View single post by Keinokuorma
 Posted: Sat Jan 19th, 2008 05:56 pm
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Keinokuorma



Joined: Mon Jun 26th, 2006
Location: Finland
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A start/run capacitor could be used in a few ways. But its main purpose is to maintain a specific U/I phase shift between windings of the motor.

Depending on the motor type, you could be starting with hard power to both windings, then running with the capacitor in series with the start/accessory winding. Sometimes you use the same capacitor in all situations. Then you might be using the capacitor to compensate the parasite power. There are other ways, more or less derived from these.

On a Watt meter, or energy meter, if wired correctly, the meter will report the correct total power or energy of the load (both meter types account for the phase shift). If you use separate V and A meters, you get the voltage and current, with the phase shift unaccounted.

I asked the BTU thing, because often (if not always) BTU is not used for reporting other energy than direct heat... while the motor power is reported in Watts or HP, heat could be reported in (k)Watt-hours or BTU... anyway, us Yurupians are SI freaks and like to use the Watt and Watt-hour in both cases.

There are many things that affect the real heat transfer capacity of a refrigeration system, although the maximum is determined by the compressor's ability to circulate the refrigerant. Anyhow, if the electrical power reported for the comp would be directly comparable to the heat transfer capacity of the system, the heat pump AC would not be very effective in heating your home - with all the losses you would be better off with direct electric heat if that was the case.

No, a compressor of certain electrical wattage can transfer a much higher amount of heat per second, than its own energy consumption would be. Unless, of course, if the temp difference between cold and hot side is too high, or the system becomes inefficient for some other reason.

I believe, if 900 BTU is reported for the system, that is the mean heat transfer capability, which would be 264 Watts, or comparable to it being able to keep the temp if there was a 264 Watt heat source in the fridge and it ran all the time. I believe that would be a roughly 80 to 100 Watt compressor at most, with optimally designed circulation.

Should anyone want to disagree with me about something, feel free to do so.

Last edited on Sat Jan 19th, 2008 06:10 pm by Keinokuorma



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