Saturday, 18 April 2015

Voodoo heliostats

Oh, the magic of the big architectural gesture!!! 

By far the most read of my blog posts are those about Nouvel's iconic carbuncle on the face of One Central Park, here in Sydney.  It is clear that there are a lot of people interested in that big and mysterious heliostat.

But what really amuses me is that it seems to have raised expectations more broadly.  Quite clearly, some people think that such technical gymnastics will also solve otherwise impossible architectural or urban design problems elsewhere.

I am thinking of a local architect, who is designing a six storey building fronting a narrow street, in one of our nicer low scale shopping precincts.  The problem is that the street runs east-west, and the building is to be on the north side of the street.  This being the southern hemisphere, in the middle of the day in our winter, a building of that height will overshadow the street.  Because the local municipality is interested in maintaining a public domain which invites active retail and  outdoor eating, it is vitally interested in minimising such overshadowing.

The relevant planning approvals officer dealing with the project does understand enough about solar geometry, to know that the allowable building heights, and winter solar access in the narrow street just don't go together.  So his automatic reaction was to suggest that the architect 'do something that redirects the sun down to street level'. I am under no illusion where he got the idea.

Those of you who have read my previous posts on the Nouvel heliostat would have worked out that it isn't the overhead structure that actually does the hard work.  It is the tracking mirrors sitting on the roof of a lower building that first capture the sun, reflecting it to the relatively simpler fixed downward pointing mirrors on the main cantilevered frame.

In his enthusiasm and ignorance, the planning officer has failed to notice key differences between the iconic prototype, and the situation in which he hopes it will be repeated:
  • The first is the fundamentals of how the heliostat actually works with separate elements in different places – importantly that in the confines of the narrow street location, the downward reflectors would be sitting over the public land, not the applicant's own site. 
  • Secondly, that unless the tracking mirrors (which could sit on the proposed building's roof) were always functioning reliably, you could end up with rogue blinding reflections going anywhere, especially to higher buildings in the vicinity.
  • Thirdly, that the substantial frame and reflecting panels which function to reflect sunlight downwards on sunny days, would also be an unwelcome obstruction to daylight on overcast days – mind you, it would also be a shade structure for summer.
  • Not finally, but importantly, on what would normally be the sunny side of the street, those floors of any prospective buildings that are above the retail level, but below such a reflecting structure, would actually have their winter sun stolen by such a canopy.
  • Let's not mention cost..... 
I think there might be latent images of glazed streets in Europe and Japan at play here, as well as the misunderstood heliostat.  But I have just had to write an 'expert opinion' for the architect, explaining much of this, so that the project could proceed with perhaps lowered expectations.  No, you can't sprinkle heliostats around the city like magic dust, to compensate for the fundamental layout and geometry of city streets, and the buildings that you built on them.

The earlier heliostat posts are:

The sky isn't falling, but I'm clueless
Clued in on the heliostat

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