Armin Rudd - Building Science Principals for Managing Moisture in Tight Buildings
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Transcript of Armin Rudd - Building Science Principals for Managing Moisture in Tight Buildings
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 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Building Control Layers
Water Air Thermal Vapor
3 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Air Compartmentalization is Key in Multifamily
Stack, Wind, and Mechanically Induced Airflow
Source: Building Science Corp.
Most moisture flow is by airflow. Need to control the airflow.
4 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Stack Effect in Cold Weather
+ NPP
Air flows in at bottom
Air flows out at top
Air leakage condensation at top stories
Source: Building Science Corp.
Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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
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
Fully adhered air barrier drainage plane and insulation
Source: Building Science Corp.
8 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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
9 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Balanced Ventilation In Each Dwelling Unit
Central-fan-integrated Supply + Single-point Exhaust HRV/ERV
Source: Building Science Corp.
10 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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
11 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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
12 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Humidity control challenges
1. 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
2. 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
13 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
3. More energy efficient cooling equipment often has a higher evaporator coil temperature yielding less moisture removal
• Larger evaporator coil by manufacturer design, or up-sized air handler unit or airflow by installer choice
4. Conventional over-sizing to cover for lack of confidence in building enclosure or conditioning system performance causes short-cycling yielding less moisture removal
Humidity control challenges, cont.
Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Typical Indoor (humid climate)Tdb RH Tdp
winter 72 40 46spring 75 45 52summer 77 50 57fall 75 45 52
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Dew
poin
t Tem
pera
ture
(F)
Monthly Average Outdoor Dewpoint Temperature
Miami
Houston
Cincinnati
Boston
Phoenix
San Francisco
Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Dew
poi
nt T
empe
ratu
re (
F)
Monthly Average Outdoor Dew Point Temperature
Baltimore
Wash DC
Norfolk
Richmond
San Francisco
Miami
Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
0 10 20 30 40 50 60 70 80 90 100 110 120
0.25 ach infiltration
0.1 ach infiltration with 50 cfm ventilation
Moisture Load (lb water/day)
Moisture load for cooling and dehumidification systemsin humid climates (75 F/55% RH indoor, 75 F outdoor dewpt)
Air exchange
People
Cooking
Dishwashing
Bathing
Clothes washing
Floor mopping
Building envelope
New const drying
Source for Cooking through New construction drying: Natural Resources Canada
Internal Moisture Gains from Boualem Ouazia, NRC-CAN, Humidity Control in Houses ERV Technology
24 lb/day
Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Cooling Load for: 50 cfm OA, Tdb,in=75, Tdp,in=55, Tdp,out=75
0
200
400
600
800
1000
1200
80 85 90 95 100 105
Outdoor air temperature (F)
Coo
ling
load
(W)
05001000150020002500300035004000
Coo
ling
load
(B
tu/h
)
Total
Sensible
Latent
19 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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. Don’t run on constant fan when the coil is wet 4. Disable fan overrun after the compressor stops
20 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
What is Supplemental Dehumidification?
Moisture removal, supplemental to the cooling system, when there is no need for cooling.
21 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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)
22 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
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
Dehumidifier and ventilation duct in interior mechanical closet with louvered door
Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Ducted dehumidifier in conditioned space with living space control
25 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
Dehumidifier process
Fan
Evaporator coil
Supply Air
Return Air
Entering Air Dew Point
Leaving Air
Fan
Condenser coil
Dehumidifiers add the heat of condensation, compressor heat, and fan heat to the space. (Supply air is typically 105 to 115 F)
Supply Air
26 Arlington County Workshop, 2013-12-11 Balancing Moisture, Ventilation, and Energy Efficiency
What about making the existing cooling or heat pump equipment also do the supplemental dehumidification?
Goals:
Provide year-around relative humidity control in high-performance (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
27
Affordable Comfort Conference 3/28/2012 Baltimore
Central system with modulating hot gas reheat
Fan
Evaporator coil
Supply Air
Return Air
Entering Air Dew Point
Leaving Air
Fan
Modulating hot gas reheat coil
Modulate the hot gas reheat to achieve a space-neutral supply air temperature.
T1 T2
Supply Air