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Topic # 240704 21-Sep-2018 08:57
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My home automation currently consists of a bunch of Sonoff devices, including TH16 thermostats driving resititive heaters. Simply controlled by the ewelink app, haven't found a need pushing me to Tasmota yet. 

 

I would like to find a solution that lets me vary the thermostat target temperature by time of day, according to a pre-determined schedule and the forecast from Weather Underground. Technically it would be the thermostat upper and lower setting, but for simplicity I'll refer to a single target temperature which is an average of the upper and lower. I've done this manually (cranking the heater when I wake up early in the morning, and turning it off at 8pm) and the house seems to have enough thermal mass/insulation to coast for an hour or two once heated. Fluctuations of this magnitude don't seem to bother us. 

 

This would serve two purposes:

 

1) Optimizing use of off peak power - ramping up the target temperature by a couple of degrees prior to peak power prices (e.g. before 7am and 5pm), and easing the target temperature down on the tail end of peak prices (e.g. before 11am and 9pm). 

 

2) Minimising use of heater ahead of a hot day (our house is a sun trap) - ramping down the target temperature by a couple of degrees in the morning (from 7am) when the forecast indicates a warm and clear day.

 

Here's a graph to convey the idea:

 

 

Can anyone suggest an approach to make this happen, ideally with my existing Sonoff hardware? I have a raspberry pi if needed to pull everything together. IFTTT doesn't pull the temperature from the Sonoff TH16, so I'm guessing I'll need to go a more custom route.

 

If I can get this working for the heaters, I'd like to apply it to my hot water cylinder - using the headroom between 50C (minimum needed for reasonable shower) and 70C to coast through peak power price periods too.

 

 

 

Thanks!


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  Reply # 2094277 21-Sep-2018 09:04
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I should add that a solution that doesn't turn my heaters off when the internet goes down would be ideal too!


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  Reply # 2094341 21-Sep-2018 09:35
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Sounds like a job for Node Red.

Run that up on your Pi. Get Tasmota (or ESP Easy) flash to your Sonoff. And the have fun building the flow.

There is a node called 'Big Timer' that is quite complex, but allows very specific scheduling. There is also a node for weather underground - I tried using it but found WU weren't giving out api keys to the public any more.

Edit: FWIW I have moved my Sonoff basics to Tasmota over esp easy. Found it more stable on those devices. Would still use ESP Easy for modules like wemos d1 and nodemcu though.

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  Reply # 2094392 21-Sep-2018 11:08
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For the hot water cylinder, install an upper temp sensor (approx 1/4 to 1/3 from the top). During offpeak, heat as normal based on the bottom thermostat. During peak, only switch the element on when the upper temp sensor indicates low temp. As that means that the cylinder is close to running out of hot water.


Although the best option is a large hot water cylinder, with both a bottom and upper element. Then you only need some simple timers to get good power savings.

Assuming that your cylinder doesn't have solar or wetback connected?







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  Reply # 2094412 21-Sep-2018 11:40
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chevrolux: thanks, looks like Node Red will do the trick. I found a blog that used Big Timer for this very purpose, so that's a base for me. You've also prompted me to think about ESP Easy though. My graph is just three different setpoints, so could potentially do a simple set of 'rules' e.g. use time of day as a trigger to write the setpoint to a variable, then compare the actual temp to the setpoint variable and activate/deactivate the heater. Might make integration with IFTTT/Wunderground (and Flick spike notifications) more complicated/impossible though. Either way, I need to order another TH16 to play with.

 

 

 

aredwood: I'll be getting an electric cylinder shortly to replace instant gas. No solar or wetback. Will see about getting a top element - good idea. Could set the lower element to only run overnight to 70C, and the upper element to run in the afternoon to 55-60C. Then just need to choose a cylinder size that will carry me through peak periods without any boost. I'm thinking that 180L @ 70C should be sufficient for modern low flow fittings/appliances and 2.5 occupants.

 

 

 

Thanks guys!


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  Reply # 2094562 21-Sep-2018 14:06
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Have you looked at OpenHAB/Home Assistant?  Both run on the pi, and would do what you want......and then like the rest of us, you'd get obsessed with automating, hooking in everything.

 

Given they're local and can be cloud enabled if you so desire, it satisfies your do something when no internet....assumes you network has power though.

 

 





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  Reply # 2094738 21-Sep-2018 19:25
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@nickb800 Get a 300L cylinder. Probably won't cost much extra compared to a 180L twin element anyway.

Then you should be fine with night only heating. And use the upper element just for quicker reheating if you run out. Or if wholesale prices are super low.





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