I have friends in Dubai and in Finland and I was wondering this the other day:
Assuming you have a 2 bedroom detached house in Helsinki with triple glazing (common for the area) and whatever insulation current regulations require new houses to have. You also have a 2 bedroom detached house in Dubai with double glazing (also common for the area). You want to maintain both houses at 21 C.
So the question is, does heating a well insulated home in ridiculously cold temps use more energy than cooling a well insulated home in ridiculously warm temps.
Assume energy use is averaged over a year.
or which is more energy efficient, air con or heating?
What you need to do is compare the heating (and cooling) degree-days of each location.
In general, heating is more efficient than cooling (it’s usually 80-300% efficient), whereas cooling is limited byCarnot-cycle efficiency limitations.
So, unless one needs drastically more heating in Finland than cooling in Dubai (doubtful), it’s probably more efficient to live in Finland.
That’s a really cool (no pun intended) question.
There’s lots of options for heating. I wonder how many there are for cooling.
They’re both limited by Carnot efficiency. There are probably practical considerations, but in principle a heat pump works just as well cooling as it does heating across a given temperature difference.
In fact, it wouldn’t surprise me if cooling were more efficient than heating on average, because many household air conditioners are ground-source heat pumps (and so can achieve >100% efficiency), whereas quite a lot of heaters (especially in the coldest climates) are just natural gas or fuel oil furnaces, and so can only achieve <100% efficiency.
Heating is MUCH more efficient than cooling, when using a heat pump. Not only can you pump heat from colder to hotter areas, but you can also use the waste heat of the compressor. That’s where my 300% figure comes from: Heat pump - Wikipedia
(ground-source heat pumps can achieve better than this - 400-500%, but this isn’t typical).
Add to this, that everything is a heater. In principle, you could protect against cold temperatures with nothing but insulation, if the insulation was good enough. This won’t work against heat, though, because you’ll always have heat sources inside the insulation that you have to deal with.
Hmm–I wasn’t thinking clearly enough about the temperatures involved. What I said was true under certain conditions (idealized heat pump, smallish temperature differences), but those may not be typical. And you and Chronos are correct that any waste in the system (pump losses, any heat sources in the house) contribute to heating, although personally I find it hard to count that as increased efficiency.
At any rate, I stand by the *possibility *that air conditioning is more efficient than heating on average (say, across the US) due to the prevalence of fuel-burning furnaces and temperatures that often are often far colder than room temp in winter than they are hotter than room temp in the summer. Though this will depend greatly on how one defines efficiency…
Yes, that’s the reason the heating/cooling degree-days of each location needs to be considered. Still, if one is using electricity to both heat and cool, it’s going to be the rare case that cooling is more cost-effective.
Well, it sure depends on the climate. I live in a quite mild area and I don’t use the air conditioner very often; when I do, it’s often only to cool from 30 C to 25 C–a range where the AC is operating very efficiently (and not very often). On the other hand, I might only use the heater when the outside temperature drops below 10 C. Carnot says heating that to 20 C is going to be less efficient. My energy-efficient lights don’t given me much of a freebie, either :-).
How wide spread are heat pumps for heating? In my house we have a force air gas heater. This has been true for most of my previous houses with the exception of one that had circulating hot water radiators from a gas fired heater. Is it starting to be the norm for new houses?
That depends on the climate. Most heat pumps will switch on auxiliary electric heating when the outside temperatures are below 30 deg F or so, which really cuts the efficiency down. In cold climates gas or oil fired furnaces are still the norm. Heat pumps in new construction are very common in temperate climates.
My auxiliary heat on my unit doesn’t work that way, rather, it comes on to “help” when I program the thermostat to heat my house 3 or more degrees higher than ambient. It just enables the unit to get the house to the desired temperature faster.