By: Shreshth Nagpal, Associate and Jagan Pillai,
Environmental Designer, Atelier Ten
Labs are far more energy intensive than typical commercial buildings, but not all labs consume energy for the same
reasons. Most available design guidance for
labs provides a list of energy-efficiency strategies that include reducing design air change
rates, decoupling cooling and ventilation
systems and employing variable-air-volume
fume hoods. However, quite a few parameters need to be evaluated for each project’s
unique requirements to assess the value of any
particular strategy. Utilizing a simple block
model and results from multiple parametric
simulations, the authors made a case based
on each project’s functional requirements and
location; different projects respond very differently to the same strategies.
This paper presents results from multiple
energy simulations and attempts to assess
relationships between the functional requirements, loads, operational flexibility, climate
and the effectiveness of various energy-efficiency measures. Savings with ventilation airflow reduction vary greatly with climate; sensible and ventilation system decoupling offers
savings only if the internal loads are higher
than a certain threshold. An all-air system can
be more efficient than a decoupled system if
an air-side economizer is effective for the climate. Variable-air-volume exhaust is effective
only if the use allows for airflow modulation.
The results discussed are from computer
simulations, which show the selection of energy-efficiency strategies in a lab project require
a thorough understanding of ventilation rates,
sensible and latent loads, operational airflow
and humidity control requirements, envelope
heat transfer and the climate.
A five zone energy model, with equal expo-
sure to all four orientations, was created using
eQuest v3.64 (DOE2.2 simulation engine) to
account for the load diversity caused by enve-
lope heat gain/loss associated with any par-
ticular orientation. The analysis utilizes the
batch processing feature of DOE2.2 to simu-
late a total of 216 parametric runs to represent
all possible permutations of varying three key
parameters—climate, usage pattern and air
change rates—to understand the effectiveness
of three key efficiency strategies—decoupling
cooling and ventilation, water-side economiz-
er and air change rate reduction with active
quality sensing. The chart above presents the
energy savings for each efficiency measure
across the entire range of climatic, operational
and functional parameters.
The results illustrate that decoupling the
cooling and ventilation systems offer maximum savings for load-driven labs in hot climates, particularly for high usage (1). In mild
and cold climates, however, where air-side
economizer is most effective, decoupling cooling and ventilation results in an energy penalty
because of reduced free cooling potential (2).
In mild and cold climates, the decision on all-air vs decoupled systems should depend on the
usage pattern of the labs ( 3). A water-side economizer should be incorporated with decoupled
systems, especially for high-usage labs in mild
and cold climates ( 4). In hot climates, however,
incorporating a water-side economizer doesn’t
show any energy benefit ( 5).
Air quality sensing doesn’t offer any savings
if the labs are load driven and high usage, offering no potential for ventilation rate reduction
( 6). If, however, high-usage, load-driven labs
are designed with decoupled systems, air quality sensing offers substantial energy savings
( 7). For ventilation-driven labs, substantial
energy savings can be achieved by ventilation
rate reduction with strategies such as air quality
sensing ( 8). Additionally for ventilation-driven
labs, incorporating air quality sensing with
decoupled systems increases the savings potential, especially for hot climates ( 9). The energy
saving potential for air quality sensing in addition to decoupling varies with climate types.
The increase is limited for mild climates, but
higher for cold and hot climates ( 10).
To summarize the results of the study, it’s
important to analyze the actual climatic, functional and operational characteristics of a lab
before making decisions regarding energy-efficiency strategies. Since most of this information depends on the end users, and may vary
once the lab is in operation, it’s important to
utilize data from past experiences or have discussions with the end users about anticipated
usage. The analysis illustrates that if strategies
aren’t carefully assessed for their application
in the particular project, the additional investment might offer little or no energy savings, or
even result in an energy penalty.
With over a decade of experience in the field
of high-performance building design, Shreshth
Nagpal is an expert in the application of building performance simulation and analysis for
architectural design and systems optimization.
A key member of the Atelier Ten Energy Analysis
practice, he brings his experience in building
energy analysis including renewable energy
systems and optimization of high-performance
building envelope, mechanical and electrical
systems. As a member of Atelier Ten’s Environmental Design and Energy Analysis practice,
Jagan Pillai has expertise in building systems
optimization, HVAC controls and systems
selection. His wide range of project experience
includes universities and corporate campuses,
healthcare and commercial high-rise buildings.
He also has experience with lab building energy
audits and retro-commissioning.
Significance of operational and climatic parameters
in lab HVAC system selection
Annual HVAC source energy savings potential with different efficiency measures for various studies climatic, oper-tional and functional.