In the first part, a friend of Automated Home, MarkB, started converting his smart home to use the Shelly module, and in the second part, he built a smart EV charger. This time he upgrades his domestic hot water system…
We installed a Drayton iTRV with a 3 channel controller, one zone for living space, one for bedrooms and a third zone for hot water, you can read about it here.
While we have heating control via iTRV and Wiser room thermostats, hot water relies on a simple layout and a traditional bimetal switch on the hot water heater. This seems like an obvious area that Drayton could offer homeowners an improved sensor to digitize hot water controls and give tank temperature visibility, but it also gives us another Shelly project.
There are a few problems with the current setup. Hot water is on a fixed heating schedule, the boiler is switched on early in the morning and late in the afternoon to heat the water. If someone uses a lot of hot water during the day, then the boiler involved may not be long enough to provide enough heat to recover the hot water boiler. Likewise, if a lot of hot water is used after late afternoon, someone needs to run a boost cycle.
I also have a Solar iBoost which will divert excess energy from my PV installation to an immersion heater. There are times when the tap water is hot and the water heater is still turned on to heat the water. This can be caused by clear stratification of the water or inaccuracy of the bimetallic thermostatic switch. Anyway, I was wasting fuel when it could have been avoided.
The search was for more control, but without the complications or expensive stuff, and Shelly will provide the answer. Shelly Add On modules allow the addition of temperature probes or external switches. These modules connect Shelly 1 or Shelly 1PM and connect to the GPIO header.
We’ve covered using Shelly to build a smart light or smart EV charger and for this project I’ll be using Shelly 1 again, but this time with the addition of a temperature module.
Shelly Add-on Module
I’ll start this off with the usual disclaimer – This is an illustration of how I use Shelly devices and is not a detailed tutorial. Mains voltage can kill, cause serious injury or damage property and equipment. Make sure you only do work for which you are competent or trained and that you comply with local regulations.
I supplied Shelly 1 local 240V power supply to power the device. I connected the previous thermostat connections to the de-energized input and output contacts of the Shelly 1. After all the main connections were made, it was time to attach the Add On. It has three fly cables to which I would connect three temperature probes via 3 Wago connectors. Spring connectors were supplied in the pack but my addiction to the Wag meant I used them as they felt more robust. I regularly use braided cable covers to ensure a good connection and no stray strands, especially when using very fine gauge cables.
Once connected, the Shelly app automatically detects the presence of the plug-in and the temperature probe, and new options will be available on the device’s control panel.
Next is the adjustment of the temperature sensors by setting the measurement units, in my case degrees Celsius. Then it’s time to name the sensors, in this setup it’s simply top, middle and bottom. The upper part measures the temperature at the outlet of the cylinder, the middle one was the place of the traditional bimetallic switch, and the lower one was a spare pocket on the cylinder intended for solar energy. These three probes would give me a good view of what is happening to the contents of the cylinder.
The next step was to use temperature automation to turn the relay on and off. I chose 65 degrees as the off temperature and 40 as the on temperature. This now meant that I replaced the previous thermostat with a more accurate setting and would have visibility into water temperature trends.
The next part of the problem was to ensure that the boiler would come on if the cylinder dropped below the minimum temperature. This would require a second Shelly 1 attached to the boiler. I designed and built a controller that would turn on the boiler and open one of the three zone valves according to which zone is calling for heat. Years ago this meant running cables to zone thermostats, but now with Shelly these cables can be replaced with Shelly devices, isn’t progress wonderful!
The controller uses three conventional relays, but now the hot water zone relay would be replaced by Shelly 1. Whenever this Shelly would turn on, the boiler would fire and the hot water zone valve would open. The live output from Drayton Wiser would be used as the Switch input for Shelly 1, replicating the existing functionality.
With this Shelly 1 in place I was also able to use the Direct Device to Device feature. When the temperature dropped below 40 degrees on the middle temperature probe, I could tell the device on the boiler to turn on regardless of Drayton Wiser’s schedule.
This project illustrates the power of Shelly, as it is able to connect separate devices in a precise and logical way. This also gives us greater control, comfort and energy efficiency.
Stay tuned for smarter scenarios with Shelly devices at the heart of the solution.
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Last Updated 2024-01-21 / Affiliate Links / Images from Amazon Product Advertising API