I have a single hose AC (renting right now). did some research on how to improve the efficiency of the unit. I ran into this report by the australian government:
Adding a second hose to a single hose AC can improve effiency by around 100%... This is because portable air conditioners are tested differently to other air conditioners.
"The DoE found the addition of a second duct that uses outdoor
air to cool the condenser would yield an efficiency gain of 103 per cent for a retail price
increase of around US$8 (from US$534 to US$542)—a price/efficiency ratio of 1:103 (i.e. a
one per cent increase in price provides a 103 per cent increase in efficiency). Because
double duct portables are no longer available on the Australian and New Zealand markets,
suppliers are unable to communicate their benefits compared with single duct products.
The existing energy efficiency regulations on portable air conditioners appear to have had
the perverse effect of removing the more energy efficient product (double duct portables)
from the market, while encouraging the marketing of single duct portables, by allowing
unverified claims to be made about the effectiveness and efficiency of these products. This
RIS considers options to resolve this perverse situatio"
"The single duct portable’s performance information is likely to have been obtained from a
test that measured the cold air produced. Fixed air conditioners, conversely, are tested to
measure their cooling effect on an enclosed space. While a single duct portable may blow
cold air onto a person, if its performance was tested in the same way as a fixed air
conditioner, it could have a net heating effect on the room it was supposed to cool."
https://www.energyrating.gov.au/sites/default/files/2020-06/...
Adding a second hose to a single hose AC can improve effiency by around 100%... This is because portable air conditioners are tested differently to other air conditioners.
"The DoE found the addition of a second duct that uses outdoor air to cool the condenser would yield an efficiency gain of 103 per cent for a retail price increase of around US$8 (from US$534 to US$542)—a price/efficiency ratio of 1:103 (i.e. a one per cent increase in price provides a 103 per cent increase in efficiency). Because double duct portables are no longer available on the Australian and New Zealand markets, suppliers are unable to communicate their benefits compared with single duct products. The existing energy efficiency regulations on portable air conditioners appear to have had the perverse effect of removing the more energy efficient product (double duct portables) from the market, while encouraging the marketing of single duct portables, by allowing unverified claims to be made about the effectiveness and efficiency of these products. This RIS considers options to resolve this perverse situatio"
"The single duct portable’s performance information is likely to have been obtained from a test that measured the cold air produced. Fixed air conditioners, conversely, are tested to measure their cooling effect on an enclosed space. While a single duct portable may blow cold air onto a person, if its performance was tested in the same way as a fixed air conditioner, it could have a net heating effect on the room it was supposed to cool."