So I think SAT autodiscovered your board. Correct?
Thatâs correct!
Installed 4.0.0 for use with my EMS-ESP connected Buderus boiler. So far it looks like SAT handles low load situations much better than Buderus themselves. Itâs only 16 hours in, but current metrics look promising. I will follow up in a couple days with more data.
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Still figuring out if I can use SAT⌠I have underfloor heating and Honeywell Evohome valves for the bedrooms. I cannot directly control those valves (can only control the target temperature). Is it now correct to assume that I cannot leverage SAT to control the temperature in the bedrooms?
Sat does not control the temperature. It tries to control your gas boiler or heat pump as efficiently as possible based on the heating setpoints you set with your thermostat.
You will need a gateway though inbetween your Honeywell and the gas boiler.
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I would like to share some more âunder the hoodâ informations about SAT.
Letâs start with the operation on most OpenTherm projects. They calculate the Control Setpoint based on a weather compensation algorithm or a PID controller. Then pass this value to the boiler and the room temperature stays near the setpoint. Thatâs fine no issue with that. The user is happy because the room temperature is near the setpoint, the thermostat is happy because is able to control the boiler and the boiler is happy because is able to heat the home.
Is this really the purpose of the thermostat? Being the master or just âactingâ as a master? Is this approach robust or a naive approach?
The real answer is that the thermostat is âactingâ as master since has no idea what is happening in the heating system. The thermostat calculates a Control Setpoint that doesnât account any of the boiler parameters ( Boiler flow water temperature, Relative modulation, Max relative modulation ) and heating system capabilities. Most of the times the boiler canât cope with such low Control Setpoint values and is cycling. Which tends to reduce the life time of the burner due to wear and tear.
Why SAT is different and actually IS the master of the heating system?
SAT controls the boiler and keeping the temperature on setpoint in a completely different way. It monitors every moment the Room temperature, Outside temperature, Boiler flow water temperature, Relative modulation and Max relative modulation to refine its calculations while respecting the heating system limitations.
Why a thermostat should respect the heating system limitations?
Every heating system is unique. Different boiler brands, sizes and minimum capacities. Different heating emitters ( Underfloor or Radiators or Mixed systems ), pipes, circulation pumps. That means every home has a different behavior. That led us to define a threshold. We call it minimum setpoint.
Minimum setpoint is the lowest boiler flow water temperature that the boiler can keep while running continuously without cycling at 0% modulation ( Lowest capacity ).
Why minimum setpoint is so crucial for the heating system?
When SAT calculates a Control Setpoint that is higher than the minimum setpoint, boiler works in a normal cycle mode. This means:
a. Sends the CS value unprocessed
b. Lets the boiler modulate itself by sending the Max modulation value of 100%.
When SAT calculates a Control Setpoint that is lower than the minimum setpoint inevitably has to control the boiler in duty cycles ( ON/OFF cycles ) otherwise the boiler will start cycling. This function is the Low-Load control. In order to achieve such a control SAT works like this:
a. Sets the Control Setpoint to the Minimum setpoint ( The lowest Boiler flow water temperature that the boiler is able to handle without overshooting at 0% relative modulation ).
b. Lowers the max relative modulation to 0% ( The boiler works as smooth as it can).
c. Calculates the duty cycle percentage based on the calculated Control Setpoint and the Boiler flow water temperature.
d. Translates the duty cycle percentage to 20 minutes ON/OFF intervals.
Low-Load control helps the boiler to work as much as it can at its minimum capacity. It is suppressing the system from a, letâs say, 24kW system to a 5 kW system. The benefits of this operation are:
a. The boiler runs longer.
b. ÎT of the system is higher.
c. Cycling is reduced.
d. Lower return water temperature which leads to higher efficiency.
e. Less burner and pipes wear.
Is SAT more efficient compared to other thermostats?
Our research showed that SAT controlled boilers are using 30% less gas than traditional ON/OFF thermostats.
I hope I made some things more clear about SAT operation.
Thanks for this great explanation! Can you maybe also indicate how we can measure how much better SAT is then the normal thermostat? Should I then think off lower gas per degree day or more around cycling of the heater?
SAT should ideally affect both gas usage and duty cycles.
In my system (which isnât using SAT at the moment for unrelated reasons), I track duty cycles, burner power modulation (as a percentage), and I track gas usage on the gas meter directly.
If your boiler runs in a high frequency cycle, moving to SAT should get you a reduced number of cycles almost immediately.
Tracking boiler modulation and gas usage, it may take several days to see a drop because itâs difficult to get comparable repeat days with the same outside temperature on order, so you will need to observe over longer time periods to get numbers allowing you to reason about average use (and reduction).
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Have been trying to get SAT to work, but every time I set it up I get the following in the logs:
Waiting for a stable temperature
Timed out during overshoot protection calculation
Unfortunately not much more info.
Anything I can do against this?
Hi! Sometimes Overshoot protection calculation is not working properly, but we have a solution for that. Run the initial configuration again and choose the second option this time Manually enter the overshoot protection value. Then enter the value 48. May I ask some more questions? How many radiators do you have? Which is your boiler brand?
Hi newbie to SAT, looks fantastic some initial questions.
Ideal Boiler Vouge Max C40, House 210sm, 19 rads
OPV manually calculated @44 as autotune failed for me at current version
So I have multiple temperature sensors around the house, currently Iâve set SAT up on an average of these and when I went through the set up it only allowed me to add one sensor for inside temp even though it would let me add multiple for outside? How to I go about adding multiple temp sensors, not climate controls, so SAT will look at the most error?
I know this maybe not possible, but Iâve been running before with daytime looking at downstairs temp averages for the setpoint and then at night looking at upstairs, is there a way to flip the sensors SAT looks at in different pre-sets for example?
what is the âCurrent Powerâ sensor? Iâve set the min/max gas and that is working but current power remains unknown is this something the boiler is not reporting?
My setup:
Remeha Avanta 24C
Honeywell Evohome Wifi thermostat
Underfloor heating
3 radiators fitted with Evohome radiator knobs
Nice, I think the value 48 is enough. But if you want to calculate this value more precisely use this guide https://github.com/Alexwijn/SAT/discussions/36.
So I have multiple temperature sensors around the house, currently Iâve set SAT up on an average of these and when I went through the set up it only allowed me to add one sensor for inside temp even though it would let me add multiple for outside? How to I go about adding multiple temp sensors, not climate controls, so SAT will look at the most error?
It is not possible to add more room temperature sensors. Better create a new sensor that uses the median of these sensors and add it in SAT instead. We give the ability to add more than one outside temperature sensors as a fail-safe solution since it is very crucial for the heating curve value calculation.
I know this maybe not possible, but Iâve been running before with daytime looking at downstairs temp averages for the setpoint and then at night looking at upstairs, is there a way to flip the sensors SAT looks at in different pre-sets for example?
Maybe you can create a template sensor for this âspecialâ operation.
what is the âCurrent Powerâ sensor? Iâve set the min/max gas and that is working but current power remains unknown is this something the boiler is not reporting?
Can you manually send the PM=15 command from the otmonitor? Then it will appear shortly after. If not please let me know.
Thank you, yep PM=15 did the trick!
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How did you find the minimum and maximum values for your heater? I found some details in the user manual (6,0 - 20,8 kW), but are those the values you should enter in SAT? Reason for my confusion: gas consumption does not neccisarily mean minimum/maximum powerâŚ
EDIT: just also found the minimum and maximum gas consumption (in M3 per hour). Is that something I should input? Ranges from 0.72 to 2.89
Yes. The minimum consumption is 0.72 and max consumption is 2.89. Just add them to the boxes