Replies

1. 
   Mike_Smith | Mar 13, 2002 11:17pm | #1

   *
   gio... every 1000 deg. F is equal to 537.778 deg. C.

   here's a handy conversion site....

   http://www.sciencemadesimple.net/temperature.html

1. 
   Wayne_Law | Mar 14, 2002 12:29am | #2

   *To convert HDD from Celsius to Fahrenheit multiply by 1.8To convert HDD from Fahrenheit to Celsius divide by 1.8This only works exactly when the degree day basis temperature is the same. For example, if the degree day basis in Celsius is 20°C this conversion gives the degree days based on the same temperature, i.e. 68°F. (Because 20°C = 68°F.) Heating degree days based on 68°F would be slightly less than degree days based on 70°F or 72°F.Mike is incorrect.

1. 
   xMike_Smith | Mar 14, 2002 03:59am | #3

   *wayne.... if my answer is incorrect it still came from the conversion site...so ?by your one place factor.... 6000 DD = 3333 in Celsius....multiplying 537.778 x 6 = 3226 Celsius..is that a round off problem ?or is the conversion site wrong ?

1. 
   David_Thomas | Mar 14, 2002 04:57am | #4

   *It is a round off problem. 1.8 is exact.boiling minus freezing = 212F - 32F = 180F = 100C - 0C = 100CThermodynamic trivia: Farenheit selected 100F as body temp. I forget his other fixed point. Then determined that the boiling point of water was 212F and freezing was 32F. Not great thermometer in those days. So the repeatable points (FP & BP) were retained and body temp was determined to average 98.6F (=37 C).

1. 
   Mongo_ | Mar 14, 2002 05:27am | #5

   *More trivia...from some rough notes from a research project my daughter did last year:"placing the thermometer in a mixture of sal ammoniac or sea salt, ice, and water, a point on the scale will be found which is denoted as zero. A second point is obtained if the same mixture is used without salt. Denote this position as 30. A third point, designated as 96, is obtained if the thermometer is placed in the mouth so as to acquire the heat of a healthy man." (D. G. Fahrenheit,Phil. Trans. (London) 33, 78, 1724) On this scale, Fahrenheit measured the boiling point of water to be 212. Later he adjusted the freezing point of water to 32 so that the interval between the boiling and freezing points of water could be represented by the more rational number 180. Temperatures measured on this scale are designated as degrees Fahrenheit (° F).I knew she wasn't totally useless!

2. 
   Gio_Robson | Mar 15, 2002 09:48pm | #6

   *Okay, so what if the degree day basis was different? Is there a way of adjusting through a formula for this? In my city the only HDD numbers I have access to are calibrated at 18.0 degrees celsius, or 64.4 farenheit. I would prefer to use one at a 20 degree celsius or 68 farneheit basis so that I can compare data to other zones across the continent (68 seems to be the average HDD basis that I have seen). I've searched this one to death on the net - could't find anything.gio

3. 
   David_Thomas | Mar 15, 2002 10:16pm | #7

   *Gio: There isn't a general-purpose conversion. You'd need to add 3.6F or 2C for each day of your heating season. Plus the same amount for a couple of weeks in the shoulder seasons. Because using 68F results in a longer theoretical heating season than using 64.4F. So in Kentucky you might add 720F HDD (= 400C HDD). Up here, you'd add about 1000F HDD (= 555C HDD). In Phoenix, maybe add only 250F HDD.

4. 
   Wayne_Law | Mar 16, 2002 12:12am | #8

   *Mike, I'm sorry for the terse reply, but did not want to give a long winded answer to the original question. But, I'm happy to explain.First, here are some conversions to reference so the explanation is easier for me to describe. 0°C = 32°F, 10°C = 50°F, 20°C = 68°F, 100°C = 212°F. A degree Celsius is larger than a degree Fahrenheit; 1.8 times larger exactly. So, for any temperature difference it takes fewer degrees Celsuis to express that numerically. For example, if it was freezing outside, and you came inside, it would be 20°C warmer (that is, from 0° to 20°). It would also be 36° warmer if you used Fahrenheit degrees (that is, from 32°F to 68°F). So, the same temperature difference would be expressed as 20° on the Celsius scale and 36° on the Fahrenheit scale. You'll see that 36 is 1.8 x 20.That's why the conversion for heating degree days is exactly a multiplication or division by 1.8. Degree days is a temperature difference between the desired heating temperature and the outside temperature, added up for each day of the year. So, if your desired heating temperature was 68°F and today it was 28°F outside, the degree days for today would be 68° - 28° = 40°F. If tomorrow it was 58°F then the degree days for tomorrow would be 10°F (that is, 68° - 58°). Add these up for the whole year and you get the annual heating degree days for a particular climate. If you did the same thing using Celsius degrees you'd have fewer of them becasue each Celsuis degree is bigger. You'd have 1.8 times fewer to be exact, that is, divide by 1.8 to make the number smaller.If the degree days were based on a different reference point, say your data references 68°F but you want 72°F, there is no "conversion". You can add four degrees for each day, but you don't know how many days there were below 68° in a year and how many not. So, you don't know for how many days to add 4°. Then you also don't know how many days were between 68° and 72°. These wouldn't show up at all for data referencing 68°, but would if you referenced 72°. So all you can do is estimate about how many days and add some to account for that. Dave in post #7 explains how to estimate that.Now, as for the conversion site you talked about. The site is not converting "how many" degrees between one temperature and another. It's converting a particular place on one scale into the same temperature on the other scale. If 0°C were the same temperature as 0°F then what you are thinking would work. But, the two scales are offset by 32°F. So if you said how many degrees are there between freezing and boiling of water you could say 100°C - 0°C = 100°C, or 212°F - 32°F = 180°F, and you could convert back and forth between them by using 1.8 to multiply or divide by. But, if the question was what temperature is 100°C equal to on the Fahrenheit scale, you'd first have to multiply by 1.8 then add 32° because 0° are at a different temperature on both scales. So, 100°C would be 100° x 1.8 = 180° then add 32° to get 212°F.

5. 
   The_Tennis_Court_Builder_...on_t | Mar 18, 2002 08:45pm | #9

   *Wayne.... Super explanation bro... So what do you do for a day job if yaa don't mind me asking...near the vibrating molecular h2o stream,aj

6. 
   Wayne_Law | Mar 19, 2002 12:10am | #10

   *Since you asked, I'm a mechanical engineer in a manufacturing plant by day. I think I'm a woodworker at night. In my dreams I'm an architect (but I can't draw). I think being a contractor would be a cool job, but I don't have the courage.

7. 
   zindpr | Mar 23, 2002 07:45am | #11

   Wayne

   I always thought the formula was:

   5F = 9C+160

   so at C=0

   F= 160/5 = 32 F

   at C=100

   F= (900 + 160)/5 = 1060 / 5 = 212

   and at c = f at -40

   Paul

8. 
   WayneL5 | Apr 10, 2002 11:45pm | #13

   Paul, I just saw your question today.  I'm not ignoring you.  It's just that I don't like the new forum and don't get on it much anymore.

   Your formula is correct, but it's for converting a temperature on one scale to the other.  It's not for converting the size of a temperature difference, which is what a HDD measures.

   I don't think I can explain it clearly by email.  Try reading my long previous message again.  If it's still not clear you may have to ask someone in person, like a science teacher.  I'm not very good at explaining things in writing.

2. 
   TooManyTools | Mar 24, 2002 10:28pm | #12

   Although it is true that 1.8 is an exact conversion factor from Celsius to Fahrenheit a HDD conversion is more complex since it is based on the median daily temperature.  Most HDD tabulations are based on 65 F as a basis.  A day whose high temperature was 70 F and a low of 28 F(yesterday here in Denver) has a median temperature of 49 F and a HDD of 16.  To convert to HDD in Celsius the high is 21.1 and the low is -2.2 and the median temperature is 11.7 resulting in (to a base of 20 C) 8.3 HDD. Since over a periond of time there might be several combinations of median temperatures which give the same HDD for an accurate calculation one must know the actual median temperatures for the year. 

3. 
   owlhoot45 | Apr 10, 2002 11:59pm | #14

   F  to  C     (F-32)/1.8

   C  to  F     (Cx1.8)+32

1. 
   HeavyDuty | Apr 11, 2002 03:44am | #15

   I can't believe we can have so much to discuss just over a conversion from C to F. I am going to throw in my 2C's worth. Wayne, the ME who can't draw is right, how can you be a ME and can't draw? Paul and Owl have the same formula. Here is something that I think what everybody is arguing about, the basis of degree days. If we are just talking about conversion of DD's, shouldn't the basis be irrelevant? If you are given X DD's in C, that's a number based on the basis where it is calculated from. In another locale, where the basis is differnt, then the DD's would be different too. We are not talking about conversion of DD's to different basis. So the conversion would be straightly the factor of 1.8 exact, no adjustment of 32 or the temperature that it is based on.

   Here is how the different scales came about. The first temperature scale developed was C. At the time people thought when water turned to ice, that's the coldest temperature that anything could achieve, so they marked it as 0 because nothing could get colder or below 0. Then they decided boiling water was as hot as things could get, they made it 100 so there was 100 divisions in between. Then they later found out that something could actually achieve a temperature below 0, I don't remember what that something was, and it was quite a bit below 0C so they thought that was it, nothing could go lower. So they designated it as 0F and with that scale ice melted at 32 and water boiled at 212. I don't remember how they made up the 180 difference in between, and the body temperature thing is new to me, never heard of it before. Then as science advances people knew they could get to a much lower temperature. So now the accepted absolute 0 is -273.16C an at that point nothing moves. So with the Kelvin scale water freezes at 273.16K and boils at 373.16K

1. 
   xMikeSmith | Apr 11, 2002 04:44am | #16

   tom.. i think the story about body temp. was more enjoyable.. so i'm stickin with that one....

   u may be right ,  but u cud use an editor.....Mike Smith

   Rhode Island : Design / Build / Repair / Restore