Low Ambiant Operation for Small A/C

[Ray9363]

Need advice, I have a requirement to provide cooling to several small communications rooms where cooling is required year around. Our winter design db temp is 25 degrees. I received a proposal that included installing an evaporator defrost control on a 2.5 ton cooling only package unit. No information on how its to be incorporated into the system. How can this aid in the operation at low ambient temperatures? The unit uses R-410 refrigerant. I’m custom to head pressure controls being used for this but not evap. defrost controls. Any help would be appreciated.

 

[imok2]

sounds like all you need is a regular AC unit with head pressure contol

 

[DRWeig]

agree with imok2.

check the manufacturer of your packaged unit, there's alomst always an option cold-start kit and head pressure control system too.

Good on ya,

Goober Dave

 

[Ray9363]

Thanks for your responses.

The manufacturer has both options, head pressure control and evap defrost control listed for low ambient operations as shown below. Personally, I just cannot understand how the defrost control will help at low ambient temperatures.

Evaporator Defrost Control (Low Ambient Cooling) Kit
Head Pressure Control (Low Ambient Cool) (208/240v) Kit

 

[DRWeig]

Ray, the defrost control is just to keep the normal condensation on the evaporator from becoming a total frosted-up blockage to air flow when the ambient is significantly below freezing.

If the package unit is outdoors, there is potential for wet coil to freeze up in layers as the unit cycles on and off. You'll need to consider heat tracing the condensate drain and pan too.

Head pressure control is to make it run properly during cold ambient times.

Good on ya,

Goober Dave

 

[Ray9363]

Thanks Dave
I just responded to the proposal as follows,
"The manufacturer offers both head pressure and defrost control as a low ambient option. I would recommend the head pressure control over the other but it's up to the manufacturer to make it work. If they feel comfortable w/ this application and will stand behind it, then I'm good with it".
Thanks again for the help, Ray.

 

[DRWeig]

Ray,

Just remember that both the head pressure control and the defroster might be needed...

Depending on load conditions, your evaporator coil might or might not frost up during 25°F nights and low load conditions indoors with some humidity in the air.

Good on ya,

Goober Dave