A Ducted Air Conditioning System that’s the wrong size for a home in Melbourne can still do the job, but that’s not the point to focus on. See, the system will run alright, the rooms will get to the right temperature, and everything will seem fine, right
up until the electricity bill comes in. The problem is not that the system fails to work, because it will, but that it works poorly for every single day it’s in use, and that inefficiency just keeps on adding up, year after year.
Melbourne’s climate throws up a whole different kettle of fish in terms of system specifications. The temperatures can drop below 5°C in the dead of winter, but then soar above 40°C in the heat of summer, that’s a pretty big ask for any Melbourne Ducted Air Conditioning system, especially when compared to say, other major Australian cities. The way things stand, with Victorian building standards getting tighter under the National Construction Code and NatHERS energy rating framework, designing the air con system is not just about how comfortable it keeps you. It’s about meeting some specific energy performance standards too.
The Sizing Mistake That Will Cost You Dearly
You might think that a bigger system is always the better option. ‘Extra capacity will cover us for those hot days’ is what people often say. But that’s not how it works. An oversized system will short-cycle, quickly cooling the room so fast that it switches off before it even gets a chance to sort out the humidity. You end up with a room that’s cold but damp, with the compressor going on and off all day long, accelerating wear and upping the electricity bill into the bargain.
The old 1kW per 10m² rule of thumb is just a rough guide, not a way to actually size the system. For a proper heat load calculation you’ve got to factor in things like ceiling insulation, the type of glazing used, the construction materials, typical occupancy levels and room-by-room usage patterns. Try comparing a 1970s weatherboard house with a 2015 brick veneer of the same size and you’ll see just how different the results are. If an installer just quotes you on the floor area without asking any questions, he’s not going to get it right, he’s just making a guess.
Zoning: When the Extra Cost Actually Pays Off
With zoning you divide the house into separate areas that can be controlled independently, usually 2-8 zones, so you’re not cooling unoccupied rooms. The biggest savings are for houses above 250m² where the living areas and bedrooms all have different usage patterns across a 24-hour period.
Zone controllers with programmable scheduling let you precool the house before the heat of the day sets in, run it at full tilt when the house is unoccupied, rather than just running flat out all day. That alone can knock a noticeable chunk off the power bill, without affecting comfort levels one bit.
Ducted Reverse Cycle vs Cooling Only: The Melbourne Case
Installing gas ducted heating as well as a ducted cooling-only system imposes additional maintenance duties, and also exposes you to any changes in the price of gas in an area known to be heading towards electrification of its domestic energy needs. The Victorian Energy Upgrades scheme provides incentives for installing heat pumps and those may make the difference in cost between a cooling-only system and a reverse-cycle system quite negligible. The installation is done by an installer accredited for the program and takes care of the paperwork. A quote from an installer not mentioning it is either not accredited or simply not attentive.
Questions to Ask before Signing the Quote
- Does the proposed brand of system and capacity level of equipment actually represent a heat load calculation for this particular house or is it just a standard package installed without calculations?
- What type of duct material, what kind of insulation level and duct sizing for balanced airflow is suggested? Unbalanced ducted systems will deliver uneven temperature distribution no matter what the controller says.
- Does the installer have a valid ARCtick licence?
A homeowner who asks these questions before signing gets monthly savings for a decade. A homeowner who does not learn about his mistake during the summer period.
