JohnMo

You would need an overall COP of 4 to be on running cost. Gas 7p electric 30p per kWh

That could be the case. They may be charging extra for inverter heat pumps, which in reality have little turndown capabilities. It's strange that every gas boiler has these figures on the datasheet and in the advertising blurb.

You would, but as you will see on this forum plenty don't?

If you are having to install two boilers you really do need to look the thermal properties of the building. Or rerun the heat calculations. If you are installing MVHR you are obviously taking airtightness seriously (or hope so), so I assume you have thought about the insulation also. Even though your building is massive, just over three times our build, we could still heat it with the gas boiler installed in our house. If your heat loss at -3 degC is more than 10kW you need to work on insulation, windows etc.

You could and just run from one thermostat and also run weather compensation.

I will bow out, way to much effort being spent discussing the thermal properties of books and book shelves. No idea what that has to do ASHP or solar thermal.

That's where you need to get creative and join different circuits in to one or two zones, to keep the system capacity large enough to keep the buffer size manageable.

There is a heat loss calculator in the boffins corner on this forum. Volumiser and buffer are the same thing. Here is how you work out if you need one. You need to calculate your system volume for a start, also you need to know the turn down of the heat pump. Example 12kW nominal inverter controlled heat pump unit (at 7oC ambient and 35oC water flow) can provide an output of 4kW at maximum turndown (minimum output) at an ambient of 12oC and weather compensated flow temperature of 30oC. What is the minimum water content to ensure cycling does not exceed six starts per hour? Assume acceptable temperature drop of fluid is 5oC and the fluid has a SHC of 4 [kJ/oC kg] because it has antifreeze in it (normally 4.18[kJ/oC kg]) Total heat energy required: 4 [kW = kJ/s x 60/6] [minutes/number]x 60 [secs/min] = 2,400 [kJ] Mass of water required [kg] = 2400 [kJ]/(4 [kJ/oC kg] x 5 [oC] = 120 [kg] Assume 1 kg of water = 1 litre, therefore 120 litres required. Now compare to the capacity of your system, if system is bigger no buffer required, if smaller buffer required, size required is the difference between the two volumes

I missed looking at the previous link. That explains why I was missing something.

If too noisy just install a second one. As a matter of interest how is air being allowed in the office replace the air removed. Is natural leakage through the building fabric or a vent?

MEV correct. dMEV decentralised. Fan in each wet room. Both uses cross flow ventilation through dry rooms, to wet rooms need a ventilator (can be trickle vent or a controlled opening in the wall. Condition based system will open the vent as required only. Stuffy rooms are a good indication that the CO2 levels may be higher than ideal.

Not a single drop of screed in our house. floor build up is 160mm reinforced concrete, 200mm PIR, 100mm fibre reinforced concrete power floated. Tile, Oak and carpets in top of that. We have UFH but don't see why that would make any difference. Where areas were not level enough used self levelling compound.

Noticed you posted in ventilation with heat recovery. The maths work against heat recovery with leaky houses as cost to install isn't proportional to the heat recovery when all other ventilation heat loss is considered Bottom line is if you are getting condensation, you need better ventilation. Condition based MEV or dMEV is worth looking into, way simpler and cheaper to install and will only ventilate when it's required. Some light reading on the merits or otherwise of different systems Atamate_SDAR+Paper+2019+(1).pdf

Not sure if you are improving the insulation of the house. If you are the existing radiators would require less output, so the reduced temperature output of the heat pump, may work. Solar thermal, most people will heat domestic hot water, hence the throw away term, one trick pony. But there is no reason it cannot contribute to heating in the shoulder months also. In fact it's yield at lower heating temperature should be better, than high temp DHW. A drain back system for instance is very simple, it is not pressurised, it has a small vessel (10L) a small pump and a simple differential temperature controller and 2 or 3 temperature probes. Oversize the system for winter performance, to displace some winter heating, most shoulder months heating and all DHW for 60% of the year. When the system has done it job it drains the thermal panels, leaving no water in the panel to overheat or possibly freeze. Your light simulations, watch for the low sun in September/October and March/April which can lead to room over heating.

I just went spray foam 256mm posi- rafter counter battened inside with 2x 50mm battens and full filled with 350mm foam. Vapour control airtight layer, further 50mm battens as service void then plasterboard. We have a large section of 12 degree roof and the normal (ish) 45 degree. 12 degree, outside rafter is covered with 18mm external ply and breather membrane, then Sarnafil standing seam, 45 degree 22mm sarking boards and breather membrane then slates

Your supplier will have to go back to the manufacturer and the manufacturer should be able to issue a certificate. Supplier is being lazy. Your lucky, we had a wind loading of 1.07kN/m requirement. So had to get structural engineering approval, prior to purchase. We ended up with triple glazed with each pane being 6mm thick toughened glass.

But the document referenced is mentioning leaky anything.

Our living room is airtight and has MVHR, the ACH is set at 0.5, even with 6 people in the lounge for several hours the ppm CO2 stays below 1000.

Still really confused why you need that many ACH for an office. From the text above the table it is referring to intermittent rates, not continuous. If you read the last sentence on the sheet. "total extract airflow rate during normal operation of a continuous mechanical ventilator eg. MultiVent etc, should be 0.3 l/s/m2. This is based on the whole dwelling volume, with provision to increase the inlet volume, as required, in moisture generation areas. A quick calc on a room with a ceiling height of 2.4m gives an ACH of around 0.3.

You can pick up solar thermal for a good price if you look around, as it's gone out of favour with PV getting cheaper in recent years. Another option is PV, two ways to do that, normal grid connected with a diverter to immersion not that good for hot water except in summer. The other is to use PV for direct water heating. You can use DC from the panel to an MPPT tracker then to the immersion. Or direct to immersion, but have to careful matching everything up.

Every day's a learning day

Alway thought it was the doors never shut properly (or other customers couldn't be bothered closing doors behind them) and the owners refused to heat place.

Why would you need 6 to 8 air changes per hour. With an airtight house you are looking at 0.3 or 0.5 to comply with building regs (depending on which part of the UK you live). Normal housing stock my leak at the rate you quote at 50 Pa, but that is equivalent to the leakage rate in a howling gale in normal terms.

By direct charge I was referring to heating the contents of the store directly, instead of by heat exchanger (coil or plate heat exchanger).

But does what you are proposing comply with the interlinked requirements. Are making it more complicated than it needs to be, with more points of failure? Shouldn't you really have a sounder at each detection point? Do you need a UPS (backup battery) to manage the system you are proposing? What happens if there is a fire and mains breaker trips? A normal install, each unit has its own battery, so it doesn't care if the power trips. It makes a loud noise at source of the fire and every other detection point. Simple.