newly installed ASHP system in southern Italy, strange issue.

[ROBINLAWRIE]

Hi all, first post! please be gentle 😁

 

I've just renovated a house in southern italy and spent a fortune on a 20kw heat pump  system with two large  inverter fancoils, ducted to all rooms for heating and cooling.  the house is large and not well insulated hence the large capacity of the system. 

the heat pumps (there are two, in master/slave config)  are 10kw Ferroli Omnia 3.2.   they are connected to a 150 litre buffer tank (i think thats  the correct term)   which then feeds the two fancoils which are situated above a false ceiling in the main corridor. 

here is a link to the brochure of the heatpumps, for reference.

 

Having lived here for one winter, and most of a summer, i have been observing the system.   

 

Firstly, in winter it struggles to get the house over 18 degrees, and in summer (when its 33+ degrees outside) it struggles to cool it under 26 degrees.

 

The installer has said repeatedly that it needs to be left on 24h a day to achieve the desired performance.     this is almost certainly true, however i have noticed a strange behaviour which is likely also contributing:

 

The control panel of the heatpumps reports the heat/cooling output of the two machines, and ive never seen the combined total go over 12kw in either heating or cooling mode.

Usually it reports around 3-4kw for one machine and 4-5kw  for the other.   Electricity consumption at the solar inverter is reported at 2.5-3.5kw 

 

The other day i checked it specifically after running for half an hour in cooling mode, with the water temperature set to 7 degrees (too low for decent efficiency i know,  but im trying to get the house cool, and i have solar panels so free electricity during the day) 

 

water output temp reported from the pumps was 12 degrees and the return temperature was 16 degrees, this means to me that the buffer tank was not yet cooled down, hopefully eliminating the fancoils from the equation, and any obvious system defect that could limit heatpump output. 

The master pump was outputting 5.2 kw, slave was 6.4 kw.  this is about as high as ive ever seen it. 

 

What could be the cause?    

 

The installer is being slippery, saying "its normal the output will vary all the time"   "you are lucky, imagine the bills if it was running full tilt"   and "leave it running all day itll be fine" 

 

Once we have a decent battery system,  ill be more happy to leave it running when theres no sun, but currently with nearly 25 cents/kwh,  leaving it on 24 hrs a day would absolutely massacre us on the bills, and thats without it running at the rated 20kw. 

 

besides, thats a different discussion. 

 

any advice on what to check, or ask the installer to check, would be most appreciated.  otherwise he will bamboozle me with excuses and i wont achieve anything. 

[JohnMo]

Welcome. Think your installer is talking sense. 

First alarm bells

34 minutes ago, ROBINLAWRIE said:

after running for half an hour in cooling mode

So you are not letting it run and find it's feet. Stopping the heat pump makes it run when restarted a little strange. Firstly it trying to get itself back to target flow temperature, for this it monitors return temperature and delta between flow and return. All these are managed by the controller. So it you have a decent sized buffer and healthy demand on fan coils it never really catches up. 

 

The other alarm bell

38 minutes ago, ROBINLAWRIE said:

with the water temperature set to 7 degrees (too low for decent efficiency i know,

Most fan coils have a design temp of 7 degs that's how they are sized. To run warmer temperatures in cooling mode that need to be big and sized to suit a higher flow temperature. As you only have two to cool or heat the whole house I doubt they would be as big as needed.

 

Once up and running in steady state conditions the heat pumps will modulate to suit the demand. Just because it's rated at xkW doesn't mean it spits out that all the time. Mine kicks out 6kW and over the last 48 hrs has consumed just over 3kW including DHW, because it has no demand, cooler weather and no solar gain.

 

43 minutes ago, ROBINLAWRIE said:

master pump was outputting 5.2 kw, slave was 6.4 kw.  this is about as high as ive ever seen it. 

Are you monitoring with a heat meter or something else?

 

Hope this helps 

[sharpener]

1 hour ago, ROBINLAWRIE said:

Usually it reports around 3-4kw for one machine and 4-5kw  for the other.   Electricity consumption at the solar inverter is reported at 2.5-3.5kw 

 

 

37 minutes ago, JohnMo said:

Are you monitoring with a heat meter or something else?

 

 

OP reads consumption off his solar inverter and 2.5-3.5 kW there would equate to maybe 7.5 - 14 kW thermal output depending on assumption about CoP so is broadly consistent.

 

Can't think of anything other than that the fancoils are undersized so cannot get rid of the heat/coolth. It would be good to know how they were sized, and the floor area and construction of the house.

 

 

Edited Thursday at 14:07 by sharpener

[ROBINLAWRIE]

3 hours ago, JohnMo said:

Welcome. Think your installer is talking sense. 

First alarm bells

So you are not letting it run and find it's feet. Stopping the heat pump makes it run when restarted a little strange. Firstly it trying to get itself back to target flow temperature, for this it monitors return temperature and delta between flow and return. All these are managed by the controller. So it you have a decent sized buffer and healthy demand on fan coils it never really catches up. 

i had assumed that letting it get going,  but measuring it before the system had arrived at a steady state (send and return temps very different and much higher than set temp)  that would be the time it should be going "all guns blazing"  trying to arrive at the set temp?     if not then, when? 

 

anyway i have checked it countless times, and as i said, it NEVER reports anything close to max output, at any stage of the day, startup, after 1 hr, 5 hrs etc etc.  and the house is way off the temps set by the thermostat. 

 

3 hours ago, JohnMo said:

 

The other alarm bell

Most fan coils have a design temp of 7 degs that's how they are sized. To run warmer temperatures in cooling mode that need to be big and sized to suit a higher flow temperature. As you only have two to cool or heat the whole house I doubt they would be as big as needed.

 

Once up and running in steady state conditions the heat pumps will modulate to suit the demand. Just because it's rated at xkW doesn't mean it spits out that all the time. Mine kicks out 6kW and over the last 48 hrs has consumed just over 3kW including DHW, because it has no demand, cooler weather and no solar gain.

 

Are you monitoring with a heat meter or something else?

 

Hope this helps 

as i mentioned, im measuring the output of the heatpumps from their control panel, which reports all of the info on performance etc. 

[ROBINLAWRIE]

2 hours ago, sharpener said:

 

 

 

 

OP reads consumption off his solar inverter and 2.5-3.5 kW there would equate to maybe 7.5 - 14 kW thermal output depending on assumption about CoP so is broadly consistent.

 

Can't think of anything other than that the fancoils are undersized so cannot get rid of the heat/coolth. It would be good to know how they were sized, and the floor area and construction of the house.

that is one worry i have,  undersized fancoils, hence measuring the heatpump output before the buffer tank had arrived at temp.      if they were the cause, the buffer tank would arrive at the set temp and sit there,  and the heatpumps would modulate down, since the fancoils couldnt dissipate the heat/cool(th) fast enough. 

2 hours ago, sharpener said:

 

 

 

[ROBINLAWRIE]

anyway appreciate the replies, thanks 

[ROBINLAWRIE]

2 hours ago, sharpener said:

 

 

 

 

OP reads consumption off his solar inverter and 2.5-3.5 kW there would equate to maybe 7.5 - 14 kW thermal output depending on assumption about CoP so is broadly consistent.

 

Can't think of anything other than that the fancoils are undersized so cannot get rid of the heat/coolth. It would be good to know how they were sized, and the floor area and construction of the house.

 

 

the house is 250 sq M  but the heated/cooled zone is nearer 200.  mostly open plan, all on one floor (its an ex countryside nursery school)   cieling height is 3.4m.  we have top quality brand new pvc  double glazing,  and the walls are 50cm thick tuff (volcanic) stone with a 10cm cavity in the middle. flat roof.   we were encouraged to add external insulation, but with nearly 900 sqm of external walls, it would have cost a fortune, and we have been advised repeatedly that its not a job to DIY.  we chose to compensate with a more powerful ashp instead.  The engineer on the job *apparently* did the thermal calculations to spec the system, but we have a strong suspicion he just eyeballed it and took our cash.  we saw some evidence of "cut and paste" in his documentation, including mention of parts of the house that dont exist. 

 

the fancoils, ill need to look up the specs but they are great big things. about 1mx 1m x 40cm thick. iirc rated for 10kw heating and 8-9kw cooling capacity each.  mounted above false cieling in the corridor,  with ducts and returns in all the rooms.  one is dedicated to the living room/kitchen (open plan 75sqm)   the other does the 3 bedrooms.    we have radiators in the bathrooms, which are disconnected when the system is in "summer" mode.   

Edited Thursday at 16:50 by ROBINLAWRIE

[ROBINLAWRIE]

one other thing to note, we have an old pellet stove we used in our previous house.   its a 10kw one that blows out hot air from the front.     we installed that due to the lack of heating power in the winter, and with it set to MINIMUM  we brought the living room and half the house to around 23 degrees.    it was waaaay cheaper to use that than the heatpumps.