Sys not cooling well

bagger

I need help figuring out a system that is not performing very well, nor has it ever from what I am told. I have two systems installed in a small house that has been converted into a restaurant. A 5 ton that is used to cool the dining area that works fine. The problem system is a 2.5 ton straight cool with a fixed orifice and no electric heat that is used to spot cool the kitchen. Both the supplies and returns are located in the kitchen and are the correct sizes. Neither of the coils are heavily soiled and the Freon charge is very close: delta-T – 85/75 degrees; ID wet – 76 degrees; OD dry - 91 degrees; suction line had 83 psig at 78 degrees; liquid line had 303 psig at 127 degrees.
To me, it seems because of the high heat load, the system might need a larger piston (if so, about how much larger) and/or add some cooler return air from the dining room into the kitchen. What would you suggest?

mechanicalDvr

Do a load calc on the kitchen area and see what you need for the area. What is being used for make up air?

supertek65

is this r22, ????????????
are you saying this is your suction pressure/saturated suction temperature?????
or are you saying this is your suction pressure and your suction line temperature??????????
Main question is?????
what is your superheat?????????????
high suction high head high load!!!!!!!!!!!!!!!!
you absolutely do not want a larger piston/orifice!!!!
then your suction will go up even more!!!!!!!!!!!!
oh no!
hard to get cold air with a 75 degree evaporator!! lol

__________________
high superheat never killed a compressor!

supertek65

r22
83 psig =50 degrees

132 degrees- 127 degree liquid line 5 degrees subcooling


are you saying you have a 78 degree suction line/ 28 degrees superheat????????

is that correct????????

__________________
high superheat never killed a compressor!

jmmech

1st question-Does this kitchen have a properly sized makeup air system?
If you don't have sufficient outdoor air coming into the kitchen, the exhaust hood fans will suck the life out of the ac and cause other issues in the entire building as well. Been there-done that.

milk man

How clean is the condenser coil. Is it sitting next to the greece exhaust and covered. Does it have a double condenser coil that needs to be split?

RoBoTeq

I'm gonna go with the exhaust/makeup air issue as well. Most home to restaurant conversions neglect makeup air when they have the required exhaust fans installed.

Jeffrey Jay

Lots of good points here. In my feeble experience 2.5 seems pretty light tonnage wise for a commercial production kitchen, add your loads and see if its up to it when it's running correctly. Your discharge air temp would be useful. Also keep in mind when spot cooling high/consistantly produced heat loads you are removing Btus and reproducing them so you will never really "cool" the room, you just keep it from building up. If your rolling heat out the condenser she's working. My .02

dilky

hey bud if you really want it done right have a qualified air balancer check out your problem this will solve and answer your guesses

beenthere

You have 2 issues.

1.
A. Load. Very very few kitchens only have a 2.5 ton load.
B. Kitchen loads are mostly latent heat.

2.
A. Equipment size/selection.
B. Equipment set up.

First. Despite how the coils look to you. Clean them anyways(sub cool should drop a little).
Check your air flow in CFM. Its probably higher then 1000CFM.
Then recheck your entering air conditions, and take the leaving air conditions, including leaving wet bulb. Convert those readings into entaphy (BTU per pound of air/cubic foot of air). And calculate the capacity your getting.
Then slow that air flow back down to 1000 CFM. And recheck capacity(with your current readings, at 1000 CFM, you only have 10,800BTUs of sensible). So your either moving more then 1000 CFM. Or your coils are a lot dirtier then you think.

At 85 indoor dry bulb, and 76 indoor wet bulb, you have almost 67%RH.
And that makes your dew point 72.7°F.
Slowing the blower will remove more moisture. And as the moisture is removed. The system will gain more sensible capacity.

That will address system performance about as much as possible.
After that. They/you, need to address make up air. And or increasing system size. Or adding a second system to the kitchen, if they really want it cooler in there.

But. A kitchen should not be cooled to 70°. That just cools the food off quicker. And makes for unhappy customers. Or, makes the restaurant get bigger heat tables to keep the food hotter. Which then increases the cooling load.


Have you been back since you made your post?

__________________
How many times must one fix something before it is fixed?

dilky

this dude is everywhere i never heard of food spoiling due to a 70 degree kitchen there is such a thing as a walk in cooler isnt there? to put it simply it sounds like the unit is undersized you can only get so much out of it have a real hvac eng due a heat load your local supplyhouse will gladly help and put it in simple terms that other so called pro should put the dictionary down its not that big a deal and very easily corrected watch his strange but funny answer i cant wait .

beenthere

LOL...

Never said it spoils the food. Reread what I posted.

It cools the food off. Customers prefer their hot meals, to be hot.

__________________
How many times must one fix something before it is fixed?

dilky

hey bud i want you to know im really just kidding you you got a lot of spunk and i enjoy your comments but cmon im just an old guy that use to measure superheat with my hands so take it easy on me and remember some of these kids out there need a how do i say it without getting you going again though i enjoy it a less complicated answer i will check in tommorow ok goodnite and take it easy

beenthere

They need to learn all aspects of the part of the trade they are in.

I think most of us know that 2.5 tons is nothing for a kitchen.
Being able to show the owner that its doing all it can. Makes a sale/upgrade easier.

__________________
How many times must one fix something before it is fixed?

dilky

i do agree with you but go slow start with delta t then pressure temp difference also then subcooling and superheat and before their brains explode grasp the electrical side after they understand the x terminal on a time clock thats when we find out if they sink or swim if that works the kids will be ready for ya go to bed i am thanks for your input this industry needs brains like you but some take longer than others to grasp what comes easy to you.

beenthere

Go slow?
Its been 2 weeks since he made his post.

I had 2 dead horses finish at Penn National raceway already since this thread was started.

I'm waiting to hear the outcome from the OP. But, he may not have been the tech that was sent back again.

Its a shame, that so many companies won't send a less experienced tech along with a senior tech on a return visit on calls like this.

__________________
How many times must one fix something before it is fixed?

dilky

hey bud your killin me i think we both have been had can you imagine this cutomer buckets for everyone .

beenthere

I see this a fair amount of the time.
Someone post a question. Lots of discussion, questions, and suggestions are given. And the OP never replies again. So you don't know if he was helped or not.

Its a real shame. 100's to 1000's of tech around the world are willing to help others out. By telling and giving their experience to them. And then, not even a thank you. is given back.

30 years ago. Life would have been so much easier, if the internet and forums would have been around like it is today. So many customers would have had quicker repairs/solutions, from me and others.

__________________
How many times must one fix something before it is fixed?

dilky

your asolutley right 30 years ago no cell phones no internet you sank or had to figure it out spent many hours of no pay trying to figure it out i started out working on republic boilers with very basic two stages. but we made it im still new to this type of support and as i go ill weed out the troublemakers. take it easy

michael zheng

very good place to exchange informatin and idea you guys here are very professional