ASHRAE Journal - July 2022 - 30

TECHNICAL FEATURE
Validating BIM
Load Calculations
BY KEVIN LAWSON, P.E., MEMBER ASHRAE
Heating and cooling load calculations can take a substantial amount of time, performing
tedious material takeoffs and counting quantities of light fixtures, furniture and
equipment. Many architects and electrical engineers are already including some of
this data in their building information modeling (BIM) systems, or models, for their
own purposes. Mechanical engineers can save time and reduce errors by identifying
the relevant BIM data, validating its accuracy, overriding errors and using the
data for load calculations. This article will discuss using BIM for load calculations, as
well as validate the results of common BIM load calculation procedures against true
measured loads on real-life buildings and traditional calculation procedures so BIM
load calculations can be adopted with confidence.
Background
Given how important space load
calculations are to a mechanical
engineer, and how much time they
spend calculating these loads, it
may be reasonably assumed that
the mechanical engineer has some
say in what the result is, but that
assumption would be wrong.
The mechanical engineer does not
make any of the decisions that affect
the load calculation. They do not
decide wall constructions, window
types, lighting power density or any
other variable that has an impact on
the result. When a mechanical engineer
is " calculating loads, " they are
essentially performing an accounting
exercise-counting windows and
lighting fixtures, measuring areas
and performing other accounting
tasks, then manually typing the data
into a load calculation engine.
Historically with pencil and paper
or CAD, this was necessary. Part
of the mechanical engineer's job
was to look at a line drawing of a
window and understand that it
was a window. Now, with BIM, that
manual interpretation is no longer
Kevin Lawson, P.E., is the founder of Ripple Engineering Software.
30
ASHRAE JOURNAL ashrae.o rg
J U LY 2022
required because the model knows
the element is a window because
it is stored in a database as a window,
along with the size, orientation,
location and, ideally, thermal
properties.
The key to using BIM to quickly
calculate loads is to identify, validate
and use the curated data and
then override incorrect data as
necessary. For example, the architect
cares deeply about the size and
location of all the windows in a
model. If those items are not correct,
the architect's construction

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ASHRAE Journal - July 2022

Table of Contents for the Digital Edition of ASHRAE Journal - July 2022

Contents
ASHRAE Journal - July 2022 - Intro
ASHRAE Journal - July 2022 - BB1
ASHRAE Journal - July 2022 - BB2
ASHRAE Journal - July 2022 - Cover1
ASHRAE Journal - July 2022 - Cover2
ASHRAE Journal - July 2022 - 1
ASHRAE Journal - July 2022 - Contents
ASHRAE Journal - July 2022 - 3
ASHRAE Journal - July 2022 - 4
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ASHRAE Journal - July 2022 - Cover3
ASHRAE Journal - July 2022 - Cover4
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