Awl --

Curious as to "fan logic".

I notice that in, say, kitchen hoods, central A/C air handlers, squirrel
cage blowers are almost always used.
btw, does "blower" imply the squirrel cage config? I will use "SC blower"
visavis traditional blade-type "fan".

The SC blowers in A/C seem to be most often single large squirrel cages,
whilst the sc blowers in kitchen hoods seem to be smaller dual cages, on
either side of a double-shaft motor.

SC blowers seem to be super-efficient air movers. I scavenged two
good-sized ones from a Lennox system, the cage about 1 foot long by 1 foot
dia, and just turning it gently by *hand* delivers quite a forceful
breeze -- which surprises even the mechanically savvy I demonstrate this to.

Otoh, blade-type fans are used in "boosters" in hvac duct, window/minisplit
A/C's, central A/C condensers, roof mushrooms/wholehouse fans.

What governs the choice, and why?
Ito of raw cfm's per $ or per "unit size" (in cu in), is one style
inherently superior to another?


The, uh, thrust of my Q is that I'm cobbling together a kitchen, and am
dizzied by prices of venting hoods that I like (*easily* $2,000-4,000 and
not super-fancy -- holy ****!!!), and am not particularly impressed with the
few I'm able to turn on, noise-wise, flow-wise. Cosmetically, tho, they are
super.

HD has a couple of decent-looking ones in the $400-500 range, but they are a
little bulky.

In particular, the fact that the dual sc blowers are located *in* the
hood-proper bulks many of the units up considerably, which in this
application creates visual line-of-sight issues, due to proximity to an
entrance door.

So, I could locate the sc blower right up at the exit vent near the ceiling,
or, even better from a visual pov, use an in-line booster type fan.
And then I would be able to use the old hood etc from the original set up,
which everyone kind of likes anyway.

With an inline fan, I realize the motor itself serves as a flow obstacle,
which in a 6" or so duct could be a considerable proportion -- which is not
the case in say an outside A/C condenser, where the blades are easily 3 feet
diameter..

Not to mention the grease/temp issues in a hood, but which I think could be
made manageable by the right motor, filters, and periodic maintenance. I
figger if I will occasionally have to clean the squirrel cage in a blower,
cleaining the fan blades AND the motor in an in-line ditty isn't such a big
deal.

But then, being up at the ceiling, line-of-sight issues would be minimal, so
mebbe a sc blower as traditionally used in this type of venting would be
better. I would lean toward a single cage like in A/C blowers, to totally
get the motor out of the ductwork.


More along shop lines, I had scavenged one of these double-squirrel cage
hood-type motors, and kluged it into the exhaust for my welding table. Wow,
orders of magnitudes better than the inline-fan ditty I kluged earlier,
super-quick fume clearance.
But, the previous in-line fan could have been just ****ty anyway, so I don't
know if apples were compared to apples.

But other in-line fan apps have gone well:
The **** motor in my mushroom eventually went, so I scavenged a window
A/C 3-speed fan unit, thermostat and all, and this works great -- infinitely
superior quality to the original mushroom innards, altho a bit of a pita to
install.

If I get lucky, I'll find a small 3 ph motor, and put a VFD on it, for
infinite speed control -- small VFD's are not that expensive. I'm hoping to
luck out with a system that's quieter than some of the expensive noiseboxes
I've seen. I'm surprised that with $4,000 price tags, they don't offer
something like this.

Opinions, suggestions for the kitchen?

--
EA

Existential Angst wrote:
Awl --

Curious as to "fan logic".

I notice that in, say, kitchen hoods, central A/C air handlers, squirrel cage
blowers are almost always used.
btw, does "blower" imply the squirrel cage config? I will use "SC
blower" visavis traditional blade-type "fan".

The SC blowers in A/C seem to be most often single large squirrel
cages, whilst the sc blowers in kitchen hoods seem to be smaller dual
cages, on either side of a double-shaft motor.

SC blowers seem to be super-efficient air movers. I scavenged two
good-sized ones from a Lennox system, the cage about 1 foot long by 1
foot dia, and just turning it gently by *hand* delivers quite a
forceful breeze -- which surprises even the mechanically savvy I demonstrate
this to.
Otoh, blade-type fans are used in "boosters" in hvac duct,
window/minisplit A/C's, central A/C condensers, roof
mushrooms/wholehouse fans.
What governs the choice, and why?
Ito of raw cfm's per $ or per "unit size" (in cu in), is one style
inherently superior to another?


The, uh, thrust of my Q is that I'm cobbling together a kitchen, and
am dizzied by prices of venting hoods that I like (*easily*
$2,000-4,000 and not super-fancy -- holy ****!!!), and am not
particularly impressed with the few I'm able to turn on, noise-wise,
flow-wise. Cosmetically, tho, they are super.

HD has a couple of decent-looking ones in the $400-500 range, but
they are a little bulky.

In particular, the fact that the dual sc blowers are located *in* the
hood-proper bulks many of the units up considerably, which in this
application creates visual line-of-sight issues, due to proximity to
an entrance door.

So, I could locate the sc blower right up at the exit vent near the
ceiling, or, even better from a visual pov, use an in-line booster
type fan. And then I would be able to use the old hood etc from the original
set up, which everyone kind of likes anyway.

With an inline fan, I realize the motor itself serves as a flow
obstacle, which in a 6" or so duct could be a considerable proportion
-- which is not the case in say an outside A/C condenser, where the
blades are easily 3 feet diameter..

Not to mention the grease/temp issues in a hood, but which I think
could be made manageable by the right motor, filters, and periodic
maintenance. I figger if I will occasionally have to clean the
squirrel cage in a blower, cleaining the fan blades AND the motor in
an in-line ditty isn't such a big deal.

But then, being up at the ceiling, line-of-sight issues would be
minimal, so mebbe a sc blower as traditionally used in this type of
venting would be better. I would lean toward a single cage like in
A/C blowers, to totally get the motor out of the ductwork.


More along shop lines, I had scavenged one of these double-squirrel
cage hood-type motors, and kluged it into the exhaust for my welding
table. Wow, orders of magnitudes better than the inline-fan ditty I
kluged earlier, super-quick fume clearance.
But, the previous in-line fan could have been just ****ty anyway, so
I don't know if apples were compared to apples.

But other in-line fan apps have gone well:
The **** motor in my mushroom eventually went, so I scavenged a
window A/C 3-speed fan unit, thermostat and all, and this works great
-- infinitely superior quality to the original mushroom innards,
altho a bit of a pita to install.

If I get lucky, I'll find a small 3 ph motor, and put a VFD on it, for
infinite speed control -- small VFD's are not that expensive. I'm
hoping to luck out with a system that's quieter than some of the
expensive noiseboxes I've seen. I'm surprised that with $4,000 price
tags, they don't offer something like this.

Opinions, suggestions for the kitchen?

The best kitchen fan I ever had was a explosion proof squirrel cage exhaust fan
I got from a friend. He had used it in a chem lab reagent hood. I ran 8" duct
about 15 feet across the attic to the fan, which exhausted through a couple 90
bends to the end wall. I had to mount the motor on a board which was sprung to
another board with 4 3/4" D x 1.5" long springs set into 1/4" deep holes in the
wood. This isolated fan vibration from the house structure, drastically reducing
noise.

The only noise in the kitchen was the air rushing out the grate. The suction
would easily hold a plate to the grate if you placed one there.

It was probably not something you'd want to run a lot during the heating season,
but sure cleared out smoke in a hurry.

I suspect that the choice of blade or cage fans in most units is a
mechanical/price choice.

I suspect that the choice of blade or cage fans in most units is a
mechanical/price choice.- Hide quoted text -

- Show quoted text -

Also diffrent blade designs produce diffrent CFM vs back pressure
curves.

SC blowers (centrifugal blowers) work well against back pressure.
Blades not so well.

Mark

Typical bladed fans don't work well when any duct is involved. A computer
case fan works well enough when fastened to a panel on a well ventilated
case (same with the outdoor A/C unit), but the same fan isn't going to
produce much airflow with a duct attached, a fan can spin without moving
much air in the desired direction if restrictions are involved.
Many fans will still run at about the same speed even if the air stream is
choked off.

A different fan that produces much better airflow is generally referred to
as an axial fan or blower (what you referred to as inline, I think), and the
commercial/industrial versions can be used with limited lengths of duct (of
specific size).

Squirrel cage/centrifugal blowers produce positive air displacement through
ducts. They can pressurize ducts or large spaces, and deliver great volumes
of displacement. They're often filtered on the intake side and still deliver
great airflow, even with filters that are partial restrictions to airflow.

The dual shaft blowers are a more compact version of a larger blower, and
the smaller cages operate better with a small motor. For many dual shaft
types, the motor is cooled by ambient air, since the motor isn't in the air
stream.
Formed metal blades in cage construction are likely to supply much better
airflow than molded plastic cages.

For many direct drive types, the motor is cooled by the airflow.

Centrifugal/SC blowers are vastly superior in airflow performance.

Cooking appliances introduce other issues, such as cooking steam/vapors, oil
spatter and potential fires from flareups.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html



"Existential Angst" wrote in message
...
Awl --

Curious as to "fan logic".

I notice that in, say, kitchen hoods, central A/C air handlers, squirrel
cage blowers are almost always used.
btw, does "blower" imply the squirrel cage config? I will use "SC blower"
visavis traditional blade-type "fan".

The SC blowers in A/C seem to be most often single large squirrel cages,
whilst the sc blowers in kitchen hoods seem to be smaller dual cages, on
either side of a double-shaft motor.

SC blowers seem to be super-efficient air movers. I scavenged two
good-sized ones from a Lennox system, the cage about 1 foot long by 1 foot
dia, and just turning it gently by *hand* delivers quite a forceful
breeze -- which surprises even the mechanically savvy I demonstrate this
to.

Otoh, blade-type fans are used in "boosters" in hvac duct,
window/minisplit A/C's, central A/C condensers, roof mushrooms/wholehouse
fans.

What governs the choice, and why?
Ito of raw cfm's per $ or per "unit size" (in cu in), is one style
inherently superior to another?


The, uh, thrust of my Q is that I'm cobbling together a kitchen, and am
dizzied by prices of venting hoods that I like (*easily* $2,000-4,000 and
not super-fancy -- holy ****!!!), and am not particularly impressed with
the few I'm able to turn on, noise-wise, flow-wise. Cosmetically, tho,
they are super.

HD has a couple of decent-looking ones in the $400-500 range, but they are
a little bulky.

In particular, the fact that the dual sc blowers are located *in* the
hood-proper bulks many of the units up considerably, which in this
application creates visual line-of-sight issues, due to proximity to an
entrance door.

So, I could locate the sc blower right up at the exit vent near the
ceiling, or, even better from a visual pov, use an in-line booster type
fan.
And then I would be able to use the old hood etc from the original set up,
which everyone kind of likes anyway.

With an inline fan, I realize the motor itself serves as a flow obstacle,
which in a 6" or so duct could be a considerable proportion -- which is
not the case in say an outside A/C condenser, where the blades are easily
3 feet diameter..

Not to mention the grease/temp issues in a hood, but which I think could
be made manageable by the right motor, filters, and periodic maintenance.
I figger if I will occasionally have to clean the squirrel cage in a
blower, cleaining the fan blades AND the motor in an in-line ditty isn't
such a big deal.

But then, being up at the ceiling, line-of-sight issues would be minimal,
so mebbe a sc blower as traditionally used in this type of venting would
be better. I would lean toward a single cage like in A/C blowers, to
totally get the motor out of the ductwork.


More along shop lines, I had scavenged one of these double-squirrel cage
hood-type motors, and kluged it into the exhaust for my welding table.
Wow, orders of magnitudes better than the inline-fan ditty I kluged
earlier, super-quick fume clearance.
But, the previous in-line fan could have been just ****ty anyway, so I
don't know if apples were compared to apples.

But other in-line fan apps have gone well:
The **** motor in my mushroom eventually went, so I scavenged a window
A/C 3-speed fan unit, thermostat and all, and this works great --
infinitely superior quality to the original mushroom innards, altho a bit
of a pita to install.

If I get lucky, I'll find a small 3 ph motor, and put a VFD on it, for
infinite speed control -- small VFD's are not that expensive. I'm hoping
to luck out with a system that's quieter than some of the expensive
noiseboxes I've seen. I'm surprised that with $4,000 price tags, they
don't offer something like this.

Opinions, suggestions for the kitchen?

--
EA

On Thu, 03 Dec 2009 11:23:58 -0500, Existential Angst wrote:

Curious as to "fan logic".

I notice that in, say, kitchen hoods, central A/C air handlers, squirrel
cage blowers are almost always used.
btw, does "blower" imply the squirrel cage config? I will use "SC blower"
visavis traditional blade-type "fan".
...
Opinions, suggestions for the kitchen?

With a squirrel cage, you can keep the motor out of the air flow with just
a straight shaft. To keep the motor out of the airflow with a blade-type,
you'd need a belt, which implies more parts and more failure modes.

Hope This Helps!
Rich

Existential Angst wrote:
Awl --

Curious as to "fan logic".

I notice that in, say, kitchen hoods, central A/C air handlers, squirrel
cage blowers are almost always used.
btw, does "blower" imply the squirrel cage config? I will use "SC blower"
visavis traditional blade-type "fan".

The SC blowers in A/C seem to be most often single large squirrel cages,
whilst the sc blowers in kitchen hoods seem to be smaller dual cages, on
either side of a double-shaft motor.

SC blowers seem to be super-efficient air movers. I scavenged two
good-sized ones from a Lennox system, the cage about 1 foot long by 1 foot
dia, and just turning it gently by *hand* delivers quite a forceful
breeze -- which surprises even the mechanically savvy I demonstrate this to.

Otoh, blade-type fans are used in "boosters" in hvac duct, window/minisplit
A/C's, central A/C condensers, roof mushrooms/wholehouse fans.

What governs the choice, and why?
Ito of raw cfm's per $ or per "unit size" (in cu in), is one style
inherently superior to another?


The, uh, thrust of my Q is that I'm cobbling together a kitchen, and am
dizzied by prices of venting hoods that I like (*easily* $2,000-4,000 and
not super-fancy -- holy ****!!!), and am not particularly impressed with the
few I'm able to turn on, noise-wise, flow-wise. Cosmetically, tho, they are
super.

HD has a couple of decent-looking ones in the $400-500 range, but they are a
little bulky.

In particular, the fact that the dual sc blowers are located *in* the
hood-proper bulks many of the units up considerably, which in this
application creates visual line-of-sight issues, due to proximity to an
entrance door.

So, I could locate the sc blower right up at the exit vent near the ceiling,
or, even better from a visual pov, use an in-line booster type fan.
And then I would be able to use the old hood etc from the original set up,
which everyone kind of likes anyway.

With an inline fan, I realize the motor itself serves as a flow obstacle,
which in a 6" or so duct could be a considerable proportion -- which is not
the case in say an outside A/C condenser, where the blades are easily 3 feet
diameter..

Not to mention the grease/temp issues in a hood, but which I think could be
made manageable by the right motor, filters, and periodic maintenance. I
figger if I will occasionally have to clean the squirrel cage in a blower,
cleaining the fan blades AND the motor in an in-line ditty isn't such a big
deal.

But then, being up at the ceiling, line-of-sight issues would be minimal, so
mebbe a sc blower as traditionally used in this type of venting would be
better. I would lean toward a single cage like in A/C blowers, to totally
get the motor out of the ductwork.


More along shop lines, I had scavenged one of these double-squirrel cage
hood-type motors, and kluged it into the exhaust for my welding table. Wow,
orders of magnitudes better than the inline-fan ditty I kluged earlier,
super-quick fume clearance.
But, the previous in-line fan could have been just ****ty anyway, so I don't
know if apples were compared to apples.

But other in-line fan apps have gone well:
The **** motor in my mushroom eventually went, so I scavenged a window
A/C 3-speed fan unit, thermostat and all, and this works great -- infinitely
superior quality to the original mushroom innards, altho a bit of a pita to
install.

If I get lucky, I'll find a small 3 ph motor, and put a VFD on it, for
infinite speed control -- small VFD's are not that expensive. I'm hoping to
luck out with a system that's quieter than some of the expensive noiseboxes
I've seen. I'm surprised that with $4,000 price tags, they don't offer
something like this.

Opinions, suggestions for the kitchen?


There is a difference in squirrel cage design for kitchen ventilation.
If I remember correctly, the blades are straight instead of curved to
help prevent grease buildup. It's what I've seen in commercial kitchen
exhaust fans but the blades in an inexpensive home unit may be curved.
I do seem to remember taking apart a cheap home range hood and it had
curved blades. I don't know about the ones them rich folks buy.

TDD

On Thu, 3 Dec 2009 11:23:58 -0500, "Existential Angst"
wrote:

Awl --

Curious as to "fan logic".

snip
The, uh, thrust of my Q is that I'm cobbling together a kitchen, and am
dizzied by prices of venting hoods that I like (*easily* $2,000-4,000 and
not super-fancy -- holy ****!!!), and am not particularly impressed with the
few I'm able to turn on, noise-wise, flow-wise. Cosmetically, tho, they are
super.

HD has a couple of decent-looking ones in the $400-500 range, but they are a
little bulky.

In particular, the fact that the dual sc blowers are located *in* the
hood-proper bulks many of the units up considerably, which in this
application creates visual line-of-sight issues, due to proximity to an
entrance door.

So, I could locate the sc blower right up at the exit vent near the ceiling,
or, even better from a visual pov, use an in-line booster type fan.
And then I would be able to use the old hood etc from the original set up,
which everyone kind of likes anyway.

Go study commercial kitchen hoods, and duplicate the design features
in a small size - or call a local manufacturer and have one made,
restaurant hoods are commonly made to size and aren't that
expensive... And if it's a new house you probably have to go this way
to satisfy the building inspector and get your Certificate Of
Occupancy... Go meet with the City or County authorities and find out
what your local inspector will buy off on BEFORE you start.

They use a standard design to keep the prices down, and just dial in
the sizes needed and bang them out of sheet stainless, using
standardized pieces. They have standard size grease catch baffle
panels that lift out of a slot for easy cleaning - for a home kitchen
sized hood you might only need one or two panels. There is a drain
gutter for the grease that collects in a pre-made stainless1/8 size
steam pan.

The fan is on the roof - commercial style "Upblast ventilator" made
with a grease collection cup to catch the gack that collects in the
fan and keep it off your roof. There are also wall mount versions.
They make small sizes in the 1/4 - 1/3 HP range which is huge compared
to a 'residential' unit, so run a speed control on it. Easy to fix
(full access) or just replace with new.

You build a hard curb on the roof with lumber, the duct comes up to
the fan with a flat flange and the roofer runs the roofing up the
sides of the curb. The fan has a flat flange on the bottom with a
rain lip, and the whole thing lifts right off for service or
replacement.

Residential calls for simple 6" or 7" round galvanized snap duct to a
simple vent jack, but overkill is allowed - commercial use ducting is
double wall welded mild steel, with an air gap - in case of a stove or
hood grease fire, this keeps the heat contained so you don't light the
building rafters. You might end up with a hybrid with spiral-lock
heavier round steel duct, but not the full double-wall - residential
stove fires won't have the heat load of a commercial double-vat
60-pound deep fat fryer.

Oh, and they do make small automatic fire extinguisher systems
specifically for residential stove hoods. Talk to your insurance
company, you might be able to get a serious discount.

-- Bruce --

Everyone is correct-- fans are more efficient from a power usage
standpoint, but only if there is little/no resistance to airflow. Then
squirrel cage type blowers are used. I have a blower that I rigged up
for a kitchen vent-- the blower is under the house and piped to a vent
in the wall. There really wasn't any way to put a hood over the stove,
but what I have works fairly well. Originally there was a vent in the
same spot with a tiny fan in it that went straight outside. It moved
almost no air, and dripped grease down the outside wall. TDD is right
about commercial units having straight vanes, likely to collect less
grease. On a resi unit, it would probably be less of a problem. The
average household is not going to be dumping frozen French fries into
hot oil every few minutes 24/7, as restaurants do. FWIW, there were some
furnaces that used dual squirrel cages on a double shaft motor on a few
certain models. I have replaced motors on a Janitrol, Payne, Fedders,
and Ruud that used that setup. They were fairly old units then, and it
was at least ten years ago when I did the last one. Larry

Lp1331 1p1331 wrote:
Everyone is correct-- fans are more efficient from a power usage
standpoint, but only if there is little/no resistance to airflow. Then
squirrel cage type blowers are used. I have a blower that I rigged up
for a kitchen vent-- the blower is under the house and piped to a vent
in the wall. There really wasn't any way to put a hood over the stove,
but what I have works fairly well. Originally there was a vent in the
same spot with a tiny fan in it that went straight outside. It moved
almost no air, and dripped grease down the outside wall. TDD is right
about commercial units having straight vanes, likely to collect less
grease. On a resi unit, it would probably be less of a problem. The
average household is not going to be dumping frozen French fries into
hot oil every few minutes 24/7, as restaurants do. FWIW, there were some
furnaces that used dual squirrel cages on a double shaft motor on a few
certain models. I have replaced motors on a Janitrol, Payne, Fedders,
and Ruud that used that setup. They were fairly old units then, and it
was at least ten years ago when I did the last one. Larry


The last dual squirrel cage blower I dealt with was on a 15 ton
unit. I think it had 1" shaft going through the darn thing. I
despise air handlers for homes that have bolt in instead of the
slides out blower housings. GRRRRRR! I'm not as agile as I used
to be, especially in a cramped attic.

TDD