2. ........ DO NOT use Air con when outside temp below 10C for heating.
Air conditioners are a form of HEAT PUMP. They work by 'pumping' heat from one place to another. 'Reverse Cycle' means it can pump heat in either direction.
In summer, heat is pumped from inside your house to the outside. In winter, heat is pumped from outside your house to the inside.
In theory, as long as the side that heat is taken
from is above absolute zero (-273
oC) a heat pump can warm up the other side. In practice, there are a few things that complicate the situation.
The main factor is simple economics - the cost for a particular benefit. Unless you are into producing liquid nitrogen, you won't need a super duper cooling cycle so, to address typical domestic demands, your materials and design can be pretty straightforward. The air conditioning market (as does any market) has found the balance on price and performance - so if you want to find out more on that - just ask a consultant (and pray they know more than you...)
Now, in terms of the energy required, pumping heat is just like pumping water - you need energy to pump it 'uphill' and the greater the difference in levels, the more energy is required. So, if in summer it's 40
o outside, and your air conditioner is set to 20
o, it's going to be working harder than if it was set to 25
o. Likewise, in winter, if its 10
o outside and your air conditioner is set to 25
o, it's going to be working harder than if it was set to 20
o.
The basic rule is quite simple: The
difference in temperature determines how much work has to be done to move a certain amount of heat.
One of the big pluses with a reverse cycle air conditioner is that on the heating cycle, under typical conditions**, you get more heat per unit of electricity than if you were to use an electric heater - ANY electric heater (includes fan heaters, bar radiators, column heaters, etc.) It is quite possible for an air conditioner to use 1500W of electricity and provide more heat than a 2400W heater. This is because the air conditioner is simply moving heat that already exists, whereas electric heaters are creating it from scratch.
** Typical conditions - don't you just know there are a couple of 'buts'.... (I'll just stick to the heating cycle, since there is a direct comparison to alternate forms of heating)
* The colder it is outside, the more work the air conditioner has to do to heat up inside which means more energy is required. I haven't done the maths, but there will be a point where the air conditioner could start using more electricity for the same heating as an electric heater ... though I expect that will be a pretty extreme situation.
* Icing up is also a problem, since it greatly reduces the amount of heat that can be absorbed. Remember that, as far as the heat pumping is concerned, the inside or outside temperature is the temperature of the inside or outside 'radiator' bit - and if its encased in ice.....
The icing up problem is one that many modern air conditioners can detect and, for a short period, work in the opposite direction to that desired, as a de-icing phase.
But the biggest issue by far is people trying to get their little air conditioner to work harder than it was ever meant to - either by setting the temperature too high (for warming) or too low (for cooling) and/or for a bigger area than the unit was designed for.
In short, if you don't hear the compressor cutting in and out every now and then ... and it's running continuously ... you are overworking it and it will work itself into the ground.
Other obvious things to pay attention to are curtains, insulation and all the other things already mentioned - to reduce the heat load the air conditioner has to deal with. Also, as stuffy as you may feel it will get, close off the air-conditioned zone. It is pointless to cool down a room on a hot day and to have a window open 'a crack' for some fresh air ... you are just allowing more hot air into the room which then has to be cooled down. The same principle applies to to winter warming.
