Walk-in freezer questions?

Status
Not open for further replies.
S

sw_ross

Senior Member
Location
NoDak
Just looked at a job where a school is getting a walk-in freezer.
I've only hooked up one before, and it's been a few years so I just wanted to throw out a few questions...

This freezer isn't assembled yet so I was only able to look at the components on pallets on the ground.

The condenser unit (mounting on top of freezer) is 208v 3-phase. Min ckt amps is 16.1, max breaker is 20amps.

The inside unit cooler is 208-230v 1phase. Nameplate shows an MCA 1.1 and a MOPD OF 20.
This nameplate also shows the "(Defrost) Heater Circuit", 230volts, 1phase, 7.8 amps, 1800 watts.

I'm assuming I need to run 2 circuits, a 3-phase 20 amp circuit for the condensing unit (3-pole disconnect on top of unit by condenser), and a 1-phase 20 amp circuit for the inside unit cooler?
Also, locating the disconnect for the inside unit cooler- is it common to mount that disconnect inside the unit adjacent to the cooler? I seem to remember using a 20 amp 2-pole toggle switch for this previously?

I'm assuming the 2 units talk to each other with low-voltage wiring? Guess I'll have to check with the HVAC company and see who's responsible for that...

Anything else I should be aware of?

Thanks!
 
You could run a single 30-amp three-phase circuit to a subpanel with two breakers in it, a three-pole 20-amp and a two-pole 15-amp, which would serve as the local disconnect.

You might need to install heat tape on the condensate drain pipe to prevent it from freezing up.

Penetrations may need to be sealed and/or insulated to prevent water & ice intrusion.
 
Over the years I've seen a half-dozen different wiring diagrams so you really need to check your units manual.
Most of the freezers I have encountered have one circuit that supplies the condenser, fan motors and heaters all controlled through the defrost timer and a 2nd circuit for door heater, light & receptacle for the heat tape mentioned above.
 
augie47 said:
Over the years I've seen a half-dozen different wiring diagrams so you really need to check your units manual.
Most of the freezers I have encountered have one circuit that supplies the condenser, fan motors and heaters all controlled through the defrost timer and a 2nd circuit for door heater, light & receptacle for the heat tape mentioned above.
Click to expand...

I agree, the more I look at the nameplates and wiring diagrams for the individual components the more I see I need to have access to an overall installation instructions to see how the overall system is designed to work.
 
Auxillary contact in condensing unit ?

Auxillary contact in condensing unit ?

Is it common to have a contactor, or an auxillery contact, in the control wiring box for the condensing unit that can/will operate the evaporator ?
 
System Wiring Diagram

System Wiring Diagram

Electric defrost systems typically take one service and the FCU slaves off the CU because the control legs pass through the defrost timer circuit on light commercial systems.
The typical way its done if for the HVAC outfit to let you know how many wires and what color to put in what conduit and they land them and run the startup as far as control wiring goes.
This reduces confusion. Its important to know and understand the exact sequence of operation that the design runs by.
The outfits I used to work for, we ran all our own electrical to eliminate and avoid mistakes, components getting fried due to misinterpretation etc.
Because Refrigeration guys work on this kind of thing daily, they generally understand the details better. This is not saying that a savvy electrician cannot wire the system perfectly, but the installs are supposed to involve Refrigeration Expertise to avoid common pitfalls of what could be considered a substandard install, both with respect to electrical, mechanical, and plumbing. Walkin Freezers are especially prone to unique problems of moisture incursio if they are " thrown " together. This includes astute sealing of all penetrations and also conduit runs past the conditioned space boundry. Otherwise water will find its way in and turn into ice and cause myriad problems.
This part is more art than science.
 
sw_ross said:
Is it common to have a contactor, or an auxillery contact, in the control wiring box for the condensing unit that can/will operate the evaporator ?
Click to expand...

LarryFine said:
In most walk-ins I'm familiar with, the fans run constantly, so no.
Click to expand...
That is what I usually see, but they usually are run through the defrost timer and fan circuit is opened when in defrost.

Temp control is usually operating a solenoid valve and compressor unit shuts down when that valve closes and refrigerant pressure builds up in the line, call for cooling by thermostat opens the valve and compressor starts again when pressure drops.

Then there is electric element defrost vs hot gas through the coil for defrosting methods. There is usually some control conductors between the two for defrost control, particularly for defrost termination - why continue to put heat in the cooler when the coil reaches a high enough temp that the frost should be gone is the logic here?
 
drcampbell said:
Correction:
Disregard what I said about a 30-amp circuit. A 20-amp circuit suffices because the compressor and the defrost heater never run at the same time.
Click to expand...
Correct - a 20 amp circuit for all - no need for feeder and separate branch circuits, still possibly need additional disconnecting means within sight of said components though.
 
Comment on my interpretation...

Comment on my interpretation...

kwired said:
Correct - a 20 amp circuit for all - no need for feeder and separate branch circuits, still possibly need additional disconnecting means within sight of said components though.
Click to expand...

Here's my take on the setup, maybe I'm a little confused, please correct me if I'm totally off base!;

-The condensing unit on top of freezer is 3phase and needs a 20 amp circuit, with a 3-pole disco near the unit....

-Then, the inside fan coolers/defrost elements are 1phase and need a separate 20 amp circuit and a disco near the unit...

-Then, (usually) a defrost time clock will get mounted (maybe on top of freezer?) and there will be interconnecting wires that go to the typical "N, X, 3, 4, " terminals...

Generally I understand how the defrost time clock shuts off power to the cooler fans and send power to the heating elements.

?The only interaction between the condensing unit on top and the inside fan unit is based on pressure in the refrigerant lines? Not any electrical interaction?

Thanks for any input!
 
There are a few different ways. Heatcraft has some good downloads.

Typically the condensing unit is separate and the only communication is through refrigerant pressure. The thermostat controls a liquid line thermostat.

When thermostat is satisfied liquid line solenoid is de energized. Compressor sucks low side return line down near zero PSI and pressure switch drops out compressor relay. When thermostat calls for cooling, liquid line solenoid opens, pressure on return line builds up closing pressure switch contacts, compressor relay pulls in, and compressor starts.

Defrost time clock powers evaporator fans and thermostat output to liquid line solenoid through normally closed contact. When defrost is called for, liquid line solenoid is de energized, which drops out compressor through pressure switch, evaporator fans are de energized, normally open contact in time clocks closes and powers heating elements. There will be a sensing element on the evaporater coil that will terminate time clock cycle if coil gets warm enough.

As mentioned the HVAC guys will usually terminate wiring.
 
You need to look at the wiring diagram. The defrost clock could be inside the condensing unit. The fans, defrost heaters, and pump down solenoid would get power from the condensing unit through the clock. Guessing will not work.
 
sw_ross said:
Here's my take on the setup, maybe I'm a little confused, please correct me if I'm totally off base!;

-The condensing unit on top of freezer is 3phase and needs a 20 amp circuit, with a 3-pole disco near the unit....

-Then, the inside fan coolers/defrost elements are 1phase and need a separate 20 amp circuit and a disco near the unit...

-Then, (usually) a defrost time clock will get mounted (maybe on top of freezer?) and there will be interconnecting wires that go to the typical "N, X, 3, 4, " terminals...

Generally I understand how the defrost time clock shuts off power to the cooler fans and send power to the heating elements.

?The only interaction between the condensing unit on top and the inside fan unit is based on pressure in the refrigerant lines? Not any electrical interaction?

Thanks for any input!
Click to expand...
On smaller compressor units, that seems to be about what I have seen the most of - all on one circuit. Fans are generally continuous operation except during defrost, you want to keep the defrost heat at the coil instead of spreading it around in the cooler, plus defrost termination thermostats keep you from adding more heat then necessary after it is defrosted.

If it is larger compressor - more common on multi section display cooler units the compressor has it's own circuit. You may even have multiple solenoid valves to different cooler sections to regulate refrigerant flow. If all valves are closed then pressure shuts down the compressor. In such setup you can individually defrost sections, shut down the refrigerant valve then start your defrost process, while other sections continue to operate off same compressor. Most the time they defrost the entire system at same time, only need one defrost timer, but is possible to do a zone at a time. Defrost heaters are circuit capacity killers in those multi section display units - you often have multiple circuits to the display units because of it and door frame heaters also add up as well.
 
I have worked on a lot of these that have LV door-switch controls that shut down the evaps when you have the door open. Also have installed leak-detection modules inside of the units for the workers inside to hear an alarm before they suffocate (poisoned?) to death from a refrigerant leak. Both are integrated into the controls and connected to the refrigeration solenoids (both lines). They used to put the solenoids inside the case but nowadays are putting them on top.

As for disconnects, I install a bell box inside on the ceiling close to the unit with a nipple to the top with a good silicone bead around the penetration. I'll either use a switch with WP cover or a twistlock receptacle with a rubber boot over the plug, the switch being my preference. For lighting I use minnys as a strapping means to keep the emt out of contact with the wall as much as possible. Saves a little bit of time bending box offsets as well. I make sure to use duct seal or silicone down inside the conduit penetrating the case as that will keep the condensation from pooling up inside the disconnect(s).
 
Status
Not open for further replies.
Top