Degree days

Sector Energy, Agriculture
Description Heating (cooling) degree days [HDD (CDD)] are a measure to estimate energy demand for heating (cooling) building interiors. The indicator is calculated based on accumulated difference between outdoor air temperatures below (above) some reference base temperature (Tb).
End User Energy companies, people working with evaluations of energy consumption, property owners
Calculation method

For HDD, when mean daily temperature Tair<Tb: HDDAnnual = ∑d=1365(Tb-Tair,d)

For CDD, when mean daily temperature Tair>Tb: CDDAnnual = ∑d=1365(Tair,d- Tb)

(Adapted from, Day 2006)
ID Title Period Statistical processing Unit Threshold Comment
heatingdegreedays Heatin degree days yearly See above °C day  17

Threshold used extensively by SMHI for Stockholm.
coolingdegreedays Cooling degree days yearly See above °C day 20

Threshold used extensively by SMHI for Stockholm.
Provenance Theese indicators are based on output from the Harmonie meteorological modell.
Validation The simulations made by HARMONIE-AROME in Urban SIS has been validated against observations in Urban SIS deliverable 5.1. In section 4.1.3 the simulation for heating degree days is compared to observations.
Calculation caveats Spatial representation:
Other caveats: O4
Could be compared to:
Could be used with:
Motivation

HDD (CDD) provides a metric to estimate energy demand for building heating (cooling) (Christenson et al. 2006) and HDD are also correlated with local greenhouse gas emissions (Christen et al. 2011). HDD and CDD indicators can be used as inputs to estimate energy demand spatial variability for building heating and cooling.

HDD and CDD indicators are provided on annual timescales for each grid cell, thus inter-annual variability or sub-annual trends cannot be assessed. Additional uncertainty arises from choice of threshold used to calculate HDD (CDD). This threshold is variable between countries and regions; for example HDD thresholds vary between 8-12° C in Switzerland (Christenson et al. 2006) and 14° C in Greece (Matzarakis 2004).

In this calculation, Tb = 17 °C for HDD and Tb = 20 °C for CDD, is based on values used in Stockholm by SMHI.

Degree days provide a proxy for energy demand, however in reality building energy consumption is also influenced by other variables such as occupant behaviour, building design, and type of heating/cooling system. 
Experience user  Ideally calculated using appropriate threshold for area of interest.
References

Christenson M, H Manz, D Gyalistras 2006: Climate warming impact on degree-days and building energy demand in Switzerland. Energy Conversion and Management 47:6, 671-686.

Christen A et al. 2011: Validation of modeled carbon-dioxide emissions from an urban neighborhood with direct eddy-covariance measurements. Atmospheric Environment 45:33, 6057-6069.

Day T 2006: Degree-days: theory and application, The Chartered Institution of Building Services Engineers, TM41: http://www.degreedaysforfree.co.uk/pdf/TM41.pdf, Accessed 18 October 2016.

European Environment Agency 2012: http://www.eea.europa.eu/data-and-maps/indicators/heating-degree-days-1, Accessed 18 October 2016.

Matzarakis A, C Balafoutis 2004: Heating degree‐days over Greece as an index of energy consumption. International Journal of Climatology 24:14, 1817-1828.