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 info@thedillongroupinc.com