JohnMo

The diagram shows the boiler control stat is set at 75. But is yours set at 65? The trouble could be the temperature is set too low at 65. So when the UFH calls for heat, the temperature in the cylinder just drops too quickly (not enough capacity in the cylinder at 65) and the boiler cannot keep up, when the temperature drops to far.

If you start over compensating things, things start to get bigger, a heat pump that's oversized is not a happy thing. You will start to need bigger and bigger buffer, to keep it happy. The power required gets bigger, more generator run time. A 12kW heat pump will need a flow rate close to 1.7m3/h to stop short cycling. Why not go a hybrid solution for heat and DHW. Heat pump size and use to use down to about 5 degs, then let the other boiler take over. If there is only four in the house, you would be reheating 300 lts of water, if you used 75l each, you seem to be sizing for 6 people.

That's not entirely true. They condense once the return is at or below 54deg. It is nothing to do with margin between supply and return. The further the return temp is below 54 the more condensing that occurs, which increases efficiency. Also on the UFH heating the output from the floor is based on the mean temperature (mid point temp between flow and return). So a big difference between flow and return (assuming the same flow temperature) the lower the floor output.

Sounds like the designers are very lazy and not doing the job they should. Maybe avoid. Quick question are you sure your coldest day never goes below zero? Jeremy spreadsheet shows slightly lower than SAP (for me), so may be worth looking at your SAP report also. You need to basically size for your coldest day, with no solar gain. Plus you need an allowance for DHW heating. But if your having an oil/biomass boiler it may make sense to run a smaller heat pump for heating only and leave the oil/bio and solar to sort out the DHW. That way you get away with something like 5-6kW heat pump. The benifit of a smaller heat pump is no buffer likely and it energy use will be low and you make use of running on solar in the summer for cooling

Can I ask why you are trying to set the delta at 15?

No not really. They are set for 4 degs delta T below 30 deg and 7 above.

If your needing heating you should be looking at way more insulation. I am in NE Scotland and our house is at around 21 with no heating on. Couple of questions how long is the heat pump running, is it going on and off a lot? How many zones do you have and how many are calling for heat?

Could you have a 'store' instead of playroom? A storage room needs no light or heat.

We used Cameron Ross, they seem to cover most of Scotland. Worth a call. Our architect did out percolation test. You may need a small digger on site for digging the holes required.

We got quotes for uPVC windows, I suggested to the wife we look at them before committing to buy. She not like, so went for wooden framed at more than double the cost. But they do look really good

Because 5.12kW is bigger than 16A, so was G99 scheme, not G98.

No I think my use of words are correct. You are not separating cooling systems, you are separating multiple pumps from interaction with each other.

You are correct, my typo

hope the homely thermostat isn't as clunky and slow to load as their website. Doesn't fill you confidence.

You could run you piping to the rads and use two close coupled tees on the return line to supply the UFH. So the return water out of the rads if no UFH is on would flow direct back to the UFH. If UFH is on, water would be borrowed from the return via the first tee, then after flowing through the UFH would return to the radiator return via the second tee. Using the close couple tee there is hydraulic separation, between to boiler pump and the ufh pump. You will need to find the min flow rate and system capacity for heat pump and make sure the system is big enough and there is enough flow Run the whole lot as a single zone, will keep the system from short cycling.

G98 is after the event, not before, permission is pre granted up to 16A per phase. G99 is prior to install, as you are seeking permission as the array is bigger than 16A

I also did my own also, did the trays, pre ran all the cables in conduit, mounted isolation switches, inverter, electoral guy did the rest and signed the G98 form. Mine is 3.1kW, just over £2.5k for everything. Electrical costs lost in the new house wiring costs. I think only the battery can go into island mode, PV cannot, not sure how legitimate be artery islanding is within G98/99 rules. Not sure of the maths of batteries yet. I self consume everything the PV gives me, via a diverter to heat hot water. Battery no use to me.

How do you manage to use 50kWh a day of electricity with a gas boiler. And export 25% of electricity generated. We're averaged around 9kWh of electricity and 2kWh of gas over the last month, we are home 24/7. With 3.1kW PV

Obviously a good at energy saving, possibly not that good on money saving

Good job you don't use a kettle for making an espresso! We would be well out of pocket, wasting all that hot water heating. Buy a coffee making for £200 to save 1p on every espresso

I would discuss with a structural engineer first. You need to ensure the existing building and foundation are suitable for the additional weight.

Basically yes, but that's the logic they are using. Somewhat not in touch with reality. But the butler makes the tea, so why would they know any different.

Reading the thread that mentioned "Which". An old kettle had the element exposed to the water, so you had to put a minimum amount of water into the kettle. Modern kettles have the elements away from the water so you have no minimum water level. So based on only putting the minimum water in the kettle, and comparing an old design to new kettle, the new kettle will use less kWh per year, as it is required to boil less water. So is more efficient in it use of energy. Not much use for most people as they just fill the kettle up, then boil it, same amount of water for 1 cup or 6 cups of tea.

We had this during the build, when ever the tilers were here, the electrics would keep tripping. The transformer they were using was good for the skip as it had an internal issue.

eBay item 354231297695 is the 3kW, they do a 5kW and bigger ones also. They do an inverter one also, which controlled via an App. You get a better price if you call them.