mvhr

Ventilation first fix begins!

Today our ventilation first fix began! We had Klaus from Heat Recovery Scotland on site, and he began by laying out all of his components - so organised I thought it deserved a photo!

The next stage was to install the ducting. We have 2 types of ducting: our extract side of the system is in rigid spiral bound ducts, and our supply side is in semi-rigid ducting. These two sides of the system connect via the Novus 300 Heat Recovery unit, which is installed in a cupboard on the first floor, and adjacent to an external wall to allow the ducts that pass to the outside of the building to be as short as possible (these should ideally be less than 1m long).

We had a slightly unusual design requirement that generated the decision to use the two types of ducting: within the hallways of our 'inner box' we are not planning to sheet the ceiling with a board material, but instead are planning to use timber fins that allow lights to be fitted between, and the services to be seen from below when looking up between the fins. We wanted to retain a slightly more industrial aesthetic in the inner box, and as we are aiming to finish as many of the surfaces in dark stained timber we thought this would provide some visual interest here. (Explaining this idea on site does seem to raise a few eyebrows but we are confident it will be worthwhile!)

This means that in the hallways we wanted all of the ducting to be rigid so that it could essentially be 'on show' between the timber fins. As the supply ducts are insulated in a flexible foil-faced insulation the MVHR system designer Stefan decided it would be simpler to maintain the original specification of semi-rigid ducting for the supply side of things but to 'sleeve' it in a larger diameter of rigid ducting, and to have the extract side of the system completely in the rigid ducting.

We also had to make sure that any fixings for the ducts on the first floor pass through the wall board on the ceiling into the roof structure above to avoid making any unnecessary (and potentially difficult to fix!) holes in the airtightness membrane. On the ground floor the concern was to make sure the fixings went into the resilient bars and not directly into the joists so as to avoid compromising the acoustic performance of the intermediate floor - so a different rule for each floor!

These photos show some of the ducting in-situ in the hallways, and the terminal points in the rooms which are temporarily blocked off until the time is right on site for the second fix. On the ground floor you can see the two layers of Fermacell on the ceiling hanging from the resilient bars. This photo also shows the rigid 'sleeve' over the insulated semi-rigid supply duct. Within the 'inner box' the extract valve to the utility room will be fitted to the lowered ceiling, which you can see in the second image.

In the ground floor hallway we have a zone where the ducts pass between the two storeys - this will be hidden within some high level storage in the entrance hallway. This can be seen in the second two images below.

This image shows the point where the ducts pass through to the upper floor.

Sleeved insulated supply ducts on the upper floor.

On the first floor the ducts are hung from the wallboard on the ceiling, with fixings only through the membrane into the structure above. The extract side of things has attenuators fitted to eliminate cross-talk noise transfer between rooms, and the supply side ducts all return to a 'manifold' (this is sometimes described as an octopus arrangement!) which acts as a silencer on this part of the system.

The extract side of things has attenuators fitted to eliminate cross-talk noise transfer between rooms, and the supply side ducts all return to a 'manifold' (this is sometimes described as an octopus arrangement!) which acts as a silencer on this part of the system.

The Paul unit now has an integrated frost protection unit, so that saves some space. We do however have a separate warm water post-heater (sometimes referred to as a 'water-battery') which can raise the temperature of the supply air slightly in winter when the incoming air is very cold. With 180 m3/h air flow volume the unit we have can transfer 1.5kW (when the water temperature is 50 deg. Celsius) and 2.5kW when the water temperature is 70 deg. C. The temperature of the water flowing through the post heater makes a big difference in the output; it should not be above 70 deg. Celsius though to avoid burning smells. We do however need to insulate this unit, to make sure that the cupboard doesn't receive all of the additional heat, so there will be a bit of re-arranging to do when that happens!

Now we just have to fit the insulated ducts that go to the outside of the building so that we can airtightness test these penetrations. Then at the point of the second fix these will be connected directly to the Paul unit. More on this later!