Split indoor unit quite loud at night

[rhymecheat]

Hi all. 
 

I’ve got a split Altherma 3 H HT and the indoor unit is wall mounted in the loft. The loft is insulated but not boarder, apart from the base built specifically for this installation. I’ve attached a picture of the setup up there for clarity. 

 

I’ve noticed that if I leave the heating on overnight (at about 35/40C) I hear a constant humming on the top floor that is rather irritating during the night as there are no other competing noises.

 

I’ve measured this noise to about 26dbA at ear level when lying in bed. The hum seems to come from the indoor units pump. It has a configurable pump speed which I’ve already set to the minimum (60%) but it’s still rather loud. 
 

Interestingly I would expect the hum to be stronger on the rooms directly below the unit but that’s not true. The room directly below the unit is actually quiet (as is the room that’s further away from the unit, but that one makes sense). It’s the other rooms that seem to have it worse. Again, attached a drawing of the layout for better understanding (green for ground level, black for first floor and red for loft)
 

my questions:

1. Is this Normal and I should just turn the thing off when I want to sleep?

2. How can I reduce this noise further?

3. Why is it not the loudest directly below it?

 

Thank you very much in advance

[Bruno]

I have a similar problem but in my case it's not the HP itself, it's the water flowing through the circuit. The circulating pump can be a bit noisy, in my case it's the pipes in the walls and even in the radiator's manifold which seem to be of an insuficient diameter, thus creating contraints in the water flow which then creates this noise.

In my case just reducing the pump's speed was enough to have that noise more or less eliminated (edit: not eliminated, but totally acceptable)

 

Are you using radiators? If so might be a good idea to check if the valves aren't too closed which also constraints the water flow.

I suggest you to stop the heat pump and activate only the circulating pump (my HP has a diagnostics menu which allows to activate and check sensors and actuators, not sure if that one has something similar), so that you can check if the problem is the machine working or the water flowing.

Edited January 24, 2022 by Bruno

[rhymecheat]

19 minutes ago, Bruno said:

I have a similar problem but in my case it's not the HP itself, it's the water flowing through the circuit. The circulating pump can be a bit noisy, in my case it's the pipes in the walls and even in the radiator's manifold which seem to be of an insuficient diameter, thus creating contraints in the water flow which then creates this noise.

In my case just reducing the pump's speed was enough to have that noise more or less eliminated (edit: not eliminated, but totally acceptable)

 

Are you using radiators? If so might be a good idea to check if the valves aren't too closed which also constraints the water flow.

I suggest you to stop the heat pump and activate only the circulating pump (my HP has a diagnostics menu which allows to activate and check sensors and actuators, not sure if that one has something similar), so that you can check if the problem is the machine working or the water flowing.

Yes, there are rads upstairs. Last night I turner the rads thermostat off and the noise was still there so we can probably discard that. I’ve also had the pump running with the compressor off (I believe this is what you’re suggesting) and the noise is still there with the same intensity which indicates it’s probably the pump. It’s rather annoying because I can barely identify the hum during the day to the point that I don’t know if it only happens at night now…

Edited January 24, 2022 by rhymecheat

[Bruno]

Yeah so your problem is most likely related to mine. Here's what I was suggested to do in order to find and minimize the problem: open all return valves on all radiators, if you have temperature dependant valves on the input set them to maximum as well (you will need to balance your radiators after). This is to try to eliminate the flow constraints as much as possible.

Then start the circulating pump again without the compressor.

If it's still noisy there isn't much you can do, as it's either the circulating pump (which is integrated in the split module) or small pipes in the water circuit.

If the noise is reduced, then you probably had your rads' valves too closed, just have that in mind when balancing again.

[rhymecheat]

6 minutes ago, Bruno said:

Yeah so your problem is most likely related to mine. Here's what I was suggested to do in order to find and minimize the problem: open all return valves on all radiators, if you have temperature dependant valves on the input set them to maximum as well (you will need to balance your radiators after). This is to try to eliminate the flow constraints as much as possible.

Then start the circulating pump again without the compressor.

If it's still noisy there isn't much you can do, as it's either the circulating pump (which is integrated in the split module) or small pipes in the water circuit.

If the noise is reduced, then you probably had your rads' valves too closed, just have that in mind when balancing again.

I see. But what if I also experience this when the flow to the rads is closed and only the downstairs UFH is on? Does that discard the rads pipes or should I still check that?

[Bruno]

You can check that, it won't hurt and might improve a bit. But if the noise appears without flow to the rads then it has to be something else...

[ProDave]

My ASHP is an outdoor monoblock unit but I still have the noise described.  It is the circulating pump and the water circulating in the pipework and the noise can be heard anywhere where there are pipes above or below the room.

 

It is not very loud but I am very sensitive to noise especially at night in a bedroom.

 

simple solution. set the timer so the heating is off at night.  In a well insulated house you will not notice much temperature drop over night.

 

And changing the circulating pump for a quieter one (Grundfoss or Wilo) will also help.

[Jenki]

Resonance in the pipework could also create this. I would look at clipping all the pipes,  I can't see any clips on yours for insulation, but you could put some waste water pipe clips over pipe and insulation. Either 32mm or 40mm but you want to reduce any vibration. So smaller may be better.

[rhymecheat]

1 hour ago, ProDave said:

My ASHP is an outdoor monoblock unit but I still have the noise described.  It is the circulating pump and the water circulating in the pipework and the noise can be heard anywhere where there are pipes above or below the room.

 

It is not very loud but I am very sensitive to noise especially at night in a bedroom.

 

simple solution. set the timer so the heating is off at night.  In a well insulated house you will not notice much temperature drop over night.

 

And changing the circulating pump for a quieter one (Grundfoss or Wilo) will also help.

I see. Okay I’m gonna try that. It’ll probably take a while to find the right time to come on for a comfortable temperature by the time I come down. 
 

by the way, speaking of pumps: My UFH manifold has a Grundfos with 3 speeds plus a setting for constant pressure instead. Should it be set to constant pressure or constant speed?

[rhymecheat]

1 hour ago, Jenki said:

Resonance in the pipework could also create this. I would look at clipping all the pipes,  I can't see any clips on yours for insulation, but you could put some waste water pipe clips over pipe and insulation. Either 32mm or 40mm but you want to reduce any vibration. So smaller may be better.

Ah that’s a good shout! I’m gonna look into that! Thanks