Walk in Cooler

[jakb21599]

Hello friends, need some advice on fixing a problem. I have a walk in cooler ( 35F setpoint with fans on while in air defrost) for a beef plant that the evaporators keep freezing up. The cooler size is 20x12x20 with 2 Bohn evaporators with original equipment still on it and coils are clean and all fans working. The model number for evaporators is BHA630CTA which is 63000 BTU. It was supposeldy sized correctly but I`m not positive about it. It has a 5 HP condensing unit outside Model number MOZ055M63C by HeatCraft. My problem is the coils keep freezing up and need some help on fixing the problem. They hang cow carcusses in this cooler directly off the kill floor. So the door is constantly opened all the time and stays loaded all the time. They will keep box temperature as long as they dont freeze up. So i am thinking the charge may not be right. I have installed air curtains and hanging flaps to try and minimize air being pulled in but it did not help much, they still freezing up. I have adjusted the air defrost timer several times trying to control it but it still freezes up about 2 times a week. I am defrosting both units and waiting for box temperature to get at setpoint (35F)
so i can check subcooling and superheat. what i am not sure about is this. The temperature outside is 42F so my head pressure is going to be low. It has 404A ***** in system. What do i need to raise my head pressure to by blocking off the condenser coil so that i can check SC and SH ? And what target am i looking for on SC and SH once i block off condenser coil ? Do i need to be concerned about suction pressure when box is satisfied going off temp and pressure chart for coil temperature ? also if the SC and SH is what ever yall tell me it should be. What are some other things to look for or other ideas to control the problem ? If you need more info i will get it for you. I will post what the SC and SH is when the box reaches temperature. but i am open for suggestions in the mean time. Thanks for your help

[Gary]

Raise the SCT to about 90-100F.

In addition to the SC and SH, measure the air temps entering and leaving the evaporator.

Low SCT can cause the coil to freeze up. You may need a fan control.

Does the evap have an EPR valve?

Does the defrost cycle terminate on coil temperature or time setting?

[charlie patt]

if the product is comeing straight from the cutting room the product is going to have very high humidity has this been always like..... this... or has production risen a lot latley

[jakb21599]

if the product is comeing straight from the cutting room the product is going to have very high humidity has this been always like..... this... or has production risen a lot latley

Has always been like this for about 3 years now. and it has always had the problem of freezing up

[charlie patt]

i would suggest if all settings ok fitting some defrost heaters as the humidity in this room will be very high check all your parameters first pressures superheat etc etc.check correct orifice then if all ok with that size comp i would fit df rods and install, most coils have the function to install.i would also think about fitting condensor fan speed control for more efficientcy,but i would advise heaters are required on a room with that product is the first job if all other parameters ok

[jakb21599]

Raise the SCT to about 90-100F.

In addition to the SC and SH, measure the air temps entering and leaving the evaporator.

Low SCT can cause the coil to freeze up. You may need a fan control.

Does the evap have an EPR valve?

Does the defrost cycle terminate on coil temperature or time setting?

I will get these numbers for you when it is at box temp. Currently with the box loaded and running the liquid line temp after reciever is 71F with low side around 60psi and high side around 160 on both units outside. The condensors have an LAC on them also, but the only way i can raise head pressure is block half the coil off. So you are saying get my liquid line temp up to around 90-100F before checking sc and sh once box is at temp? The evap does not have EPR valve. the defrost does not terminate. runs the entire hour 4 times a day with each condenser set at different times so they are not off at same time. I will get delta-t for you when they finish up and can get in their and let you know that also. Thanks

[tonyelian]

hi
you need a defrost heaters.air defrost is not enough unless you have too much extended time &number of defrost&thats is not good for the product.i prefer if you have a room to fit some heaters or switch to hot gaz defrost

[mikeref]

Sounds to me like the equipment is too small for the load. I do refrigeration work at one abattoir where one room can hold up to 80 head of beef off the killing floor. There is two by 23kw open drive systems for pull down on R22. Requirements are to get the meat to 2 deg.C. Ambient in Australia can exceed 35c. This may help for a comparison.. Mike

[jakb21599]

hi
you need a defrost heaters.air defrost is not enough unless you have too much extended time &number of defrost&thats is not good for the product.i prefer if you have a room to fit some heaters or switch to hot gaz defrost

I talked to the company that made these evaporate and they said they do not offer electric defrost for them and that it would not work any way. They probably full of s*** any way. What type of heater are you referring to that would work and how many would it take ?

[Gary]

http://www.heatcraftrpd.com/products...D-HAD-.5-6.pdf

[Gary]

The condensors have an LAC on them...

What is LAC?

[jakb21599]

What is LAC?

Low ambient control on the condenser. Sorry. Must have abbreviated wrong

[Gary]

Low ambient control on the condenser. Sorry. Must have abbreviated wrong

Would that be fan control?... flooded condenser?... air dampers?... something else? There are all sorts of low ambient controls.

[jakb21599]

Would that be fan control?... flooded condenser?... air dampers?... something else? There are all sorts of low ambient controls.

flooded condenser. Once the box reached temperature 35F i had 10 sc and 28 sh on one condenser and the other condenser was 10 sc and 34 sh. I blocked off half of the coil to get SCT to about 92F and then checked the sc and sh. I could not get the delta-t for the evap. i will get that this evening and post. If i read your Tech Method book right sc should be around 15 ? Also i think i seen in the book also with a long line set run the sh would be higher. is that true ? From condenser to evap is around 165 feet. with the current info. would this be a cause of continually freezing up ? What does my sc and sh need to be ?

[Gary]

Flooded condenser changes everything. Normally the SC is limited to 15F in order to avoid flooding the condenser. In this case, we want to flood the condenser in cold weather, so this system will need a lot more refrigerant. Enough extra to completely fill the condenser.

[jakb21599]

Flooded condenser changes everything. Normally the SC is limited to 15F in order to avoid flooding the condenser. In this case, we want to flood the condenser in cold weather, so this system will need a lot more refrigerant. Enough extra to completely fill the condenser.

What Target sc and sh am I looking at getting ? And do I still need to block off condenser to get 90-100 F sct

[Magoo]

Rapid chill times for quartered beef carcases straight from slaughter floor are critical. The deep butt temperatures need to be acheived quickly to set the meet and stop bacteria.
Evaporator need to be sized for small/ low system delta t, so high air volumes required, they through water /condensate everywhere. Louvers are recommended.
So increase air flow, standard evaps will not do the job.

[mikeref]

Good call Magoo. If problem of freezing was there from the start, then this might not be a quick fix. How many head does the room hold on average?.. Mike.

[Gary]

What Target sc and sh am I looking at getting ? And do I still need to block off condenser to get 90-100 F sct

There is no SC limit for a flooded condenser system. Keep adding refrigerant until the condensing temperature is 90-100F without blocking off the condenser.

[jakb21599]

There is no SC limit for a flooded condenser system. Keep adding refrigerant until the condensing temperature is 90-100F without blocking off the condenser.

what effect will this have when the summer time heat comes if any ? Will it be over charged?

[jakb21599]

Good call Magoo. If problem of freezing was there from the start, then this might not be a quick fix. How many head does the room hold on average?.. Mike.

around 70 head. one of the evaporators is in direct line of the door when it is opened a 100 times a day. i know that this is one of the problems and air curtains and door flaps did not help.

[mikeref]

Did you make a mistake in original posting about 5HP condensing unit? Maybe 15 HP?.. Mike.

[Gary]

what effect will this have when the summer time heat comes if any ? Will it be over charged?

If the system is designed properly, being a flooded condenser system, it will have an oversized receiver to hold the excess refrigerant.

[jakb21599]

Did you make a mistake in original posting about 5HP condensing unit? Maybe 15 HP?.. Mike.

Their are 2 condenser. 5 HP each and 2 evap.

[tonyelian]

hi
can you provide room size product capacity.look like there is miss calculating heat load&heavy heat infiltration from opening door

[Pierre Felteau]

You need more capacity for the pull down time. According to ASHREA, you need to remove approximately 5 btus/pound, so 70 carcasses x 700 pounds x 5 btus = 245,000 BTUS/hr capacity for the first 4 hours after product enters the room. It may be less if the product is loaded over 8 hours. You need electric defrost because the room should be maintained at 32-33 deg.F maximun, and humidity level is very high during pull down period. Don't worry with door openings, this is not critical in this case, the biggest load is from the carcasses entering at 102 deg.F and nearly 100% surface humidity (in design calculations).

Also, you may loose efficiency because of the distance between evaps and units, more often with R404a, because of flash gaz in the liquid line. Install a sight glass near the evaporator to verify this aspect. If presence of flash gaz, install an heat exchanger.
Another system with electric or hot gaz defrost to increase the pull down capacity may be the solution.

The selection in your installation is not correct. The condensing units deliver 37,000 btus/hr at 25 deg. f succion temp, while the evaporators are rated at 63,000 btus at 10 deg.f TD.

[Magoo]

It would seem refrigeration capacity is undersized, based on 70 head of cattle either in half or quarters. they were walking around probably 30 minutes before going into chiller, so meat temp close to +30'C, washed down on the slaughter floor and steaming hot.

[mikeref]

Hi Magoo, i made noises back in post #8 that equipment was undersized, but thought o.p. had typed 5hp instead of 15 hp. 160,000 BTU/ Hr cooling is what the equipment delivers for max 80 head at abattoir here for that specific pulldown room. These beasts are killed and disected quickly then hung as halves overnight. Quality control has data loggers throughout the many interconnecting rooms( that have their own cooling plants), to ensure temperatures remain constant. Honestly, i can't see how two by 5HP can do this job for 70 head. Maybe origional equipment of OP's was meant for much smaller heat load. Evaporators are icing because they can't cycle on temperature.. Mike.