"dpb" wrote in message
news
On 04/30/2017 6:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:
...

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint,
when power comes back on the relay won't close to restore power to
AC if the temperature is below the turn-on setpoint.

...

It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing when the users leave. They are supposed to drain the
water
as well.

But sometime they don't set it, and sometimes they don't drain the
water system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to
the pump) and a electrically operated valve, but for b) I need a
switch that will cut power to the relay.
...

You're still going to have to have aux power to operate the valve
when power goes out for a) then.

Are these "other people" family or renters? Would seem a damages
clause would be appropriate in the rental agreement if the latter;
some personal responsibility in case of the former altho that seems
often the most lacking place to find same, unfortunately.

--

A normally open solenoid valve to drain the pipes and a vacuum breaker
outside faucet should do it.

Here's a valve that opens below 35F.
https://www.bradleycorp.com/safety/t...tection-valves
-jsw