I don't have MVHR but I do have an A2A ducted heat pump ( AKA aircon) shouldn't the flow and return volumes roughly match. If you have 2x return registers then your sums seem awry, I may have that wrong.
Like I said I don't have MVHR.

Much depends on the temperature of the air. At my work (hospital) people we blow in 18 degrees air, people in offices start to complain around the 20 l/s mark. Although much depends on the terminal design and the positioning of the small twizzly things. At home we have ASHP and the outdoor vents have approx 6 l/s - gets uncomfortable at around 4 degrees outdoor temp. 44 m3/h is 12 l/s - I don't think you'd notice anything, plus the air will get warmed up on its way down(?) to the living room, if I've understood correctly

And intumescent closure devices to prevent the spread of flame between rooms

Posted By: djhSorry, but under what circumstances are they necessary (or recommended)? Many people, including us, leave internal doors open or ajar.

My take would be where building regulations would require them. HMO's, public buildings, Care homes etc. Normal dwellings most unlikely but could depend on the size of rooms I think. I had a conversation with my BCO when I was running ventilation ducting from one ceiling void to another as to whether the ducting needed boxing in where it went from one room to another and he said rooms were too small to come under the regulation but I do not know what that size is. Think it is a sq M value.

* the Scottish Building Standards still requires self closing fire doors from living or bedrooms onto the stairwell, for 3 storey houses. And the rules are different about mhrv connecting to the stairway. IDK if it's always been different in Scotland.

Ventilation rates guidance is a mess! Occupancy is barely considered, l/s by number of bedrooms , floor area, then air changes per hour

Generally ventilation rates suggested are way too high. Flow rates through ducts and terminals can cause noise problems.

I think I should have said that I was looking for the air flow rate formula. Our MVHR is fitted and commissioned now but being a constantly cold person I'm finding the bedroom has a cold draught directed at me despite being super careful with supply valve location (will get another thread started on this).

I did find the air flow valves from the Passivhaus Trust Good Practice Guide MVHR for Single Dwellings https://www.passivhaustrust.org.uk/UserFiles/File/Technical%20Papers/2018%20MVHR%20Good%20Practice%20Guide%20rev%201.1.pdf

(2018 version)
Air flow rate per room

Each space should have mechanical ventilation; either supply, transfer or extract, room.
Supply —consideration should be given to the planned/likely use of spaces.
A good starting point for bedrooms is ~20m³/h for single rooms and ~30m³/hr for double rooms.

Extract air flow rates are sized based on moisture generation rates and thus are based on periods of moisture generation, i.e. air flow rates required for peak ventilation (fan speed 3) typical figures used for Passivhaus design are below, note that certification does not require compliance with these:

Kitchen 60 m³/h
Bathroom, utility room 40 m³/h
WC 20 m³/h