John M. Steele
Mon, 09 Aug 2010 04:10:43 -0700
I agree with Martin's response, but the more immediate effect to you is that you are heating at electricity rates, which are normally much higher than natural gas or other heating fuel rates. Use the electricity you need to, but the waste heat is a cost-ineffective offset to heating fuel use in winter and pure waste in the summer. ________________________________ From: Carleton MacDonald <carlet...@comcast.net> To: U.S. Metric Association <usma@colostate.edu> Sent: Sun, August 8, 2010 9:23:19 PM Subject: [USMA:48340] RE: Air-conditioning On the other hand, in winter, wouldn’t all that heat mean the furnace has to run less often? Carleton From:owner-u...@colostate.edu [mailto:owner-u...@colostate.edu] On Behalf Of Stanislav Jakuba Sent: Sunday, August 08, 2010 15:34 To: U.S. Metric Association Subject: [USMA:48339] Air-conditioning Undoubtedly, the USA members on this forum noticed the flood of air-conditioning energy-consumption news. I responded to one of these. That Letter to Editor is below, and I am adding a paragraph beneath it for USMA that addresses SI units. Letter to Editor: The "How Air Conditioning Is Sapping Our Society" omitted one reason for the skyrocketing air-conditioning electricity consumption. It is not just the growing number of air-conditioned homes that contributes to the steep rise, it is also the higher electricity consumption in homes. And in commercial buildings for that matter. As everyone was taught in school, all electricity at home changes into heat. Thus the electricity consumed by each lightbulb, TV, stove, computer, freezer, down to the cell-phone charger, heats the building interior thereby raising the temperature if the walls are not "cooling" such as in hot weather. More then in the past, these electricity consuming devices are left on longer such as lights burning during daylight for decorative purposes, computers and TVs always on (and when off they still consume electricity unless unplugged), icemakers running at full tilt, dishwashers providing electrical drying, etc. In commercial buildings, there are more lights, more computers and devices on 24/7. In supermarkets there are heat blasting bakeries, cooled food counters, drinking water and soda-fountains, freezers, etc. whose coolers are not vented outside. The heat the compressors in these devices generate must also be removed by the main air-conditioners in addition to their basic load of cooling people, walls and ceiling. It all adds. Air-conditioners use close to the same amount of electricity for the removal of heat as is consumed by the individual appliances. To illustrate, it takes between 50 W to 100 W by the air-conditioning compressor motor, fan and controls to remove the heat flow a 100 W lightbulb produces. Total power: up to 200 W. Conversely, a simple turning off (better yet, unplugging) appliances in the hot, humid weather saves up to twice the amount of electricity they would consume. And it is not just air-conditioners that gobble electricity for cooling. Ice makers are another culprit. About 1 kg of ice is melted/made for every person in the US daily. If melted inside the home, some of the energy helps cooling the interior but most of the ice goes "down the drain" cooling the underground and picnic grounds. I calculated that 2.5 GW is utilized for ice making in the US. That is more than the capacity of the nuclear power plants in Connecticut combined. Or, to involve renewables, the power of some 12 500 typical wind mills. Lastly, the misuse of fans. Leaving a 500 W fan on in a closed room when nobody is there, as is often done in homes, schools, and businesses, is not cooling it. To the contrary, it is adding 500 W to the room thereby heating it. It is the evaporation from skin and convection that cools us; the wind only intensifies it. When there is an air-conditioner on concurrently with the fan and nothing to evaporate, another 500 W load is added to the compressor, a total of up to 1 kW more is spinning the meter. USMA members will appreciate this addition: Many writers of the air-conditioning, energy-consumption analyses illustrate the numbers on the example of the 100 W lightbulb as above. Then they take the Btu rating of an air-conditioner and thru convoluted conversions among various energy and power units provide a number in yet another unit. In the analyses, they often refer to Btus and omit specifying whether it is Btu per something such as per hour or minute. Contrasting, the “tons of refrigeration” is treated as an energy unit. And sometimes units are invented as if these I-P-units numbers were not hard enough to compare even if the terminology were unified. Why, oh why, don't writers recognize that since all (or most) electricity coming to a house changes to heat, and that both electricity and heat can and should be measured in the same unit? If they did, one would learn that to remove 100 W heat flow coming from that lightbulb requires up to 100 W electricity flow into the air-conditioning unit to power its fans, compressors, and controls. That would reduce the usual gibberish to the simple "a 100 W lighbulb, if lit, requires up to 100 W of electrical power to remove its heat in hot weather." To be a bit more informative, a writer could add that if the electricity comes from thermal power plants, it takes 300 W of fuel energy flow to power the 100 W lightbulb and consequently 300 W to power the air-conditioner, or 600 W altogether. And perhaps also hint that a person contributes about 100 W sitting idle. Not much can be done about the latter load short of going outside, which, come to think of it, may be healthy as well as frugal. The impact of metabolism is obscured by the usage of the DV measured in Calories (or calories) in the U.S. so that nobody can correlate that heat production to cooling without converting. Stan Jakuba