JohnMo

As I said if the oscillating is on the house side the ASHP circulation pump is not related to the issue, the buffer hydraulically separates the two sides of the system. Why not switch off all the pumps on the house side of the buffer and revert the ASHP back to it's original settings. That should leave one pump running (?) and nothing else. If the issue goes away or remains, you know which side of the buffer is the issue is coming from.

Are you sure you don't have a mid point valve/actuator instead of a diverter?

@rhymecheat You have two sides of the buffer, each side has hydraulic seperation. If you have oscillations of the house side of the buffer it's not related to the ASHP circulation pump, only the house side pumps. Switch you UFH off, does the oscillating stop?

Gledhill data as I had on the computer for heat pump cylinder, reheat time given for two flow temps So for a 210L cylinder at 80 degree flow, reheat time is 17 mins or with 55 flow 17 mins. A standard boiler cylinder from Gledhill is 32 mins reheat time at 80 degree flow.

No ideas to your questions, but the way you run the ASHP has a huge impact on the energy consumption and costs, small changes seem to go a long way. Not letting your house get too cool for one, then just setting the flow temp to drip feeds to keep with the heat losses.

Lot of pumps. Change to constant speed, lowest speed you can get away with and not have flow drop of the flow meters. If you only have UFH the pump after the buffer is possibly not needed as the UFH will draw from the buffer itself. One oscillation time period, it will either oscillate or or won't.

Definitely sounds like you have two pumps not hydraulically separated and both set to modulate. Both end up chasing their tails. Would suggest the one controlled by the heat pump is left in modulation mode the other (UFH) set to a fix duty point at the lowest speed you can. The UFH dT is set via flow meter on each loop, not by pump speed variation. If you want a set dT install Salus self balancing actuators, but leave the UFH pump set to a fixed speed.

Do yourself a favour and go onto heat geek site and read up on legionnaires, if you consume all your hot water daily there is zero point doing the cycle. If it's vented cylinder you are going to have bigger losses as you have a vertical pipe out the top of the cylinder. Insulate with 25mm wall thickness foam. As a side note - Insulation with gaps isn't any good. So make sure the mitred ends match up with the next piece and tape all the joints nice and tight together, along the length and at the corners - use electric insulating tape. Take the insulation a good couple of meters away from the cylinder. Go to a plumbers merchants they do 2m lengths. Use 19 or 25mm wall thickness at valves or compression joints use 35x9 insulation.

Look at the cylinder datasheet it should have that information. You need to look at the boiler manual not the cylinder manual. X plan uses a 3 port diverter, S and Y use either mid point valve and a two port or two 2 ports valves. Cheap boilers maybe don't do X plan, this is an Intergas wiring for X plan. X-Plan-diagram-Rapid-HRE-Eco-RF-low-voltage-option-V1.pdf And an Atag boiler all the connections are within the boiler Last thing you want to do is run hot water in 28mm, as it will never get to the taps. Mine comes out the top of the cylinder in 22mm, goes into a tee and is reduced to 15mm (Hep2O), one side goes to the kitchen and the other side to a manifold and then to shower room, 2x ensuites and a utility room.

Pressure drop calculation takes the worst case duct, not all the ducts added together. So when calculating all the shorter lengths you can ignore, the longer lengths you calculate and take the worst one - that is is your pressure drop. So you do during commissioning the longest run the terminal stays fully open and you adjust the shorter duct pressure drops with the adjustable terminal to get the flow you need.

I used 4" posts with a 45 deg support on each post. All post-creted in place. Then unistrut horizontal to mount the panels to. Had 70 mph winds the other day and few other storms - no issues so far.

Have a 45 degree array on house also, but it is generally generating 1/3 or less the vertical generation, at this time of year.

Last 7 days generation, generation to grid actually goes into hot water. On cold frosty morning

Did 9kWh the other day from my vertical panels. Well pleased. Was just generating 3.2kW between the clouds, but wife has dishwasher and washing machine on, so that's all disappearing very quickly.

Forgot to mention at the moment we are doing hot water via immersion during cheap rate as a trial for a few days, while I get the weather compensation curve setup. Found there is quite a delay restarting CH mode after DHW mode, while everything cools down from 50+ to low 20s to enable restarting CH mode.

We also have UFH in the main part of the house, the fan coil is in a summer house we always keep hot. UFH used as a big buffer. I would normally batch charge the floor in the house on cheap rate, but doing that we had issues with the fan coil and heat pump short cycling during the day, fan coil stopped heating effectively. So have reset back to weather compensation running 24/7. For this to work we have set the WC to match the fan coil (10 degs OAT 31, -6 OAT 36) and use an electronic ESBE mixer for the UFH in the house. ESBE mixer can run two different temperatures (T and T2) via a volt free contact. Our house thermostat moves the control point between T and T2, depending if the house is above or below 20 degs. T is set for a fixed flow temperature of 28 deg and T2 set to 36 so it takes whatever flow temp is available from the heat pump. So above 20 in house, fixed flow temp, below 20 variable flow temp (based WC curve) Today it's 7 degs OAT, flow temp is about 31.5 from ASHP, house mixer about 80 to 90% open flowing 28 degs, heat pump is cycling 30 mins on, 30 mins off. During an off cycle the flow temperature drops to about 23 degs before the heat pump restarts, so mean temperature is just below 30.

Oil boiler, stick in a thermal store, draw UFH from that via pump and mixer. You can have as many or few zones as you wish. But smart controls with UFH are a waste of money. So keep it simple. Oil boiler happy with a thermal store, as it can run for as long as needed and will nit short cycle. But the thermal store needs to larger than UVC, also get one with a decent size DHW coil or heat exchanger, so you don't need to run the TS really hot.

One thing I have noticed with our fan coil for heating, is if the heat pump switches off for a period of time, or is doing hot water, the room temps drop, as the fan keeps going and start active cooling. You need a buffer really, which is in effect kept hot by the heat pump, so the fan coil can have a steady stream of similar temperature water and is not affected by any off periods of the HP.

Couple questions buffer yes/no Weather compensation yes/no When you measured the dT of 2 was the heat pump on an on cycle, just starting or just stopping? You don't normally have any control dT, as it's managed by the heat pump. Why would you need it?

Scottish Water have testing facilities in most bigger towns. Our was tested in Elgin. Your local council web site should have details.

Just been back through the email trail and the data came directly from the glass supplier

If it's a building regs job and council is checking, then yes, otherwise all depends, are you competent?

Agree it lets you add ACH figure, but not a direct airtightness figure. If you were ventilating at 0.5ACH with MVHR, you add that figure and the efficiency of the MVHR. The spreadsheet assumes you are pretty much airtight and well insulated. If you know a target airtightness you can say add 10% of your airtight figure to the ach and drop the MVHR efficiency slightly. But if your airtightness is 3 or below, and you are using MVHR it's good enough as is - nothings exactly correct, but better than a ballpark away.

Sorry no clue, the window supplies provided the information to our structural engineer and I was copied on the email.

We are in a high wind area and all our windows were subject to structural approval. Take a look at the allowable deflection - quite surprising