Knowledge/Reference/The conversions that come up on Australian HVAC work
The conversions that come up on Australian HVAC work
Five come up often enough to keep handy. Airflow per kW, air changes per hour (ACH), m³/h against L/s, electrical conductivity (EC) to total dissolved solids (TDS), and ozone depletion potential (ODP) tonnes to refrigerant mass. Each one says where it came from, because a conversion factor without a source is just a number.
- Airflow
- 54 L/s per kWflagged unverified, see below
- Air changes
- L/s × 3.6 ÷ m³gives ACH
- Water quality
- TDS = EC × 0.6mg/L from µS/cm
- Airflow units
- 1 L/s = 3.6 m³/hexact
Which conversions come up, and where does each one come from?
| Convert | Factor | Source and confidence |
|---|---|---|
| Litres per second to cubic metres per hour | × 3.6 | Exact, by definition |
| Airflow to air changes per hour | ACH = L/s × 3.6 ÷ volume in m³ | AIRAH (Australian Institute of Refrigeration, Air Conditioning and Heating) Skills Workshop Module 48 |
| Electrical conductivity to total dissolved solids | TDS in mg/L = EC in µS/cm × 0.6 | Commonwealth evaporative air conditioner research |
| Airflow per kW of capacity | About 54 L/s per kW | Flagged unverified in our own research. Use a manufacturer figure |
| ODP tonnes to HCFC-22 mass | 1 ODP tonne is about 18 tonnes of HCFC-22, which is R22 | Derived from the scheduled ODP value of 0.055 |
Watch the fourth row. 54 L/s per kW is flagged unverified in our own research. Airflow per kW changes with the system type, the temperature difference and the static. If it matters, use the design airflow from the unit's data, not a rule of thumb.
Which of the four pressure units goes where?
- 1 bar = 100 kPa = 0.1 MPa
- 1 kPa = 1,000 Pa
- Evaporative fans are specified at roughly 80 Pa external static
- Gas ducted pressure switches close at 55 Pa and 18 Pa
- Refrigerant pressures are usually quoted in bar gauge (barg), and R744, which is CO2, reaches about 63 barg at 25°C
Duct static is measured in Pa and refrigerant in bar, and one bar is 100,000 Pa. Mix them up and you put the wrong gauge on the job.
Left out on purpose
Why there's no kW to BTU (British thermal unit) factor here
It's the conversion people expect on a page like this, and we've left it out on purpose. No BTU conversion factor turned up anywhere in our sourced research, so publishing one would mean pulling a number from memory.
Yes, that's a bit silly for such a well-known conversion. But we'd rather say so than slip in a number we can't back up. Every figure on this page comes from something we actually read.
In practice Australian equipment is rated and registered in kW, the GEMS register (Greenhouse and Energy Minimum Standards) works in kW, and the Victorian Energy Upgrades (VEU) categories are defined in kW. If you're being quoted in BTU, you're probably reading imported marketing material, which is worth noticing in itself.
Something here you would use more of?
These pages exist because somebody needed the number and could not find it quickly. If there is one missing, that is worth knowing.
Tell Kevin what you went looking for.
Who this is for: small and medium HVAC contractors in Victoria. If you're a homeowner after a rebate or a repair, you need a licensed contractor, not us, and yours can point you the right way.
Review date: 1 April 2027. Figures in this area change without much notice and this page carries some that will go stale. Every number above is dated and sourced so you can check it yourself. If you find something out of date here, tell us and we will fix it.