**Of course, no one is saying such a thing. An air con with an EER of 5, will produce as much heat (under ideal conditions) as a 5kW resistive heater, with 1kW of electrical power input.
The short answer is yes. Reverse cycle air conditioning is a cheaper form of heating than gas - it uses less energy to produce the same amount of heat inside, as you are effectively "stealing" heat from outside and transferring it inside - even when it's cold outside.
Since heat rises, you get better temperature distribution in a room by feeding in warm air from the bottom. If you fed it in from the roof, you'd get a hot head when you were standing, but would feel cold while sitting down.
Similarly, ducted cooling systems are best installed with the registers mounted in the ceiling.
It's all in the terminology and how you measure it. Reverse cycle aircons have a greater "efficiency" than that of an equivalent output electric heater. If the electric heater is deemed to be "100% efficient" then a reverse cycle aircon that produces say 2kW of *heat energy* for 1kW of electric energy, then it can be said that the aircon is 200% efficient compared to the electric heater. That is the way reverse cycle aircons are rated and marketed, but it's *not* a marketing gimmick. It is the actual practical heat energy output that heats up a given volume of air.
A 7kW reverse cycle aircon for example actually gives you 7kW of *heat energy* for only a few kW of electrical energy input. That is much better than what you can achieve with an electric heater.
It all has to do with how you measure the heat energy in a system. One formula for heat energy output of a system is : Heat Energy(kW) = Specific Heat of Air (kJ/kg degK) * Air Mass (kg/hour) * (Temp differential /3600)
I beg to differ! Heat energy IS free, as supplied from our sun. The part that is not free is concentrating and directing it for our use. The heat from a rev cycle AC costs nothing. The electricity to collect and move that heat is the only thing we pay for. On the other hand, the heat from a radiator style heater costs heaps due to the fact that electric energy is converted to heat. Therefore the 500% efficiency figure quoted is realistic IF compared to a radiator.
I meant the recirculating inlet, where air is sucked in before being heated and blasted out into each room. In every house I've seen it is near floor level, regardless of whether the outlets are inside the floor or on the ceiling.
(Side note... I'd happily take a 5 or 10% efficiency hit just to have some fresh air drawn in occasionally!)
We are being serious. Of course you can't get energy for nothing, or get more energy out of something than you put in in total, and nobody is claiming that is the case. The thread is about reverse cycle aircons, and they *are* more efficent than electric heaters for what they are designed to do, and they *are* rated in kW of *heat energy* that is greater than the electrical energy in kW put into it. There is a big difference between kW of heat energy and kW of electrical energy.
Which of course many systems do with an outside air inlet. Some allow you to adjust the ratio with a sliding cover. It is simple enough to make a similar inlet for any ducted system. Or simply remove the draft excluders from you entrance doors :-)
Which of course many systems do with an outside air inlet. Some allow you to adjust the ratio with a sliding cover. It is simple enough to make a similar inlet for any ducted system. Or simply remove the draft excluders from you entrance doors :-)
We have one of those new fangled units that sits inside the roof. The last time I saw it was just before the plasterboard went on. ;) Outlets are in the ceiling as well, since the floor is concrete.
Perhaps I just need to run some ducting from the outside door, across the dining room floor, and into the inlet. ;)
OK, instead of quoting faint memories i decided to pull out the uni books and dust them off. Seems I was right, so i decided to hound wikepedia for some quotes.
First is
formatting link
which is a full of mathematical formula, so not so easy to read.
Next is my physic book from first year eng. @ QUT, Serway & Beichner.
This is a direct quote: In a refrigerator or heat pump, the engine absorbs heat energy from a cold reservoir and expels energy to a hot reservoir. This can be accomplished only if work is done _on_ the engine. From the first law, we know that the energy given up to the hot reservoir must equal the sum of the work done _and_ the energy absorbed from the cold reservoir. Therfore, the heat pump transfers energy from a colder body to a hotter body. In practice, it is desirable to carry out this process with a minimum of work. If it could be accomplished without doing anywork, the the heat pump would be 'perfect'. Again, the existance of such a device would be in violation of the second law of thermodynamics, which in the form of the Clauius statement states: "It is impossible to construct a cyclic machine whose sole effect is the continious transfer of energy from one object to another object at a higher temp without the input of energy by work" In simpler terms, *energy does not flow spontaneously from a cold object to a hot object*
Serway & Beichner then go on to provide examples of how to calculate thermal efficiency then go on to further describe the theoretical carnot engine (which is the most efficient engine).
SO I went on to check the second law efficency, and find that wikepedia describes exactly what i described here:
formatting link
"It should be noted that the energy efficiency quoted by appliance makers is the "first-law" thermodynamic efficiency; it only tells one how well the particular appliance converts one form of energy, usually electricity, into another, usually heat. It does not tell one how the appliance compares to, say, a Carnot heat engine or any other cyclical process."
Folow the link to:
formatting link
we see "The thermal efficiency () is a dimensionless performance measure of a thermal device " and "Heat pumps, refrigerators, and air conditioners, for example, move heat, rather than convert it, so other measures are needed to describe their thermal performance. The common measures are the Coefficient-of-performance (COP), Energy Efficiency Ratio (EER), and Seasonal Energy Efficiency Ratio (SEER). " Which i think someone else described.
LAst but not least, this sums it all up very well
formatting link
So to claim that a reverse cycle air con is 500% efficent is not true, but rather if you were to say that it were 500% more efficient relative to a resitive element, then you are probably right.
Not quite, Dont forget that the sun has put 500W in. You have used 25W to move 500W, sum total is 525watts needed to produce 500w, which is not quite 100% efficient, but getting close. Second law of thermodynamics.
What I am proving here is that no matter what you do it is not possible to have a heat pump that is more than 100% efficient. Therefore the energy in your home is not free, its provided by using energy to move energy. Sum total = more in than out. My response was not directed specificially at you, more so at the posters claiming that heat pumps can be greater than 100% efficient.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.