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Thread: Warren/Sherer Rack
04-25-2010, 08:52 AM #1
Hi all you old refrigeration dogs. I am NANOTECH and I am new here and this is my first post. I look forward to contributing and learning! Here it goes.
I have a medium size supermarket just installed with older equipment. All Hill/Phoenix cases and Warren/Sherer Racks all R404a. Queston is on the med. temp. rack. Md# TD3-4005-TC-A Sn# 110361908 It has 3 copeland semi hermetic compressors on it. From left to right 1.) 3D53A150E-TFC-800
2.) 3D53R17ME-TSK-800. 3.) 4DE3A-2000-TSC-800. There are a total of 9 cuircuts with SORITS using off cycle defrost. Using a Danfoss AK-255 controller.
The case arrangement is as follows: 36' dairy, 24' dairy, 24' beer, 16' beverage, 24' produce, 48' produce, 48' low deck produce, 16' cheese island, 16' produce island. I do not know the btu rating per foot to calculate total btu's required wich leads me to my first question.
Question Number 1: How do I know that my total btu's at +15 SST header is enough to match total required btu's for the cases (load)? I am assuming that i need a +15 header based on a 10 deg. TD to maintain SORITS. I am not truely sure on how to determine what the target header temp should be?
I am gussing that the controller will stage the compressors according to the load and capacity based on the hp so I put in from left to right 15hp 15hp and 20hp. Set the suction target at +15 (50psig) and the discharge at 90 (205). Is this correct?
On start-up with the sight glass full and reciever level at 20% all cases at or below 35 my suction pressure is at 48 psig and 4 fans running on the condenser cycling one set on off to maintain 205 psig set point. (75 deg. ambient day)
Question Number 2: Is my suction to high due to being undersized? I do not seem to have quite low enough header pressure to set the SORITS. If this is the case would'nt my head pressure be to high also? I really do not want to run all the cases on rack pressure due to not having a t/stat or llv installed.
Hope this is'nt to much for a first post but it is where I am at. Greatly appricate any input. Oh by the way how do you post a pic with username?
04-25-2010, 10:12 AM #2
Welcome to HVAC-Talk!
I'll start off with your first question. To check the total system capacity you always start with the loads.
1. Gather all the case model numbers, their published load ratings in Btuh/ft and their required evaporator temperatures. (you don't list any walk-ins so we won't go into those here.)
2. Total up the load Btuh and then determine your rack design suction temp by subtracting about 2ºF from the lowest case evap temp to account for suction line pressure drop.
Now you will have your total load requirement and a design suction temperature for your system. Next you have to find what the rack will do at that condition based on the compressors and the condenser model:
3. Gather all the compressor model numbers and download their published performance curves from the Emerson website. Find their capacity and KW input at that design saturated suction temperature (SST) and at a saturated discharge temperature (SDT) of 110ºF, which is typical for an air-cooled, medium temp system with a 95ºF ambient. (This 110ºF SDT is an assumption at this point, but we can verify it later on.)
4. Total up the compressor capacity and compare it to your total load. If the capacity is at or above the load you're rack is probably OK...but we need to check the condenser capacity and verify that assumed SDT of 110ºF.
5. Total up the compressor KW input, multiply that by 3.412 and add it to the total compressor rack capacity. That will give you the Total Heat of Rejection (THR) of the rack at your design condition.
6. Get the model number of the condenser and find its specific capacity which is expressed in Btuh/ºF TD. Divide the THR by the condenser's specific capacity and you'll arrive at a calculated condenser TD (SDT - Ambient Temp). This should be in the neighborhood of 15ºF TD if our assumption of 110ºF SDT was correct. If it's less you're OK because it says the condenser is a bit oversized. If it's more, then you may want to back a recalculate the rack capacity at a higher SDT.
Now you should have a good picture of you system load vs its capacity and your design operating conditions. This has been nothing more than a little "back door engineering" to find where you stand. I hope it has helped you.
QUESTION: I don't understand what you mean by needing 10ºF TD for setting the SORITs? Unlike a standard EPR, these valves are externally piloted regulators which don't requires any pressure drop to operate.
04-25-2010, 11:09 AM #3
Thank you Icemister for the info! I understand how to determine total required btu's and then matching up the compressors for this but, what I do'nt get is- how you determine what your target suction header ott to be. What I meant on the 10 TD in relationship to the SORITS is If desired case temp. is 35 deg.f I would want to set my SORIT at 25 deg.f SST (64psig). If discharge air temp. is 10deg. difference from sst. then the suction header will have to be lower than the desired SORIT setting. Using the example above would you want your suction target set at +15 or 20 or 25? And if the suction is running to high with all compressor on and cases down to temp. would this be an indicator of undersized? Head pressure is normal. In a nut shell the problem I have is my suction header is too high not letting me set the SORITS. Target setpoint on controler is set at +15 (50psig)
04-25-2010, 11:32 AM #4
Now I see what you were thinking with the 10ºF TD thing.
That's a rule of thumb approach, which may be OK for a generalization of where you want to be, but not a good way of determining your actual system design SST.
Look at this Hill/Phoenix case data chart:
It lists all the info you need to know. Check out the case dicharge air vs the evap temp numbers and you'll see that for many of these cases the evap temp is in fact about 10ºF lower than the DA, but there are some which are as low as 4ºF difference.
Use this chart and then finding your target rack suction should be spot on for the system you have.
04-25-2010, 11:47 AM #5
1. You have sufficient capacity to satisfy the case load at that condition, but possibly not enough capacity to pull down to your rack setpoint...especially with all the SORITs wide open.
2. Your rack suction setting too low.
If the lowest required case evap temp is say, 22ºF...set the rack at 20ºF. The 2ºF difference allows for suction line pressure drop.
To set your SORITs, you sometimes have to shut down some circuits to get the rack suction below the required SORIT setpoint.
I'm sure some of the more modern and up-to-date rack guys will be along shortly to add to all of this. I've been out of the market loop for nearly 20 years.
04-25-2010, 11:48 AM #6Professional Member
- Join Date
- Apr 2010
How I miss the sorit days, electronic are all I run across now.
04-25-2010, 03:25 PM #7
04-25-2010, 04:51 PM #8
04-25-2010, 05:55 PM #9
Avatar & Pics
Thanks Icemeister, I read that under the help files and there is no edit avatar there in my settings. That link is missing and it said that the site manager might not have approved them yet. I figured it might be because I am new or they just have not had time yet. Also there is no link to download pics. I guess all in time, thank you for answering quickly and being so through.
04-25-2010, 06:23 PM #10
Welcome aboard nanotech. Lot's of great info to be had here.Get your post count up to 15 and apply for pro membership were theirs even more info and it'll get ya access to the EF.
04-25-2010, 06:40 PM #11
04-25-2010, 07:12 PM #12
Thanks for the welcome guys! Would anybody happen to know the web address for all the copeland models specifications? Years ago before Emerson bought them I used to have it but I can't seem to find them in Emerson's webb site.
04-25-2010, 09:07 PM #13