Glad of some advice on this one:

We are planning to put in a conservatory on the south side of the new house. I am worried about excessive solar gain and want to do some calculations on the energy we are likely to have to deal with.

Clearly there is scope to use the space for heat in the spring and autumn. In the winter it will be capable of being isolated if too cold, and in the summer I am expecting to need to provide some ventilation in there to keep it from cooking, but trying to get a handle on that is proving a bit hard!

The house to which this will be attached will be well insulated with a heat recovery/ventilation system. Air will be taken from the conservatory by the ventilation system, but I don't want to overwhelm it! The slab for the conservatory will be insulated underneath & I plan to zone it onto the underfloor heating from the heat pump. (We may well not use this zone if it will mean a nett energy loss)

The conservatory will be all glass with argon fill.

Anyway, the main thing at the moment is for me to get some sort of calculator that can help me get a grip on the energy I will be receiving.

Glad of a steer.

No technical guru, but we have a similar situation.
We have opted to turn the conservatory into a 'sun room' as a conservatory will be too hot in summer and too cold in winter, irrespective of type of glazing.
Why not put a solid insulated roof on it and optimise big windows for solar gain in the winter. With suitable shading you will avoid overheating in summer
Just wondering what would happen if your MVHR intake is in a conservatory. Surely in summer you will be pulling very warm air into the house ?
Heating a conservatory has been equated to physically burning £5 notes to provide heating - again irrespective of type of glazing.
If you do opt for a conservatory, as you say, you must be able to isolate it from the rest of the house to save loosing a lot of heat in the winter and gaining a lot of heat in the summer.
Conservatories are 180 deg. out of sinch with our requirements so think about it carefully.
That said it would be interesting to see some calculations on this issue.
Hope this helps.

Conservatories have horrendous heat losses and should not ever be heated by anything except the sun. They are part time living areas for occasional use as and when habitable. It is not green to heat them though it could be green to collect heat from them but totally uneconomic.

Don't do it.

Regarding the SAP and HRV design - I am working on some projects at the moment with conservatories (I do Part L(SAP) and Part F ventilation (HRV) and air tightness testing, so I aim to have some joined up thinking on this)

Key points:

As soon as you heat the conservatory your SAP rating will most likely fail.

Incorporating the HRV into the conservatory also links the conservatory into the conditioned air space and also means that it sould be included inthe SAP, irrespective of local heating.

If it is included then the air should be Supplied to this room, not extracted (as per Part F building regs for a living space).

The problem, generally, is that you will have too much heat in summer, too little in winter and find it difficult to use the heat available in Spring/Autumn.

Like the other comments above my default reply would be to build as a sun room, although is still substantialy glazed there will still be a big heat gain and loss
(At building reg levels 1m2 of glazing is approx 0.175m2 of wall and 0.08m2 of roof, in terms of heat loss!!!)

You may still need roof lights to provide borrowed light for rooms falling behind the conservatory, although these can have external roller shutters - good in summer and winter.

If HRV is extended to the conservatory I use variable flow rate grilles that give a low supply trickle and only open up fully if the temp is high enough (user defined) and maybe an occupancy sensor (etc). This will generate air flow into the house when there is usable heat and also provide adequate ventilation on a demand control basis. (there will need to be an air flow path to the main home).

In summer a dump extract is used to get rid of excess heat, again on a thermostat. Roof trickle vents (normally closed) can be opened to get rid of excess heat reducing the need for the fan under normal conditions. (The main HRV may also have a summer dump system working on an automatic night time cooling system)

Lastly - air tightness - for any solution to work as desinged then build as air tight as possible; it takes up no extra space and will be the biggest single improvement to heat loss/ gain you can do