[Greenbuilding] HDD and how they are calculated (daily avg. vs hourly avg)

elitalking elitalking at rockbridge.net
Fri Nov 25 08:38:40 PST 2011

HDD and CDD are used for quickly estimating seasonal energy loads that can be applied to envelope heat losses and efficiency of the HVAC equipment.  This is useful in making decisions regarding the thermal envelope and equipment cost and benefit.  Where as insuring comfort is dependant on the coldest or hottest extremes, the design temperature.  Satisfying the extremes can sometime reduce the seasonal efficiency.  This is likely the case with cooling.  Even though there is global warming that can have catastrophic consequences with only a few degrees, the annual variations in any climate can be far greater than the global warming trend.  The best number is achieved by data collected from as many years as possible.  



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