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01/09/2011
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With the emphasis firmly on lowering CO2 emissions, where does that leave air conditioning, now to be found within the vast majority of cars?
Long gone are the days when air conditioning was the preserve of executive and luxury class cars. It is now perceived to be standard equipment on any class of car, albeit with varying levels of sophistication: from single to multiple zones that tailor temperature and airflow requirements to individual vehicle occupants.
However, challenges still remain, not least of which is energy consumption. At a time when virtually every vehicle development is being driven by the need to reduce CO2 emissions, heating ventilation and air conditioning (HVAC) systems – and, in particular, the latter – are coming under close scrutiny, especially in small cars. The recently launched diesel Kia Rio is a case in point. Its EcoDynamics model achieves 85 g/km, but add air conditioning to the car and that figure increases to 94 g/km; still well inside the 100 g/km barrier, but a penalty nevertheless.
Compressor drag
Yet, as Delphi Thermal systems general director of engineering, Dave Kauppila, points out: "The biggest drag is in the compressor. There are movements towards electric compressor technology and we're developing those, but primarily for electric vehicle (EVs) and hybrid applications."
The implication being that, in such a price sensitive sector as that in which the Rio and similar models compete, those customers would be unwilling to pay for the additional cost of an electrically-driven compressor over a mechanical one, despite the obvious fuel economy benefits.
At the same time, Kauppila points out, there are other, less costly, solutions when it comes to downsizing HAVC systems. "Condenser technologies are shrinking in size, with more efficient folded tube condensers, in place of the traditional extruded aluminium tubes for the refrigerant passages," he states. The smallest and lightest are a new family of 16mm and 12mm, the latter being unsurpassed at present in the marketplace. The advantages of folded tube technology is cost and "more importantly" material longevity.
Key advantages
Small, five-cylinder variable compressors, with 100-110cc capacity, are already on the horizon, with a view to being launched in a 2014 model year product.
One of the key advantages to variable compressors is that, depending on load, it can adjust its pumping capacity so that, at very
high temperatures, it will use the compressor at full capacity, while at lower ambient temperatures, where there's still a need to dehumidify the air, it will destroke and use less pumping capacity, thereby reducing the draw on the engine.
The switch from R134a refrigerant to HFO-1234yf will have an overall impact on the ozone, as the former has a Global Warming Potential in the region of 1,400, compared to HFO-1234yf's four.
The downside, according to Kauppila, is the effect it can have on sealing and lubrication systems – something that has necessitated the development of specific lubricants – and its higher basic cost, due partly as a result of being restricted to two suppliers, DuPont and Honeywell. "Cost will depend on how rapidly they ramp up production," he observes.
Dual and four-zone systems are beginning to make an impact, but only in high end products, and it does beg the question as to why the industry continues to heat or cool the entire vehicle cabin when there might be only one occupant, the driver, or driver, plus front-seat passenger. Heating or cooling a car that is only one quarter or 50% occupied is, patently, a waste of energy.
Kauppila admits that Delphi is "developing" spot cooling systems that effectively duct air specifically to individuals and there is potential for "shower effect" air streams through the roof liner, as seen in last year's Visteon's C-Beyond concept.
However, the challenge with visions like this is that they require a fundamental change in the vehicle's architecture and, if the body structure is also used to duct the air around the vehicle, it has a potential influence on non-HVAC issues, such as crash structures.
Wasted energy
That said, not all changes need to involve radical engineering or structural solutions, as Behr revealed at the recent Frankfurt motor show. American consumers tend to prefer stronger, colder air conditioning, compared to Europe, explained Markus Wawzyniak, director of advanced engineering HVAC, and this can cause discomfort, especially to contact lens-wearing occupants.
Behr's 'Natural Breeze' system is designed to overcome that, without making significant alterations to the basic HVAC system and its ducting. "It's designed to provide both focused and diffused airflow from the same vent. There are some luxury cars that deliver diffused air, but they require additional space and parts, and impact the design.
"Occupants can have a very focused airstream onto their body for quick cool-down and then regulate it for a gentler draught."
It's a breeze
In the spot mode setting, it appears and feels like a conventional circular vent. Changing to the 'Natural Breeze' mode brings into play a series of vanes that rotates the airflow, which then uses its own momentum to disperse itself, creating a very low pressure drop design.
"In current cars, you either reduce the airflow or direct it away from you," comments Wawzyniak, "and lose the high quality of the air. With this, you could switch off all the other zones and just activate one, so using the energy that much more efficiently. We sense it would appeal to a lot of end customers, because it's not going to be that costly for its effectiveness."
HVAC developers are taking incremental steps in improving air distribution within vehicle cabins, while minimising power absorption. But clearly there's still further scope for improvement.
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Author
Ian Adcock
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