Mike

Well it looks like I may be choosing Crydom after all. After checking the wiring information for the Siemens units, only selected models are suitable for use with MCBs, and they can only be driven by 0-24V DC, or 4-30V DC (models ending -1DA06 & -1DA44; 3RF2330-1DA06 for example). Their other models require fuses, which aren't permitted in domestic installations...

Yes, the frames are a huge problem. You may, perhaps, be able to fix thin closed cell insulation tape to the inner face of the frame, but it may not look so good even if painted. The glazing itself would help, but may not be cost-effective, and you need to check that the hinges seem strong enough to take the extra weight, if you have opening lights. Personally I'd probably choose secondary glazing; depending on the window design you may be able to get something made up to align with the metal frame. And weatherstripping is definitely a good idea. I've seen silicone bead weatherstripping work reasonably well - where you extrude a silicone bead along the edge, put a bond breaker tape on it, shut the window while the silicone cures to a 'custom fitted' profile, then remove the tape.

@TerryE thanks again for your feedback - it's good to have someone looking over my shoulder and pointing out potential problems. Enclosures are still plastic on this side of the channel, so WiFi will probably work, however the Pro range of Shellys also have Ethernet ports, so I can hook up to that if it doesn't. The Pi and network switch will be in the (mandatory) Communications Cabinet directly below the consumer unit, so it would only need a couple of patch cables. Keeping the DoC to hand is certainly a good idea; I'd like the electrician and inspector to be as equally disinterested as yours was! The French system is stricter than Part P, in that no electrician can sign off their own work. On the other hand - if you live in a detached house and don't sell it for 10 years after certification (to sidestep other legal issues) - then it's still possible to do a complete DIY installation over here, provided it meets the standards and is signed off by the inspector.

Thanks for checking, and for the warning! Having read the Siemens datasheet more closely, the section on the control inputs does seem unclear to me - I've posted it below. There's a line for "control supply voltage 1 at AC" of 110 ... 230 V ; I had read that as meaning a voltage in that range switched it on - and a lower voltage off, which is as far as I'd got. There's also a line for "control supply voltage at AC... at 50 Hz full-scale value for signal<0> recognition" of 40V - meaning below 40V switches it off? And another "control supply voltage... at AC initial value for signal <1> detection" of 90 V - meaning over 90V switches it on? Are you able to add any illumination? I'm not used to analysing electronics specs in depth, as you may have spotted As for my intended voltages, I was planning to indirectly switch the SSRs at mains voltage. That is, I'm planning to use a Raspberry Pi + MQTT + NodeRed for control, but to switch a Shelly Pro 4PM, which outputs 230V to drive the SSRs. The Shelly's in there for a couple of reasons. Partly because it could be used to control the SSRs directly, either via the manual control buttons or the Shelly app, or its onboard access point (which also allows the setting up of weekly programmed schedules) - so a good fallback if there's ever a problem with the Pi. And also because it doesn't rely on a 'DIY solution', so I hope will not perturb the electrician or the inspector; being France all new installations have to be signed off by a national electrical inspectorate before they'll turn on the supply! In fact, it's slightly more complicated that the above. The Shelly will actually switch the SSRs via a load-shedder, which can temporarily shut down the SSRs & which also operates at 230V; in France your standing charge depends on the mains supply current that you subscribe to, so shedding the load from low-priority circuits at times of peak household demand has a short payback period, and flattens peak demand on the national grid. BTW, although I need 230V control, other Siemens models, such as the 3RF2330-1AA44, can apparently control using 4 to 30V DC (perhaps switching on at 4V and off at 1V, subject to the correct interpretation of their datasheet).

What's the reason for not just using a contactor?

Well after a few hours investigation, I'm inclined to specify a Siemens model instead - probably the 30A 3RF2330-1AA22 in my case - for a few reasons: It has a significantly bigger heat-sink At the planned loading it doesn't require additional space around it (though the 30A module is 45mm wide, thanks to the sink) The datasheets are clearer on the acceptable currents : 22A @ 40°C according for resistive loads (category AC-51 of IEC 60947-4-3) for the 30A version; 13.2A for the 20A version* Prices not too dissimilar to Crydom The range is certified for domestic use to IEC/EN 60335-1 (fairly certain I spotted only a reference to industrial applications for the Crydom models). *Siemens have an article discussing current specifications & the need for additional precautions in higher ambient temperatures for this range here.

On the question of durability, and looking at the thermal de-rate graph (below), while the 20A model has enough headroom to switch 3kW, I guess it may be worth paying the extra £10 to upgrade to the 30A version? Presumably it either handles the heat better, or generates less, as all models seem to have the same finned case.

Thanks - that's what I'd hoped! The fins were a clue that there may be a heat issue. The installation guide mentions that 'to achieve maximum ratings, there must be a minimum spacing of 0.8 in (20 mm) between the devices (horizontally) and of 3.15 in (80 mm) measured between DIN clip tabs (vertically)', so I was going to follow that. I'm planning this one in France so don't want to frighten the electrician (or the inspector who has to sign off the installation) with anything non-DIN rail, if I can avoid it

As SSRs I'd expect the Crydom CKR range to be quiet, however I can't spot any claims to them being 'silent' on the Sensata website, nor anyone having mentioned it here. It's perhaps more of a consideration for my project as they'll be sitting in a cabinet in the hallway, rather than a plant room... I know that a few of you have used them - well, @TerryE at least - so I'd be interested in your experience.

For deeper information, these may be of interest: The effects of bedroom air quality on sleep and next-day performance; Strøm-Tejsen, Peter ; Zukowska-Tejsen, Daria; Wargocki, Pawel; Wyon, David Peter Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: Allen, Joseph G., Piers MacNaughton, Usha Satish, Suresh Santanam, Jose Vallarino, and John D. Spengler.

Lack of oxygen isn't a problem, other than that it will be displaced by carbon monoxide in the blood if you have a carbon monoxide problem - possible if you cook with gas or have a fire. CO2, however, is a significant; research has shown that brain function & sleep quality decline as CO2 levels rise. Less than 700ppm is generally regarded as acceptable*, based on current knowledge. It's possible to control MVHR ventilation rate using a CO2 sensor, and that would be advisable rather than cutting the rate manually. Volatile Organic Compounds (VOCs) are also a concern. VOC levels are likely to be high for around the first 3 years of use, so better not to rely on CO2-based control during those first years - unless you have consciously built & furnished your home with low-VOC materials (see my post here) BTW, if you're in an urban area you may also need to filter your air to to remove outdoor pollution (particularly PM2.5 and NOx). *The recommended level for schools is 800ppm; it's concerning that many schools with monitors show CO2 levels >1500ppm - see https://www.nasuwt.org.uk/article-listing/survey-shows-government-failing-ventilation.html

Not online, but if you have a university nearby check if they have a printing service open to the public. Mine does, with excellent quality and unbeatable prices. .

Check your deeds - there may be provision for repairs I'd imagine that should be possible under the Party Wall Act, if you can get planning permission.

How about a 55" TV + virtual fireplace screensaver / video (which can come with a soundtrack too). Even better if you can raise it up and use it as a spare TV...

That's not a Building Regulations requirement for regular homes, though I wouldn't normally put them closer than that anyway. If you can plan far enough ahead, coordinate the positioning - vertically and horizontally - to suit your planned wall tiles (if you're planning to have any). For light switches, I always have them coincide with the axis of the door handle, where possible.