Using the local climate conditions, analysis.tool automates climate studies and multiple passive design recommendations based on the project location.
What is Climate?
To understand how the climate is analyzed for a building's energy performance, we must first clarify what a climate is.
Climate is the statistics of weather over an arbitrarily defined time span. It is the set of exterior environmental conditions that will impose a load on the building enclosure, including temperature, humidity, rainfall, wind, and solar radiation.
A weather file is a collection of data variables such as dry bulb and wet bulb temperature, relative humidity, wind speed and direction, solar radiation, and precipitation at each hour of a typical year.
To visualize the weather data, several representative diagrams are typically generated to understand different parameters and draw conclusions on climate responsive strategies. Weather files are automatically associated with a project based on the building location. More on weather files in cove.tool here.
How can Passive Strategies help?
Designing with passive strategies is about understanding the constraints and creating design responses that do not require active mechanical systems. Examples include using ambient energy sources to cool, heat, shade, or ventilate a building space. The challenge with designing for passive strategies is that they must be incorporated in the early stages of the process if they are to be effective. Architects who understand the passive impacts of climate will be better able to deliver cost-effective, energy-efficient, buildings.
Climate Diagrams and Passive Strategies
Relative Temperature & Humidity
These two diagrams provide a quick, preliminary snapshot of the prevailing climate conditions. They make up the primary comfort conditions and form the basis of several other climate diagrams.
Both relative humidity and dry bulb temperature are used to predict the thermal comfort of occupants during critical time intervals. In certain climate zones, they may determine most of a project’s Energy Use Intensity (EUI).
ASHRAE Standard 55-2017 recommends an indoor comfort temperature range between 67 to 82F, depending on the season. When the temperature goes beyond 90F, fans and other ventilation strategies are needed to cool. While at temperatures below 50F, increased insulation and solar access are recommended.
50 to 60% is the ideal relative humidity inside a building. Conditions of high humidity could be improved by using dehumidification and water-absorbing materials. Dry conditions or those with less than 29% RH would benefit from using water features, to cool and circulate air with water.
Radiation by Sky Segment
Also known as the radiation dome, this diagram chronicles the sun angle and solar intensity at which sunlight strikes an area. It is used in the design process to determine how to orient the building, and if the flexibility of orientation is not applicable, where to locate the maximum glazing percentage in the project.
By identifying where the maximum direct sunlight (kBTU/sq. ft.) is incident, users can reference the diagram on the right to pick a strategy. Windows and openings are best placed in areas with low radiation (in a cooling load dominated climate i.e. Hot and Tropical climates) and orientations with high radiation protected by overhangs and cantilevers. For solar heat gain, skylights and areas with low roof insulation should be placed in the high radiation zone (in a heating load dominated climate i.e. Cold climates). Openings in the medium radiation zone will allow some heat gain, which can be mediated with fins, overhangs, light shelves, shadow boxes, etc.
The Radiation Benefit diagram has a similar representation to the Radiation by Sky Segment above, but a different focus on the conclusions that should be drawn. This diagram differentiates “good radiation” from “bad radiation” based on the season. The orange/red zones show the helpful wintertime sun and darker blue regions show the harmful summertime sun. In another word, you may want to block the blue radiation in summer since it leads to overheating of spaces while take advantage of red radiation which provides beneficial solar heat gain in colder times of the year. This climate diagram is helpful when it comes to evaluating building massing and shading strategies.
A standard for thermal comfort in naturally ventilated buildings included in ASHRAE Standard 55. In free-running buildings (no mechanical system), the internal air temperature can be calculated successfully by taking into account several factors such as the interaction of the inhabitants with their surroundings including when they change their clothes, opening/closing windows, the use of low-energy fans, drinking water, and drawing shades. The adaptive comfort chart showcases the expected daily comfort profile for the project location. Using this diagram, users can determine the likely heating, cooling and de/humidification schedule throughout a typical year.
Using the graph, one can determine the number of hours per year a specific physical and thermodynamic condition occurs. Each opaque block (blue to yellow to red) represents the number of hours where a specific condition occurs. Overlaid polygons are used to identify strategies that add to the annual percentage of hours an occupant would be comfortable. A higher percentage is better, i.e. more hours where no mechanical support is necessary. Users can refer to the polygon glossary below to understand which strategy would be most useful to improve comfort.
Using these monthly graphs one can identify the prevailing winds - direction and speed. The length of each arc segment represents the frequency while the colors represent the speed (mph). Based on these trends, users can identify the best building facades to locate passive ventilation strategies such as operable windows. In warm and humid climates, maximizing ventilation by utilizing the prevailing winds will be an effective way to induce comfort. Cooler climate would instead benefit from blocking out cool winds that may add to the wind-chill factor inside a building.
In each case, help diagrams to the right explain the graphs and indicate which strategies would have the greatest impact, under which conditions.
Some sites that users may find useful for large climate data sets include: