Do you mean MVHR Des? If so it does work a treat, but no loft access available for the landlord in this case. If you mean something else what is it please as am curious..
I presumed there was a attic after reading his comment below,I did have a dry air unit in mind which would be mounted in the attic
I have fitted many of these units over the years and have had good feedback in all cases
quote(Not aware of trades accessing the loft space but the council's contractors are inspected the roof at the end of the month).
If he has no attic there is a unit designed by the company I use for the fans specific for flats but I have never installed one myself
Nuaire | Flatmaster - http://www.nuaire.co.uk/our-products/catalogue/residential/positive-input-ventilation-piv/flatmaster/