walk in freezer refrigeration sizing?

here is my problem........
I have 2 different freezer contractors quoting me two different equipment sizes for the same walk in freezer box.
Here is the backstory:
Freezer will be 15x30x8 with floor. 4 inch urethane. 1 60x84 door. The box will need to maintain a storage temp. of -20F for ice cream. Product will enter @ -10F. (200 lbs/day) for the purpose of storage w/ low door traffic.
On to the mechanicals:
This will be a (2) Cond. unit / (2) Evap setup. (separate systems) Both contactors quoted with 5HP Low temp scroll cond. units (Russell # ML0500L44) that are rated at 13200 BTUH @ -30F Suction temp. @ 95F ambient for a total of 26400 BTUH.
The evaporater selection is where it gets tricky! one Co. choose the (Russell # AE46-164B)4 fan / elec. defrost rated @ 15000 BTUH capacity @10 Degree T.D. at a -30 Evap temp. total capacity = 30,000 BTUH (2 evaps) The 2nd Co. chose the russell # AE36-140B which is rated @ 13,300 for a total of 26,600 BTUH at the same specs.

Summary: System 1 Cond. units 26,400
System 1 Evaps. 30,000
=8.8 T.D.

System 2 Cond. Units 26,400
System 2 Evaps. 26,600
=9.9 T.D.

System 1 quote argues that 8.8 T.D. is acceptable with short pipe runs etc. for a freezer.

System 2 quote says that 9.9 T.D. system is more efficient and is better matched. Also that I cant squeeze the extra capacity out of the evaps. if the condensing units cant provide it!

O.K. which is the better designed system?? What are the pros and cons to each, or is it a matter of right and wrong.
I am in Western WA state where the average daily temp is 50F. these are outdoor units.(Box and Cond. units.)
If anyone has the ability to run box load calculations on this set-up please do as I wish to know if they are even sized right for my application.

Thank you for any and all feedback!

When sizing a walk in you must first size and select the evaporator to handle heat absorbed from product,transmission of heat from outside refrigerated space,air infiltration through door use and other misc loads such as lighting,machinery in room,req'd air changes and people working in room.
I haven't done a load calc on your setup but if the room needs 30,000 Btu then it needs 30,000 Btu ! Putting in req'd evaps and shortchanging the cond. units is stupid. Your system will suffer in the hotter ambients, mind you it may run fine the rest of the year but what's the point if it dies on the hottest day of summer and its fully loaded - if it can happen it will happen!
Quote two appears to be a more evenly matched system providing it has the req'd evap capacity. In my experience I have found it better to slightly oversize cond. unit. The result is you usually have to cycle or speed control one condensor fan to balance system during low ambients but customer ends up with a system that works 365 days per year. If evap load is 30,000 Btu personally I'd like to see condensing units rated at approx 31,000 to 34,000 Btu at max ambient for your area, this also allows for dirt that WILL collect on evaporator and condenser surfaces and other wear.

750 valve, The box load calculations on this box, factoring in all variables comes to 26,000 figuring 18 hour run-time in 95 F ambient.

I am leaning toward the larger evap with the 8.8 TD (sytem 1) as I have been told to go with the smaller T.D. in freezers.
(7.5 to 10 TD )

any thoughts??

What TD are you referring to? Why should the TD be between 7.5 & 10? Is this a long term storage room? What product are you storing? What refrigerant are we talking about? We usually use 6K (that's 6 kelvin or 6 degrees celcius) evap design TD (that's air on compared to saturated suction temp) as a rule of thumb for general storage frozen food rooms.

refrigerant is R404, the "TD" is the temperature difference between the room air and the Suction temp in F.

...........and this is storage for ice cream. (i was told by an engineer that freezers 7-10F TD, and coolers 10-15F TD) to calculate TD at a given temp/ambient: divide Cond units capacity by the evaps capacity in BTUH. Note i ran a couple of load situation on my freezer and it will require about 25,000 BTUH so looks like system 1 is best suited for my situation??

I'm sorry but I don't understand what you mean by dividing cond. units capacity by evap capacity to get the evap TD. Sorry for all info in metric but I'm not familiar with Imperial (only pipe size and pressure). My understanding of selecting equip for a specific TD is as follows. Required avg. room temp (-20 deg C), if we wish to design a system to 6K TD we would select our evap on a saturated suction temp of -26 deg C. If we were to select on a 4K TD it would be -24 SST. Lets say we select an evap at -26 SST and its capacity is 8000 watts (just an example), we then begin our comp or unit selection. We want a unit that has equal to evap capacity at -26 deg C SST and at maximum possible condensing temp under summer ambients, lets say 50 deg C (always pays to know unit manufacturer's condenser design TD - it's usually on the selection/rating chart). Here is where we appear to differ in opinion, I would try to match the two capacities as close as possible but would never end up with a unit with less capacity than the evap. Let's say it was a choice between a unit with 7800 watts capacity at -26CSST/50C SCT and a unit with 8300 watts at -26CSST/50C SCT I would definitely go for the latter.
In conclusion I think quote two appears to be the better quote. More closely matched but I'd still prefer the values the other way around, don't forget this system will have to recover from defrost three to four times per day, you don't want it to run for three hours pulling down off defrost.

750 -- I just read your summary and agree with you. Evap first then unit to match ( always larger ) . Learnt that from a clever **** in Adelaide SA. Also 750 I have just realized your picture has a double meaning saw another recently called Hilters son .

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Dear Trammd,

I saw your load and the details provided by you. We are doing projects for Ice Cream Hardening and Storage, and I shall be too happy to provide you with the full details load analses within a couple of days as at present am outside my office on business( in connection with projects for Ice Cream ) and shall return to my office on 6th Sept.

In case you want me to give the full details with equipment selection, please do mail me and let me know.

i guess we could ask how the system is going now which system you went with and how is it going now? LOL!