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.

3 comments:

Anonymous said...

Let’s face it; energy efficiency, cost and sustainability are the issues of A/C. Knowing your alternatives is an indicator for the poorly designed properties of your building.
Air conditioning and passive design shouldn't be contradicting to each other. The latter serves to reduce running costs on A/C systems. It is not surprising to find that students or generally, people misunderstand the conception of A/C units and energy efficiency. Most people believe what is guzzling large amounts of energy are to be avoided. No, not entirely, but minimised.
True, it is important that understanding A/C principles enables you to see the issues of efficiency sensibly, which will allow architects to tackle the design in a conservative manner. But, a sacrifice for aesthetics and priority on good passive cooling features in a building is what makes it a sustainable building.
Personal comfort systems sound like a good idea, but to what extent? Like Tim’s device may be ‘another way of using ingenuity’. A research that is currently being funded at the centre for the built environment at Berkeley, will aim to optimise the efficiency and demonstrate the practicality of these types of devices. While savings vary by climate, widening the dead-band by one degree Celsius can reduce building-energy consumption by 5-15%.
While this may seem practical, the research lacks a perspective on the cost on investment which seems to be the issue for all businesses. The sustainable idea is to design a building such that it removes stale and heat from a dead zone and minimize the need for cooling.
But, definitely with air conditioning being the most established method for cooling massive areas, it comes down to how the architects design for sustainability and also a shift towards a more efficient system.

Links:
CBE - Advanced Personal Comfort Systems Development and Testing
http://www.cbe.berkeley.edu/research/personal-comfort-systems.htm

Energy.gov - Air conditioner problems
http://energy.gov/energysaver/articles/common-air-conditioner-problems

Anonymous said...

Let’s face it; energy efficiency, cost and sustainability are the issues that some architects face when dealing with A/C. They mostly think that A/C units consume loads of power, but really little do they know, it’s because they have poorly planned their space.
“Appreciating the principles of A/C”, true. An appreciation of how efficient these A/C systems offer, will allow architects to tackle the design in a conservative manner. So essentially, a sacrifice for aesthetics and priority on good passive cooling features in a building is what makes it a sustainable building.
Personal comfort systems sound like a good idea, but to what extent? Like Tim’s device may be unsustainable. While others like Berkeley’s centre for the built environment are trying to research alternative options at the centre for the built environment at Berkeley, will aim to optimise the efficiency and demonstrate the practicality of these types of devices. While savings vary by climate, widening the dead-band by one degree Celsius can reduce building-energy consumption by 5-15%.
While this may seem excellent, the research lacks a perspective on the cost on investment which seems to be the issue for all consumers, also a lack of appreciation on space minimization. Work like theirs applies an incentive for the A/C market to show the true value that it has.
The message to architects is to know a little more about A/C before you go doubting it, and implement passive cooling features into the building design to minimize the load for cooling.

Links:
Advanced personal comfort systems development and testing –
http://www.cbe.berkeley.edu/research/personal-comfort-systems.htm

Steve King said...

I think I understand what you mean...But certainly thank you for the excellent link to the Berkely Centre for Built Environment. I just spent a little while following up the article, and even more importantly, some of the other research links on the site. I especially liked their interactive Thermal Comfort Tool