Dear Forum,

I am soliciting input from you regarding your experience in using full, 8760
hour energy models for energy audits of existing buildings. I have used
EnergyPlus for a few of these and am starting to get an opinion about what
is important for an existing building energy model. I am convinced that the
rules are different than for a new building, but would like to know what
your experience has been.

My primary interest is the "big picture" factors, not so much the fine
details. I have made an outline of factors and considerations below and will
appreciate your feedback and comments as you are able!

p.s., I suspect that I am not the first to ask this question! If you are
aware of past conferences or papers, please point me in the right direction.

Energy Audits Which Utilize an Energy Model

Factors which imply the need for an energy model

. Multi-use (different schedules for portions of the building)

. Radically different construction types in different portions
of the building

o e.g., lightweight construction added to massive construction,
high % glazing added to low % glazing

. Multiple air handlers of different types

o E.g., RTUs for one portion, baseboard heating only for another
portion

. Anticipation of changing to one of the above

. Other???

What is the minimum data needed for a defensible / reliable energy model?

. Correct total wall area plus window area by elevation?

o With low regard for a perfect match to actual geometry

. Schedules of operation?

. Motor power for fans, pumps?

. Air and water flow for fans and pumps?

. Special uses?

o Pool

o Assembly

o Specialized equipment such as servers, X-ray

. Plug loads?

. Outdoor air flow?

. Lighting loads in W/sq.f.t? W / zone or room?

. Exterior lighting?

. Temperature / humidity setpoints?

. Air handler control setpoints?

o Which ones?

. Shading elements?

What method should be used for evaluating hard-to-measure data such as
actual lighting and plug load use, outdoor air flow, heating / cooling
system efficiency at part loads, infiltration, insulation (especially for
old buildings with no construction drawings), process power

. Trial & error? Using user-imposed restraints?

. Benchmark or past project data?

. ???

How closely must the energy model match past energy use?

. Match annual consumption +-10%? >75% R2 month-by-month?

. Is actual weather data important? (vs. TMY / "typical")

. ???

How carefully must the energy model match define ECMs?

. Annual? Peak? Efficiency of new components

. Generic or manufacturer-specific performance data?

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