Page 47 - Build 152

Ventilation
Trickle ventilators are a good passive option.
● Pros – typically cheap, easy to t and with good control for diligent occupiers.
● Cons – ventilation performance is depend- ent on wind and stack pressures and energy impact, and they require a degree of occupier involvement and education. Extract ventilation is usually required to remove pollutants at source.
Mechanical options
These include extract ventilation, supply ventilation and balanced ventilation with heat recovery.
Extract ventilation
Typical examples include bathroom extract fans and rangehoods. Extract ventilation is an e ective way of dealing with moisture at its source and can simply be left on after a polluting event for a few minutes to help remove contaminants.
Care is needed to locate intakes in the optimal position to capture the contaminant source e ectively. Where the make-up air is coming from also needs to be considered, for example, an open window or internal door.
● Pros – very e ective at source capture,
easy to install and cheap.
● Cons – can have an energy impact, though
this is minimal as they are run intermit-
tently. They require user intervention.
Supply ventilation
A supply-only system takes roof space air and ducts it to several rooms in the
Poor installation is often the cause of high moisture levels.
home through ceiling-mounted di users. Examples of this style of ventilation system commonly include a bypass where intake air is taken from the eaves of the building in the warmer months.
Drawing air from the roof space doesn’t comply with clause G4 which requires venti- lation with outdoor air.
● Pros – relatively inexpensive, simple to
install. Roof space air can have some
energy bene t in the shoulder seasons. ● Cons – roof space air is not the cleanest air source, but filters will help with this. Controlling system flow based on temperature difference alone can lead to additional moisture in the home, although some manufacturers are now incorporating humidity measurement in
their controllers.
Balanced ventilation with heat recovery
Balanced ventilation offers a great solu- tion for ventilating your home e ciently. However, it is not well suited to retro tting. A balanced system requires a very airtight building to be cost e ective.
Balanced systems extract air from the building and pass it through a heat exchanger. Intake air is drawn through the other side of the heat exchanger, pre- warming the building’s replacement air.
Heat exchanger cores can be very e - cient – over 90% in some cases – however, systems require two fans to work. Given
the temperate climate in New Zealand, it is possible that the energy recovered can be less than the cost to run the fans driving the system.
Given they are trying to get the absolute maximum energy efficiency possible, running ductwork inside the building insula- tion is an important consideration.
● Pros – very e cient, good track record of use overseas.
● Cons – most expensive option, di cult to retro t. Requires an airtight building for maximum e ciency. Requires careful commissioning and regular maintenance.
What’s next?
With the completion of WAVE, the energy- e cient ventilation project has recently begun. It seeks to answer a raft of questions about getting the right ventilation option into a home to minimise the energy impact while maximising pollutant removal.
Part of this involves investigating just how much of an impact in ltration air is having and what the right ventilation option is given the airtightness of a building.
Although increasing airtightness – by decreasing in ltration – will result in energy saving, there is evidence the relationship is not completely linear. The rst part of the energy-efficient ventilation project will investigate this in more detail in the context of our lightweight construction.
Build 152 — February/March 2016 — 45
FEATURE SECTION