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Existing Homes vs
New Homes: Properly Sizing HVAC Equipment
Brett Dillon CEO
Midwest Regional Energy Conference
About Me• Author of:
• Guide to HVAC Design, Construction & Commissioning
• Developer of:
• ACCA RSI Verifier Manual & Certification Program
• NATE HVAC Verifier Training Program
Overview of HVAC Design Process
Manual J Inputs
Existing vs New
Tips
Code Requirements
Manual J Manual S Manual D
Blueprints & Specifications
Design Temperatures
Orientation
Internal Loads
Ventilation
Infiltration
Duct System
Manual JOEM Performance
Manual JMaterial
Devices
Length
2015 Code Requirements• Outdoor Thermostat for heat
pumps
• R403.1.2
• R-8 ducts in attics
• R403.3.1
• Ducts sealed and tested
• R403.3.2, R403.3.3
• HVAC sizing based upon Manuals S & J
• R403.7
• Duct Design according to Manual D
• M1601.1
Replacement / Repairs of Systems
• Meet requirements for new installations
• M1202.1
System Concept
Load Calculation
Equipment Selection
Air Distribution
Duct Size Calculation
Adjust, Test & Balance
Manual RS
Manual J
Manual T
Manual S
Manual D
Manual J
Manual J
• Room-by-Room
• Process, not software
Manual J• Indoor Design
Temperatures
• Outdoor Design Temperatures
• Windows
• Walls
• Ceilings
• Floors
• Infiltration
• Appliances
• Occupants
• Ducts
• Ventilation
Infiltration
• 2009 IRC
• Maximum 7 ACH50
• 2015 IRC
• Maximum 3 ACH50
Internal Loads• Appliances
• 1200 Btu/hr
• 2400 Btu/hr
• 3600 Btu/hr
• Occupants
• BR + 1
• 230 Btu/hr x occupants
Duct Loads
• Location
• Leakage
• Code maximum
Ductwork
• R-8
• R-6
• Sealing
• Outside air inlets
2009 IRC
• N1103.2.2 Mandatory duct testing
• Post-Construction, 8% leakage to outside or 12% total leakage
• Rough-in, 6% total leakage, 4% if air handler not installed
2015 IRC• N1103.3.2 Mandatory duct sealing
• N1103.3.3 Mandatory duct testing
• Prescriptive leakage rates
• Rough-in, < 4% total leakage, < 3% if air handler not installed
• Post-Construction, < 4% total leakage
What’s the Diff?
• Windows & Skylight Performance
• Wall Insulation
Manual S
OEM Performance Data!!!
Manual D
Manual D• Sizing Ducts
• Friction Rate
• (pressure drop x 100) / total effective length
• Slide rule
• Static pressure
Manual D• Peak loss = 1967 Btu/hr
• CFM = 1,967 / (1.1 x ∆T)
• ∆T = ℉ between return & supply
• Heat pumps, 25℉
• Furnaces, 55℉
• CFM = 1967 / (1.1 x 25) = 1967 / 27.5 = 72
• CFM = 1967 / (1.1 x 55) =
Manual D• Peak gain = 1189 Btu/hr
• Sensible gain = 932 Btu/hr
• Latent gain = 257 Btu/hr
• SHR = 932 / 1189 = 0.78
• CFM = 932 / (1.1 x ∆T)
• ∆T = ℉ between return & supply
• SHR < 0.80, 21℉
• CFM = 932 / (1.1 x 21) = 932 / 23.1 =
< 0.80 21℉
0.80 - 0.85 19℉
> 0.85 17℉
Manual D• Required under IRC M1601.1
• Implies room-by-room load calculation must be performed
• CFM
• SHR
• ΔT supply-return
• Sensible load
• Friction rate
• Pressure drop x 100 / total effective length
Supply Duct Sizing
• What temperature does the air need to be to meet the load?
• How many CFM of air must be delivered to meet the load?
• Sensible Load / (1.1 x ΔT)
Return Airflow
• 350 fpm
• Return register face velocity < 400 fpm
• 90º bend between register & airhandler
Sizing Return Ducts
• Sized according to Manual D
–All areas that are conditioned should have an adequate return path
•And undercutting doors 1” isn’t enough!
Other Sources
• http://www.acca.org/standards/acca-speed-sheets/
• http://www.acca.org/qa/resources/
• RESNET/NATE HVAC Verifier Training & Certification
Questions?
Brett Dillon CEO
www.thedillongroupinc.com [email protected]