Page 58 - Build 151

Internal moisture
Condensation on the double-glazed window framing and glass.
situation that occurs for only short periods of time, and the actual in ltration is signi - cantly lower.
For the apartments, most of the in ltra- tion, if any, would have been occurring at the aluminium joinery of the windows and glass doors. Since that is also where the moisture was condensing and accumulating, it would seem to indicate that in ltration was negligible.
Likewise in the house, where there seemed to be no ex ltration loss of moisture. Any reduction in moisture was directly linked to the use of mechanical ventilation.
For the periods when the house was unoccupied, the temperature and relative humidity decreased relatively slowly with time.
Moisture trapped inside
In both these cases, the moisture was accu- mulating because there was a continuous daily cycle of condensation on the windows at night and evaporation back into the internal air during the day.
A lot of the condensation was spilling over into the carpet where it would have been di cult to mop up each morning.
Lessons in BRANZ ndings
The most obvious shortcoming with the moisture control process in both cases was the ventilation of the laundry area and the absence of sheltered areas to dry clothes outside. Clothes dryers can give o 5 kg of water per load into the indoor air.
There were several points worth noting: ● The house had a clothes dryer that vented directly into a laundry alcove that was open to the main living area. The ventila- tion fan in the laundry area seemed to be too small and the ducting either kinked or
not connected.
● For the apartments, the single laundry
vent was used for the dual purpose of venting both the dryer and the laundry area and had an inadequate partial connection to the dryer.
● The air being extracted by the bathroom fans was in most cases so low that it was di cult to detect at the outlet. That, and nding a disconnected duct in the ceiling of one apartment, suggests there was no commissioning step following installation of the fans and ducting. With no access to the ceiling of the house and some ceilings in the apartments, it would have been very di cult to rectify mistakes discovered after the buildings were completed.
● A particularly noisy and relatively inef- fective extraction hood in the kitchen of the house would have discouraged its use.
● Long runs of relatively small-diameter flexible ducting connecting extraction fans to the outside increase the potential of moisture condensing.
● The relatively small drop in temperature when the heating systems were turned o points to there being minimal heat loss associated with air leakage.
● Unreliable drainage of window and glass door sill channels.
● There were clearly some periods, albeit short, when open windows and doors or the use of mechanical ventilation tipped the balance in favour of there being no condensation on the windows.
E cient ventilation systems a priority
Attempts to reduce energy use by making houses even more airtight than they currently are need to factor in additional costs for improvements to the design and commissioning of the mechanical ventila- tion systems.
Building a house or apartment so it is signi cantly more airtight is relatively easy, even without resorting to specialist airtightness products. The design and maintenance of a comprehensive ventilation and heat recovery system is much more di cult.
Using specialist airtightness products and systems to further reduce the in ltration or completely eliminate it can add considerably to the building cost and may result in an unjusti ably extreme and unmaintainable airtightness.
These two cases seem to indicate that the impact of heat loss associated with in ltration is of secondary importance, and improvements to the ventilation should be the higher priority. Options include passive vents, opening windows or properly design- ed e ective mechanical ventilation.
Remove most moisture at source
The $1,000+ cost of two airtight tests for a new house might well be better spent on the design, implementation and commissioning of an efficient ventilation system. This would run for short periods, removing most of the moisture at source and the rest – such as moisture from exhaled breath – through passive trickle venting and ventilation fans in background mode.
The need, or otherwise, for expensive heat recovery can then be made in the full know- ledge of how much in ltration and ventila- tion heat loss there is to recover.
56 — December 2015/January 2016 — Build 151
FEATURE SECTION