Controlling vacation mode in weekend house with multi-zone hydronic heating

Just thought I’d share this as I couldn’t find a solution to this particular conundrum: we recently finished building a weekend home with hydronic floor heating, split into four zones, with a Honeywell Aquatrol boiler control. All I really want is to be able to remotely turn the heat off if I forgot to do it in person before I left, and turn the heat on when I know I’ll go there so the house isn’t freezing when I arrive. The contractor was saying that yes this could be controlled via internet through Honeywell’s RedLink and that’s what I use at home, so I trusted that. However, come time to actually get serious about this, since all the smarts are in the boiler control and the four thermostats (one per zone) are dumb, RedLink doesn’t really help unless I switch out all of them and then have to remotely fiddle with all four. I contacted Honeywell support for that, and they told me to

  1. program the Aquatrol to interpret the auxiliary input as the “vacation mode” input and
  2. use any RedLink thermostat’s fan control output as a means to tickle that input.

That struck me as quite a hack, but thinking about it I realized that given the first part, that there was an input that could be used to toggle vacation mode, all I really needed was a relay that I could reach via internet. After a little bit of research I went with a SmartThings hub and the Evolve LFM-20 relay, wired that onto the controller and tada - the vacation home furnace has a remote control. The boiler control is smart enough to keep an eye on temps and not let it drop into the freezing range.

Now I am looking for a way to remotely control the hot tub - The Wife requires the hot tub to be hot within a couple of hours of arrival, and I require it to not waste insane amounts of power. I am thinking I’ll have to go with just a monster 50 Amp relay to flip the power on/off, but then the freezing protection in the hot tub is off too, so this will need some more smarts about checking for temp and turning the power back on when things are getting icy in there. I don’t see a solid solution for that but I may be just not looking into the right places ? This seems like a relatively common scenario to me. Any pointers appreciated on the hot tub topic, hope the boiler control vacation mode hack helps somebody,

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Great ideas and “hacks” … in the good sense!

Regarding the hot tub – if you do the simple thing and control the tub heater activation via the main power relay, you are putting in a bit of a “master override” to the built in thermostat. For normal heating operations, that’s fine … as you can flip the relay on in advance and you know the tub thermostat will take over and heat up the tub and maintain the temperature from that point forward (as long as the main power stays on).

So the only unsolved problem is reinstating “anti-freeze” protection that the first part of the solution, unfortunately, disables …

Perhaps reinstating = replacing? If you can use a reliable air temperature sensor and/or local weather source to determine if near freezing conditions exist, you could have a SmartApp just cycle the full main power on for a certain reasonable duration … i.e., long enough to warm up the tub, but much too short to let it reach the temperature of the “locked in” normal hot operating temperature set in the thermostat.

For more accuracy, instead of using air temperature sensors, it is possible to find ones with submersible ends, and wire these into an Arduino with ThingShield or WiFi (if you can’t find a “connected” submersible sensor). I think ambient air temperature is fine for anti-freezing estimation.

This would be an imprecise solution which may use more or less power, but gets the job done without having to actually replace the thermostat with a “smart” one; for the long term, that may be worthwhile … heck, it may be possible to hack a home heating thermostat into the system, but you are then messing directly with the electrical of the tub, which is a bit dangerous.

What I ended up doing was

  • put a 60 amp contactor in the hot tub circuit
  • control contactor that with an LFM-20 zwave relay
  • putting an AeonLabs temperature sensor not in the water but on the underside of the hot tub, inside the housing. This is only a couple of degrees off.
  • have a dedicated energy meter on that

I’ll write an app that flips the big breaker on when the temp goes below 50 or so and off when it goes above 70 or so.

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