5 4 ASHRAE JOURNAL ashrae.org DECEMBER 2018

NIST’s Testbed for 

Optimizing Building 

System Performance

BY MARY KATE MCGOWAN, ASSOCIATE EDITOR, NEWS

The National Institute of Standards and Technology’s Intelligent Building Agents 

Laboratory (IBAL) is a “building in a laboratory,” said Steven Bushby, Fellow ASHRAE. 

Actual buildings are not conducive environments for conducting reproducible 

research due to changing internal loads and outside weather conditions, so NIST 

created a testbed to remove those concerns. 

The IBAL testbed is a controlled environment with 

reproducible weather and building loads that NIST 

uses to analyze real building mechanical systems. The 

testbed reflects the complex control optimization problems of real buildings, said Bushby, who is the leader 

of the Mechanical Systems and Controls Group of the 

Energy and Environment Division of NIST’s Engineering 

Laboratory.

The IBAL demonstrates agent-based optimization 

and control approaches on real equipment and allows 

researchers to understand the challenges when moving 

out of simulation into reality, said Amanda Pertzborn, 

Ph.D., Associate Member ASHRAE, who is a mechanical 

engineer in NIST’s Mechanical Systems and Controls 

Group.

Real HVAC equipment has dynamic operations and 

discontinuities that need to be considered in a real 

control system, but system models often neglect transient behavior and only model steady-state conditions, Pertzborn said. So a testbed allows researchers 

to develop data-driven models using machine learning that will be used in the optimization of system 

operations.

Bushby said the industry is skilled at local loop control 

of a single piece of equipment but generally uses heuristics to make supervisory control decisions that affect 

energy-efficiency, indoor environmental control of a 

building and campus-scale energy performance based 

on chilled-water setpoints.

“We think that the industry can do much better, and 

that the use of intelligent agents may be part of the solution. The IBAL is a research platform to test and demonstrate these potential solutions,” said Bushby. 

Most of the IBAL’s optimization efforts so far have been 

focusing on minimizing energy consumption while still 

meeting comfort requirements, he said.

Finding the Best Ways to Meet Building Loads

The IBAL has the major types of equipment found in 

real commercial buildings: air handling units, variable 

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air volume units, multiple chillers with differing capacity, a simulated cooling tower and ice storage. 

The systems allow the researchers to model complex operations and challenge a control system to 

determine the best way to meet a building load, said 

Pertzborn, adding that they define “best” in terms of 

cost, thermal comfort and energy efficiency.

“Unlike a real building, we have carefully determined 

the measurement uncertainty of all our measurements. 

We can test one optimization approach, and then change 

it or substitute another and run the tests again with the 

same internal loads and the same ‘outdoor’ weather to 

allow direct comparisons,” said Bushby.

The IBAL’s first order of business was exploring 

techniques for developing agent-based models of the 

mechanical equipment performance in the context of 

optimizing the use of thermal storage, said Pertzborn.

“...Our early results seem to confirm that there are 

potentially significant benefits to an agent-based 

approach,” she said. 

Challenges and Advantages

The IBAL presents challenges, just like real building 

projects, said Bushby. They have discovered some of 

the lab’s design assumptions do not match the as-built 

systems.

“For example, I had anticipated that the chillers would 

operate over a range of loads without cycling, but in 

reality, they have a very limited range,” he said

Because the IBAL is a lab and not a full-size building, 

the thermal mass of the water in the system is small. 

When a chiller cycles off, the temperature spikes rapidly, and the impact of cycling is more significant than it 

would be in a real building, according to Bushby.

Simplifying assumptions in models may mean things 

do not work as expected in a real system. Bushby said 

these challenges show the importance of evaluating 

new technologies on real equipment. Despite the challenges, dealing with non-ideal situations is a benefit to 

using real mechanical systems instead of simulation, 

he said. 

“Real control systems must be able to adapt to these 

kinds of problems. We expect that, in the future, we 

will take techniques that are successful in this laboratory and test them in actual building systems,” he said. 

“It will be important to prove the ideas in a variety of 

buildings.”

Affecting Different Parts of the Industry

The IBAL is expected to help different industry professionals from design engineers to equipment manufacturers to facility operators, said Pertzborn.

For design engineers, the testbed should support the 

development of guidance on how advanced control algorithms can influence their designs, such as the sizing 

and selection of equipment. For researchers, the lab’s 

results and data can help stimulate academic and corporate research to build industry knowledge and improve 

products.

Regarding equipment manufacturers, the lab is 

expected to provide strategies for developing datadriven models of real equipment and strategies for 

integrating agent-based intelligent control into building 

controllers. 

“One level of complexity is that the data-driven models require data before they can be used, so the control 

algorithm will require a non-data-driven model to 

control the building in the short-term. The solution 

An AHU with a 68 kW (20 tons) cooling coil, 60 kW electric heater, and steam 

spray humidifier is used to create reproducible weather conditions.

CREDIT: DENISE HERBERT

The IBAL has two chillers with capacities of about 35 kW (10 tons) and 25 kW 

(7 tons) when chilling a 30% propylene glycol mixture to 7.2°C (45°F).

CREDIT: DENISE HERBERT
5 6 ASHRAE JOURNAL ashrae.org DECEMBER 2018

FEATURE

to this problem is something we hope to define,” said 

Pertzborn, adding that NIST hopes to work directly with 

HVAC equipment and controls manufacturers to test 

ideas on a common platform.

For facility operators, the testbed is expected to provide tools that track equipment performance, so operators can see if their equipment is degrading. Data-driven 

models will update over time and can alert the operators to significant changes from previous versions of 

the model, said Pertzborn. The testbed is also supposed 

to help facility operators automate decision making, so 

they can focus on other work.

Facility owners could benefit from the performance 

and cost benefits of a more optimized operation, said 

Bushby.

“We expect this research to inform the development 

of guidelines, standards, methods of test and possibly 

industry-run product or design certification programs,” 

said Bushby. 

Future Possibilities

The IBAL does not interact with NIST’s other testbeds 

but could in the future.

Researchers have considered integrating it with the 

Virtual Cybernetic Building Testbed (VCBT) and the 

Smart Grid Testbed Facility, said Pertzborn. She said the 

testbed could help projects in NIST’s Fault Detection and 

Diagnostics and commissioning work.

As NIST is involved in research and standards development related to a future smart electric grid, Bushby 

said progress in that area would require much more 

collaborative interactions between buildings and the 

grid. 

“A smart grid environment complicates the optimization challenge because it introduces other opportunities and constraints. Linkage with the NIST Smart Grid 

Testbed in the future will create an opportunity to 

explore these building-to-grid interactions and how 

they impact system optimization,” said Bushby, chair 

of ASHRAE’s Smart Grid Application Guide Ad Hoc 

Committee. 

NIST will engage collaborators from industry and academia to take full advantage of the capabilities of the 

IBAL. Data will also be posted on the lab’s website. 

“Researchers are always on the lookout for reliable 

data sets that can be used to advance their work. We 

have taken great care to understand and document our 

measurements. We plan to archive our experimental 

data along with meta information about what was being 

tested,” said Bushby. 

The IBAL contains four simulated zones, stacked one above the other at the center 

of this image, that generate cooling loads for the water system. Each zone is connected to a VAV unit, shown at the left.

CREDIT: DENISE HERBERT

An ice storage tank can be used to meet the cooling loads instead of the chillers 

or water side economizer. This system allows loads to be shifted to times of the 

day when electric rates are lower.

CREDIT: DENISE HERBERT

The National Institute of Standards and Technology’s Intelligent Building Agents 

Laboratory (IBAL) is a controlled environment with reproducible weather and 

building loads that NIST uses to analyze real building mechanical systems. The 

testbed demonstrates agent-based optimization and control approaches on real 

equipment and allows researchers to understand the challenges when moving out 

of simulation into reality.

CREDIT: KIKKERI/NIST