Probably more exhaustive to just link to the manuals for the unit I have!

https://www.aereco.co.uk/wp-content/uploads/2019/09/TF4496_E_V4Apremium_display.pdf

The unit does have a connection to the outlets, but my understanding is it's just to power them (via 12v wiring). The outlets themselves are responsible for opening/closing with their own sensors - their is no communication between the outlets and the unit. It just relies on constant pressure - when the outlets open more, the unit can run faster.

I think that's important for simplicity and it's an elegant solution. It also means no batteries etc to maintain. The only thing I have to do is occasionally dust the outlets and annually clean the filter on the unit.

Not airtight 'enough' for MVHR, and it would involve more ducting. I only required a point solution for extract in wet rooms.

The outlets are in the kitchen and two bathrooms. The unit is in the loft. The unit extracts through a roof tile. Mostly solid ducting. Anything else you were wondering?

Regarding DJH comments on costs, it might be more useful to present the total cost of ownership, (including installation, filter changes and servicing) along with power consumption.

There used to be an interesting comparison on the Glidevale site comparing ownership costs for their iPSV with MVHR, MEV, and simple extractor fans. The costs for MVHR have been reduced due to grants, but taken broadly it still supports Dr Rickaby's larger assertions that simple, reliable (and cheap) is best for improving the lives of more people for longer.

Much as I'd like to buy into the church of MVHR, increasing household financial constraints, (and personal infirmities) lean me towards a system that provides healthy air without relying on a maintenance budget, (or continued ease of using grid electricity).

The original report might still be on the Glidevale site somewhere, the only place I can find a snippet is in the picture gallery for an article here:

https://www.house-builder.co.uk/products/companies/glidevale-building-products/glidevale-ipsv/

I also can't find Rickaby in print on the subject. You've prob already seen this layman-terms comparison from Aereco
https://www.aereco.co.uk/knowledge-centre/how-to-choose-between-a-humidity-controlled-mev-and-mvhr

In energy terms, "When the climate is temperate, the MVHR and the humidity sensitive MEV are almost equal."
Plus other comparisons on other criteria.

I should probably add that by 'healthy air', I meant good internal CO2 and moisture levels.

'Smart' trickle vents and moisture-detecting extraction is simple and effective.

Most Trickle vents are rubbish however, even the 'smart' ones don't do enough to properly seal the penetrations and reduce the thermal performance of the whole window frame even when the vents are shut.

With mine, I've sprayed foam into the frame to seal the window frame chambers before adding the vents. This means that outside air is only able to pass through the relatively small slots, rather than circulating all around the window frame.

<blockquote><cite>Posted By: sgt_woulds</cite>Passive House + magazine - but their search function is useless</blockquote>
True, it's wierd. I may go thro my back issues for Rickaby articles. 'Peter Rickaby in Passive House + Plus magazine' in DuckDuckGo got a lot more. But PH+ Search did produce
https://passivehouseplus.co.uk/articles/ventilation/thin-air?highlight=WyJtdmhyIiwibXZocnMiLCJtZXYiXQ==
with some interesting insights.

Hi Thomas,

Don't take it personally, neither Tom nor I are saying there is anything wrong with MVHR as a technology - it produces fantastic results and I'd love to buy a house with MVHR fitted - as long as the previous owner had absorbed the upfront installation costs :-)

Regarding maintenance, the examples you quote are not equivalent; phones update automatically, (until the manufacturer no longer supports the hardware and you are left with an unsecured device) so there is no need for user input. Hoovers stop working with a full bag, so users are 'forced' to change them. Cars require an MOT every year, skimping on servicing might mean a fail - so again, car users are forced to maintain them - although most do the bare minimum to scrape another year of mobility.

In terms of maintaining cars out of warranty, it is already hard to find OEM parts for some vehicles made 15 years ago and repro parts can be overpriced and of a quality that is downright dangerous. Luckily we still have a fairly good availability of parts from scrapped vehicles. This won't be the case for MEV or MVHR units.

My mum has a 35 year old boiler. It has failed on 2 occasions in the last 20 years and generic parts have been available to replace it off the shelf for less than £25.

My brother has an 11 year old combi boiler which has needed replacement parts almost every year of service. At the last visit the boiler man told him the control board he needed hadn't been made for two years and there were no NOS or repro parts available so the boiler needs replacing. Obsolescence is built-in to all modern products and we don't have any 'right to repair' laws to protect consumers from sharp practices.

They are both unusual because they have their boilers serviced under contract every year. Mum's next-door neighbours have the same boiler and only have work done when it goes wrong. I doubt she's had more than 4 call- outs in the same period. I imagine most owners with a humming box in the loft will pay just as little attention to it until it goes wrong.

So in 10 to 15 years customers with PIV, MEV, or MVHR will all likely face a bill for replacement units, but the MVHR owners will be left with a much larger hole in their wallet.

I agree the cost of heat vs replacement parts is cheap - unfortunately, I don't see a future where that changes.

So yes, I agree with Rickaby, for most people the important thing will be to have healthy indoor air quality - peeing away heat will always be cheaper and easier.

Sad, but true.

Posted By: sgt_woulds11 year old combi ... control board he needed hadn't been made for two years and there were no NOS or repro parts available so the boiler needs replacing

Just scrapped 8yr old Miele d/w and w m/c simultaneously, the w m/c for exactly that reason, the d/w because new pump would be £360. A firm in Sunderland claimed to repair control boards by return post, but failed after two attempts (lasted less than one cycle ea time). Miele f'crissake - superbly built, supposed to last forever, like a Mercedes. Which BTW our 23yr old 18mpg caravan-tractor does, parts available, at a price, prob no worse than any newer Merc parts.

Posted By: fostertomTrue - but a demand-controlled MEV will pull less air than a constant-rate MVHR when CO2/RH levels are low

Compare like-for-like. If the MEV has a humidity sensor, then include one with the MVHR too!

And lack of filtering is not a feature. Just as more dust and flies is not either.

Posted By: djhCompare like-for-like. If the MEV has a humidity sensor, then include one with the MVHR too!

I assumed any repectable MVHR would have one, but a different thing from the multiple humidity sensors of a demand-controlled MEV.

The latter adjust individual rooms' flow rate, from zero/nominal to 'BOOST' depending on ea room's instantaneous humidity (as proxy also for CO2). Nett flow over time is then alleged to be lower than a MVHR's, thus alleged less elecricity consumed. This room-by-room economy measure is vital to the case for demand-controlled MEV vs MVHR.

Whereas a MVHR, with or without a single humidity sensor in the mixed entry to the fan unit, must maintain a minimum flow that's adequate for the humidity/CO2 of the worst-case room, meaning wasteful for all the other rooms.

Fairer to say would be "If the MEV has individual room control by multiple humidity sensors, then include similar individual room control with the MVHR too!"

Not meaning to be adversarial - it's useful tho, bringing relative merits and differences to light.

With ventilation you need to get somebody who knows what they're doing to design a custom layout for your particular situation. IIRC we got a couple of designs done and one was OK so they got the business.

What's the situation in countries where good airtightness and mechanical ventilation have been around for a longer time? (I'm guessing places like Canada, Sweden, maybe Germany? et al)

i.e. Is our problem due to lack of exposure to such situations, as well as apparently poor workmanship either in construction or maintenance?

Posted By: VictorianecoIf only they did a 50mm radial ducting system that would be the easiest solution for retrofit

The problem with smaller diameter ventilation ducts is that you then require a faster flow speed to shift the same quantity of air. So most radial systems use 75 mm diamter. Even then we had to run two ducts in parallel to our kitchen extract point to get the required rate. Our ducts are 50 mm vertical and 100 mm wide.

BPC Advised:

By installing paired Single Room Heat Recovery units it is possible to provide cross flow ventilation through a room or rooms.
This utilised the principle of supply in one and exhaust out the other thereby providing a push/pull scenario of air movement.

The paired units operated for a period of time in one configuration before swapping to the opposite direction providing a constant change in air direction, air freshness and heat recovery.

With a property design utilising multiple Single Room Heat Recovery units, this should provide a full property ventilation solution and negate the requirement for natural ventilation methods such as wall passive vents and window vents (depending onfinal design and background ventilator reduction allowance to the calculations).