Temperature control

[Matt]

I have one freezer with redundant condensing units. As is, each unit is controlled by it's own thermostat.Naturally one sys. becomes the lead and the other the lag. Is there an easy way to equalize run times between each unit?

[Brian_UK]

Is there an easy way to equalize run times between each unit?

Matt are you looking for a 'cheap' method or an all singing and dancing 'expensive' system ?

[Matt]

I'm sure the customer would say a cheap method.They have that reputation!I prefer something reliable, whatever the cost.I can give them a proposal for both senarios.

[Brian_UK]

Matt, what we have done in the past is construct a lead/lag changeover control which can be either a simple hand switch, (1 or 2), or you could perhaps integrate a timeswitch changeover.

Thinking back, I seem to remember someone creating an auto changeover switch which activated everytime (or every several) the thermostat called.

[shogun7]

Matt try these people
http://www.macromatic.com/literature.../pdf/arp-3.pdf
Roger

[chemi-cool]

hi matt,

its simple to make a control system that based on simple, relable, weekly timers,

how many condensing units do you have?
let me know and I will make you a diagram.

chemi

[Gary]

I recall seeing auto changeover switches on dual air compressors. Each time a compressor is needed it changes over.

[Matt]

I have two cond.units per freezer.
Atotal of two freezers!

[Peter_1]

Why not using a simple Logo of Siemens?
This is a (very) low cost PLC, easy to program.
Did it many times in the past and is in py opinion the cheapest solution.
The logo will count the hours the real compressor running hours and they will switch at the moments you programmed them.

We used it to reverse the condensor fans to remove leafs of trees from the underside of condensors. (Sort of autocleaning)

Have a look at http://www.ad.siemens.de/logo/index_76.htm and you even can download a demo software to play a little bit around.

Crouzet introduced some weeks ago a comparable product but with tge possibility of analog in/out (0-10 V or 4-20 mA), mobilephone alert modules, fax modules, wireless links.... an amazing piece of electronic.