Planned Obsolescence is your fault

[Thomas Okken]

(01-03-2019 04:54 PM)Maximilian Hohmann Wrote:  

(01-03-2019 02:02 PM)Thomas Okken Wrote:  The EER ratings I'm googling suggest a usage of about a quarter of a joule, or less, of energy used per joule of heat removed by modern AC units. That strikes me as plausible since it's also in line with heat pump efficiency ratings I'm seeing.

There can be no fixed numbers as it very much depends on the process temperatures. My figures above were for the worst case. Unfortunately this is what I see very often: Protable AC units with a hot-air hose that is supposed to be routed through a hole in the window (or wall), but which are operated with the window half open so that the hose can hang outside. Used like this, they have a negative efficiency because they add the heat from their electrical motor to the room temperature and really only cool their immediate surroundings. But even when operated properly these things are very inefficient.

I didn't see you qualify that four-for-one number as "worst case" anywhere. Now that you are suggesting an actual scenario of how to get that kind of terrible performance, all I can say is that that may be a common scenario in Germany, but in places like the U.S. where residential AC is a lot more common, central or wall-mounted AC is the norm, and in those kinds of units, there is no mixing of inside and outside air.

I've seen the portable units with hoses that you describe, and they come with an adjustable plastic piece that fits in a sliding window, so that the inevitable slit is closed off and only air from the hose goes through. I'm not sure how much it matters though, because if it blows air out, air must come back in somewhere. And in Germany where you tend to have pivoting windows, not sliding ones, it wouldn't fit anyway.

(01-03-2019 04:54 PM)Maximilian Hohmann Wrote:  For the studio of my wife (which is above the garage in a separate building) we use an electrically driven heat pump with an air-to-air heat exchanger. Under optimum conditions (say outside temperature 15°C for a room temperature of 20 degrees) it will add about 2.5kW to the 2kW that the motor draws, thereby more than doubling the electrical energy. Today (-5°C outside) it will "harvest" less than 0.5kW with those 2kW input. And operated the other way round (for cooling) the figures can only be worse because other than with heating the heat lost by cooling the engine is really lost.
(Heat pumps that can use ground water or geothermal energy the efficiency is much better.)

I'll admit that I'm not an expert on this, but I know someone who is, and they opined that the yield you're getting out of your unit is rather bad. You're quoting coefficients of performance of 2.25 and 1.25 for ideal vs. cold conditions, but you should be able to get around 6 and 3, respectively. It could be your unit is dirty, or just not very good. You may want to get that looked at.