Week 32, Day 5

Week 32, Day 5:

  • Little visible progress on the outside but plenty of progress on the inside – plastering, air-tight taping, more ventilation ducting and electrical first fix
  • Today’s featured topic is the installation of the new underground electricity cable – it’s not connected yet but getting it in the ground feels like a big step in the right direction; more details below the photo
Week 32, Day 5

Week 32, Day 5

The original electricity supply came overhead from the pole-mounted transformer. Some of the cables were a little bit thin (especially for the 32A start-up current required for the Ground Source Heat Pump) and had seen some damage over the years so Western Power Distribution agreed to replace them and elected to bury the new cable underground.

The new cable has an impressive specification: 3 cores, each of 185mm^2 and with steel wire armouring – roughly 48mm diameter overall. On agricultural land cables need to be buried at least 1m deep. Sam the digger driver was an expert and very respectful of farming practices – the photo below shows the turf and topsoil piled on the left with the subsoil piled on the right. Note the transformer in the distance.

Installing the underground electricity cable

Installing the underground electricity cable

While there is a crop (oil seed rape) in the field right by the transformer most of the cable run was through a field currently in set-aside or over my land, along the line of a fence that had seen much better days and needed replacing anyway.

New electricity cable being laid

Close up of the tractor and drum-trailer

At the “house” end the cable runs south along the line of the fence. It will be joined onto a smaller cable underground before running into the existing GRP cabinet – see the original electricity re-connection post for more details of that.

Cable trench alongside outbuildings

Cable trench alongside outbuildings

The new cable is scheduled to be brought into service on 2016-06-07, after which the old overhead cables and poles will be removed.

Week 32, Day 4

Week 32, Day 4:

  • More general progress – electrical first-fix, plastering etc.
  • Today’s featured topic is the ventilation ductwork – see below the photo for more details
Week 32, Day 4

Week 32, Day 4

The majority of the ventilation ducts are 80mm Lindab LFPE semi-rigid tubing which run from plenum chambers near the MVHR unit to the intake and extract vents in the various rooms. Since some of the rooms are quite large the air flow rates are also relatively large and necessitate multiple runs of the ducting per room, coming together where they attach to the room vents.

Twin ventilation ducts for a single extraction vent

Twin ventilation ducts for a single extraction vent

The “semi-rigid” ducts are reasonably flexible and can normally be “cabled” through the joists. However, in some cases a tight bend is required and this is achieved with a metal elbow.

Metal elbow fitting for 80mm semi-rigid ventilation ducts

Metal elbow fitting for 80mm semi-rigid ventilation ducts

In a few places, it makes sense to run few metres of rigid metal ducting to a plenum chamber some distance away from the MVHR unit.

Plenum chamber for transition from rigid metal to semi-rigid plastic ventilation ducts

Plenum chamber for transition from rigid metal to semi-rigid plastic ventilation ducts

Ventilation ducts in second Bedroom ceiling

Ventilation ducts in second Bedroom ceiling

There are strict limits on the noise levels permitted from a ventilation installation (part of the Passivhaus standard) and despite using a high-quality unit some silencers are required.

Silencers for ventilation ducts

Silencers for ventilation ducts

It can be difficult to get an accurate sense of scale from the photo, but those are full-size (215mm x 440mm) concrete blocks in the wall and the silencers are 1.25 metres high and 400mm diameter (for 200mm ducts). Fortunately they get installed in the Plant Room, where there is plenty of space for them.