Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat

[sailorboy1]

Ok should the fan blow or suck the air. Should the fan on the condenser be sucking air through it or should it be blowing air through it? I have 2 systems and 1 of each.

Does it even matter? If so why?

[jkleins]

Originally Posted by sailorboy1

Ok should the fan blow or suck the air. Should the fan on the condenser be sucking air through it or should it be blowing air through it? I have 2 systems and 1 of each.



Does it even matter? If so why?

Mine move air from inside the case (pulled in from a inlet on the other side connected to a hose from a fresh air source) to the outside of the case. That would probably be “sucking”. I suppose if the inlet hose was attached to the fan side the fan could be turned around and work just as well by pressurizing the case and replacing the hot air that way. I have never had one installed that way.

Jim

[S/V Adeline]

*IF* it matters to a specific installation, i would believe it would deal with temperatures. Typically *suck* off the condenser, *blow* onto the evaporator, when practical. The condenser being cool, sucking the cool air cools the fan, where sucking heated air off the evaporator *may* overheat the fan. With modern fans it may be a non-issue.

[sailorboy1]

the one that sucks pulls air through the condenser into the fan and blows it across the compressor housing, this is a BD50 unit

the one that blows draws air into the fan and blows it through the condenser, this is a BD35 unit

[guyrj33]

i've been told it's more efficient to pull air than it is to push air.

[redhead]

I asked my HVAC captain your question and his response was "that's a good question, I don't know". He says it has more to do with the volume of air moving over the coil.

If this is as helpful as mud, I apologize. I get a lot of answers like this one. But he's been in business for 40 years, so that makes it an expert muddy opinion.

(oh and he just told me that HVAC is NOT refrigeration which is not his strong suit.)

[LeeV]

Originally Posted by redhead

I asked my HVAC captain your question and his response was "that's a good question, I don't know". He says it has more to do with the volume of air moving over the coil.

If this is as helpful as mud, I apologize. I get a lot of answers like this one. But he's been in business for 40 years, so that makes it an expert muddy opinion.

Now THAT is funny!

I’m watching this thread because I have 2 computer fans for our new Isotherm fridge when it gets here, and can’t figure out which direction they should face.

[Bellinghamster]

Fans in general, do better at pushing than pulling. Pushing results in higher density air through blades and the higher density of air through the condenser will transfer more heat from it, whereas pulling results in lower density air through the condenser and moving through the blades, giving them less of a "bite" of air therefore lower CFM coupled with less heat transfer due to the lower air density.

Tubaxial fans (i.e. computer fans), have fairly low static pressure, and CFM falls off very significantly with increased pressure differential across it, so minimizing restrictions is critical. To move the most air, push through the condenser, minimize intake restrictions, and make sure your condenser fins are clean and the air has an easy way out (if you're exhausting it elsewhere) with minimal flow restriction.

[Pauls]

It depends upon the application (like most engineering things, it's about the details. Both sides of the fan are moving the same amount of air, of course. But the blow side is a higher velocity directed stream of air. The suck side is lower velocity flowing from a 180 degree arc around the fan. If you want a directed stream of air use the blow side. If you are trying to move air evenly thru all of the inside of a box I'd use the suck side.

[rslifkin]

Within the realm of computer fans, some will push against more static pressure than others, so definitely read the specs. For a condenser design that allows it, you can also arrange fans in a push/pull setup (one on each side) if a single fan can't move enough air.

[sailorboy1]

I googled it and get results for both being best. Blowing provides more turbulent flow across the condenser, so that would seem best. But if that means the fan draws air across the compressor and is warmer then it isn't better. Overall it appears were weighting the 2 choice it is best to have the air flow direction being from coolest area and blowing into the hotter area.

[bernardsnatager]

Interesting question at its heart - is it better for cooling to BLOW across that which needs to be cooled, or better to SUCK away that which needs to be cooled. And, also interestingly enough, there is an answer! When trying to cool an enclosed space, it is always better to SUCK out the air which is generated inside the controlled space. Crucial to making the system work is ensuring that an adequate intake space is provided on the other side of the device to be cooled, so the hot air can be constantly removed... Just from 30 years experience on cooling darned devices!

[Brewgyver]

Originally Posted by S/V Adeline

*IF* it matters to a specific installation, i would believe it would deal with temperatures. Typically *suck* off the condenser, *blow* onto the evaporator, when practical. The condenser being cool, sucking the cool air cools the fan, where sucking heated air off the evaporator *may* overheat the fan. With modern fans it may be a non-issue.

You've got things backwards. First, the condenser is always much warmer than the evaporator.

In virtually all compression cycle refrigeration systems, the condenser fan (if present) pulls air through the condenser coil. i

In most small fridges, there is no evaporator fan. For that matter, most self-contained small fridges don't have a condenser fan either, just a large static coil on the back of the cabinet. When you have a system using a separate condensing unit, then you typically have a small condenser coil with a shrouded fan pulling (sucking) air across the coil, with keel-cooled units excepted of course.

[Brewgyver]

Originally Posted by sailorboy1

I googled it and get results for both being best. Blowing provides more turbulent flow across the condenser, so that would seem best.

Turbulence = inefficiency.

Condenser fans always pull air through the coil. Is it possible that a unit exists that works the other way? Sure, but I've never seen one, and I've dealt with all kinds of air cooled units up to 100+ tons.

Here's a typical remote condensing unit for a marine fridge:



Note the shroud around the fan. This is to maximize even airflow across the entire condenser coil. Now think about what it would take to clean the coil if the airflow was reversed.

On units using evap fans, they generally pull through, too. The big exception in that case is in conventian residential A/C systems in which the evaporator is attached to the discharge of a furnace. OTOH, on most cooling only units and mini-splits the evap fan or blower is pull through.


On this MagicAire fan coil, note the blower wheel visible, this is where the discharge duct is connected. The copper stubs near the far end denote the evap coil location.

[S/V Adeline]

Originally Posted by Brewgyver

You've got things backwards. First, the condenser is always much warmer than the evaporator.

In virtually all compression cycle refrigeration systems, the condenser fan (if present) pulls air through the condenser coil. i

In most small fridges, there is no evaporator fan. For that matter, most self-contained small fridges don't have a condenser fan either, just a large static coil on the back of the cabinet. When you have a system using a separate condensing unit, then you typically have a small condenser coil with a shrouded fan pulling (sucking) air across the coil, with keel-cooled units excepted of course.

Absolutely correct!! Got lost in my train of thought visualizing different cooling systems i have dealt with over the years and crossed the terms.