Factors Affecting HVAC Design

Factors affecting Heating, Ventilation and Cooling Design

Factors affecting HVAC Design

The factors affecting HVAC Design should be considered from the outset. This sounds simple enough but is often not properly thought out. It leads to changes through the building process which causes costly variations. Therefore, put some time and effort into thinking this through as the first step.

Your needs affect the design of your heating, ventilation and cooling (HVAC) systems. The hidden problem can be that you ‘’don’t know what you don’t know’’ and changes occur as awareness develops. New products come onto the market continually, which open up new possibilities and new ideas. More information.

If you choose an all-electric home, then it is most important that your home is efficiently designed.

Ensure your energy rating is at least 6 Stars or possibly 7+ Stars with good design choices. This will give you lower heating and cooling needs enabling lower powered inverter heat pumps or air conditioners to be used effectively, powered largely by your solar power.

Solar Power

Solar power is a good example of changing thinking and revision of needs. Pricing has come down whilst performance has gone up. Hence, solar power has become cost-effective and affordable. In fact, a quarter of Australia’s 9 million homes in 2020 now have solar power.

Battery storage

Battery storage is the next major product going through similar development. We can expect them to become cost-effective in the future and then batteries will likely be bundled in with solar power. This will give us solar power to use in the evening and also help balance the power grid, clearly both important.

Thermal Mass

Store your daytime heating or cooling in the thermal mass of your home. This is important if you live in a southern or inland Australian location like Victoria or Tasmania because these climates have large temperature swings (diurnal range) between day and night. In winter, useful heating energy is absorbed into your home’s thermal mass by day and released at night.

Add thermal mass to your home if it has been built from lightweight materials. This typically includes weatherboard homes with suspended floors. In addition, brick veneer homes with suspended floors will also benefit from added thermal mass. This is because the high-mass bricks are on the outside of the building fabric and therefore useless at providing thermal mass for energy storage inside.

Ideas for adding thermal mass include:

  • Internal feature walls made of stone or bricks
  • Water stored in thin wall tanks
  • Thin underfloor screed with heating circuits laid over suspended floors just 15mm high

Harness the Sun’s Energy

Locate your high-mass walls so they can absorb radiant sunshine. Place roof windows or clerestory windows strategically so high-mass walls can absorb radiant sunshine. This will improve your home’s thermal performance because the sun’s short-wave (visible ultraviolet) radiation travels easily through glass. This energy is later re-radiated inside your home when the sun goes down. Importantly, your home’s thermal mass re-radiates in long-wave form (infrared) which doesn’t travel through glass easily.


Having gained thermal energy during the day, it is important to hold onto it by reducing heat loss. Cover your windows with blinds or curtains and trap the air underneath pelmets. This will prevent the air from moving so you don’t lose heat from air convection.

Air is the best insulator providing it doesn’t move. For example, it is the air in insulation batts that does the insulating whilst the fibreglass or rockwool traps the air from moving.

Insulate your ceilings, walls and floors. Sustainability Victoria recommends insulation resistance ratings of R5.0, R2.5 and R2.0 respectively for Victoria. Reflective foil and window treatments have other benefits for controlling heat loss or gain. 

Room Zoning

Think about the size of your home, the purpose of your rooms and whether they can be effectively zoned. Save operating costs by not heating or cooling the whole house all the time. At least, separate your kitchen/family, living rooms and studies from your bedrooms because they have different operating and comfort requirements.

Other Design Considerations

There are many other design considerations depending on your location, needs, preferences and budget. Hydrosol can provide assistance in the early design stages and provide thermal performance assessments in accordance with the Nationwide House Energy Rating Scheme (NatHERS). 

Hydrosol uses First Rate 5 software developed by Sustainability Victoria to provide NatHERS thermal performance assessments. This shows your home’s likely heating and cooling energy use and provides an energy Star Rating for your building permit.

We can suggest things to improve your energy rating

The aim is to achieve a Star rating of at least 6 out of 10. A completely passive house requiring no mechanical heating or cooling can achieve a Star rating of 10.

HVAC Design Approach

We suggest this approach for your HVAC design:

  1. Identify your needs as a family.
  2. Seek advice about the factors affecting the thermal performance of your home.
  3. Incorporate these ideas into your building plans.
  4. Seek a thermal performance assessment (energy Star rating) as soon as possible before you have locked in your building plans.
  5. Be prepared for some iteration if your provisional thermal performance needs improvement (i.e. if the energy rating is less than 6 Stars).
  6. Identify the heating and cooling loads provided by the thermal performance assessment.
  7. Having thought through the factors affecting HVAC design, you may wish to consider an all-electric HVAC design.
  8. Installation plans can then be created with your HVAC design integrated with your building plans.
  9. HVAC system installation usually starts at the beginning of your build by roughing in hydronic pipes, ducting and/or underfloor heating circuits along with associated wiring and fittings.
  10. Towards the end of your build, equipment is delivered and fitted.
  11. HVAC system commissioning occurs just before project completion including WIFI connection to your electronic devices. This allows you to operate and monitor your system from anywhere in the house or remotely.
  12. Finally, a maintenance plan should be established to protect your HVAC investment and to ensure optimal performance and long operating life. This will reduce your overall life cycle cost which includes both the initial capital, ongoing operating costs and time before replacement is required.

Contact us for assistance with your new build or renovation.