An affordable cool.

July 27, 2010 8:40 PM

Keeping Cool at Lower Cost. A fine summary of the latest innovations in the technology of air conditioning. e.g. "If [fan] blades were designed for better aerodynamic efficiency, instead of being stamped from sheet metal as cheaply as possible, the electricity consumption of many cooling systems could be cut by a third.". Includes a look at how to cool a building using hot water in a device called a thermal cooler.
posted by storybored (26 comments total)

While several of these systems are interesting, the author seems to be an otherwise intelligent person who has a very distorted understanding of thermodynamics.

The first thing to understand about air conditioning/refrigeration is you are not really creating cool so much as you are removing heat.
posted by jcking77 at 9:17 PM on July 27, 2010 [3 favorites]

The first thing to understand about air conditioning/refrigeration is you are not really creating cool so much as you are removing heat.

uhh TLDR? He or she actually seems pretty clear on this: "Most air-conditioning units, like refrigerators, use tubes containing chemical refrigerants which vaporise as they draw heat out of the air passing over them."
posted by Locobot at 9:24 PM on July 27, 2010 [1 favorite]

If you can cut AC electricity usage by a third with a better fan blade it seems like there should be a huge market for replacement fan blades.
posted by jeffkramer at 9:37 PM on July 27, 2010

But there are things like the idea of an evaporating water "removing" heat, and ice "cooling" a room which can be a dangerous way at looking at it.

Evaporating water absorbs heat, it doesn't remove it.

The comments in the article have it best: spending more on preventing heat from entering the building in the first place is the most cost effective means of keeping our spaces cooler.
posted by jcking77 at 9:46 PM on July 27, 2010

i havent seen blades made from metal (as opposed to plastic) since the 80s.
posted by 3mendo at 9:51 PM on July 27, 2010

But there are things like the idea of an evaporating water "removing" heat, and ice "cooling" a room which can be a dangerous way at looking at it.

Ice does cool a room, assuming the refrigeration unit involved in producing the ice exchanges the heat outside the building. Evaporative cooling does cool a room, it takes energy (latent heat) to cause a phase change from liquid to gas, and that heat is removed from the room. (Or your body in the case of perspiration.)

People talk casually about cooling all the time. I have no idea why you're so concerned with the phrasing in this article, which is really not indicative of any misunderstandings whatsoever.
posted by knave at 10:07 PM on July 27, 2010 [3 favorites]

Air conditioner condensor fans are often stamped metal rather than plastic because they have to hold up in outdoor use. There also hasn't been much incentive to optimize the fan because the fan uses only a small fraction of an AC's power, - 10% is probably generous (The compressor is by far the biggest energy hog.) A 20% savings on 10% would net only 2% more system efficiency - not worth spending a lot of money on.
posted by Popular Ethics at 10:09 PM on July 27, 2010 [2 favorites]

Air conditioner condensor fans are often stamped metal rather than plastic because they have to hold up in outdoor use. There also hasn't been much incentive to optimize the fan because the fan uses only a small fraction of an AC's power, - 10% is probably generous (The compressor is by far the biggest energy hog.) A 20% savings on 10% would net only 2% more system efficiency - not worth spending a lot of money on.

If a more efficient fan blade design means less power usage, not because it's easier to turn but because turning it accomplishes more, then it starts to become a lot more worthy of investiture. The article claims a 33% reduction in energy costs.
posted by kafziel at 10:38 PM on July 27, 2010 [1 favorite]

jcking77 wrote: "Evaporating water absorbs heat"

Which is why a lot of newer A/C units sling water on the hot condenser coil to help cool it, thus increasing efficiency.

The fan simply doesn't use that much of the energy. My window unit draws about a third of an amp for the fan. The compressor, on the other hand, draws a little over 10 amps. You could reduce the energy use of the fan to zero and hardly impact the power draw. Granted, if every air conditioner had a significantly more efficient fan, the overall reduction in power consumption could become a large number, although still small relative to total power usage. But every little bit helps.

People would be better served by cleaning/replacing their filters often and cleaning their coils every once in a while, though. Dirty filters and coils really destroy the efficiency of the system.
posted by wierdo at 11:09 PM on July 27, 2010

A 20% savings on 10% would net only 2% more system efficiency - not worth spending a lot of money on.

I can't post any details, but at Google, optimizing the fans is serious fucking business. Those little efficiency gains accrue geometrically, like compound interest. And compound interest at 20% yields fairly epic returns (see form 10-K).
posted by ryanrs at 11:18 PM on July 27, 2010 [2 favorites]

The article claims a 33% reduction in energy costs.

If it was that easy, all the HVAC companies would be doing it. They are under a fair bit of pressure to meet efficiency targets while meeting consumers' price points -- they would happily accept a freebie like a better fan blade if it meant a 33% more efficient system.
posted by Forktine at 11:24 PM on July 27, 2010 [1 favorite]

Living in Tucson has taught me that evaporative cooling does work very well ... provided that the weather is dry outdoors. It's actually much nicer than standard air conditioning in the early and late summer (which you may know as spring and fall). It uses much less electricity and puts some humidity in the air which feels wonderful during the dry seasons. This time of year though, when we get the summer "monsoons" and the air outside is wet, evaporative, or swamp cooling as some people call it, is mostly useless. Where evaporative cooling uses less electricity it does use up water which is another issue.

There are large university buildings around here which use night time ice creation for cooling, but this doesn't really save too much electricity, just puts usage off peak hours.

The solar coolers described in the article would probably work great here, as would large scale solar electricity production, but unfortunately our state government majority and most of the influential people in Arizona are reactionary. Sure we have 300+ sunny days a year, but for some reason those trains full of coal keep rolling in...
posted by Locobot at 11:29 PM on July 27, 2010 [3 favorites]

The comments in the article have it best: spending more on preventing heat from entering the building in the first place is the most cost effective means of keeping our spaces cooler.

This may depend on where you are, in the UK (and simiilarly in much of Europe) we are looking at bringing in more efficient buildings, primarily to reduce heat loss rather than cooling, but it will be interesting to see how this impacts on summer conditions. in the UK we have seen the number of days commercial premises require air conditioning go up by about 1 day a year for the last 20 years, largely as a result of office equipment used within the building. So how will that interact with more thermally efficient buildings? At the same time however, the forward looking models for thermal demand by these premises tends to assume that equipment heat output will drop off over time as efficiencies improve.

One other potentially interesting point in Europe is that many states seem likely to have to introduce policies to stimulate renewable heating technology (solar thermal, heat pumps, biomass boilers, etc) as part of their commitment to hitting the EU target for 20% of all energy use to come from RE by 2020 and that some of there systems have the potential to also act as cooling providers (reverse cycle heat pumps for example, improving the economics not only as they substitute for A/C but also as they improve the efficiency of the heat pump).

Genereally the economics of renewable cooing are pretty weak, with little in the way of installed capacity even in Mediterranean states.
posted by biffa at 1:27 AM on July 28, 2010

I suspect our children and grandchildren will marvel at our failure to cool environments using the energy generated by whatever is making them too warm. Why on earth would you not build a car with AC that is powered by solar energy or engine waste heat for example?
posted by rongorongo at 2:27 AM on July 28, 2010

I recently saw a brief science news story on an alternative method of air conditioning used in Japan.

In the winter, they plow the snow from the surrounding roads into an insulated building and then use that stored snow to cool buildings in the summer.

Apparently, this elegant system had been used in the past, and is referred to as an ancient technology in this article about a similar system in Sweden.
posted by fairmettle at 3:22 AM on July 28, 2010 [1 favorite]

"i havent seen blades made from metal (as opposed to plastic) since the 80s."

I think it is the shape rather than the material. The plastic blades you see in fans would essentially lie flat if you were to heat them to where they were pliable. What the article is getting at unless I'm mistaken is that a shape with volume similar to that of an airplane propeller is more efficient.

The one that boggles me a bit is the propane powered refrigerator with no moving parts. I need an animation.
posted by vapidave at 4:29 AM on July 28, 2010 [1 favorite]

This is just a trick to get me to buy one of those cool Dyson fans for a million bucks, right?
posted by inturnaround at 6:02 AM on July 28, 2010 [1 favorite]

The one that boggles me a bit is the propane powered refrigerator with no moving parts. I need an animation.

The ones that I've seen use the heat from burning propane to drive a small Stirling engine, which pumps the refrigerant through the system.
posted by kuujjuarapik at 6:37 AM on July 28, 2010

Most air-conditioners using refrigerants consume lots of electricity because they employ mechanical compressors, which are piston-like machinery that squeeze the heated vapours. This turns the refrigerant back into its cooler liquid state to be used again.

Science journalism fail. Ruined the rest of the article, how can it be taken seriously when that sentence is there, mocking me. Maybe its splitting hairs but compressing just about anything makes it hotter, not colder. PV=nRT, making the volume smaller is gonna make the pressure and temperature greater. The only reason the liquid cools is that it goes through a heat exchanger with a fan blowing over it. And that only gets it somewhere in the area of there surrounding atmosphere's temp. The real cooling comes when the liquid is allowed expand into a gas again.

Also, I highly doubt the fan uses anywhere near as a much power as the compressor. It takes a fair amount of energy to compress a gas, its pretty easy to blow some air around. A 1/3 power savings by improving fan blades seems absurd, I don't think this guy knows what he's talking about. I bet somebody told him fan blades would save 33% on the fan motor's power consumption and he was all like, ZOMG 1/3 powah savings, somebody phone Al Gore!
posted by no_moniker at 6:47 AM on July 28, 2010 [1 favorite]

Seem to be a lot of people getting hold of the wrong end of the stick. While I'm dubious about these claimed fan savings, they're at least not completely absurd. As kafziel said:

If a more efficient fan blade design means less power usage, not because it's easier to turn but because turning it accomplishes more

If a better fan meant that the whole system worked 50% better for the same power consumption, you'd presumably be able to translate that into a 1/3 power saving. The actual consumption of fan itself is irrelevant.
posted by howfar at 7:06 AM on July 28, 2010 [1 favorite]

Whoa, who knew HVAC nerds were so touchy?
posted by Locobot at 7:19 AM on July 28, 2010

i havent seen blades made from metal (as opposed to plastic) since the 80s.

Clearly you do not have central air conditioning. Go to any subdivision, look at the central air units in the back of the house. Metal blades.
posted by spicynuts at 7:29 AM on July 28, 2010 [2 favorites]

If a more efficient fan blade design means less power usage, not because it's easier to turn but because turning it accomplishes more

If a better fan meant that the whole system worked 50% better for the same power consumption, you'd presumably be able to translate that into a 1/3 power saving. The actual consumption of fan itself is irrelevant.

Total Power = Power(fan) + Power(compressor). (We'll put anything like a pump, etc. in with the compressor.)

You're saying that moving more air lowers Power(compressor). This could be true, but only if the system were poorly designed. As mentioned above, the refrigerant, in the heat exchanger of which the fan is a part, won't get any cooler than the surrounding air. If the refrigerant leaves this heat exchanger at much above ambient temperature, then that is an inefficiency that could be solved by enlarging the heat exchanger or by pushing more air over it. I'm no cooling engineer, but I highly doubt this would be overlooked by a designer unless there were strange constraints on the design of the heat exchanger.

In short, the heat exchanger, of which the fan is a part, is most likely already doing the best job it can do, in that it gets the refrigerant down to the ambient temperature. Pushing more air won't improve it. Basically, Power(compressor) won't be reduced by anything you do with the fan. All you can do with the fan is reduce Power(fan), which is a very small part of the total power.

I welcome someone who knows more about this than I do correcting me. Maybe normal A/C units do have constraints on their heat exchangers that can't be worked around by just blowing harder. In any case, it's fun to argue things on the internet about which you know very little!
posted by whatnotever at 8:17 AM on July 28, 2010

"If a better fan meant that the whole system worked 50% better for the same power consumption, you'd presumably be able to translate that into a 1/3 power saving. The actual consumption of fan itself is irrelevant."

That's not how it works. The refrigerant cycle components don't care how the air passing over a coil is moved. (Some coils don't even use air, they are cooled by water.) The coil could care less whether those CFMs are being provided by a regular fan, a super efficient fan or rat farts. So all energy savings would have to come from the reduced power consumption of the fan motors via the more efficient fan blade. Even if 1/3rd of the electricity use of the system were from the fans (which it isn't) you'd have to completely eliminate the fans to get that kind of power reduction.

PS: the fan blades in central systems are already fairly sophisticated. The big flattish blades in condensing units feature compound curves and the evaporator fan (IE: furnace blower) is a squirrel cage.
posted by Mitheral at 8:17 AM on July 28, 2010

I suspect our children and grandchildren will marvel at our failure to cool environments using the energy generated by whatever is making them too warm. Why on earth would you not build a car with AC that is powered by solar energy or engine waste heat for example?

Becuase the ability to extract significant energy (rather than just increasing the load on a gasoline engine by 2% to run your AC) out of waste exhaust gasses has been tested and the equipment needed would be so heavy as to reduce fuel economy dragging all that weight around, and add significantly to to the complexity of the car, driving up costs.
posted by lalochezia at 9:16 AM on July 28, 2010 [1 favorite]

Any aerodynamics geek will tell you that at the speeds of ordinary fans there just isn't much efficiency to be gained, a properly curved flat plate works just fine. It's only when you're dealing with hundreds to thousands of horsepower -- aircraft propellers/rotors and gas turbines -- that you can improve significantly on a curved flat plate.
posted by phliar at 10:00 AM on July 28, 2010 [1 favorite]