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Heat/cold degree days and Chill hours: Difference between revisions
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Heat/cold degree days and Chill hours (view source)
Revision as of 16:02, 7 September 2013
, 7 September 2013→Chill Hours and/or Air Frost: mention calendar day caution
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==Chill Hours and/or Air Frost==
A related measure is '''Chill Hours''', also reported by Cumulus counting the ''hours'' below a (different) configurable temperature threshold for the 12 month period starting at 00:00 hours on the 1st day of a configurable month.
This measure is sometimes called ''Growing Degree Days'', because it relates to plants or insects rather than heating systems, but that seems a strange labelling because growth in most plants and insects responds to warmth, although some seeds need a period of chilling to stimulate germination and as described below some fruit needs chilling to promote development. However, [http://sandaysoft.com/forum/tracker.php?p=1&t=262| enhancement request #262] reports a different definition of ''Growing Degree Days'' based on summing daily: ((MaxTemp - MinTemp)/2 - BaseTemp) for all days where the value is positive (negative values are not subtracted).
The traditional way of calculating the accumulation of Chill Hours is the number of hours the temperature is below 45 degrees Fahrenheit or 7.5 degrees Celsius for the period of 1st October to 30th April in the Northern Hemisphere. One applicability is to stone and seed fruit as their exposure to low temperatures during the winter months will have a significant effect on the following harvest. Too few cold hours can result in poor quality and quantity of the crop. Fruit tree varieties prefer a Chill Hour rating from about 200 hours to around 1500 hours.
On Cumulus that threshold, and start date are the default, so you simply observe the reported value at the relevant time on 30 April/1 May. The current figure is viewable on the 'This Year' screen accessed from the View menu (only when the current year is selected), stored in [[today.ini]], and is available via web tag <#chillhours> to be added to a web page template of your design. Should you miss checking the reported value on 1 May, then for a few days, you can look in the backup sub-folder for the necessary archived today.ini. In the current version of Cumulus, a new archive of the data sub-folder is taken just after each rollover, but note that Chill hours are counted in Cumulus by calendar day (therefore some interpolation is needed if your rollover is 9am/10am).
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