Friedrich sl28m30 conversion to DIY glycol chiller

[Red Pill Green]

Not sure if any HVAC people haunt this board, but... I'm considering a conversion of a used Friedrich sl28m30 unit (28,000 BTU thru-wall AC 230V) into a DIY glycol chiller. The application would be for helping to keep a (very small) backyard skating rink frozen in marginal winter weather. Based on my rink size, a ~2ton chiller would be sufficient to handle it all on its own, so I figure even with the big efficiency loss of running the unit at very low temp (~14F), I should be able to get ~1ton of cooling out of it - to supplement the freezing ambient air at night and help the ice stay frozen in the daytime.

You may have seen similar builds floating around, but the basic idea is to:

• immerse the evap coil in a glycol bath (either fold it over without damaging the plumbing, or possibly build the reservoir around it)
• override the controls to use an external thermal controller to get the desired temp (~14F)

The unit uses R410A so I believe I should be able to get the evap coil down to this low temperature without major issues, besides reduced efficiency. It does have an accumulator so I hopefully won't wreck the compressor right away if I go too cold. I have a copy of the service manual with wiring diagrams, everything looks fairly straightfoward. This is a cool-only unit so no reversing valve or heater elements to worry about. I know to the discharge the capacitor and not to lick live wires. :grin2:

If anyone has any advice, or some experience with tearing into the Kuhl units and anything to watch out for, would really appreciate it - thanks in advance!

 

[Red Pill Green]

Update - it works! AMA.

 

[Cool Modine]

Sweet!

 

[AmigaPhreak]

What modifications (if any) did you have to make to get it to work at such a low temperature?

Just thinking about it, the only limit to low temp operations is usually having the evap coil freeze up, but by keeping it in glycol, you avoid that problem.

Assuming that part is straight-forward, I'd just like to know about the implementation of it. How did you build the enclosure, how did you over-ride the controls, any special challenges with respect to glycol circulation, etc?

I assumed you borrowed alot of knowledge from 'in floor heating" kinds of applications. Foam board to insulate from the ground, coil spacing and material, pump requirements, etc.