MikeSharp01

Can you not drop your kVa requirement to a smidge below the limit?

Useful info. I will havea play over the weekend. Is that a thing - Steamy will be along shortly, no doubt, with his cosh.

Why 28?

Let's hope someone here has some ideas for you as otherwise pragmatism rules and you will need to get that planning application in and start the process. You may just be able to amend your existing planning enough to encompass the requirements. As long as you can be confident you would get it out of the other end there is no reason not to carry on with the build and use a generator to supply power when needed to the site or perhaps your neighbour would allow a hefty extension lead to be run.

I get that but it assumes a static envelope if, using your analogy, the rugby ball is shape shifting as you measure the curve would work only when the ball hits the shape it was when you measured it. In my terms if I leave the windows open when it's cold outside the heat will be removed faster than you are making it up so the temperature will drop and once you close the windows the temperature difference will linger for a period which, in a well insulated building, could last a reasonable time. Obviously the reverse also applies so if you have a big party the house will overheat and stay overheated! Have I got that wrong? We do have a number of internal temperature sensors and via the BMS connection to the heat pump we should be able to adjust things if the Weather Compensation (WC) is not effective. On the whole I suspect when I get it all going that the edge cases I set out above, windows open and parties, will not be an issue but I do think it is important to stress test all the assumptions built into the accepted truth.

The heat pump is running, it has some teething problems but it works very effectively at warming the slab. The heat Meter (EMON Pi) is also up and running. So now I want to move on to setting up the Weather Compensation and see what happens. Looks like you choose a curve setting as best guess and then observe what goes on to fine tune. One thing I cannot see anywhere in the system we have is an internal temperature monitor the typical systems seem too open loop to me. I get the system does not use a thermostat but I don't get how it can get away without having some sort of measure of the internal temperature of the house because it doesn't know how the house is being used, what is coming in via the sun or indeed if the house is cooling or heating more than the output is providing for. Still the heating period has a few weeks to run yet and I want to make every day a school day learning how to heat the place so I guess I should just give it a go, any definitive advice as to the process I should follow.

Yes, sorry, tomorrow I will make a short video of what's going on, I wonder if the thump is happening out at the machine so I will check that as well.

Its a diverter not a mid position, this is what is on the invoice: "CE-ZVD28PW - 28mm 3 Port Diverter Valve" sorry for the misdirection.

I did have them almost wide open, little red floaty things as close the bottom of the dial as possible but I backed off the outer two in an attempt to balance the flows a bit as the middle loop is twice as long as the other two happy to leave it all wide open. Will experiment tomorrow.

No fault codes. I think so it is all 28mm, one clip at least every 500mm, more often usually inside, although not on the risers to the tank entry points albeit they are fixed at the top of course - can look at that and see if there is any flexing. Outside runs are clipped outside the insulation to cable trays with a flexi at the end to the heat pump. As to air I cannot be sure but there is a trap at the highest points of both the tank and UFH loops (see pic for UFH) and I bled the stubs that will be running to the fan coil units upstairs. (Although I could check those again now its been running for a bit.) Here is a pic of the valve and the UFH pipe work

Interesting thought and entirely plausible. Here is the basic circuit I used from the install manual - except that the Underfloor Heating (UFH) is where the buffer tank is as we have no buffer tank. This circuit makes sense this way round although I guess you could put the valve in the return junction. The valve is normally open to the UFH and the Heat Pump sends a signal to the valve to change over when Hot Water heating is called for. So the flow comes up the middle of the valve and goes out either to the UFH circuit or the Tank circuit. Hence as the valve closes, on the spring, to the tank circuit it will have the flow helping it close. If that is the cause of the thump then it's a control problem. Perhaps the Heat Pumps circulating pump should be shut down while the valve changes over although that would be a firmware issue in the controller?

Its controlled by the heat pump and its the valve that came with the heat pump - this one I think: The ZVM28

Been running the new heat pump today testing and commissioning the EMON heat meter. The heat meter is working well and telling me I get about 4.2 COP on heating the slab - with a cold slab at about 12oC. When I switch to heating the hot water the changeover happens smoothly and the heat meter starts reporting HW correctly BUT when I switch back at the end of the valve close we get an awful thump, I guess water hammer? Is this common and what might the / a cure be?

No we decided to get a new one, well two new ones, which I fitted yesterday. Yuk job.

Yes sorry name mix up. To much happening in my world. After 20 years of trouble free service a cistern in one of our bathrooms just cracked without provocation, not been used since Christmas, drowned the router in the stairwell below, left us with no Internet and water everywhere. Sadly its a Fired Earth unit so no guarantee possible- still as I say it has done 20 years.