ASHPs louder when cold?

[kron77]

Hi - got my ecodan R32 installed in October and it's been purring away ever since quite nicely. This morning, in Edinburgh anyway, it was near on 0 degrees and there was a noticeably louder noise coming from he unit, as if the fans were spinning much faster etc. I gather it's normal for an ASHP to work harder, and therefore be noisier,  when it's cold? 

 

When the manufacturer publishes its decibel rating, is it best case or worst case - i.e. on a lovely summers day when doing a DHW top up or at -5 degrees in winter? 

Thank you in advance! 

[ProDave]

Ours works hardest when doing DHW and then towards the end of the cycle when the HW is nearing it's target temperature so the water temperature from the ASHP is at it's highest.

 

Could your unit have been defrosting this morning, that usually only takes a couple of minutes.

[SteamyTea]

What is your DHW temperature set to?

[kron77]

Thanks @ProDave it was not doing a DWH cycle, it was on central heating for sure. It could of being doing a defrost I guess, didn't hang around long enough to check. Will keep an eye on it.

May I ask why the ASHP works harder for DHW then for central heating? I've also noticed that it does work harder for DHW. 

[kron77]

29 minutes ago, SteamyTea said:

What is your DHW temperature set to?

@SteamyTea it's set to about 50 degrees but it wasn't doing a DHW cycle at the time. 

[joe90]

Most .ASHP deliver DHW hotter than UFH so it will run harder. Mine only delivers one temp, set to 48’ in my case but yes it does work harder in colder weather.

[ProDave]

How hard it works depends on the temperature difference between flow and return pipes.  It tries to maintain the flow temperature at a set target.

 

Usually when heating the house particularly with UFH the return temperature will not be much lower than flow so it does not have to work hard, but heating DHW the flow temperature will usually be a lot lower than flow so it works harder to deliver as much heat as it can.

[SteamyTea]

33 minutes ago, kron77 said:

@SteamyTea it's set to about 50 degrees but it wasn't doing a DHW cycle at the time. 

Well that is not excessive.

Is a fan blade damaged.

 

[kron77]

21 hours ago, ProDave said:

How hard it works depends on the temperature difference between flow and return pipes.  It tries to maintain the flow temperature at a set target.

 

Usually when heating the house particularly with UFH the return temperature will not be much lower than flow so it does not have to work hard, but heating DHW the flow temperature will usually be a lot lower than flow so it works harder to deliver as much heat as it can.

that does make sense thanks @ProDave. I downloaded an app on the phone to register the decibel readings. I appreciate it won't be very accurate but the decibel reading yesterday when it was around 0 degrees was average 75db (peaking at 90) at one meter. The advertised decibel output for the ecodan is 49 at one meter.

 

This morning - when the temp is up around 7 degrees it's back to it's normal sound output (haven't taken a reading yet). So I wonder what about the outside temp makes the ecodan run so loud? Might have to get the installer out, i don't think I can live with the noise every time the temp drops below 5 degrees c. Remember it wasn't doing a DWH at the time, just regular central heating and I reviewed the flow/return temps and they were pretty close together (normal sort of 5 degree drop). 

[SteamyTea]

6 minutes ago, kron77 said:

average 75db (peaking at 90) at one meter

A car is limited to 74 dB, so something don't seem right.

[kron77]

1 hour ago, SteamyTea said:

A car is limited to 74 dB, so something don't seem right.

yeah agree and i checked all the fans, they look fine. 

[J1mbo]

Take the phone dB meter with a big pinch of salt. It will be noisier when colder as the compressor is going to be working at higher output as well as the fan speed most likely.

[kron77]

I wanted to come back to this thread with an update. With the temp here in Edinburgh dipping to below 5 degrees now more often than not I just couldn't take the noise anymore, as the ecodan was running at full speed all of the time it was below 5 degrees. So I got mitsubishi out and they agreed to replace the whole ASHP. Unfortunately it didn't resolve the issue, at 5.1 degrees runs like a charm and super quiet. At 4.9 degrees it spins up to 63 decibels (I bought a proper decibel reader) and it never, ever comes down until the temp goes above 5 degrees. 

 

So in talking with the tech guys at mitsubishi he seems to think this is the freeze stat function kicking in. We checked and the freeze stat is at 5 degrees bang on. He mentioned that if they system is filled with glycol then you can switch this function off and it should then run at normal speed at any temp. So i'm waiting for a refractometer to come today to confirm the glycol settings and then if they are correct, i'm moving to switch off the freeze stat function. 

 

 For anyone else out there with an ecodan this might be interesting. Also, I want to mention that there is a quiet mode setting for the ecodan r32. If you go into the settings you can find it and there you can choose 3 different settings of quietness. This will reduce the output somewhat, but will solve the immediate noise problem when below 5 degrees. My plan is to remove the freeze stat once I confirm the gycol vs going down the quiet mode as I'd rather have it running at full efficiency all be it without the fan speed increase. 

 

Will report back here when I switch off the freeze stat function.