Thermostats / Nest

I researched this during my renovation. My building has what is known as a '2-pipe system'. In the summer the pipes deliver cold water to the unit, and an electric fan blows air across the coils, in the winter, hot water. There is no local compressor or temperature control -- just a high/med/low/off rotary switch, which switches the 120v line current. The Nest is not directly compatible with this configuration, as it can't switch 120v -- only 12v, meant to operate a relay which switches the 120v. To use a Nest, you would have to install a relay, and would switch high/med/low settings from the existing switch on the unit. Peco (www.pecomanufacturing.com) makes a programmable unit which puts on/off + fan speed control + programming on a wall unit which is compatible with 2- and 4-pipe systems. Note that for best operation you have to run a bunch of 120v wiring to the thermostat location from the unit, which is a pain (conduit enclosed, etc.). Because of a communication screw-up during installation, I ended up with low-voltage wires to the PECO, with additional relays in the a/c unit. Not optimal, as the relays are noisy. Ultimately, I rarely use the programming, as the power draw by the motor is so low compared to a full a/c that the effect on the electric bill is minimal.

Aaron, thanks so much for the insight. It sounds like you ultimately ended up with the additional relays in the a/c so you could have utilized a Nest allowing for a wireless solution. Was the installation of the Relay particualrly cumbersome or costly? My purpose is far more for convenience.

Unless they've changed the features since I looked at it (2 yrs ago), the Nest (even with relays) won't be able to change the fan speeds automatically. It will just do on/off, at the speed you've set via the old switch on the a/c unit. Depending on how your building delivers the hot/cold water to the unit (2- vs 4-pipe), there's a risk that the Nest will get confused during your building's semi-annual switch between heating and cooling, and keep heating the place, even though you want it cooler -- you may have to shut it off on the days when you'd like it cooler, but the building is only delivering heat.

The cost was built into my overall renovation contract, so it's hard to estimate it's contribution -- I'd guess around $1000 (the Peco thermostats are about $250/each -- I've got 2). As I said above, it's a somewhat sub-optimal installation, mostly because I think the relays are too noisy.

Ultimately, for the convenience, the cost was hardly worth it. I run the unit from a wall thermostat rather than walking over to the unit. Big deal -- I'm able bodied enough to do it, and don't adjust things often enough for it to be an inconvenience. I'm also in a 60s building, and given my preference for cold rooms, and the minimally insulated construction, the a/c runs on low 24/7 once summer gets started (i.e., last week).