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High Efficiency HVAC for a Net Zero Capable Austin Home

Who doesn’t want to use less energy to heat and cool their home? Conventional wisdom may be to seal your home and to add a more efficient central air conditioning unit, but given that your ducts leak and your Central HVAC sucks if you’re remodeling a home without existing central air, you should consider a ductless mini-split system.

Here’s a quick video of Kristof Irwin – who has been spearheading some of Austin’s net zero capable green construction and building performance testing.

Why are these systems more efficient than a regular central HVAC?

  1. No leaks. They don’t move cold air around leaky ducts, they move refrigerant around pipes. Given that even newly constructed air ducts typically leak around 10%, you’re already saving by having a transmission system that doesn’t leak.
  2. Condition only what you need. You can configure the spaces to cool or heat independently – not all rooms in a home are typically occupied at the same time, so it allows for only using energy to bring your desired climate to the rooms you’re using.
  3. Variable energy usage. You have a throttle on your energy usage. As Kristof mentions in this video, you can run your system at 10% capacity up to 130% capacity. Compare this to your typical central system which is either on or off, and you can see it’s easier to control temperature and humidity more accurately with the mini-split system. Some days you only need a 10% effort, so you don’t use as much power, and the unit doesn’t cycle on and off so much, leading to longer service life of the components. This is better for the grid too which no longer has to account for simultaneous spikes in usage as compressors cycle on and off.

One comment I often hear about ductless mini-split AC systems is that they’re more expensive, and they have big old head units in each room. Neither of these is true. As mentioned in the video, it is possible to have supply and return vents in the ceiling of your home while the head unit is in the attic – this appears to the building users to be central air, though they may notice a proliferation of thermostats allowing them individual control on a per-head basis.

As for expense, there are certainly federal incentives to reduce energy usage through the purchase and installation of high-efficiency AC systems. There are four fiscal costs of a typical HVAC system – initial installation cost, running costs, maintenance and replacement costs and external costs (costs to the environment and supply grid).

It’s certainly worth getting a HVAC installer to do a cost benefit analysis for you of a traditional system for your needs versus a mini-split system. You might be pleasantly surprised that the system which gives you more fine-grained comfort control and lower bills works out to be the best for your situation.


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Garreth Wilcock is an Austin EcoBroker®

Specializing in: New Green Homes in Austin.

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