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
Section titled “Weather Station Selection”Automatic Selection
Section titled “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.
Choosing a Different Station
Section titled “Choosing a Different Station”The nearest weather stations are shown on a map, each connected to your project location by a line. To use a different station:
- Navigate to Basis of Design > Weather
- Click a station marker on the map to open its preview
- Review the station’s latitude, longitude, elevation, climate zone, and design temperatures
- Click Select in the preview to use that station
The selected station — along with its latitude, longitude, elevation, and climate zone — appears in the read-only summary at the top of the pane. Change the Project Address to load a different set of nearby stations.
Design Conditions
Section titled “Design Conditions”Cooling Design Temperatures
Section titled “Cooling Design Temperatures”The outdoor conditions used for cooling load calculations. HVAKR uses the 0.4% annual design condition by default, meaning the outdoor dry-bulb exceeds this value only 0.4% of the year (approximately 35 hours). Each cooling percentile provides both a design dry-bulb (Summer Design DB) and its mean coincident wet-bulb (Summer Coincident WB).
Heating Design Temperature
Section titled “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 Percentiles
Section titled “Design Percentiles”Summer and winter percentiles are set independently:
- Summer Design Percent —
0.4%,2%,5%, or10%(default0.4%). A lower percentile is more conservative. - Winter Design Percent —
99%or99.6%(default99.6%). A higher percentile is more conservative.
Changing a percentile updates the looked-up Summer Design DB, Summer Coincident WB, and Winter Design DB for the selected station.
Weather Data Display
Section titled “Weather Data Display”Monthly Peaks
Section titled “Monthly Peaks”The Monthly Peaks dialog shows a table of monthly peak temperatures and humidity conditions, useful for understanding seasonal variations.
Psychrometric Chart
Section titled “Psychrometric Chart”A psychrometric chart plots the summer and winter outdoor design points alongside your space-type set points. When the station has typical meteorological year (TMY) data, a heatmap underlay visualizes the relative time spent at each condition during a typical year.
Elevation
Section titled “Elevation”The site elevation from the weather station, which affects air density calculations.
Impact on Calculations
Section titled “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 Design Conditions
Section titled “Custom Design Conditions”For locations where the looked-up values don’t match local conditions, you can override the design temperatures directly. Edit the Summer Design DB, Summer Coincident WB, or Winter Design DB fields with your own values; each field shows the station’s looked-up value as a default you can reset to.