Help on cooling/heating on 2nd story extension

I need some help and advice on heating and cooling for a 2nd story extension in Melbourne. The existing house is brick veneer (built in the 60) has an old gas ducted heating (~70 vintage) 1 ~5yr old 6.5kw reverse cycle ac for the living room at the back. There are ceiling fans in the bedroom and living room for cooling. surface area is ~160 sq m.
The upstair extension is ~65 sq m. 2 bedroom, 1 study and 1 retreat area. The existing ducted heating to the back of the house is disconnected. (where the old reverse cycle ac is...) to reduce clearence space. There is no room to run ducts between 1st level and 2nd level.
There are 3 ideas: a) install an evaporative cooling with vent on upstair only. Rely on the stair well to let the moist air to vent out down stair, rely on the stair well to let the heated air rise up to heat upstair. (cost ~4K)
b) install 2 2.5kw cooling reverse cyclesplit system (inverter type) in the bedroom upstair. 1 ~5kw split system in the study to blow out to the retreat area. cost ~7k
c) install a ducted reverse cycle, 5pts. 7.5kw plus machine (do you need an inverter type) cost ~7K-10K
Ceiling fan in living room and rooms. for b) and c)
Any good suggestions? Running cost for a) is lowest but would it be ok? The insulation upstair is max out except the window is not double glazed.
Any suggestion on how you would approach the problem? The pro and con on all 3 options?
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Does evaporative cooling work well in Melbourne? It looks like the relative humidity is about 50% at 3 PM on an average summer day. http://www.bom.gov.au/cgi-bin/climate/cgi_bin_scripts/idl_RH_graphs/rh_script.cgi?86071

Is that a heat pump? What's an "inverter type"? Variable speed drive?

You might run a whole house window exhaust fan upstairs with a window inlet downstairs (and also run the ceiling fans) at night when outdoor air is cooler than indoor air, using a differential thermostat, and close up the house during the day and let its thermal mass provide coolth. The average daily min and max temps are 13 and 25 C (56 and 78 F.)
To prevent reverse airflow during the day, the inlet and outlet windows might have one-way passive lightweight plastic film or motorized dampers. With large enough windows, the dampers might keep the house cool without the fan :-) With dew point control to avoid condensation, they could also provide heat.
If there isn't much mass on the 2nd floor, you might bring up cool air from the 1st with a fan and a 2nd floor thermostat and occupancy sensor. You might bring down warm air in wintertime.
A 2500 cfm fan and a 500 Btu/h-F house with 20K Btu/F of thermal mass might be modeled like this, viewed in a fixed font:
1/500 Ta (56 min, 78 max) -------www------------ Ti (59 min, 63 max) | | | / 1/2500 | -- ---www----| | --- 20K Btu/F --- | - 10 PI=4*ATN(1) 20 GP0'house conductance (Btu/h-F) 30 C 000'house capacitance (Btu/F) 40 CFM%00'fan cfm 50 FOR DAY=1 TO 10'simulate 10 average days 60 TIMIN0'initialize min temp 70 FOR HOUR=0 TO 23 80 FANMARK=0 90 TA=(78+56)/2+(78-56)/2*SIN(2*PI*HOUR/24)'outdoor temp (F) 100 IF TI>TA THEN Q=(TA-TI)*(G+CFM):FANMARK=1:ELSE Q=(TA-TI)*G 110 TI=TI+Q/C'new house temp (F) 120 IF DAY<10 GOTO 170'stats for last day 130 IF TI<TIMIN THEN TIMIN=TI 140 TITOT=TITOT+TI'total for average 150 IF TI>TIMAX THEN TIMAX=TI 160 FANHOURSúNHOURS+FANMARK 170 NEXT HOUR 180 NEXT DAY 190 PRINT TIMIN,TITOT/24,TIMAX,FANHOURS
Min house Avg house Max house Fan hours temp (F) temp (F) temp (F) per day
59.30385 61.30324 63.40533 8
Nick
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