Monday, 3 June 2013

Clued in on the heliostat

This post is authored by Jeremiasz Sieczko and follows from my attempt to unravel the workings of Jean Nouvell's heliostat installed at Central Park in Sydney Australia.  Jeremiasz' comment on my original post was too long for Blogger to accept.  Here it is in full.

As I understand it, a few misconception have been made in the blog post The sky isn't falling, but I'm clueless and in a few of the referenced articles. 

Firstly, the 110 tonne cantilevered steel frame will NOT be supporting the 42 x 6.2sqm Heliostat mirrors but the 320x1.5sqm Reflector Panels. A heliostat can be described as "a device that includes a mirror, which turns so as to keep reflecting the sunlight towards a predetermined target, compensating for the sun's apparent motions in the sky". In this design the 320 cantilevered Reflector Panels are the target for the heliostat mirrors. The heliostat mirrors are located on the roof of the 16 storey West Tower. 

These mirrors will track the sun into the target cantilevered Reflector Panels which will then reflect (or scatter/diffuse) the sunlight into a number of location in the complex (from the diagrams provided in the original blog post, it is suggested this will include the shopping arcade in the podium of the One Central Park towers and the actual park in the centre of the development). The Reflector Panels appear to be fixed and as far as I understand there is nothing to suggest that these function as secondary heliostats tracking the primary heliostat which will be tracking the sun. 

Secondly, the Jean Nouvel's building is made up of two towers: the taller 33 storey ‘East Tower’ (with the cantilevered garden + reflector panels) and the shorter 16 story ‘West Tower’. The street facade on 'Broadway/Parramatta Rd/ George St' of both towers should be noted as being north. 

After a quick overview of the plans ( I found that the 33 floor 'East Tower' appears to have only one small south facing apartment per a level and the majority of the apartments are on the larger surface area East and West facades (one small apartment per a level also occurs on the North facade). Ignoring the Heliostat system and the immediate environment for just a moment, it would appear that the East Tower responds rather reasonably to the sunlight conditions. The majority of the apartments within this tower are provided as much sunlight as possible. Remembering that western sun is usually considered to be less favourable and harsher than the eastern sun it would make sense if the design responded accordingly to this conditions. Reintroducing the cantilevered panels/platform on the west façade of the East Tower and the immediate environment, the cantilevered platform might act to improve conditions under the harsher western sun by shading a large number of apartments (especially in summer). Surely there was also at some point a consideration for winter lighting conditions, especially since such an elaborate sun lighting system is being employed. Considering that the cantilevered platform will create a lot of shading of apartments on the west façade of the East Tower it really wouldn't make sense if the heliostat didn't work to compensate this problem.

In the circumstance of the 16 storey 'West Tower' the conditions appear to become a little bit more complex. The East Tower shades the eastern façade of the West Tower. Depending on what visualisation you look at, the western facade is also shaded by surrounding buildings. The majority of apartments in this tower also occur on the East and West facades. One would imagine that the heliostat system and reflector panels have been employed for the very reason that the sun lighting conditions are so unfavourable in tower. It would essentially bounce sunlight into the interiors of the eastern facade apartments. In viewing the plan it can be observed that a portion of the plan has been recessed, potentially to provide more favourable incident angles for the reflected sunlight from the heliostat. Additionally, the plan shows a number of ‘mysterious exterior panels’ (in red on the above plans) that may possibly act as reflector surfaces designed to bounce reflected sunlight from the heliostat system deeper into the interiors of the apartments. These mysterious panels appear on both towers on the facades facing the heliostat void, exactly the location they would be needed to perform a reflector function. Though these mysterious panels are also a feature of the southern façade of both towers where they couldn’t serve a reflector function. Their appearance on the southern façade might then just be for aesthetic consistence or cost reduction. An argument could also be put forward that these mysterious panels are actually garden boxes, though these would appear to be excessively large to serve such a function as can be noted from the following image.  
If these mysterious exterior panels are in fact reflector panels as first speculated then it would seem to suggest that some very serious modeling of lighting conditions has been done for the heliostat and reflector panel system.

As for the reason why a detailed description of the heliostat system mightn't be included in the advertising material: This is the first time such a system is being employed in Australia. There is little precedent to suggest that it is going to work exactly how it has been designed to work. Therefore, the architects might not be willing to make any promises that they mightn’t be able to keep. To avoid any future lawsuits it might just be easier to avoid explaining the system in too much detail (especially in writing!), just incase it doesn’t end up working as planned.
At best the heliostat system will provide favourable lighting conditions for as many apartments as possible, at worst it will be a very clever (and probably very expensive) way to get a building approved that doesn't ensure 70% of the apartments have reasonable sun lighting conditions (which would be a shame because it's such an awesome sci-fi solution!). 

Of course, the building has been opened since this post. Explanations of the heliostat are not much better, but it's no longer 'mysterious'.  See a typical video here.



Jock Sinclair said...

Comment 1 of 2

This is an interesting assessment of the potential uses of the heliostat and the ways in which it might function. It is probably worth noting that the heliostat currently under construction is allegedly significantly smaller than the initial proposal, and which can be seen in all the pretty the advertising material. My memory is not perfect but I believe I was told of this variation by a member of an engineering company working on the project.

Unfortunately, nothing in any of the material printed on this project suggests that the heliostat provides light to the southern facing apartments. A quick look at the geometry makes it seem that the cantilevered panel would have to extend an absurd distance out to the south for this to work, and given that it is attached to a structure located on the northern half of the west facade, makes it more unlikely. Contrary to the suggestion that the reflector mirrors are fixed in place, for the purposes of variation in lighting scemes and the LED light show that is to take place at night, i believe that these will be actuated just the same as those mirrors located on the roof of the western building.

I have come to believe that this device might function to different ends than that suggested in the post above. By looking at the 3D renderings of adjacent outdoor spaces, the over-exaggerated "fingers of god" (a reference to Jean Nouvel, not the alleged omnipresent supreme being) seem to suggest that it will be used to provide sunlight to the open space directly to the south of the buildings. This assessment seems to be more or less confirmed when reading through the article linked below. Due to the height of the buildings directly to the north of this area, without the heliostat this area would become much like the rest of Chippendale, dimly lit and pretty crappy.

comment continued in next post...

Jock Sinclair said...

Comment 2 of 2

It has also been suggested in the post above and in promotional material that the heliostat will serve to provide natural lighting to the retail spaces that are to be houses in the lower six levels of the building itself, via an atrium located between the two vertical portions of the building.

How the heliostat will serve the two different spaces (open space and retail) is where I believe the true value of the design lies. When providing lighting to the open space to the south, the mirrors will be aligned to spead the light evenly over the area, with the aim of reducing its directionality and intensity. However, the portion of the heliostat that targets the atrium roof of the retail space with be more intensely focused with the intention to maximize the penetration into the interior spaces. This may have implications such as glare and solar gains, but without any details of the type of roof, or any diffusing devices located below, it is difficult to tell how this has been dealt with.

The mystery panels illustrated in the images above, are indeed planter boxes. Several things indicate this to be the case. For one, the thin planters shown on the outward facing north, east and west facades are not continued around to the southern and inward facing facades, thus the only place for these planters to show up on the plans is in these red areas. From discussions with the company responsible for the vegetation design of the project, one of the main issues they were having was one of too much sunlight, as opposed to not enough. I believe that the reason for the increased size of the planters in this area is to maximize planting opportunities on the facades that are most advantageous for it, ie. the southern and inward facing facades. This brings me to another point that Jeremiasz touched upon in his post: making grand claims about yet to be proven design solutions.

I was lucky enough to attend some lectures during a summer course, taken by two people responsible for the design and engineering of the green facades. I happened to asked then if they were required to make their facade systems easily removable in case the planting did not take off as planned. They seemed to confirm that a contingency was designed to remove the planter boxes should the plants not survive the harsh conditions, with minimal visual impact to the look of the facade, minus the obvious loss of climbing vegetation. They suggested that nobody involved was really sure if the plants would survive due to wind and sun factors. It is for this reason, the remaining unknowns, that I believe the roles of the heliostat and green facades have not been detailed extensively in advertising material, aside for the glossy renderings.