I would be wary, @pie_eater. Using liquid to cool means you will get condensation on any uninsulated surfaces, including the pipework itself. That includes inaccessible places, and I doubt persistent moisture under floorboards, through joists and in wall cavities is going to do your home any good. That’s why most air to water systems try not to allow the functionality. Don’t get me wrong; it can be made to work, but it’s much more involved than it first appears.

Posted by: @pie_eater

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Given the high temperatures of late plus my abundant solar generation I was thinking of figuring out how to enable cooling on the daikon altherma. This is disabled at the machine (i believe as a condition under the UK subsidy scheme)  , but surely someone has figured out how to bypass?

I don't know how to enable cooling on Daikin and @majordennisbloodnok is correct to sound a note of caution re condensation, although some heat pumps will measure and run above the dew point in an attempt to circumvent.  Also you will only get material cooling with fancoils or UFH, ordinary rads don't cut it.  

Its not a condition of the BUS scheme that cooling is disabled (I dont know about ECO4).  It was a condition of permitted development rights (England and Wales) that the system is 'used only for cooling'  which again didn't require colling to be disabled, just not used.  The recent amendment to pd rights has further relaxed this and now only requires that is 'not used solely for the purpose of cooling.'   

As I have reported elsewhere we turned on the cooling option on our Mitsubishi Zubadan unit after installation.  It was just a case of flipping a dip switch and restarting.

But - we have invested in Jaga Strada fancoils which are designed for light cooling and this works fine so long as you keep the chilled water above 16C.

Any condensation is a minor inconvenience in the scheme of things when you can get a decent reduction in room temps of 5 - 7C.  Powered by solar so zero running cost (after the considerable capital outlay).

@downfield 

may I ask whether the pipework in your barn [you shared this, including pictures, in another post] is insulated?

I am trying to understand whether 'light cooling' -

JAGA.COM "https://jaga.com/uk/light-cooling-heating/"

Light Cooling & Heating - Jaga

Light cooling (sometimes referred to as comfort, dry, or non-condensing cooling) is a form of gentle cooling used to cool down a room by 3 to 5

needs insulated pipework.

if it does need insulated pipework, then it's impractical ASHP retrofit; it would need changes to pipework in walls and floors, that are impractical.

@comfortablehomeseeker I have the usual combination of insulation under the suspended ground floor and no insulation where pipes are in the heated space i.e. under the first floor.

The whole purpose of light cooling is that you don't need insulation if you keep the water temp above the dew point.  Jaga recommend using 16C but obviously on a humid day that might be a bit low.  But it's not a problem in normal UK conditions on a hot day which is when you need the cooling.  If you feel the pipes as they go into the radiator at worst they might be slightly damp.

I’m sort of keen to try it , seems like a good solution provided condensation is kept under control. 
no idea how to change the daikin for it to cool though. Found some very limited info that you may have to change the pcb from edla to ebla or so. 

@pie_eater Try asking the Perplexity AI engine how to turn on cooling on your specific model.  It's available through your web browser or as a free iOS app.  Or just ask Daikin.

We changed three rads in our bedrooms first to see how well it worked.  If you buy through a supplier like GoGeothermal they seem to give a decent discount on the list prices.

@pie_eater I have been thinking of adding cooling to my system over the last 12 months+. I am not too keen on the condensation issue as I have had to fix a lot of condensation issues in the house in the past due to old building design and lack of ventilation.

To avoid condensation issues I am going to see if it is feasible to have a separate insulated pipe system going from the heat pump to the loft space with suitable fan coil units installed and a divert valve fitted at the heat pump to direct the hot or cold flow accordingly. I can then run it during the cheap power hours so we can sleep better at night 🙂

All subject to me finding someone who can do the appropriate cooling calculations and approval from "the boss!" 😀