Building Science Principles for
Managing Moisture in Tight Buildings
for Arlington County Workshop on
Balancing Moisture, ...
Building Control Layers





Water
Air
Thermal
Vapor

Arlington County Workshop, 2013-12-11
Balancing Moisture, Ventil...
Air Compartmentalization is Key in Multifamily
Most moisture flow is by airflow. Need to control the airflow.
Stack, Wind,...
Stack Effect in Cold Weather

Air leakage condensation at top stories

+
NPP

Air flows
in at
bottom

Source: Building Sci...
Controlling Stack Effect by Compartmentalization of Floors,
Elevator Shafts, Corridors, Stairs, Chutes, and Units

Source:...
Elevator Vestibule

Floor to Ceiling Critical Sealing
Unit-to-Unit and Unit-to-Corridor

Source: Building Science Corp.
Ar...
Fully adhered air barrier drainage plane and insulation
Source: Building Science Corp.
Arlington County Workshop, 2013-12-...
Maximum Air Leakage Targets
Air Barrier Metrics
Material

0.02 l/s-m2 @75 Pa

Assembly

0.20 l/s-m2 @75 Pa

Enclosure

2.0...
Balanced Ventilation In Each Dwelling Unit
Central-fan-integrated Supply
+ Single-point Exhaust

HRV/ERV

Source: Building...
System engineering trade-offs


Start with high-performance building enclosure


Improves the more permanent features of...
Humidity control goals



Comfort, and Indoor Air Quality




Control indoor humidity year-around, just like we do
temp...
Humidity control challenges
1.

2.

In humid cooling climates, there will always be times of the
year when there is little...
Humidity control challenges, cont.

3.

4.

More energy efficient cooling equipment often has a higher
evaporator coil tem...
Monthly Average Outdoor Dewpoint Temperature
80

Dewpoint Temperature (F)

70
60
Miami

50

Houston
Cincinnati

40

Boston...
Monthly Average Outdoor Dew Point Temperature

Dew point Temperature (F)

80
70
Baltimore

60

Wash DC
Norfolk

50

Richmo...
Moisture load for cooling and dehumidification systems
in humid climates (75 F/55% RH indoor, 75 F outdoor dewpt)
Moisture...
Internal Moisture Gains
from Boualem Ouazia, NRC-CAN, Humidity Control in Houses ERV
Technology

24 lb/day
Cooling load (W)

1200

4000
3500
3000
2500
2000
1500
1000
500
0

Total

1000
800

Latent

600
400

Sensible

200
0
80

85...
Conventional Cooling System Dehumidification
Enhancements
1.

Lower Airflow (costs more but increases moisture removal)
40...
What is Supplemental Dehumidification?

Moisture removal, supplemental to the cooling
system, when there is no need for co...
When is it needed?





Mostly when the house is floating between cooling
and heating setpoints
Spring/Fall swing seas...
What is a good metric for determining the need?
Hours above 60% relative humidity
and
Condensation on windows

Arlington C...
Dehumidifier and ventilation duct in interior
mechanical closet with louvered door

Arlington County Workshop, 2013-12-11
...
Ducted dehumidifier in conditioned space
with living space control

Arlington County Workshop, 2013-12-11
Balancing Moistu...
Dehumidifier process
Evaporator
coil

Condenser
coil

Fan

Supply Air
Entering Air
Dew Point

Return Air
Supply Air

Leavi...
What about making the existing cooling or heat pump
equipment also do the supplemental dehumidification?
Goals:






...
Central system with modulating hot gas reheat
Evaporator
coil

Modulating
hot gas
reheat coil

Fan

Supply Air
Entering Ai...
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Armin Rudd - Building Science Principals for Managing Moisture in Tight Buildings

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Presentation by Armin Rudd as part of the workshop, Balancing Moisture, Ventilation, and Energy Efficiency in Arlington, VA on December 11, 2013

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Armin Rudd - Building Science Principals for Managing Moisture in Tight Buildings

  1. 1. Building Science Principles for Managing Moisture in Tight Buildings for Arlington County Workshop on Balancing Moisture, Ventilation and Energy Efficiency by Armin Rudd, ABT Systems, LLC (www.abtsystems.us)
  2. 2. Building Control Layers     Water Air Thermal Vapor Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 2
  3. 3. Air Compartmentalization is Key in Multifamily Most moisture flow is by airflow. Need to control the airflow. Stack, Wind, and Mechanically Induced Airflow Source: Building Science Corp. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 3
  4. 4. Stack Effect in Cold Weather Air leakage condensation at top stories + NPP Air flows in at bottom Source: Building Science Corp. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency Air flows out at top 4
  5. 5. Controlling Stack Effect by Compartmentalization of Floors, Elevator Shafts, Corridors, Stairs, Chutes, and Units Source: Building Science Corp. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  6. 6. Elevator Vestibule Floor to Ceiling Critical Sealing Unit-to-Unit and Unit-to-Corridor Source: Building Science Corp. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  7. 7. Fully adhered air barrier drainage plane and insulation Source: Building Science Corp. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  8. 8. Maximum Air Leakage Targets Air Barrier Metrics Material 0.02 l/s-m2 @75 Pa Assembly 0.20 l/s-m2 @75 Pa Enclosure 2.0 l/s-m2 @75 Pa 0.30 cfm50/ft2 surface area 1.5 l/s-m2 @75 Pa 0.23 cfm50/ft2 surface area 1.0 l/s-m2 @75 Pa 0.15 cfm50/ft2 surface area Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 8
  9. 9. Balanced Ventilation In Each Dwelling Unit Central-fan-integrated Supply + Single-point Exhaust HRV/ERV Source: Building Science Corp. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 9
  10. 10. System engineering trade-offs  Start with high-performance building enclosure  Improves the more permanent features of a home which has longer-term sustainability benefits   Bulk water management, low loss/gain glass, controlled air change, ducts inside conditioned space, pressure balancing Allows for reduced cooling system size   Helps pay for the enclosure improvements More compact duct system lowers cost and helps get the ducts inside  Makes overall building performance more predictable  Gives confidence for right-sizing equipment    No short-cycling: Better moisture removal, Higher average efficiency, Better spatial mixing Controlled ventilation instead of random infiltration Results in decreased energy consumption along with increased occupant comfort Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 10
  11. 11. Humidity control goals  Comfort, and Indoor Air Quality   Control indoor humidity year-around, just like we do temperature Durability and customer satisfaction  Reduce builder risk and warranty/service costs Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 11
  12. 12. Humidity control challenges 1. 2. In humid cooling climates, there will always be times of the year when there is little sensible cooling load to create thermostat demand but humidity remains high • Cooling systems that modify fan speed and temperature set point based on humidity can help but are still limited in how much they can over-cool More energy efficient homes have less sensible heat gain to drive thermostat demand but latent gain remains mostly the same • Low heat gain windows • Ducts in conditioned space • More, and better-installed, insulation • Less heat gain from appliances and lighting Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 12
  13. 13. Humidity control challenges, cont. 3. 4. More energy efficient cooling equipment often has a higher evaporator coil temperature yielding less moisture removal • Larger evaporator coil by manufacturer design, or upsized air handler unit or airflow by installer choice Conventional over-sizing to cover for lack of confidence in building enclosure or conditioning system performance causes short-cycling yielding less moisture removal Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 13
  14. 14. Monthly Average Outdoor Dewpoint Temperature 80 Dewpoint Temperature (F) 70 60 Miami 50 Houston Cincinnati 40 Boston Phoenix 30 San Francisco 20 10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec winter spring summer fall Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency Typical Indoor (humid climate) Tdb RH Tdp 72 40 46 75 45 52 77 50 57 75 45 52
  15. 15. Monthly Average Outdoor Dew Point Temperature Dew point Temperature (F) 80 70 Baltimore 60 Wash DC Norfolk 50 Richmond San Francisco 40 Miami 30 20 10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  16. 16. Moisture load for cooling and dehumidification systems in humid climates (75 F/55% RH indoor, 75 F outdoor dewpt) Moisture Load (lb water/day) 0 10 20 30 40 50 60 70 80 90 100 110 120 Air exchange People 0.25 ach infiltration Cooking Dishwashing Bathing Clothes washing 0.1 ach infiltration with 50 cfm ventilation Floor mopping Building envelope New const drying Source for Cooking through New construction drying: Natural Resources Canada Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  17. 17. Internal Moisture Gains from Boualem Ouazia, NRC-CAN, Humidity Control in Houses ERV Technology 24 lb/day
  18. 18. Cooling load (W) 1200 4000 3500 3000 2500 2000 1500 1000 500 0 Total 1000 800 Latent 600 400 Sensible 200 0 80 85 90 95 100 Outdoor air temperature (F) Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 105 Cooling load (Btu/h) Cooling Load for: 50 cfm OA, Tdb,in=75, Tdp,in=55, Tdp,out=75
  19. 19. Conventional Cooling System Dehumidification Enhancements 1. Lower Airflow (costs more but increases moisture removal) 400 cfm/ton normal cooling in non-humid climate 350 cfm/ton for normal cooling in humid climate 300 cfm/ton (down to 250 cfm/ton) for extra dehumidification 2. Overcooling Limit any overcooling to 2 oF below setpoint to avoid comfort complaints 3. 4. Don’t run on constant fan when the coil is wet Disable fan overrun after the compressor stops Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 19
  20. 20. What is Supplemental Dehumidification? Moisture removal, supplemental to the cooling system, when there is no need for cooling. Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 20
  21. 21. When is it needed?     Mostly when the house is floating between cooling and heating setpoints Spring/Fall swing seasons and summer shoulder months Summer nights and rainy periods Sensitive to internal moisture generation too  High occupant density  Lack of local exhaust use in kitchens and baths  Cooking habits (open boiling water) Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 21
  22. 22. What is a good metric for determining the need? Hours above 60% relative humidity and Condensation on windows Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 22
  23. 23. Dehumidifier and ventilation duct in interior mechanical closet with louvered door Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  24. 24. Ducted dehumidifier in conditioned space with living space control Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
  25. 25. Dehumidifier process Evaporator coil Condenser coil Fan Supply Air Entering Air Dew Point Return Air Supply Air Leaving Air Fan Dehumidifiers add the heat of condensation, compressor heat, and fan heat to the space. (Supply air is typically 105 to 115 F) Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 25
  26. 26. What about making the existing cooling or heat pump equipment also do the supplemental dehumidification? Goals:     Provide year-around relative humidity control in highperformance (low-sensible gain) dwellings Without over-cooling the space At lower installed cost than the same efficiency heating and cooling system with an additional high efficiency dehumidifier By making standard DX cooling equipment switchable between normal cooling and dehumidification-only using condenser reheat Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency 26
  27. 27. Central system with modulating hot gas reheat Evaporator coil Modulating hot gas reheat coil Fan Supply Air Entering Air Dew Point Return Air Supply Air Leaving Air Fan Modulate the hot gas reheat to achieve a space-neutral supply air temperature. Affordable Comfort Conference 3/28/2012 Baltimore T1 T2 27

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