Evaporative vs refrigerated air conditioning in Perth: which works with solar?

Western Australia has one of the highest rates of evaporative cooling in Australia. Many Perth homes — particularly older suburban homes built before the 1990s — use ducted evaporative coolers rather than refrigerated reverse-cycle systems. Newer homes and apartments tend toward reverse-cycle.

If you're getting solar and wondering which cooling system works best with it, or you're upgrading your cooling and want to know the trade-offs, here's the full picture for Perth's climate.

How each system works

Evaporative cooling (ducted or portable) Air is drawn through water-saturated pads; as water evaporates, it absorbs heat and cools the air. Cooled air is pushed into the house through ducts. Windows or doors must be partially open to allow exhaust.

Works well when: outdoor relative humidity is below 30–35% Stops working effectively when: humidity rises above 40–45%

Refrigerated reverse-cycle AC (split system or ducted) A refrigerant cycle transfers heat from indoors to outdoors, independent of outdoor humidity. Both cool (summer) and heat (winter).

Works in any humidity and any temperature — performance degrades slightly at extreme temperatures (above 45°C outdoor, below -5°C for heating), but Perth's climate is within comfortable operating range year-round.

Perth humidity: when evap coolers fail

Perth is one of the driest major cities in Australia most of the year. But summer brings two scenarios where evap coolers struggle:

Sea breeze days: Perth's afternoon sea breeze ('the Fremantle Doctor') arrives between 1pm and 4pm and dramatically drops temperatures — but it raises humidity from 15–25% to 35–55% as it crosses the coast. During the sea breeze period, evap coolers become less effective precisely when the sea breeze makes conditions more tolerable anyway.

Northerly events before a change: Humid northerly air masses sometimes push in before a cold front, delivering a day or two with humidity above 50% and temperatures of 35–40°C. On these days — the most uncomfortable days of the Perth year — evap coolers provide little relief. These events are less common than the sea breeze pattern but more miserable.

Statistical frequency: Perth averages approximately 10–20 days per year where afternoon humidity exceeds 50%. On those days, refrigerated AC provides comfort where evap cannot.

Running costs: solar compatibility

Evaporative cooler power draw:

• Small portable/room unit: 0.3–0.6 kW
• Ducted whole-home unit (4–5 bedroom home): 0.8–1.5 kW
• Annual running cost (ducted, all summer): approximately $80–$200/year at A1 rates

Reverse-cycle AC power draw:

• Small split system (2.5–3.5kW cooling): 0.7–1.5 kW input
• Large ducted (10–14kW cooling capacity): 3.5–7.0 kW input
• Annual running cost (whole-home ducted): $600–$1,500/year at A1 rates

Solar compatibility:

| System type | Solar match | |---|---| | Ducted evaporative | Excellent. 1.0–1.5kW draw easily covered by solar even on partial-output days. Can run all day on solar without meaningful grid draw. | | Small split system | Good. 0.7–1.5kW input fits within solar output for much of the day. Pre-cooling during solar hours is highly effective. | | Large ducted refrigerated | Fair. 5–7kW input exceeds typical solar output (unless you have a large system). Pre-cooling + battery + Midday Saver is the optimal strategy. |

Evaporative coolers are the most solar-compatible cooling choice by a wide margin — their low power draw means a modest solar system can cover cooling loads through most of the day.

Cost to install

| System | Typical Perth installed cost | |---|---| | Ducted evaporative (new install) | $3,500–$6,500 | | Ducted evaporative (replace head unit, existing ducts) | $1,800–$3,500 | | Split system reverse-cycle (1 unit, 2.5–7kW) | $1,500–$3,500 | | Ducted reverse-cycle (whole home) | $8,000–$20,000 | | Ducted reverse-cycle (replace head unit, existing ducts) | $5,000–$10,000 |

Ducted evaporative is significantly cheaper to install than ducted refrigerated — a major reason why many Perth homes chose it historically.

Which to choose for a Perth solar household

Keep your evaporative cooler if:

• It's working well and relatively new
• You have separate split systems for the rare humid days
• Your solar system was sized assuming the low draw of evap cooling

Replace with refrigerated if:

• Your evaporative system is failing and needs replacement
• You find yourself regularly uncomfortable on humid days
• You want to run heating and cooling from the same system
• You're willing to invest in a larger solar + battery system to offset the higher running costs

Best of both (common Perth solution): Many Perth households keep ducted evap for dry-weather cooling (80% of summer use) and install one or two split systems for the humid-day exceptions and for winter heating. Evap handles the volume at low cost; reverse-cycle handles the edge cases. This split approach is lower cost than a full reverse-cycle ducted installation.

Running cost calculations use Synergy A1 rate 33.26c/kWh effective 1 July 2026. Evaporative cooler and reverse-cycle AC power draws are indicative ranges for typical residential units.