Weather

Weather conditions determine the outdoor design temperatures used for heating and cooling load calculations. HVAKR uses ASHRAE weather data to provide accurate design conditions.

Weather Station Selection

Automatic Selection

When you enter a project address, HVAKR automatically selects the nearest ASHRAE weather station. This is usually the best choice for most projects.

Manual Selection

You can manually select a different weather station if:

• The project is between two weather stations
• You want to use a specific design condition
• The automatic selection doesn’t match local conditions

To change the weather station:

1. Navigate to Basis of Design > Weather
2. Click the weather station dropdown
3. Search for a station by city or WMO number

Design Conditions

Cooling Design Temperature

The outdoor dry-bulb temperature used for cooling load calculations. HVAKR uses the 0.4% annual design condition by default, meaning outdoor temperatures exceed this value only 0.4% of the year (approximately 35 hours).

Heating Design Temperature

The outdoor dry-bulb temperature used for heating load calculations. HVAKR uses the 99.6% annual design condition by default, meaning outdoor temperatures are below this value only 0.4% of the year.

Design Day Selection

You can choose different statistical levels:

• 0.4% / 99.6% - Most conservative, suitable for critical applications
• 1.0% / 99% - Moderate, common for commercial buildings
• 2.0% / 98% - Less conservative, suitable for residential

Weather Data Display

The weather pane shows:

Monthly Data

A table of monthly peak temperatures and humidity conditions, useful for understanding seasonal variations.

Psychrometric Conditions

Outdoor air conditions at the design point, including:

• Dry-bulb temperature
• Wet-bulb temperature
• Humidity ratio
• Enthalpy

Elevation

The site elevation from the weather station, which affects air density calculations.

Impact on Calculations

Weather conditions affect:

• Transmission loads - Heat transfer through walls, roof, and windows
• Infiltration loads - Heat loss/gain from air leakage
• Ventilation loads - Conditioning of outdoor air
• Solar loads - Based on latitude and typical cloud cover

Custom Weather Data

For locations without nearby ASHRAE weather stations, you can enter custom design conditions:

1. Click Use Custom Weather
2. Enter the cooling and heating design temperatures
3. Specify humidity conditions

Caution

Custom weather data should be based on local meteorological records or engineering judgment. Inaccurate weather data will result in undersized or oversized equipment.