I’ll try to summarize a slightly more complex case:
I live in central Europe, in a 10 year old family house,
- I use a gas instantaneous heater (max 24kW) for hot water and radiator heating (Viessmann from 2006),
- I use solar vacuum tubes approx 20pcs (for hot water heating), Resol (Deltasol bs 2009, VBus), 200 litre storage tank, connected in front of the water supply to the gas boiler,
- I check the opening status of windows/doors, measure gas and energy consumption, measure the temperature in different parts of the house/outside and for the storage tank/gas heater, control the boiler to heat the hot water boiler/storage tank and drain the water from the 200 litre storage tank when it overheats…
For some time each system lived “its own life”, later I tried different controller strategies for solar tubes but mainly for heating…
Chronologically - for two years the house was without insulation and solar tubes, then the gas consumption was reduced by about 35%, I don’t know if it was more because of insulation or hot water heating, for heating I used a simple space thermostat (ON/OFF) and Deltasol bs 2009 for water heating. Now I don’t use the gas boiler for hot water from April to October, in the summer months I need to drain the hot water from the tank as it reaches 70 degrees centigrade at the top of the tank if I leave the house for two days.
I gradually moved all automation to OH (2,3), using GPIO for relays, window sensors and DS18b20 thermometers (9), before the arrival of OH4 I moved much of the automation to the ESP32 chip, Tasmota.
Strategies for a family house with central heating radiator valve with manual control):
Turn off the house heating if:
a) the out temperature rises to 3.5 °C below the heating start temperature, via the Tasmota Rule
b) if more than 2 windows/doors are opened the heating is blocked for 30 minutes (minimum 15) from the time the second to last window is closed (one window can remain open for ventilation - bathroom…), if the heating is running there is no point in stopping it during heating,
c) heating will be locked for 30 minutes after the heating is finished, after 30 minutes it will be activated again (for the thermal inertia of the heating system), locking via Tasmota Rules - unlocking via OH Rules,
d) manual blocking of heating - for example service… , via OH Rules
e) if someone is using WiFi/Zigbee radiator valve, it is enough to block the valve if the window is open for more than 6 minutes,
f) I can set 4 kinds of temperature, Day (22), Night(21,8), Eco(21), Away(18) - realistically I only use Day/Night, via OH Rules
g) schedulling Day/Night via OH Rules (Time cron “0 0 23 1/1 * ? /*”,Time cron “0 15 6 1/1 * ? * *” ), ECO if I leave for 1 more than 1 day, AWAY more than a week,
The heating method for the family house from the central heating radiator valve with manual regulation):
0) heating is OFF, via both OH Rules and Tasmota Rule
- PI (Proportional-Integral) control e.g. Thermostat (Thermostat - Tasmota) or PID (PID Controller Automation - Automation | openHAB), I have tried both models, now I use Thermostat via Tasmota,
- PI Thermostat, with adjusted time readout to 1 second accuracy according to Duty Cycle, via Tasmota Rule
- Fixed heating time, ON is treshold temperature, OFF is adjustable heating time value, via Tasmota Rule
- Efficient mode, ON is treshold temperature, OFF is max temperature from hot water heating, via Tasmota Rule,
- ON is treshold temperature - hysteres, OFF is treshold temperature + hysteres,
I have the hysteresis set to 0.1 °C for modes 1 and 2, 5.
For modes 3 and 4 the hysteresis is meaningless.
The Treshold thermometer is placed 10 cm from the ceiling, away from heat sources like radiator, TV, Fridge…, about 3 meters from the door in the middle part of the house - the hallway. The location of the thermometer affects all parameters, it is important for the overall result of gas consumption (about 10%), because a gas boiler consumes 54 litres of gas in 1 minute of burning (that is why Mode 2 was created).
The efficient mode (4) probably deserves more space for explanation:
- the manufacturer quotes an efficiency of gas to heat conversion in the range of 80-110% for different types of gas boilers (90% in my case). Unfortunately, the maximum value can only be reached at full boiler output, i.e. until the boiler starts to “modulate” output (then the efficiency drops to 70% or less). Efficient mode therefore means that the boiler switches on at treshold temperature (temperature sensor in the room) and switches off as soon as the temperature (temperature sensor on the exchanger in the gas boiler) in the boiler heat exchanger starts to drop (the boiler starts to reduce output because it has reached the internal temperature set on the panel for heating the radiators). This mode can save about 10-15% of gas.
The second in order of economy is Mode 2 (5-10% gas saving), the disadvantage is more frequent switching on and off of the boiler because the Thermostat does not have an automatic Duty Cycle change. This Mod is basically an extension of Mod 1 which copies the ON/OFF state of the Thermostat output Relay (Mod 1 speeds up the DutyCycle time to whole minutes). Essentially, the boiler will consume extra gas by rounding the DutyCycle time to whole minutes and at an average consumption of 50 litres per minute and about 15 ON states per day and 5 months of heating.
Mode 3 was created as part of the code for OH PID (PID Controller Automation - Automation | openHAB) and can be used, but you have to set the derivative part of the PID correctly so that the PID can calculate meaningful numbers, basically you can use this Mode for any PI heat controller.
Mode 5 is a replacement for a regular room ON/OFF thermostat.
One more fact worth mentioning, try measuring the temperature “up” in the hottest place and the temperature “down” in the coldest place in the house, apartment. If the temperature difference is more than 3.5 °C the “sensible” temperature decreases significantly. Modes 1,2 and in fact 3 were the worst in terms of feeling, the temperature difference was up to 4,5 °C. Conversely, Modes 4-5 were the best feeling, with a temperature difference of less than 3 °C. This is due to the fact that the PID/PI i.e. PWM control really “machine” calculates the heating time and keeps the hysteresis to a minimum, Modes 4 and 5 basically have no hysteresis. In Mode 4 the temperature overshoot was about 0.5 °C, in Mode 5 up to 1 °C behind the set temperature (22 °C).
In addition to heating, I have also optimised the hot water heating. In the 200 liter tank I have 2 thermometers, one at the top of the tank which I use to control the hot water heating by the gas boiler. If the water in the tank is above the treshold value of the sensor (40°C) the gas boiler does not heat the water for showering or washing dishes, and if it is below this value the gas boiler heats the water coming from the tank to the set temperature.
It is worth mentioning that solar vacuum tubes can produce water at 30 degrees even in winter (when the sun is shining), so the gas boiler only heats the water at 30°C to the desired temperature (max 50°C).