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openeemeter / caltrack

Shared repository for documentation and testing of CalTRACK methods
http://docs.caltrack.org
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Add heating and cooling efficiency metrics as additional model validation #98

Closed steevschmidt closed 5 years ago

steevschmidt commented 6 years ago

Background: Most modern residential buildings have heating and cooling systems which use either electricity or natural gas. The efficiencies of these systems tend toward norms, and usually fall within a fairly narrow range. When both electricity and natural gas use are measured on a daily basis, the disaggregation of heating and cooling energy (via regressions with outdoor temperature) allows for calculation of annual heating and cooling efficiencies. When these efficiency values are similar to norms across a range of buildings we have more reason to be confident in the disaggregation methods being used.

Issue: In a cohort of 80+ homes in the SF Bay Area, a number of homes analyzed using CalTRACK methods had extremely low heating loads compared to HEA internal results, which would result in unusually low heating efficiencies when measured in BTU/square-foot/degree-day. This should raise flags in an area with cool winters, where very few homes rely on other unmetered heating fuels (such as propane or firewood). It may very well indicate a modeling error on these buildings that should be investigated and improved.

Validation: The DOE says a "modern, efficient home" should have a heating efficiency around 5 BTU/sf/hdd. This figure assumes a furnace or boiler; if electric heat pumps are used for space heating the target drops closer to the cooling efficiency targets of 1.5 to 2.5 BTU/sf/cdd. HEA has used these metrics for over 6,000 homes and have found them to be very useful, not only to energy consultants and occupants, but also to our engineering team to identify data & analysis errors on specific buildings. Below is a chart showing the range of values for about 2,000 homes (single family, townhomes, condos & apartments) mostly in the Bay Area. The metric includes both electric and natural gas heating loads in each home. heatingeff

Requested CalTRACK change: Provide heating and cooling efficiencies in units of BTU/sf/dd in the standard output, and flag results outside of normal ranges. (See related details in March 16 comment on issue #73.)

steevschmidt commented 6 years ago

[This issue was intended for "Existing Daily Methods Improvements"]