multifamily ventilation - best practice?
TRANSCRIPT
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Multifamily Ventilation – Best Practice?
Dianne Griffiths
April 29, 2013
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Presentation Outline
• Basic Objectives
• Exhaust Systems
• Make-up Air Systems
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Two Primary Ventilation Objectives
1) Providing Fresh Air - Whole-House 2) Removing Pollutants - Local Exhaust
Our goal is to find the simplest solution that satisfies both objectives while minimizing cost and energy impacts.
Common Solution: Align local exhaust with fresh air requirements (Ex: 25 Bath + 25 Kitchen)
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Exhaust-Driven Fresh Air Design
• Exhaust slightly depressurizes the units
• Outside air enters through leaks, cracks, or planned inlets
• Widely used in the North
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Multifamily Ventilation Best Practice
• Step 1: Understand ventilation requirements
• Step 2: Select the simplest design that can achieve both air quality and energy objectives
• Step 3: Build a tight building
• Step 4: Pay attention to installation quality
• Step 5: Check to make sure ventilation works
• Step 6: Educate users
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Exhaust: Central and Unitized
Central Exhaust Unitized Exhaust
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Standard Central Exhaust Practice
Roof or mushroom fans Vertical shaft with
horizontal take-offs Sidewall or ceiling grilles
at each floor Continuous operation
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Mechanical Designers’ Intent
• Balancing damper transferring responsibility to balancing contractor
• Many grilles, many floors, relatively low flow targets, plus wind and weather on balancing day = balancing is difficult
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Automatic Balancing Dampers
60 CFM
40 CFM
20 CFM
30 CFM
20 CFM
10 CFM
30 CFM
30 CFM
30 CFM
30 CFM
30 CFM
30 CFM
Balance in two ways: • Provide restriction in size of
opening (increase static pressure)
• Dynamically self-adjust to changes in the system (automatic balancing)
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Duct Leakage
Roof curb?
Takeoffs?
Transverse (sectional) joints?
Register connectionsLongitudinal (lengthwise)
joints? can be the largest set of leaks
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Best Practice
• Include performance specifications for duct tightness in construction documents
• Call out specific details to be sealed: all joints, takeoffs, connections, registers, etc., etc.
Then test for leakage: • Good =
10 CFM50/register • Better =
5 CFM50/register
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Duct Sealing Methods
Aeroseal® aerosol duct sealant sticks to holes in ductwork and seals them
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Working elevators and power on the roof are helpful.
• Prepare a plan.
• Check weather report!
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Mastic Spray
Rotating spray head -Simple concept applies mastic directly -Very effective on to leaks identified by straight shafts camera
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In-Unit Exhaust Systems
Small fans, relatively low flow (50-100 CFM), low power consumption, easier to balance floor to floor
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In-Unit Ventilation Quality Control
• Duct sealing • Avoid kinks, long duct
runs; use rigid duct
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Exhaust System Design Parameters
Central Systems
• Constant Air Regulating (CAR) dampers to balance flows
• Airtight ductwork, including fan and grille connections
• Tightly compartmentalized units
Unitized Systems
• ENERGY STAR fans with variable speed where appropriate
• Short straight duct runs
• Tightly sealed ducts
• Tightly compartmentalized units
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Exhaust-Driven Make-up Air Strategies
Current Research Focus
Where is the make-up air coming from?
• Leaks • Trickle vents • Make-up air supplied to corridor • Vent or fan within PTAC
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Trickle Vents - Designed Inlets
• Intentional openings in building envelope that allow a trickle of air into buildings in response to pressure differential
• Trickle Vents often built into window frames
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Trickle Vents – Installed Performance
• Flow from trickle vents measured with hot wire anemometer in a building under actual operating conditions.
• Also measured inside/outside pressure difference across exterior window.
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Trickle Vent Airflow vs. Pressure Difference
Air flow at typical building operating pressures is expected to be about 5-10 CFM per trickle vent – a “trickle”
AAMA = American Architectural Manufacturers Association
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Comparison of trickle vents in two buildings
1st bldg.
2nd bldg.
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Airflow patterns in a tight unit with trickle vents
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Airflow patterns with trickle vents
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This Year’s Research Plan
1. Evaluate performance of more systems in more buildings – Corridor supply systems – Trickle vents – PTAC outside air vents
2. Measure pressure variation within buildings and apartments over time – 2 weeks in winter and 2 weeks in summer
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Earlier Testing
• Airflow through gaps in apartment door
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Latest Test Rig
Powered Flow Hood Energy Conservatory’s FlowBlasterTM
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Other Make-up Air Inlets
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Variability in Driving Forces
Typical for Winter – But what about summer, windy days, …
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Pressure Monitoring
Locations of pressure sensors
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Pressure Monitoring
Data logger
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Best Practice Summary
• Step 1: Understand ventilation requirements
• Step 2: Select the simplest design that can achieve both air quality and energy objectives
• Step 2: Build a tight building
• Step 3: Pay attention to installation quality
• Step 4: Check to make sure ventilation works
• Step 5: Educate users
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Thank You