Anti-Passive Solar

Anti-Passive Solar

There are lots of ways to do passive solar horribly wrong.  Some design with too much glazing (not enough mass to absorb all the solar energy) and end up with rooms that are too hot or bright to be comfortable in.  Over a winters night, the lower R value of the windows allows these same rooms that were too hot during the day to cool off quickly and become too cold to be comfortable.  In summer, cooling these homes can cost a fortune.   This often happens with green house spaces that people build assuming they will be a wonderful addition to their homes, but all they do is keep it constantly out of balance and at odds with the sun.

Painted over Wendys Solarium

Restaurants can no longer afford to heat and cool their “anti-solar” solarium. These retrofits are to slow the bleeding. New Wendy’s locations are without this classic feature.

For a while there, many restaurants featured a solarium in their design.  For Wendy’s, in particular, a curved glass solarium became iconic with their brand.  However, with the costs of heating, and especially cooling, these solariums, new Wendy’s locations have stopped adding them to their new buildings and have covered or painted over the south or west facing sunrooms in the older restaurants.

Others may color their homes with dark roofs or not provide enough natural ventilation and wonder why their AC units never shut off during the summer. In some cases, it is the heat distribution system that is lacking (one room is hot while the sun is shining, but the others are still cold), etc.   From time to time, I will come back and add examples of “Anti-Passive Solar” designs.

My current home is not well oriented for passive solar gain. We get no solar heat gain in winter, but get plenty on warm summer evenings.  On the other hand, we do appreciate our shady back patio (East side) that works well for afternoon parties.

Solar Orientation 

Of course, if they don’t know the orientation of the home with respect to the sun, the architect can’t create an effective passive solar design.  This is a common problem when people orient their pre-made house plans based on the street rather than the sun.   A badly oriented passive solar design can be worse that a home without any passive solar intentions at all.   Ideally, a passive solar house should have its long axis east to west with its glazed side pointing as close to south as possible (I am writing from the northern hemisphere where the sun spends most of its time in the southern sky).  I have seen studies showing that within 15 to 20 degrees of true south is acceptable. My own home is in a neighborhood of about 5 different house styles.  Because it is a tightly packed neighborhood, the homes were designed without any windows on the gable ends.  This leaves all the windows on the front and back of the homes.  Looking at my own court (one of many in the subdivision), most of the homes are oriented facing east or west, with a few homes facing north or south.   My own home is facing 25 degrees north of west, with no windows at all on the south side.  We do get a lot of heat in the front windows during summer evenings.  I wonder if neighbors would be willing to share a years worth of energy readings with me?  It would be interesting to compare. (I have since got the records from several neighbors and will chart soon).  I did check last months electric bill with my nearest neighbor, and it was actually 50% higher than ours, but their house is a different style and they run their AC constantly…  Also, none of us have window overhangs, so I wouldn’t really expect much summer benefit from the orientation… I read a white paper on urban planning that concluded that if a city orients its tightly packed residential streets east to west instead of north to south, it gains a huge free solar energy bonus (since most of the windows in tightly packed neighborhoods are on the front or back of the homes).  I will link to the paper if I find it again, but the numbers were staggering.

These OnRoute rest stops are passive solar on the north side of the highway (west bound), but “anti-passive solar” on the south side (east bound)

I often travel the 401 highway thru Ontario and noticed these new OnRoute rest stops going in over the past few years.  They were designed by “Quadrangle Architects Limited” and received LEED silver certification for their innovative design, including an obviously passive-solar atrium with a generous overhang.   However, when they were actually constructed, they were oriented to face the highway (as a giant lantern for weary travelers) rather than the sun.  Those built on the north side of the highway do well with direct solar gain in the winter and shade all summer.  However, those on the south side of the highway must run air-conditioning units heavily to compensate for high solar gain during the summer, particularly in the afternoon.  I have spoken with a manager of one of these on-route stations and am working on getting access to the heating and cooling bills.  If I get it, I will publish the data here.

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