jimmytavino 16 #1 July 12, 2011 contribute to the oppressive heat conditions???? I see 90's all over the US Map today, and 100 and even 110's in the south and Over the Texas OK and New Mexico areas.. i KNOW that summer = Heat ! but i was wondering just HOW MUCH does the exhaust coming off AC units... especially rooftop mounted systems of HUGE capacity.. contribute to RAISIng the ambient air temps,, in the first place. have never measured to see what the temperatures ARe for the exhausts from an AC machine, but i have to believe that as we cool interior space, we HEAT up the exterior, which then requires More cooling and so the cycle just continues.. Anyone able to guess what percentage of commercial Buildings in The South use Central Air??? ( i would guess over 75 % , maybe More ) and any guess about the percentage of AC use in residential properties???? i know it's a function of economics but do Poorer folks have to endure ADDED discomfort, cause the AC units in their areas are ADDING heat.. while they cool living/working space..?/ Could be that exhaust heat is inconsequential, but maybe the heat in the outdoor air is generated by MORE than just Mother NAture... comments???/ jmy Quote Share this post Link to post Share on other sites
piisfish 135 #2 July 12, 2011 how much heat and pollution is caused by drivers who leave their engines + A/C on while they are parked for some shopping ?? how much additional pollution/fuel consumption only when driving with the A/C on (which you could turn off once the car is fresh inside and you are driving at good speed... (I must have a total of 10 annual hours use of A/C in my car) scissors beat paper, paper beat rock, rock beat wingsuit - KarlM Quote Share this post Link to post Share on other sites
normiss 622 #3 July 12, 2011 Feeling guilty for buying the a/c system Jmmy??? Quote Share this post Link to post Share on other sites
jimmytavino 16 #4 July 12, 2011 Quote Feeling guilty for buying the a/c system Jmmy??? Hell NO my friend !!!! i have Plenty of OTHER things to feel Guilty about.....but finally getting central air in our house, after 20 something years. is NOT one of them !!!!! the couple of window units,,, just weren't getting the job DONE... still,,, around here,,,,,,,we do NOT get temps in the 90s for the same extended lengths of time, like You folks.... and almost NEVER hit 100... I cannot fathom.... how those in Texas can TAKE it !!!!especially Day after DAY !!!true enough about automobile AC... that must ALSo add to the outdoor temps... HOW much of this "people generated" warm air rises Up and into the atmosphere??? a bunch i'd guess!!! stay COOL folks....jmy Quote Share this post Link to post Share on other sites
skydiver30960 0 #5 July 12, 2011 You forget the units aren't necessarily "adding" heat, they're just "moving" heat from inside to outside. So, while there's heat outside, there is cooler air inside. Sooner or later, though, the heat of the residence re-equilibrates, so there is no net heat change when you look at the world as a whole. EXCEPT: that damn entropy. There is no perfect machine, and despite the fact that Newton told us energy cannot be made or destroyed (don't get me started) we know that some of the electrical energy, when used by the machine (the A/C unit) is lost as waste heat through friction. So, in fact, running an A/C unit does generate a net positive heat gain, even though we use it to cool an area down. Now: are all the a/c units in the world putting out so much waste heat that they're somehow competing with the sun as a heat source? Negative ghostrider, the pattern is tiny. Elvisio "my past life in engineering haunts me" Rodriguez Quote Share this post Link to post Share on other sites
DougH 270 #6 July 12, 2011 I agree, the major impact of an AC is moving heat from inside a structure to outside a structure. Sure they create some additional heat through friction and resistance, but it is minimal. Way more heat created by manmade structures, roads, driveways, buildings. Our cities are their own little heat islands!"The restraining order says you're only allowed to touch me in freefall" =P Quote Share this post Link to post Share on other sites
skyjames 2 #7 July 13, 2011 Quotebut i was wondering just HOW MUCH does the exhaust coming off AC units... especially rooftop mounted systems of HUGE capacity.. contribute to RAISIng the ambient air temps,, in the first place. Actually the energy making the power to run these units (lets argue a 10 megaton sys) which would be airport sized (small airport) produces more wast heat than the units running. Todays systems are so efficient you would not believe it. Plus most newer systems have heat recovery which lowers power consumption Then there is co-generation, but you didn't mention them. The waste heat from the roof tops is mixed with fine water vapor. This evaporates, which produces... ahh hell with it, I say let them all sweat and I would not have to be on that damn roof fixing the heat producers :) "exit fast, fly smooth, dock soft and smile" 'nother james Quote Share this post Link to post Share on other sites
kawisixer01 0 #8 July 13, 2011 QuoteI agree, the major impact of an AC is moving heat from inside a structure to outside a structure. Sure they create some additional heat through friction and resistance, but it is minimal. Way more heat created by manmade structures, roads, driveways, buildings. Our cities are their own little heat islands! lol yup, you quickly figure this out when you ride motorcycles. Some nights get the shivers out in the country, yet warm right up when you come into a city. Quote Share this post Link to post Share on other sites
billvon 2,400 #9 July 13, 2011 >but i was wondering just HOW MUCH does the exhaust coming off AC units... especially >rooftop mounted systems of HUGE capacity.. contribute to RAISIng the ambient air >temps,, in the first place. Numbers I've seen indicates that A/C waste heat is a minor contribution (<1%) to the overall urban heat island effect. The big contributors are: 1) Blockage of re-radiation of heat at night due to all that insulation (i.e. empty floors) between the ground and the sky. 2) The urban canyon effect, where sunlight/heat is trapped by the "canyons" between buildings. 3) Loss of transpiration from plants and grasses. 4) Blockage of wind by buildings. 5) Change in albedo; often cities are a lot darker than the landscapes they replace, and thus absorb more heat. However, it is definitely true that urban heat islands end up requiring a lot more A/C due to higher temperatures. Some cities are starting to try to mitigate this with green roofs, white-painted buildings and light streets, and increased vegetation (think tree-lined streets.) Quote Share this post Link to post Share on other sites
billeisele 122 #10 July 13, 2011 QuoteSure they create some additional heat through friction and resistance, but it is minimal. Way more heat created by manmade structures, roads, driveways, buildings. Our cities are their own little heat islands! the cities don't "make" any significant amount of heat, they simply collect it, store it and radiate it longer than the surrounding environment the mass and color of the roads, sidewalks, building walls and roofs collect the heat all day and slowly radiate it for hours, just put your hand on a stone/brick wall a couple hours after the sun goes down and see how hot it isGive one city to the thugs so they can all live together. I vote for Chicago where they have strict gun laws. Quote Share this post Link to post Share on other sites
DougH 270 #11 July 13, 2011 QuoteQuoteSure they create some additional heat through friction and resistance, but it is minimal. Way more heat created by manmade structures, roads, driveways, buildings. Our cities are their own little heat islands! the cities don't "make" any significant amount of heat, they simply collect it, store it and radiate it longer than the surrounding environment the mass and color of the roads, sidewalks, building walls and roofs collect the heat all day and slowly radiate it for hours, just put your hand on a stone/brick wall a couple hours after the sun goes down and see how hot it is That is what I ment, I wasn't trying to suggest that the actual activity of the city was creating the heat."The restraining order says you're only allowed to touch me in freefall" =P Quote Share this post Link to post Share on other sites
Nutz 0 #12 July 13, 2011 You know if you use a magnifying glass in the sun you can burn ants? "Don't! Get! Eliminated!" Quote Share this post Link to post Share on other sites
normiss 622 #13 July 13, 2011 as well as the kid down the street. Quote Share this post Link to post Share on other sites
squirrel 0 #14 July 13, 2011 QuoteQuoteSure they create some additional heat through friction and resistance, but it is minimal. Way more heat created by manmade structures, roads, driveways, buildings. Our cities are their own little heat islands! the cities don't "make" any significant amount of heat, they simply collect it, store it and radiate it longer than the surrounding environment the mass and color of the roads, sidewalks, building walls and roofs collect the heat all day and slowly radiate it for hours, just put your hand on a stone/brick wall a couple hours after the sun goes down and see how hot it is i would submit that cities do "make" heat. (but really the energy is here, on the planet, already, we just change its form and location) and this is done through the lighting of the interior of the buildings. when a light "burns" it produces energy in the form of light, and heat (essentially the same, but not viewed as the same). the energy to power the lighting system came from outside the city. this heat must be "moved" to the outside of the building, but remains "in" the city. this "heat" load is small on a home, but take a minute to think about how many lights are in a, say, 30 story building. i remember this from my thermodynamics classes in school, and having to add the "lighting load" to a calculation to select the proper size cooling equipment for a structure. ________________________________ Where is Darwin when you need him? Quote Share this post Link to post Share on other sites
