Help with used WIC dilemma
Background... A customer of ours owns a bar. He recently has obtained a used walk in cooler that used to belong to a large BBQ restaurant that closed. The cooler is actually in pretty good condition. He will be using it to store his beer kegs, with chilled glycol lines going to them. The box was previously used to quickly cool down hot BBQ ribs and stuff. I don't have any of the btu info, but my boss and the bar owner agree that the refrigeration systems are way over sized for what it will be used for now. It came with 2 separate evaporators and condensing units that were piped and controlled independently.
Here is the deal... We got the box set up in it's new location and were getting ready to run the refrigerant piping to the condensing units which were going to be mounted on a homemade rack about a foot off of the ground in the back of the bldg. Well, someone stole the condensing units over the weekend. Now we need to figure out what to replace them with.
We already have the evaporators hung and partially piped in. The old plan was to keep the 2 independent systems but only run one of them by setting one t-stat around 33* and the other about 10* or so higher, or maybe just by shutting off the disconnect to the unused one. Now the bar owner needs to come up with new condensing units.
My question is... If we run a proper load calc. on the box and come up with a smaller load number, could we pipe the 2 oversized evaporators together and run the piping to one condensing unit that is sized to the new load? Would we just need new expansion valves sized to the new condensing unit, or wouldn't this work?
Any opinions are appreciated. Thanks.
Run the heat load and see what you come up with.
Then check the coil capacity numbers are see if you can match the coil to the heat load by manipulating the TD.
If not; use the closest coil capacity number which is larger that the box load and buy a condensing unit which does the same numbers at those conditions.
If there any chance that one coil will not be big enough?
It's somewhat hard to answer you well without knowing all the numbers.
1. Box's present heat load calcs.
2. Coil capacities of existing coils at projected suction pressure.
Originally Posted by ammoniadog
The conventional view serves to protect us from the painful job of thinking.
If you can find the mfg and serial number, they will tell you what the box came with and/or what it needs..
We know what the box came with, I guess I was just wondering if we could de-rate the evaporators by putting different txv's on them. The bar owner is working with the company he got the used cooler from to try to find a couple more used condensing units the same as the old ones. My boss has a new smaller condensing unit and evaporators that have been sitting at our shop for a while that he wants to get rid of. I told him that I would rather keep the existing used evaporators, even if he sells him the smaller condensing unit since the evaporators were a pain to install and I don't want to mess with taking them down and hanging up new ones. (The box is set up in a basement with less than 4" of clearance between the top of the box and the ceiling. We had to put the nuts and washers and threaded rod through the ceiling panels before we put the ceiling panels up). My boss will be working on the numbers basically to see if his smaller unit will work in there or if they would be better off with replacing the condensing units like-for-like. I was wondering if we could put a smaller condensing unit and different txv's in the existing oversized evaporators to get it to work.
Originally Posted by Joe Harper
-Thanks for your suggestions Poodle Head, you gave good advice. Like I said, my boss will be doing the heat load calc and running the numbers. We will see what he comes up with.
Here's what I would do.
First, determine the specific capacity rating for the evaporators in Btuh/ºF TD. Most evap coils have this incorporated into their model numbers...ie, a Bohn ADT090 would have a specific rating of 900 Btuh/ºF TD.
Then, with your desired box temperature...let's say 35ºF...pick an initial TD of 10ºF. This will give you an initial evaporator temperature of 25ºF for checking the capacity of your available condensing units at that condition.
Now, divide the unit's capacity by the evaporator's specific rating and you'll get your initial estimated TD. If it's close to 10ºF TD you're good to go. Since you state that the units you have are a bit smaller than the original, I'd expect to see a slightly lower TD number...like 7ºF or 8ºF. The evap will work fine at that low a TD. I wouldn't go lower than 6ºF TD though.
You then need to check the expansion valve capacity at the new condition and resize as needed. The distributor nozzle capacity should also be checked and resized if necessary. Of course, you'll want to be sure the new lower system capacity can handle the expected box load by running a load calculation.
One point to consider here however is with the lower TD you'll get a resulting higher RH in the box. This wouldn't be a problem for kegs, but you may find the cardboard cartons getting too damp and soggy.
Thank you Icemeister and Poodlehead. You both give very good information.