There’s the temperature differential

Apparently some Europeans think that air conditioning uses more energy than heating. Well I suppose it depends on what is meant by that. If they meant that so many more people use air conditioning than the number of people who use home heating (and whether that’s true or not I have no idea, and I absolutely don’t care) then they could be right due to overwhelming numbers, but in terms of average Southern home cooling verses average Northern home heating, no way.

The typical AC scenario involves maintaining a far smaller temperature difference than the typical heating scenario.

It’s below freezing much of the time here in North Idaho, for example, from November through February, and it is often well below freezing. Freezing can and often does occur from September into May. Occasionally it is below zero F and sometimes it gets to thirty below.

From freezing outside to 72F in your home is a difference of 40 degrees F. Most people tend to be OK with 80 degrees inside while using AC. How hot does it ever get in any vaguely typical city, ever? To reach that very typical 40 degree differential for home heating would mean that it would have to be 120F outside and 80 inside while cooling. That is not what I would call common.

When the temp is zero F outside, which happens for up to weeks at a time in much of the U.S. in winter, that’s a 72 degree difference. To ever even see a 72 degree difference in AC usage, it’d have to be 152F outside. To equal the difference from a not-at-all rare 30 degrees below zero, it would have to be 180 degrees outside and 80 inside for our AC scenario. In some parts of the U.S. it gets a lot colder than 30 below, but I’m pretty sure it doesn’t get to 180 anywhere, without the aid of a volcano or a fire.

Not bloody likely then, is it, that it should require more energy to cool than to heat? Energy-wise, it’s mainly about the temperature difference that is being maintained, so if someone is yapping about the subject and they’re not mentioning temperature differentials, they’re either blind or dishonest, or both.

It just occured to me; in the north we are careful to insulate our ceilings well, and tend to put our HVAC outlets in the floor, whereas in a hot climate it would make more sense to extra-insulate the floor and put the outlet vents in the ceiling.

30 thoughts on “There’s the temperature differential

  1. You are correct that heat loss/gain in most cases is directly proportional to the temperature difference. But unless you are using a heat pump to heat with you get far more BTU removed using the AC per joule of electricity consumed than you do when heating directly with something like baseboard electric.

    Hence AC uses far less energy than heating if you have somewhat cold winters.

    • Yes; thank you.

      What Joe is sayiing, again, (and correct me if I’m wrong) is that you can move more heat that the energy it takes to move it, if you’re using a heat pump, and so it is at least in theory possible to achive “greater than 100% efficiency”. All compressor type air conditioning uses a heat pump.

  2. you forget commercial high rises, covered in glass. i think if you look it up, more electricity is consumed by “air conditioning” than by heating. that’s what i’ve read. i suppose i really don’t know.

    you should look it up.

    p.s. i live in a 75 year old house, in n.e. oregon. it has no air conditioning, except for a free standing unit in one room. it knocks the temperature down to aroud 80 on a very hot day. the rest of the house is around 90 on a very hot day. one just uses the old fashioned way of dealing with it …. retreat to the basement, or, perspire. simple, really.

    great for setting epoxy on a hot day.

    • IIRC, those tall buildings run AC to counter the solar heat that passes through all the glass, but mostly due to the heat generated by all the lighting, and body heat from the occupants.

  3. I’ll give a Florida datum.

    Summers are about 93-96 or so and we set our house at 75. So less than 20˚ differential most days.

    Spring and fall are more like ten degrees difference, because the AC remains on even though it’s cooler because the humidity makes it seem like it’s much warmer.

    In the winter we still trend that 10˚ differential in the other direction as the house gets heated (though most times just normal life does it and not the heat in the HVAC).

  4. In hot climates, the insulation still goes in the attic and walls. It insulates from the heat of the sun. The AC registers are in the ceiling as well, because Florida homes have no basements. The water table is too high.

  5. Not bloody likely then, is it, that it should require more energy to cool than to heat?

    This assumes a furnace and an A/C unit use the same amount of energy to change the air temperature by one degree.

    • Actually, cooling with an A/C compressor system (or heating, on the heat pump side) is MORE efficient in that regard. A/C – HP systems move heat around, so you can get multiple BTUs where you want them per input watt, whereas electric heat generates heat at the source, 1 watt in = 1 watt out.

      To take an example from a job I’m doing right now, an A/C unit generating 36K BTUs of cooling requires a total input of just over 5.1 kW, which translates to about 17.5K BTUs @ 208V. Just over 2 BTUout / BTUin.

      So the combination of temperature differential and efficiency is a double whammy on the Europeans. As if we cared what they think.

      • I admit to being innocent of the knowledge of what percentage of residential heating is electric versus gas. I don’t think I’ve lived anyplace that heats with electric in fifteen years, but I imagine most newer construction is electric?

        • Depends on what area of the country you’re talking about, and whether natural gas is available. Most places NG is a first choice due to cost, or a heat pump with backup electric heat for when it’s too cold for the HP to operate. IDK if anybody’s first choice is straight electric heat.

          • And, don’t forget dual-fuel systems, and “accessory systems.” The builder of my abode took the cheap way out – a heat pump to cover both AC and heat, and as is common, the heat side used electric resistance to bridge the gap between falling HP efficiency below about 38F and the heating demand (there are now “cold climate” heat pumps that maintain good eficiency down to +5-10F, and yes, they’re more expensive than regular HPs). I replaced the HP air handler/electric resistance “furnace” with a high efficiency NG condensing furnace for two reasons: it’s cheaper than electric resistance and the NG furnace (incuding blower) draws 13 amps at 115 volts – in a power failure I can run the gas furnace, fridge and freezer easily with a 115V 3K watt generator, and in an extended outage NG delivery is more reliable than electric (when I was in FL the threat was hurricanes and thunderstorms – here it’s ice storms). I cannot afford a generator big enough to run the 240V heat pump or electric resistance heat. The new thermostat has an outdoor temp sensor and switches from HP to NG at 40F, but I can control that in 5F increments from 10F to 70F, and manually switch entirely to NG by selecting (“emergency heat” at the thermostat.

            Spring and fall here (mid-Atlantic, on the lower eastern slope of the Applachians) are a PITA – too warm to need heat, too cool to need AC – but the humidity remains. With the NG furnace I also put in a whole-house dehumidifier, controlled through the same thermostat. I can select indoor humidity levels from 45% to 80%, usually just leave it on 50%. According to my Kill-A-Watt the dehumidifier costs about $15-17/month to run during the months I need neither heat nor AC, much less when the AC is performing the dehumidifying function.

        • It also depends on what you mean by “electric”.

          There’s baseboard electric, a.k.a., “resistance heating”. which is 100% efficient — it turns electric energy in to the same quantity of heat. As a system, it isn’t particularly economical — the reason is that generation of electricity (from heat) is only about 40% efficient, and there are transmission losses on top of that. So even though residential fuel is more expensive than power plant fuel, heating with oil or natural gas is more economical.

          But there are also heat pumps — air conditioners and refrigerators are the same device. These run a compression/expansion/heating/cooling cycle that moves energy from the cold end to the hot, or vice versa. The efficiency of this process depends on the temperature differential, and is way above 100% for modest temperature differences. So you can (and people do) use a heat pump not just for air conditioning but also for heating. And that is a good option if the climate is moderate. I don’t think you see much of this in New Hampshire, but you probably do further south.

          • My dad, at fairly high expense, put in a heat pump in his north Idaho home. We don’t have mild winters there. The expensive part was the, IIRC, half mile of underground pipes to exchange heat with the dirt several feet below the surface.

          • That’s different. That’s a geothermal heat pump. The efficiency of a heat pump depends on the temperature differential it is acting on. In a simple AC system, or analogous heat pump, that’s the difference between inside and outside air temperatures. But if you use an underground heat exchange as your external temperature reference, you have a differential very different from that of the outside air — one that’s much smaller in most cases. So your efficiency goes up.
            If he had used an air-referenced heat pump, he’d be paying a lot in mid winter. With this setup, the running should be quite economical (though the capital investment is substantially higher).

          • Yes. It is different. That is why I mentioned it.

            I got an A+ in my thermodynamics class. I understand the principles very well. But the explanation was probably useful for others.

  6. I hate to keep quoting the same thing, but when you say, “…if someone is yapping about the subject and they’re not mentioning temperature differentials, they’re either blind or dishonest, or both.”

    All I can think of is Rand’s stating that, “…they are neither blind nor innocent”.

    They are, plain and simply, lying when they say that A/C takes more energy than heating. We can look at it in terms of degree-days of either heating or cooling, we can look at relative efficiencies of heating versus cooling, and a huge variety of other factors. It’s quite simple: We use FAR more power (measured in BTU/Hr, kW, dyne-centimeter/second, or any other unit of power) to heat than we do to cool.

    They’re not stating physical facts, they’re simply making clear the standard collectivist, statist position that Western Civilization is evil, that humanity in general is a plague on the planet, and that they are far superior to us ordinary mortals because they have the Vision of the Anointed ™.

    Here in Minnesnowta we heat with natural gas, (relatively new furnace/boiler, fairly efficient) and cool with a mini-split A/C (incredibly efficient). For the electrical bill, running the A/C adds only a few dollars per month to the baseload usage. For the gas bill, running the furnace takes the gas bill from $30 to upwards of $120. A really cold January sends that bill to over $150 if the temperatures stay below zero (as they’re known to do for weeks on end).

    It’s simply liying in order to gain control of other people’s lives, and it’s evil.

  7. When I read about the Europeans crying and moaning about my AC use I had 1 comment.
    “Turn off the AC? Is Texas. Is Hot. Most Days. And Nights. Fuck You Europe.”

    Sorry for the profanity. But until those morons live where hot means something other than a nice 85°F they can kiss my fat ass.

    • No doubt. My wife and I visited Europe in July a few years ago. We brought typical summer clothes and ended up having to buy long pants and shirts because it turned off 45 degrees in Vienna….

      • When I was stationed in Germany I always felt cold. There’s something in the air there that chills even it the temperatures are mild.

  8. “Most people tend to be OK with 80 degrees inside while using AC”

    I would have to disagree with that. 80 degrees here in AL in August, inside or out is pure misery. Typical temperature is 90-95 degrees with terrible humidity. With only a 10-15 degree temperature differential, the AC doesn’t run as much. The concurrent result of that is that the AC doesn’t remove was much of the humidity from the air.

    I’ve seen people go on long vacations with the AC set at 80, only to come home to mildewed furniture and the like. Short periods at those temps are OK but at some point you have to pull the humidity out of the house….

  9. Of course, the big environmental cost of A/C isn’t the use of energy, it’s Glowball Warming! Say it’s a typical Tucson, AZ summer day of about 115 degrees, and you reduce the temp of your home’s interior to a livable 75. And so do all your neighbors – where does all that interior heat go? Directly to the polar ice cap, where it melts the pack ice, drowns polar bears, and warms up the baby seals!

    So – turn off your A/C to save the baby seals!

  10. Another factor that may or may not make a difference is the use of alternate fuels for heating, that aren’t usable for A/C or cooling.

    We run our heat pump in the summer to cool the house. This uses electricity. I’ve never found an A/C unit that runs on anything else.

    In the winter, though, we primarily heat with a wood-burning stove. This does not use electricity (except for a few rare occasions when a draft or VERY cold night will cause the heat-pump/electric-furnace to kick on, but that’s the exception, not the rule). Other homes may use natural gas or oil furnaces, which use very little electricity (mostly for monitoring temperature and pushing the air around).

    Thus, our home uses more electricity for cooling than for heating. This fact is reflected in our utility bill.

    I won’t claim that the sum of all (or even most) buildings matches our experience, but the use of non-electric heat is a factor to consider.

    • Exactly. I would bet that if you look at the power draw from the electrical grid only, there is much higher utilization for cooling than for heating. This is would be because a lot of people use other means of heating the house. Wood, natural gas, heating oil etc.

      Of course a lot of climates cooling of course costs more than heating because you almost never have to heat. What is the average Floridian’s cost for heating vs cooling for instance?

  11. I should point out that the main point here, which is implied but not explicitly iterated in the post, is that this “cooling uses more of our precious and limited energy resources” meme was created to support the AGW (Anthropogenic Global Warming) hoax.

    Blackwing1 and Defens made the point too, but I’m acknowledging it. It’s a lie to support a lie, and because this one is so easily exposed, I’ll take it is a gift.

    So thank you, Progressives, for once again making it crystal clear that you are liars (but you know you can’t help it – you’ll expose yourselves more and more in the future too, out of pure arrogance and pride – you have no choice).

    • Catastrophic anthropogenic global warming.
      Because if it isn’t catastrophic, who cares?
      Besides the frothingmouthed human-hating enviro-leftists, I mean.

      • Good point. A lot of people at high latitudes would welcome some long-term warming (which would in turn reduce their heating costs for one thing). From now on I’ll call it CAGW. As you say, catastrophe is the main feature.

  12. The article in the post starts off by claiming that the weather in Berlin has been similar to that in Washington DC. If that is the case it must be unusually warm in Berlin and unusually cool in DC. Looking at the average daily high temps for the two cities shows that the average for DC exceeds the peak July average for Berlin from mid May to late September. In other words, Berlin never gets as warm as the air conditioning season in DC. The article starts off with a statement that, if not an outright lie, at least demonstrates that the writer does not understand what he is saying.

  13. Air conditioning primarily removes humidity — which is very high in much of North America. If all it did was cool the air, you’d still be miserable. Here in Indiana, with gas heat and conventional air conditioning, my utility bills total about the same Summer and Winter.

    The EU doesn’t get a vote

  14. Pingback: SayUncle » Others react to Europeans thinking air conditioning is stupid

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