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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hey all!<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Something new occurred to me recently triggered by a photocell scheduling question. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>To ground and set up this idea – first check out this interesting online visual explaining how annual day/night hours vary based on latitude… play around a bit with the bars to see how daylight hours vary based on latitude and time of year: <a href="http://astro.unl.edu/classaction/animations/coordsmotion/daylighthoursexplorer.html">http://astro.unl.edu/classaction/animations/coordsmotion/daylighthoursexplorer.html</a><o:p></o:p></p><p class=MsoNormal>Note that regardless of location, the yearly average on a daily basis always works out to 12 hours.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Now take the typical case of a simple ON/OFF photocell control for exterior lighting. From an exterior lighting control standpoint, the model linked above is simplified from reality in that the effects of cloud cover/weather are not accounted for. While the sun on a given day may officially set at 6PM, for example, overcast cloud cover, rain, smog, fog and similar conditions may cause a photocell to turn on the exterior lights hours earlier, by reducing the daylight illumination reaching the photocell/ground. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Based on some explorations – the current PHOTOCELL-CTRL schedule appears to demonstrate something like a “simplified” model per the above link, assuming clear skies. I’m observing approximately 12 hrs of photocell operation per day averaged over the year for different locations’ TMY weather files (slightly less, actually… ~11.95). I would assume by extension it’s using a function based on the location’s latitude or perhaps referencing something like the “sun up flag” in the weather files. Does this jive with what anyone knows to be going on under the hood?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>If my understanding is correct, I would like to suggest a few improvements for present discussion and future development:<o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>First I think it’s worthwhile to retain the “clear sky” PHOTOCELL-CTRL function as it currently exists – I can conceive applications where a simplified “on when the sun sets” model could be both desirable & useful, such as in comparing output with simple daylight simulation models. It could also perhaps be more specifically named “ASTRONOMICAL-CTRL” in reference to mechanical/digital astronomical timeclocks which calculate daily on/off times very much like the animated model linked above.<o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>An improved PHOTOCELL-CTRL scheduling function could be defined working around the following:<o:p></o:p></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>a.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>It’s my understanding that weather files may contain hourly measured illuminance readings that inherently account for cloud cover and other weather conditions. <o:p></o:p></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>b.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>Actual photocell systems will turn on and off at prescribed, sometimes different levels. For example, here’s a link to a product which turns fixtures on at 3fc and off at 8fc, with a nominal delay to minimize nuisance cycling: <a href="http://www.cooperindustries.com/content/dam/public/crousehinds/Industrial%20EX%20Products/Catalog%20PDFs/Lighting/Photocells%20for%20Champ%20HID%20Luminaires.pdf">LINK</a>. The equipment literature I’ve checked cite values from 1fc to 10fc. <o:p></o:p></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>c.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>Per the above, an improved PHOTOCELL-CTRL scheduling option could accept inputs for one (possibly two) exterior footcandle levels to define on/off behavior. Hourly ON/OFF behavior could then be determined directly referencing the exterior hourly horizontal ground illuminance measurement from the weather file used, switching lights when the appropriate threshold is crossed.<o:p></o:p></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1'><![if !supportLists]><span style='mso-list:Ignore'>d.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>Such a scheduling option could more accurately gauge the full impact of exterior lighting retrofit and controls upgrades. This is often relatively low-hanging fruit, in my experience.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>A related query for the weather gurus: I’m uncertain whether TMY weather files, representing averaged data over many years, would be particularly constructive or not for representing the effects of cloud cover and so forth… Growing up in FL, I recall a definite “rain-season” mid-summer which I expect would be captured in the daylight measurements of any FL weather station… but where weather/cloud cover is much less regular (such as here in KS), perhaps the effects would be lost in averaging?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thoughts?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>~Nick<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img border=0 width=119 height=37 id="Picture_x0020_1" src="cid:image001.jpg@01CCD9BC.FC033750" alt="cid:489575314@22072009-0ABB"><b><span style='font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p></o:p></span></b></p><p class=MsoNormal><b><span style='font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p> </o:p></span></b></p><p class=MsoNormal><b><span style='font-size:12.0pt;font-family:"Stylus BT","sans-serif";color:#2D4D5E'>NICK CATON, P.E.</span></b><b><span style='font-size:12.0pt;font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:7.5pt;color:#CC9900'>SENIOR ENGINEER<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:7.5pt;color:#CC9900'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>Smith & Boucher Engineers</span><span style='font-size:7.5pt;font-family:"Times New Roman","serif";color:#CC9900'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>25501 west valley parkway, suite 200<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>olathe, ks 66061<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>direct 913.344.0036<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>fax 913.345.0617<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><a href="www.smithboucher.com" title="blocked::www.smithboucher.com"><span style='font-size:10.0pt;color:blue'>www.smithboucher.com</span></a></span><u><span style='font-size:10.0pt;color:blue'> </span></u><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>