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<P>Hi Lars,<BR>
I'm a new user of eQuest so I can't answer all your questions, but I can answer your question about calculating the Coefficient of Utilization (CU). </P>
<P>The CU refers to how much light is available in the space. It takes into account the distance between the lamp and the working plane, which is called the Room Cavity Ratio (RCR), the efficiency of the light fixture and the reflectance of the wall, ceiling and floor surfaces. Shiny white surfaces have a higher reflectance that dark surfaces. </P>
<P>The first thing to do is to calculate the RCR using the following formula, which I copied from the following website:<BR>
<A href="http://www.lightingdesignlab.com/articles/formulas/useful_formulas_zonal.htm">http://www.lightingdesignlab.com/articles/formulas/useful_formulas_zonal.htm</A></P>
<P>Room Cavity Ratio = [(5)x(Cavity Height)x(Cavity Width+Cavity Length)]/[(Cavity Width)x(Cavity Length)]</P>
<P>The cavity height is the distance between the light fixture and the working plane. If the light fixture is recessed in the ceiling at a height of 8' above the floor, and the working plane is a desk at a height of 2.5' above the floor, then the cavity height is </P>
<P>8' - 2.5' = 5.5'</P>
<P>The cavity width and length are the room width and length. For example, for a cavity height of 5.5, length of 20' and width of 30' then:</P>
<P> RCR = [(5 x 5.5) x (20 + 30)]/(20 x 30) = 2.3</P>
<P>Most spec sheets for the lighting fixtures have a CU table. Check out the following website for a sample CU table:</P>
<P><A href="http://www.lightcalc.com/lighting_info/cu_tables/cu_tables.html">http://www.lightcalc.com/lighting_info/cu_tables/cu_tables.html</A></P>
<P>Click on the Lithonia LB240 CU Table. At the bottom of the table you'll see FCR (floor cavity refl) = 20%. This value is fairly typical.</P>
<P>Now you'll need to approximate the CCR (ceiling cavity refl). 80% is a good number to use for dropped white acoustical tile ceilings. 50% for the WCR (wall cavity refl) is also typical. If you use the RCR of 2.3 and the reflectance's listed above, you'll see that the CU is about 61%.</P>
<P>I don't know the answer to your 3rd question yet about daylight harvesting. It's something I need to learn so I'll update you if I find anything.</P>
<P>Lee<BR>
<BR>
Lee D. Consavage, PE <BR>
Electrical Engineer, Principal <BR>
Seacoast Consulting Engineers <BR>
261 Jennie Lane <BR>
Eliot, Maine 03903 <BR>
207-439-1721 ext 2 <BR>
Cell: 207-475-7054 <BR>
www.SeacoastEngineers.com <BR>
<BR>
For Renewable Energy Advice, Please Visit Our New Website: <BR>
www.BetterEarthEnergy.com <BR>
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<B>On Wed Aug 5 17:40 , "Lars Fetzek" <LFETZEK@PHOENIXENG.US>sent:<BR>
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</P></B>
<BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #f5f5f5 2px solid; MARGIN-RIGHT: 0px"><DEFANGED_META content="text/html; charset=us-ascii" http-equiv="Content-Type"><DEFANGED_META name="GENERATOR" content="MSHTML 6.00.2900.5848"><DEFANGED_BODY>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Hello, eQuesters,</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN> </DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> I have a few questions regarding how to model lighting loads. Bear in mind that I have treated each HVAC zone as a "space" and have modeled internal walls only along the edges of each such "space" regardless of architectural reality, so rigorous photometric consideration of daylighting, etc., would blow my budget with re-work. Thus, I'm trying to simplify.</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN> </DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> First question:</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> What exactly is the "Coefficient of Utilization" used in defining a lighting system? Is this simply a coefficient used to determine what fraction of the relevant lighting schedule's "on" time is to be used for calculating lighting energy use? For example, if a certain lighting system is modeled with a certain lighting schedule such that it would consume 100 kWh during a week, but a Coefficient of Utilization for that lighting system of, say 70%, is used, then does the model then calculate that that lighting system consumes 70 kWh during that week?</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN> </DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> Second question:</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> If my speculation in my first question (above) about the effect of the "Coefficient of Utilization" is incorrect, then what can I do to acheive that effect?</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN> </DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> Third question:</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> To acheive the effect discussed in the previous two questions (above) in particular application to daylight harvesting for LEED(v2.2), I will need to know what typical values are acceptable to the USGBC. ASHRAE 90.1 table G3.1 #6(g) references table G3.2, which does not mention daylighting. Table G3.1 #6(f) says that I may model this one of the following two ways: (1)..."modeled directly in the building simulation"... OR (2)..."modeled in the building simulation through schedule adjustments determined by a separate daylighting analysis approved by the rating authority." At this stage, option 1 is not realistic. If I try option 2, can anyone tell me how to know what "schedule adjustments" are acceptable to the "rating authority" (USGBC)? It would be great to have a simple number similar to those in table G3.2. By the way, my daylight harvesting occurs in the perimeter of the building. If the answer is on the USGBC website, I am clueless on how to obtain it.</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN> </DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> Thank you much for your advice/answers.</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN> </DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Lars Fetzek, EI</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Phoenix Engineering Group</SPAN></DIV>
<DIV><SPAN class=118000221-05082009 style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Tampa, Florida</SPAN></DIV></BLOCKQUOTE></HTML>
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