I have a Nibe F470 Exhaust air heat pump.
Builders didn't install room temperature sensor, because other system takes care of room temperature.
However, it seems heat pump produces too much heat at least at summer time. Yes, it is possible to alter temperature settings
and heating curves without room sensor, but I decided to make some basic investigations.
The temperature sensor model is Nibe RTS 40. Same room sensor is used in many other heat pumps, not only made by Nibe.
Depending on the market and shop it may cost up to 50-100€.
In Russia, it is possible to find it for more affordable price like 10€ but you still have to pay for delivery etc.
Also I found some forum discussions where people is asking about sensor type and parameters.
I took 47K Ohms potentiometer and connected it to the system. Right after that, on the fly, system begun to show
room temperature. I made a little table of of impedance and temperature numbers shown on the display:
0.1 32.65 KOhms
9.8 20.15 KOhms
25.0 10 KOhms
34.4 6.63 KOhms
Basicly, this means that system uses simple thermistor with negative coefficient having 10 KOhms at 25 celsium degrees.
I found similar sensor specifications in the Internet. It just should have 10 KOhms at 25 degrees and about 33 KOhms at 0 degrees.
Sensor type is NTC 10K+-1%. 3950 is just perfect.
I have ordered water proof sensor with these characteristics for 0.84€ from the Aliexpress. Similar sensors can be found on Ebay
as well. I just hope this information will help somebody to improve heat pump system, so I'll leave it in English here.