Quote:
Originally Posted by Viking House
I have some data from a data logger but the file is too big to upload. I remember last January when it was -13 degrees C the return air temperature was +17 degrees C, and the house temperature was 19 degrees.
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Just a couple of questions. was it 18,50C or 19,49C indoors? What about return temperature? 16,50 or 17,49? If we take the most extreme cases, the best one gives ( 100 * ( 17,49 + 13 ) / ( 18,50 + 13 ) ) = 96,8% efficient, while the worst case gives 90,8% efficient. Both very good, but the last is about three times the energy loss of the first. (first one is 3.2% lost, second is 9.2% lost). I did not also calculate the outside temperature insecurity, but that would only push it even further apart.
Also very important for the total efficiency is the power usage of the fans. I guess they are both placed before the exchanger to recover as much of the heat as possible, but what wattage where they during the calculation? If they where running very hard because of frost, firstly you would have overpressure inside, which you really do not want, also, you would have a lot of heat from the fans contributing to the "efficiency" of the unit. Of course, all units have this, but the numbers at the time of measurement are important.
Also very important to the numbers is the relative humidity indoors and outdoors, and the rate of airflow. With that high an efficiency, and no humidity recovery system, I can see no way there will not be frost on the outgoing circuit. Of course, with no airflow, the efficiency would be very high indeed, but there might be a defrost safety system?
-Ko_deZ-
EDIT: The reason for there having to be frost is that the outgoing air would have to be about 2C apart from the incoming air, so -11C. That is about 22 below freezing in F. Unless the indoor air was remarkably dry, there would be condensation, and at below freezing temperatures, there will be ice. There is no way around that.