Acceptable system static pressure?

ChrisJ

I'm curious what the acceptable range is for static pressure on a system. I'm talking return and supply losses, even across the A\C coil. Basically measuring the difference from the return of the AH to the supply.

I've seen comments of some air handlers expect 0.5" or less, but I also see many show a range of 0.1 all the way to 0.9"

What's considered great, good, acceptable and poor? Also, what's typical?

It seems like a good pleated filter can have as much as 0.2" drop alone.

bob_46

It depends on the specs of the air handler. As long as the total pressure drop of the registers, ducts, filters doesn't exceed the total external static of the air handler you are in good shape. Check to verify if the coil (wet) is included.

ChrisJ

bob said:

It depends on the specs of the air handler. As long as the total pressure drop of the registers, ducts, filters doesn't exceed the total external static of the air handler you are in good shape. Check to verify if the coil (wet) is included.

Have not bought the unit yet so I can't check the name plate, but this is what the manual shows.

I assume the fact it shows it running as high as 0.9" suggests that's acceptable (with clogged filters, shut diffusers etc) ? I believe I'd want to use constant CFM mode rather than constant torque.

I was more curious what most residential systems expect rather than this specific one.

ChrisJ

Need to start this thread back up with what is hopefully an easy to answer question.

If an air handler or furnace says it's designed for a total static pressure of 0.5", does this mean with new filters, or is that the ultimate pressure it wants to see with a dirty filter? I.E. never, ever let it go over 0.5"?

I'm assuming 0.5" is the maximum with a new filter, expecting to creep up towards 1" with a dirty filter?

Harvey Ramer

.5 is the max rated ESP.

ChrisJ

Harvey Ramer said:

.5 is the max rated ESP.

So, never expected to go over half an inch, ever.

I wonder how often that actually happens in real life with typical duct work and typical filter changing habits?

Harvey Ramer

ChrisJ said:

Harvey Ramer said:

.5 is the max rated ESP.

So, never expected to go over half an inch, ever.

I wonder how often that actually happens in real life with typical duct work and typical filter changing habits?

Most systems go over .5. No doubt about it. Once you get above .8, you are out of the safe zone. 1" and up, guaranteed problems.

With proper design and regular filter changes, you can stay below or at .5.

ChrisJ

Harvey Ramer said:

ChrisJ said:

Harvey Ramer said:

.5 is the max rated ESP.

So, never expected to go over half an inch, ever.

I wonder how often that actually happens in real life with typical duct work and typical filter changing habits?

Most systems go over .5. No doubt about it. Once you get above .8, you are out of the safe zone. 1" and up, guaranteed problems.

With proper design and regular filter changes, you can stay below or at .5.

Is 0.5" a new standard, or has it been the standard for a long time?
Or does it vary from appliance to appliance?

Harvey Ramer

ChrisJ said:

Harvey Ramer said:

ChrisJ said:

Harvey Ramer said:

.5 is the max rated ESP.

So, never expected to go over half an inch, ever.

I wonder how often that actually happens in real life with typical duct work and typical filter changing habits?

Most systems go over .5. No doubt about it. Once you get above .8, you are out of the safe zone. 1" and up, guaranteed problems.

With proper design and regular filter changes, you can stay below or at .5.

Is 0.5" a new standard, or has it been the standard for a long time?
Or does it vary from appliance to appliance?

Pretty much all current equipment uses a .5 standard, save some high static commercial units.

newagedawn

every system comes with a rated static pressure before duct is attached, weather it is .05 or .09 each static pressure should push a certain amount of CFM, for heating or cooling or both, when duct is attached and flex and diffusers and coils and filters this can change.the static pressure of the system,
thats why after the system is installed you need to check static and CFM to see where it falls, and make your adjustments accordingly, some retrofits the duct is to small and there are problems with air flow(CFM), others the duct is sized properly and it works within the manufactures specs,.but the only way to know is to test it after install.
there are ways to tell if the duct is sized properly before install but thats another question

EBEBRATT-Ed

Start with the basics. ANY air handler is a box with air going through it. In most cases the "size of the box" is determined by the square footage of the chilled water or DX coil. Max air flow velocity through a cooling coil (chilled or dx) is in the neighborhood of 500fpm. If the air goes faster water gets pulled off the coil. Can't defy mother nature

In a specialized commercial job I have seen 6-700fpm but you get into mist elimenator territory and potential problems.

so once the required cfm is determined the size of the cooling coil face area is determined once that is selected the "size of the box" is known.

To change the amount of cooling the coil is made thicker or thinner to get the capacity needed for the selected cfm. Cooling determines the ahu physical size because heating coils can take much higher velocities 1000fpm.

Once all the accessories are installed, coils , filters the manufacture calculates the required blower size. . there is static required to move air through the ahu plus whatever ESP (external static) both of them together =total static external static is for the ductwork.

as far a residential jobs It's not my area but .5 sounds right

ChrisJ

The air handler I'm working with states 0.5"WC but then shows a chart of what CFM you get from 0.1" all the way to 0.9" and they're fairly close as it's a variable speed AHU.

But it seemed confusing to specify 0.5" but then show a chart all the way to 0.9".

ChrisJ

My guess was the 0.5" standard is to ensure the cabinet meets leakage requirements which are apparently done at 0.5" and or 1".



For example :




Thoughts? Opinions?

Rich_49

Follow this series ChrisJ .

http://www.energyvanguard.com/blog/basic-principles-duct-design



The total system static pressure when complete should not exceed .5" . Unfortunately computer programs have even very good duct designers installers believing they are doing well . Not the case since the program does not recognize velocities low enough for newer buildings to promote COMFORT in almost every sense of the word . Think ASHRAE 55 .

Harvey Ramer

At or above .8" an ecm motor begins hunting. The constant cfm it is designed to provide is reduced and it may not receive adequate cooling any more. At this level, the life expectancy of the motor is greatly reduced.

It's really a balance between fan design and motor design, the goal being to move the required amount of ait with the least amount of energy. To run a higher static, the fan blades should have a different pitch and the motor may need additional cooling.

ChrisJ

Rich said:

Follow this series ChrisJ .

http://www.energyvanguard.com/blog/basic-principles-duct-design



The total system static pressure when complete should not exceed .5" . Unfortunately computer programs have even very good duct designers installers believing they are doing well . Not the case since the program does not recognize velocities low enough for newer buildings to promote COMFORT in almost every sense of the word . Think ASHRAE 55 .

Thank you for commenting @Rich
That's a good read, I remember reading one of their articles on flex duct (sags, turns etc) a few months ago.

I'm reading a few more as we speak, I forgot about the website.

Rich_49

Allison promotes duct design how it's done by true ducted system Titans ChrisJ . I have collaborated on several projects with a few of them . They truly know how to do ducted right .

Rich_49

Part 2 , Allison Bailes
http://www.energyvanguard.com/blog/duct-design-2-available-static-pressure

Rich_49

Part 3 ,

http://www.energyvanguard.com/blog/duct-design-3-total-effective-length

Rich_49

Part 4

http://www.energyvanguard.com/blog/duct-design-4-calculating-friction-rate

ChrisJ

Total static in low stage







Total static in high stage




I'm using a MERV 8 20x25x5 AirBear.

ratio

I'm not sure that's enough static to keep the air from getting confused about which way to go. </humor> (???)

ChrisJ

ratio said:

I'm not sure that's enough static to keep the air from getting confused about which way to go. </humor> (???)

It's a close race between the steam system and the central AC system.

Steam runs around 0.25" when things are cold, around 0.5" during moderate use and 0.75" when things are kept fairly hot.

ratio

I'd take the static across my furnace, but I'm afraid it'd make me cry.

Gordy

ratio said:

I'd take the static across my furnace, but I'm afraid it'd make me cry.

Is that a steam, water, or hot air furnace? @chris gets confused

ChrisJ

> @Gordy said:
> I'd take the static across my furnace, but I'm afraid it'd make me cry.
>
> Is that a steam, water, or hot air furnace? @chris gets confused



Do you live in a condo or apartment? I get the two confused

Gordy

Duplex.......

newagedawn

i like to see around .5 total eternal static, if its higher there is a restriction( in duct, in filter, in coil), if its low there is to much leakage in duct
FYI, had one last week on a 16 seer A/C was .82 with pleated filter with blue filter .52
same on a rooftop .68 with pleated filter, .49 with blue filter
im begining not to like the pleated filters
why is this important, comes down to cfm and the energy the motors use the higher the static pressure the more energy is used to move the air
hope that helped

ChrisJ

newagedawn said:

i like to see around .5 total eternal static, if its higher there is a restriction( in duct, in filter, in coil), if its low there is to much leakage in duct
FYI, had one last week on a 16 seer A/C was .82 with pleated filter with blue filter .52
same on a rooftop .68 with pleated filter, .49 with blue filter
im begining not to like the pleated filters
why is this important, comes down to cfm and the energy the motors use the higher the static pressure the more energy is used to move the air
hope that helped

The problem is, I assume those blue filters are woven fiberglass?
They don't work very good as a filter compared to a good pleated filter.

Of course, if the system isn't set up to use a properly sized one, you're kind of stuck.

It seems like 1" thick pleated filters are troublemakers. There's usually not enough surface area.

Rich_49

newagedawn said:

i like to see around .5 total eternal static, if its higher there is a restriction( in duct, in filter, in coil), if its low there is to much leakage in duct
FYI, had one last week on a 16 seer A/C was .82 with pleated filter with blue filter .52
same on a rooftop .68 with pleated filter, .49 with blue filter
im begining not to like the pleated filters
why is this important, comes down to cfm and the energy the motors use the higher the static pressure the more energy is used to move the air
hope that helped

Sometimes a low external static pressure is a good thing . This is usually when the ductwork is ample enough to lower the esp and also quiet the system . As long as it is balanced there is no problem of the esp is below .5 .

ChrisJ

Biggest regret I have in my system, is running 10" round all the way to the first floor diffusers.

If I was doing it again I'd do hard pipe into each closet from the attic, and then 5 or 6 feet of flex, and then continue with hard pipe through the floor to each diffuser.

That 14" and 10" round pipe doesn't attenuate anything, at all.

Harvey Ramer

Those ESP's look perfect Chris. Nice job!

newagedawn

chris said,The problem is, I assume those blue filters are woven fiberglass?
They don't work very good as a filter compared to a good pleated filter.

Of course, if the system isn't set up to use a properly sized one, you're kind of stuck.

It seems like 1" thick pleated filters are troublemakers. There's usually not enough surface area.

chris depends on your living habits, i just changed a blue filter in a long standing customers house yesterday and its been 2 yrs the filter was full of dust, but 1 its in the cieling and 2 she keeps her house clean, i have another customer that has floor returns, havnt changed that one yet but next yr we will see if it hold up to the dirt and debris from the floor, the point those blue filters do help lower static pressure if needed, but if you design and install your system correctly you WILL BE ABLE TO USE PLEATED FILTERS and have that pleated filter protection!!!
if you really want clean air ,design your system around a hepa filter, but youd need to find the pressure drop of whatever manufacture you choose and factor that into the duct design
hope that helps my friend