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Construction Automation 61.6 Application Examples 1075

giving the design team and the owner real-time cost

data. The use of DProﬁler instead of manual-based es-

timating resulted in a 92% reduction of time used to

develop the estimate.

The team developed an initial concept design and

created a model in DProﬁler with links to cost informa-

tion. The model took into consideration regional cost

factors, building type, and other components using tem-

plates that have been developed with experience from

similar projects. As the team constructed the building

mass, the cost data was updated in real time. Then, as

all components and assemblies were associated to cost

in a database, when the team included more details the

cost was automatically updated. In addition to linking

components or assemblies to the cost database, DPro-

ﬁler also allowed the creation of relationships and rules;

for instance, it included one speciﬁc component that

was not part of the model. In this way, as the model was

developed, real-time information linked to the database

was presented. The team also used DProﬁler to run

different scenarios and make informed decisions on

ﬂoor-to-ﬂoor height, square footage, location of com-

ponents, etc.

The team realized several beneﬁts after using BIM

to aid the conceptual estimate process. They found a re-

duction of labor hours to produce an estimate. DProﬁler

avoided the take-off process and also had an automatic

link to commercial cost databases. The design team was

able to produce an accurate estimate in real time, re-

ducing the time spent in verifying the accuracy of the

estimate, thereby spending more time in the ﬁnancial

analysis of the different options. Also, a visual represen-

tation ofthe estimatewas created, reducing the potential

for errors.

61.6.4 Construction Progress Monitoring

Automation

This example illustrates a method of automated

progress monitoring; the inputs are the as-planned 4-D

model and a sequence of on-site time-lapse photographs

that represent the as-built model. The objective of this

method is to automatically overlay the as-built images

with the as-planned model to determine and update the

progress status. It consists of putting the real-world

camera into the 4-D model; then, the image taken of the

On schedule Behind scheduleAhead of schedule

Fig. 61.6 Site photograph, superimposed photograph, and color

coding [61.59]

4-D model is overlaid with the site photograph taken

at the same time. The 4-D photograph displays the ex-

pected progress; therefore, superimposition of images

allows comparison of discrepancies between what was

intended and what was performed [61.59]. The method

uses earnedvalue analysis to present progress indicators

and uses a color code to provide a visual representation,

where a dark red colorrepresents objects that are behind

schedule/cost and dark green represents objects that are

ahead of schedule, as shown in Fig.61.6.

Future trends in this domain include implement-

ing combined progress tracking method that consists

of generating a BIM model of the project that contains

3-D geometry, schedule, and cost information with the

as-planned data. An as-built model is then generated

using the combination of two automated data collec-

tion technologies: machine vision and Wi-Fi.Togather

real-time object information, that information can be

translated using an IFC language to generate a 4-D

model with cost information on demand. Both models

can be superimposed, detecting graphically in real-time

the objects that are on time, the objects that are behind

schedule, and the objects that are ahead of schedule. In

addition, this application will allow the calculation of

earned value indicators with the information stored in

both models.

Part G 61.6

1076 Part G Infrastructure and Service Automation

61.7 Conclusions and Challenges

The cyclical nature of the construction industry, fea-

turing longer periods of reduced activity combined

with imminent shortages of skilled labor, increasing

quality expectations from costumers, tighter safety reg-

ulations, greater attention to computerized scheduling

and project control, and technological breakthroughs

led by equipment manufacturers, has once again put

construction automation on the map of researchers and

practitioners alike. In spite of challenges, such as cost,

lack of governmental incentives, regulatory barriers,

disbelief by the majority of the construction sector, or

the lack of research and development, much advance-

ment has been possible in construction automation in

the past three decades. Presently, the demand for ac-

curate, up-to-date, and timely information to manage

construction projects is growing, so automating the

construction management process presents enormous

beneﬁts. It has been proven that the use of technolo-

gies, such as automated data collection: reduces the

time required to gather information at the job site; al-

lows the use of real-time information; decreases the

response time when corrective actions have to take

place, reducing the costs associated with late response;

and enhances the visualization and communication in-

teractions within the project team. In addition, the use of

BIM to support different project management processes

also presents several beneﬁts. It enhances communi-

cation with and understanding of stakeholders, and

enables constructability decisions to be made during

the design phase and not only during construction. It

reduces the time spent in redesign and in answering re-

quests for information, and allows a better sense of the

time and the cost of the project, since estimates and the

schedule are more accurate and do not have delays or

overruns because of unexpected change orders.

However, there are still several technological gaps

that need further research and development. A signif-

icant drawback is the lack of major research in the

construction industry. The major challenges faced by

the industry in regard to construction management au-

tomation are: reduction of the technological gaps and

interoperability issues, the cost and availability of such

technologies, and the systematic education of construc-

tion practitioners on these subjects.

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Part G 61

1079

The Smart Bui

62. The Smart Building

Timothy I. Salsbury

Buildings account for a large fraction of global en-

ergy use and have a correspondingly signiﬁcant

impact on the environment. Buildings are also

ubiquitous in virtually every aspect of our lives

from where we work, live, learn, govern, heal,

and worship, to where we play. The application of

control and automation to buildings can lead to

signiﬁcant energy savings, improved health and

safety of occupants, and enhance life quality. The

aim of this chapter is to describe what makes

buildings smart, provide examples of common

control strategies, and highlight emerging trends

and open challenges. Today, the most prevalent

use of automation in buildings is in heating, ven-

tilating, and air-conditioning (HVAC) systems. This

chapter reviews common control and automation

methods for HVAC, but also describes how automa-

tion is being extended to other building processes.

The number of controllable and interconnected

systems is increasing in modern buildings and this

is creating new opportunities for the application of

automation to coordinate and manage operation.

However, the chapter draws attention to the

62.1 Background .........................................1079

62.1.1 What is a Smart Building? ........... 1081

62.1.2 Historical Perspectives ................ 1082

62.2 Application Examples............................1083

62.2.1 Control without Feedback ........... 1083

62.2.2 Feedback Control ....................... 1083

62.2.3 Energy Management Control

Strategies.................................. 1085

62.2.4 Performance Monitoring and

Alarms ...................................... 1087

62.3 Emerging Trends ..................................1088

62.4 Open Challenges...................................1090

62.5 Conclusions ..........................................1092

References ..................................................1092

fact that the buildings industry is very large,

fragmented, and cost-oriented, with signiﬁcant

economic and technical barriers that can, in

some cases, impede the adoption and wide-scale

deployment of new automation technologies.

62.1 Background

The worldwide energy used to heat, cool, ventilate,

light, and deliver basic services to buildings was, on av-

erage, approximately 2.4TW(= 2.4×10

W) in 2004.

Afurther5.6TW was attributed to industrial plants,

with a large fraction of these housed in buildings such

as factories, power plants, and other manufacturing fa-

cilities [62.1]. In developed countries, buildings can be

responsible for as much as 50% of total energy use.

These dramatic statistics coupled with the fact that hu-

man beings spend most of their lives inside buildings

make this application of critical importance to the well-

being of our planet and its global population.

There are many different types of buildings, rang-

ing from simple places of shelter to highly complex

ecosystems that provide a range of specialized services

to support speciﬁc functions. One common purpose

of buildings is to create a modiﬁed environment that

is comfortable for occupants even when outside con-

ditions are unfavorable. Comfortable conditions are

maintained through the operation and coordination of

mechanical and electrical systems and through the con-

version of energy from one type to another. The control

of indoor environmental conditions is the most com-

mon and widely exploited application of automation

Part G 62

1080 Part G Infrastructure and Service Automation

technologies in buildings and will be the main focus

of this chapter. Factors that affect the indoor environ-

ment are air quality, temperature, and humidity, as well

as lighting, and safety from ﬁre and security threats.

For a building to be smart it must have some form

of automatic control system. Building control systems

vary widely in complexity from simple mechanical

feedback mechanisms to a network of microprocessor-

based digital controllers [62.2]. At the latter end of the

spectrum, the network of controllers is often known as

the building automation system (BAS). A BAS needs to

interface with physicalsystems in order to effect desired

changes on the building, and the interfacing is usually

made through means of sensorsand actuators.Buildings

can contain many types of physical systems, the most

common of which are described in more detail below.

HVAC and Plumbing. In terms of energy, the most im-

portant systems in buildingsare those used to heat, cool,

and ventilate theindoor environment. These systems are

collectively known as the heating, ventilating, and air-

conditioning (HVAC) plant. The HVAC plant is used

to condition the psychrometric properties (temperature

and humidity) of the indoor environment as well as air

quality. HVAC systems range in complexity from sim-

ple residential units that may have only heating units to

advanced systems for high-performance buildings such

as clean roomsand chemicallaboratories [62.3].Plumb-

ing systems are closely associated with the HVAC plant

but are often handled by a different group of companies

and contractors on a building project. Plumbing serves

the HVAC systems with water supplies used for heat-

ing and cooling and also handles distribution of potable

and waste water. Plumbing and waste disposal systems

are critical elements in ensuring occupant health [62.4].

Automatic control is widely used in HVAC systems

and ranges from simple feedback loops to complex

sequences of operation that manage scheduling and in-

teractions between systems.

Lighting Systems. Lighting systems are responsible for

a large fractionof building energy use,close to that used

by HVAC for the commercial sector. Most buildings

have both artiﬁcial and natural lighting and the interac-

tion between these sources is important in creating the

right level of illumination. In most buildings, both arti-

ﬁcial and natural lighting are operated manually using

electric switches and window shades. However, auto-

mated lighting systems are available and are starting to

be used in modern buildings. For these systems, sen-

sors measure illumination levels in a space and also

whether a space is occupied and this information is used

to regulate artiﬁcial light levels and control shades on

windows.

Fire and Security. Fire systems are found in large build-

ings and include ﬁre detection and alarming as well

as sprinkler systems for abatement. Security systems

are used to control access to buildings and internal

areas and trigger alarms when unauthorized access is

detected. Both of these systems are evolving rapidly

largely due to the availability of more advanced sen-

sor technology and imaging devices. The additional and

richer sensor information available from these systems

is creating new opportunities for intelligent responses

to particular situations. For example, having knowledge

of where people are located in the case of a ﬁre can be

used to manage evacuation routes, improve emergency

response team planning, and also provide input to the

HVAC system to mitigate the spread of smoke.

Specialized Systems. Many buildings require special-

ist services to support speciﬁc tasks and functions. For

example, a hospital might require oxygen supply and

distribution and fume hoods for extracting dangerous

and toxic chemicals. In common with other building

services, these systems require piping or ducting for

containment and distribution, and pumps/fans, valves,

and dampers for ﬂuid movement and control. Local-

ized power generation and combined heat and power

plants that use waste heat from electricity generation

to power heating and cooling systems are also found

in some buildings or campuses. These systems may in-

clude renewable sources of energy such as solar, wind,

and geothermal, and other power generation technolo-

gies such as fuel cells and microturbines. Specialized

systems, and in particular those that are packaged, often

have dedicated embedded controls, but in some cases

the BAS might be deployed to provide some higher-

level control and supervision.

Supporting Infrastructures. Modern buildings contain

systems powered by electricity and an increasing num-

ber powered by natural gas. Buildings therefore need to

have a distribution network for these energy supplies.

Key components include wiring, switch panels, circuit

breakers, transformers for electricity, and valves, pip-

ing, and various safety devices for gas. Another key

infrastructure in modern buildings is that associated

with information technology (IT). The IT infrastructure

in a building is usually considered to be separate from

the other systems mentioned so far because it is han-

Part G 62.1

The Smart Building 62.1 Background 1081

dled by a different group of companies outside of the

construction business. Similar to electricity distribution,

IT systems require wires, switch panels, and access

points in order to facilitate the transmission of both dig-

ital and analog data for devices such as computers and

telephones. Specialized cooling systems may also be

needed for high-powered computing devices and data

centers. Electricity, gas, and IT distribution systems in

a building will usually have some control elements, par-

ticularly for safety reasons.

The range of systems and processes in buildings is

clearly very broad and cannot be covered comprehen-

sively in the space available here. For this reason, this

chapter will focus more on the control and automation

aspects of a building rather on the systems that are under

control. The chapter will also concentrate on the soft-

ware and algorithmic aspects of control systems, which

are the source of the smartness in buildings, rather than

the hardware and supporting infrastructures. The out-

line of the chapter is as follows. The rest of this section

provides a discussion on what makes buildings smart

and concludes with a historical perspective of building

technologies. An overview of common control strate-

gies and their applications is presented in Sect.62.2,

followed by a discussion in Sect.62.3 on emerging

trends that are affecting the buildings industry. Sec-

tion 62.4 describes open challenges and, in particular,

business and technical barriers to the adoption of new

technologies. Finally, Sect. 62.5 draws conclusions and

reiterates some of the key points identiﬁed throughout

the chapter.

62.1.1 What is a Smart Building?

A building is made smart through the application

of intelligence or knowledge to automate the oper-

ation of building systems. In modern buildings, the

intelligence or smartness of building operation is en-

capsulated in algorithms, which are implemented in

software on microprocessor-based computing devices.

Many of these computing devices are part of the build-

ing automation system, which can be decomposed into

the following four main components:

•

User interface – allows exchange of information be-

tween a human operator and the computer system

•

Algorithms – methods or procedures for performing

certain tasks such as control and automation

•

Network – includes information transmission media

(e.g., wiring), routers, and appropriate encoders and

decoders for sharing information among devices

•

Sensors and actuators – these represent the inter-

faces between the computing systems and the plant.

The user interface, network, sensors, and actuators are

critical components of a BAS, but these are all en-

abling technologies that only provide the means by

which the intelligence inherent in the algorithms can

be applied. The algorithms fundamentally determine

the operational behavior of the controlled systems and

are the source of the smartness. In a typical building,

numerous objectives can be deﬁned suitable for the ap-

plication of control methods. Examples are regulating

a room temperature to a set level, turning off systems

at a certain time, and controlling access to a room based

on information read by a card reader. Controlling a vari-

able, such as temperature, to a set level is probably

the most common control objective and is most often

carried out using feedback. Feedback is a fundamental

building block of control and automation and its ap-

plication in buildings will be discussed in more detail

in Sect.62.2.

Recent technological advances in information tech-

nology, including networking, computing power, and

sensor technology, have meant that the number of con-

trollable devices in buildings has proliferated. Not only

are there more devices to control, but information can

now be shared more easily between disparate systems.

Information is more easily accessible both within sys-

tem groups as well as across different groups. The

HVAC group of systems is particularly notable in mak-

ing information available to the BAS from multiple

types of subsystems including boilers, chillers, fans,

pumps, cooling towers, and measured by numerous

types of sensors. Opportunities abound within just the

HVAC group of systems for applying control strate-

gies that take advantage of the available data to improve

overall system performance.

The idea of combining information from different

systems to implement new and smart control and au-

tomation strategies extends easily to system groups that

traverse traditional boundaries. The example of com-

bining data from the ﬁre and access control systems

to provide improved emergency response information

and also more effectively manage evacuation was cited

earlier. Another example is in utilizing access control

data to estimate the number of people in a building and

then using this estimate to operate the HVAC systems

more energy-efﬁciently. Although huge potential exists

for coordinated system operation, the reality today is

that the handling of interactions is limited and in most

cases ad hoc. However, despite the primitive nature of

Part G 62.1

1082 Part G Infrastructure and Service Automation

current automation strategies, the sharing of scheduling

databases and responses to alarms represents signiﬁcant

progress toward smarter building operation.

Building operation is not the only way in which

buildings have been made smarter. The lifecycle of

a building includes its planning, design, construction,

installation and commissioning, operation, mainte-

nance, retroﬁt and remodeling, and destruction. Each of

these tasks not only consumes energy and resources, but

affects subsequent tasks. For example, a building will

only operate energy-efﬁciently if it has been correctly

designed and constructed. New and smart technologies

are being utilized at each stage in the lifecycle to im-

prove the overall process. A prime example is in being

able to simulate the performance of a design before it is

built [62.5]. This is a powerful technology that can lead

to cost and energy savings for a project. The ability to

simulate building systems is also enabling the develop-

ment of innovative algorithmic smart technologies such

as automated design and optimization [62.6].

It is also important to mention the signiﬁcant en-

ergy and resources used during the construction phase

of a building. Energy is used at every step; from the

production of the building materials, to their trans-

port to site, through to the operation of machines for

excavation and assembly of the materials. The busi-

nesses devotedto this one phaseof the buildinglifecycle

are numerous, diverse, and employ various forms of

automation to enhance efﬁciency. The term smart is

frequently encountered in various construction tech-

nologies including prefabricated components, advanced

supply chain and project management, and on-site ma-

chinery, to name only a few examples. However, the

term smart buildings has come to mean smart operation

more than anything else, and for this reason the opera-

tion phase will be the focus of this chapter. The smart

operations, enabled by technological advances, guaran-

tees cost savings in construction and operations, and

improved functionality [62.7].

62.1.2 Historical Perspectives

Modiﬁcation of the environmental conditions inside

buildings is not new, with records showing that the an-

cient Egyptians used aqueducts for cooling as long ago

as the second millennium BC [62.8]. Heating systems

were also used by the Romans in 100 AD in their north-

ern territories based on underﬂoor distribution of air

heated by furnaces [62.9]. From the perspective of the

building plant, evolution had been slow until the ad-

vent of commercially viable electrical air-conditioning

systems in the ﬁrst decade of the 1900s. The ori-

gin of these systems can be traced to discoveries by

Michael Faraday in 1820 on how to create a cool-

ing effect by compressing and liquefying ammonia, but

it was the commercial success of the early electrical

air-conditioners that triggered a new interest in the in-

door environment and its control. Activity in this area

was probably at its height in the ﬁrst half of the 20th

century. During this period, the ﬁeld of heating, venti-

lating, and air-conditioning (HVAC)wouldhavebeen

considered a high-technology ﬁeld that posed some

of the most interesting engineering challenges of the

time [62.10].

The application of automation technology to build-

ings has paralleled its application to other industries,

with the idea of feedback playing a central role. The

feedback concept is a fundamental element of automa-

tion and has a history of its own dating back to the

water clocks of the ancient Greeks and Arabs [62.11].

The Dutch inventor Cornelis Drebbel is credited as cre-

ating one of the ﬁrst feedback temperature controllers

for a furnace in the early 1600s [62.12]. The ﬁrst

thermostats for space temperature control using heat-

ing plant appeared in the late 1800s. The thermostat

feedback system is an implementation of an intelli-

gent human concept, or procedure, to solve the problem

of temperature regulation. These early applications of

automation thus led to the creation of the ﬁrst smart

buildings. Implementation of feedback and other con-

trol methodsoriginally used mechanical transmission of

information, such as pneumatics. These systems were

replaced by electrical devices with controllers ﬁrst be-

ing implemented using analog circuits. Today, most

analog controllers have given way to digital devices

where earlier feedback strategies are now implemented

as algorithms in software.

The feedback concept has remained central in build-

ing automation. It is the most common type of control

strategy and is used to control everything from air-

conditioning to lighting to ﬁre and security to toilet

ﬂushing. Although the common room thermostat prin-

ciple is still widely used, building automation systems

now encompass an evermore sophisticated array of

control algorithms that not only provide regulation

of individual variables to setpoints, but also provide

high-level coordination and management of building

assets.

Part G 62.1

The Smart Building 62.2 Application Examples 1083

62.2 Application Examples

Possibly excepting certain types of chain stores, every

building is different, having a unique mix of structure,

geometry, orientation, location, number of people, and

types of building plant. The control and automation sys-

tems mirror this bespoke nature and are usually speciﬁc

to each particular building. Finding common elements

of control logic that run across all building types is

therefore a challenge. This problem is particularly ex-

acerbated at the higher levels of control logic hierarchy

that are used to coordinate the operation of different

systems. The aim of this section is to identify and re-

view a sample of control strategies that are generic and

found in buildings of different types. Although these

strategies are outnumbered in practice by ad hoc and

rule-based logic, they usually have a better scientiﬁc

basis and are more easily adapted and scaled across

different buildings.

62.2.1 Control without Feedback

A very simple and yet effective form of building au-

tomation is to operate systems based on a time clock;

for example, a heater in a building could be turned on

at a certain time every day and turned off at another

time. These times can be determined from some ex-

pected behavior that is known to be linked to time, such

as people coming in to work, or even the sun rising and

setting. This kind of control logic can be used to con-

trol everything from building access, lights, and HVAC.

Time-based control is also a type of event-triggered

logic where the event being monitored is time of day.

The strategy does not contain feedback because time is

unaffected by the action of the systems being operated.

Time-based operational scheduling is commonplace in

modern buildings as an overriding or supervisory logic

even when more advanced control and building man-

agement strategies are employed. The logic is usually

implemented as rules such as: IF TIME = 9.00AM

TURN ON CHILLER; IF TIME = 5.00PM TURN OFF

CHILLER.

Closed-loop control is synonymous with feedback

control. Open loop refers to the case where no infor-

mation associated with the controlled variable is used

in deciding how to adjust the manipulated variable; the

loop is thus open. In the HVAC industry, reference is

sometimes made to open-loop operation. In most cases

this involves having an operator make adjustments to

a manipulated variable manually. However, if the oper-

ator is making adjustments in response to observations

of the controlled variable, this is not truly open loop

because the operator is providing the feedback mech-

anism. An example of this is when a room in a building

has a heating device that can be either on or off but only

activated by a human operator. When the room is too

cold the person will turn on the heater and when it is too

hot they will turn it off. Manual operation of this sort is

common in buildings and may be carried out by a ded-

icated building operator who oversees plant operation.

In many situations, preexisting automated feedback sys-

tems may be overridden by the operator because of

lack of conﬁdence or trust. The operator then manu-

ally adjusts things such as control valves and dampers

to maintain comfort conditions.

62.2.2 Feedback Control

Single Loop

Feedback control is the most widely used automation

concept in buildings, with the temperature thermostat

being the vanguard of this strategy. Early examples of

these devices were based on pneumaticsand mechanical

transmission of information [62.13]. Modern buildings

use thermostats that contain a temperature sensor and

a small integrated circuit that determines when the tem-

perature is outside an acceptable range. The thermostat

triggers a switch to operate a device which is then

expected to bring the temperature back into its accept-

able range. Thermostatic temperature devices usually

require speciﬁcation of a setpoint and a control band.

A device would be switched either on or off whenever

the measured temperature was outside of the control

band, which surrounds the setpoint. Figure 62.1 shows

an example thermostatic control strategy for a heater

in a room with a setpoint of 20

◦

C and a control band

of 1

◦

C. There is a trade-off between the closeness of

control, determined by the control band, and the wear

and tear on the equipment resulting from cycling be-

tween on and off states. Some equipment types may

also have constraints on how long they can remain

in an on or off state and these are called minimum

on and off times. The maximum cycle frequency is

the reciprocal of the sum of the minimum on and off

times.

Thermostatic control is an example of single-loop

feedback control where the controller is a switch or

relay-type device that has inﬁnite gain. Theswitching of

the controlled device causes oscillations to occur in the

controlled variable around its setpoint. These oscilla-

Part G 62.2

1084 Part G Infrastructure and Service Automation

Control actions (On/Off)

Room

Measurements

Off

20.5°C

19.5°C

Setpoint = 20°C

Off

On On

Fig. 62.1 Thermostatic temperature control of a heater

tions areusually undesirable,especially if the amplitude

is large due to minimum on and off times being large

relative to the dominant time constant of the controlled

device.One wayto avoidoscillations isto usea physical

device whose output can be modulated. Instead of being

only on or off, the device output can be modulated by

manipulating an input between 0 and 100% of its range.

Having a manipulated variable that can be varied opens

the way forﬁnite-gain controllersto be usedin feedback

loops. Modulated systems make up about two-thirds of

controlled devices in buildings, with switched systems

representing the other third.

Proportional, integral, and derivative (PID) action

controllers are the most common type of ﬁnite-gain

controllers used in building feedback loops. These

controllers modulate the input to the controlled de-

vice based on the difference between the setpoint and

the controlled variable, and the theory behind the al-

gorithm is well established [62.14]. Proportional-only

(P) controllers are still common in buildings where

control exactly to setpoint is not critical. As is well

known, these controllers yield a steady-state offset from

setpoint and, when this is not desirable, proportional–

integral (PI) controllers are used. This complexity of

feedback control works well for most building control

loops that are dominated by one time constant.The inte-

gral action of the controller ensures that the error signal

can be maintained at zero and propertuning allows good

control without oscillations for most loops. Adding the

derivate action can yield better results for common ap-

plications such as room temperature control, but the

drawback is that tuning is more difﬁcult.

PI(D) controllers can also be used in buildings to

control switched devices. This is achieved by using an

element in the control loop that converts the output sig-

nal from the controller (usually between 0 and 100%)

to a pulse train (either 0 or 1). Pulse-width-modulation

(PWM) logic can be used to provide this conversion,

as illustrated in Fig.62.2. PWM and other variants have

been appliedto HVAC systemapplications withpromis-

ing results [62.15].

Although the PI algorithm is well established and

almost ubiquitously deployed for building control, it

has been recognized for some time that control perfor-

mance is often poor in practice. One reason for this is

that many plant items in buildings are nonlinear. When

a PI controller is used to control a nonlinear system, its

performance will vary with operating point. In severe

cases, the control might be too aggressive, causing os-

cillations at one point and yet be too slow at another.

These kinds of performance problems can jeopardize

comfort and energy use and also wear out equipment.

There are several methods for counteracting nonlin-

earity that are used in nonbuilding applications, such

as gain scheduling and model-based control [62.16].

The research community has investigated using some

of these methods in buildings including generalized

minimum-variance control [62.17] and model-based

control [62.18]. However, the industry has been reluc-

tant to adopt these methods because of the extra time

(and money) required for setup and tuning. More suc-

cessful approaches in the building industry have been

those that are self-tuning or automatically adaptive to

changes; examples include neural networks [62.19]and

pattern-recognition adaptive control [62.20]. The lat-

ter method of Seem has been commercialized and is

PWM

algorithm

Analog

input

Pulse

train

Cycle

Time

time

Fig. 62.2 PWM conversion of analog to switched signal

Part G 62.2