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Thread: Static Pressure

  1. #27
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    Quote Originally Posted by hvacmike85 View Post
    What is better than a 4-5 inch filter? I dont have alot of faith in eac units but I know they came out with the filter/eac in one yrs ago havent seen too many though. I have heard of hepa filters in holmes but I would think that would have to have a good blower to overcome a 13-19 merv?
    Depending on the merv rating of the filter has a huge impact on the pressure drop across the filter along with the velocity of the air traveling across it.

    You can have 1 inch pleated filters with a pressure drop above 0.35 and have a 5 inch merv 16 with a pressure drop of 0.36 new out of the box rated at 1200 cfm and 375 feet per minute.

    The other factors to look at is at what cfm and face velocity that the filter was tested under using ASHRE 52. standard. The velocity used during testing can be less than 1/3rd of the velocity in a home system.

    The bottom line before changing to a higher merv filter have the system tested to see what the available static pressure is left after all other items have been installed in the airflow, then determine what filters are available that will work with a lead-way for loading as the filter is in use.

  2. #28
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    Jul 2012
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    hcong,
    The dew went away yesterday. It was extremely damp and threatening to rain but never did. I'm taking that the condensation had to do with that. The wet part was not on the interior, but I'm not sure if it was outside or middle.
    I only have a return in the basement, but the return was made with a standard supply type register, meaning I have the ability to shut it out.
    I did check yesterday and I have a 20X25X4 filter on this trouble basement system already. My upstairs has teh 16x25x4.
    This puts me back at a loss on how to get my static pressure from .8 to the standard of .5. The idea I saw earlier that I've gone from 100 watts in using the fan to a potential of 300 watts, seems to be something that should be fixed. Correct?

  3. #29
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    Quote Originally Posted by Gurney View Post
    hcong,
    The dew went away yesterday. It was extremely damp and threatening to rain but never did. I'm taking that the condensation had to do with that. The wet part was not on the interior, but I'm not sure if it was outside or middle.
    I only have a return in the basement, but the return was made with a standard supply type register, meaning I have the ability to shut it out.
    I did check yesterday and I have a 20X25X4 filter on this trouble basement system already. My upstairs has teh 16x25x4.
    This puts me back at a loss on how to get my static pressure from .8 to the standard of .5. The idea I saw earlier that I've gone from 100 watts in using the fan to a potential of 300 watts, seems to be something that should be fixed. Correct?
    Fixing it may be ideal but a lot of systems out there are worse off it might be an expensive fix

  4. #30
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    Quote Originally Posted by hcong View Post
    I haven't done that much research on static pressure loss of a 4" vs. a 1" but I think all the manufacturers I saw... a 1" has lower pressure drop. I could be wrong though.
    For the same MERV rating, a 4" pleated media filter will have less pressure drop than a 1" pleated media filter. It's all about surface area.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #31
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    Jul 2012
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    hvacmike85,
    So do you think the fan is working 2-3 times as hard as it would if I were at the right Static Pressure?
    When you mention repair would be expensive, is that resolution to add more returns or something else?

  6. #32
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    Quote Originally Posted by Gurney View Post
    hvacmike85,
    So do you think the fan is working 2-3 times as hard as it would if I were at the right Static Pressure?
    When you mention repair would be expensive, is that resolution to add more returns or something else?
    Neat quirk of most blower wheels.

    When they are restricted like that, they actually do LESS work than if they were properly supplied with air.

    That doesn't mean that it is a great idea to starve the fan for air, just that you aren't overloading or overworking the blower by doing so.

  7. #33
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    Quote Originally Posted by jpsmith1cm View Post
    Neat quirk of most blower wheels.

    When they are restricted like that, they actually do LESS work than if they were properly supplied with air.

    That doesn't mean that it is a great idea to starve the fan for air, just that you aren't overloading or overworking the blower by doing so.
    jp that is true for a standard PSC motor but not for a variable speed ECM.

    When faced with higher static resistance from the system the ECM will increase its rpm to maintain selected CFM, and in doing so the energy consumption will sky rocket and the efficiency of the system goes out the window.

    Think of it like your car with the emergency brake partially on you are still moving but it is taking more energy to do so.

  8. #34
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    Quote Originally Posted by Gurney View Post
    hvacmike85,
    So do you think the fan is working 2-3 times as hard as it would if I were at the right Static Pressure?
    When you mention repair would be expensive, is that resolution to add more returns or something else?
    its def not working 2-3 times harder at .8 but the return isnt for sure your culprit either,we cannot know without being there to test ourselves, total static of .8 is really about average for an ecm sytem and quite honestly your duct cant be too bad or it would be higher. If you have a 4" filter thats the first step, keeping it changed 3-4 times a year is next. when I say expensive it could be replacing duct to fix it, but it doesnt sound like you have much of a problem, was the system acting up/?

  9. #35
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    May 2012
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    San Diego, CA
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    I checked your furnace... a 0.8 compared to a 0.5 is only roughly 35 CFM less for your system.

    http://www.docs.hvacpartners.com/idc...s315a.45.7.pdf
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  10. #36
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    Jul 2012
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    hvacmike85/hcong,
    Thanks gentlemen, i think you've got me where I need to be and to understand. Let me see if I can summarize and let me know if anything is incorrect...
    So, I'm at .8 and ideal is .5 static pressure. .8 is higher, but still within normal operating parameters (even in the data sheet). The comment that was made to me that normal is the elctricity of 100W bulb is standard, but the comment that I'm using 2-3 time was totally incorrect. If I can remain at .8 static pressure, sounds like I should shut off that return that is in the basement.
    Net here being, .5 is ideal, .8 is still normal, and net sounds like it may minimal SEER impact and maybe a few pennies for electricity, but nothing significant. To alter my system to ideal would probably be a few hundred dollars and how to achieve such would have to be reviewed by an expert.
    After spending several thousand dollars on this 17 SEER system, I can live with it's not perfect, but it's within normal ranges.
    Sound accrate?

  11. #37
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    Quote Originally Posted by Gurney View Post
    hvacmike85/hcong,
    Thanks gentlemen, i think you've got me where I need to be and to understand. Let me see if I can summarize and let me know if anything is incorrect...
    So, I'm at .8 and ideal is .5 static pressure. .8 is higher, but still within normal operating parameters (even in the data sheet). The comment that was made to me that normal is the elctricity of 100W bulb is standard, but the comment that I'm using 2-3 time was totally incorrect. If I can remain at .8 static pressure, sounds like I should shut off that return that is in the basement.
    Net here being, .5 is ideal, .8 is still normal, and net sounds like it may minimal SEER impact and maybe a few pennies for electricity, but nothing significant. To alter my system to ideal would probably be a few hundred dollars and how to achieve such would have to be reviewed by an expert.
    After spending several thousand dollars on this 17 SEER system, I can live with it's not perfect, but it's within normal ranges.
    Sound accrate?

    You got it!

  12. #38
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    Jan 2009
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    I still wouldn't call it "pennies".

    FOr comparision I looked at a Trane XV80 (jsut because i had it handy) data sheet.

    With a 60kBTU 3 ton blower, at 1200CFM nominal and 0.5" your at 440Watts. 0.8" = 480 Watts and you lose 50CFM because you're "falling off" the blower curve and getting close to max RPM.

    With a 80k BTU furnace with 3 ton blower (wider furnace), it's 370Watts @ 0.5", 430 Watts @ 0.8".

    With a 80k BTU with a 4 ton blower, 285 Watts @ 0.5", 370 Watts @ 0.8".

    Just something to consider. With the Evolution series, you should have a 4 ton blower on the smaller furnace sizes, and Carrier runs at 350CFM/ton or less for normal airflow.

    But I think I showed that the difference could be anywehre fo 40-90Watts. That's still significant. At 85F, that could be anywhere from 1-4% in 2nd stage, or as much as about 0.6 SEER.

    So I was a little off before.

    But then again, if the unit is oversized and short cycles it can impact effciency by as much as 25%.

  13. #39
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    Jul 2012
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    Hvacmike85,
    Thanks.

    motoguy128,
    So I don't follow quite everything your stating. But backing up. I had a 75,000 BTU Heil single speed furnace. I've upgraded to this Bryant Evolution 90K variable speed furnace. End of the day, am I not using significally less electricity than I had before?
    I pulled the data sheet from Bryant that was included in a prev thread reply, it shows for my unit CFM airflow setting 1050; External Static Pres Range (0-1.0); @ .5 = 1040; @.8 = 1030. I don't really see how this all equates to energy usage to run the fan. But if I'm hugely less than what I originally had, and only off optimal a little, I'm happy. Thoughts?

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