Saturday, 30 November 2013

Getting personal: how do you use air conditioning?

Sometimes a little thing is worth talking about.

I regularly deliver a lecture, in various settings, about air conditioning.  It's interesting; most  young architects and architecture students think of air conditioning as inherently the opposite of energy efficiency.  They assume it's to be avoided, if you can only crack the magic 'passive' cooling conundrum, possibly even evil.  But the same idealistic young architects design buildings that in even moderate climates can't maintain comfort without some sort of conventional air conditioning, and guiltily value it's contribution to their own productivity.

Yet if you understand the principles of refrigerative A/C, or even better, absorption chillers that run on low grade heat to generate cooling, you can sometimes admit the nagging reality.  At the heart of most air conditioning systems lies a ruthlessly efficient way of creating heating or cooling.

To understand this, you need to understand that the energy efficiency of air conditioners is indicated by the EER (Energy Efficiency Ratio) for the cooling mode, and by the COP (Coefficient of Performance) for the heating mode. These indicators give the ratio of the total cooling or heating output and the energy input, because the heat pumps in an air conditioner move heat around, rather than convert fuel to heat.
With EER and COP of around 6 for a modern split system, air conditioning can be getting a very big bang for the buck you spend on your primary fuel source.
What makes air conditioning profligate, is the WAY it is most often used, to cool big lumps of otherwise ineffectively designed space.  Yet we are aware of alternative approaches that leave most of that unoccupied volume to overheat as much as it likes, while we cool where the people are.  So we have 'displacement systems' from floor plenums, driving pollutants towards the ceiling to be exhausted with much of the heat from the lights, and low speed registers built into theater seats to create bubbles of conditioned space. And in our most perceptive moments, we remember about the personal comfort systems found on airplanes and long distance coaches.

So it was with some delight I came across the work of a young academic at UTAS in Launceston Tasmania.  Tim Law took inspiration from those personal systems we already know, and married the thought up with the fact that existing buildings will continue to dominate our built stock, often inhibiting aggressive interventions. He has designed and got to production stage a climate control device that effectively air conditions the minimum space of the desk-bound worker, 'the person rather than the space'.  At first, it may not seem novel, but it actually is, because it is not tethered by a way of disposing the hot air that conventional portable air conditioners produce.  Tim's device rejects the heat directly to a fixed volume of phase change material, installed within the unit itself.

OK, it's not immediately obvious how the phase change storage regenerates efficiently overnight. Is this just another way of using ingenuity, not to cut down energy use at all, but like ice storage before it, merely to level out the usage to take advantage of off-peak tariffs?  I suspect the key is in the total loads the system tries to handle.  It's not the small conditioned bubble that saves the money, but the large volume that can be left to swing much further away from comfort.

I suspect we will be seeing  quite a number of improvements on conventional air conditioning, and that air conditioning will remain in the spotlight in climate change adaptation scenarios.  So we need the work of people like Tim Law, to turn air conditioning from part of the problem, to part of the solution.

See an enthusiastic presentation video by Tim Law here.

Heliostats happen (updated)

There is obviously interest in heliostats.  While I have been a bit preoccupied with other things, and failed to add much new to my blog, the heliostat pages seem to attract the most readership.  So, here is a bit of an update.

I have now had the opportunity to visit the retail areas of Central Park, since their 'hard opening' some weeks ago.  The heliostat mirrors do not appear to be functional yet, so my initial impressions cannot advance our assessment of what they actually do, or how well they do it.  But some aspects of the design do become easier to understand, and therefore if one is so inclined, open to criticism.

The thing that immediately struck me was that there is a big difference between the architectural renderings of the key spaces, and the sensation of those spaces in real life.  The scale of both outdoor and indoor 'public' space is much less expansive that the renderings suggest.  But in particular, the sectional complexity of the shopping spaces turns out to be rather humble in its impact as you move around what is in reality a very small retail mall.

Even more disappointing is that when the heliostat mirrors are finally tracking a beam to the skylight at the top, it's hardly likely it will make a positive difference to the lighting of the central indoor space.  There is a significant 'diffuser' on the skylight: a glass bottomed pond.  The rippling water varies the transmitted light continuously at a rate far greater than the rate at which daylight normally changes.  Normally, one of the arguments for natural light as opposed to artificial is the psychological value of its variability.  But this arrangement goes far beyond the intrinsic subjective value of natural light as opposed to artificial.

I can't convince myself that this is a rigorous technical lighting decision, because of other issues with the general lighting quality.  So, for instance, on going inside the mall, one realizes that the highlighted portions of the interior will be significantly brighter than the adjacent areas, and to balance the user's adaptation levels, quite large amounts of permanent supplementary artificial lighting is required. That lighting is provided by some designerly chandeliers, which even on a cloudy day struggled to achieve any liveliness.  But wait, there is more.
Once one tunes in to the technical issues of the lighting, one questions the material finishes in a different way.  The distribution and modelling characteristics of daylight are everywhere hugely affected by the internally reflected component.  So it comes as something of a surprise that at Central Park there is a cute faux 'timber look', even down to the dark brown planked floor.  The colour and the material are very low reflectance, and literally suck out the diffuse reflections on which better daylight distribution would depend.  And to make things seem almost laughably inept, there are long walls finished in similar materials, taking up major portions of the places where a competent shopping mall would have had shop windows spilling their own light.
Genzyme HQ, Cambridge, Ma
I hate sounding unrelentingly negative.  But these few comments go to the heart of my recurring themes.  First, I have a pet project of encouraging people to actually look at the pretty pictures that accompany the spin doctors' press releases. When you do that, you see what I am describing, even in the official photographs of the opening of this aspirational shopping experience. Second, when you take the trouble to tease apart the principles of technical performance, you can more easily find positive precedents for inspiration.  In this case, for instance, the heliostat and reflective chandelier of the Genzyme HQ building in Cambridge Ma. is a much better technical solution to daylight distribution.

Back to the iconic cantilevered frame of the heliostat.  It is remarkably close in every way to the renderings, yet it too undergoes a strange perceptual shift as one walks into the site.  Closer to the buildings than the usual hero shots illustrate, the cantilevered plane closes up the normal sky view between buildings. It is a very counter-intuitive sense of intimacy, and on balance wasn't a good feeling. Certainly from below, the experience is not exhilarating, though it may well be for those privileged to access it from above.  Some time soon, I will take the trouble to photograph the views that don't yet appear on the internet..  But to be fair, I am waiting for the heliostat to be commissioned.  When that happens, I will top up this post.

Other heliostat links:
A nice little review article on DesignBuild Source by Justin McGar here.

A more recent press release, with the image of the whole heliostat that actually includes the motorised primary reflectors on the roof of the shopping centre building.  Click here for the article.

I dread to think how inconvenient it would be for residents looking down if one or more of the lower mirrors' tracking goes awry.  But that is just my paranoia about depending on moving parts!