I concur this Stephen’s suggestion. I was going to suggest something similar. In the end, economics and lock in inertia drive the uptake of anything to do with modifying roofs. Not something most people want to do unless other maintenance issues drive them to look at this.
David Sevier Carbon Cycle Limited 248 Sutton Common Road Sutton, Surrey SM3 9PW England Tel 44 (0)208 288 0128 Fax 44 (0)208-288 0129 <http://www.carbon-cycle.co.uk> www.carbon-cycle.co.uk This email is private and confidential From: [email protected] [mailto:[email protected]] On Behalf Of Stephen Salter Sent: 13 November 2017 09:30 To: [email protected] Subject: Re: [geo] Re: ?Micro-climate engineering? green roofs in cities Hi All Chameleons have got there first. Put two sheets of polythene together and run close lines of ultrasonic seem-welding to form an array of small diameter tubes. You can then pump air or fluids of different colours at different times of day to suit temperatures or your mood. District housing groups near airports can also sell advertising space. Stephen Emeritus Professor of Engineering Design. School of Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland [email protected], Tel +44 (0)131 650 5704, Cell 07795 203 195, WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change On 13/11/2017 00:19, Russell Seitz wrote: Alan, absent a white or green roof you might benefit as well from a wet black one-- Since your solar panels are designed to soak up as much of the solar spectrum as posible, their temperature may rise 25-50 C when the sun is high. As the temperature dependence of their internal resistivity naturally reduces their efficiency, and their conductive transparent coatings retard radiative cooling at night , it might be worthwhile to run the numbers on a water misted cooler roof On Sunday, November 12, 2017 at 2:45:12 PM UTC-5, Alan Robock wrote: Certainly white roofs and green roofs are not free, and the green ones require maintenance. I have 100% of my roof covered with solar panels, and they require no maintenance. My point was, for the same roof area, are white roofs, green roofs, or a roof with solar panels the best economic or environmental solution, making assumptions about the cost of electricity, the source of energy to heat or cool the home, SRECS, time of year, and climate of the installation? Alan Alan Robock, Distinguished Professor Editor, Reviews of Geophysics Department of Environmental Sciences Phone: +1-848-932-5751 Rutgers University Fax: +1-732-932-8644 14 College Farm Road E-mail: [email protected] <javascript:> New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock <http://envsci.rutgers.edu/%7Erobock> ☮ http://twitter.com/AlanRobock 2017 Nobel Peace Prize to ICAN! Watch my 18 min TEDx talk at http://www.youtube.com/watch?v=qsrEk1oZ-54 On 11/12/2017 12:24 PM, [email protected] <javascript:> wrote: > > Solar panels produce electricity at a cost. > > Most cool roofs save you energy and money at no cost. > > It is an economic comparison. > > Not all the roofs will be covered 100% with solar panels. > > Hashem > > Quoting Alan Robock <[email protected] <javascript:> >: > >> Wouldn't solar panels on your roof be preferable? Obviously they would >> create energy for you. But they would also shade the roof in the >> summer, preventing almost all sunlight from reaching it. One would >> then have to figure out the additional downward longwave from them to >> the roof, estimating the temperature of the bottom of them and their >> emissivity. Does anyone know of such a calculation? In the winter, >> the longwave would be good, as it would make up for the missing Sun. >> >> Ignoring the initial cost of the solar panels, would this be >> cost-effective in terms of cooling and heating a house? And if the >> cost were distributed over time, and accounting for the electricity you >> would generate, how long would they take to pay for themselves? In NJ >> we get SRECS of about $0.20 per kWh in addition to the electricity, but >> that changes with the market. And currently the Federal tax credit >> pays for 1/3 of the initial cost. >> >> Alan >> >> Alan Robock, Distinguished Professor >> Editor, Reviews of Geophysics >> Department of Environmental Sciences Phone: +1-848-932-5751 >> Rutgers University Fax: +1-732-932-8644 >> 14 College Farm Road E-mail: [email protected] >> <javascript:> >> New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock >> <http://envsci.rutgers.edu/%7Erobock> >> ? http://twitter.com/AlanRobock 2017 Nobel Peace Prize to ICAN! >> Watch my 18 min TEDx talk at http://www.youtube.com/watch?v=qsrEk1oZ-54 >> >> On 11/11/2017 6:27 PM, John Harte wrote: >>> I assigned that problem as a homework assignment in a course I teach. >>> >>> >>> 2. Consider a house in a relatively hot, sunny location such as >>> Southern California. >>> >>> a. To keep the house cool without air conditioning, and thereby >>> reduce energy demand, its inhabitants decide to do one of two things: >>> >>> i. They can paint the roof white, increasing its albedo from 0.1 >>> to 0.8, or >>> >>> ii. They can grow a green roof, using a productive species of >>> grass that will increase the albedo of the roof from 0.1 to 0.2 and >>> that, if watered and fertilized adequately, will cool the house by >>> transpiration. The rate of transpiration can be estimated from the >>> following: for every kg of grass produced, 300 kg of water are >>> transpired, and the grass grows with an overall photosynthetic >>> efficiency of 1%. >>> >>> a. Ignoring the issue of water supply, which of these strategies (i. >>> or ii.) will result in a cooler house? (20 pts.) >>> >>> Solution: 2. a. First, let?s examine the effect of painting the >>> roof white. We?ll assume an average solar flux on the roof of 250 >>> watts/m^2 (if you assumed anything between 170 and 300 we will >>> accept it.). By changing the albedo from 0.1 to 0.8, the home is >>> avoiding the absorption of 0.7 (250) = *175 watts/m^2 *, *which is >>> the benefit of plan i.* For plan ii., we need to estimate NPP on >>> the roof first. At 1% of available energy, the plants are converting >>> 2.5 watts/m^2 to biomass. Over a year, this is (2.5 joules/sec-m^2 ) >>> x (3.1 x 107 sec) = 77.5 x megajoules/m^2 incorporated into >>> biomass. Using the conversion: of 16 megajoules(dry biomass) per >>> kg, we find that biomass is produced at an annual rate of 77.5/16 = >>> 4.8 kg (dry biomass0/m^2 . Now using the 300:1 ratio of transpired >>> water to photosynthesized biomass, we get 4.8 x 300 = 1450 >>> kg(transpired water)/year. Transpiring a kilogram of water requires >>> about 2.4 x 10^6 joules (see COW Appendix) and so each year about >>> 2.4 x 10 >>> ^6 x 1450 = 3.5 x 10^9 joules/m^2 annually are causing transpiration >>> rather than heating the house. Expressed in power units, this is >>> 3.5 x 10^9 (joules/m^2 )/3.1 x 10^7 sec= *113 watts/m^2 , which is >>> the transpiration benefit of plan ii. *But there is also a small >>> albedo benefit of grass versus dark shingle, so we get an additional >>> benefit which is 1/7 of the plan i. benefit (due to an albedo >>> increase of 0.1 rather than 0.7), so now we have 113 + (1/7) 175 = >>> *138 watts/m^2 , which is the albedo benefit of plan ii.* *So plan >>> i. wins by a little. * >>> >>> >>> The problem went on to evaluate the added benefit if you burn the >>> grass on the roof for fuel. >>> >>> I actually replaced my dark shingle roof this autumn with >>> light-colored composition shingle. It makes a huge difference! >>> >>> >>> >>> John Harte >>> Professor of Ecosystem Sciences >>> ERG/ESPM >>> 310 Barrows Hall >>> University of California >>> Berkeley, CA 94720 USA >>> [email protected] <javascript:> <mailto:[email protected] >>> <javascript:> > >>> >>> >>> >>>> On Nov 11, 2017, at 2:22 PM, Russell Seitz <[email protected] >>>> <javascript:> >>>> <mailto:[email protected] <javascript:> >> wrote: >>>> >>>> How do green roofs, which cool by evapotransportation ( rooftop >>>> lawns require water much as those on the ground do) compare in >>>> cooling efficiency with higher albedo white roofs combined with >>>> an equal volume of water spraying when the sun is high? >>>> >>>> On Saturday, November 11, 2017 at 12:16:10 AM UTC-5, E Durbrow wrote: >>>> >>>> >>>> Perhaps, tangental. Seville planners think they can cool their >>>> city despite significant temperature increase with 204-700 >>>> hectares of green roofs. >>>> >>>> Summary: >>>> >>>> https://www.sciencedaily.com/releases/2017/11/171110113938.htm >>>> <https://www.sciencedaily.com/releases/2017/11/171110113938.htm> >>>> >>>> >>>> Comment: My layperson?s understanding is that it is very >>>> difficult to predict and simulate city-wide changes in >>>> temperature when a modification (e.g. reflective roofs, green >>>> space, etc) occurs. I though I remember that reading that >>>> reflective roofs might have no effect on local temperature >>>> (city?s micro-climate). Modelers, is this the case? >>>> >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "geoengineering" group. >>>> To unsubscribe from this group and stop receiving emails from it, >>>> send an email to [email protected] <javascript:> >>>> <mailto:[email protected] <javascript:> >. >>>> To post to this group, send email to >>>> [email protected] <javascript:> >>>> <mailto:[email protected] <javascript:> >. >>>> Visit this group at https://groups.google.com/group/geoengineering. >>>> For more options, visit https://groups.google.com/d/optout. >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "geoengineering" group. >>> To unsubscribe from this group and stop receiving emails from it, >>> send an email to [email protected] <javascript:> >>> <mailto:[email protected] <javascript:> >. >>> To post to this group, send email to [email protected] >>> <javascript:> >>> <mailto:[email protected] <javascript:> >. >>> Visit this group at https://groups.google.com/group/geoengineering. >>> For more options, visit https://groups.google.com/d/optout. >> >> -- >> You received this message because you are subscribed to the Google >> Groups "geoengineering" group. >> To unsubscribe from this group and stop receiving emails from it, send >> an email to [email protected] <javascript:> . >> To post to this group, send email to [email protected] >> <javascript:> . >> Visit this group at https://groups.google.com/group/geoengineering. >> For more options, visit https://groups.google.com/d/optout. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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