JohnMo

What you are seeing is fine, in fact very good.

Good to see, you will find your gas consumption drop considerably. Mine did similar to you first and second graphs, then closer to your final graph, gas consumption dropped by around 30%

You need to take account of running costs (electric) and filters also, for the complete cost saving.

Not completely correct. They actually state NOTE: Installing thermostatic room controls may not be technically feasible in some cases. These may include the following. a. Dwellings with very low heat demand (e.g. less than 10W/m2). b. Dwelling with buffer zones for heat absorption or dissipation with high thermal mass. The regs don't define b. in any details, so thick screed UFH could comply and not require room thermostats 5.21 It may be justified to control a heating zone rather than individual rooms in either of the following cases. a. In single-storey open-plan dwellings in which the living area is greater than 70% of the total floor area. In such cases, the dwelling should be considered as a single heating zone. b. Where two adjacent rooms have a similar function and heating requirements (e.g. kitchen and utility room). In such cases, the adjacent rooms should be considered as a single heating zone.

Confused, what are you saying? I used fibre reinforced concrete, mine was installed before the walls went up.

So does the law, I believe

Possibly due to shrinkage cracks? If they say don't exceed and you do and something is not right after, they will just say you exceeded the max depth, the problem is yours to sort out.

I have seen a lot of telegraph articles come up on the news feeds all seem biased against heat pumps, and a lot of miss information like they cost lots to service etc.

Our floor is 200mm PIR, 100mm concrete screed. UFH pipes at 300mm centres. Running low flow temp (about 32 at -3). Slow reaction time to heat inputs, long release of heat after heating turned off. You have to be careful with flow temps, to little heat up time takes forever, to much heat you overheat the house. House has a nice feel as no real heat occurs in the house, think that comes from the low flow / floor temp. Either batch heat or low and slow with thick screed. Thinner the screed the more like a radiator it becomes from I can gather. The thinner the insulation the higher the flow temp required. So if you are going heat pump now or in the future, add more insulation at that depth use 150mm PIR.

Not sure that is entirely true. The principles of plumbing are just the same no matter what the heat source. What is important is the rules of thumb everyone seems to use, should not be used on heat pumps, but that is also equally true for any low temperature heating system, no matter the heat source. My heat pump install is just unplug the gas boiler plug in the heat pump, because it was designed from scratch to use a gas boiler at the lowest possibly temperature, to promote as much condensing as possible. The only real difference is a heat pump system is always designed to be a low temperature heating system and will always be one. The warmer the flow temperature the larger the cost to run. The issue with large drafty poorly insulated properties is the radiators have to be huge to use really low flow temps, so big that it's not really practical, so a compromise size is used and higher flow temp, CoP drops, costs go up beyond what you pay for gas. The press say heat pumps are rubbish, manufacturer get a bad name...blah, blah..

Try setting the ch part load to minimum and see what it does.

It on the return leg which good

That is why you have a large coil in your cylinder, the cylinder becomes the engaged volume. You don't need a volumiser or buffer on the DHW side of the system. It is normal to have a buffer on the central heating side of the 3 way valve. I think I have added the CO2 manual for you. Chofu-Operating-Installation-Manual.pdf

No just have a well insulated floor and house job sorted. My floor is currently 22 deg, room is 23 degrees from solar gain, floor therefore absorbs heat instead of outputting heat - no digging required. Just design right before you start.

To give you an idea of the process I used to design my system. My 6kW heat pump is located 10m from the house. Have run 28mm from HP to house (10m each way), then dropped to 22mm inside house (500mm), short run to a 22mm 3 way valve, then 500mm to UFH manifold. Not using mixing valve and pump on UFH (many will not like that). From the 3-way valve to cylinder is a further 10m and is already existing in plastic 22mm, so my pressure drop is at the end of that allowable for the ASHP circulation pump, so have installed a second pump on the return leg to run only in DHW heating mode. This will be run at a constant volume flow. I downloaded pressure drop charts for the different pipes, bends and calculated the system pressure drops to make sure I was ok on the curve for the flow required. You need a buffer if the smallest possible open circuit volume is below the minimum volume specified within the manual. The more you are over this volume the better. I will have over 60l circuit size, so will not use a buffer. My Manifold will have no actuators on it so will always be open. I would if you can, keep it simple Try not to keep it simple. Generally keep it as simple as possible, if you only have UFH and no radiators just run on weather compensation.

You need to stay on the correct side of allowing air in for combustion, otherwise its a path for trouble etc... If you really want to make a difference, you may need to dump those appliances that use room air, as this air needs to come from somewhere

Or they would be termed as loops not zones. The zone would be how a single or group of loops are controlled. Zoning Per regs Heating zone - A conditioned area of a building which is on a single floor and has the same thermal characteristics and temperature control requirements throughout. There are plenty of get out clauses within the regs on how you zone or don't. Even not installing room thermostats is allowed. High thermal mass (so lots of UFH systems), heat demand below 10W/m2, these don't need thermostats. Floor area below 150m2 can a single zone. But you basically need a zone per floor, which makes sense. Your room thermostats if needed don't have to control temp they can be limit stops, nothing is explicitly stated.

Look at d.43 Heat curve. Mentioned on page 42 of the installer manual. I reduced my setting (Atag boiler) and it made a big difference. Sorry called it ramp rate, instead of heating curve. Here is background reading https://tech-controllers.com/blog/heating-curve---what-is-it-and-how-to-set-it

How much of the heating system is open, all of it or just a room. To me it looks like it's short cycling after a decent run time. A short period ramping up temperature, then off time locked out repeat. You need to bring the flow temp down so your return is as far below 53 deg as you can to promote condensing and improve efficiency. Either make sure all your system is engaged, and or look at the installer manual and find out if you can change the ramp rate, this is the rate the boiler adds temperature, you may be able to slow this down, so you get a longer run time by slowing or extending the time it takes to 65 deg.

You need to find and download the technical manual for the heat pump, these are normally available but hard to find

Follow what your structural engineering drawings show, don't make it up as go along. If you don't have structural drawings get them and then ask the structural engineer why he has specified what he has. Who are most people, mine is nothing like you suggest, but exactly as your drawings show.

That's a good cylinder design, you have, that possibly explains why there is always stratification in your buffer. It's a pity they are not all designed that way. Most are designed with a compression fitting swaged or brazed to the cylinder shell and nothing to actively promote stratification, just an empty cylinder full off water swirling and sloshing about. Cannot measure my temps as I am away for a few days. But I have a 2 port design with oversized tees to give hydraulic sepereration. Mine is on a low flow temp gas boiler at present. When the heat pump is installed there will be no buffer.

Your inlet outlet temp for flow and return? Your flow in-out should be the same temperature, if working as you describe if no mixing is occurring. So your temps are?

My twin wall flue is packed with rock wool at the suggestion of the installer, that's how they always do it.

My 160 litre buffer is almost alway not stratified unless the heating is off - your evidence is...?