i have a quite good task.
My heatpump cant communicate to my Home Assistant, and i need to make a fake state of temperature when electricity price is high, then i will set temp for 25 degress outside. and when its very cheap i will set it to -12, so that the heat pump heat up very hard.
in this case i would like to know if it is possible to install a ESP8266 board in serial with the PT100 sensor outside and again back to the heatpump, or is there any possible ways to do this simple ?
How does the HP currently get its external temperature? Is there already an external sensor?
Did you also see the first part of this thread which is on the PT1000 probe. Similar probe to the PT100 except that it has a different resistance at 0C (and probably trickier to work with).
i have this heat pump with a already existing PT100 sensor.
the heat pump is controlled by the outdoor sensor, so if its cold outsite it calculate how much heat to produce, to hold the temperature in the house.
what i would like is to “cheat” the temperature to be very cold when the price is extremly low so the heat pump will produce heat, and when the price is extremly high i would like to change the temperature to be very hot so it stop produce heat.
the heat pump cant be connected to the Home Assistant, so i need a unit to be in serial that can cheat the outdoor sensor.
That sensor communicates over the SPI bus. You would need to persuade the ESP unit to replicate the PT100 output over SPI to feed the heat pump, having received the temperature from elsewhere (perhaps the PT100 on another SPI bus).
This isn’t a trivial project. What’s the heat pump model? Perhaps there are easier ways to work with it…
I have a feeling that the approach is wrong here.
How is the heat delivered from your “evi heat geosun ii”, is it into low-temperature rads or do you have underfloor?
If the heat-pump is working well then it should be maintaining the internal temperature on the basis of the demand from the internal thermal sensors and the external sensor. The HP will react accordingly and the house should maintain a stable temperature.
Telling the HP that it’s colder outside will push up the initial generation of heat, but I’d suspect that it will back-off when there is no corresponding call for additional heat on the interior (that’s the closed-loop system).
If you want to operate the HP on the basis of the cost of a kW unit, then there are some issues around that as normal HPs which use underfloor heating cannot be used for instantaneous heating as they must heat up the floor-slab which is a large thermal mass and can take a week to respond thermally. That’s also true for low-temp rads as they won’t instantaneously heat up.
I think that if you really want to do this by kW price then your best bet would be to adjust the internal set-point in relation to the kW price, such as 21 degrees C for a “normal” unit price and 19 degrees C for a high unit-price.
I do think that these types of adjustments are going to be detrimental to the HPs compressor as the system may cycle excessively due to the demand changes.
The basic principle is just as in my PT1000 thread that was already referenced: Take a relay to switch between direct connection and a resistor between probe and controller. Same would be to “lower” the temperature, just put the matching resistor in parallel.
Some things you should think about:
with the heating curve you can only control the heating, not hot water. So if somebody uses hot water and the buffer is too cold, it would start regardless the outside temps.
Heat pumps’ efficiency depend on temperature delta. My heat pump has a trigger contact and I could increase target temp by 10 degrees by it - this could be switchable by HA so IF there is lot of sun THEN heat to 52° instead of 42°. Sounds good but the efficiency loss does not justify that. Same would apply for your “either on or off” heating.
You are losing the whole intelligence of the heating control. Do I want to cheat my AC a bit? Yes. Do I want to sacrifice the temperature curves for it? No.
the automation is not the issue.
the issue is to find a methode to connect the heatpump outdoor temperature sensor to my home assistant where I have a chance to change the the temperature sent to the heatpump by home assistant.
so no change and auto when the price is normal, when its cheap maybe change automated resistance or something to change the temperature.
Is it possible to connect a D1 mini and X9C103S Digital Potentiometer with the PT 100 ?
And how should it be connected and how can I make the sensor by ESPhome ? So I can adjust it up or down ?
Maybe, but the “minimum wiper increments” for the 1k ohm version is 10.1 ohms which probably does not give you sufficient resolution for your needs.
If you are determined to do this by adjusting the resistance, then you need to think about doing it like in the first link which I posted.
You have to check the PT100 table and look up what resistor values you have and what needs to be added/substracted. If you insist on stopping heating completely, presumably you have to bring the system above 14°C (which is the temperature where my heating curve is zero) but also if you just add 10°outside would massively reduce the heating.
You have the same setup as I have, just with PT100 instead of PT1000 so all discussed in the abovementioned thread applies, just check the resistor values you need. For me 40 Ohm would be >10° shift, yours will be different. So either go with A) keeping the PT sensor and adding a relay for switching resistors (which may have lower values than calculated because you have to add the relay boards resistance) or B) completely dump the current PT sensor and simulate the values = resistor with a X9C102 board
