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Load Calculations Overview

HVAKR calculates heating and cooling loads using industry-standard methods based on ANSI/ASHRAE/ACCA Standard 183. These calculations determine the required capacity of your HVAC systems.

Calculation Methods

Section titled “Calculation Methods”

Cooling Load Calculation

Section titled “Cooling Load Calculation”

HVAKR uses the Radiant Time Series (RTS) method for cooling loads:

  • Accounts for thermal mass effects
  • Calculates hourly loads throughout the design day
  • Identifies peak cooling hour
  • Separates sensible and latent components

Heating Load Calculation

Section titled “Heating Load Calculation”

Heating loads use a steady-state calculation:

  • Based on design heating temperature
  • No solar credit (conservative)
  • Includes transmission, infiltration, and ventilation

Ventilation Calculation

Section titled “Ventilation Calculation”

Outdoor air requirements per ASHRAE 62.1:

  • People-based ventilation
  • Area-based ventilation
  • Zone air distribution effectiveness
  • System ventilation efficiency

Load Components

Section titled “Load Components”

Transmission Loads

Section titled “Transmission Loads”

Heat transfer through the building envelope:

  • Walls, roof, and floor
  • Windows and doors
  • Skylights

Solar Loads

Section titled “Solar Loads”

Heat gain from solar radiation:

  • Through windows (direct and diffuse)
  • Absorbed by walls and roof
  • Time-varying throughout the day

Internal Loads

Section titled “Internal Loads”

Heat generated inside the building:

  • People (sensible and latent)
  • Equipment and appliances
  • Lighting

Ventilation Loads

Section titled “Ventilation Loads”

Conditioning of outdoor air:

  • Sensible load (temperature difference)
  • Latent load (humidity difference)
  • Required for indoor air quality

Infiltration Loads

Section titled “Infiltration Loads”

Uncontrolled air leakage:

  • Depends on envelope tightness
  • Wind and stack effects
  • May be significant in older buildings

Design Conditions

Section titled “Design Conditions”

Outdoor Conditions

Section titled “Outdoor Conditions”

Based on ASHRAE weather data:

  • Cooling: 0.4% design temperature
  • Heating: 99.6% design temperature
  • Humidity conditions

Indoor Conditions

Section titled “Indoor Conditions”

Typical design setpoints:

  • Cooling: 75°F, 50% RH
  • Heating: 70°F
  • Adjustable per space or zone

Calculation Hierarchy

Section titled “Calculation Hierarchy”

Loads are calculated at multiple levels:

  1. Space Level - Individual room loads
  2. Zone Level - Sum of spaces in the zone
  3. System Level - Sum of zones (with diversity)
  4. Building Level - Total building load

When Loads Update

Section titled “When Loads Update”

Calculations update automatically when you change:

  • Weather or location
  • Building envelope properties
  • Space types or assignments
  • System configurations
  • Space geometry

Viewing Results

Section titled “Viewing Results”

View load calculation results in the Reports section:

  • Loads Summary report
  • Space-by-space breakdown
  • Load component charts
  • Peak load identification