Hot Water ?

Posted on
Tue Sep 20, 2016 4:25 am
Scotfree offline
Posts: 21
Joined: Sep 26, 2014

Hot Water ?

Can you please tell me how to find the HW on/off variable ? None of the states displayed seem to be assigned to the HW relay being switched on and off.

Thanks.

Posted on
Tue Sep 20, 2016 7:21 am
Chameleon offline
Posts: 611
Joined: Oct 04, 2014

Re: Hot Water ?

Scotfree wrote:
Can you please tell me how to find the HW on/off variable ? None of the states displayed seem to be assigned to the HW relay being switched on and off.

Thanks.


It's a good question. The NEST API doesn't actually provide a temperature setting for the hot water on it's own nor does it seem to switch it on or off independently of the heating. At the normal boiler switch the hot water is continuously on and is controlled by the boiler thermostat (or immersion thermostat). It is only the heating/cooling that is managed through the NEST from what I can tell.

The NEST Home plugin follows the same structure as the official NEST API from Google. I've provided the structure and a like to the explanations for each field below. However, none of them refer to the HOT WATER only because I don't think that's how the NEST works. It simply manages the heating not the hot water which is on all the time.

The states that refer to heating or not are:

    can_heat = true if heating is available
    heatorCool = heating if heating is on
    hvac_mode = heat (only), cool (only), heat-cool (both) or off
    hvac_state = heating, cooling or off
    isHeating = Yes or No

The API data looks like this:

https://developers.nest.com/documentation/api-reference

Screen Shot 2016-09-20 at 14.06.16.png
NEST API
Screen Shot 2016-09-20 at 14.06.16.png (143.96 KiB) Viewed 492 times


The meaning and setting of each flag is listed here:

https://developers.nest.com/documentation/api-reference/overview

Hope that helps - if not drop me a line.

Regards

Mike

Posted on
Tue Sep 20, 2016 9:05 am
Scotfree offline
Posts: 21
Joined: Sep 26, 2014

Re: Hot Water ?

Thanks for your reply Mike. That's certainly true of the 1st and 2nd Gen thermostats but the 3rd Gen has a second relay on the base unit for calling HW on the combi boiler or for switching on a heating element in the tank. It is separate from the heating relay and controlled/scheduled separately on the app. It doesn't know HW temperature, just whether it's on or off and this is the info I need in Indigo. Can't see the state in any of the below, perhaps we have to ask them to add it to the API ?

Posted on
Wed Sep 21, 2016 4:04 am
Chameleon offline
Posts: 611
Joined: Oct 04, 2014

Re: Hot Water ?

Scotfree wrote:
Thanks for your reply Mike. That's certainly true of the 1st and 2nd Gen thermostats but the 3rd Gen has a second relay on the base unit for calling HW on the combi boiler or for switching on a heating element in the tank. It is separate from the heating relay and controlled/scheduled separately on the app. It doesn't know HW temperature, just whether it's on or off and this is the info I need in Indigo. Can't see the state in any of the below, perhaps we have to ask them to add it to the API ?


Fair enough. It certainly doesn't appear in the API nor the simulation test system. I'll add it to their change request log for the API. They've added a few fields in the past from developer requests so I'll see what they say and keep in touch.

Regards

Mike

Posted on
Wed Sep 21, 2016 7:44 am
chase offline
Posts: 25
Joined: Oct 27, 2013

Re: Hot Water ?

I have the Nest thermostats (Gen2 and Gen3) and I am not aware of a relay for controlling the production of Hot Water ( I am assuming you mean DHW (Domestic Hot Water). I am not sure why you would even want this or how a thermostat's purpose would relate to the production of DHW. I have searched the iOS app and I see no place where the app mentions or displays a call for DHW.

The Specs for the Gen3 controls are :
Heating: 1, 2, and 3 stages (W1, W2, W3)
Cooling: 1 and 2 stages (Y1, Y2)
Heat pump: with auxiliary and emergency heat (O/B, AUX, E)
Humidifier or dehumidifier (HUM, DEHUM)
Fan (G)
Power (C, RH, RC)

There are no controls labeled HW.

Can you elaborate on the HW control you are talking about as I can't find anything about it.


FYI I deployed my Gen3 and it controls a Combi boiler with electric boiler as a back up, and a heat pump with fan.

Posted on
Wed Sep 21, 2016 8:47 am
Scotfree offline
Posts: 21
Joined: Sep 26, 2014

Re: Hot Water ?

Chase, you can read about it here;
https://nest.com/uk/support/article/Lea ... er-control

Pretty obvious why you would need it - to schedule HW being switched on or off, separate from UFH.

Normally not used with combi boilers because they produce heat on demand but even though I have one, I prefer to turn off my HW when away for extended periods as there is a reserve tank which is heated constantly.

To get the HW option to display in the app, you need to set your equipment setting to 'System Boiler', it won't display when it is set to Combi Boiler.

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