Sizing walk in coolers for new condensing units.

[Swiney]

a new customer of ours called and was having problems with two walk in coolers. One is just for beer and the other one has everything from fruits, vegetables, meats and pastas.
The problem is both coolers are ran off of one condensing unit, so when they have a condensing unit issue both walk-ins go down. When I went to look at the system I noticed the condensing unit is only six years old and the compressor was replaced two years ago. After talking with the manager he says the compressor is replaced about every two years or so.

I checked out the piping and noticed that there is not any traps anywhere on the system. I advised the manager that the best way to fix the system was to install a condensing unit for each walk in and run new lines with the proper traps to get the oil back to the compressor.

The problem I'm having is that I've called two different supply houses to get help writing up an estimate. I figured all they would need to help me size new condensing units would be the size of the box, if they were indoors or outside and the info off the evap coil. Man I was way off, they're asking me what kind of %RH I want inside the cooler, the watts per square from the lights, motor hp, maximum load per day in pounds. The temp of the food going into the box and how many people are in the box per day and for how long.

My question is, does anyone have any idea what the humidity level should be inside of a walk in used just for beer. Then how about the other one that has a little bit of everything in it. Also if there is anything else that you more experience guys can think of that I need to be aware of please let me know. Thanks in advance

[pecmsg]

http://www.industrialcontrolsonline.com/training/online/refrigeration-load-sizing-walk-coolers-freezers-other-boxes

[icemeister]

These coolers appear to be fairly typical uses with nothing out of the ordinary, so while you can go through the motions of doing a full load calculation, a quick selection should do fine.

Tecumseh has a very good online calculator which you can do either method. The main page allows you to input some basic job info and has a handy user's guide to walk you through it. If the beer cooler has glass display doors or if they get deliveries of 200 cases that they need cooled down quickly, use the detailed selection method.

http://boxload.tecumseh.com/BoxLoad.aspx

Heatcraft's Engineering Manual has all of the details you need for the load calc and the equipment selection. For the humidity requirements, see p.21. Read what they say on that page about how the box's relative humidity and the coil TD relate to each other.

If the meats and vegetables in the other cooler are wrapped, I'd use 10ºF TD. If not, 8ºF TD. The beer cooler can go as 15ºF TD because the RH can be lower.

http://www.heatcraftrpd.com/PDF/Misc/EM.pdf

[lytning]

It has always been my thoughts that you didn't want to suck out all the humidity in a meat or fish cooler. You don't want either shrinking. Am I wrong about this. I have been wrong once or maybe twice in the last 40 years. (:- As for keg coolers you want the beer coming out of the tap at 37

[Swiney]

Thanks for the info guys, I was able to use the apps and get him the estimates,,,,

[IRBH]

a new customer of ours called and was having problems with two walk in coolers. One is just for beer and the other one has everything from fruits, vegetables, meats and pastas.
The problem is both coolers are ran off of one condensing unit, so when they have a condensing unit issue both walk-ins go down.


I don't consider that to be the problem at all.

Lots of non-critical coolers are paired on a condensing unit.

Fix the problems causing the repeated failures, don't guess.

Unless you're situated further N than me, I would think that a system failure should be resolved in 4-5 hrs.

[DaveinOzark]

These coolers appear to be fairly typical uses with nothing out of the ordinary, so while you can go through the motions of doing a full load calculation, a quick selection should do fine.

Tecumseh has a very good online calculator which you can do either method. The main page allows you to input some basic job info and has a handy user's guide to walk you through it. If the beer cooler has glass display doors or if they get deliveries of 200 cases that they need cooled down quickly, use the detailed selection method.

http://boxload.tecumseh.com/BoxLoad.aspx

Heatcraft's Engineering Manual has all of the details you need for the load calc and the equipment selection. For the humidity requirements, see p.21. Read what they say on that page about how the box's relative humidity and the coil TD relate to each other.

If the meats and vegetables in the other cooler are wrapped, I'd use 10ºF TD. If not, 8ºF TD. The beer cooler can go as 15ºF TD because the RH can be lower.

http://www.heatcraftrpd.com/PDF/Misc/EM.pdf

I must be thinking about this backwards but the higher the TD, the lower the run time right? Lower run time equals less moisture/humidity removed… or does it? I'm not catching something here and I'm not afraid to ask- what gives?

[icemeister]

I must be thinking about this backwards but the higher the TD, the lower the run time right? Lower run time equals less moisture/humidity removed… or does it? I'm not catching something here and I'm not afraid to ask- what gives?

I suspect you are think of TD in terms of the temperature drop or difference of the return minus supply temps. In commercial refrigeration, we use the TD to mean the box temperature minus the evaporator temperature. If the airfow and Btu/hr are the same but the evaporator temperature is lower, more moisture will be removed from the air. Therefore, a higher TD = lower RH% in the box.

[DaveinOzark]

Where does run time play into all this? The higher the TD the lower the run time, right? Not being argumentative at all apparently I have been thinking backwards (relating it to comfort cooling) all this time.

[icemeister]

Where does run time play into all this? The higher the TD the lower the run time, right? Not being argumentative at all apparently I have been thinking backwards (relating it to comfort cooling) all this time.

If the Btu/hr are the same, then the run time will be the same = Fact.

If coolers with the same Btu capacity, but with evaporators selected with different TD, will result in different RH% in the box.

Try to remember also, the TD is determined at the time of equipment selection. It cannot be changed for a given system, so the expected resulting box RH% will remain the same.

[Brewmaster101]

Where does run time play into all this? The higher the TD the lower the run time, right? Not being argumentative at all apparently I have been thinking backwards (relating it to comfort cooling) all this time.

Provided the system is charged properly and the TXV is adjusted properly.... The box should pull down nice and easy. When people oversize the equipment the box pulls down in minutes and the moisture is left in the box. Remember.....refrigeration is removal of humidity AND heat. I see this a lot. You walk in and it smells musty and looks moldy on the walls. Almost like someone just hosed out the cooler. I got one up on the split system though!! I changed a low pressure switch on a cooler the other day... No big deal. One cooler, for beer kegs, 2 evaporators, each evap had its own condenser. R12 to boot. Yeah, pricing him a new unit this week. System is looking rough.