VENTILATION PRINCIPLES
Not all ventilation systems work in the same way.
Here's a few fundamentals to help you make an informed decision.
System Types
There are two popular ventilation methods in NZ.
You may only be familiar with the most common - Positive Pressure.
POSITIVE PRESSURE
Conventional Positive Pressure systems simply push air from the roof cavity into your home.
The theory is that the pressurized air will leak out through gaps around doors & windows, taking moisture with it.
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It’s a simple concept and these are the most common systems in NZ but there are concerns around air quality and their effectiveness in newer, more air-tight homes.
BALANCED PRESSURE
Works by extracting stale, damp air from the home, while introducing fresh outside air to replace the stale air. All Airconics ERV systems are Balanced Pressure.
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Air passes through a heat exchanger which works to retain heat from the outgoing air.
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This cycle of air through the home improves air quality and results in the removal of moisture and condensation.
The detail is important.
POSITIVE PRESSURE
You need to know:
Air from the roof space can be of questionable quality (glass fibre insulation, dust, pollens, mould spores, and rodent droppings are found in most roof cavities).
Does not meet the NZ building code NZS4303:1990 “Ventilation for acceptable indoor air quality”.
Effectiveness is limited in newer homes due to modern insulation & construction methods designed to create a tighter building envelope. More insulation, less “gaps”, and air tight rubber seals around windows and doors means damp air cannot freely escape as it did in older homes.
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No heat recovery means 100% heat loss. When the home is pressurized and air escapes through "gaps", all heat in that air is lost entirely, placing additional heat load on any source of heating that you use. Incoming air will be ceiling temperature unless an electric heating element is added (which come with very high running costs).
A 2011 Otago University study found claimed “free heat” available from the roof space air was grossly overstated and often non-existent when needed during winter. Our experience tells us that “smarter” positive pressure systems won’t actually run in the middle of winter because the roof cavity isn’t getting warm enough, and that the “unintelligent” or basic systems will blow cold air into the home, pushing your heat out.
BALANCED PRESSURE
You need to know:
Two separate air streams:
1. Extracting stale and moist air
2. Introducing filtered, fresh outside air
Incoming air is always fresh from outside and
meets the NZ building code NZS4303:1990
“Ventilation for acceptable indoor air quality”.
Works well in both older homes and in modern homes, no matter how tight the building envelope because you are simultaneously extracting & introducing air. This circulation of fresh air means moisture and condensation are removed while indoor air quality is improved.
Heat recovery ranging from 84% to 96%. Airconics ERV units recover useable heat from extracted air during winter, transferring it to the incoming fresh air. This recovered heat reduces the load on your primary heat sources when heating and ventilating the home. When air conditioning the home in summer, excess heat is transferred from fresh air to the outgoing stale air, reducing the cooling load required.
There are a number of types of heat exchanger core on the market with varying heat recovery abilities, durability and serviceability. Some systems offered in NZ have a very small heat exchanger with poor real-world heat recovery abilities. Airconics ERV units have a large, durable, resin core heat exchanger which simply slides out via the front cover for cleaning & maintenance.