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  1. #27
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,537
    Quote Originally Posted by thorton View Post
    Hi Teady Bear: In your sig line you indicate use a +10 merv filter. I have been led to believe that high merv filters are too restrictive. Would you be so kind to elaborate on this subject for me?

    Thanks

    thorton
    ____________________
    You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals
    +11 MERVs are ok if designed for your air flow-pressure drop requirements. The large, 4"-5" deep MERV 11 filters are able to provide good filtering with minimal pressure drop. Most filter include in their specs pressure drop/air flow details. These filters have 2X-4X more media than the 1"-2" filters. We use a few HEPA filters on our dehus for special applications, but they are grossly over-sized with <.1" pressure drop. In other words with enough media, any of the high eff. filters could be designed to function on typical air handlers. In reality, the major benefit of filtering is to keep the equipment clean. Extra filtering has little effect on the dust in the space. Most dust enters via clothes, open doors/window, and wind caused infiltration. The dust settles to the floor before passing through a filter. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  2. #28
    Join Date
    Apr 2007
    Posts
    6,285
    TB what is the typical Merv rating of a wet coil? I was thinking 8 but I can't seem to find the info now.

  3. #29
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,537
    Quote Originally Posted by BigJon3475 View Post
    TB what is the typical Merv rating of a wet coil? I was thinking 8 but I can't seem to find the info now.
    I Imagine a clean wet coil has a very low merv. But as the mat of fiber and dust thickens, the MERV increases. About the time the air flow declines to the point where the coil freezes, the MERV is even more than 8! Good filtering removes the fibers that form the mat. Hopefully, the finer dust is washed down the condensate drain. I never thought about that before. Cool Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #30
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Quote Originally Posted by pstu View Post
    It might be very interesting as Teddy Bear says, to discuss the latent capacity at low AC duty cycle, i.e. mild temperatures. Sure wish it were easy to measure condensate removed, then we could talk empirically, and learn more about AC systems which do and don't remove humidity effectively to needs. But near as I can tell the mechanism to do so is either labor intensive (a calibrated container) or expensive, so we seem doomed to talk theory.

    The point I am wondering about is, just how much does this worst-case weather pattern for humidity occur, that TB talks about as an example. In my S.Texas region, there is a narrow temperature range where it applies, and we don't spend much time with rain in that range. Below about 65F and the temperature will tend to help the house out in terms of outdoor dewpoint. Above about 75F and we do want to run the air conditioner, and the concept of overcooling seems debatable.

    Of course I don't want to talk only about my region, but any and all. I'm still trying to get my mind wrapped around the principles that apply here.

    Best wishes -- Pstu
    I believe any dehumidification discussion needs to address the primary source of excess humidity in the average home...infiltration. Anytime outdoor dew points are higher than 55 degrees, infiltrating moisture from outdoors will affect indoor comfort at normal room temperatures (72-78 degrees F.).

    Slavishly seeking to keep relative humidity below 50&#37; at all times to me is a bit misleading. If one rather were to desire a consistent indoor dew point held to 55 degrees, the sensible temperature can vary from 72 to 78 degrees dry bulb, with relative humidity varying from ~56% to ~45%, respectively, and still be within the ASHRAE comfort zone.

    In humid climates, fresh air exchange requirements in a residence are best done in a controlled manner, vs. the uncontrolled aspect of structural infiltration. We must have fresh air exchanges to keep the indoor air quality healthy...tightening up a house without making this provision is unhealthy and counterproductive. The best way to introduce fresh air into a home in a humid region is either through fresh air intake on the cooling system, or fresh air intake through a dehumidifier.

    Humid climates like Houston, TX are typically warm climates...cool, rainy days are not as common as warm, rainy days, followed by breaks in the clouds with bright sunshine, spiking wet bulb and sensible temps. Internal sensible and latent heat generation in a well insulated, tight house combined with sensible and latent gain via normal ingress/egress traffic should be enough to cause the cooling system to run, providing fresh air exchange, dehumidification, and sensible cooling. In a general sense, with a high latent load in a house, the possibility of overcooling is not as great, since more of the coil's capacity is being used for latent heat removal.

    The first rule to successfully create a controlled indoor environment is containment. If the air isn't well contained, it requires more energy and effort to control, which in today's high energy cost and envrionmental concern reality, no longer makes good sense. We've been conditioned to throw active technological solutions to flaws in passive technological design. For any discussion of indoor comfort, the thermal design and performance of the structure MUST enter into the mix at some point.

    Regarding amount of condensate removed by an actual running a/c system, that's not hard to determine. A psychrometric chart, wet and dry bulb temps of both supply and return air at air handler, known airflow in cfm over the coil, a little number crunching...done:

    4.5 * CFM * 6 grains of moisture delta = 32,400 grains/7000 grains per pound of dry air = 4.6 lbs/8.34 pounds per gallon = 55 ounces or less than 1/2 of a gallon per hour...IF I'm doing this formula correctly.
    Last edited by Shophound; 11-08-2007 at 06:09 PM. Reason: to add the number "6" to the formula

  5. #31
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    That is a valuable insight, Shophound. Here I was thinking the only way was to physically capture and measure it. I'm very partial to automated methods of data collection and yours has the advantage.

    Best wishes -- Pstu

  6. #32
    Join Date
    Aug 2006
    Posts
    34
    Pstu, what is the picture of in your avatar?

  7. #33
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304
    Quote Originally Posted by brian e View Post
    Pstu, what is the picture of in your avatar?
    It's a Dwyer Mark II red oil manometer. In the past these have been available cheap on Ebay. I got one which apparently was like new, had been sitting unused in a laboratory for 30 years. It's kind of antique and archaic and funky:
    http://www.dwyer-inst.com/htdocs/pdf.../mark2_iom.pdf

    It is mounted with the low pressure side on the return plenum and high pressure side on the supply plenum. The intent is to measure external static pressure (ESP) on an ongoing basis, the pressure pickups are not ideal but they are documented by Dwyer as acceptable. An AC pro would probably prefer a digital manometer or Magnahelic gauge of the correct range, and a probe for more professionally consistent pressure measurements. However a digital is a bit pricey, and you would need many Magnahelics to cover all the range that this one manometer can.

    The installation is to mimic a commercial setup recommended by Dwyer for monitoring air filter loadup. Plus I was real curious how much ESP would improve upon installing additional return capacity a couple years ago. Have found that I can easily watch ESP changing with different airflow on a variable speed air handler. It's the most direct way I have to identify whether the 2-stage AC or heat is on high or low. I like to watch all that stuff.

    Best wishes -- Pstu

  8. #34
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    An AC pro would probably prefer a digital manometer or Magnahelic gauge of the correct range, and a probe for more professionally consistent pressure measurements. However a digital is a bit pricey, and you would need many Magnahelics to cover all the range that this one manometer can.

    This little dude from Testo:



    ...is a digital manometer which can measure in inches of water column from 0.0 to over 4.0", can also measure in PSI and pascals...one tool, decent range, three measurements, under two hundred smackers. Not a bad deal at all. Someday I may even get one!

    The installation is to mimic a commercial setup recommended by Dwyer for monitoring air filter loadup. Plus I was real curious how much ESP would improve upon installing additional return capacity a couple years ago. Have found that I can easily watch ESP changing with different airflow on a variable speed air handler. It's the most direct way I have to identify whether the 2-stage AC or heat is on high or low. I like to watch all that stuff.
    Maybe in another life you can have my job, part of which involves monitoring a computerized building management system that measures static pressure on all my air handlers and variable air volume (VAV) boxes. I have found that as far as monitoring the loading up of filters in an air handler with a variable speed blower, it's pretty much useless, since the pressure drop will change with the rate of air velocity moving through the air handler. For a residential air handler/furnace that is variable speed...it would depend on how "variable speed" is defined. Shifting between various motor speed windings or an ECM that varies to maintain a predetermined static pressure? The latter would prove more interesting to monitor, IMO, to see how the thing reacts to various heat loads and dirt loading of the filters. The former would indicate, as you state, when the blower is on high or low speed. Either one would also show differences between a wet cooling coil and a dry one.

    In your avatar pic, it looks like you have the instrument propped above a door frame or some other form of trim. If it's door frame, that instrument appears to be HUGE! My wife would surely declare me off the deep end if I hung something like that outside our mechanical closet.

  9. #35
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,213
    Quote Originally Posted by teddy bear View Post
    +11 MERVs are ok if designed for your air flow-pressure drop requirements. The large, 4"-5" deep MERV 11 filters are able to provide good filtering with minimal pressure drop. Most filter include in their specs pressure drop/air flow details. These filters have 2X-4X more media than the 1"-2" filters. We use a few HEPA filters on our dehus for special applications, but they are grossly over-sized with <.1" pressure drop. In other words with enough media, any of the high eff. filters could be designed to function on typical air handlers. In reality, the major benefit of filtering is to keep the equipment clean. Extra filtering has little effect on the dust in the space. Most dust enters via clothes, open doors/window, and wind caused infiltration. The dust settles to the floor before passing through a filter. Regards TB
    Thank-you, sir! I have a better understanding about merv ratings and their application. I guess most chaps who recommend using very low merv filters or using those cheap fibreglass filters assume that most duct systems are somewhat restrictive. I would love to know how restrictive mine are. When I had my new heat pump and fancoil installed about six years ago there was never a mention of manuel D, or a manual J, for that matter. My system seems to work pretty good, anyways. Maybe I got lucky. It might be slightly oversized, but with the VS fancoil, it keeps the humidity under control without overcooling.

    Thanks so much again......Bears Rule!!!!

    thorton
    ______________________
    We cannot change yesterday. We can only make the most of today,
    and look with hope toward tomorrow.

  10. #36
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,537
    Quote Originally Posted by shophound View Post
    I believe any dehumidification discussion needs to address the primary source of excess humidity in the average home...infiltration. Anytime outdoor dew points are higher than 55 degrees, infiltrating moisture from outdoors will affect indoor comfort at normal room temperatures (72-78 degrees F.).

    Slavishly seeking to keep relative humidity below 50% at all times to me is a bit misleading. If one rather were to desire a consistent indoor dew point held to 55 degrees, the sensible temperature can vary from 72 to 78 degrees dry bulb, with relative humidity varying from ~56% to ~45%, respectively, and still be within the ASHRAE comfort zone.

    In humid climates, fresh air exchange requirements in a residence are best done in a controlled manner, vs. the uncontrolled aspect of structural infiltration. We must have fresh air exchanges to keep the indoor air quality healthy...tightening up a house without making this provision is unhealthy and counterproductive. The best way to introduce fresh air into a home in a humid region is either through fresh air intake on the cooling system, or fresh air intake through a dehumidifier.

    Humid climates like Houston, TX are typically warm climates...cool, rainy days are not as common as warm, rainy days, followed by breaks in the clouds with bright sunshine, spiking wet bulb and sensible temps. Internal sensible and latent heat generation in a well insulated, tight house combined with sensible and latent gain via normal ingress/egress traffic should be enough to cause the cooling system to run, providing fresh air exchange, dehumidification, and sensible cooling. In a general sense, with a high latent load in a house, the possibility of overcooling is not as great, since more of the coil's capacity is being used for latent heat removal.


    Regarding amount of condensate removed by an actual running a/c system, that's not hard to determine. A psychrometric chart, wet and dry bulb temps of both supply and return air at air handler, known airflow in cfm over the coil, a little number crunching...done:
    I slavishly use <50% RH because we are concerned about %RH under carpets on concrete slabs. Dust mites do well at +65%RH. Slab temps are commonly -10^F of ambient air. So even with <50% RH in air, the relative humidity can be 65%RH at the slab interface. Thats a small point. Generally, I agree with your thinking.
    Using the weather data from underworld, I set up a spread sheet with calcs and graph to show the moisture load in in 1lbs. /day using mean dewpoints for Houston for 07. I have also done the calcs. on a/c moisture removal and supplemental dehu load, although not included. Interesting data. I am attaching Underground weather chart and spreadsheet graph. Looking forward to more discussion with those interested. Regards TB
    Attached Files Attached Files
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  11. #37
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    The Dwyer Mark II is pictured in closeup, it is actually 7.5 inches wide and 6 inches high. Bigger than that nifty handheld Testo. Location is inside a closet so my wife did not see the thing until it already had been installed.

    Does not the Carrier Infinity control have a function that advises the homeowner when to change the filter, based on an increase in ESP?

    Sounds like an interesting job you got.

    Best wishes -- Pstu

  12. #38
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    238
    Quote Originally Posted by pstu View Post
    It's a Dwyer Mark II red oil manometer. In the past these have been available cheap on Ebay. I got one which apparently was like new, had been sitting unused in a laboratory for 30 years. It's kind of antique and archaic and funky:
    http://www.dwyer-inst.com/htdocs/pdf.../mark2_iom.pdf

    It is mounted with the low pressure side on the return plenum and high pressure side on the supply plenum. The intent is to measure external static pressure (ESP) on an ongoing basis, the pressure pickups are not ideal but they are documented by Dwyer as acceptable. An AC pro would probably prefer a digital manometer or Magnahelic gauge of the correct range, and a probe for more professionally consistent pressure measurements. However a digital is a bit pricey, and you would need many Magnahelics to cover all the range that this one manometer can.

    The installation is to mimic a commercial setup recommended by Dwyer for monitoring air filter loadup. Plus I was real curious how much ESP would improve upon installing additional return capacity a couple years ago. Have found that I can easily watch ESP changing with different airflow on a variable speed air handler. It's the most direct way I have to identify whether the 2-stage AC or heat is on high or low. I like to watch all that stuff.

    Best wishes -- Pstu
    I put one on my Envision. But I hooked it up differently. I have the low side plumed into the Air handler and the high side into the return plenum. So I am measuring the pressure drop only across the coil and air filter. Doing the air filter only was too difficult and probably would not give accurate results. My 3 ton Envision requires a 28"x30"x2" filter. I use MERV 11. It has already saved me two filters and therefore paid for itself already. The MERV 11 are suspose to be replaced every 3 months. The current filter has been in for 7 to 8 months and the coil is still almost the only contributer to the PD.

  13. #39
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304
    Congratulations. I am always glad to hear about people measuring things instead of using a rule of thumb. Wish there were more like you!

    Best wishes -- Pstu

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