Talk:Heat pump

From Academic Kids

On efficiency

I am not sure what the potential for bias is here, but it would help us non-specialists to know what the standard for efficiency is; is there an absolute standard or is it entirely relative; is the relative efficiency of heat pumps being compared to other pumps; can we have details on relative efficiency among heat pumps (for example, what is the most efficient refrigerator; what is the least efficient refrigerator; how efficient are average household and inudstrial refrigerators -- can this be included without endorsing any specific product?) Slrubenstein

Bias, because I am a great supporter of heat pumps. Now that I have explained the efficiency, I feel the text shows that even more. - Icarus

Well, bias or no, I think the more information the article presents, the better it is -- so I appreciate your additions. Nevertheless, they raise more questions. First, what does it mean that an 100 watt electric heater delivers 100 watts of heat? I thought watts = volts x amps. How does this measure "heat?" Are electric heaters really 1005 efficient? You still haven't explained how efficiency is being measured. Does an electric heater convert into the electricity into exactly the amount of heat that was originally used to generate the electricity? Is this really possible? Also, the article is still vague on how, and under what specific conditions, a heat pump can excede 100% efficiency. I am not an engineer or a physicist so the answers to these questions are not at all evident to me -- I hope you ro someone else can develop the article so it will be clearer to a mass audience, Slrubenstein

Watts are units of power (= energy/time), and yes, you can work out electrical power from voltage x current, but that's not the basic definition of power. Efficiency is generally defined as (energy in)/(_useful_ energy out), however this does not appear to be the definition of efficiency being used in this article - nothing can be 100% efficient by this definiton, let alone more so. It might be best to quote the efficiency of a heat pump and that of an electric heater by this (widely accepted) definition, and allow comparison. (This is all complicated by the fact that in most cases the heat is the _useless_ energy, not the useful ...) -- Bth

This article should be written by someone with at least a good knowledge of basic Thermodynamics (Ch415 as we teach it here). I dont really have the time for it now. Yest if the product you want is heat the effciency can well be above 100%. -- 152.1.193.141

Okay, the previous two comments just confuse me (nothing can be 100%efficient by one definition, but that isn't the definition here) -- as I said I am not a pysicist or engineer, but I assume the article is being written to help educate people just like me. The point is not to deocument an argument over how efficiency "should" be measured, the point is that the article has to explain clearly what is going on. I wish it did, but so far it does not, Slrubenstein

I suppose if you imagine that the heater is 100% efficient because all of the heat it produces heats the room. Now consider a fireplace consuming an amount of would equal to 100 watts, it might be only 50% efficient because half the heat goes up the flue and only half goes into the room. A heat pump might be 200% because it uses the same 100 watts to move twice as much heat into the room as the heater. I think. -- rmhermen

Okay, I know the flu allows for airflow, and also the exhaust of smoke; I know electric heaters do not need airflow and do not produce smoke, so it doesn't need a flu -- is this the main reason why it is so much more efficient? Is it possible for someone to explain all this -- and the physical laws behind it -- in the article in a way that is still accessible to people like me? I appreciate the answers to my questions, but I also pose them as suggestions, hopeful of improving the article. As far as I am concerned, the article still does not "explain" efficiency, at least not clearly. That said, I do think the article has improved significantly today.Slrubenstein

I would suggest following the link that someone (rmhermen, I assume?) put in to the Carnot heat engine article, and the link to Thermodynamics (which I just wikified). The theory is explained in those articles (including a definition of efficiency, though perhaps not one you would find very helpful). Apologies for the lack of clarity in my earlier attempt to explain, I was getting confused myself (shame on me for skipping those Thermo classes). -- Bth

As a device to bring light into a room a standard lightbulb is only 5 percent efficient. 5 percent of the electric energy you put in comes out in the form of light, 95 percent in the form of heat. Efficiency is generally defined as (energy in)/(_useful_ energy out) A 60 Watt bulb requires 60 Watts, and provides (5 percent) 3 Watts of light (useful energy). So it's not very efficient as a light source.

As a heater it is more efficient: A 60 Watt blub still requires 60 Watts, but now it provides (95 percent) 57 Watts of usefull energy, in the form of heat.

An electric heater is 100 percent efficient (not counting the energy lost in transport fom the power plant). No energy is lost in any form but heat. 100 Watts go in, 100 Watts come out, in the form of heat. Don't argue, they do. For example, if the goal is to heat water, it takes 4.18*10³ Joules of energy to heat 1 kilogram of water 1 degree Celcius.

So an electric heater of 100 Watts (100 Joules a second) can heat 1 kilogram of water at a rate of 1.43 degrees every minute.

A heat pump is a miraculous device. It does not produce (the bulk) of the heat it 'produces', it gets it from another source, such as groundwater or the air. It uses mechanical devices to do so, which of course require electricity to run.

Depending on the source (temperature) of the heat a heat pump is less or more efficient. It can theoretically 'pump' ten times more energy around than it could ever hope to produce. And as an added bonus:

The machinery also produces heat as a by-product, as do all electrical devices (feel up top your monitor, or around a lightbulb). In fact, if you put 100 Watts of electrical power into the machinery, 100 Watts of power (1.43 degrees of temperature rise a minute) will come out again.

So no, technically nothing can be more than 100 percent efficient. But they can do more with the energy they are given.

Let's say the heat pump has found a loophole.

And let's say it is several times more energy efficient than an electrical heater, if you want to heat say your house.

And let's say an electric heater is 100 percent efficient, (prove me wrong).

Efficiency is generally defined as (energy in)/(_useful_ energy out)

Define efficiency as (electrical energy in) / (useful energy out)

Do the math. -- Icarus

Try explaning, not insulting. And all the electric heaters I know also produce light so they are not 100% efficient. --rmhermen

I'm not trying to be insulting, I'm just a little shortfiused today, sorry.

Well, I appreciate the time that you, rmhermen, and bth are putting into this. The point is not to be argumentative, but to make the article as informative and clear and accesible as possible. When I have asked questions it wasn't in the hopes of proving anyone wrong, but rather in learning more. And I am... Slrubenstein

You will find that much of the light emitted by an electric heater is infrared and red light. Have you ever noticed how the sun feels warm on your skin? That's because a lot of the energy emitted by the sun is in the form of infrared light. Technically (IR-)light is not heat, but as soon as it strikes a (black) surface it will be. The IR radiation will be converted into heat, or reflected away. Black absorbs absolutely, other colors do not.

So the light from your electric heater will still become heat, and unless you aim your heater outside, or use mirrors you reflect the radiation outwards, the radiation will always heat your house.

ps: of course some energy will escape, it always does. It'll go out your window, or through cracks underneath doors. But all energy will be(come) heat. - Icarus

Efficiency omitted from article

Wouldn't it be more conventional to define efficiency as (useful energy out) / (electrical energy in), or more generally (useful energy out) / (useful energy in)? That is, the other way up from the definitions used above. This is particularly important for heat pumps as they are fairly unusual in that for them this number can be greater than one (or 100%, if you prefer). This is because this definition of efficiency ignores the useless energy input. Perhaps the main article should make this point explicit. Ed Davies