The energy cost in petroleum for air conditioning in vehicles is staggering. Auto A/C consumes about 7 billion gallons annually, which is 10% of our oil imports. Auto A/C has a huge effect (equal to or greater than the proposed 55 mph limit) on our balance of payments and energy security. There has been a topic of much study (e.g. see “Human Thermal Environments” http://books.google.com/books?id=4oxA6W_Os50C&pg=PA251&lpg=PA251&dq=%2B%2B%22thermal+comfort%22+%2Bcars&source=web&ots=p876-1WUnb&sig=cxwDsFdletB6-zEcADdQUktgKLw&hl=en&sa=X&oi=book_result&resnum=1&ct=result ).

The National Renewable Energy Laboratory (http://www.nrel.gov ) proposes a three-part approach (http://www.nrel.gov/docs/fy07osti/41155.pdf ) to A/C fuel use reduction: reducing the thermal load, improving delivery of conditioned air to enhance thermal comfort, and increasing the efficiency of equipment. Their approach is focused on Thermal Comfort and Solar Load Modeling, Parked Car Ventilation, Solar-Reflective Opaque Surface Coating, and Advanced Automotive Seat Concepts (large contact area, ventilation, fan, liquid heating/cooling).

One of their studies (http://www.nrel.gov/vehiclesandfuels/ancillary_loads/pdfs/evs15paper.pdf ) focuses on efficient delivery through the use of advanced automotive seat concepts. Another area is solar load. Modern car designs have increased the use of window glass. In view of current gas prices, the incorporation of solar reflective coatings in series hybrids and BEVs, particularly for high solar heat load southern states, appears to be a no-brainer cost-of-use/AER tradeoff, but GM’s advertised 40 mile All Electric Range (AER) driving profile does not include A/C. There is no spec penalty to GM for the effect of A/C on AER.

Incorporation of these concepts into the Volt can have a significant impact on real world sunny day (~15%) AER.

Maybe it would be more efficient to capture braking energy to pressurise the AC loop, instead of generating electricity. Tom put your calculator to work....

Though it adds a little complexity to the cooling system and another tank to periodically fill, AC efficiency can be kicked up by 25% or more in the hotter/drier climates through evaporative condensing. This would involve spraying a little water on the condenser coil. 5 gallons of water, when evaporated, can cool a 1/2 ton AC system for 9 hours. Mineral deposition can become a problem in hard-water areas, but there are a couple of evaporative-condensing AC unit manufacturers who have pretty much licked that problem. Just one more thing on your daily Volt service list - Top off your batteries and fill your AC water tank.

For an example of a home AC unit using evaporative condensing, see link (http://www.freus.com/products.htm)

For an example of a home AC unit using evaporative condensing, see link (http://www.freus.com/products.htm)

Thanks for the link hvacman. I've thought this was a good idea and only found limited information on evaporative to lower the ambient temperature that a condenser sees. Of course, being in Florida's high humidity dramatically decreases the benefit compared to the dryer climates. I wish they would state the ambient conditions for the graph at the link. I'll search a little more on their site, perhaps it's discussed elsewhere.


I thought about using irrigation misting jets in conjunction with a AC canopy and controlled by the thrmostat as a retrofit application and a new install accessory. Of course, retrofitting a well sized installation will cause short cycling. This is an issue for the high humidity climates but I suspect, not so much for the dryer climates. For me, I want to do an addition to my house and the extra effective cooling capacity might work perfectly. This seems like a very simple and cost effective way to increase AC efficiency.

It would be neat to see this applied to all car air conditioning systems. Energy consumption is energy consumption regardless of if it comes from a guzzler, a hybrid, or a pure EV. 500 Wh hours used to keep your self cool, is 500 Wh you have used to push air out of the way on you daily journey to the rat race.

That being said, I think everyone should consider investing in one of those ugly sun shades, look into widow tinting, and maybe crack their windows if weather and security permits.

Koz,

A lot of Florida sits on a shallow aquifer that can be pumped. You might talk to local contractors about a direct-well-fed water-source heat pump from Florida Heat pump. Link (http://www.fhp-mfg.com/residential.htm). These units do a great job of de-humidifying if properly sized, and have EER's with well water that can get up to about 29, beating the pants off of an evaporative condensing unit. They also will produce very efficient electric heat, with COP's of 5. The two-stage is especially effective for dehumidifying, as it really reduced the short-cycling issues during part-load conditions.

Evaporative condensing units base their efficiency on the outdoor wet-bulb temperature, since that is what drives the evaporative effect. Freus units are rated for wet-bulb temperatures around 68 degrees. Design wet-bulb temperature in Florida varies, but can get into the high 70's, which would reduce EER by at least a couple of points.

The advanced two-stage air-cooled condensing units currently available from most major AC manufacturers (Carrier, Trane, Lennox, etc.) can be very efficient in humid climates, since their ratings are based on dry bulb temperatures, which rarely go over 95 degrees. Mated with a variable-speed indoor blower with an ECM motor (electronically commutated DC motor), they can achieve EER's of 14-15 and not have the messiness of water wells or evaporative cooling maintenance.