Ämne: SMO40 / F2120 Compressor Frequency

[biscaya]

Hello together!

before i'm describing my problem with my heatpump, sorry that i have to write in english. Tried to get an answer for my questions here, but no one seems to be able to me. I'm from germany and got a Nibe F2120 heatpump with a SMO40 built in a VVM. I have a strange behaviour with my heatpump, which happens at higher outdoor temperatures between 10-16°C. The problem is, that at this point the heatpump won't get down to the minimum frequency as it should. It runs at 50-60hz and the supply temperature gets too high, so that the degree minutes reach 0 very fast. I've got a floor heating system and the heatcurve is set to 4, so for example the outdoor temperature is 15°C, the calculated supply is 24°C but the real supply is 29°C and the compressor frequency is at 56hz. It won't get down to the expected 25hz and stays at the 56hz. I don't have any thermostates, so there should be enough waterflow (fixed pump speed 75% - 1200 liters per hour). Also got no indoor temperature sensor indoor which impacts the heat curve. What might cause this behaviour?

Second question is about the menu point, which is also available in the wizard, which checks the dT and the flow. Does this affect the control of the unit or is it an optional step? When i complete this test it seems to get more worse than descibed above. The installer skipped this test. Test says dT ok = 5.2°C.

Thank you very much!

[HBerggren]

There is a chance that fixed pump speed is the issue, try auto.

Also, try to adjust 4.9.3, compressor start from -60 to -120. If your indoor temperature is wrong please check offset or curve.
Offset is temperature. Curve is something you need to adjust if the indoor temperature drifts away when it gets colder.

Offset 0 and curve 5 is a great basepoint.

Please check that your outdoor temperature sensor is facing north, else the sun will mess up the reading and heat calculation.

[biscaya]

There is a chance that fixed pump speed is the issue, try auto.

Also, try to adjust 4.9.3, compressor start from -60 to -120. If your indoor temperature is wrong please check offset or curve.
Offset is temperature. Curve is something you need to adjust if the indoor temperature drifts away when it gets colder.

Offset 0 and curve 5 is a great basepoint.

Please check that your outdoor temperature sensor is facing north, else the sun will mess up the reading and heat calculation.

Thank you for your answer. I already thought that there might be a connection between the pump speed set to auto and the compressor control. Problem is, that the pump speed goes always down to the minimum and thats not enough flow for my house. Unfortunately the minimum setting of the pump is limited to 50% and can't be configured higher. But what i don't understand is, why the pump speed needs to go down to get the frequency lower, as in my opinion it should go higher to get more flow which would decrease the supply temperature which is too high, as the heating energy generated on high outdoor temperatures is high in this case. So this seems to be a good fix for that problem in my case, but i have nothing to compare if this behaviour is normal.

Compressor start is set to -180 already, this results in less starts but only extends the run a bit as the supply is a lot too high when there is 5 degree difference between calculated and real supply. Outdoor temperature sensor is facing north already, i changed that because the installer mounted it on west side, which didn't work like you descibed.

[HBerggren]

It is complicated to describe the connection between frequency and pump speed.

Have you tried to adjust individual zones? It makes the heat balanced with a low pump speed.

First, make sure you have no bypass. Instead, make sure for all bathrooms that there is no actuator installed, and the flow is open without an actuator installed. This is how it should be long-term.

To adjust all zones, remove all actuators temporarily. Then, adjust the other end of the same zone until all returns have equal temperature in return. Check temperatures a few times a day. You can compare with your bare hands; it is not bad at all. An IR thermometer or thermal camera is a bit better. After a few days, see if each room has the same temperature. If not, adjust that zone a little bit.

The base setting is that the longest line zones have wide-open adjusters, and the zones closer to the manifold have the most restricted setting.

If all zones share this low flow and still appear to have a balanced flow, the issue should be resolved with the pump in auto mode.

High flow does compensate for bad adjustments; keep that in mind.

If all zones have both hot and cold areas, the flow is actually too low. Then, you should get a tank and a second pump with higher flow all the time, and Nibe will control the first pump in auto mode.

If each zone return has an equal flow, it means the return temperature will be as low as possible. The supply will also be lower until the floor is saturated because the supply will only rise a few degrees when passing through the heat pump.

[biscaya]

Thank you, the zones on the heating circuit distributors are set. However, not via the return temperature but according to a calculation by the installer. But that certainly won't be that accurate. I will make the settings as you described as soon as possible and then get back to you. I even have an infrared thermometer. It might take a while because it's too warm again in Germany at the moment.

I think it's a shame that it doesn't say anywhere exactly how the control really works and which settings influence the behavior and how. Some things can be found in forums but nothing documented from Nibe directly. It would be really interesting to know what's behind it, especially in terms of influencing the compressor frequency.

[HBerggren]

I agree your concern about the behavior documentation.

It seems there might be a discrepancy in the requested frequency by VVM in the field and the actual frequency the outdoor unit is running. This discrepancy is not well-documented, making it challenging to understand the reasons behind it.

[hoegge]

Hello together!

before i'm describing my problem with my heatpump, sorry that i have to write in english. Tried to get an answer for my questions here, but no one seems to be able to me. I'm from germany and got a Nibe F2120 heatpump with a SMO40 built in a VVM.

Is it an SMO 40 or S40? I have the same issue in S40 that supposed to be smarter. But seems like the problem has not improved since the SMO 40.

[biscaya]

Sorry for the late answer. It's now "cold" here in germany, so i finally optimzed the system. Sadly it's very hard for me to get into this forum as i don't understand the language and to login is already very hard.

It's an SMO40 that i got. I try to describe the process i did and what the problem was:

It is important what heatpump you got. The F2120 is way different from the S-Series. This is already because of the minimal heat delivery it got, the S-Series can get lower, which is better (20Hz). So the problem is with that F2120, that it runs at 8°C outdoors and above on minimum of 25Hz and under that 8°C it runs at ~35Hz. There is also a point lower where it gets a little higher. This is the behaviour when you change the compressor curve to minimum (i set it at 0°C minimum, then to get up to 100% at -9°C, this is the minimum temperature at my point).
First thing i did is what HBerggren said, balance the system by setting the return temperature to that one, which is the lowest return. Then i set the pump to fixed speed instead of auto at 73% (this is then 1100 liters per hour in my case). Then i saw that the rooms get the same temperature, but some didn't. Now i corrected this a bit by adjuisting the flow of these rooms a little higher or lower.
After waiting a few days what i did now is i noted all the temperatures that were made at the different outdoor temperatures but only when it was at lowest compressor curve. Then i created my own curve by this values, so that the generated temperature almost meets the calculated temperature by the control all the time. Now it runs 24/7 at under 9°C outdoor temp. Room temp everywhere 22°C. Runs perfectly now as i think.

Hope this helps you to improve you system but this is only a workaround. In my opinion the system should be much smarter, it wouldnt be too hard to let it modulate at X degree minutes. What this thing does is only set compressor frequency to 200% when degree minutes drop. Not very smart. The control is very bad in my opinion.

Tthis will only you to understand the outdoor unit, but as you got a S-Series control you can't set the compressor curve i believe. You should take a look at heat delivery at NAT (this is the nominell outdoor temperature). I don't know how the configuration point exactly is named in the control, but i read somewhere that this is the setting how you can affect the compressor frequency.

[fyrbil]

Hi, I have the same issue. I would like to have 25hz possible down to around +3°C. Is it the F2120 itself that controls this? Or SMO40(in my case vvm320). I think it would be easy to fool the tempsensor to think it is warmer than +8°C, and only do that above +3°C real outside temperatute.