Would this setup work?

Paul S_3

I know there is a few commercial refrigeration techs that hang around here, I'm looking for some answers on this type of setup. I do not work on a whole lot of commercial refrigeration I have learned a lot these past couple of years from **** Wirz 's book , manufactures, Hvactalk.com etc, and I have learned that refrigeration is a lot different than air conditioning and a lot less forgiving. I have a friend who owns numerous grocery stores throughout the NYC area I service all of his refrig equipment. He is in the process of opening another store and I have been hired to install equipment. I have done installations for him in the past with no problems, all of the equipment was 1 condenser with one evaporator. I posted a pic below of the setup I was suggesting. I have seen multiple refrigeration equipment installed with 1 condensing unit and multiple evaporators. I myself have never done the an install. The equipment he has there is
(1) 6 door cooler
-(2) evaporators
(1) 8 door cooler
-(2) evaporators
Each evaporator has its own TXV, each cooler will be operated by its own temperature control, liquid line solenoid and will be on a pumpdown cycle. The product in these coolers will be drinks soda, milk ,juice ETC. kept around 35F.
My concerns are the piping for proper oil return should I trap the main suction line? individual traps for each cooler(total of 2)? or trap each individual evaporator (total of 4)? I know the trap should be at the lowest point its not in the drawing....Another concern is the liquid receiver in the condensing unit it seems pretty small, If you guys need the size I can get it. If one cooler is satisfied where would all that refrigerant go?This system will NOT have a head master control for low ambient operation, it will have a fan cycling control to maintain 95F condensing temp. Refrigerant will be R404A. I'm trying to do this right and maximize compressor life. Am I on the right track ?

Paul S_3

Setup

jumper

How effective is separator? Ladder,ladder,ladder.I always worry that with rooftop condensing units oil will eventually end up in evaps .Prefer basement compressor.

Paul S_3

Oil seperator? Install one?

GreenGene

If the compressor is above either the evap or condenser the oil will end up there. Consult Manufacturer for their proper piping but you're talking traps and an oil separator.

....and fan cycling is junk, ICM makes good head pressure controllers, fan cycling makes your pressures crazy and kills the motor from too many starts and short cycles.

JUGHNE

In my limited commercial refrigeration work over 30+ years, I work on mostly of old stuff, from 5 to 40 years old. The units without the Head Master pressure controls have had the most problems. None of those old controls have failed. But without them there have been problems with fan cycling controls themselves and short cycling motor running. Variable speed controls can fail unnoticed by owner.
Probably not in your case, but fan cycling will limit air flow over compressor if needed.

But here in NE, the wind can overpower everything except a flooded cond coil.

Just less things to worry about in the future, for you and owner.

Paul S_3

I'm sorry this unit has a head master....would the added evaporators cause an issue with the standard receiver in the unit? and I should still install an oil separator on a med temp application even with the correct p traps in place?

RJ_4

You might consider a multizone system like Coldzone if you haven't already selected the equip. I found this type of system was the way to go for multiple walk-ins and under counter refrig. In the old school systems we would also figure in evaporator pressue regulators (EPR ) for the evap coils. The multizone systems sometimes would use multiple compressors pumping into a common condenser and extra large receiver with a headmaster valve. Each evap coil would draw off this receiver when refrig is needed. There were several options for the suction line piping but i don't remember the exact details

Paul S_3

that would be like a small compressor rack....with EPR valves on the med temp evaporators to keep pressure up when a system is mixed with med and low temp evaporators...customer did purchase equipment already though....he has a even larger store he will be starting construction in 2017 I was looking into something like that....

njtommy

I always install traps. Any time the suction line goes up I install traps at the bottom of the riser and then At the top I install inverted traps. Also on your riser you need a trap every 10' of vertical rise.

Paul S_3

@njtommy rise is about 18 feet to condensing unit...I should install one trap at base of suction riser then one about a few feet from roof penetration?( a total of 2 traps).... about the inverted trap at the roof I thought that was only for the discharge line from compressor to the remote condensers on roof with the compressor below it to prevent liquid refrigerant falling back to compressor....with my current setup and a pump down I eliminate all migration issues, am I correct?

njtommy

Inverted trap on the suction will keep the oil from falling back down. Pump down will stop migration and hopefully flooded start ups. I like having acumulators if at all possible to. They help with liquid slugging back.

njtommy

@RJ I've worked on a few of the cold zones that you are talking about. They are pretty nice units. Makes life a bit easier.

Paul S_3

accumulator on a low temp I always see....as a extra protection I should install one on this med temp system? what is the manufacture of the coldzones ?

njtommy

They are really inexpensive to install. Never a bad idea.

Coldzone is the manufacturer. I believe they are the same as Russell as well.

Paul S_3

@njtommy do you see an issue with the current setup in the drawing....im just worried about all the extra refrigerant when one case satisfies...can the head pressure rise if the receiver is undersized? and how would I know its correctly sized?

njtommy

Looking at the drawing I wouldn't install it that way. I would do 2 compressors. 1 for each box I'm thinking you will have capacity control problems when the 1 side is running.

From what I have seen and worked any time you run multiple Evaps off 1 compressor all the LLSV are energized at the same time.

Paul S_3

i was thinking the same thing but customer has a similar setup with 2 walk in freezers on one condensing unit and a deli case with a 3 door cooler on another condenser at a different location...these units have never had compressor issues....its a hard sell to him he is dead set on one condensing unit

njtommy

I would just confirm the design then from the manufacturer and local rep.

Paul S_3

thanks @njtommy

jumper

Ladder,ladder,ladder. Then it will take more time before compressor goes dry. Rooftop compressors are crimes.

Techman

I see compressor changes in you future.

Paul S_3

Explain @Techman

unclejohn

I also would use two condensing units. At some point that 1.5 hp comp. is gonna be running to cool the smaller box only. You will need a separate suction line run at say maybe 3/4 to handle oil return when that happens.

Techman

Hi ASM, I think that I am seeing the common suction riser as being too large when just one case is running,with resulting oil related problems.

aircooled81

Vertical Gas lines should have 1000fpm velocity for oil return. If the line is sized for 1000fpm, you shouldn't need traps other than top and bottom.
You will need to consider the lowest load, like the only the smallest single evap running. Can your compressor unload to the capacity of that txv? Can your suction line maintain the required velocity to return the oil at that low load, in a large pipe.
When the line is too large, you loose velocity at the lower loads and may require a double riser, trap and tee, so when the oil fills the trap suction gas enters the smaller line. Problem with this is when the equipment loads up you can send a slug of oil back to the compressor. That's where the acumulator can save an oil slug.
Manufacture can tell you what the total volume that receiver can hold. Total liquid line length and evap volume will give you an idea of your total refrigerent volume. The liquid charge is typically determined by finding the total lenght of the condenser tubing in feet, and multiplying by pounds of refrigerant per foot for the given tubing size. You will 'fill' the condenser to the lowest ambinet condition forseen.
I beleive the liquid lines will hold their charge wile not in use, imo thats just where the extra liquid storage will be in its associated off cycle.
Remember 2 to 3% of your total liquid line charge should be oil. If you add a large volume of refrigerent, make sure you account for additional oil if needed.
Pump down is great, keeps the refrig from condensing and migrating.
You will want to trap the leaving side of each evap, so when it's off refrigerant and oil wont migrate in while others are running. Put your txv bulb before the trap (between leaving evap and trap). If you are using external equalizers on the txv's, make sure they go before the trap too.

Let me know if you want me to dig up a pipe sizing chart, and line capacity.

Paul S_3

@aircooled81 can you dig up a chart for pipe sizing ....i would really appreciate it thank you

aircooled81

Check out this one by daiken, quick read, not too bad for big stuff. Doesn't cover line sizes below 1/2"
http://lit.daikinapplied.com/bizlit/DocumentStorage/AirCooledChiller/ApplicationGuides/AG_31-011_120407_1.pdf

If you really have patience, and want to fine tooth comb this, check out chapter 11, 11.4 starts out on pipe sizing.
http://www.gmpua.com/CleanRoom/HVAC/Cooling/Handbook of Air Conditioning and Refrigeration.pdf

pecmsg

Paul S said:

@aircooled81 can you dig up a chart for pipe sizing ....i would really appreciate it thank you

Paul S_3

Thanks guys

aircooled81

just a thought here btw. If you draw up your design, just like your pic. List the components, line sizes, cabinet design temp, I'll bet the manufacture or distribution rep will give it a once over. Those engineers over there love a good chance to show-off and let you know if you missed anything.
I had the heatcraft rep help me out with an evap one time, sizing was close but equipment was way off on pressures. He looked over everything and made a change regarding the orifice size in my distributor. I went to the supply house, they let me yank one out of another unit, put it in that night. That saved an unneeded txv replacement, and worked like a charm.

They want to support their installers, so their equipment runs like a swiss clock.

aircooled81

Paul S , howd the project turn out?

Paul S_3

@aircooled81 ....I went with individual condensing units. I called Hussman direct and they gave me the btus for each glass door somewhere around 1500 btus each....im using a 3/4 hp for the 6 door and a 1hp for 8door cooler..... I replaced all txvs from danfoss to sporlans(customer purchase used reach ins) I'm installing traps at each evaporator and traps half way up to roof penetration..... I see a lot of systems with multiple evaporators with different temp controls with no compressor capacity control....that's why I drew the picture like that....I guess its wrong....project is still going on...