Controlling Moisture in Commercial Buildings

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1 Controlling Moisture in Commercial Buildings Part Load Problems Raymond E. Patenaude, PE, CIAQP, RPIH The Holmes Agency, Inc. Consulting and Forensic Engineers

2 Historical Perspective Willis Carrier Air conditioning is the control of the humidity of the air by either increasing or decreasing its moisture content. Added to the control of humidity is the control of the temperature by either heating or cooling the air, the purification of the air by washing or filtering the air, and the control of air motion and ventilation

3 Book cover

4 Chapter 3 - Managing Ventilation Air

5 Chapter 5 - Avoiding Bugs, Mold & Rot

6 Comfort - Keep the dew point under control, and comfort happens at warmer, more energyefficient temperatures

7 ASHRAE Std Ventilation for Acceptable Indoor Air Quality

8 Ventilation - If it s not dried you re in trouble

9 Mold - It s the surface rh that counts.. So keep the dew point down, and things go well

10 Mold Growth Enzymes on mold spore combine with surface moisture to dissolve food source paper, wood, ceiling tile Osmotic pressure causes liquid nutrients to diffuse across spore wall allowing spore to absorb the nutrients Spore germinates producing filamentous hyphea Hyphea grows quickly creating mycelium mat Mold grows conidia which generates and releases spores into the air

11 Water Activity Water activity indicates how much water is biologically available to fungus in its food source. Water activity of 0.8 refers to the amount of water absorbed into a material when the surrounding air is at 80% RH Water activity of a material is very different from the relative humidity of the material Mold growth is a risk when surface relative humidity stays above 85% for extended periods

12 Moisture Content and Surface Relative Humidity

13 Uncontrolled air flow Buildings which have never reported relative humidity above 65% still may have mold growth

14 THE MOISTURE PROBLEM Highest enthalpy occurs at peak dew point.. NOT peak dry bulb ASHRAE 2005 Fundamentals lists Extreme DB with MCWB.example Kansas City, MO (1%) 93db/75wb (107 gr/lb) 68dp Extreme DP with MCDB (.4%) 75dp/85db (137 gr/lb) (78wb).. poor performance at part load!!

15 THE MOISTURE PROBLEM ASHRAE 2005 Fundamentals lists extreme DP with MCDB.example Orlando, FL (0.4%) 83db/77dp (142 gr/lb) (79 wb).. again poor performance at part load!!

16 TYPES OF MOISTURE PROBLEMS Dry wall Outdoor air 85 deg F 137 gr/lb 72%rh Vapor transport Mold growth on backside of drywall 75 deg F dp Interior Design 75 deg F Building Envelope with poor vapor barrier

17 Ventilation - If it s not dried you re in trouble

18 VAV AIR CONDITIONING Full Load Supply air 58 F 80% rh 58 gr/lb VAV Supply Fan VAV Box with Heat F 90%rh 58 gr/lb 7,710 OA 11,9 RA 19,6 SA ChW Evap Coil Constant volume OA Fan Return Air 75F 65 gr/lb %rh Outside ventilation air 93F db 107 gr/lb 44%rh

19 ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: INCHES OF MERCURY R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL DRY BULB TEMPERATURE - F HUMIDITY RATIO - POUNDS MOISTURE PER POUND DRY AIR WET BULB TEMPERATURE - F % 80% 70% % % % SA lat Mtr Room RA eat 85 Mix OA eat SENSIBLE HEAT Qs TOTAL HEAT Qt ENTHALPY HUMIDITY RATIO h W 30% 20% 10% RELATIVE HUMIDITY

20 VAV AIR CONDITIONING Part Load Supply air 57 F 92% rh 65 gr/lb VAV Supply Fan VAV Box with Heat F 100%rh 65 gr/lb 7,710 OA 2,4 RA 10,1 SA Resultant Room 74F db 61.4% rh ChW Evap Coil Constant volume OA Fan Return Air 75F 65 gr/lb %rh Outside ventilation air 85F db 137 gr/lb 72%rh

21 NEW Note # 1 Here... ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: INCHES OF MERCURY R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL DRY BULB TEMPERATURE - F HUMIDITY RATIO - POUNDS MOISTURE PER POUND DRY AIR WET BULB TEMPERATURE - F % 80% SA lat 70% Mtr Room % % % RA eat 85 OA eat Mixed SENSIBLE HEAT Qs TOTAL HEAT Qt ENTHALPY HUMIDITY RATIO h W 30% 20% 10% RELATIVE HUMIDITY

22 OA Pre Treatment with Post Cooling Full Load VAV Supply Fan ChW Post Cooling (sensible) Constant volume OA Fan DX system Chw Pre Cool F Outside ventilation air Supply air 58 F 75% rh gr/lb VAV Box (NO Reheat) F 85%rh gr/lb Return Air 75F 65 gr/lb %rh DX Cond Reheat 75F DX Evap 42F (Remove Moisture) 93F db 107 gr/lb 44%rh

23 ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: INCHES OF MERCURY R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL DRY BULB TEMPERATURE - F HUMIDITY RATIO - POUNDS MOISTURE PER POUND DRY AIR WET BULB TEMPERATURE - F % 80% 70% % % % OA CW pre cool SA lat post cool Mtr OA DX pre cool RA eat Room Mix OA reheat OA eat SENSIBLE HEAT Qs TOTAL HEAT Qt ENTHALPY HUMIDITY RATIO h W 30% 20% 10% RELATIVE HUMIDITY

24 OA Pre Treatment with Post Cooling Part Load VAV Supply Fan ChW Post Cooling (sensible) Constant volume OA Fan DX system Chw Pre Cool F Outside ventilation air Supply air 57 F 65% rh 46 gr/lb VAV Box (NO Reheat) F 71%rh 46 gr/lb Room Resultant 74F db 46.3% rh Return Air 75F 65 gr/lb %rh DX Cond Reheat 75F DX Evap 42F (Remove Moisture) 85F db 137 gr/lb 72%rh

25 ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: INCHES OF MERCURY R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL DRY BULB TEMPERATURE - F HUMIDITY RATIO - POUNDS MOISTURE PER POUND DRY AIR WET BULB TEMPERATURE - F SENSIBLE HEAT Qs TOTAL HEAT Qt OA eat 1000 ENTHALPY HUMIDITY RATIO h W % 80% 70% % % % 30% OA CW pre cool SA lat post cool Mtr RA Room Mix OA DX pre cool OA reheat 20% 10% RELATIVE HUMIDITY

26 OA Pre Treatment with Post Cooling Part Load reset DX VAV Supply Fan ChW Post Cooling (sensible) Constant volume OA Fan DX system Chw Pre Cool F Outside ventilation air Supply air 57 F 70% rh 49 gr/lb VAV Box (NO Reheat) F 76.5%rh 49 gr/lb Room Resultant 74F db 49.3% rh Return Air 75F 65 gr/lb %rh DX Cond Reheat 75F DX Evap F (Remove Moisture) 85F db 137 gr/lb 72%rh

27 ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE: INCHES OF MERCURY R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL DRY BULB TEMPERATURE - F HUMIDITY RATIO - POUNDS MOISTURE PER POUND DRY AIR WET BULB TEMPERATURE - F SENSIBLE HEAT Qs TOTAL HEAT Qt OA eat 1000 ENTHALPY HUMIDITY RATIO h W % 80% 70% % % % 30% OA CW pre cool SA lat post cool Mtr Room RA Mix OA DX pre cool OA reheat 20% 10% RELATIVE HUMIDITY

28 Design Considerations It s a system not just a unit The habitable space is a plenum Uncontrolled air flow ASHRAE Journal Don t operate in a vacuum it s a team effort Sequence of operation Control outside air at the source Control condensation

29 ASHRAE Standards and Publications Available from ASHRAE in Atlanta, Humidity Control Design Guide For Commercial and Institutional Buildings

30 ASHRAE Standards and Publications Available from ASHRAE in Atlanta Design Data for Weather Weather Data Viewer ASHRAE Design Weather Sequence Viewer

31 ASHRAE Standards and Publications Psychrometric Analysis CD Available at ASHRAE Book Store Long Beach, California

32 ASHRAE elearning On-Demand Interactive Courses in Modules Online course reference book Online self assessment

Energy Efficient Building Design College of Architecture Illinois Institute of Technology, Chicago. Relative Humidities RH% 49.4. 0.

Energy Efficient Building Design College of Architecture Illinois Institute of Technology, Chicago. Relative Humidities RH% 49.4. 0. Psychrometrics Psychrometric Chart Relative Humidities RH% 49.4 100% 80% 0.030 Enthalpies 70% H btu/lb 46.5 0.028 85 Not to Scale 0.026 Humidity Numbers and Values 43.7 60% Ratios are approximate 0.024