I agree with the subcool claim but not superheat. He shouldnt even be looking at SH at 22Degrees.
You have to fight through some bad days to earn the best days of your life.
If he doesn't open it up he may never get there. Once the box pulls down he can bring it back. I would shoot for 5*
Originally Posted by thermofridge
Maybe someone taught you that Subcooling is what it is? Did you know Subcooling plays a huge roll in capacity. Ontop of that did you know you cannot achieve a solid column of liquid to the metering device without Subcooling? You should change your line to "Why aren't you using Subcooling in refrigeration?". Subcooling = Capacity / Superheat = Efficiency
Originally Posted by VTP99
You sound like a supermarket installer. You've taken 4° SH and slapped it on every freezer application. Do you know where the job is located? If the walkin is inside or outside of the facility? What the humidity is? If the door has a kill switch. Tuning lower SH = more refrigerant in the Evap = lowering subcooling/capacity = faster frosting = less surface area to transfer heat = impeeding air flow = iced coil = liquid refrigerant reaching the compressor.
He said he cleared the coil and couldn't go below 22F because of frosting. His suction saturation averages at -6/-5F. Superheat reading averages 9°-10°. It's obviouse that since he's trending at 22F, SH was the right thing to check. Subcooling let's him know if he has refrigerant/capacity. Choking the expansion valve will lower refrigerant metered into the Evap = raising Subcooling/capacity = less frosting at the coil = more surface air to transfer heat = unrestricted air flow through the coil. At 22F he shouldn't be reading a 10° SH. Should be more like 16°-26° SH. Once he reaches set point (which I'm guesstimating is 0F) his SH should be closer to 8°-12°. From there he should tune SH to Evap spec if available. After which he should then charge the system and bring his Subcooling up to 8°-12° if needed.
If the thought of just lowering SH to 4° is going to do the trick then why not just go all the way with 0°SH? Maybe you can explain how lowering SH and metering in more refrigerant on a coil that ices up at 22F with 10° SH will help?
Regardless of what he does
-Lowering SH risks compressor damage.
-Raising SH risks a higher temperature trend.
If it was my 4 point of contact on the line, you best believe I'd skip the risk of compressor damage first.
He stated that the coil would start to frost over and trend at 22F. If the walkin isn't dropping any lower than 22F why would checking SH be the wrong choice? If anything his "shouldn't" readings show there's a good amount of liquid refrigerant in the Evap.
Originally Posted by thermofridge
What would be your advise on the next step after finding out there's excessive frost on the coil and the walkin trends at 22F?
Did this really come up? Non-condensables take up space in the condenser, raise head / suction pressure, clog filter driers, cause restrictions at the expansion valve and help cause acid to form in the system. SH and SC readings also become unreliable.
Originally Posted by K_Neil
Restrictions can starve the Evap coil and you know the rest. Matter of fact you guys knew all along.
Originally Posted by R&J-R
Originally Posted by R&J-R
You might want to cool out a little.
What we're saying is true. I know all about subcooling and how it correlates to system capacity, BUT I don't use it to check to see if my walk-in freezers are charged properly. In fact, I don't measure it much at all.
See, once you add a receiver to the system, the subcooling ceases to be a proper charging metric. Adding more gas won't change it until you fill the entire receiver and stack additional charge in the condenser.
Since when was moisture a non-condensible?
That sounds good to me. The high box temperature points towards added freezing load. Water in the insulation from a breakdown thawing did it to me in the rookie days. It was homemade meat freezer with no vapor barrier in the attic and previous solution was to add insulation. When I crawled up there to see and reached into insulation I touched ice 1 armlength in. The owner said the insulation was twice that thick. (Wood shavings). Took 4 days of added shorter defrosts to refreeze the water in the insulation before the box temp. would drop.
Originally Posted by 1firebaugh
The water drain is ok?
Another question is, Where are you taking your subcooling and superheat readings at? The compressor/condenser on the roof? You need to try and take the superheat reading from the evaporator and not the compressor.
If the manufacturer data is not available, recommended superheat is as follows: high temp 10-12*F SH, medium temp 6-8*F SH, low temp 4-6*F SH.
You must make sure that you have at least 20*F SH 6 inches from the compressor at all times to prevent flood back.
jp......HELLLLP I don't know how long I can keep biting my tongue.
Originally Posted by jpsmith1cm
The absolute very last thing I would check in this problem is................................................ .................................................. .................................................. .............subcooling.
10* Superheat is a tad high, but not terribly....especially since its 20* in the box.
Also it's a freezer, frost on the coil is normal.......BUT
If you are starting with a 100% clear coil and it is frosting up enough to block airflow through the coil.
I would take a real good look at airflow. Are your fan blades the proper scoop and in the correct position?
Maybe your box has some seriously high moisture content in the air equaling excess frost formation. Do you have spots of air infiltration?
I'd also look into defrost, does the coil clear 100% during defrost. If not, why?
Going off of what phase loss said, just because all your fan blades are turning doesn't mean they are all operating. Also, is your condensate drain draining properly?
One thing that stands out here...at least to me...is while the system appears to be doing all it can do (except for some possible fine tuning), there seems to be an abnormally high latent load present.
As was mentioned earlier, saturated/frozen insulation in the panels, once thawed, will take a heck of a lot of time to refreeze.
It may be advisable to go for a core sample or two of the wall and ceiling insulation. I've found a few where the urethane foam would wring water out like a sponge. In my experience, the ceilings have been the worst.