Refrigeration Control for Greenhouse
 

We have a greenhouse with an evaporative cooler that is switched on
and off by a White-Rodgers 1609-101 (or 1609-105) temperature
controller. This is a hydraulic action controller (with a probe or
"bulb")that will close contacts on rise in temperature and open them
on fall. The controller handles a full load of 7 amps at 120 volts.
Our temperature controll needs are in the 60 to 90 F range, though the
controller extends well beyond this. Our problem is that the high
humidity in the greenhouse causes these mechanically-based controllers
to fail within a few years. We are wondering if any growers can
suggest an alternative controller with similar characteristics that
would be more suitable for a greenhouse environment? White-Rodgers
does not make any controllers of different design than the
1609-series.

Refrigeration Control for Greenhouse
 

kapecki wrote:

We have a greenhouse with an evaporative cooler that is switched on
and off by a White-Rodgers 1609-101 (or 1609-105) temperature
controller. This is a hydraulic action controller (with a probe or
"bulb")that will close contacts on rise in temperature and open them
on fall. The controller handles a full load of 7 amps at 120 volts.
Our temperature controll needs are in the 60 to 90 F range, though the
controller extends well beyond this. Our problem is that the high
humidity in the greenhouse causes these mechanically-based controllers
to fail within a few years. We are wondering if any growers can
suggest an alternative controller with similar characteristics that
would be more suitable for a greenhouse environment? White-Rodgers
does not make any controllers of different design than the
1609-series.



What you describe sounds like a thermostat. I have been using Dayton
thermostats in a couple of greenhouses for 10 years now without any
problems, although I don't use evaporative coolers. I don't have the
Dayton model number available at the moment, but the Griffin Greenhouse
(http://www.griffins.com/) part number is 24-2225 (single stage
thermostat). They have double-throw switches, so they can be used for
heating or cooling. The cost is on the order of $50 (last time I bought
one) and they're really easy to install. I also have a Dramm T42-SV
double stage thermostat, but it's only been in use for about a year.

If you're worried about failure, you might install them in parallel
pairs. There are two normal failure modes for a switch: open and closed.
If the thermostat fails closed, the fan stays on and the greenhouse is
kept cool, although you might waste some power. If the thermostat fails
open, the greenhouse is not cooled and the plants bake. A second
thermostat in parallel with the first (set a degree or two above the
first) will then take over and run the fans. An annual check on the
operation of the two thermostats can tell you if one has failed
(although there's probably a way to have one light a lamp to indicate
failure -- getting complicated here).