hvac install - trust but verify
DESCRIPTION
2009 IECC, Air Leakage Testing Requirements, How to seal an existing leaky duct system,HVAC System SizingTRANSCRIPT
Quality HVAC System Installation
Trust But Verify
Quality HVAC System Installation
The goal for a Heating, Ventilation and Air Conditioning (HVAC) system is to provide proper air
flow, heating, and cooling to each room
Instructor
Barbara Collins
ERH West
Building Performance Consultant Certified NAHB Green Building Verifier Certified RESNET HERS Rater Energy Star Homes Partner Certified Environments for Living Verifier
Class Objectives
Understand HVAC system air leakage testing requirements in the 2009 IECC
Recognize the benefits of sealing ducts for savings, system performance and indoor air quality
Understand how ducts are tested for leakage Identify resources for local building departments Identify the best techniques to seal duct systems; what
inspectors should see on inspections Understand the IECC requirements for sizing of HVAC
equipment
Current Code Requirements
Must comply with all aspects of UL181 standards
Fittings, joints & seams of duct system shall be made substantially air tight by means of tapes, mastics, gasketing or other means.
Ducts - IECC
Insulation (Prescriptive) Ducts outside the building
envelope: R-8
All other ducts: R-6
Sealing (Mandatory) Joints and seams shall comply with IRC,
Section M1601.4.1
Building framing cavities shall not be used as supply ducts
2009 IECC Duct Tightness Tests
All ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed (Section 403.2.2)
Duct tightness shall be verified by testing
Only Exception: Duct tightness test is not required if the air handler and all ducts are located within conditioned space
Mandatory Requirements
SEAL DUCTS,
SAVE ENERGYSealing ducts is a cost-effective
energy efficiency practice that gives a high return on investment
HVAC System
Poor design and installation increases energy costs 10 –30%
Sizing Design Installation
Home Energy Use
Residential energy use 22% of U.S. total 25% of carbon emissions in U.S. Heating & cooling is 40 – 60 % of home
energy use
Why seal ducts
Leaks waste energy and money Average system leakage
New construction 20% Existing homes 30%
Duct sealing reduces heating and cooling energy losses and saves money
Other Problems
Duct leakage reduces air flow, conditioned air isn’t delivered to rooms which can cause wide temperature swings between rooms
IAQ issues with return leaks drawing in air from attics, garages, crawlspaces
Pressure differentials can cause excess building air leakage and back drafting
Duct Tightness Tests
Post construction tests Option 1
Leakage to outdoors: ≤8 cfm/per 100 ft2 of conditioned floor area
OR Option 2
Total leakage: ≤12 cfm/per 100 ft2 of conditioned floor area
Mandatory Requirements
Duct Tightness Tests
Rough-in test Options Option 1
Total leakage ≤6 cfm/per 100 ft2 of conditioned floor area
OR Option 2
If air handler not installed at time of test total air leakage ≤4 cfm/per 100 ft2
Mandatory Requirements
Exceptions: Duct tightness test is not required if the air handler and all ducts are located within conditioned space
Thermal Boundary is also used to define whether testing is required.
Insulation installed on underside of roof sheathing, AHU and ducts in attic, can be considered within thermal boundary
Ventilation
Outdoor air intakes and exhausts shall have automatic or gravity dampers that close when the ventilation system is not operating
Mandatory Requirements
Test Protocol
Pressurize the HVAC system, measure CFM of air required to reach pressure
Test at a pressure differential of 0.1 in w.g. (25Pa) across entire system, including manufacturer’s air handler enclosure
Test Equipment
Testing at rough-in
Testing Post Construction
Testing leakage to outside
Testing leakage to outside
Mastic Sealant
Non-toxic – Low VOCGreen credits
Recommended Set time = 20 hours
More on Mastic
High strength adhesive compound Usually applied by trowel, brush, caulking gun
or hand 3 types- water-based; solvent-based; and
two-component curing systems Water-based is the safest and easiest to use
It performs as well and in some cases better than the other 2
VOCs in mastics
Volatile organic compounds In water-based mastics, the only volatile
compound is water which is inorganic VOCs are infinitesimally small (not
recordable) Water-based mastics pose a low health risk
compared to solvent-based and two-component mastics
Safer for the user, better IAQ, greener
How to apply mastic
Step 1 - Clean Duct Surface Wipe dust oil and grease from the duct surface
Step 2 - Apply the mastic
Gaps less than 1/4″, load brush with mastic and coat entire joint with a continuous strip
Use brush end to work mastic into joint Spread mastic at least one inch on each side
of the joint. The mastic should be thick enough to hide the
metal surface of the duct.
Mesh for Gaps
If gap is larger than 1/4 inch use fiberglass mesh too
If mesh is sticky on one side, cut enough to cover joint, press in place, then completely cover it with mastic.
If mesh does not have a sticky side, apply a thin layer of mastic, press mesh into the mastic, then apply a finish layer of mastic.
AIRTIGHT DUCT SYSTEM
Boots and Cans Seal seams with
mastic
Thin mastic will crackMake seal permanent Plug Don’t PaintThick as a Nickel = .077 in1/16 inch = .0625 in
FLEX DUCT TO METAL
Flexible Ducts Seal inner sleeve & outer
sleeve
Plastic strap holds the inner liner firmly to the duct or fitting.
Mastic seals liner to connection and covers the end of the liner
Use draw band to hold outer sleeve (vapor barrier)
Vapor barrier should be complete. All holes, rips, and seams must be sealed with mastic or approved tape
AIRTIGHT DUCT SYSTEM
Metal Ducts and Plenums, Duct Board Boxes
Openings greater than 1/4 inch should be sealed with mastic and mesh
Openings less than 1/4 inch should be sealed with mastic
Special attention to collar connections to duct-board and/or sheet metal; seal around the connection with mastic
Ts Ys & Ls
Use mesh tape to strengthen the joint where ducts of different shapes meet.
Seal all seams, even manufactured ones.
Seal Gores
Sealant applied, still leaks
FABRICATION & INSTALLATION GUIDELINES
The air handler box should be air-tight
AHUs & Plenums
Fill all openings for wiring, plumbing and refrigerant lines.
Seal all seams in the air handler and plenums.
Tape around access panels, so they can be opened for service.
Air Handler Leaks
Mechanical Systems & Equipment
AIRTIGHT HVAC SYSTEM
Air handlers on platforms May be located in a closet indoors Framers must be told not to put plywood top
on before walls are sheetrocked (or duct board) to underside of platform floor
All wall surfaces must be sheetrocked next to and in platform
Seal all joints
Boots
Seal all joints, including manufactured seams.
The transition between the duct and boot may require mesh tape.
AIRTIGHT DUCT SYSTEM
All Duct Types
Register boxes should be sealed to the drywall or floor with caulking or mastic
AIRTIGHT DUCT SYSTEM
All Duct Types
Register boxes should be sealed to the drywall or floor with caulking or mastic
SHEET METAL CONNECTIONS
Start the inner fitting into the outer fitting Apply a 2” wide band of mastic to the exposed part of
the inner fitting Fully seat the joint and mechanically fasten with
sheet metal screws or rivets Apply a 2.5” wide band of mastic to the outside of the
joint covering the screws or rivets and joint gap Allow at least 12 hours drying time before starting
system Temperature and humidity conditions can vary,
longer dry times may be required
Locating ducts within thermal boundary Within thermal boundary means within
insulated space and within the air barrier boundary.
Attics and crawlspaces can be but are usually not conditioned space
Critical that space is truly indoors and sealed from unconditioned areas
Multi-level dwellings more easily accommodate ducts in conditioned space
Ducts in Unconditioned Space
Usually ducts are located in attics and crawlspaces
Big temperature differences increase conduction losses and loads Long duct runs in attics lose 15%+ of cooling
capacity before end Convection losses by leakage
Benefits of locating ducts in conditioned space Ducts can be smaller May have shorter runs reduce pressure drop
and improve efficiency Can reduce HVAC system costs by reducing
loads Improve comfort No Testing in 09 IECC
EXISTING HOMES
In existing homes, not unusual to find disconnected duct components, takeoffs loose from ducts or ducts disconnected from register boots
Tools & MaterialsHead lamp, hat with light, or flashlightA work board to span joists in attics Gallon pail and 2-3 caulk tubes of masticCaulk Gun, mastic brush, fin and plenum brushRoll of mesh2-3 pairs of latex gloves 2-3 cloths, can of coil and fin cleaner to wipe joints clean before applying mastic and clean upUtility knife and telescoping mirrorPliers, screw driver and tin snips
For Sealing Existing Systems
Sealing Priorities
1. Disconnected components
2. Connections between the air handling unit and the plenums
3. All seams in the air handling units and plenums, takeoffs, boots, and other connections, especially site-built items.
EXISTING HOMES
Leaks connected to the outdoors are more important than leaks inside home’s thermal envelope
Holes near the air handler are more important than distant holes with relatively low pressures
Supply system leaks waste more energy than return system leaks
Furnaces
Remove tie holding duct to connection
Roll back insulation and outer cover
Seal inner core with mastic and band
Roll insulation down and vapor barrier/outer cover
Put band and seal with mastic
Wrap Ducts with insulation Insulation may be installed over wet mastic
but do not move the ducts too much or mastic seal could be damaged.
All duct support work should be done before applying mastic
Wait 2 -4 hours and water based mastic will be dry to the touch
Oversizing
What do you get when you combine cognitive bias with inaccurate information?
Oversizing
Old Rules of Thumb One Size Fits All
US Department of Energy Most systems are oversized, increasing
installation cost for every house
Oversizing
Sizing example
2000 SF House with standard metal windows w/ .75 U-Value and .88 SHGC and 20% duct leakage
Calculated Sensible cooling load = 58880 Btu
Equipment Sizing
Load calculations determine the proper capacity (size) of equipment
Goal is big enough to ensure comfort but no bigger
Calculations with ACCA Manual J protocol or other approved methods
Mandatory Requirements
Oversizing
Sizing example Same 2000 SF house with Low-E windows
and tight duct system @ 5% leakage Sensible cooling load = 43877 Btu Average of 1-2” decrease in duct diameter
sizes
Oversizing
Installation cost is higher Operating cost over life of equipment is
higher Can cause comfort problems Improvements in building envelope reduce
loads
Right Sizing
Costs less to install – saves builder money Costs less to operate - not starting and
stopping all the time Short cycling can cause bigger swings in
supply air, less comfort Better humidity control
DESIGN HVAC SYSTEM
Loads and CFM Calculation ACCA Manual J Load Calculation or
equivalent required Calculate heat loss and heat gain for each
room
Total room loads to determine system requirements.
Manual J –Load Calc
The local climate – ASHRAE 30 year average Size, shape, and orientation of the house Insulation levels Window area, location, and type Air infiltration rates Number of occupants Types and efficiencies of lights and major home
appliances (which give off heat)
ACCA - Air Conditioning Contractors of America www.acca.org
“It’s tough to make predictions, especially about the future.”
- Yogi Berra
U.S. Dept of Energy
30/30 Vision
2012 IECC 30% More Stringent 2006 IECC
More verification testing
A Quality HVAC System
Be properly sized to provide correct air flow, and meet room-by-room calculated heating and cooling loads.
Have sealed ductwork that will provide proper air flow.
Be installed with a return system designed to provide correct return air flow.
Have balanced air flows between supply and return systems to maintain neutral pressure in the home.
Be properly charged with refrigerant
Verifying Charge
Ductwork
Single most important energy measure for most homes- low hanging fruit
Locating inside conditioned space is optimal
Seal joints with mastic not duct tape
Equipment Size
Oversizing is common and expensive – upfront and during life
Sizing properly can reduce cost and help pay for increased cost of other efficiency features
Learn from the mistakes of others. You can't possibly live long enough to make them all yourself
--Sam Levinson
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