View Full Version : NEST Thermostat and Daikin

Peter Beak
19-12-2016, 01:30 PM
Whilst perusing the internet yesterday, I was suprised to see that Nest Thermostats and Daikin are to be working together so that the AC 'talks' to the house, and so will do clever things through your mobile phone, PC, or 'smart' tele' - presumably without needing a separate app since it can be controlled by the Nest room stat.

Having done a bit of digging, it appears that the new Daikin units will have a Nest Labs chip inside them to provide all of the connectivity (apparently the same chip as in the CSM-101, but a revised version, honestly) - which although very nice for people looking for a new system, doesn't help anyone who would like to (erm...) improve their existing setup. The new breed of smart room stats also look visually very flash.

Having a bit of spare time on my hands at the moment, (road traffic accident keeping me from work) I was thinking about adding one to my Daikin Ducted system, and this is where the complexities begin since the smart thermostats offer either dry (relay) outputs or 24V AC outputs which of course can feed a relay and provide dry contacts. Daikin etc all use a 2 wire bus, and at first glance no out-of-the-box way to connect to non Daikin thermostats.

Options that I have considered so far, starting with the cheapest, and one of the most elegant:

1/ My Daikin air handler, I have discovered to have a set of terminals called X40A :p which when shorted together hold-off unit operation, which if the AC is only used for cooling allow a NC set of contacts from a relay to prevent the Daikin from cooling until the third-party thermostat activates the relay for cooling and so removes the contact between the two connections. There is even a Daikin-supplied wire with a connector on the end of it called EKRORO to make this connection.

2/ If I wanted a cheap, but far less elegant solution that would allow cooling or heating, then I could connect the Nest (or other) thermostat to two double pole relays, for cooling and heating, and connect them to the AHU or room stat such that the relay being activated switches the thermistor used by the AC for a resistor of a suitable value to coerce the indoor unit that cooling or heating is required due to it being fooled as to the temperature.

3/ If I want a solution that would also allow dehumidification (which would be good in an ideal world) then I could use a computer program called ITTT and a Daikin WiFi adapter to botch a system whereby the Nest (or other) thermostat, and its software wouldnt realise that it was controlling the Daikin, but software rules could be implemented to make it work. I dont like this idea - it doesn't seem elegant or professional at all.

4/ There are lots of other Daikin add-on modules for conrolling the system from BMS's of various flavour - but these could require further stepping stones to interface from BMS bus protocol.

5/ There are other Daikin interface adapters - but would any of these give me dehumidification?

:confused:Gentlemen, your thoughts please.......:confused: