Daylighting is the art & science of delivering visible solar light into a dwelling during daylight hours.  This is easy to do if one considers only the natural light gained and, therefore, the lights turned off during the day.  However, daylighting is a very delicate balance between light & heat gain/loss.  In order to gain natural light, we must provide fenestration.  The best windows on the market (without breaking the bank) may provide an R-value of 4.0.  The wall immediately adjancent that window can have an R-value of  40 with nearly normal construction methods.  So, for example, I design a house with large amounts of fenestration, place them without regard, and never turn on a light during the day – wonderful.  You were probably at work all day anyway.  However, the huge amount of glazing caused your A/C to run at full speed during the 100°F ambient temperature of the daytime.  This is not the intent of daylighting!  It is more eco-friendly to use no windows and LED lighting throughout the home than it is to convert the well insulated walls into glazing in the name of daylighting.  These are the types of the issues that frustrate me – people on soapboxes preaching about something they know nothing about.  Residential glazing should be used for two things.  First, provide us glimpes of the outside and bring nature inside.  Second, exchange heat as required – provide UV heat (passive solar heating) in the winter and convection cooling in the summer.  This requires shading of the window during the summer months when the sun is high and full penetration of the UV light in the winter when the sun is low.  However, these issues are aspects of passive solar heating & cooling – not daylighting.  Daylighting is a concept that must be discussed in the realm of commercial dwellings – the lights are on all day.  I will discuss daylighting concepts in my next posting – you need to know the difference between passive lighting & passive heating first.  In conclusion, understand that daylighting should be secondary to passive thermal controls in residential design.  We want to bring in large amounts of natural light but we also want to avoid large, negative effects placed on our HVAC systems.

One Response to “Daylighting – Get the Story Straight”

  1. Mike Barker says:

    Well said. There are two many myths about daylighting. Its complex and needs carful consideration. Climate plays a big part – in warmer climates you can get away with more shaded glazing than is practical in cooler climates.

    When you model a building the occupancy schedule palsy a part, and that is the difference between residential and commercial.

    Look forward to the rest of you articles

    Thanks, Mike Barker, South Africa

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