I installed it by the book, with the outside exhaust duct half extended and fed through a hole I had made in the wall, as the supplied window kit didn't suit our wind-out windows. I turned it on for the first time in the late afternoon with the inside and outside temps both about 31C. Pretty soon, it was gushing cool air, but was very slow to make any difference to the room temperature, although the compressor was hammering away all the time (quite noisily for a "silent" model). Armed only with a hand-held Skymate anemometer/thermometer and a plug-through electricity meter, I decided to find out why.
Output of the appliance can be measured by the amount of heating of the room air discharged from the 125mm exhaust duct. The highest air speed I could measure from the this duct was 10.5m/sec, so it would be generous to assume that the appliance was moving about 100L/sec of air out of the room. A series of measurements under different ambient conditions during the evening and the following day indicated the difference between the room air temperature and the outside exhaust was usually around 23C, but varied from 21C to 27C. A difference of 24C at 100L/sec airflow represents an output of 2800W.
The inputs to this process are the electricity consumed, which I measured, and the heat extracted from the room, which I determined by difference (as the airflow from the front is well diffused and I couldn't estimate it with the equipment I had). The heat extracted from the room is actually the sum of the "coolth" blown out of the front of the unit (at a refreshing 12C or so) and the heat radiated back into the room from the plastic exhaust duct at the back (duh!). For most of the time the appliance was only pulling 960W from the mains (the highest reading was 1100W when the temperature difference was 27C).
At 1000W, the typical cooling output (heat extracted from the room) is thereby 1800W, with a maximum just over 2000W. This is unlikely to match the heat infiltration into even a reasonably well-insulated room on a hot day.
The errors involved in this admittedly rudimentary evaluation are insufficient to change the conclusions, which include a couple of game-stoppers:
Problem 1: Excess Ventilation
The 100L/sec of hot air blown out of the exhaust duct has to be replaced, so that much outside air is being sucked into the house somewhere. This would change the air in a reasonable-sized living room every 10 minutes, which is getting close to evaporative air-con territory and negating the benefit of all that insulation that Juliar squandered our taxes on.
Problem 2: Poor Efficiency
By my measurements at least, the implied EER of 2.99 (4700/1570) is actually closer to 1.80 (1800/1000). A lower exhaust airflow or higher wattage consumption would worsen this figure drastically, as it does for all practical purposes anyway when the inflow of replacement air is taken into account. If the outside temperature is 15C higher than the inside temperature, then even if the house could be perfectly insulated, the heat transfer into the house caused by this appliance becomes equal to the 1800 watts of apparent benefit, and the nett effect of operating this unit is NIL (apart from increasing your electricity bill).
I appreciate there are reasons (renting comes to mind) why people can't install a decent split system, however a portable air-con would appear to be an appliance of last resort if a window air-con can't be installed temporarily. There appears to be no benefit to owning a portable air-con unless:
- You can find one with dual ducts, so that it doesn't pull all that hot air into your house (I haven't);
- Your house is poorly insulated (an evaporative air-con may work better and would be cheaper);
- You only want to cool the house down faster after it has become cool outside (a fan in the window may work better and would be cheaper);
- You only want to sit in front of it (sitting in front of an open fridge may work better and would be cheaper).
These appliances would appear to be a waste of both money and resources; if this thread results in a few tempted by end-of-summer sale prices to buy a split system instead, I won't have done the environment or the retailers any disservice
If there is a demand for these things, there must be a need for a new generation of window air-conditioners, designed to fit a sliding window and to operate efficiently on a 10A circuit using modern inverter technology. How about it Fujitsu and Panasonic?