Degree Days.net - Custom Degree Day Data
Degree Days.net calculates degree-day data for energy-saving professionals worldwide. The software is developed by BizEE Software based on temperature data from Weather Underground.
Degree Days.net
Degree Days.net is aimed at the energy-saving professionals that are already experienced in using degree days for energy-related calculations. Provided you fit this description, you will probably find most of the options above to be fairly self explanatory. However, we do suggest that you read the tips below as they do cover some important points.
If you are new to degree days, you might want to skip straight to the brief introduction at the bottom of this page.
Choosing the best weather station for location and accuracy
Degree Days.net calculates its degree days using temperature data from Weather Underground, a weather-data service with thousands upon thousands of weather stations worldwide.
You will typically want to find the weather station that's closest in climate to the location of the building whose energy consumption you're analyzing. This should give a better representation of the weather at the building than any "reference" station for the larger region in which the building sits.
However, there is an important caveat: a lot of the weather stations have missing or erroneous data. In our experience, this is particularly true of the "personal weather stations" (the ones that aren't marked as airports). The quality of the data from these stations varies considerably: some have years of apparantly flawless temperature readings, whilst many others have lengthy periods when they clearly weren't working properly.
We have programmed Degree Days.net to tolerate a certain amount of problem data: it makes estimates where necessary, and marks each estimated degree-day figure with a "% estimated" value so that you know where the detected problems lie. This works well when a station has just a few days of problem data here and there, but there does come a point when Degree Days.net will suggest that you try to find another station nearby.
If you're lucky, you'll find that the station that's best for you in location terms has little or no problem data. If not, you may need to look a little further afield. If you're struggling to find a station with good data, you might want to focus on the airports: we've found that a good proportion of the airport stations have consistently high-quality data.
The airport weather stations also tend to go further back in time than the personal weather stations (many of which were only set up recently).
Do make sure to use your own judgement when selecting whether or not to use data from any particular station - only you can determine the level of accuracy that you require. Also, please bear in mind that even though Degree Days.net has been carefully programmed to detect obvious errors in the source temperature data and to minimize the chance of calculation errors, we can not vouch for the accuracy of any degree days that Degree Days.net generates.
How can I get data for my "degree-day region"?
The practice of splitting a country into a limited number of "degree-day regions" stems from a time when degree days were disseminated in print. Since that time the internet has made it feasible to make much larger quantities of data readily available.
We think that it's generally much better to use degree-day data from a local weather station, as that will typically represent the weather at your building better than the data from any "reference" station further away.
Searching for weather stations in the US
Weather Underground is a US company, and it holds data from a huge number of US weather stations. You should have no trouble finding nearby stations by searching for your city, state, or zip code.
(US visitors might be interested to know that the 10 most popular US states for degree-day downloads are, in descending order of popularity: New York, California, Massachusetts, Pennsylvania, Texas, Ohio, Michigan, Maine, Connecticut, and Florida. And the most popular US cities are: Boston MA, Philadelphia PA, Denver Colorado, New York NY, Atlanta Georgia, Minneapolis Minnesota, Phoenix Arizona, Houston TX, Detroit MI, and Portland MA.)
Searching for weather stations in the UK
There are a lot of UK weather stations stored in the Weather Underground database. In our experience, searching for city name and country name together works well (e.g. "London, UK"). The database doesn't currently hold postcode information, so there's no point in searching for that.
Searching for weather stations elsewhere
After the United States and the United Kingdom, our 10 most popular countries for data downloads are, in descending order: Canada, Spain, Ireland, Germany, France, India, Italy, Australia, Greece, and Sweden. India's coverage is patchy (although there are some good stations dotted about), but the rest of those popular countries, and many others (particularly in Europe), have good weather stations in the more populated areas at a minimum. Some countries are very well covered, although availability does vary greatly from country to country.
We suggest that initially you try searching for city name and country name together, using anglicized names (e.g. "Copenhagen, Denmark", or "Amsterdam, Netherlands"). Some countries just don't seem to register despite having stations in the database, so if searching for city and country doesn't work, try searching for city name alone.
If you're struggling to find a good station...
You might try searching for towns and cities near to your location. The search facility isn't perfect, and you'll often find that, whilst a search for one city won't turn up anything useful, a search for a nearby city will.
If all else fails, you should hopefully find success by searching for the three or four letter international airport code of the airport that's closest to you. Airports tend to be particularly well represented in the Weather Underground database - there are lots of them and most of them have high-quality weather data going back a long time.
If you should discover any other useful tips for weather-station searching, please let us know!
Choosing the best base temperature
Degree days have traditionally come in a limited range of base temperatures such as 15.5°C, 18.5°C, and 65°F. It is rare for real-world buildings to align accurately with any of these pre-prescribed base temperatures, and degree days with an inappropriate base temperature are a significant cause of inaccuracy in calculations relating to weather-dependent energy usage.
Our article on the problems with common degree-day-based calculation approaches explains this issue in much more detail.
Degree Days.net will generate degree days to any base temperature you choose. If you check the box to "Include base temperatures nearby", Degree Days.net will calculate your degree days to a range of base temperatures around the one that you specify. This makes it easy for you to estimate an appropriate base temperature for your building, and then refine your choice by correlating your kWh energy-consumption figures with the base temperatures nearby until you find the best fit.
Generating data to match your utility bills or fuel consumption records
Gas and electricity bills often don't line up neatly with calendar weeks or months. And it's rare for records of oil, LPG, or wood-burner consumption to fit the calendar.
But haphazard dates are not a problem: Degree Days.net enables you to get daily degree days, and you can add these together to get totals for each period of consumption that you have records for. This is a perfectly valid thing to do.
Degree days for beginners
Degree days are unfortunately rather easy to use badly (in a way that leads to erroneous and misleading figures), and rather difficult to use well. There are much better ways for beginners to get started saving energy (like, for example, obtaining and using a Kill-A-Watt meter). For these reasons, Degree Days.net is primarily aimed at the energy-saving professionals that are already experienced in using degree days.
However, if you are a degree-days beginner that isn't afraid to delve further into a deceptively complicated form of data analysis, please read on:
So what are degree days?
Degree days are essentially a simplified representation of outside air-temperature data. They are widely used in the energy industry for calculations relating to the effect of outside air temperature on building energy consumption.
"Heating degree days", or "HDD", are a measure of how much (in degrees), and for how long (in days), outside air temperature was lower than a specific "base temperature" (or "balance point"). They are used for calculations relating to the energy consumption required to heat buildings.
"Cooling degree days", or "CDD", are a measure of how much (in degrees), and for how long (in days), outside air temperature was higher than a specific base temperature. They are used for calculations relating to the energy consumption required to cool buildings.
Degree days also have applications relating to plant growth ("growing degree days"). However, our focus is on making software for energy saving, so our expertise are in the energy-saving applications of heating and cooling degree days.
Further information
For a really basic introduction, you might like to read this Google Knol about degree days - it's ideal if you're looking for an easy-going explanation of degree days and what they're used for.
If you are interested in finding out more, we suggest that you read this article on degree days. It describes degree days and how they are commonly used, and, more importantly, it highlights the critical issues that you should really be aware of if you are planning to use degree days in your own energy-related calculations. Although the bulk of the article is pitched more at energy-saving professionals than beginners, it does explain the basics as it goes along.
Be warned, however: you might find it a little heavy going!
What next?
- The articles linked above are well worth a read...
- Our Degree Days.net quotes page has some of the comments that people have made about this site...
And that's about it at the moment - it's mainly about the data after all. If you've not done so already, why not head back up to the top of this page and give Degree Days.net a go?!