Climate analysis - solar radiation - design impacts

This analysis is done by reviewing solar radiation conditions at the site and determining how the intensity of those values will influence features of the facade and roof and shading design. It may help answer such questions as:

• Do we need to control solar gains?
• Do operable windows for natural ventilation or free cooling make sense?
• When will HVAC systems be necessary for providing heating and cooling?

Because the weather data is a large table of numbers, it would almost certainly be overwhelming to present numerical data to non-technical members of the design team. Include some visual representations of the data to help illustrate the key points.

Building Science and Design Concepts

• Direct sunlight entering a building through windows can result in visual comfort (glare) and thermal comfort (too hot) issues for occupants. This direct sunlight is often referred to as direct solar gain, or shortwave radiation.
• Solar heat gains can be one of the largest contributors to the thermal cooling loads of spaces along the building's perimeter. These gains must be removed by air conditioning, and if not controlled, will result in increased energy use by the HVAC system.
• Occupants in areas receiving direct solar gain will experience higher temperature sensations than those who are not in direct sunlight. In larger building zones where some occupants are in the sunlight and some are not, it is very difficult to control the HVAC systems to provide adequate comfort to all the occupants. If the space temperature is lowered to satisfy the occupants in the sunlight, then the occupants not receiving direct solar gain will likely be too cold.
• Some strategies to reduce solar gains include reducing window areas on walls that receive direct solar gains, shading the windows, and selecting windows that reduce the amount of solar gain transmitted to the space, i.e., windows with a low Solar Heat Gain Coefficient (SHGC).
• While solar gains in the summer (cooling season) are often undesirable, they can be beneficial during the winter (heating season) as a source of passive heating. Buildings with passive heating designs aim to allow solar gains into the space to provide free heating. These buildings tend to have windows with high SHGC, interior surfaces that can absorb heat, and well-insulated windows to keep the heat inside.
• In the northern hemisphere, solar gains can be effectively controlled on the South facade by shading overhangs. The design of overhangs should consider
• Solar gains are difficult to control with overhangs on the East and West facades due to the low sun angle. Vertical fins or operable shades/blinds may be more effective for these orientations.
• Other strategies to consider include automatic, mechanically-operated exterior blinds, or interior blinds and shades. For interior shades, manually-operated shades may or may not be operated effectively by the occupants. There is a trade-off between controlling solar gains, and allowing natural light into a space or allowing the occupants to enjoy views out the windows. Automatically controlled blinds or shades can achieve this balance, though their control should be coordinated with the occupants desires.
• This section's tutorials provide a guide on how to understand the climate's solar availability and to give the designer some concepts to consider. Additional tutorials are provided in the conceptual and schematic design sections of this site. These early design-stage tutorials will provide further guidance on how to design and refine solar control strategies once a project's design begins to take form.

Analysis Steps

Select the appropriate data

The important weather file variables for this analysis include:

• Global horizontal radiation - sum of direct and diffuse radiation.
• Direct normal radiation - beams from the sun that fall directly on a surface.
• Diffuse horizontal radiation - radiation that reaches the earth's surface after direct beams have been relflected by particles in the atmosphere.

Many BEM and climate software tools also have the ability to calculate sun angles based on project location, and time of day/year. While this data imay not be included in the weather file, it is calculated (by the software programs) as a function of the project location's latitude and longitude, so the information is available and it is useful at this stage to understand how this impacts solar gains on a building. It will certainly become a key part of analyzing solar gains on early models beginning in Conceptual Design, and continuing into later design phases.

Review the data

• At this stage, the goal is to understand how the sun moves around the project site, and its intensity at different times of the year. This data can give you ideas for when it's most important to control solar gains to reduce cooling energy, and when it may be most effective to use the sun for passive heating. Those ideas can then be tested later (as early as the Conceptual Design phase) on a building model to come up with effective designs to meet these goals.
• When you determine the times of year with highest solar radiation, cross-reference this against the outdoor temperature data (described above). Identify sun angles during hot and cold periods of the year as this can help design effective overhang shades that block sun when the building needs cooling, but lets sun in when the building needs heating.

Present the analysis

Presentation of the analysis should answer the question "should we look for ways to control solar gains on our project?" The answer is almost always YES. When communicating to the team, it may be useful to underscore how solar radiation has a negative impact on energy use and occupant comfort if left uncontrolled (as described above in the building science concepts).

Try to present the information in terms that can be understood everyone on the team, including less technical members. It may be helpful to present the data in relative terms rather than trying to explain the values of direct normal radiation in units of W-h/m2. For example, consider comparing the project location's solar radiation to the city where you live. ---------make a graphic for this--------

Sun angle viewer (IES) - July

Sun angle viewer (IES) - July

Sun Shading Chart (Climate Consultant) - Summer

If you tend to do most of your design work in one geographic region, this may be a study you do once or twice, and then once you understand the concepts, you can apply what you've learned to future projects. If you work a firm that designs buildings all over the country or the world, then this type of study will be useful to help get the design team up to speed and understand how big (or small) an impact solar radiation will have compared to past projects in other regions.