Residential HVAC Load Sizing Training October 14, 2015

David Kaiser

Green Code Plan Reviewer

DCRA - Green Building Division

Regulations of green codes including: • Green Building Act • Green Construction Code • Energy Conservation Code

Operates within the structure of DCRA’s permitting and inspections groups, with work including reviews of construction documents, conducting building inspections, and collaborating with the community to further the efforts to build a more sustainable DC.

Training Objectives

• Identify why HVAC load sizing is important.

• Understand the basic science of load sizing

• Identify the EVS measure that is satisfied with load sizing.

• Recognize the exemptions to load sizing.

• Identify documentation and details necessary to comply.

• Determine how to size HVAC systems to the Manual J outputs.

Navigating EVS

IECC R403.6: Equipment sizing (Mandatory)

• Requires heating and cooling equipment sizing in accordance with

– ACCA Manual S-10, Residential Equipment Selection.

– ACCA Manual J-11, Residential Load Calculations, 8th edition.

Heating/Cooling System Sizing Why it matters

• Provide comfort & humidity control

• Reduce the possibility of indoor mold and mildew.

• Translate to smaller equipment.

• Optimize installed cost. • Reduce operating cost.

• Improve reliability.

• Reduce airflow noise both internal and external.

• Minimize service loads imposed on utility grids.

• Keep utility cost more constant

Understand the Basic Science of Load Sizing

• What Affects your Load:

– Primary Summer Loads • Windows • Internal Loads: Lighting,

Oven, Dryer, Dishwasher • Other Exterior Walls

I.e a Pizza Making party at 4PM on a hot day of the year.

Understand the Basic Science of Load Sizing

• What Affects your Load:

•Primary Winter Loads

– Heat Loss Through Exterior Walls Via Conduction

– Outside air into your home (Ventilation, Infiltration)

– I.e. Middle of the night with no lights, equipment going on very cold day.

Understand the Basic Science of Load Sizing

Time

Heat (Btus)

Time

Temperature

Over-Sized System

Max Temp

Min Temp

# HVAC Cycles = 9

Understand the Basic Science of Load Sizing

Time

Btus

Time

Temperature Max Temp

Min Temp

Manual J Right-Sized System

# HVAC Cycles = 6

DCRA Exemptions to Load Sizing

• A replacement in kind of an existing system

• When extending ductwork from an existing system into an addition

• When HVAC system is 1.5 tons or less

• HVAC system has multiple stages of cooling or is variable refrigerant flow

Understand the Basic Science of Load Sizing

Time

Btus

Time

Temperature Max Temp

Min Temp

Dual Speed Compressor System

# HVAC Cycles = 4

Understand the Basic Science of Load Sizing

Time

Btus

Time

Temperature Max Temp

Min Temp

Variable Refrigerant Volume System

# HVAC Cycles = 1

So you want to use Manual J...

Now What?

5 Steps to Manual J Compliance

• Step 1: Use Approved Software • Step 2: Define Building Thermal Envelope Areas • Step 3: Select Values of Components • Step 4: Fill In DC & Project Specific Inputs • Step 5: Select HVAC System

Step 1: Use Approved Software

Manual J Step 2: Define Building Thermal Envelope

The "Building Thermal Envelope" represents the boundary that separates conditioned space from unconditioned space

or the outdoors.

Manual J Step 2: Define Building Thermal Envelope

Manual J Step 2: Define Building Thermal Envelope

Manual J Step 2: Define Building Thermal Envelope

Manual J Step 2: Define Building Thermal Envelope

How Many Systems do we need?

Where is the Thermal Boundary for bottom unit? Where is the Thermal Boundary for top unit?

Manual J Step 2: Define Building Thermal Envelope

Where is the Thermal Boundary for bottom unit? Where is the Thermal Boundary for top unit?

A building thermal envelope includes all components of a building that enclose conditioned space:

•Roof •Walls •Floor •Doors •Windows

Step 2: Elements of the Thermal Envelope

Manual J Step 3: Select Values of Components

• For new construction assemblies:

Manual J Step 3: Select Values of Components

• For existing construction components: - Use the current assembly value

• Used during level 3 alterations and additions when a portion of the building is being left alone but a new HVAC system is being added.

Step 3: Manual J Inputs, Select Values of Components

• conditioned floor area • window area • ceiling area • building orientation • wall construction • insulation values • window construction or U-value • window solar heat gain coefficients (SHGC)

Step 4: Fill In DC & Project Specific Inputs

• Summer exterior Temperature = 91 • Summer interior Temperature = 75 • Winter exterior Temperature = 17 • Winter interior Temperature = 70

• number of occupants living in the home = # of bedrooms + 1 • estimated or measured building air-leakage values (infiltration) - If software gives option choose “average” or equivalent

between 5 and 7 ACH50, (between 0.25 and 0.35 natural ACH) • mechanical ventilation = amount required by IMC • summary of lighting and appliances • Sensible Heat Ratio (SHR) = between 0.70 and 0.75

Example of Manual J Input Report

Example of Manual J Output Report

Step 5: Select HVAC System

Example of Manual J Output Report

Step 5: Select HVAC System

Heating Load 65,774 x 1.4 = 92,083 Max output Btu

100,000 BTU rated furnace puts out 80,000 BTUs at 80AFUE

Example of Manual J Output Report

4000

26,923

Step 5: Select HVAC System

Heating Load 30,923 x 1.15 = 35,561 Max output Btus

36,000 BTU rated AC Total Cooling

30,000 BTU rated Sensible Load

DCRA Necessary Details - Outputs

• Component Summary (Areas, Uvalues, SHGCs)

• Project Summary

• Mechanical Schedule

– Model numbers of compressor AHU

– BTUs of Heating and Cooling

– Compressor Stages if applicable

– Efficiency

Step 5: Select HVAC System

Questions?

Green.Building@dc.gov