Andy W.
RE: Humidity control in casual dining restaurant, beach location
It's tough to control on a DX system unless you have the ability to mix with return air or induce room air. Maybe even add some reheat. Of course, it's really expensive for the owner to cool the place 24/7. A tough problem, but stick with it. Keep the ideas coming. Let us know what solves it!
Good on ya,
Goober Dave
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RE: Humidity control in casual dining restaurant, beach location
So, does anyone expect the kitchen makeup air to be a serious player in this problem? Personally, unless we take new measurements and show the MUA flow is much lower than the 90% stated, I can't see how it would affect the dining room at the level indicated.
What do you think about using a dehumidication system for the dining room, or using ERV's on the RTU's?
JLL
RE: Humidity control in casual dining restaurant, beach location
RE: Humidity control in casual dining restaurant, beach location
2- you said the problem mainly noticed in the summer, and you want to temper the fresh air while the hood contractor wants to cool the make up air?
3- did you talk with the engineer who did this project.
4- did you check the original design with the actual installation.
5- is ther a condensation on the walls
6- did you check the temperature and RH inside dining room.
21 ton over 2200 sqft look like oversized
RE: Humidity control in casual dining restaurant, beach location