Crankcase heater "long period of shutdown" defined?

[PM93455]

All references to crankcase heater usage seem to use the following statement: "long period of shutdown"
Now I get the variables - i.e. ambient temperature, etc. that could complicate a simple definition of "long period" but, in a general sense and in a temperate climate region, how long would this long period be? A few hours? A few days? A few months???
As given, it's maddeningly vague.
Thx

[pecmsg]

Is this a class project?

[rundawg]

All references to crankcase heater usage seem to use the following statement: "long period of shutdown"

The way I read the vagueness is, if the unit is “OFF” longer than the time the Crankcase Heater (CCH) needs to be energized before start up, then that is the time you go by.

Example: Carrier states the CCH must be energized 24 hours before start up, so if the unit is “OFF” (CCH not powered) greater than 24 hours, 24 hours is the time you use for the “long periods of shutdown”.

The specs are different depending on the manufacturer. Some list an outdoor temp below which the CCH must be energized, some don’t. Some say it must be energized for 1 hour, some say 24 hours. Some have a temp. switch to turn the CCH on, some don’t.

Obviously, if you pick a temp of anything below 70ºf and an "OFF" time longer than 1 hour as your minimum, you should be safe in any application.

[PM93455]

Is this a class project?

No it's not (a class project)...

I'm the plant/facilities manager of a manufacturing concern, and my responsibilities encompass equipment maintenance and care (physical plant/production); this includes defining best practices for all Mech Equipment.

Air Handler equipment servicing our Clean Rooms (Environmentally Controlled Areas) are equipped with compressor crankcase heaters; during normal operation this equipment runs 24/7. There are instances however when same is turned off (de-energized) for longer periods of time. Short shutdowns are a result of PM duties (off for a couple of hours while condensor coil cleaning and protection take place, or when 1st/2nd stage filtration is inspected/replaced) while occasionally longer periods of shutdown are incurred. An example of this would be an ECA remodel project such as one recently done over the Christmas/New Years time-frame, when equipment was de-energized for approximately 2 weeks. (Note, we're located at the central coast of California, so during the lengthy shutdown we experienced outdoor ambient temps ranging from 29F at night to 65F during the day.)

Without clear guidance from me, my staff would assume that the AH equipment could be brought back on-line at finish of PM work or completion/recommissioning of the ECA post-project; as being simply one of the punch-list items: "Step XX: Restore power to AH XX"

They're not HVAC techs nor do I expect them to be. They wouldn't begin to think about the physics of refrigerant striation, etc. I need to be able to instruct them with specifics. i.e. "at completion of PM task, Restore power to AH XX" or "at (project completion) ECA recommissioning, set thermostat XX to OFF, restore power to AH XX and restore thermostat settings after XX hr delay."

This is the guidance I'm looking for...

[timebuilder]

Your best source is the manufacturer.

Bear in mind that many units are sold without a CHH at all.

In many applications, once a repair or a replacement is complete, there is no 24 hour period that precedes a return to service. Once you are done, it's showtime, and you may not be back at that site for months, literally. There is no provision for returning the following day to engage cooling.

In your case, you can be back the next day. If you want to use 24 hours in your situation, that would be more than acceptable.