Ecobee Air Conditioning Update

Ecobee 3 thermostatIn honor of the bouncing seasons, I turned on my air conditioner a couple of weeks ago. In Minnesota that means you remove the wintertime weather covers from outdoor compressors and then turn on the dusty circuit breakers.

Fortunately I had performed a best-effort wiring of the AC into my new thermostats. All I needed to do was tell the Ecobees to look for AC, and to turn it on. It worked.

AC and heat in our home are completely different systems: while all air conditioners use blowers, not all heating systems do. Our heat uses hot water radiators. I set up a separate “comfort setting” in the Ecobee so that heat sensors wouldn’t confuse the AC system.

When the Ecobee arrives in its Apple-inspired tech box, it includes three comfort settings:

  • Home
  • Sleep
  • Away

These interact with the occupancy sensors to try to save energy when no one is home. The “Sleep” setting ignores occupancy and assumes you’re home asleep. The “Away” setting assumes you’re away. You can set different heat and A/C temperatures for each.

Heat zones in our houseThe diagram on the left shows how the thermostats and the heating zones are laid out in our house. Each zone controls heat in a vertical slice of the house.

Each is controlled by a mechanical valve. The valves were the reason for the isolation relays described in an earlier post: they work with old-fashioned electricity, not modern electrical signals.

Air conditioning zones in our houseThe diagram on the right shows how the air conditioning zones are laid out. The AC units are connected to the Zone 1 and Zone 2 thermostats.

Each AC zone controls the temperature in a horizontal slice of the house.

The Ecobee Sensor Challenge

Traditional thermostats have a single built-in thermal sensor. The Ecobee often comes with two additional sensors, each reporting temperature and occupancy to its thermostat. You can add more sensors to each thermostat if you wish. I have had as many as six on a single thermostat, and they can probably handle more.

The two diagrams show how the heating and zones overlap and differ. The upstairs AC is wired into Zone 1: the upstairs Zone 1 sensors keep things comfortable in the upstairs hall and master suite. The downstairs AC is wired into Zone 2: the downstairs Zone 2 sensors keep things comfortable in the kitchen and dining room.

But what about the front parlor, downstairs in Zone 1, or the playroom, upstairs in Zone 2? Here’s my solution:

A pair of Ecobee sensors in one room

If the established heating zones and sensors don’t give the right signals for a room’s AC, then I add another sensor to control that room’s AC. The two sensors above are in the playroom. The left sensor talks to Zone 1 for AC and the right one talks to Zone 2 for heat. There is a similar pair in the front parlor.

Zone 3 heats some downstairs parlors and upstairs bedrooms. Air flows freely between the downstairs parlors and the dining room, site of the Zone 2 thermostat. That’s enough to manage comfort in those areas both summer and winter. The bedrooms are mostly unoccupied; their sensors are connected as needed by season and occupancy.

AC Comfort Settings

Ecobee comfort settingsOut of the box, the Ecobee assumes that all sensors are used all the time for both heat and AC. I tell it to handle different sensors differently through the comfort settings.

  • Away – heat and AC settings for when we’re away
  • Home – heat settings for when we’re at home
  • Sleep – don’t really use it
  • AC – a custom comfort setting I set up for running the AC

The Home comfort setting is configured to ignore sensors outside of each thermostat’s heat zone. We only use it during the heating season.

Our customized AC comfort setting is similar to the Home setting, except that we only use it in AC season. In Zone 1, the AC setting includes all upstairs sensors that aren’t used by other zones for heat. In Zone 2, the AC setting includes all downstairs sensors that aren’t used by other zones for heat.


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