Wacha think
Results 1 to 2 of 2

Thread: Wacha think

  1. #1
    Join Date
    Aug 2001
    Location
    Eastern Washington
    Posts
    2,990
    Past couple years I been taking psychrometric readings in our district buildings during the cooling season. ( from Heating-to-cooling transition, to, cooling-to-heating trans.) I been doing this just for kicks, and to learn something about our buildings. What I found out was that our buildings generally run about 45% RH at 76* indoor air temp with no moisture difference from the outside air. We have chilled water circulated through fan coils in each classroom. 45* chilled water temp, and DDC controlled 3-way diverting valves, modulating to maintain the warmest coil temp possible, and still keep the room at setpoint. Consequently, the coils dont sweat, only the manifolds of the coils do a little, but only enough to stain the drip pan a bit, not puddle and reach the drain.


    Floors are carpeted, and generally about 4-5* cooler than the air temp, puting the carpet RH at about 50%. Maintenance director insists there is no mold problem in the district, yet I find what I believe to be ripe conditions, and we have 3 yr old school buildings developing their own smell.

    Ambient air in this country seems to be about 60 gr. water per lb. of air most days


    Other consernes of mine are operating habits. We shut down the chiller from 3pm to 7am every day, so at least we get a bit of dehumidification in the am when valves modulate wide open, but none the rest of the day. Local Carrier techs dont like the habit bldg. engineers have of running warm coils this way either. We do run 40% prop glycol in the systems. When they clean the carpets, we make no attempt to run cooling longer to aid in drying.

    What do you guys think?
    TB
    Everyone knows something I don't.

    2 Chronicles 7:14
    14 if my people, who are called by my name, will humble themselves and pray and seek my face and turn from their wicked ways, then will I hear from heaven and will forgive their sin and will heal their land.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,231
    Originally posted by TB
    [B---- What I found out was that our buildings generally run about 45% RH at 76* indoor air temp with no moisture difference from the outside air. We have chilled water circulated through fan coils in each classroom. 45* chilled water temp, and DDC controlled 3-way diverting valves, modulating to maintain the warmest coil temp possible, and still keep the room at setpoint. Consequently, the coils dont sweat, only the manifolds of the coils do a little, but only enough to stain the drip pan a bit, not puddle and reach the drain.
    Floors are carpeted, and generally about 4-5* cooler than the air temp, puting the carpet RH at about 50%. Maintenance director insists there is no mold problem in the district, yet I find what I believe to be ripe conditions, and we have 3 yr old school buildings developing their own smell.

    Ambient air in this country seems to be about 60 gr. water per lb. of air most days

    Other consernes of mine are operating habits. We shut down the chiller from 3pm to 7am every day, so at least we get a bit of dehumidification in the am when valves modulate wide open, but none the rest of the day. Local Carrier techs dont like the habit bldg. engineers have of running warm coils this way either. We do run 40% prop glycol in the systems. When they clean the carpets, we make no attempt to run cooling longer to aid in drying.

    What do you guys think? [/B]
    During typical 60 gr. outdoor weather, ok. What about 10 days of cool 100 gr. outdoor weather? What about the relative humidity between the carpet and concrete for a couple weaks after cleaning the carpeting? If the isolated %RH is +70% for several days, mold grows. Also check in areas with carpeting/concrete on grade. Concrete on grade is much cooler and therefore high %RH under the carpet. To check this, place a %RH meter under a piece of carpeting on the ongrade concrete. Try carpet cleaning with the same check. During wet cool weather with 30 occupants in a 1,000 sq.ft classrom for 8 hours, the grains will be much higher. The moisture input from outside air and students may be 2 gallons per hour. A couple weeks of this will give a classroom a distinct odor! This a indication of mold growth.

    Cooling alone does not solve the problem. A relatively small amount of dehumidification during the nights, weekends, and vacation is very effective and much more energy efficient than making it cold with the a/c. Three pounds of dehumidification per hour per 1,000 sq.ft. of classroom will maintain <50%RH during the unoccupied time with a/c. I have used this concept with several hundred classrooms. The most noticable change of maintaining <50%RH is the absence of the odor. Hobo data loggers are ideal for monitoring this condition. Mold is never a problem until an occupant finds it. Preventive maintaince is important. I impressed with your observation and investigation but be careful, nobody wants to here about this.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event