Sitting here in my deck swing enjoying a cup O joe I looked over at my heatpumps outside unit and observed that the fan mounted on top pulls the air through the coils then up & out,similar to an auto's fan. I'm no mechanical engr, but I'd swag that this orientation causes the air moving through to contact more of the heat exchangers surface than if the fan pushed air down from the top out out through the coils.
My thesis is such, with the fan being a puller, it causes the entire inside area of the coils to become a low pressure area. I think one of the rules of thermo dynamics is air cannot stand the presence of a low pressure area and will rush to fill it, through every available void, thusly causing the rushing air to contact every surface of the heat exchanger.
Conversely if the fan was a pusher the rushing air would only contact the surfaces that constituted the shortest exit through them and not contacting them all.
This sounds good but seems the opposite of how our autos cooling systems are set up. But I can see where adding a shroud makes a low pressure area which increases efficiency. But our older Bolts didn't come with shrouds. So it seems in earlier autos the engrs depended on moving air from the vehicles forward motion to get enough airflow to make contact with all of the heat exchangers surfaces and that the fan was to be an aide when there wasn't enough air flow at idle and slow speed. In this case the fan being on the engine side didn't interfere with max air flow at speed. So how does this relate to the angle of the dangle? I dunno, just musing over a cup o joe.
