This is the first in a series of blogs that explore Autodesk’s Energy Analysis solutions.
Here we explore Daylighting. The goal is to provide a passive design that provides natural daylight to help achieve ideal lighting conditions so that demands are decreased significently for electrical lighting and greater environmental comfort is reached because more occupants are experiencing natural light.
To understand the quality of daylight within a space typically requires three types of simulations.
- Sunlight simulation (visual) at different times of the year.
- An illuminance study (direct sunshine) again at different times of the year.
- A Daylight Factor Study, overcast day with uniform light from all directions.
Revit has a direct link to the Autodesk A360 cloud rendering service which can provide all three simulations.
Firstly, you will require an Autodesk Account to gain access to the Cloud Rendering service, if you don’t already have one, you can register here. It’s free and provides many additional benefits.
Once registered, sign in.
To start the process, use the ‘Location’ command and specify an address where you are offered a range of nearby weather stations, the nearest weather station is automatically selected unless you select a different one from the list provided.
Turn on the Sun. Select ‘Sun Settings’ and define the time and date and the type of Solar Study, in this case, ‘Still’.
What does the space look like? - We need a visual to be able to get an impression of the daylighting.
Select the ‘Render in Cloud’ icon, specify an Output Type of ‘Still Image’ the other options can be adjusted to suit your preference, if requested, you can be emailed to inform you it’s complete.
Here we need to consider direct sunshine within the space. CIBSE offer recommended Lux level guidelines that quote an office typically requires 500 Lux. A range of 0-2000 lux should be sufficient in this example. (Above the results are shown using the Logarithmic option.)
Illuminance is a measure of how much light falls on a surface. It’s useful for determining whether there is enough light to perform different activities (like reading, office work, or draughting). Illuminance is measured in lux.
Typical values are approximately 50 to 1000 lux, depending on the activity. An illuminance rendering shows you whether your lighting design meets the requirements of the space, and it also helps you understand how much of this light you’ll be able to get from daylighting.
For example CIBSE recommended Lux level values of:
- Offices 500 Lux
- Bedrooms 50-100 Lux
- Café 450 lux
- Lecture theatres 300 Lux
- Supermarket 750 Lux
Select the ‘Render in Cloud’ icon, specify an Output Type of ‘illuminance’, select ‘Use date from View’ to specify the desired date & time as defined by the location.
Next specify the ‘Sky Model’ – simply the ‘type’ of sky, the ‘Perez-All weather Sky’ option is most commonly used as it provides accurate results from clear to overcast skies, or as is the case here, you can select a specific option – ‘CIE Clear Sky’(If you are unsure of which sky model to use, a good place to start is the CIE Overcast Sky model. This model will not have the unique characteristics of direct sun, and represents an overcast condition that could happen at any time of day and is a good way to put your design to the test. It is often standard practice to also render using the Perez model at an equinox and the solstices at noon, 9am and 3pm to visualize a range of standard conditions)
DNI – DHI values specify the suns intensity for the quoted location, follow this link for information on how to determine these values.
Finally, specify the units – Lux in this case, also the Min and Max values for the desired scale, I’m interested in the values for the worksurfaces and expect them to be approx. 300-500 lux so the Min will be 0 and the Max 2000. This scale should provide valid feedback.
- By default, a linear scale is used with 10 proportional subdivisions based on the range chosen.
- If you choose Logarithmic, the scale will be logarithmic so that you can more easily visually distinguish between values in the lower portion of the range while still capturing very high values.
DAYLIGHT FACTOR STUDY
This is the percentage of natural light falling on surfaces compared to that which would have fallen on a completely unobstructed horizontal surface under the same sky conditions. This figure is presented as a percentage.
CIBSE Lighting Guide 10 suggests:
- Under 2% = Not adequately lit.
- 2-5% = adequate but artificial lighting may be required part of the time.
- Over 5% = Well lit, but glare and solar gain may cause problems.
Therefore a range of 0-10% for the scale provides informative values.
Select the ‘Render in Cloud’ icon, specify an Output Type of ‘illuminance’, select ‘Use date from View’ to specify the desired date & time.
Next specify the ‘Sky Model’ – as ‘Daylight Factor Sky’ and lastly define the percentage range as 0 -10%.
Once all the simulations are complete, it’s possible to download and analyse the results.
Select the ‘Render Gallery’ icon for an overview of the previously generated simulations.
Select the image of the simulation and download.
Armed with the results you will have a quantitative understanding of the daylighting within the space.
Look out for the second instalment in this series where we explore daylighting analysis using Autodesk ‘Insight’ Analysis suite. If you would like to learn more about rendering in Revit, do not hesitate to get in contact with us through the link below for more information regarding this and other Autodesk software, or to request a quote.