@Ursa9501
Yes; my system with security grills in the ceilings is still proving to be very effective and my house is not safe for visits from brass monkeys at the moment. So what will help significantly is venting the system through the ceiling rather than out open doors and windows. This will address the heat but not unfortunately all the humidity on the few extremely humid days. Sometimes referred to as relief outlets or security relief grills Polyair and others evap parts suppliers sell them; these for example https://www.polyaire.com.au/products/grilles/security-relief-grille/
Ceiling vents like these https://www.bunnings.com.au/haron-250-x-250mm-adjustable-ceiling-vent_p0810083 from Bunnings can also be used in smaller rooms, as I have done, and probably even large rooms if you fitted enough. You just need to ensure that to be effective the area and air flow rate of the security outlet grill or vent in each room matches that of the evap air inlet in that room (just measure air speed coming in with a hand held anemometer with and without open doors windows etc). Venting in this way also means you can close all or any of your internal doors when needed.. The only downside is you will freeze in winter unless you remove each on the little security grill pieces (six in each polyair grill) and replace them with some insulating material over winter. I have a post elsewhere here about doing that. The advantage of the small Bunnings vents is that they can be easily closed in winter but I have found they don't flow air as well because of the plastic mesh used in them.
Not only does this help home security but a) it expels warm air from the ceiling space and b) circulated cooler air around the vents so help cool the air flowing through them. I got this tip some years ago from the USA publication "Easy Cooler Care". Sadly no longer readily available and when it is at 10X it's original price e.g Amazon want $200 plus shipping when the have stock. People in the states have also reported that it works even better if you replace the usual insulated ducts with flexible aluminium or steel ones as it increases the cooling effect but this is not something I have tried (yet) and I suspect the metal ducts may rattle and shake and be noisy if not secured along their length in several places in the ceiling.
You also need to fit roof vents (the Bradford Windmasters and Brutus ones from Bunnings work well) so the air in not trapped in the ceiling. I also have fitted a few soffit vents but they are probably not necessary.
