Having our air conditioner out of service at the start of Summer was an opportunity to demonstrate how a passive solar home in Melbourne doesn't rely on mechanical cooling to keep the occupants comfortable.
March is a tricky month for a passive solar home. With the Sun lower in the sky, the increasing amount of sunlight hitting the concrete slab is moving the house into passive heating mode. However, the occasional flashback into Summer means the heating isn't required. Covering the pergola with a deciduous vine should eliminate the issue in future.
Passive cooling with nighttime natural air circulation was all that was required to maintain a comfortable temperature indoors. Solar power production remains high with exports ensuring our energy bill was a slight credit.
Our passive solar design home performed well for comfort and cost during a record run of hot weather in Melbourne. Natural air circulation during the cooler nights eliminated the need for air conditioning during the day. Solar power production far exceeded our needs, resulting in a slight credit on the power bill.
Despite increasing temperatures, passive cooling was all that was required to keep indoor temperatures within a comfortable range. The energy bill for December was a credit of $8 due to continuing low household demand and increased solar power production.
While discussing sustainable home design with others, I realised the word "passive" mu;st be used carefully. Passive solar design is different to Passive House design. It's important to understand the differences and similarities.
While the indoor temperature felt comfortable during hot summer days, I was left with the nagging feeling that wishful thinking was keeping me cool. Passive solar design should minimise the need for mechanical cooling for everything but a run of very hot days. Temperature monitoring data confirmed this is the case for our design.
Using heat pump technology for both the reverse cycle air conditioner and the hot water system is an efficient way to meet those needs. Despite the warm weather, the air conditioner is yet to be fully tested as the passive cooling features in the house have kept this heat pump on standby duty.