Thermia Atria recently struggling to heat house

[KTPKTP]

 Hi all, I’m looking for some help with mine & my neighbours ASHPs.

 

I live in a small development of 5 houses that are all about 12 years old. Each house has a Thermia Atria (same as Danfoss DHP-A), but all the installations are slightly different. The installer has gone bust many years ago and we now really struggle to get anyone out to look at the systems. While we try and find someone willing to visit I have been trying to help diagnose and fix some of my neighbours issues. 3 systems have problems, I think I have worked out the problem on 2 of them, but am really not sure on the 3rd. So I’d be interested to hear people’s thoughts on this one first:

 

House 1 Problem: Working fine until this winter. Now high electric bill, in auto mode it is running for 2.5 hours a day on auxiliary heater. Heat pump running around 20 hours a day. No alarms.

 

Background info: From what I understand the Atria does not have any control on the compressor, it’s just on or off. I can put my hand on the output pipe of the compressor when it is running, it’s warm but not hot. I can’t do this on mine or the other neighbours systems.

Heating supply line temp is only reaching 33 degrees in heating mode, with a return line temp of 29. For ref the outside temp was around 10 degrees when I took these values over 24 hours. Supply line temp goes up to 50 degrees in hot water mode, but strangely the return line is quite often higher by a degree or 2. The hot water itself gets to about 48 degrees before the operating switch shuts it off.

Brine temp delta is 2 degrees.

It seems to make hot water every 1.5 to 2 hours as the hot water temp drops below the trigger point (44 degrees). I’m not sure if this is normal heat loss or if the 3 way valve may not be completely closing when it switches to heating mode. I think this is a secondary issue though.

 

Brine Installation. Not sure if this is a red herring.

This install has a sealed but unpressurised brine circuit. It is installed exactly as per the Thermia/Danfoss manual with the fill point/see through expansion tank about 1m above ground level. However the Atria has a brine defrost jacket on the outside of the hot water cylinder. The pipe for the defrost circuit peaks inside the indoor unit at about 1.8m above ground level, with a bleed screw at the top. The manual makes no mention of this circuit in the install section. I can’t get my head around how you can fill/bleed the system properly if the fill point is not the highest point. The manual is explicit that the expansion tank must be higher than the top of the outside unit, but no mention of its position in relation to the indoor unit and defrost circuit piping.

I am sure there is some air in the brine circuit but I can’t work out how to bleed it with this set up. I got some out initially from the bleed point on the outside unit, but now neither brine or air comes out as I think the brine in the sight tube has dropped below the level of the outdoor unit.

 

I’m not sure if the brine is the root cause though, as the in/out temperatures seem similar to my system. Although my brine delta T is usually between 2 - 4 degrees, whereas this system never seems to be more than 2.

 

So next thought was lack of refrigerant or the compressor not working correctly. Would this cause the symptoms described above? This would need someone external to leak check and re-gas, so want to make sure I’ve ruled out anything I can fix first.

 

I’ve attached some pictures of the supply line temp (graph is 90 minutes of data) and hot water temp while the system is in heating mode. The supply line graph looks completely different to my system. Mine is a square wave where you can clearly see the heat pump turning on.

 

Also the install guide.

http://mbaudin.free.fr/dhp_h/DHP_Total_install_VMBMA702_en.pdf

 

System has been installed with the expansion tank option, as per my arrow. It is installed exactly as the diagram I.e. about midway up the side of the indoor unit. The pipe at the top on the indoor unit has been capped off with an automatic bleed valve about where “8” is shown.
 

 

 

shown.

[KTPKTP]

My screenshot from the manual didn’t attach 

[KTPKTP]

An update to this, in case anyone can help. Will also keep updating in case this is useful for anyone else with a similar system. 
 

The refrigerant engineer came out today and confirmed gas circuit is fine.

 

So to me, that means gas going into heat exchanger is ok, but the heat is not being transferred to the supply line. Could the heat exchanger be coated with crud making it inefficient? There is a strainer right before it, so I will check that tomorrow too. Could air in the heating circuit also cause these symptoms? This is a bungalow with UFH so ASHP unit is effectively the high point in the heating circuit.

[J1mbo]

If it was working fine, and now isn't and nothing has changed, perhaps the compressor is simply end of life? The DHW would continue to be heated (more slowly) as it's a closed system, when nothing drawing, whilst if the effective output is lower than the heating circuit loss then it will never heat up fully. That said it looks like it is reaching target, I presume the 31°C in brackets? As the energy integral is -57° minutes.

[KTPKTP]

Thanks for the reply - it has reminded me that the compressor on another neighbour’s system failed about 4 years ago. However the refrigerant engineer said pressures were fine, so I had assumed that meant the compressor was likely to be ok too. However I’m not overly confident.

 

The 31 in brackets is the target temp as you said. This goes up as the outside temp goes down - default setting is when it is 0 outside target temp is 40. These systems don’t have inverters (at least as far as know!) so this unit produces 33 - 34 supply line regardless of target temp in brackets.
 

The heat pump kicks in when the integral reaches -60 degree minutes. So when outside temp is below around 5 degrees the integral just keeps getting lower as the supply temp is lower than target temp. The auxiliary heater then kicks in when the integral is -600 degree minutes.

 

For comparison, my system (working correctly I think) the supply temp is approx. 45 when it is in house heating mode. 

Edited March 19, 2021 by KTPKTP
Typo

[KTPKTP]

So more investigation this evening - I am even more confused!

1. Checked the circulation pump and it was fine.

 

2. Checked the strainer on the heating circuit. Found half a strainer ? well I found the rim, the basket was nowhere to be seen. The fact the rim was there makes me think the basket has become detached/disintegrated and is lodged somewhere in the pipe work (surely no-one would put just the rim back in?!). So this could be be blocking the flow. Or maybe there is no strainer, so a risk all the crud is in the heat exchanger.

 

3. Checked refrigerant circuit temps. The output pipe from the compressor does heat up eventually after about 2-3mins and becomes too hot to hold. On my system this is more like 10 seconds though - would that tie in with the compressor wearing out? The gas pipe is hot going into the heat exchanger and cold coming out though, but hard to tell if it’s quite as hot as it should be.

 

Is it likely a refrigerant engineer would have spotted an underperforming compressor? He checked the temp and pressure on the low pressure side and said it was fine, but I don’t know what this means exactly - he was an air con engineer and didn’t have the manual for the ASHP. Only checked that the output was getting warm by hand. 

 

 

[MikeSharp01]

 

6 hours ago, KTPKTP said:

2. Checked the strainer on the heating circuit. Found half a strainer ? well I found the rim

Is it remotely possible that the strainer has corroded away?

[KTPKTP]

Attached is a picture of the strainer in my system, so this is what should have been there. The basket is crimped to the rim.

 

There were no remnants of any of the basket at all, which is why I though perhaps it had become detached. If it had corroded, would you expect to see some of the basket still attached by the rim? 
 

My neighbour would not have been able to check this themselves. I recon they had someone out to service it around 3 years ago, so it should have been checked then.

 

Interestingly the pump was actually very clean.

[J1mbo]

If the compressor is fixed speed and the flow rate is at least as fast as yours and the return temperatures are the broadly the same then the compressor hot side should surely heat up at the same rate if the compressor is within spec.

 

Is there any diagnostic menu giving the refrigerant circuit pressures, high pressure in particular? 

[KTPKTP]

There’s no pressure readings unfortunately, but the service menu does give the temperature of the compressor output pipe, so I have compared:

The compressor output pipe climbs to 67 degrees over 2-3 minutes. The supply line temp rises in line with this from 29 to 34.
 

To compare with my system, the compressor output pipe goes to 65 degrees a few seconds after the heat pump turns on and then gradually climbs to 80 over 2-3 minutes. The supply line temp goes to 42 almost immediately and then climbs to 46 over 2-3 mins.

So the compressor output is definitely cooler than mine. Also even when my compressor is at 65 at the start, the supply line temp is 42 - so 8 degrees hotter than my neighbours system. Our return lines are the same temp (29). So could there be 2 issues here - a faulty compressor and an inefficient heat exchanger? 
 

 

[J1mbo]

It sounds to me like it's end of life.

[KTPKTP]

Thanks, yes it does sound like it. I was hoping it might be something less expensive. Looking online the same compressor is around £600 and I would think a couple of days labour to get someone to install and re-gas.

 

I’m a bit nervous about what to advise neighbour, as at 12/13 years old it’s a big investment on an old system. Especially if there could well be secondary faults. The guy that came out to look is understandably keen to recommend a new system. Any one know what the recommended lifespan of an ASHP is?