I'm fairly new to commercial construction and I've never really run into "Plenum Air Spaces" before. My first question is on construction drawings how are plenum air spaces usually noted? What does a plenum air space look like if I was looking at lets say a set of mechanical drawings? Is the area hatched or is there some other standard notation as to denote the plenum areas? I was under the impression that it is the area/void in the drop ceiling where air is circulated/moving from a return grill up into open air space(plenum) and then into air handler then out into supply air duct work. This area (Plenum Air) needing specially rated wiring and or plumbing piping/wiring? My second question is if the area is directly ducted by that I mean the return grill is ducted directly to the air handler in the space above the ceiling then would I be correct is saying there is NO plenum air space?
corkywg
As heated Air rises, and cooled/dehumidified air is denser, it "falls" thus Air returns are often installed in or near the floor to improve in air mixing.
Ensuring adequate duct sizes and positions will save $$ every year in blower costs and improve air quality even when the fan isn't running.
Next to a two speed or variable rate cooling and heating system, proper ducting will increase the livability of the home for decades.
According to most dictionaries some sort of fluid/Gas is PUSHED through a plenum... But a return air plenum functions on the suction side of the furnace fan.
In general a "plenum" will have more branches then a pipe....but not always.
A few minutes a day studying a construction and or a regular English dictionary will allow you to form thoughts much easier then using a vague nomenclature like "That thingamabob"....
I'd suggest a night class for the blueprint reading, or better yet a Blue print DRAWING class... Easy cheesy, watch some on-line classes.
Ensuring adequate duct sizes and positions will save $$ every year in blower costs and improve air quality even when the fan isn't running.
Next to a two speed or variable rate cooling and heating system, proper ducting will increase the livability of the home for decades.
According to most dictionaries some sort of fluid/Gas is PUSHED through a plenum... But a return air plenum functions on the suction side of the furnace fan.
In general a "plenum" will have more branches then a pipe....but not always.
A few minutes a day studying a construction and or a regular English dictionary will allow you to form thoughts much easier then using a vague nomenclature like "That thingamabob"....
I'd suggest a night class for the blueprint reading, or better yet a Blue print DRAWING class... Easy cheesy, watch some on-line classes.
Been a while since I did commercial installs.
We also called it, a plenum ceiling.
And if its a ducted return, then there is no plenum ceiling/plenum space.
We also called it, a plenum ceiling.
And if its a ducted return, then there is no plenum ceiling/plenum space.
rrk: a plenum ceiling would be a dropped ceiling grid used for air handling, such as a office cubicle farm...:jester:
Modern multi-story offices will use the concrete floors as thermal "flywheels' blowing air over the bottom of the floors thermal mass to moderate the building's HVAC system and allow a smaller heater and AC unit to provide a control temperature....
I've worked on 80-100 year old college blds. that used pipe chases and steam tunnels for air handling...plenums.
Regarding the original post, any penetrations of fire walls would require all ducts to have some sort of auto duct closer that operates when fire's heat melts the retaining device.
Who do you think reads those MEP funny papers to lay out the holes in walls that the tin knockers run their stuff through?:laughing:
Modern multi-story offices will use the concrete floors as thermal "flywheels' blowing air over the bottom of the floors thermal mass to moderate the building's HVAC system and allow a smaller heater and AC unit to provide a control temperature....
I've worked on 80-100 year old college blds. that used pipe chases and steam tunnels for air handling...plenums.
Regarding the original post, any penetrations of fire walls would require all ducts to have some sort of auto duct closer that operates when fire's heat melts the retaining device.
Who do you think reads those MEP funny papers to lay out the holes in walls that the tin knockers run their stuff through?:laughing:
"dust Pan": a few seconds of thought tells even the HVAC ignorati that any dust in a typical space would be created outside of the metal ducts, and secondly,that it would tend to drop "out" in the UNFILTERED return ductwork, As Dust Bunnies rarely hop around well ventilated parts of a room...
Return plenums are in a state of partial "vacumn" while the supply ducts are in a state of positive pressure
Having spent the first 6 years of life in a 2 story (and basement) farm house that had a "gravity" unforced coal heated air system, placement of hot air grills and returns determined whether or not if you melted or were cold in the winter.
Note that a gravity furnace might occupy upwards of 5-6 % per cent of the living space of a typical install and weigh a few thousand pounds due the concrete bonnet used to moderate heat flow....
I thinks that the air handling models used in the pre- R-40 ceiling-ed homes (9-10' wall heights) might bear some experimental confirmation to ensure the common default operation modes haven't changed.
As some constant air movement even when no heating or cooling is needed become the norm, and multi stage HVAC installs rarely operate at 100% loads for more then a few minutes, modern homes will of course have a tiny fraction of the temperature stratification of legacy tech, IMHO.
What % of dust would you think collects in a typical home's carpeting vs its air ductwork?
Why isn't some Genius working on a "Dyson" style semi-automated dust removal system for home air handlers? Free multi-Million dollar Patent-able idea?
Return plenums are in a state of partial "vacumn" while the supply ducts are in a state of positive pressure
Having spent the first 6 years of life in a 2 story (and basement) farm house that had a "gravity" unforced coal heated air system, placement of hot air grills and returns determined whether or not if you melted or were cold in the winter.
Note that a gravity furnace might occupy upwards of 5-6 % per cent of the living space of a typical install and weigh a few thousand pounds due the concrete bonnet used to moderate heat flow....
I thinks that the air handling models used in the pre- R-40 ceiling-ed homes (9-10' wall heights) might bear some experimental confirmation to ensure the common default operation modes haven't changed.
As some constant air movement even when no heating or cooling is needed become the norm, and multi stage HVAC installs rarely operate at 100% loads for more then a few minutes, modern homes will of course have a tiny fraction of the temperature stratification of legacy tech, IMHO.
What % of dust would you think collects in a typical home's carpeting vs its air ductwork?
Why isn't some Genius working on a "Dyson" style semi-automated dust removal system for home air handlers? Free multi-Million dollar Patent-able idea?
My "dustpan" statement wasn't literal but an oversimplified working model of how returns are said to work by some professionals in the trade who *appear* to be well versed in the art, i.e. HVACtalk forum. Yes, I understand that the dirt and dust must by necessity originate outside the system and are drawn in by airflow under vacuum. But it doesn't have to enter the return in a straight linear fashion like it can exit the supplys under pressure. What I mean is that the air entering a return can come at it from a right angle to the internal face of the duct (along the face of the wall, like going in a dustpan), but the air exiting a supply (without a grill) tends to go straight out before it creates eddies, and mixing the stratified air. A working model, not a scientific model, just like Newtonian physics works quite well for most things even though we understand there is more at play. This is why the experts say the supply size, shape, location, and grill deflection style are the most important factors in mixing the air, and very little to the "dustpan" returns that simply pick it up to be reconditioned. I am only repeating what I've read.
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One clarification, that is their analogy for a forced air system, not your gravity furnace. Brrrr.Shiver.
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the discharge end of a SUPPLY duct is somewhat like a garden hose, the air is in a near laminar flow state, like the water from a 100' long straight hose...and the nozzle/ grill can if designed right "spray" the air where you want it, the drain in a tub or cattle trough, can't change the degree of chaotic flow/mixing to any large degree....
residential or commercial HVAC with constant air movement even when not heating or cooling or dehumidifying will be more comfortable for more of the space, more of the time, all other things being =. IMO
Active air mixers like ceiling fans will remain popular to improve air mixing in high use spaces.
Look for high end systems to use active grills that change patterns to increase air mixing a pennies a day.
For long term health and mental productivity, variable temps and drafts keep ones internals at higher levels of performance then near steady state conditions that atrophy one's natural metabolism capacity to tolerate a range of temps, wind and humidity.
residential or commercial HVAC with constant air movement even when not heating or cooling or dehumidifying will be more comfortable for more of the space, more of the time, all other things being =. IMO
Active air mixers like ceiling fans will remain popular to improve air mixing in high use spaces.
Look for high end systems to use active grills that change patterns to increase air mixing a pennies a day.
For long term health and mental productivity, variable temps and drafts keep ones internals at higher levels of performance then near steady state conditions that atrophy one's natural metabolism capacity to tolerate a range of temps, wind and humidity.
Thanks everyone for all the information, in my effort to expand my construction knowledge I do appreciate y’all taking the time to pass down some of that knowledge. I’m still not clear on one item though.
In regards to blueprint reading how are these plenum airspaces or plenum ceilings normally identified in construction drawings. Is the area hatched or boxed in or something? I ask because in a lot of spec books there are notes that say any cables or conduit running through these plenum areas must have a special fire rating/coating. So knowing exactly where these areas is crucial. Thanks in advance for the info.
Kind Regards,
-Corey
In regards to blueprint reading how are these plenum airspaces or plenum ceilings normally identified in construction drawings. Is the area hatched or boxed in or something? I ask because in a lot of spec books there are notes that say any cables or conduit running through these plenum areas must have a special fire rating/coating. So knowing exactly where these areas is crucial. Thanks in advance for the info.
Kind Regards,
-Corey
Usually the first or second page of the building plans will have a Key to all symbols used on the following pages, if you can't find it RIF the HVAC engineer.
If I were involved with HVAC internal wiring, I'd have personally highlighted ALL the plenums that would need special fire code attention by the various subs, such as the electrical and low voltage(s) sub(s) on my master plan(s).
The submittals phase should have the code legal products presented for approval....
Furthermore I'd want some sort of "proof of Life" the various subs are aware of the Law, and were conforming their materials and installation to these life safety issues.
I would forward that piped wiring is far safer, even with Teflon wire( which still produces masses of toxic gases (at higher temps) then PVC based insulations. And make changing data lines far cheaper down the road. And metal conduit has security advantages too....
Yet another line on Your "Captain Sully" check list for Commercial Construction.
If I were involved with HVAC internal wiring, I'd have personally highlighted ALL the plenums that would need special fire code attention by the various subs, such as the electrical and low voltage(s) sub(s) on my master plan(s).
The submittals phase should have the code legal products presented for approval....
Furthermore I'd want some sort of "proof of Life" the various subs are aware of the Law, and were conforming their materials and installation to these life safety issues.
I would forward that piped wiring is far safer, even with Teflon wire( which still produces masses of toxic gases (at higher temps) then PVC based insulations. And make changing data lines far cheaper down the road. And metal conduit has security advantages too....
Yet another line on Your "Captain Sully" check list for Commercial Construction.
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