JohnMo

Wouldn't get to bogged down with that. If room temp is 20 and you have UFH, then your minimum return is not likely to be lower than house temp (assuming you have insulation under the screed etc). If you are operating a flow to return dT of 5 you minimum flow temp will be lower than 25. Most R290 will go down to 20, some may be limited to 25, but they are mostly R32.

I would try to find the engineering tables for various heat pumps, the minimum modulation figure is more important than the max output figure as your heating requirements are around half your design day for the average heating season day. Plus you will get an idea of expected CoP at you flow temps.

Isn't that the current situation in Scotland loads of wind, hydro etc, almost zero electric comes from gas, but unfortunately our pricing is driven by English policy. In fact SNP use that as a reason for independence.

Lots of panels on a G98 inverter, massive overclock is the way to go. Easy no permission needed, just a G98 notification. Self consumption is fine in theory, in practice difficult especially in the summer, you just end with loads of hot water you can't use. Just go with Octopus and pay £250 and get the export (wish I did it 3 years ago), East Suffolk you will generate tonnes of energy even with a 3.68kW export limits. My advise, self install as many panels as you can to stay within the max voltage limits of your inverter, it's cheap, spend £250 to get with octopus. Export everything you don't normally consume.

Umbrella route has been done by many. But everything is done via umbrella company with respect getting grants and paperwork, you do the work and report back, they may need to commission also. 9kW sounds big based on your other posts. If it's an R290 Grant, they don't do cooling. Have it confirmed from Grant technical.

If you are in the build stage and it's likely to see near freezing temperatures and the loops are being left water filled, yes. If no water in system yet, just pressure test with air and leave pressurised. But you could blow out the water and replace with air pressure if already water filled. If house is built and heating system in use, no point. But you do need corrosion inhibitors and biocide (from same company to ensure chemistry compatibility)

Be careful as it doesn't do cooling out the box, without a widget being added. Most will take a zero volt switch permissive to ask for heat/cool. If you want to do dew point control, plenty of simple thermostats will do do control for cooling, a Computherm Q20RF has everything built in for £65.

You're obviously had a bad day and need to get your own way.

Others will be along soon and tell you I don't know what I'm talking about. But having had UFH cooling for a few years plus a fan coil. I do have some actual experience. I would look for simple install, fan coils will compensate for over sizing by varying it's fan speed down (good, less drafts, less noise etc). So size fan coils for heating and then actually install one size bigger ones to allow for cooling. Then operate the system as a single zone on a single flow temp in cooling (16-17 degs) and WC for heating. This may not be perfect, but will give you a comfortable house year round and good performance (CoP and EER).

Sorry for applying real life experience of cooling v your theory. Room temp down 3 degs is huge for comfort, plus the actual house temp feels way cooler than that, as @jack says more like going into a cave. Passive design is best, but I actually prefer the views, so some active cooling is needed, plenty of solar pays the bills.

We got used to switching off the Aircon at bedtime and opening the windows and letting the 32 Deg near 100% humidity in (Singapore), better than the cold draft and head ache it caused. Extremely good (expensive) does get around this slightly, by adding humidity to the airflow and better control of airflow direction, but nothing I would invest in.

Who knows, still not really relevant to heat pumps currently being installed or installed in the last decade or more, they all had/have 4 way valves. If someone has a historic ASHP, that doesn't do refrigerant defrosts, good luck to them.

Article from 2012 discusses how a 4 way valve is used on a heat pump https://www.danfoss.com/en/service-and-support/case-stories/dcs/components-for-heat-pumps-part-5-four-way-reversing-valves/ Carrier started using them in production models in the 1970/80s. So for all purposes of this discussion, 4 way valves have been about for ever.

To support the above. An a2w heat pump is really a2a with a water heat exchanger added instead of a house internal fan coil. Cooling is a pretty simple concept for the actual heat pump, heating is quite complex, as you need to accommodate defrosting, hence the addition of the 4 way valve. ALL heating ASHP can do cooling, as they all have a functioning 4 way valve. Many manufacturers deploy ASHP without cooling controls or add the controls as an option extra. Interesting fact, my Hiaer heat pump comes with cooling out the box, but add a smart optimization system, cooling becomes no longer available - go figure.

Last year I automated mine via flow temp set point and stop start hysterisis, and ran circulation pump 24/7. Ran on a pure demand cycle. New heat pump won't be run that way, as 8 don't have the freedom change some of the parameters, now will have a room sensor doing the automation, so I get cooling whenever I need it, heat pump run on fixed flow temperature