SEER v EER for warmer climates
I would appreciate comments on whether or not the new SEER rating (EU directive 626/2011) is a good indicator for efficiency in warmer climates. It is interesting to note that for heating they have divided Europe into 3 zones but cooling is one zone when summer temperatures can vary dramatically from Helsinki to Rome.
SEER takes partial loads into account with external temperatures of 20, 25, 30 and 35 degrees for an internal temp of 27DB/19WB. These temperatures represent loads of 21, 47, 74 and 100%.
My first issue is with that 35 degrees limit. Most outdoor units on sale in southern Europe have max operating temperatures of 45/46 degrees but their efficiency can be very different at 40/45 degrees when you examine the manufacturer tables for power input v production of cool air. Further, cooling is typically needed May to Oct but few people would have their units on with external temperatures of 20 or 25 degrees, most people would need AC from 30-50 degrees in built up urban areas.
So do these lab condition points indicate well how the units perform with higher external temperatures? Is the 50% case in the lab (ie external 25 degrees, internal 27) really a good indicator of the efficiency of the same unit working at 50% capacity to maintain a target internal temperature with an external temperature of 40 degrees? Should people in southern Europe really be choosing units with higher SEER over EER?
There is a some confusion. The new ratings came into effect this January and some models passed from "B" grade EER to SEER A+ or even A++ (probably with a little tweaking from the manufacturer but you can still divide nominal cooling in kW by power input in kW to confirm the EER) So units nobody wanted last year are now "the best" but still consume more power at higher loads and external temperatures...
Europe is a whole different market than US. I think minisplits are far more common. Northern Europe, other than commercial buildings, AC is pretty rare from what I saw. Not really nessesary since it's a West Coast Temperate climate. Southern Europe is more hot and humid. I'd say southern europe compares closer to maybe San Diego climate, but just a little hotter mid summer. But it's not a humid climate like the South. Northern Europe si more like Seattle towards the West coast, and past the northern Alps and into Northern Germany, more like Northern Michigan or maybe Toronto or Montreal but still less humid.
There should be design conditioins available for these regions to guide your design same as the US. I would say SEER is still relevant. EER only becomes more important in hot dry climates more like Northern Africa and maybe some parts of Spain Italy and Southern France on the Mediterranian.
EER is the effciency at 95F and I think it's 80F Indoor (who honestly keeps it that warm, except in dry climates?) with 50%RH. SEER I beleive is either weighted or uses 82F outdoor, 80F indoor and represents a common part load conditions where equipment cycling impacts effciency. That's why 2 stage equipment often has slightly higher SEER rating but the same EER. Even higher SEER equipment adds a 2 speed condenser fan to further improve effceincy at part load conditions, but again, the EER does not change significantly.
In Europe, I believe mini splits are more common than conventional split systems since you are often dealing with refrofits, in masonry buildings, rather than new construction.
All that being said, as you point out, if the system is only being used on hotter days, than EER will be a better measure. Be carefuly not to oversize. Old buildings with good shade and a lot of mass from stone, brick, tile, etc will heat up and cool off very slowly and usually a much smaller system can be installed making it more comfortable and more effcient. The longer it can run between cycles the more effcient it will be. In an ideal hoome, there's enouhg mass that the system will always run at least 20-30 minutes just to cool the space by even just 1F.