JohnMo

My only gripe about MVHR is that you have a base flow rate and it can only upwards with a boost. When it does boost, it boosts across the whole house. There doesn't seem to be an automated lowering of duty point when humidity levels are low. Have seen on MEV systems they can have modulating extract terminals based humidity, the MEV unit is constant pressure controlled, so if the extract terminals close in because no one is home, making humidity, the unit almost stops. If the house is full of people showering ect the unit speed is increased as the terminals start to open. No idea why MVHR doesn't feature the same sort of logic, it's just a matter of running supply fan to match the extract duty, to keep the system in balance.

That was a good answer. It does demonstrate that following building regs ventilation flow rates does over ventilate, by quite a large margin. I think I need to turn my down my flow rates further. Currently at 0.3 ACH.

Often thought about UFH control. Most systems are controlled on flow temp via a mixing valve, and with with room thermostat(s). Most use a mechanic mixer, some use an electronic mixer. With an electronic mixer, there is normally a temperature of probe on the supply pipe - but could you just look at water return temperature and then modulate the flow into the system via the mixer. So run a set return temp and modulate the flow temp going in. My thoughts are, it may give faster warm up times. It may automatically compensates for how much heat given off by the floor; flow/return dT changes, as floor to room dT changes, shows up in the return temperature moving up or down, so could you have more stable temps? Anyone any thoughts?

Comparing with a humidity controlled MEV and humidity controlled inlet devices, so it only just ventilates enough, how does it compare? Trouble with MVHR is it runs 24/7/365 at a rate of 0.3 to 0.5 ach. Ventilation is whole living space, need it or not. If you didn't need the ventilation on, although recovering lost heat, it recovering need less lost heat.

PV, battery and ASHP can be a good combination, if the heat pump does cooling, summer cooling is free. In winter depending on the angle of the PV you can offset some running cost of the ASHP in the late part of Jan, Feb, March, Oct and early Nov. But paying someone to do it, even with grants, costs can stack up. You may be better concentrating on insulation and airtightness to reduce size of heat pump. MVHR for ventilation to reduce your ventilation heat loss and recover the otherwise lost heat.

You can still use the same principles of cascade with a normal MVHR unit.

Remove type 1, replace with soil or sand, form the deck with 3 to 4" posts, post-crete into the ground. A lot to be said for SuDS. Lots of hard landscaping no use for rising water levels and residential run off into rivers.

So although classed as a condensing boiler they are not really keen it being operated that way, with the advised baseline operating settings.

Just let your heat pump control look after temps, if you are using adaptive control.

Not sure you are understanding condensing mode correctly. An oil boiler goes into condensing mode when the return water temperature is below 47 deg. Condensing is when the water vapour in the exhaust stream is converted from water vapour to water, the heat exchanger basically collects the latent heat and increased efficiency. Nothing to do with cycling or not in hot or cold weather.

Bit of fine tuning over the last few days (still a little more to do, to optimise flow temps) have added a double set point to the heat pump. This is selectable by volt free contacts. Both high and low temperature run the same WC curve but start at different flow temperatures. Normal curve Start temp is 28 at 12 deg outside temp increasing to 32 degs at -9 High temp curve Start temp is 31 at 12 deg outside temp increasing to 35 degs at -9 So basic operation is the garden room has a thermostat, which is timed to call for heat about an hour or so before I need it hot. This opens the double set point contacts via the thermostat and brings the heat pump on to its higher operating curve, all other times it's on the lower operating curve. The house thermostat is set to 0.5 degs hotter than at the same time, and house floor then acts as a buffer. The heat pump runs continuously during this period except for defrosts. The fan coil is left in auto mode, with a target temp of 22. It was -5 overnight and has got up to 1 deg today, no issues with the fan coil room temp didn't drop below 20 degs was up to 22 this morning.

And most places you wish it was actually hot, most the time it's just cold.

If you have mixer taps no need for a TMV

Look at the price of an Ideal branded cylinder they are exactly the same, several hundred pounds cheaper

Your bathroom, reduce spacing to 150mm, you never have enough heat. I would be inclined to the kitchen area on 225 to 250mm centres. Dump the hall loop, use the loops transiting through the hall and borrow that heat. I do similar, my kitchen loop does the shower room first, then zig zags by the front door, then does the kitchen diner. Works well, do hottest area first. Operate as a single zone, electric towel rail in bathroom, that adds a second heating zone and keeps building regs happy as well. Unlikely your dT will work, you will be nearer 4 to 7 in reality.

I think you have a few options 1. MEV, but get one with that varied speed base on humidity with humidity activated extract terminal, not much cost increase over a fixed speed unit. Add to this humidity activated trickle vents. 2. dMEV as above, but no duct. 3. MVHR - Almost what you described but do not supply to study, supply as far away as possible so the air washes through as much of the house as possible. Look how FreshR and similar units are used to get an idea. A through wall fan can get air movement, a dry room blows into a wet room for example. As @Nickfromwales says you have to be careful, a leaky house and MVHR even though it recovers heat it's is constantly moving air that may not need to move. You have natural ventilation AND you have forced ventilation on top of that plus running costs of 2 fans running 24/7/365.

I started my Warrant process with ACJ, didn't finish the process with them we parted way.

The thing with a passivhaus the heating demand is very low, therefore the floor surface temp only needs to be about 2 or 3 degrees above room temperature. Correctly setup the system should self regulate. The floor output is a factor of area and dT between the floor surface temperature and room temperature. So if your room temp is 21 and the floor is 23. Once room hits 22 the floor output is halved, so it looks after without any outside influencers. Solar gain who cares the floor output drops to zero without any intervention.

If you are running a weather comp curve, you just need to actively make sure on different temp days you are not running too hot or cold and make tweeks to the curve to fine tune. You really shouldn't be bouncing off thermostats ever. If you do your flow temp is too high. Our house isn't passive, possibly about 50% more heat demand due to form factor and some massive windows, our house will stay very stable down to zero degs just running the ASHP at around 30 and mixing down to 28 degs. So 38 was possibly way to high. For context the 8 degs possibly represents about 3-400W extra power while the heat pump is running, compared to 30 flow temp.

I parted ways, it really was just as quick to start from scratch, get all the changes you want done dealt with at the same time. Nothing is quick with architects even if everything is handed to them on a plate, plus they will charge you just as much.

When you get to low outputs (less than about 20W/m2) it make almost no difference to flow temp. We have 300mm spacing in a non-Passivhaus (around 600m pipe in a 195m2 slab), it was -5 last night and doing a batch charge our flow temp didn't go above 33 the house is at 20 degs and garden room is at 21. If I set my flow temp at or below 28 deg, it means my heating is effectively off, as there is 8 deg restart hysteresis from set point to restart after a heating cycle, so the house floor would have to drop to 20 degs to allow the heat pump to start, that just never happens, as that is below the house temp. Practically gets in the way, unless you want to install a buffer to draw heat from, but the heat runs hotter to charge the buffer. Never understood, why anyone needs 100mm pipe spacing unless the house leaks heat like seize. Installer may strive to get 100mm spacing but to what gain in a low heating requirement house or Passivhaus.

Why - are they too wide or too narrow a spacing?

Fill it with cold water and circulate through the floor?

As above, the probe needs to be in the bottom probe pocket. You are only heating about 50L in the tank