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Daikin Altherma 3 with Fan Coils in Puglia (Italy)… Sanity Check on System Operation

Air Source Heat Pumps (ASHPs)

Last Post by Mars 1 hour ago

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Simon_JM

(@simon_jm)

New Member Member

Joined: 12 hours ago

Posts: 1

Topic starter 18/05/2026 9:54 pm [#3007]

Hi all
This is my first post, but i've been a long-time lurker both here and watching the youtube channel etc...

I’m looking for a technical sanity check. (maybe just a sanity check)

Firstly I have deeply researched heatpumps more than I could have imagined, for what should be a straightforward install, so I’m not asking from a standing start and I am reasonably technically minded. My query is borne possibly more out of frustration.

I have a heatpump quote for supply and installation in what will be my permanent home in Puglia, southern Italy, I am still in the UK for then next year or so.

Question: for an air-to-water heat pump with fan coils in a mild southern Italian climate, should the heat pump normally stay powered and controlled, or is it technically sound to treat it as an on/off appliance?

Proposed system: Daikin Altherma 3 EBLA 16 kW, three-phase/380V, with 8 fan coil emitters for heating/cooling. Two adults, my partner and I, living there year-round.

The (native english) project manager person, who is neither a heating engineer, system designer or heatpump owner, has told me how the heatpump system will be operated, and all heatpumps are operated like this apparently:

> “You’ll use cooling in July/August.”
> “You don’t need heating April to October.”
> “So you’re not using the heat pump a lot of the year.”
> “If you want to use the heatpump, turn it on. If not, turn it off.”
> "turning it off will cut down on electricity usage, so I will be saving money in the long run anyway"

Is the on/off usage logic suggested by the Project Manager technically sound, or should the unit stay powered/controlled while schedules, thermostats and fan coils manage demand?

My due diligence tells me it is fundamentally wrong to do this as the ASHP is not a gas boiler, 'low and slow' is the preferred mode, but I'm told I do not know about these things as I am not the professional, and it works differently in Italy to how it works in the UK.

Incidentally, no room-by-room heat-loss or cooling-load calculations have been provided. I have asked and been told categorically they won't be supplied because I am not a professional in this field thus it could offend the heating engineer / plumber. (I know...I'm only the client). I did my own heatloss calcs in the end...

I am just putting this out for a sanity check, and to a community of more informed and experienced people than me.
appreciate any comments, queries etc

Many thanks and sorry in advance for wasting peoples time...

Simon

This topic was modified 1 hour ago by Mars

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4612

18/05/2026 10:51 pm

Welcome @simon_jm, and this is not a dumb question at all. Your instincts are correct, and your project manager’s advice is, to put it plainly, wrong.

A heat pump is not a boiler. It does not respond well to being treated as an on/off appliance.

The fundamental operating principle is low and slow… the unit runs continuously or near-continuously, modulating its output through weather compensation to match the heat demand of the building at any given moment.

The colder it is outside, the harder it works. The milder it is, the gentler it runs.

That steady, modulated operation is precisely where the efficiency lives. Every time you force a cold-start by switching the unit off completely, you lose that efficiency, you stress the compressor during the ramp-up phase and you end up running at higher flow temperatures to catch up… which costs more, not less.

This is not just my opinion. The training and industry guidance used across the UK and Europe is unambiguous on the point: any form of on/off control forces the compressor to operate at or near full capacity on restart, which is the least efficient way to run an inverter-driven unit. The project manager’s logic (that switching off saves money) is the same logic that leads people to believe flooring the accelerator and stamping the brakes is more economical than cruise control. It isn’t.

Fan coils in a mild southern Italian climate could be an excellent choice for this kind of low-temperature continuous operation. They respond quickly to changes in flow temperature, making them well-suited to a modulating heat pump running on weather compensation.

Puglia winters (after a quick Google search) appear to be mild… the shoulder seasons are precisely where a well-commissioned heat pump earns its keep, running at low flow temperatures with a COP that a boiler could never match.

On the heat loss calculation, the refusal to provide one is a serious problem, and the justification offered is remarkable.

A room-by-room heat loss calculation is not a courtesy… it is the foundational document from which everything else (emitter sizing, heat pump selection, flow temperature design, etc.) is derived.

Without it, neither you nor anyone else can know whether the 16kW Daikin Altherma is correctly sized, whether the eight fan coils are adequate for each space, etc. How big is the property?

The idea that asking for this document is somehow impertinent is, to be blunt, a deflection.

You did the right thing by running your own calculation. I’d encourage you to push for the installer’s version in writing. If they are unwilling to provide one, that tells you something important about how the rest of the project will be managed.

The community here will have more to add, and I suspect this thread will develop some useful detail around the Daikin Altherma specifically in warmer climates.

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