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sailorboy1 09-09-2020 08:09

Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 09-09-2020 09:18

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

Originally Posted by sailorboy1 (Post 3228509)
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 09-09-2020 09:20

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
*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 09-09-2020 11:35

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 10-09-2020 08:10

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
i've been told it's more efficient to pull air than it is to push air.

redhead 10-09-2020 09:21

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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. :thumb:

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

LeeV 10-09-2020 09:33

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

Originally Posted by redhead (Post 3229314)
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. :thumb:

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 10-09-2020 09:53

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 10-09-2020 10:01

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 10-09-2020 10:02

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 10-09-2020 10:23

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 10-09-2020 11:56

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
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 10-09-2020 12:02

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

Originally Posted by S/V Adeline (Post 3228562)
*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 10-09-2020 12:31

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

Originally Posted by sailorboy1 (Post 3229383)
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:

https://static.grainger.com/rp/s/is/...536&$adapimg$=

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.

https://www.magicaire.com/wp-content/...ne-624x460.jpg
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 10-09-2020 12:34

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

Originally Posted by Brewgyver (Post 3229463)
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.

wingssail 10-09-2020 12:45

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

Originally Posted by Brewgyver (Post 3229482)
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.

Virtually all window unit air conditioners blow air through the condenser and suck air through the evaporator.

SV Bacchus 10-09-2020 12:46

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
Not to muddy the waters but.. When I had my fridge/freezer converted from cold plate to evaporator style everything was replaced except the BD50, which the installer/business owner said was working perfectly.

However, the gentleman said the fan was set up incorrectly. He said in colder climates people actually switch them seasonally. I don't remember the directions as it wasn't important to me being a Florida boat hanging out in the Eastern Caribbean. It blows, or sucks, in Summer and the opposite in Winter.

The downside to my setup is the unit gets air from the lazarette in the port sugar scoop. That is the same place my genset is located. The gentleman suggested I plumb cooler air via a tube to the BD50. The unit works extremely well without it and I wasn't keen to make a new hole anywhere, even if it was in a inside bulkhead.

He did replace my fan with a higher flow rate unit and switched the direction to what was recommended "for hot climates".

Brewgyver 10-09-2020 13:02

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

Originally Posted by wingssail (Post 3229496)
Virtually all window unit air conditioners blow air through the condenser and suck air through the evaporator.

True, but in that case it's an expedient. They use one double-shaft fan motor and have to achieve flow over both coils with one motor and in as small a package as practical. The evap and condenser coils are both vertical, and at most only about 8-10 inches from each other. The evap fan has a molded styrofoam shroud. If the condenser side pulled air through it would be directing the heat in toward that shroud, adding heat back into the cooled air stream.

sailorboy1 10-09-2020 13:51

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
Some of you should consider publishing papers to counter the other PhD papers out there. You know one of the ways you generally can tell if someone is wrong? They start using absolute words like "always" etc.

It was mostly a curiosity question and in the end I am pretty sure of the answer being that it is better to draw from which ever side of the condenser has the cooler air.

Madehn 10-09-2020 18:40

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
how do cars with electric fans do it on their radiators-- if you have a transvers engine then you probably have electric fans moving the air- since they could mount it either in front of or behind the radiator, i am thinking they ( detroit engineers with huge budgets )would have used the most efficient way to get rid of the heat?

S/V Adeline 10-09-2020 19:52

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

Originally Posted by Madehn (Post 3229716)
how do cars with electric fans do it on their radiators-- if you have a transvers engine then you probably have electric fans moving the air- since they could mount it either in front of or behind the radiator, i am thinking they ( detroit engineers with huge budgets )would have used the most efficient way to get rid of the heat?

That is actually the train of thought that caused me to reverse condenser and evaporator. On a traditional inline engine, the fan sucks air through the radiator and blows same air over the engine. With most early electric fans (mounted behind the radiator) they are doing the same. Later came electric mounted in front, blowing through. When the vehicle travels down the road, ram air is forced through the radiator and to operate the fan against that would defeat the purpose and quite quickly burn up the fan.

Vinnie1966 11-09-2020 01:22

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
Hello everybody,

if the blower blows, it blows a bit of the heat generated by the fan motor. If it sucks, then this does not happen. Right? :)

cheers
vin

Brewgyver 11-09-2020 08:28

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

Originally Posted by Vinnie1966 (Post 3229839)
Hello everybody,

if the blower blows, it blows a bit of the heat generated by the fan motor. If it sucks, then this does not happen. Right? :)

cheers
vin

No, but also the answer isn't that simple. With a typical simple propeller fan, the fan blade attached to the motor shaft, the motor is effectively cooled by the air moved by the fan, no matter which way it blows. If you look at the specs of such fan motors you'll find "Air over" meaning they need to be in the airstream to prevent overheating. There are also propeller fans that are belt driven, with the motor typically out of the path of flow, as in a Whole House Fan:
https://static.grainger.com/rp/s/is/..._AS01?$mdmain$
They typically have motors with internal fans, as do motors that are generally used for other purposes, such as pumps.

thinwater 11-09-2020 14:55

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

Originally Posted by guyrj33 (Post 3229274)
i've been told it's more efficient to pull air than it is to push air.


This is true of pumps, which can cavitation. But at the pressure differentials were are talking about here, it makes no difference. Also, as others have pointed out, fan motor cooling and exposure to dust and condensate must be considered.


You need to consider the whole unit design. No one answer.

David B 11-09-2020 21:25

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

Originally Posted by sailorboy1 (Post 3229533)

It was mostly a curiosity question and in the end I am pretty sure of the answer being that it is better to draw from which ever side of the condenser has the cooler air.

Correct in my book. With a typical remote compressor/condenser unit, if you have the fan sucking air through the condenser, it will be blowing that hot air over the compressor (which without fins, has very little surface area to dissipate heat anyway).

If you have the fan blowing air through the condenser, it will be taking that air across the hot compressor. Good for the compressor, not as good for the condenser, but unless the ambient is really high (and the condenser needs all the cooling it can get), then that seems the best compromise.

Better - significantly more airflow, and duct the hot air overboard (or keel cooling).

In our case, the freezer unit (Vitrifrigo) blows through the condenser, and the hot air exhausts straight into the galley under the oven onto my First Mates ankles. Nice in winter, but we sail in summer - in the Med.
Ask me why I am considering changing this ........

GordMay 12-09-2020 02:14

Re: Blow or Suck - refrigeration fanpenses of Cruising and Living on the Boat
 
Standing alone (there’s more to this, but), the blow side of a fan produces a more concentrated, faster moving, and more turbulent airstream, compared to the intake side, where air is drawn almost equally from all directions. The velocity of the air downstream of the fan is roughly twice that of the air passing through the fan.*
The turbulence also greatly improves the efficiency of the heat transfer. Turbulence is in fact your friend.
So from those points of view alone, the blow side does appear the better cooling side.
If you're trying to ventilate (cool) an entire room/compartment), exhausting (sucking out) air is more efficient.

* Have you ever tried to suck out a candle?

SV Bacchus 15-09-2020 05:39

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

Originally Posted by sailorboy1 (Post 3229533)
It was mostly a curiosity question and in the end I am pretty sure of the answer being that it is better to draw from which ever side of the condenser has the cooler air.

Which, I believe, may be the reason the tech in Grenada said in some climates it is best to switch the direction of airflow twice a year as noted in my previous post.


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