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 10:53, 1 December 2012

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==Heat Degree Days==
You may have a thermostat that makes your heating come on when the temperature falls below a threshold.
Cumulus calculates thean timeintegration thatof the temperaturenumber isof degrees below thatthe threshold and reports it as 'Heat degree days' usingover the unittime of ''days''. Cumulus reports this by month as part ofthat the NOAAtemperature report.is below Itthat also appears in the annual NOAA reportthreshold.
 
Cumulus reports this by month as part of the National Oceanic and Atmospheric Administration (NOAA) style report, in the annual NOAA report, in dayfile.txt, and via heating degree days web tag. (NOAA is an Operating Unit of the U.S. Department of Commerce).
So if for each day of November, there was just one hour below the threshold, the total for the month would be 30 hours reported as 1.5 days.▼
 
▲So if for eachthe daywhole of November, there was just one hour at one degree below the threshold, two hours at five degrees below, and three hours at seven degrees below; the total for the month would be 30(1*1)+(2*5) +(3*7) hours reported as 1.532 degree days.
==Chill Hours==
A related measure, also reported by Cumulus counting the ''hours'' below a (different) configurable temperature threshold for the 12 month period starting on the 1st day of a configurable month, is Chill Hours.
 
The traditional way of calculating the accumulation of Chill Hours is the number of hours the temperature is below 45F or 7.5C for the period of 1st October to 30th April in the Northern Hemisphere. This is available onOn Cumulus as that threshold, and start date are the default, so you simply observe the reported value on 30 April. The current figure is viewable on the 'This Year' screen accessed from the View menu, and is available via web tag <#chillhours> to be added to a web page template of your design.
 
The main 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 below 200 hours to around 1500 hours.
However, the way it can be configured on Cumulus will allow you to track air frost hours, ground frost hours or any other below the threshold parameter.
 
[[User:Sfws|Sfws]] 10:53, 1 December 2012 (UTC) (with thanks to Randy who raised Enhancement Request #117 and supplied some of the above text)
==Cold Degree Days==
You may have a thermostat that makes a cooling system come on when the temperature rises above a threshold.
 
Cumulus calculates the time that the temperature is above that threshold and reports it as 'Cold degree days' using the unit of days.
SoCumulus ifcalculates foran each dayintegration of June,the therenumber wereof 3 hoursdegrees above the threshold, over the totaltime forthat the monthtemperature wouldis beabove 90that hours reported as 3 daysthreshold.
 
Cumulus reports this by month as part of the NOAA report, in the annual NOAA report, in dayfile.txt, and via cooling degree days web tag.
 
So if for one day in June, successive readings at one minute intervals above the threshold were 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, then it stayed 10 degrees above for 1 hour, before falling in successive minutes to 9, 8, 7, 6, 5, 4, 3, 2, and 1 degrees above the threshold, the total for that day (of 1440 minutes) would be 150 degree minutes reported as 150/1440 or 0.1 degree days.
<br>▼
[[User:Sfws|Sfws]] 10:53, 1 December 2012 (UTC) (with thanks to Mark Crossley for help with understanding ''degree day'' unit)
 
=Setting the threshold=
[[File:NOAA_Setup_extract.jpg‎]]The thresholds for '''Heat and Cold Degree days''' are set in the ''NOAA Setup'' option within the ''Configuration'' menu. The picture shows just parts of the setup screen. It allows you to specify the two thresholds in the units you have selected to use in your implementation of Cumulus. Cumulus stores your selected threshold values in the [NOAA] section in '''Cumulus\Cumulus.ini''', Heating and Cooling Degree Days are stored in dayfile.txt, and are available via heating/cooling degree days web tags.
 
CAUTION: Think carefully, about what threshold to use. If you later change the threshold, only subsequent calculations use the new threshold. All retrospectivepast calculations remainwere based on the old threshold, so values shown on a NOAA report for a month or a year with a threshold change will be rubbish, and(the neednew tothreshold beis manuallyshown recalculated.on Thethe figuresreport, arebut onit thehas reportsnot been applied retrospectively), soand makeneed to be manually recalculated making any consequent edits directly on past reports.
 
The '''Chill Hours defaults''' are configurable by adding entries to the [Station] section in Cumulus.ini:
 
''ChillHourSeasonStart=10''
 
''ChillHourThreshold=45''
 
The season start figure is the month number, and the temperature threshold is specified in the units that you use in Cumulus.
 
The current figure is viewable on the 'This Year' screen, and is available via web tag <#chillhours>
 
[[Category:Terminology]]
▲<br>
[[User:Sfws|Sfws]] 07:42, 29 November 2012 (UTC)
Sfws
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