A descriptive overview of Radiation analysis, what the diagram means, and how to leverage cove.tool for design insights.

Written by Patrick Chopson
Updated over a week ago

What is the Radiation Analysis in analysis.tool?

To understand how cove.tool defines and calculates radiation, you'll first need to know these 4 terms:

• Radiation (kWh, W) - also called solar resource or just sunlight, radiation is the amount of energy emitted from the sun. Scientists measure the amount of sunlight falling on specific locations at different times of the year. Depending on the measurement methodology, a radiation analysis can have many insights.

• Solar irradiance (W/m2/yr) - also known as solar exposure or solar insolation, is the annual energy received from the sun over an area. This methodology is used in environmental surveys when creating weather files. Solar irradiance is what will be calculated to generate a skydome that will in turn be used to recreate the environmental conditions in your radiation simulation.

• Global Horizontal Irradiance, GHI (kWh/m2/day) - is the total irradiance from the sun on a horizontal surface on Earth. It is the sum of direct irradiance (after accounting for the solar angle due to the geographic location) and the diffused horizontal irradiance (the energy lost due to a surface's non-tangential orientation from its energy source).

• Maximum Solar Potential - is the Peak day maximum GHI for a given location based on the daily recordings in a weather file. This value represents the maximum radiation that can be calculated on-site, regardless of whether this is achievable on building geometry. However, buildings with zero obstructions and perfectly horizontal surfaces (oriented towards the solar angle) may also display this value.

This analysis type is used to evaluate the high-or-low radiation potential of each facade and envelope element. Shading devices & interior walls are omitted from the radiation visualization to better see the results. More information on radiation basics here.

Calculation Methodology

cove.tool uses a Ray-tracing method to project sky conditions onto your model's envelope geometry. Environmental conditions are based on the Tregenza sky constructed from your location's weather file with 576 subdivisions. In addition to these, additional strategies are implemented in order to speed up the simulation:

1. We keep the reflectivity percentages (materiality) fixed with the following assumptions: Interior Floors 40%, Interior Walls 70%, Ceiling/Roof 70%, Exterior Façade (shading devices, mullions, light shelves, etc.) 50%, exterior Walls 35% (including context buildings), and Outside Ground 40%.

2. Rather than sub-diving geometry into a regular grid, we use a triangulated mesh grid system to generate the facade's final gradient visualization. Unlike sDA and ASE's equally distanced quad grid, the triangulated mesh grid approach is the most efficient breakdown of connection points (a.k.a. vertices). The fewer analysis points we have to calculate solar irradiance, the faster we can display your results.

Also note, that radiation is critically impacted by location, orientation, and context. To have accurate results you must have an accurate 3D environment in cove.tool. If any changes to the site or context are needed, please follow the tutorial in the Navigating 3D Mode article]. Automically cove.tool will generate context use and OpenStreetMaps API.

Before generating the radiation map on the model envelope, a legend for the location is calculated that will represent your site's spectrum of Solar Radiation Potential. The maximum solar potential is displayed at the top right as the highest amount of radiation that may be achieved, ie. maximum solar potential (Peak Day Maximum GHI), also seen as 100% (gold) of the colored heatmap. While low-to-no radiation will display at 0.0% (royal purple) on the map and legend.

With the regular grid, we would calculate the average measured value at the center of each grid point, but with the triangular mesh, radiation is calculated at each vertex. Then color is provided at each vertex according to the legend, and stitched to the next nearest vertexes to generate the gradient. From here, streaks may appear depending on how your surfaces were being segmented. Especially if the connecting vertex values span large areas and both endpoints showcase extreme polarities that don't neatly cohere well together. Therefore larger facades may show a more extreme transition from low-to-high radiation locations. Segmenting your facade pre-upload can help prevent this as small spans between vertex will have more detailed graduation, but will take longer to calculate.

The gradient shows the diffusion of radiation along with the envelope. The result is a gradient heat map of the building envelope with areas of lower exposure colored purple and areas of higher exposure colored gold.

In older radiation studies, building envelopes have been wrapped in a Radiation or GHI heatmap (below left & center). The studies colored each surface by their kWH/m2 performance, it is difficult to understand the intensity of each study. converting the analysis to a Radiation Percentage (right) presents more clearly the impact of the sun on your project.

Users can also generate their site's radiation skydome using the climate analysis report in cove.tool. The two radiation studies are helpful in the early stages as the massing is still being explored to anticipate the radiation potential of each facade. Be sure to use the help diagrams to interpret these diagrams.

Key takeaways of a Radiation Analysis

This overview covers why radiation studies matter for designers, and how accurate design insights can be extracted.

• Radiation analysis indicates which facade glazing products should be high-performance and where low-performance products would be more acceptable.

• Radiation analysis can help with early-stage indications of outdoor comfort levels for summer and winter seasons.

• Radiation analysis provides an indication of where to place Photovoltaic (PV) or Solar Hot Water panels for optimal renewable energy production. Fun fact: the percentage for radiation is an indication of the same exposure for solar panels lying flat. If the heatmap is 100%, and the solar panel is flat, it is receiving 100 percent.

• Radiation maps can let you know where you have heat and do not have heat

Knowing the natural exposure to solar radiation is critical for optimizing solar power, specifying high-performance glazing products, and provides insight for optimal positioning of outdoor seating spaces or naturally radiant heating or cooling for winter and summer months. cove.tool offers predictive tools, and radiation analysis is exactly that.

Radiation can mean different things so it's important to be specific. Some insights might seem logical at first, but can be misleading if they are discussed as rules of thumb rather than running the simulation. Your climate will be the most important factor when determining whether high or low radiation would be beneficial for your building design.

How solar irradiance reaches the Earth's surface.

Understanding Radiation Skydome diagram from cove.tool (below).

Solar exposure is different throughout the world and differs greatly between the northern and southern hemispheres. In the AEC industry, solar irradiance has various applications like predicting energy generation of photovoltaic systems and the impact on heating and cooling loads of buildings at specific locations on Earth. There are also various types of irradiance that can be calculated. You can find out more of the science here, or more detailed information of regionally specific irradiance from NREL here.

Heatmap of annual GHI Solar Irradiance for the North American continent, by NREL.

# FAQs

1. Will it tell me to change their insulation depth?

Long answer: This is a common misinterpreted assumption. The heat entering the building through glass is much more critical to building energy when it comes to radiation. When a surface is hit with sunlight only a fraction of the heat will absorb, where the majority of the sunlight entering through glass will heat up the building if not blocked. You need solar heat for winter heating and too much insulation can be bad.

2. Is heat gain bad or good?

3. What do I need to generate a Radiation Study?

A model imported through one of cove.tool geometry plugins, and building site (street address or longitude/latitude coordinates). Once you reach the Daylight Page (sun icon), the several 3D visualizations will initiate. Each analysis type will run in parallel but take different calculation times to complete. The radiation analysis will take the longest to complete, and therefore the button is grayed-out until complete.

4. Why is my Radiation Gradient not consistent on a flat surface?

Because the calculation for Solar Irridance is incredibly resource and time-intensive, our calculation method uses a triangulated mesh grid system instead of the traditional quad grid system to generate the facade's final gradient visualization. Unlike sDA and ASE's equally distanced quad grid, the triangulated mesh grid approach is the most efficient breakdown of connection points (a.k.a. vertices). The fewer analysis points we have to calculate solar irradiance, the faster we can display your results. The traditional workflow with an industry-standard tool for Radiation averages runtime at 30 minutes, this approach can have the results in a fraction of that time.