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  1. #40
    Join Date
    May 2006
    Location
    Warren, MI
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    940
    Quote Originally Posted by Carnak View Post
    won't get a shock at 35 & 40%
    So, if they were getting a shock their RH was below 35%. Would that be considered excessive RH? I think not. I think 35% RH is suggested for a outside temperature of 0F-20F.
    Bill

  2. #41
    Join Date
    Apr 2002
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    11,808
    I keep my place 40% year round, it gets into the high 30s when I need to change my filters. It is comfortable, I do not get static shocks. I do not live anywhere cold now, I did for the first 37 years of my life however.

    The suggested RH is typically 40 to 60% for human comfort, the fatter you are the lower the RH you will like.

    35% is a recommendation to keep your windows clear. 35% is a typical winter time indoor RH in commercial buildings.

    35% is a magic number to try when it is below freezing out, you can adjust up as much as your windows can take from there, or if they are really poor you will be adjusting humidity down.

    I have seen decent Andersens keep close to 40% RH in cold subarctic weather, I have never seen someone maintain both over 40% and and clear glass unless they had the Wilmar windows, R12 value, were over $100 a square foot back in the day.

    You need some ventialtion to get your RH down if you want your windows to be clear. Windows tell you when you need more fresh air.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  3. #42
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    940
    Quote Originally Posted by Carnak View Post
    I keep my place 40% year round, it gets into the high 30s when I need to change my filters. It is comfortable, I do not get static shocks. I do not live anywhere cold now, I did for the first 37 years of my life however.

    The suggested RH is typically 40 to 60% for human comfort, the fatter you are the lower the RH you will like.

    35% is a recommendation to keep your windows clear. 35% is a typical winter time indoor RH in commercial buildings.

    35% is a magic number to try when it is below freezing out, you can adjust up as much as your windows can take from there, or if they are really poor you will be adjusting humidity down.

    I have seen decent Andersens keep close to 40% RH in cold subarctic weather, I have never seen someone maintain both over 40% and and clear glass unless they had the Wilmar windows, R12 value, were over $100 a square foot back in the day.

    You need some ventialtion to get your RH down if you want your windows to be clear. Windows tell you when you need more fresh air.
    My winter time RH is below 35% now, why would I need more air flow????
    Bill

  4. #43
    Join Date
    Apr 2002
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    11,808
    you don`t, I do

    I am in a year round cooling environment now. When my filters plug up my airflow drops and my Rh drops down below 40%, time to change the filters.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #44
    Join Date
    Nov 2008
    Location
    Houston, TX
    Posts
    77
    Quote Originally Posted by Carnak View Post
    you don`t, I do

    I am in a year round cooling environment now. When my filters plug up my airflow drops and my Rh drops down below 40%, time to change the filters.
    I get the reverse problem. When my air filter plugs up, supply temperatures increase. A/C that is blowing 58 out the ducts will drop to about 53 when I take the filter out. Humidity level goes down.... The temp output will rise back to about 56 when I put a new filter in.

    System is a simple 3.5 ton single stage single speed package unit. Filter is a 20x20" in the ceiling return grille. I've been using the highest rated 3M 1" filters. Thinking about going one level lower. (The purple ones instead of the navy blue ones)

  6. #45
    Join Date
    Apr 2002
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    11,808
    I have minimal infiltration in my home so I run a counter intuitive high cfm per ton. As my filter loads I drop down towards the traditional "400 CFM" per ton and even a little lower.

    If your ducts are up in a vented attic, maybe return static goes up as the filter grille is getting clogged (my filter is in the unit) and you are getting increased leakage into your return duct and the AHU casing itself, more than your system can handle
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  7. #46
    Join Date
    Apr 2002
    Posts
    11,808
    lower airflow should mean colder air off of the coil, so if your supply temperature is going up, sounds like it is drawing in more 'hot humid" air, either from return/casing leaks downstream of plugged filter or a from a fresh air intake with increased 'suction' on it.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  8. #47
    Join Date
    Nov 2008
    Location
    Houston, TX
    Posts
    77
    I live in a 40 year old apartment. So no fresh air duct for me. I wouldn't be surprised at all if there is a leak in the ductwork somewhere. No attic. Package unit up on the roof. But ducts do run between the ceiling and the roof. That space is vented (open soffits)

    It would probably explain why I had $350/month electricity bills during July/August this year. (1300 sq ft, top floor apartment). Although lack of maintenance is probably just as likely in that regard.

    What kind of bill do you run down in the tropics?

  9. #48
    Join Date
    Apr 2002
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    11,808
    well I pay about 30 cents a kwH down here, in prime time my electric bills are about 250 a month I am in an end unit short east, west exposure long south wall. There are four units staggered so also a short north wall.

    My interior units are about 150 a month. The north exterior unit is a single guy and a bit of a miser, he keerps the place at 80, he hardly cooks- his primetime bills are not much over 160.

    Units all single story with a roof, 1000 square feet in size.

    Packaged unit probably has a fresh air intake. Maybe keep changing the filters in the Packaged unit and do not use a filter grille. Packaged unit should take 2 inch pleated filters, be good for say 3 months. Two inch is less restrictive than the one inch pleat you are probably sticking in your return grille, your RH will drop substantially if I am correct.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  10. #49
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    For the OP...when your windows were installed, was there any low expanding foam insulation used around the perimeter of the window frame between it and the studs? Thermal bridging is a problem around window frames, especially when the gap between the window frame and the studs (due to rough-in size of framing to accomodate window) is not insulated.

    Your window might perform better if it has a thermal break between the frame and the surrounding studs.
    • 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.

  11. #50
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Quote Originally Posted by Baseboard Gord View Post
    System is a simple 3.5 ton single stage single speed package unit. Filter is a 20x20" in the ceiling return grille. I've been using the highest rated 3M 1" filters.
    That is a restrictive filter. Too much pressure drop for a 1" thickness. Few understand that you can have equivalent level of filtration with thicker media AND less pressure drop. It's all about surface area. I really would like to see 1" filters die an overdue death. 2" minimum pleated should become the norm. 4" or greater is rockin'.
    • 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.

  12. #51
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Quote Originally Posted by shophound View Post
    That is a restrictive filter. Too much pressure drop for a 1" thickness. Few understand that you can have equivalent level of filtration with thicker media AND less pressure drop. It's all about surface area. I really would like to see 1" filters die an overdue death. 2" minimum pleated should become the norm. 4" or greater is rockin'.
    That filter size is 2.78 sqft and at 1400 CFM the face velocity is over 500 feet/min... if it were 250 feet/min I submit the 3M filter would be far less of a problem, am I correct?

    Regards -- Pstu

  13. #52
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    940
    Quote Originally Posted by shophound View Post
    For the OP...when your windows were installed, was there any low expanding foam insulation used around the perimeter of the window frame between it and the studs? Thermal bridging is a problem around window frames, especially when the gap between the window frame and the studs (due to rough-in size of framing to accomodate window) is not insulated.

    Your window might perform better if it has a thermal break between the frame and the surrounding studs.
    I can't say for sure if it went all the way around the perimeter of the frame but a foam was used from the outside before the trim and caulking was done.

    I've found the answer. Double pane LoE glass is better but it still isn't perfect when it comes to eliminating window condensation. The bottom of the fixed pane will be colder and if goes below the dew point, BINGO!
    Bill

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