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01-11-2013, 05:39 PM #1Professional Member
- Join Date
- Jul 2011
- Lehigh Valley, PA
Old pizza upright options for refurbish
I want to refurbish an old McCall pizza retarder originally designed for R12. I work on more than a few of these old units. Theses units are constantly under heavy usage and the existing refer units just barely keep up in summer. Pizza Retarders are simply large upright reach in coolers, tall & wide enough for a large cart holding pizza doughs.
These units need be between 34F-39F. The door is opened often and the unit is usually near the ovens.
The units have all been converted to R409A, a few to R414A hotshot using Tecumseh 1/3hp skids, AEA4440AXA R12 compressors and Sporlan 1/4 ton R12/R134 TXV's. Some have been converted to a thermostat. Original equipment I believe used pressure control for temp control. I prefer the pressure control myself. I can dial these in between 16-34psi with R409 for suitable temp control. The TXV's are original equipment. Nobody has changed, no reason to. The evaporator sits about waist high on the inside wall, the condensing unit on top or the unit.
Moving forward, I want to beef up these units for no nonsense service in a hot kitchen with normal PM maintenance, In other words, I want to avoid the above 40F calls. The 1/3hp compressors work nice when new but grow weak with 2yrs or so and suffer in summer.
Can I move toward an 1/2hp skid? If I move to a 1/2hp skid, will this cause issues with an undersized evaporator? What if I convert to R134 along with a 1/2hp. The charts show slightly higher btu's with the R134 vs R12 skid in the UR catalog. Can 404A be considered with the old McCall retarder with the correct TXV? I don't understand how evaporator sizing comes into play with the different compressors & refrigerants.
01-11-2013, 08:21 PM #2
Seems like you would need to do new evap with more rows and also move more air. But, i don't know!!!
01-11-2013, 09:20 PM #3Professional Member
- Join Date
- Jun 2009
- Garland, TX
By increasing the condensing unit only, you will lower the evaporator temperature (lower suction pressure) which will increase the TD on the evaporator, which will increase the BTU rating of the existing evaporator. So, you do not necessarily have to also replace the evaporator.
However, if the evaporator's are deteriorated, it would be smarter to replace the whole system, maybe a 1/2hp med temp r404a like a copeland FJAF-A050 or something similar, that's a nice condensing unit. Size a similar BTU evaporator as the condensing unit, and let that baby rock and roll.
In a worst case scenario, (if the condensing unit is grossly oversized for the evaporator,) it may short cycle because it does not have enough of a load. But probably won't happen just going from 1/3 to 1/2hp.
01-11-2013, 11:53 PM #4Professional Member*
- Join Date
- Nov 2009
- Richmond, working under tarps
You need to resize the units, ie do a load calculation.
what HP you need is up to what load you have.
01-12-2013, 08:46 AM #5
Done a few of these also. Stick with 1/3 hp and 404a, use ranco constant cut-in stats to maintain proper temps with auto defrost. Used to use r-22 but now 404a should be fine. If you go with 1/2 hp for extra capacity the stat will work better than pressure control and protect the compressor from short cycling.
01-12-2013, 11:33 AM #6
Generally speaking, the evaporator really doesn't care what refrigerant is running through it. Its prime concerns are entering air temperature, the saturated temperature of the refrigerant and the airflow.
We'll assume the airflow to be fixed...and hopefully close to design. Then it's a matter of determining its capacity. If you're dealing with a standard, off-the-shelf commercial evaporator like those for a walk-in box or the smaller ones designed for reach-ins, you'll be able to find its capacity from the manufacturer's published performance data. That data typically includes the evap's Btuh capacity at a 10ºF TD, where the TD is the design box temperature minus the design evaporator temperature.
In this case, the evaporator is OEM specific and as such won't typically have any published performance info available. This is when I do a bit of reverse engineering.
You stated the existing unit has an AEA4440AXA compressor and it satisfies the box well on R409A with a pressure control setting of 16# CO and 34# CI. Looking at the CO, that's 17ºF with R409A. Since the CO is usually a little lower than what would be considered the design evap temp, let's say the design evap temp for this evap is 20ºF when the box is at 35ºF. From this we then know that the design TD of this evap is about 15ºF (35ºF-20ºF).
Now, if we look at the compressor's performance data, we find that its capacity at 20F Evap and 90ºF ambient is 2540 Btuh. That say the evap's capacity at its design TD is also 2540 Btuh. If we take that capacity and divide it by the evap's TD we'll get the evap's specific capacity, which is 2540/15 = 169 BTUH/ºF TD.
Since you want to get a unit with a little more capacity, let's look at an AEA4448YXA, which is Tecumseh's 1/3+ HP unit. It has a capacity of 2770 Btuh at a 20ºF evap temperature. If you divide that by the your evap's specific capacity and the new TD would be 16.4ºF, but now since the evap temp is 1.4ºF lower than before. Looking at the compressor charts again (and doing a little extrapolation) you'll find the compressor has lost about 81 Btuh due to the lower evap temp for a new capacity of 2689 Btuh and a new TD of about 16ºF. This results in about a 6% capacity increase over the original.
If you did the same exercise for a 1/2 HP, a Copeland M2FH-0049 R134A unit would give you about a 15% increase and the TD would be around 17-18ºF. I've done this much of a jump in size with pizza preps remoting the condensing units and it works quite well.
01-13-2013, 03:00 PM #7Professional Member
- Join Date
- Jul 2011
- Lehigh Valley, PA
Hey, thanks for the tutorial. I enjoy learning theory. (In fact, I read all of your posts in this area)
I like the idea of converting to R134 where I can. What is your take on using R404 on this style unit? I have never seen a R404 unit using pressure control. Could it work? Looking the the P/T chart, we'd be CI@82 #, CO@51 #. I'm not sure if a R404 commercial temp TXV would feed at 80# on CI? All of the newer R404 equipment is set up with pump down circuits & electronic controllers using the Ranco ETC-111. There must be an engineering explanation for this. Do you know?
What manufacturer prep table did you increase the condensing unit? Was it a 10'? I see a lot of the Traulsen 10' units using the 3/4 Copeland skids running R404. They are always stationed next to the rertarders! Same abuse. Lids open all day! The two biggest issues other than summer heat, food clogging the evaporator drains causing water leaks underneath & greasy condensers.
01-13-2013, 05:27 PM #8
There's nothing wrong with using R404A for this application as long as all else in properly sized and set up. I see no reason why it would work with a pressure control either. It has a smaller glide than R401A or R409A and those seem to do OK with pressure controls.
Also, there's no reason why a proper R404A TXV wouldn't work. Are you maybe thinking there's some kind of MOP feature in there?
In your case I would probably stick with R134A only because of the existing TXV (and possibly your pressure controls). The selection of R134A units is a little better than the R404A models too.
I've done a few True TPP-93's and a couple of other 8 foot pizza preps...usually with R134A, but either works well. It depends on the job and the customer's budget.