MVHR
The MVHR (Mechanical Ventilation & Heat Recovery) seems to be working well and silently. The automatic programme works continuously and is currently set with fan speed 2 at night and 1 during the day, these can be altered to suit occupation A temporary 'boost' fan speed 3, can be switched on when cooking or after the shower is used to purge spaces of smells or excessive humidity and operates for a set period - currently 45mins, via a bell-push switch in the kitchen.
 |
| Spot the typo |
Filters
The frequency of filter changes (recommended between 3 - 12 months) depends on several factors; intensity of use of ventilation system and amount of internal and external contaminants. The purpose of filtering is to remove airbourne contaminants from entering the dwelling; fumes, dust, pollen etc. and most importantly to protect the very low power fans from clogging up.
I read that an MVHR user had installed a power meter to measure watts used by fans to help determine when to change filters that are quite expensive (3 filters @about £12 each).
I installed a meter measuring power in watts, but the increased consumption hardly registers. The fans are constant volume so as the filters become blocked the fans work a little harder to move the same volume of air. We are now approaching 1 year of occupation so I have changed filters. The main filter that protects the frost heater was pretty dirty, fairly black from city pollutants.
Insulation
It is very important to insulate the incoming and outgoing ducts to avoid condensation which would form if warm humid air inside came into contact with steel ducts that could be approaching freezing temperatures.
The MVHR system is provided with a heater battery (contained in the dark grey square polystyrene box), to warm air during very cold periods and a condensation drain in the MVHR fan unit.
The original insulation installed around the incoming ducts was an incorrect specification, (foil covered mineral wool) and the insulation was not in contact with the external wall insulation. For some reason the correct Armaflex insulation went missing towards the end of the contract, so I elected to install the replacement materials myself.
I stripped off the MDF patris around outgoing ducts and found that the holes through outer walls were a bit hit and miss and were not sealed airtight, or fully insulated.
Externally some 'making good' was required around ducts and fortunately I was able to get a sufficient offcut of the insulation board. The voids were neatened up, and tight-fit infill pieces cut on the bandsaw and finished with expanding foam. The external aluminium grilles were relying on friction fit so I made some birch ply panels and drilled the grilles to secure them. |
| Insulation repaired |
 |
| External duct inlet |
 |
| Cutting insulation from template on bandsaw |
Internally I made some thin birch ply surrounds, close fitting around ducts to give support and close the gaps around OSB.
Plasterboard damage was repaired, missing Rockwool insulation replaced and enlarged holes cut by hand around duct and silencer. These holes were cut 60mm larger than ducts to allow the total thickness of 50mm Armaflex to be in close contact with the wall structure.
Walls were filled and plasterboard re-painted.
Ductwork was reassembled, with addition of a small shelf to support the frost heater. Armaflex, a lightweight and flexible insulating foam with a skinned surface, was added in two 25mm thicknesses.
 |
| Cutting schedule |
Armaflex is fairly easy to work with with a sharp kitchen knife and careful measurement, although the surface is pretty fragile and snags quite easily with finger nails for example.
I did spend some time plotting out how each section was to be cut to ensure I had enough material and reduce wastage.
 |
| Printed pattern transferred to cardboard template |
The corners are made by using 90º or 45º templates transferred onto cardboard and gluing 2 sections together to make pre-formed corners.
All butt joints are made using a very runny contact adhesive with a consistency of golden syrup and the finished joints neatened and reinforced with self adhesive foam tape.
 |
| A few missing ductwork seals were installed |
 |
| Preformed corners made from 2 pieces of Armaflex with curved butted joints |
 |
| Finished job |
