Right Sizing
Laboratories typically consume 600 kWh per square metre per
year or more, three or more times the energy consumed in a typical
office building. However, energy consumption and operating costs
can be reduced through "right sizing," choosing the
most efficient and cost effective combinations of equipment
and equipment sizes as well as managing the laboratory load,
all to achieve energy efficiency. Right sizing is an iterative
process; although new techniques are developed continuously,
the basic elements are:
Life-cycle cost analysis
Life-cycle cost (LCC) analysis accounts for all costs incurred
for the HVAC system from installation through a chosen period
of time, usually 20 years. Life-cycle cost analysis is a "yard
stick" to measure the relative benefits of the choices
available to the design team. When an energy-efficiency measure
(EEM) happens to have the lowest first cost, an LCC analysis
is not necessary. Click here for more information from US Labs21
on life
cycle cost analysis
System sizing
Estimating the conditioning capacity necessary for a laboratory
includes a myriad of choices to determine the laboratory's HVAC
system type and size. To make these choices intelligently, the
engineer must understand the variability of the laboratory facility's
load profile. Airflow rate through the facility is a subject
of considerable debate that is primarily driven by the air change
rate per hour (ACH) and the design fume hood face velocity.
Click here for more information from US Labs21 on System
sizing
Diversity
Diversity in laboratory design can permit downsizing of equipment,
reducing capital and operating costs. Diversity analysis in
a laboratory ventilation system accounts for the fact that not
all laboratory spaces or fume hoods are operated at 100 percent,
24 hours per day. The larger the facility, the smaller the probability
of simultaneous use of all available capacity. Studies and practical
experience have shown that, for large laboratories with many
fume hoods, at least 20 to 30 percent are closed or only partially
used at any one time. Therefore, HVAC systems can be sized for
70 to 80 percent of peak ventilation capacity. Sizing the HVAC
system at 70 percent of peak load decreases operational and
first costs, gives better system control, increases system stability,
and reduces mechanical space requirements. Taking advantage
of diversity is particularly valuable when retrofitting existing
facilities where available space is limited. Therefore, it is
very important to consider diversity when sizing a large laboratory
HVAC system. Small, single-room laboratories should always be
sized for full 100 percent capacity without downsizing. Click
here for more information from US Labs21 on Diversity
Load management
A comprehensive analysis of the laboratory loads should include
an interview between the researchers and the energy engineer.
Such interviews often produce unexpected results and increased
energy efficiency; identification of equipment and occupancy
schedules helps clarify system capacity needs, and, in some
cases, reveals that demand-controlled ventilation is a viable
option.
Finally, control is the single most important design variable
in an HVAC system that meets a laboratory's exacting environmental
requirements. The control scheme must address temperatures as
well as safe ventilation and stable control of building pressures,
duct static pressures, and air migration patterns. Click here
for more information from US Labs21 on Load
Management.
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