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
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.
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.
c) install a ducted reverse cycle, 5pts. 7.5kw plus machine (do you
need an inverter type)
Ceiling fan in living room and rooms. for b) and c)
Any good suggestions? Running cost for a) is lowest but would it be
The insulation upstair is max out except the window is not double
Any suggestion on how you would approach the problem? The pro and con
on all 3 options?
Does evaporative cooling work well in Melbourne? It looks like the
relative humidity is about 50% at 3 PM on an average summer day.
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
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:
Ta (56 min, 78 max) -------www------------ Ti (59 min, 63 max)
| / 1/2500 |
--- 20K Btu/F
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
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
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
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