I agree with MH, there are some errors that should be addressed.
First, the LSB (least significant bit) error roundoff of the temperature meter could easily throw the COP below 1.00.
Those meters are notoriously inaccurate at the low end of the scale, and chances are the specified error is as a percentage of full scale. Errors around zero are usually not specified.
Some of these meters do not even have suitable reference junction compensation, or reference junction tracking. Just holding the meter in your hand can throw the reading off, should you accidentally heat the reference junction (the end that plugs into the meter).
Further, these meters typically use a type "K" thermocouple, one of the worst for low end measurement. Chromel / Alumel (type K) is usually used for high temperature measurement, up to 2000 F.
So a COP of 1.05 is to be expected given the imprecise instrumentation used for the test.
Considering the above, and using a bathtub as a thermal chamber, I think it is amazing that he was able to get a reading within 5% of the actual value i.e. COP= 1.00
But then again, if you wait for that LSB to flip up or down, you can bias your test result in the desired direction.
Unless you have access to a high quality electronic thermal measuring instrument, you might be better off using a calibrated mercury thermometer.
Alternately one of those cheap indoor outdoor thermometers might serve as they use thermistors instead of thermocouples so don't suffer reference junction problems. They are designed to be fairly accurate over the range of 0 to 100 F. Also they read in tenths of a degree so can bury the LSB error by one order of magnitude.
Over this range, doing the measurements in degrees F and manually converting to C afterwards will improve granularity errors.
Can anyone find an English language manual for the ELRO M990, so I can look further into this?
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