Passive Solar – Simple Engineering? Hardly!

Passive Solar Concept

Passive solar design for residential dwellings is appears rather straightforward.  First, design an overhang that controls seasonal UV (Ultra-violet – the portion of visible light that contains heat) light penetration through a building aperture – usually fenestration (a window or a door).  The idea is to construct the overhang such that UV light penetrates deep into the dwelling in winter but is blocked out during the summer.  Second, install some form of mass (concrete, fluid, etc.) in the floor and the walls that can store the heat generated during the day.  Then, sit back and let convection and conduction perform the miracle of thermal dynamics.  All this sounds so simple, so why not do it on every house?  The answer is that it isn’t simple – we are dealing with a moving heat source (the sun), variations in outdoor temperature (climate), weather patterns (we need sunny days to make this work) and real estate assets (which direction are my views).  For example, here in sunny Colorado where we have 300 days of sunshine, a temperate climate, and a high altitude that allows intense UV rays to reach our altitude – but our views in Denver and the front range are typically west.  Well, our solar source in the summer is at its lowest point in the afternoon and producing the highest heat levels of the day.  The overhang required to shade any west facing fenestration would be nearly 20′ – you would essentially need a west facing wrap around porch with a concrete surface.  So, once again, we are faced with an architectural dilemma.  We need to capture the views that the property offers in order to enhance the value of the home.  Yet, we need to engineer systems for the dwelling that mesh with the architecture and reduce the use of fossil fuel burning devices necessary for controlling the indoor climate.  In conclusion, just like daylighting, it may prove more effective to reduce fenestration and mass absorbing materials and install local power generating elements such as solar and wind.      

This is the notion of Ecotecture – blend all the architectural elements, engineering systems, and the natural environment into one entity.  Too many people buy into one notion of reducing our carbon footprint without fully understanding the ramifications.  We, as stewards of the earth, must first educate ourselves properly and then enact and build dwellings that are organic and smart.  They must be analyzed for local conditions, designed to produce the smallest carbon footprint and then made beautiful to make others take note of Ecotecture.
Daylighting – Final Answer

Commercial Daylighting

Having studied the engineering of daylighting for four years – it’s applications, model predictions, the techniques used, successful designs and analysis – I consider myself rather well versed in this form of engineering.  In fact, I wrote thousands of lines of codes that calculated the interaction of daylight in room surfaces using form factors and other advanced mathematics at the time.  That is why it pains me to write this article.  With the advancement of PV’s (DC generating solar panels) and wind turbines (i.e. on-site electrical producing devices) and the advent of LED lamps, daylighting concerns may become a thing of the past.  The engineering devices used in daylighting (light shelves, monitors, specially engineered fenestration) are expensive.  And, despite some of the greatest efforts, it is still difficult to get light to the interior of a building without adding heat.  This is a rather ironic result considering that commercial buildings are rarely heated – they are cooled the majority of their existence due to latent and sensible heat loads.  Thus, the dilema.  Spend thousands of dollars on daylighting features such as glazing, light shelves, “skytubes”, etc. (when in the right hands, I might add, enhance the look of a commercial building) or limit gazing (i.e. heat gain) and use those dollars on PV & wind turbines and LED lamps.  Currently, with the incentives from the government and utilities, the winner is hands down the latter.  There are no incentives for daylighting – the technique is too difficult for most to do correctly and it is difficult to quantify the costs vs. the savings.  In conclusion (as my heart bleeds to type this) it is currently far more economical and straightforward to integrate electrical generation elements (wind & solar) and lighting controls into the architecture of a commercial building than daylighting elements.  However, daylightng elements should be used and considered because the impact on the architecture can be stunning when integrated correctly – and allow commercial buildings to turn off the lights.  A proper focus and engineering analysis can produce stunning ecotecture that is both beautiful and sustainable.

Daylighting – Get the Story Straight

Daylighting

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.

PV Structures are Green & Beautiful

Example PV Canopy

You can read about my beliefs on how PV’s (Solar Panels) should be integrated into architecture at www.ecotecturestudios.com/sustainable.html.  I believe that they should be used as elements of art such as awnings, patio covers and pergolas.  There is no need to place them on your roof as an afterthought and eye-sore.  They can be blended seemlessly into new architecture or added onto existing homes in beautiful and useful ways.  Some great examples I found for commerical applications can be viewed at FlickrSolargen1 and Sunengineer.   For residential examples of PV structures you can visit GoGreenSolar, FlorianSolarProdcuts , GreenEdmonton and SolarLiving.  You can see from these examples that PV systems can be beautifully integrated with your Green building or home.  These examples clearly show that being Green can make your building architecturally stunning and unique!