Smart/As needed evap defrost?

[dkemper]

All, Are there any "smart" defrost controls that can sense when a low temp evaporator needs to be defrosted?

It seems to me a air pressure differential system between the front and back of the coils could be used to trigger an as needed defrost cycle rather than simply using a regularly scheduled time clock.

In my case, the humidity loads on my evaporators can change significantly with production demands. If possible, I'd rather not pump heat into a freezer to defrost a unit if not needed.

Thanks!

[alpha]

Hi, sounds like your talking about defrost air switch maybe, it's something I come across quiet regular on transport fridges. The way I have seen it done is the air switch is usually located outside the load space with two 1/4inch rubber pipes running from the switch to the evap, each pipe is run to two plastic air funnels, one at air on and one at air off. When you get a plugged coil, the pressure differential switches the air switch putting the unit onto defrost. Defrost termination is taken care of by a temperature klixon mounted on the evap coil somewhere. You may have to put the evap fans on a timer to stop warm air being blown out when it comes off defrost or I guess you could use another temperature klixon to switch evap fans back on when evap temp is at a suitable temperature perhaps. I am sure a system could be devised with a little cunning if there is not one commercially available already.

[dkemper]

Alpha,

BINGO! Once I knew the name of it, was easy to find.

White Rogers makes an Air Switch rated down to -40 degrees, well within the temps my freezers are maintained at.

I'm sure there are others and along with a couple simple timers and relays, I can easily achieve an as-needed defrost.

I think the hardest part will be pulling some new wiring through the existing conduit to get control/sensor trigger from the evaporator to the controls.

From there it'll be a simple matter to adjust the differential switch to trigger correctly.

Many thanks!

[walden]

Kuba make a defrost on demand refrigeration controller. It needs special temperature sensors and a Kuba evaporator. Those who use it, say that it works.