Not really that surprising, though, as we've had very efficient electric motors for around half a century or more. The efficiency gains in motors over the past 20 years have been quite modest, from around 88% to maybe 90 to 92%, not enough to make a significant difference.

Interestingly I've been looking at the fan efficiency problem recently, by modelling fan performance with airflow. If the fan diameter is increased, and the fan rpm reduced, then at the very low air flow speeds that are typical for an MVHR unit in "trickle" mode there is a significant efficiency gain. The snag is that when you increase the speed of a large diameter fan, to deal with the boost requirement, efficiency falls off.

There's certainly a case for looking at using big (as in around 300 to 500 mm diameter) fans, directly driven by BLDC motors (with neodymium magnets) for a whole house MVHR. The loss in efficiency during boost mode operation may well be compensated for by the increased efficiency in trickle mode.

One other thought I had was to use chimney effect to reduce fan power consumption. I know that it's been done before on commercial buildings, but I've been wondering if there might be enough residual buoyancy in exhaust air exiting a heat exchanger to still get an appreciable pull, assuming the outlets ducts were vertical.

Come off it, Ed. That's a scene from the TeleTubbies set, surely.

“MVHR development at a standstill?”

The only part of the referenced thread which could be said warrant that title is the point that brushless DC motors haven't improved much in efficiency but, as Jeremy says, they're pretty efficient anyway and that's only one aspect of MHRV anyway.

Viking House's FiWi is an interesting development. It could also be said that that adsorption thingy is an MHRV developement of sorts.

What's interesting to consider is what avenues for development exist. Efficiency, obviously: both at recovering energy from the outgoing air and reducing electrical power consumption. Quietness. Controls. Cost. Ease of installation (particularly for retrofits). What else?