NBSIR 80-2065

Microprocessor Applications and

Building Control Systems to

Achieve Energy Conservation

Yui-May L Chang

James Y. Shih

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

QC

100

.056

|N0.80-2065

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 80-2065

MICROPROCESSOR APPLICATIONS AND

BUILDING CONTROL SYSTEMS TO

ACHIEVE ENERGY CONSERVATION

Yui-May L. Chang

James Y. Shih

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

July 1980

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technoiogy. and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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MICROPROCESSOR APPLICATIONS AND BUILDING CONTROL SYSTEMS TO

ACHIEVE ENERGY CONSERVATION

Yui-May L . Chang

James Y. Shlh

ABSTRACT

A well Insulated building may be considered a thermally efficient building.

However, the systems and controls within the building must also be energy

efficient in order to conserve energy. Thus, building controls is an important subject in energy conservation. In recent years, building control engineers have been developing energy conserving control methodologies. The availability of microprocessors and minicomputers has made it

possible to apply many control strategies requiring extensive computations.

Since a large segment of energy is consumed in buildings, the enhancement

of control methodologies will help achieve national energy goals. This

report is mainly to investigate the capabilities of microprocessors in

building control applications so that requirements to expedite these applications may be developed. Microprocessor applications in both conventional

control systems and in local-loop energy conservation devices are examined.

In addition, special applications of microprocessors in buildings are

explored. The development of microprocessor technology is also discussed.

KEY WORDS: Building automation; building energy management systems;

building controls; chiller controls; distributed control

systems; energy conservation; energy conservation devices;

microcomputers and minicomputers; microprocessor applications; programmable controllers.

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TABLE OF CONTENTS

Page

ABSTRACT iil

1. INTRODUCTION 1

1.1 Background 1 1.2 Purpose 2

1.3 Microprocessors and Microcomputers 3

2. AUTOMATION OF FACILITIES MONITORING AND CONTROL SYSTEMS 4

2.1 Centralized Control Systems (Non-Computer-Based) 4

2.2 Computer Based Automation Systems 5

2.3 Distributed Energy Monitoring and Control Systems (EMCS) . 13

3. TECHNOLOGY AND APPLICATION OF MICROPROCESSORS 15

3.1 Architecture and Performance of Microprocessors 15

3.2 Microcomputers and Supporting Chips 17

3.3 Single Chip Microcomputers 20

3.4 Single Chip Microcomputer With On-Chip A/D Converter 21

4. MICROPROCESSOR APPLICATIONS IN BUILDING ENERGY CONSERVATION ... 21

4.1 Building Energy Management Systems and Devices 21

4.2 Residential Buildings 25

4.3 Local-Loop Energy Control Devices 26

4.4 Solar Energy Applications 27

4.5 Chiller Control Methodology with Microprocessors 27

5. MICROPROCESSOR IN EMCS - CASE STUDIES 36

5.1 Minicomputer Control Systems 36

5.2 Distributed Microprocessor Systems 37

6. CONSIDERATIONS FOR DESIGN OF MICROPROCESSOR CONTROLLED EMCS ... 38

7. CONCLUSIONS 40

REFERENCES 41

BIBLIOGRAPHY 42

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I U J 1
MICROPROCESSOR APPLICATIONS AND

BUILDING CONTROL SYSTEMS

TO ACHIEVE ENERGY CONSERVATION

by

Yui-May L. Chang and James Y. Shih

1. INTRODUCTION

1.1 BACKGROUND

It is estimated that approximately one third of total energy consumption

in this country is expended in heating, ventilation, and air conditioning

(HVAC) of residential and commercial buildings. Energy consumption for

HVAG is a function of building envelope design, mechanical systems design,

and performance of the energy consuming equipment, such as boilers and

chillers. In general, a thermally efficient building implies a well insulated and sealed building envelope and an efficient mechanical system.

However, a building with efficient energy consuming equipment and a tight

envelope will not necessarily perform in an energy efficient manner. The

controls of the HVAC system are vitally important in determining the energy

consumption of a building.

The growing complexity of HVAC systems and the energy shortage have spurred

the design of more sophisticated HVAC control systems and the rapid growth

of energy management control systems in buildings. In recent years, computers and microprocessors have been used in building control systems.

Such systems, which are commonly known as energy monitoring and control

systems (EMCS), permit close supervision of building conditions. Through

the use of audible and visual alarm systems, the occurrence of problem

areas in the building can also be recognized by the EMCS. The advantages

of EMCS have resulted in a demand for these systems in numerous new

buildings and building complexes.

EMCS are available in a wide variety of sizes and functional capabilities,

with a range from less than 100-point capacity systems for small buildings

up to more than 1000 points for large building complexes, where a point is

defined as a finite address of a field Input/output device which may be

discrete or analog. Regardless of the number of points, the basic functional capability may include, but not be limited to, indication of status,

change of status alarms, and energy demand monitoring. For large systems,

two-way audio communication, data logging, slide projecting, and start/

stop programming are generally available. Currently, most computer-based

EMCS are capable of including energy conservation routines. However, most

of these energy conservation routines must be written in a "custom"

fashion. There are no universally adaptable routines that are applicable

under all building conditions. Of course, some energy conservation techniques require custom programming. For example, chiller loading optimization requires knowledge of the configurations of chilled water and

condensed water piping layouts, which could be parallel or series, in

order to optimize energy consumption based on the individual chiller

performance characteristics.

1
Energy management techniques used in computer-based EMCS may include the

following strategies [1]: enthalpy optimization for mixed air systems,

secondary-loop chilled and hot water optimization, chiller-loading optimization, start-time optimization, electric demand limiting, and night

ventilation purge. Besides energy conservation functions, the EMCS may

include a life-safety system, a building management/maintenance system,

and a door security/access system.

1.2 PURPOSE

Reduction of demand growth is part of national energy goals. Since a large segment of all energy is consumed in buildings, it is important

that the building industry help meet the national goals. The building

industry has been working on energy conservation for a number of years.

During the last 20 years, the attention of the building industry has

been focused on the building shell. The heat transfer characteristics

of wall materials have been studied extensively. In more recent years,

much attention has been focused on the prime energy consuming machines,

such as chillers, boilers, and package equipment. Control strategies

for building controls also play important roles in energy conservation

to optimize building energy consumption. The advent of microprocessor

technology will allow more sophisticated control strategies to be used

due to the capability and flexibility of the technology. Hence, indepth study of building control strategies, as of building shells and

equipment, is another requirement to achieve the goal of building

energy conservation.

In order to investigate the effect of replacements and Improvements of

control strategies, computer simulation xd.ll have to be developed as a tool for hypothesis testing. Today, the understanding of the building

shell and prime energy consuming machines has led to successful simulation of building heat transfer characteristics and the simulation of

energy consuming machines. Accordingly, it is difficult to estimate

the effect of control strategy on energy consumption with existing simulation programs because they simulate only load and mechanical systems

without control system simulation logic. In order to extend the capability for building energy consumption calculations, it is necessary to

include building control strategies in simulation programs. As for the

building control system Itself, both hardware design and control strategies can benefit from microprocessor-enhanced components. From the advent

of the microprocessor, the development of distributed control xd.th intelligent control devices and sophisticated programmable controllers will

expand system capability to achieve significant energy conservation.

In order to better meet national energy conservation goals, a project

is undertaken to anticipate what is happening in the building control

field with the development of microprocessor technology and the impact

of microprocessors on building controls. This report looks into

microprocessor utilization in EMCS, distributed control systems, and

local-loop energy conservation devices as well.

2
1.3 MICROPROCESSORS AND MICROCOMPUTERS

Microprocessor technology is one of the latest significant advancements

in solid-state electronics. The microprocessor was introduced as a device to handle simple control and computation problems. Due to its

low cost, small physical size, and expansion capabilities, the microprocessor has become a powerful device containing a complex package of

logic functions that may be used in many applications. During the past

25 years, the creation and development of this microelectronic technology

have contributed to successful space flights as well as a strong computer

industry.

Since the introduction of integrated circuits (IC) in 1959, the number

of components being placed on one chip has almost doubled every year.

The implementation of very large scale integrated circuit (VLSI) technology has made it possible to incorporate an entire computer processor

in one VLSI chip. Because a single chip of VLSI could contain as many

as one million discrete components, much more flexibility is available

for designers to Implement operations of complex systems. During the

last few years, numerous single chip microcomputers have been produced

by manufacturers, such as the INTEL 8748, MK3870, M6800, Z8000, and

others.* By definition, a microprocessor is a computer processor on one chip which includes an arithmetic unit and control circuits. The microprocessor, together with memory and input/output (I/O) units will form a microcomputer. The system including the microprocessor chip with memory

chips (read-only memory, ROM, and random-access memory, RAM), I/O chips

and other components gives a much greater flexibility than hardwired

systems in many general applications. ROM can be programmed to define

logic that has previously been possible only in hardware, and RAM allows

the user to store temporary information. The trade-off of hardware for

software by utilizing microprocessor-based systems will be significant,

since hardware logical circuit testing and trouble shooting can be

eliminated. In case of malfunction, it is much simpler to replace a RCM

than to change hardwired circuits.

Because of the demand for the microprocessor/microcomputer , the cost of

each unit is very low compared to hardwired devices. The low cost and

small physical size have allowed the microprocessor to gain wide acceptance among electronic design professionals. The computational flexibilities of the microprocessors is now utilized for many applications.

Microprocessor-based systems for building control and monitoring already

exist. It is evident that potential applications of microprocessors

in future building management and control will be high since, besides

EMCS and local-loop controls, other types of sensors, controllers, and

controlled devices could also utilize microprocessors effectively.

* Names of chips mentioned as examples do not indicate any NBS endorsement

of these products.

3
A negative aspect of the microprocessor revolution Is that manufacturers

are not working together to develop common standards so that all users

are benefited. Programming language and I/O devices for most microprocessors differ among manufacturers, and a consensus on standard

hardware and software for microprocessors within the near future Is

unlikely. These diverse methods have caused difficulties In utilizing

microprocessors In building controls.

2. AUTOMATION OF FACILITIES MONITORING AND CONTROL SYSTEMS

2.1 CENTRALIZED CONTROL SYSTEMS (NON-COMPUTER-BASED)

HVAC control systems have been playing an Important role In the building

Industry for the past 80 years. During this time, most of the accom- plishments of control devices have been In comfort control. Only In

recent years has energy Influenced the development of controls. The

centralized control system, and the beginning of building automation

systems, dates back a quarter of a century. Centralization of controls

was first used to reduce manpower. Large buildings Included many fan

systems, each of which had gauges and thermometers In the fan room to

Indicate the building variables. Periodically, the building maintenance

crew took readings of temperatures, steam pressures air flows, etc. A

large building required a large maintenance crew to take data routinely.

Maintenance and repair were carried out depending on the results of the

routine data collection. Without manual data, malfunctioning of mechanical equipment was difficult to forsee. In addition, control adjustments

had to be made manually. As Instrumentation and control techniques

advanced, the hardwired data panel was Implemented. Data could then be

collected at a central location In the building. It was no longer

necessary for the maintenance crew to go to each equipment room to collect data. Wltb experience. It appeared that the centralization scheme

with Individual hard wiring from each element of the control system was

too costly and too cumbersome to be effective. The technique of multiplexing [2], which Involves sending Information from a number of data

channels sequentially down a single conductor, was used In the second

generation of centralized systems. Newer systems were capable of status

Indication, analog and control point alarm Indication, remote analog setpoint adjustment and remote start/stop. Status and analog Indication at

the central console provided Information on building conditions. Including warning building operators of any abnormal conditions In the system

before there was any effect on occupied spaces. Although these non- computer-based systems were basically hardwired, some of the systems

could be expanded Into a computer-based system.

During the 1970 *s major developments In building automation systems

occurred In the building control Industry. Centralized control systems are currently being adopted by building management due to economic reasons. For most buildings, maintenance man-hours saved by the use of a central

control system can be utilized more effectively In other assignments, or

to reduce the number of personnel. Also, the control system operator can

4
identify system irregularities in a glance at the status summary sheet

Instead of checking out the building physically. In addition, the logging of equipment status provides for preventive maintenance of the

equipment in the building systems. Early detection of malfunctions and

routine maintenance may be performed to maintain a high level of equipment performance. However, a trained operator is still responsible for

the efficient operation of the total system based on his own decisionmaking capability. Therefore, this type of system is dependent upon the

operator for optimum system operation.

2.2 COMPUTER-BASED AUTOMATION SYSTEMS

During the 1960’s, attempts were made in computer-based building

automation systems. Several installations were created using custom

programming for each system, and medium-sized computers were used. Since

minicomputers were introduced in the early 1970’ s, computer based automation systems have proliferated. The minicomputer-based automation systems

provide a number of features unavailable with the conventional automation

systems, such as faster alarm reporting, and power-failure restart capabilities or uninterruptible power supplies. Input/output devices such

as printers and alarm-reporting devices, logging printers, cathode ray

tubes (CRT's), projectors, and intercoms are usually available from man- ufacturers. Special features which include machine run time totalization,

special English language mnemonics for Input/output, and passwords for

operation of the systems are easily accomplished through software on the

computer-based automation system. Functions of a building automation

system may be performed through hardware or software logic or a combination of both.

The available energy conservation routines, which are part of the application programs for minicomputer control systems, are not direct digital

control types, but are supervisory-control types. Instead of giving

command signals directly to an activator device, the computer usually

resets a controller set-point. Furthermore, only large buildings or a building complex have had building automation systems with sophisticated

energy conservation routines.

Basic monitoring/controlling functions that a central computer control

system would perform include various optimization schemes. These optimization schemes will either increase operating efficiency or conserve

energy. Examples of these optimization schemes include:

o start/stop

o enthalpy optimization

o chiller optimization

o solar system optimization

o fan system optimization

o heating/cooling optimization

o lighting optimization

o electrical demand limiting.

5
The essential energy conservation strategies used by the computer-based

automation systems are described in reference 1. Figure 1 is a functional block diagram of a typical centralized computer-based automation

system. The field concentrator is wired to sensors in the same vicinity.

The sensor signal is transmitted to the central console by the transmission system of m.ulticonductor wire, coaxial cable, telephone line, or other means of transmission.

The physical configuration of building automation systems is generally

similar among manufacturers. The central console is comprised of a central general purpose computer, input keyboards, alarm devices, logging

devices, optional CRT’s, graphic displays, intercoms, etc. Distributed

within the building are sensors that communicate with the local concentrator, which may be called a data gathering panel, field cabinet, or field input device. In this report, a field concentrator will be termed

a field Interface device (FID). All FID's may accept a plurality of

sensor Inputs. There are two ways a sensor may be wired to the FID [3].

One method, which is not common today, is to wire all sensors in series

to the FID. The other method is to wire sensors in parallel to the FID.

Figure 2A shows direct wiring from sensor to FID and Figure 2B shows

series wiring between sensors and FID. For the arrangement in Figure 2A,

the identity and location of the sensor is either stored in the FID or

the central console. The "intelligence" is centralized at either the FID

or the central console. On the other hand, the arrangement in Figure 2B

requires intelligence at each sensor because each sensor must "remember"

its own identity in order to be addressed independently by the FID. The

advantage of the layout in Figure 2A is lower cost at the sensors, and

the advantage of Figure 2B is the lower cost for wiring between sensors

and FID. As electronics technology progresses, either configuration may

prove to be most economical in the future.

A variation of the communication between the central console and FID's

is the hierarchy configuration. Figure 1 shows the non-hierarchy con- figuration of building automation systems. The hierarchy configuration

Includes in the wiring between the central console and the FID, a loop

controller, or middle manager, as shown in Figure 3. The purpose of

this configuration is to allow multiple-loop systems to operate efficiently. The central console monitors the operation of loops by commun- icating with each loop controller, which in turn monitors the FID's

within its loop. The loop controller may be a minicomputer- or microprocessor-based and designed to allow a stand-alone configuration.

The following paragraph will describe several typical arrangements of

actual systems, As an example, the A-2 system* is one of the centralized control and monitoring systems for large facilities up to 250,000

square feet (23226 m^) of floor space. Basically, it is considered to

be a computer-compatible system because it contains a custom central

* Code letters A, B, C etc. indicate different manufacturers.

6
OTHER FIELD

Figure 1 Functional Block Diagram of a Centralized Computer Based System

PARALLEL WIRING

SERIAL WIRING

Figure 2 Connections of Sensors and Field Interface Devices

7
Figure 3 Hierarchy Configuration of the Centralized Control Systems

8
processing unit (CPU) and it can also be expanded to a computer-supervised

control system by adding a real-time general purpose computer similar to

the configuration of Figure 1. For smaller buildings, with fewer control points, the CPU can be replaced by a microprocessor (A-1 system).

The A-1 system has the advantage of being small and of lower cost. It

is mainly used for s tart/stop, security, and fire alarm systems. Depending on the application, systems may be wired using coaxial cables or through telephone lines, as shown in Figures 4A and 4B. In addition to

the coaxial cable, additional voice transmission wiring is required for

intercom.

Special features of systems from each manufacturer are distinctly

different. For example, the "loop" concept of manufacturer B is unique

among manufacturers. Figure 5 Illustrates this concept. By transmitting data frames continuously through the loop, trouble points can be

easily identified using the loop concept. When frames are not received

after a certain period of time, the first FID will send an alarm frame

back to the loop controller, and the building operator is advised of the

condition. This provides constant digital supervision of the entire loop,

and very rapid annunication and location of trouble in the loop. The

data transmission rate of manufacturer B is much higher than that of the

other manufacturers. However, in terms of practical use, elapsed times

between an event and notification of the building operator are quite similar among manufacturers.

fid's of the automation systems are usually fixed logic used for

transmitting information between central console and field sensors. Recently, a microprocessor-based type of FID has been offered by some manufacturers. These microprocessor-based FID's are programmable so that they allow a high degree of flexibility to implement more sophisticated functions, such as stand-alone capabilities vdien the central computer is out of service. This is an example of the concept of distributed systems — the distribution of intelligence among lower level

devices within the system.

Some advantages of computer-based automation systems include:

o Reduce manpower — central computer operator can look at the

status summary from display devices instead of reading the data

locally at the sensors.

o Better record keeping — format printouts from the computer

output, such as teletype, can be formatted according to the

building management's needs.

o Provide contlnous operation of safety and mechanical

systems — with systems unattended, it is important that

safety systems and essential mechanical systems be monitored

at all times in order to receive alarm reporting continuously.

For example, locks on fire exits can be unlocked by the automatic system in case of fire.

9
4A

4B

Figure 4 Typical Connections of Field Interface Devices and Central Console

10
Figure 5 Interconnections of the "loop" System

11
o Routine maintenance — maintenance records and scheduling can

be automated, providing a daily printout of required maintenance and an improved basis for scheduling. For example,

lubrication schedules for motors and fans can be based on the

length of operating time.

o Computer hardware and software availability — the system

designer can fit the computer to the application through a wide

choice of machine sizes and speeds, mass storage equipment,

peripherals, operator interface terminals, graphic displays and

I/O Interfaces.

o Capababllity of data storage and retrieval — by use of memory

devices, such as magnetic tapes and disks, permanent data of

building operation can be stored for record keeping as future

reference or for processing at a latter date.

In contrast, there are problems with computer-based automation systems:

o Dependence upon manufacturers — presently, there are few

standard specifications for computer-based control systems.

Each manufacturer has designed their own system with hardware

and software that are incompatible with products of other

manufacturers

o Training requirement for automation personnel — the computerbased automation system depends largely on capable operators.

The operation of such a system requires personnel with sufficient training in electronics and computer systems technology.

o System reliability — the reliability of computer-based

automation systems still needs improvement because of the

technology is relatively new. A number of hardware and software problems are yet to be resolved, and specification of system

performance will have to be documented.

o Software problems — the current state-of-the-art for computerbased automation systems is to utilize the standard software

package provided by manufacturers. The user's extension or modification of this software package is cumbersome because these

software packages are essentially written in assembly language

for the particular minicomputer manufacturer. Currently, highlevel-language software packages are becoming available so that

special application programs will become feasible for users to

design and install.

o Cost and lead time — frequently, a computer-based automation

center may be awarded to a manufacturer based on the understanding that the installation and start-up of the system will be one year later. This is due to the nonstandard hardware and

software. Most installations require certain features which

involve additional costs in software development. Thus, lead

12
time also Increases. In addition to special hardware and software

costs, wiring of the field equipment costs may be appreciable.

The total system cost is usually quite high. However, most

owners of automation systems justify the purchasing of building

automation systems based on the operating cost reduction and

energy savings.

o Rapid obsolescence — due to the rapid growth in electronic

technology, most computer-based automation systems developed

during the past 10 years are relatively obsolete. Although

they are functional and continue to fulfill the design purpose, they are technically out of date. The newer automation

systems based on state-of-the-art electronic technology can outperform the older systems by far.

In spite of the disadvantages, computer-based centralized automation

systems are becoming more and more popular. As energy costs continue

to increase, and electronic technology continues to advance, the return

on investment for these systems will become increasingly attractive to

building owners. Furthermore, development of feedback controls and the

utilization of microprocessors for local control purposes will become

a natural application in the near future. The microprocessor is capable

of handling many control loops with ideal control characteristics because

of its programmable nature.

2.3 DISTRIBUTED ENERGY MONITORING AND CONTROL SYSTEMS (EMCS)

As discussed previously, fixed logic in the FID of a building automation

system acts as a "dumb" field cabinet for the communication between the

central computer and field controllers and sensors. This concept centralizes all the building information in the central computer for monitoring and controlling purposes. The tasks involved in processing the

data received are the responsibility of the central computer. The CPU

overhead Involved in checking for bad data, converting to engineering

units, scanning, routine Intertogation, checking the response to alarm

conditions, making routine control decisions, etc., can require a tremendous amount of computation and become a major portion of the system load.

As building automation and control technology have Improved, engineers

have applied larger portions of the plant monitoring and control functions to the computer. In addition to the routine building monitoring

activities, many energy optimization routines, building maintenance

instructions, life safety and security functions and computer graphics

features, can easily cause "data" congestion. The larger and more com- plex the system is the greater processing time that is required to

handle all these functions. The physical limitation is real. The con- cept of distributive computing can be adequately defined as the concept

of physically and logically separating a computer control system into

functional units. Each unit is dedicated to a portion of the overall

control task. For example, by placing a processor in the FID it becomes

a so-called "smart" FID. Thus, it possesses the capability of being

a "stand-alone" local control loop of the distributed control system.

13
Basically, the intelligence of field hardware is the difference between

the distributed computer control system and the centralized computer con

trol system. In distributed systems, computations at the local level,

including local data scanning and calculations on data, are done by the

field equipment; therefore, much of the computation burden for the central console is shared by the local FID. The more responsibility the

field equipment can share, the more efficient the central console can

be. Distributed system FID's are usually microprocessor-based. The

computation power and the speed of the microprocessor lent itself well

to local data gathering and data manipulation tasks.

Some advantages of using distributed automation systems are:

o Stand-alone capability — the programmable CPU in the remote

terminal can be programmed such that the remote system may

operate in a stand-alone fashion as well as communicating

with the central computer. All desirable control functions

for the local loop may be implemented without having to rely

on the computation power of the central CPU.

o Improved systems reliability — since remote terminals are sharing the load of the central computer, the load on the

central computer is greatly reduced. It follows that the

number of necessary functions dependent on the Information

from the central computer, is also reduced and therefore,

most of the routine functions are able to continue when the

central computer is out of service; this Increases the reliability of the overall system.

o Better expandability — to accommodate new data points and

controlled functions, each extension stage may be added to

distributed systems without replacing the central computer

system data base. The "intelligent" FID may be programmed

such that the local data base is d3mamically created and

automatically communicated to the central computer without

sustaining any system downtime.

o More flexibility — with distributed control systems, each

FID may be programmed such that the special requirements of

a particular area of the building will be met. For example,

certain FID's may carry on security or door access functions

in addition to building monitoring duties. Such special

programming does not require the system to shut down for

the entire building, only those points governed by the particular FID.

By adopting the concept of distributive intelligence, the building control industry has begun to promote energy management systems for small

buildings by utilizing the capability and compactness of microprocessors

These systems could be operated independently, or interfaced to a host

computer. Concurrently, major manufacturers of building automation

14
systems are producing new systems with microprocessor-based FID*s. Some

of these systems have the capability to interface with the existing

automation systems. For example, system A-5 is a microprocessor-based

distributed building management systems that offer two types of FID’s,

P-5 and P-4. The P-5, which is microprocessor-based, has its own operating systems, data file, and application programs. The P-4 which is in

fixed logic could link the P-5 and control point sensors in areas of high

data density, as illustrated in Figure 6.

fid's of systems A-1 and A-2 (central systems) could be tied in directly

to FID P-5 of the distributed system A-5. Thus, the centralized systems

A-2 and A-1 could be converted to a distributed system without changing

any field wiring. Figure 7 shows the connections. Alternatively, independent microprocessor-based central control system A-1 could be tied

directly into the distributed system A-5. Figure 7 depicts the direct

connection.

The distributed control system lends itself readily for long distance

transmission through telephone lines using sophisticated software logic.

As an example, building automation systems of two facilities, 40 miles

apart, could "talk" to each other by dialing to each other automatically.*

3. TECHNOLOGY AND APPLICATIONS OF MICROPROCESSORS

3.1 ARCHITECTURE AND PERFORMANCE OF MICROPROCESSORS

A microprocessor, which is a single crystal of silicon, has the capacity

to contain a circuit of up to more than 1000 transistors. It is a program-controlled component, used to execute the following three categories

of instructions:

o Move data from one place to another within the system -- such as from an input line to a storage register

o Perform arithmetic or logical instruction on data — such as

to add, subtract, or perform logical operation

o Instruct where to go next in the program.

The internal architecture and instruction sets are essentially similar in

most microprocessors.

According to their performance, microprocessors may be classified as memory-oriented or register-oriented. The former are mainly used for

data processing applications and the latter are for dedicate applications where a large number of registers are needed.

* See Section 5.

15
SYSTEM A-1 Figure 6 Configuration of Expanding Existing Central System

to the Distributed System

SYSTEM A-1 (MICROPROCESSOR CPU) SYSTEM A-2 (conventional CPU)

Figure 7 Configuration for Replacing Existing Central

System with a Distributed System

16
Based on their word length, there are four major types of microprocessors.

o 4-bit: Low-End Microprocessor — for simple applications which

stand alone, such as in hand calculators, microwave ovens, TV

games

o 8-bit; Mid-Range Microprocessor — flexible, complex, efficient, hardware-oriented, and most suitable for general-purpose

use. This type, used in most controls and automation applications are currently dominating the microprocessor market.

o 12-bit; Upper-Range Microprocessor — most suitable for doubleprecision calculations and straight memory referencing. This

type is more accurate than the lower-bit type. For example,

the IM6100 is a 12-bit microprocessor that recognizes instruction sets of the PDP-8/E minicomputer.

o 16-bit; High Level Microprocessor — most complex, highperformance, and basically software oriented using high level

language. Microprocessors of this type are able to recognize

instruction sets similar to sets used in many computers, and

some are ideally suited for industrial control motors, relays,

solenoids, actuators, etc.

The selection of a microprocessor depends upon a combination of desired

word length, speed, and memory efficiency. Manufacturers of microprocessors are continuously looking at various ways of using compact processing

elements in relatively high performance applications. Today, the technology has matured to such an extent that microprocessors with impressive

specifications are being offered by many manufacturers, utilizing virtually all available Integrated circuit technologies. The interpretation

of high performance depends upon the viewpoint and applications of the users

Possibile applications of microprocessors in data communications, signal

processing, and real time control will be likely to proliferate. The

complexity of integrated circuits is becoming so high that subsystem and

system level designs in the future cannot be separated from the design

of the integrated circuit Itself.

3.2 MICROCOMPUTERS AND SUPPORTING CHIPS

In conventional computer systems, the major components are a central processing unit (CPU), memory, and input/output (I/O) facilities. Together

with memory and peripheral circuitry, microprocessor chips form complete

microcomputers in which each of these components can be single chips.

Regardless of the technology used, microprocessor systems are organized

in basically the same way as conventional computer systems. The microcomputer utilizes a microprocessor as its central processing unit which

will sequence through all instructions and execute each one. In complexity, these microcomputers fall somewhere between conventional minicomputers

17
and small, handheld calculators. Since both the CPU and the memory

are large scale integrated circuit (LSI) components, a microcomputer has

the advantage of being low cost, compact, and with low power consumption

as compared to other computers built without LSI components.

For the I/O circuits, transistor-transistor logic (TTL) compatible I/O

ports are available from most microcomputer manufacturers. Standard

peripherals, such as displays, keyboards, data modems, paper tape readers

and punches, cassette tape, printers, graphic plotters, and floppy disks can utilize these I/O ports to link the microcomputer to the real world.

Additionally, analog to digital (A/D) converters, digital to analog (D/A)

converters, functional modules. Isolated digital I/O systems and other

systems also require I/O ports to enable the microcomputer to monitor

and control mechanical and electrical systems.

Later enhancement of microcomputer systems offers a complete package of

development software aids in ROM, which is referred to as the firmware

of the microcomputer system. The firmware package can be a single chip

ROM, such as the operating system for microcomputer software support,

or a group of ROM’s to provide the ability to generate, edit, assemble,

load, execute, and debug programs for all type of applications. Including system firmware in microcomputer systems can speed up the process

of software loading from some peripheral devices into RAM. Additionally,

with the development aid software in ROM, all RAM is available for the

user's program.

The development of memory chips by the solid-state Industry has another

successful advance for microcomputer technology. Large memory systems,

such as multi-disk drives, derive their low cost per bit by spreading the

high fixed costs of electromechanical components over a large number of

bits. If the actual data capacity needed in a system is less than a few

megabits, disk costs per bit go up substantially. The mini-floppy-disk

drive is a partial answer to the reduced storage requirements, but actually the cost per bit will rise with lower storage capacity even as the

hardware cost goes down.

The trade-off of faster and more expensive semiconductor memory and

slower but lower cost magnetic disks and tapes is no longer necessary

due to the Introduction of CCD, (charged-couple-device) and MBM, (magnetic bubble memory) [4]. The relationship of cost per bit and access

time is shown in Figure 8. The production of MBM resolves the problem

of increasing the memory-access rate, as compared to the disks in the

minicomputers. MBM, which is non-volatile, contains up to 1 million bits

per chip and has an access rate of approximately 5 K bits per second.

It is anticipated that the mass storage disk drive for microcomputers

today will be replaced by the new bubble memory in the future.

The microcomputer is undergoing both hardware and software development

so rapidly that the difference between a microcomputer and a minicomputer

is difficult to distinguish. In essence, the level of support from

minicomputer manufacturers has been higher than that from microcomputer

18
MEMORY

COST

PER

BIT

|c|

ACCESS TIME |sec|

Figure 8 Comparison of Cost and Speed of Memory Systems

19
manufacturers, with more peripherals, more software, and more applications provided for minicomputers. However, the inexpensive microcomputer

has more flexibility to control industrial applications, especially with

16-bit systems. The system reliability is reduced as the number of functions served by each computer increases. Therefore, it is practical to use distributed computer controls if the cost remains the same.

Regardless of developments in microprocessor technology, there are numerous problems, including software, interfacing, and maintenance

problems, in utilizing microcomputers in building control systems today.

The hardware design for many control functions has been in existence

for many years. However, to duplicate the same function with microprocessors, extensive programming will be required. This is an added

cost in utilizing microprocessors. Hopefully, the software cost per

function will decrease in the future as small-applications-oriented

languages become available. The cost of interfacing the microcomputer

to external devices is the greatest hardware cost. Field sensors and

actuators are expensive as well as the voltage and current conversion

circuits necessary to interface these devices with the microcomputer.

The problem with microprocessor maintenance is the difficulty in identifying hardware malfunctions, since the microprocessor is basically a new device, and system diagnostic is not common or well debugged. Once

the hardware problem is identified, the field repair of a microcomputer

itself can be done on a module replacement basis.

3.3 SINGLE CHIP MICROCOMPUTERS

A single-chip microcomputer contains the CPU, memory and I/O ports in a single unit. Only power supply and I/O devices are required for them to

be operated. Some single-chip microcomputers are either not expandable,

or very difficult to expand. They are mainly used for dedicated applications. In the future, the expected trend will be an increase in flexibility and computation power in these devices, such that a more complete

and complex general-purpose microcomputer system may be packed on a single

chip.

Early production of the single-chip microcomputer has been limited to

4-bit BCD (binary code decimal) and numerical processing type, such as those used in hand calculators. Later developments have included the

8-bit midrange microcomputer to handle more complicated processes.

Again, they are still designed for dedicated controls and are difficult

to expand. Some need an external resistor-capacitor (RC) network for

timing control. As the technology advances rapidly, 8-bit and 16-blt

single-chip microcomputers will have the I/O features similar to the

multi-chip microcomputer system. They could support more ROM and RAM

to expand the microcomputer system extensively. Zilog's Z8 is an example

having this extension capability. General Instrument's PIC 1656 las

a crystal attached directly to the chip. Motorola's MC6801 is a 16-bit

microcomputer with a clock and a 16-bit programmable timer. Some manu- facturers make available proprietary application programs which may be

built into single-chip microcomputers at a nominal cost.

20
3.4 SINGLE CHIP MICROCOMPUTER WITH ON-CHIP A/D CONVERTER

A significant advancement of the single-chip microcomputer is to include an analog-to-digital converter on the microcomputer chip. The INTEL 8022

is an 8-bit single-chip microcomputer having processor, memory, and twochannel A/D converter all packed into a 40-pin package. The chip

includes 2 K bytes of ROM, 64 bytes of RAM, CPU, internal time/event

counter, a clock oscillator, a 2-channel 8-bit A/D converter and 26 digital I/O lines. The A/D converter, which requires no external circuitry,

has two multiplex 8-bit channels. Conversion is completely hardwarecontrolled using the successive approximation technique, and occurs in

40 microseconds. For general applications, analog devices, such as temperature sensors and pressure sensors may be directly connected to one

of the channels of the A/D converter. The software capability of this

single chip microcomputer includes filtering the input analog signal

digitally for special purposes. For example, the software can easily

be designed to average several input analog readings or to apply different weights to different readings before accepting them. For some applications the 8-bit resolution of the A/D converter may be a limitation.

However, future development of the one-chip microcomputer and A/D con- verter may circumvent this limitation. ^ It appears, in the feedback control application of microprocessors, that the addition of A/D converter

is an important milestone in revolutionizing the feedback control methodology.

4. MICROPROCESSOR APPLICATIONS IN BUILDING ENERGY CONSERVATION

4.1 BUILDING ENERGY MANAGEMENT SYSTEMS AND DEVICES

The concern over energy supplies and their cost during recent years has

led to the concept of building energy management methodologies, especially

in commercial facilities. Any form of depletable prime energy, electrical, natural gas, petroleum, or coal, is under consideration for energy

conservation. The benefit of energy management systems, is to minimize,

or optimize, energy usage in buildings. The energy management methodologies include considerations of "static" losses, such as building insulation and HVAC system, and "dynamic" losses, such as energy consumption

and the rate of energy usage. For large facilities, centralized computerbased automation systems, or distributed control systems can be utilized

to optimize energy usage. As for smaller buildings, the microprocessor

type programmable controllers in the form of small energy management

systems or energy control devices, can be employed to control energy

usage

In the case of electrical energy, more concern will be on peak usage of

a facility, because the changes for demand are sometimes higher than

for the actual electrical consumption. Hence electrical load shedding

is the most common central scheme used in energy management.

21
The method of load shedding is the practice of reducing electrical loads

without adversely affecting comfort, safety, or production and is usually

carried out using one of the following control schemes:

o duty-cycle control

o time-of-day control

o demand control.

Duty-cycle control consists of grouping a number of building loads, and,

after determining the duration and frequency by which each load can be

shed, off /on times for the loads are staggered so that a minimum amount

of load is on at any time. The tlme-of-day control involves turning a load on and off based on a predetermined schedule. Different schedules

may be used on weekdays, weekends, and holidays. For example, lights,

heating systems, and air conditioning systems may be scheduled to be

turned on an hour before a building is occupied and turned off an hour

before a building is unoccupied. Demand control, or demand limiting, is a scheme to minimize the demand charge. The actual energy conservation

is not significant because the load at peak time is removed and Incurred

at different non-peak time. The strategy of demand limiting, generally

included in most energy management systems, is to minimize the coincident

occurrence of large loads.

Energy management systems should include the generation of routine

reports which can consist of:

o management reports

o maintenance reports

o summary for failure or alarm reports.

A management report summary showing how a system is performing and how

much energy, or manpower is used or saved may be printed out on a daily,

weekly, or monthly basis. A maintenance report can be generated to

indicate how many times a load has been cycled, and the cycle duration,

or the report can describe the operating efficiency of subsystems. The

maintenance report could list pieces of equipment that require preventive

maintenance, so they can be scheduled for maintenance. A report of the

alarm summary could be generated whenever an input or output module of

the system failed, or on demand by operator.

A programmable controller can be considered as a special purpose digital

computer that can replace hardwire circuits; such as relays, counters or

timers. As engineers implement programmable controllers by designing

around microprocessors, microprocessors will become powerful devices to

handle sophisticated control functions. Having significant advantages

of low cost, small size, and low power consumption, microprocessor-based

programmable controllers have been applied to stand-alone energy management systems which are usually used in smaller buildings having less than

100 control points. The majority of these energy management systems from

the commercial control companies are using general control strategies of

demand limiting, duty cycling, time-of-day control, and load shedding

22
with priority levels. The programmable controller also Includes manual

override, and alarm features for malfunctions. The commonly used

demand limiting methods are forecasting and ideal curve [1].

Some manufacturers employ the sliding window method to continuously

monitor actual demand, such that current (sliding window) interval

energy consumption as well as peak interval energy consumption are retained and automatically updated for each meter input. Some also use the intermittent "sample and hold" technique, with the "hold" being the

period between control points at which forecasts are made. These energy

management systems usually have battery backup supply to ensure that

power failure will not destroy memory. Access code is also used to prevent tampering. There are systems with additional environmental temperature control capabilities to adjust the cycling strategies, such as increasing the air conditioning off time if the outside air temperature

falls.

Another important feature for some portable energy management systems is

their use for distributed systems of a host computer. That means they

have the flexibility to be extended whenever the facility needs to be

enlarged or improved. For example, systems IM-1 and IM-2, PT-1 and PT-2,

and AC-1 have the capabilities to be interfaced to central computers.

o MC-1 — In addition to the peak control, MC-1 is also designed

to be adaptable for control of other forms of energy, such as gas, oil, steam, etc.

o AC-1 — Permits the Introduction of a supplementary or alternative energy source. Off-peak power usage and solar heating

can be optimized by the system. It is also capable of performing enthalpy control. If more controlled points are required,

several AC-1 systems can be connected serially.

o IM-1 — Is capable of performing nine energy functions by

monitoring sensing points in a building. It can perform sur- veillance of security, fire, flood, sump-pump, etc.

o PT-1 — There is an input for a photocell so exterior lights

will go on only if it is dark outside. It can override the

programmed timer for these lights.

o C-7 — Has up to 55 points capability using special sensors named accensors. This is an "intelligent" sensor which "remembers" its own address, type, and scaling factor. A custom LSI

chip is used for the addressing and point characteristic identification. These sensors can be wired in a serial manner

because of their intelligence. The term accensor stands for

access and sensor, and is a unique feature with this manufacturer.

23
o AT-1 — Is a microprocessor-based system designed to reduce

electric energy cost in a hotel/motel environment. It provides

monitoring of occupied and unoccupied rooms for the desk clerk.

It is possible for the desk clerk to control room air conditioning and heating systems remotely from a central location.

A natural extension of this capability is to provide an indication on a central panel when a room has been cleaned.

o RC-1 — Is a microprocessor-based programmable controller for use with HVAC systems of various solar-assisted facilities. It

has the capability to accept different types of inputs such as temperature, pressure, flow and others. After input signals are converted to engineering units, customized control equations can be solved for outputs. In such a manner, the HVAC

system will perform according to individual control function

requirements. For example, the controller can turn on appropriate pumps by monitoring differential temperature measurements,

or turn on the backup system in the event that solar radiation

is not sufficient.

Because it is inexpensive, flexible, and small, the microprocessor has

played an important role in programmable controllers in feedback controls

The building control industry has employed microprocessors in the applica

tlon of energy conservation devices such as temperature controllers, and

special timers for home and commercial users. In general, the microproce

sor based temperature controllers, or thermostats, are designed around a microprocessor chip to give the user choice of temperature and scheduling

controls via simple programming for the purpose of energy conservation.

They usually provide the capability to have more than one temperature

setting in the 24-hour period. Some have battery backup power systems to

maintain continuous temperature control. Manual overriding features are usually provided to handle any unusual circumstances. The following are some of the examples of the programmable temperature controllers.

o CP-1 — A temperature controller built from a single chip

microcomputer, INTEL 8049. It can accommodate up to six

changes per day in two different 24-hour schedules, including

weekday and weekend. There is also an outdoor temperature sensor that allows the user to see the outdoor temperature

display on the device.

o PC-1 — The thermostat utilizes mercury sensor technology

to avoid drift from the temperature setting. It is also a microprocessor-based temperature controller providing four

temperature settings, proof of heating, and proof of cooling.

o RT-1 — The thermostat includes a clock in the unit with a 3-way switch to offer time indication only, or temperature

indication only, or both, alternating every 5 seconds. The

clock does not contain a battery, and it is supplied from the

24
same two wires that power the thermostat. This microprocessor-based thermostat has two settings for temperature

control.

o TC-2 — Is a programmable timer for special applications

to be used as a multi-load, and multi-function time clock.

TC-2 is also a microprocessor-based controller with software

capability to provide time-based scheduling and cycling of

electric loads. Up to 16 loads can be controlled by this

programmable timer. A unique control plan for each of the 7 weekdays plus special holidays could be set up for individual

loads. Manual override and battery backup are provided.

4.2 RESIDENTIAL BUILDINGS

As the cost of utilities continues to rise, homeowners have become con- cerned about energy conservation in their houses. Builders and owners have been addressing this problem by increasing insulation, reducing air

infiltration, and decreasing thermostat control settings. Sophisticated

control strategies for residences has not yet been feasible; and the

only control in most residences has been limited to the temperature control, or thermostat. With the advent of microprocessors and their supporting chips, numerous energy control strategies have been developed

for home applications. However, products to implement the strategies

are new entries to the market and there is insufficient data for ana- lyzing the payback period required for the justification of the initial

cost. An example of an available product is an interactive computerized

control system built around the INTEL 8085 microprocessor by manufacturer

H and installed in a $350,000 home [5]. Six months after installation,

the energy savings was estimated to be about 50%. This microcomputer

unit has the capability to open and close a sunshade using a time control

unit, which also has priority scheduling for other appliances. The unit

also has a theft security system and connects to the smoke detector for

fire protection. The system shuts down all appliances if an emergency

occurs. Water conservation via lawn watering control using a sensor

in the lawn is also provided by the system. Although the manufacturer

claims that this interactive microcomputer unit will soon become standard

in new homes, further evaluation is necessary before any conclusion can

be made.

Another example of a home energy management and control system is a microcomputer system designed for use in buildings under renovation, or

in new buildings [6]. This system is installed in facilities with a solar energy system consisting of "active windows" of double-pane glass

on the south walls. This microcomputer energy management system has the

capability to close the shutters of active windows automatically when

night-sky cooling or solar heating systems are not in operation. It also

monitors the air quality, control relative humidity and utilizes ultrasonic motion sensors to monitor occupant activities for ventilation control programs.

25
Residential energy control management systems have some drawbacks, such

as climatic dependence and lack of local maintenance facilities.

Standard hardware and software are difficult to apply in some areas

since the building situation and climate conditions will make a big

difference in system design.

4.3 LOCAL-LOOP ENERGY CONTROL DEVICES

Some control system components may be located in the general area of the

equipment or space being controlled, and these are referred to as localloop devices. Although a large number of microprocessor-based building

energy management systems are in use, the number of microprocessor-based

local-loop energy conservation devices is somewhat limited, with the

exception of the demand-limiting device. The main reason for the wide

acceptance of the demand limiter is the demand charge penalty. The

penalty for exceeding the demand limit is to pay a demand charge for

a period of several months following the establishment of the new peak.

Building automation systems have adapted a variety of optimization schedules for energy conservation (section 2.2). With the concept of distributed control systems using microprocessors, each local loop can continue

to be functional even when the central computer is off line for service.

Apparently, the energy optimization schemes of the EMCS can be replaced

by microprocessor-based stand-alone devices. The most probable developments by the control manufacturers are the energy conservation devices

such as enthalpy optimizer, chilled water optimizer, secondary-loop optimizer, and start-up controllers. However, in some cases, the potential

return of these devices may not be as high as for the demand limiter.

As microelectronics devices become relatively inexpensive, it is anticipated that these control devices could be designed around microprocessors

with the advantage of small size, flexibility, and low cost; or even become "off the shelf" items for standard HVAC systems in the future.

Furthermore, the application of microprocessor-based control devices

would not only be limited in large building automation systems but

include residential facilities as well. For example, a microprocessorbased temperature controller could include several sensors to Indicate

temperature readings in different locations. The control logic of a single zone system, may be designed in a variety of ways. It may be

based on either "most occupant" or "scheduled" logic. The "most occupant" logic requires some sensing means of occupancy within the zone. The controlled variable is the space temperature of the "most occupant"

space. If no occupant is present, the space temperature will be con- trolled at minimum energy level. As for the "scheduled" logic, one could select family room sensor as evening temperature, bedroom sensors as night temperature, dining room sensor as dinner time temperature, etc.

It follows that many other generic ideas may be developed for energy

conservation application, even though such control devices might be

costly at the present. However, the consideration of this and similar

26
apparatus for residential controls should not be overlooked as the high

performance microprocessor becomes more capable, reliable and inexpensive.

4.4 SOLAR ENERGY APPLICATIONS

Since the Arab oil embargo and the resulting rise in the cost of energy,

energy conservation has played a key role in building automation systems.

In many conventional controls, the individual control loop is an independent feedback control system, although the control variables in the loop

are frequently related to other control loops.* The application of adaptive controls in energy conservation requires the analysis of the entire

system so that dynamic relationships between subsystems can be taken

into account. The complexity of system optimization increases if the

control system includes many subsystems. Thus, the control logic under

such circumstances requires the capability of microprocessors and microcomputers. Recently, new control methodologies have been investigated,

especially in the area of solar energy controls.

There are numerous projects sponsored by Federal agencies and private

industry to develop microprocessor-based adaptive controllers and control algorithms for solar energy homes. The purpose of these projects

is to evaluate the cost effectiveness of certain controllers and to

explore a variety of control strategies. For example, from the same manufacturer of the RC-1 programmable controller, a microprocessor-based

programmable data acquisition system (PDAS) has been developed to be

custom-programmed for three solar energy conservation houses to monitor

all energy-related parameters [7]. The Information from the subsystems

is to be used for energy-related engineering studies for the Pacific Gas

and Electric Company.

Another project, developed by Middlebury College, Vermont, is to compare

different control strategies for two solar hot water collector systems

interfaced to a microprocessor-controlled data acquisition system. These

identical systems are being operated simultaneously under the same load

and environment conditions, but different control strategies will be used

for the purpose of energy conservation testing.

4.5 CHILLER CONTROL METHODOLOGY WITH MICROPROCESSORS

The microprocessor control of a chiller plant is a new concept in building controls. This section of the report will demonstrate a generalized

chiller control logic, designed to be usable in centrifugal chiller

plants. The control logic must be tested by simulation and actual field

conditions before final programming can be completed.

* In adaptive controls, the control process enables the controller to

improve its decision-making ability and the system performance on the basis of its experience and to adapt Itself to its environment.

27
Many conventional controls in chiller plants may be replaced with microprocessors. These microprocessors can be programmed so that more sophisticated control logic and algorithms will be incorporated for energy

conservation and safety controls. In building complexes with EMCS and

distributed control systems, chiller control microprocessors may also

be used to communicate with the central minicomputer.

One microprocessor is sufficient to control all of the variables in a chiller. Each chiller microprocessor needs an independent timer for

self-clocking, in order to determine the chiller's availability for

start-up when it is off-line. For a multi-chiller cooling system under

a central EMCS an interface microprocessor is required to act as a con- centrator for communication between the central minicomputer and the

microprocessor-controlled chillers. The chiller microprocessors mush be

bit-synchronized to communicate with each other when an "interrupt" signal is generated by the building control minicomputer. Thus, all microprocessors can function as either receivers or tranmitters to complete

the communication link. The interface microprocessor maintains a transaction directory of the status of each chiller for the purpose of reporting to the minicomputer. The microprocessor must be equipped with full

battery back-up systems so that, in case of power failure, the microprocessor can still keep the central computer informed of the status

of each chiller.

A central minicomputer may be programmed to optimize the chilled water

temperature and chiller loading. After the minicomputer receives the

status information of all chillers, it may give commands to the concen- trator to take proper actions. A printer is generally used to keep a log about the chiller status and/or error/alarm conditions. Figure 9

illustrates the transmission links of the microprocessors with the

minicomputer

.

Basic chiller operation requires a number of safety controls to protect

the equipment against potential damage. The chiller microprocessor con- tinuously scans the status of each chiller operation and uses one of

two possible status flags, "ready" or "error," to indicate status.

For the common operation of chillers, four subroutines are constructed to

carry out the process of the "turn on" command. After the execution of

each subroutine, either the "error" flag or "ready" flag will be set to

identify the status of the chiller. In case an "error" flag is set by

any of these subroutines, sensing inputs of the chiller should indicate

the nature of malfunctioning. Then, besides turning the chiller off, the

microprocessor will inform the central minicomputer about the situation

so necessary action can be taken to protect the equipment accordingly.

Figures 10 to 13 show the generalized chiller control logic with microprocessors. The general description of each subroutine is as follows:

o Status Subroutine (Figure 10):

28
Figure 9 General Layout of Chiller Control Microprocessor

with Minicomputer
This subroutine is mainly used to determine the chiller

availability for start-up when it is off-line. Continuous

scanning within this subroutine is necessary. If the chiller

has been stopped under normal operation, a normal status will

be required to restart the chiller. Figure 10 demonstrates

some significant variables, as examples, to be monitored; other

variables could be added if desired.

o Pre-Start Subroutine (Figure 11):

This subroutine is to check the conditions of all the variables

prior to start-up. If the status is normal, this subroutine

will turn on the oil pump and monitor the oil pressure before

starting the condensing water and chilled water pumps.

(Normally these two pumps are interlocked for starting). When

the flow switches in both condensed and chilled water circuits

are closed, the chiller is ready for start-up.

o Start Subroutine (Figure 12):

This subroutine is employed to start up the chiller initially.

After the chiller is on-line and the chilled water temperature

has reached the set point temperature, this subroutine will be

phased out until the chiller is required to restart.

Prior to the dynamic starting of the chiller, it is necessary

to determine the preset and additional increments of vane positions according to the chilled water return temperature (T(|.jjj^),

and chilled water set point temperature (Tgp) in order to set

the proper chiller capacity. The latter can be read from the

building minicomputer if the building EMCS and the optimization

routine are available. Otherwise, table look-up is required to

find this value. Once the vane positions are obtained, the

chiller can be started by opening the vane position according

to the preset value. Afterward, the minimum load limitation

will be monitored and the vane position will be adjusted,

enabling the chilled water temperature to reach the set point.

Then, the ready flag will be set to indicate a normal status

for the run time load control subroutine to begin.

This subroutine utilizes much of the capability of a microprocessor when it is used as a controller and overcomes the

many drawbacks in conventional controllers. For example, the

minimum load limitation in chiller control is one of the many

advantages in using microprocessors. In conventional controls,

the chiller is shut down whenever the electric current consumption drops below a minimum level. The minimum load limitation

prevents the compressor from being operated with low efficiency

for energy saving purpose. However, in the microprocessor control, the nuisance of shut-down and restart by the motor-winding

high temperature cutoff can be avoided, because the vane may be

30
STATUS SUBROUTINE

Figure 10 Generalized Chiller Control Logic with Microprocessor-STATUS

31
PRE START SUBROUTINE

Figure 11 Generalized Chiller Control Logic with Microprocessor- PRE-START

32
Figure 12 Generalized Chiller Control Logic with Microprocessor-START

33
RUN TIME LOAD CONTROL SUBROUTWE

NO

TEMP WILL

BE DRIFTED WITHOUT CONTROL

Figure 13 Generalized Chiller Control Logic with MicroprocessorRUN TIME LOAD CONTROL

34
opened so that a load is always created to exceed the minimumload requirements of the chiller.

Another advantage of the microprocessor control is preload control of the chillers. With the conventional proportional control, during startup of the chillers vanes are wide open, and

therefore, a drastic overshoot in the response of the chillercontrolled variable, chilled-water temperature, occurs. In contrast, the time response during preload of the microprocessor

control is always in an overdamped fashion, because the microprocessor holds the vanes at a fixed angle without allowing them

to reach wide-open position during the time response. It usually

takes many small increments, such as one Fahrenheit degree

step, to reach the desired control point. By preventing the

overshoot, energy is conserved.

An additional energy-saving factor is the stability of the

control. The conventional strategy for controlling the chilled

water temperature is proportional control. Due to the high

gain requirement, the system tends to be highly under damped

and oscillation has been frequently observed. As a result

of the microprocessor control, the system always responds

to any step change in an overdamped fashion because of the

small step increment.

o Run Time Load Control Subroutine (Figure 13):

This subroutine is used to control the chiller load during run time by continuously monitoring the minimum load limitation, electric demand, and chilled water return temperature.

The minimum load limitation check will be performed here as in the start subroutine. If demand limiting routine exists

in the building EMCS, no controlling is required for the

electric demand, since any overload will be shed automatically

by the demand limiter. In the case that an overload condition

causes the chilled water temperature to rise above the set

point, it is necessary to seek help from the next chiller

if there is one available. Otherwise, the chilled water

temperature will drift upward without control.

When there is more than one chiller available in the cooling

system, each chiller control microprocessor will remain in

stable operation at a certain chilled water supply temperature (Tjnjjg) and a certain chilled water return temperature

(Tcjjr). As the need arises to start up a second chiller,

the same algorithm shall be followed. If the EMCS and

chiller optimization route are available, the percentage

load shared among chillers will be determined and automatically performed by the building EMCS. Otherwise, table

look-up is required to start the next chiller, in order to

share the chiller load.

35
There are many ways of utilizing microprocessor in building EMCS. This

microprocessor chiller control algorithm merely demonstrates one of the

many applications of microprocessors in building controls. It is recom- mended that the control logic be tested on a computer-simulated system

and the hardware /software be field tested under the actual building con- ditions before any "generalized" package is used in building EMCS.

5. MICROPROCESSORS IN ENERGY MONITORING AND CONTROL SYSTEMS (EMCS) >- CASE STUDIES

5.1 MINICOMPUTER CONTROL SYSTEMS

A computer system was installed at the Earle Cabell Federal Building

(ECFB) in Dallas, Texas in 1976 for the purpose of controlling and monitoring the building's heating and air conditioning systems.* Prior to

the decision to utilize a computer control system, an attempt was made

to conserve energy by reducing lighting levels, shutting down unnecessary equipment and running only minimal equipment during non-working

hours. However, in order to Increase operation efficiency, additional

operating engineer manhours were required. The building was operated as designed until 1974, with the following profile:

o Electric demand: 87,086 kW/year

o Electrical consumption: 31,902,159 kWh/year

o Required operating engineer manhours: 5,592.

By 1975, with efforts toward energy reduction, the operating profile of

the building was as follows:

o Demand: 56,525 kWh/year

o Consumption: 22,292,516 kWh/year

o Required operating engineer manhours: 8,760.

This state of affairs represented the limit for energy conservation with

the existing control systems and available human resources; any additional improvements without increasing operating manhours would require

computer control. In February, 1975, a decision was made by the Building Management Division, General Services Administration to purchase an Integrated minicomputer system to control the environmental system of

the ECFB, which had a floor area of over one million square feet (92903

m ), 2,460 tons (8659 kW) of air conditioning capacity and 32,775 pounds

per hour (14866.5 kg/h) of steam heating capacity. The minicomputer was

to be utilized as a control device to operate the heating and air conditioning systems. In the process of controlling the building environment

the system was to perform control functions such as start/stop, reduce

*Information was provided by the Assistant Building Manager, Dallas, GSA

Region 7, and their internal reports.

36
electrical demand and consumption through load-shedding techniques,

reduce operating manpower, maximize efficiency of boiler and chiller

operation, and provide capability for additional functions. The computer system was on-line in December, 1975. After a trial period, the

system was found to be realiable and the third and weekend shifts of the

building operators were reduced. At mid-1977, the building energy profile was as follows:

o Demand: 42,124 kW/year

o Consumption: 15,325,492 kWh/year

o Required operating engineer manhours: 260.

The reductions were not all the results of the computer system, as the

building was partially vacated. Taking into account an approximate

adjustment for vacancies of 120,000 kWh/month consumption, and 500 kW/

month of demand, the reductions of building energy and manpower by the

computer system during the first seven months of 1976, as compared to

the first seven months of 1975, were as follows:

o Demand reduced: 543 kW/month

o Consumption reduced: 174,986 kWh/month

o Required operator reduced: 556 manhours /month.

5.2 DISTRIBUTED MICROPROCESSOR SYSTEMS

During the period of system Installation and debugging for computer system at the ECFB, distributed control systems were being developed using

microprocessors. The decision was made to expand the existing system to

monitor another facility remotely via telephone lines. The second building, a 50,000 square foot (4645 m^) underground federal building in

Denton, Texas, is the Region 5 Headquarters for the Defense Civil

Preparedness Agency. The security activities and the equipment installed in this underground facility require the building to be monitored 24

hours per day, seven days per week. The agency responsible for providing

on-site security, fire, and equipment alarm monitoring was to eliminate

their non-working hour shifts on August 1, 1976. Thus, if the building was to be operated as required, an alternative approach was to provide

remote monitoring.

In late 1976, a multiple microcomputer control system was installed at

the Denton Federal Center in Denton, Texas to reduce building security

cost, control HVAC equipment, and provide smoke and fire detection. It was a distributed energy management and security system, fully standalone and able to communicate with another environmental computer con- trol system in the ECFB located in Dallas, 40 miles away. From January

through May, 1977 the savings over the previous year from the

microprocessor-controlled system in the Denton facility were reported to

be 33% for electric demand, 45% for electric consumption and the elimination of three previously needed additional employees. The major impact

37
of the computer systems on the two facilities, beside savings of energy, was the reduction of operating manpower as all 2nd, 3rd and weekend

shifts were removed.

Five microprocessors have been employed to perform supervisory control,

as well as ocher functions. One battery backup microcomputer performs

all supervisory functions for the system; two other microprocessors monitor both electrical demand and consumption, sense building temperatures,

operate heating, ventilating and air conditioning (HVAC) equipment,

detect smoke and fire, and provide security; a fourth unit controls a local status printer; and a fifth serves as a telephone line communications controller to link the system with the other building forty miles

away. These five microprocessors make up a distributed system with preset priority levels; the entire system may either function in unison

or each microcomputer may function in a stand-alone fashion. Furthermore, the microprocessors are programmed so that they may diagnose each

other continuously. The microcomputer system in this building monitors

all the control functions independently during office hours and reports

all security and safety alarms, and equipment malfunctions to a host

minicomputer, in the Dallas building during non-working hours. The man- power for security is drastically reduced in this building during

unoccupied hours.

Another example of a distributed microprocessor system consists of two

control systems for two buildings in Louisville, Kentucky. The Federal

Office Building, FOB, and the Louisville Post Office, LPO, with a total

floor area of approximately 1.2 million square feet (1 million square

meter), are separated by a distance of one city block, and connected

by a shielded 300 conductor underground electrical cable. The control

center in the FOB performs monitoring and controlling functions for the

system in the FOB as well as for the LPO system. In the LPO, there

is a microprocessor designed to obtain a stable reading of various space

temperatures; these temperatures can be read by the control center in

the FOB.

6. CONSIDERATIONS FOR DESIGN OF MICROPROCESSOR CONTROLLED EMCS

The evolution in computerized building control systems has been dramatic

in the past decade. With the recent development of microprocessors,

these systems can have total stand-alone capability and provide distributed intelligence. Currently, a total system approach to EMCS will

require the system to provide efficient utilization of energy and operating manpower, to provide life safety and property protection, to record

factual operating data for building manager's decisions, and to maintain

environmental conditions for the specific activity or work function of

the building.

To design an EMCS for an existing building, personnel with background in

HVAC system, computer, and applied mathematics will be needed. Building

management also plays an Important role in decision-making. From the
standpoint of systems analysis, the HVAC system is considered to be a complex system in the sense that it is non-linear, time-variant , and

nondeterminlstic, which implies that techniques from statistics, decision

theory, and game theory will have to be applied. At the beginning of

EMCS design, the HVAC system will be analyzed theoretically. Concurrently, decisions will have to be made to determine whether the analytical approach will achieve the target by optimization of system operation.

After the installation of EMCS computer system, its software will be

employed to perform analysis on a set of system performance criteria with

strategies determined by the building manager. The strategies, which are suitably weighted by parameters beyond the control of the data environment, (e.g. temperature, humidity, etc.) are then correlated with the

target. The performance of each strategy is then evaluated in terms of

its ability to reach desirable targets. A particular strategy, which

most closely approximates the initially chosen performance criteria, is

selected as "optimized". With the help of the building manager, variables and parameters of the problem are isolated to make decisions in

order to achieve the optimization. For example, the following shows some

of the parameters that can be chosen for optimizing:

o latest morning start up

o earliest evening shut-down

o maximum efficiency of existing HVAC equipment

o psychological factors (e.g., after turning an air handler off,

regardless of comfort levels, occupants will notice and begin

to complain about the lack of air movement)

o most optimal interactional effects (e.g., which combinations

of equipment turned off at which time of the day will produce

the most desirable effects)

o number of fans and fan speed of cooling towers operating

as a function of external temperature, humidity, and

chiller load

o morning start-up sequence (e.g., as a function of ambient

temperature during the weekend, it is more desirable to bring

equipment on at 2 am and slowly set the building under control,^ as opposed to starting the equipment at 6 am, which is

the normal operating procedure).

Initially, the methodology of optimization will be to study the overall

problem in a localized sense to select one parameter at a time for a hypothetical test. For each parameter, different strategies are tested

in order to select the most suitable strategy to meet the performance

criteria, and this strategy will become the initial hypothesis of the

interactive process among parameters. After all parameters have been

exhausted, higher order effects will be studied by changing more than

39
one parameter. The EMCS computer system will be set up deliberately as a learning instrument to permit sequential and interactive interplay

between an operator and the machine from the set of performance criteria

in such a way that the building operation can eventually be totally

optimized. As far as the software is concerned, it should contain sufficient mathematical sophistication in performing predictor/corrector

analysis, autocross correlation analysis, and weighted analysis of

variances, in order to avoid such errors as a hypothesis accepted as being valid when it should have been rejected and vice versa.

In a complex installation of EMCS, functionally decentralizing the data

environment is a helpful way to understand the operation of HVAC equipments. Accordingly, the idea of the microprocessor approach will be

adapted successfully with the following examples:

o Installation, debugging, and maintenance will be simplified

by the substructure of the data environment. Specifically,

without worrying about any sophisticated analytical algorithms, the microprocessor can be validated locally and

debugged. Once it is thought functional, the only remaining

task is the communication with the central computer.

o The distributed hierarchy will leave the option of performing

routine data acquisition and preprocessing in the microprocessors. The minicomputer can use statistically robust data

for calculations immediately.

o Interactional effects among all the multitude of equipment

will be difficult to determine, assess, and debug within the

central system. Therefore, for ease of comprehension and

experimentation, most stand-alone microprocessors would be

structured to interface with various signals from specific

HVAC systems.

o If further signals or controls have to be added, it can be

done easily.

7 . CONCLUSIONS

The advancement of microelectronics technology has enabled building con- trols to become highly sophisticated systems. Microprocessors have

helped to improve the feasibility of distributed control systems and

could also replace the traditional controllers. By designing programmable controllers around a microprocessor, controllers may be given

computer-like capabilities such as signal converting, data storing, and

data analyzing.

Because of the concern with energy shortages and the rise of energy

costs, building controls have been an important Investment, together

with building envelope design, for depletable resources conservation as 40
well as for energy cost reduction. A microprocessor-based programmable

controller in the form of an energy management system or an energy

control device is capable of controlling energy usage in small buildings.

For larger facilities it will be necessary to employ microcomputers in

building automation systems that require greater sophistication including

extensive computation, data storage, printouts, displays, and interfacing.

The enhancement of microprocessors will make progress in improving the

performance of energy conserving equipment, such as boilers and chillers,

desirable and will allow development of local loop control of this equipment. It is anticipated that direct digital controls will be ultimately

adapted in building automation systems. With the advantages of versatility and low cost, the microprocessor may be used in a tremendous number

of applications in control systems as well as in other areas. Microprocessors are capable of being utilized in controllers, communication

links, signal conditioners, actuators, sensors, and even in operation

of central minicomputers as display terminals and keyboards.

Due to the high demand and low cost of silicon chips the semiconductor

industry is likely to produce so called firmware, which is a variety of

packaged programs on ROM. The enhancement of the firmware, instead of

the software, allows the end-users to link the miniprocessor to the outside world by mere interfacing. Thus, sophisticated control system

design may be accomplished without complicated software development and

program debugging. Furthermore, new advances are being made in semiconductor process technology to achieve the package density needed for

future applications. Due to the rapid growth of today's technology it

is not unrealistic to predict that the 32-blt microprocessor will be

available from manufacturers in the next few years.

REFERENCES

1. Shih, J. Y., "Energy Conservation and Building Automation," ASHRAE

Transactions Vol 81, Part I, January, 1975.

2. Rains, R. W. , "Control Systems for Heating, Ventilating, and Air

Conditioning," 2^- Ed., Ch. 10, Van Nostrand Reinhold Co., 1977.

3. Shih, J. Y., "Automation System with Addresable Sensing Devices,"

ASHRAE Transactions, Vol 83, Part I, 1977.

4. Bailey, S. J., "Memory Developments Will Impact Control Systems,"

Control Engineering, Volume 26, No. 1, January, 1979.

5. Costlow, T., "Micros Join in the Conservation Battle," Interface Age,

June, 1979.

6. Miller, M. , "Microcomputer: A New Era for Home Energy Management,"

First Computer Faire Proceedings, April, 1977.

41
7. "System Design and Installation for RS 6000 Programmable Control

System for Solar Heating and Cooling,” Contractor Report, DoE/NASA,

CR-150535, January, 1978.

BIBLIOGRAPHY

1. Berger, E. R. and Coxe, E. F., "Automation and Centralization of

Facilities Monitoring and Control Systems,” U. S. Army Facilities

Engineering Support Agency, January 1976.

2. "Central Control and Automation Systems," A Management and Procurement Handbook by The Association of Physical Plant Administrators of

Universities and Colleges, Second Edition, 1978.

3. Lin, W. C., Editor, "Microprocessors: Fundamentals and Applications,

IEEE PRESS, 1977.

4. Savelyev, M. K., "How to Use PCs for Energy Management Systems,"

Control Engineering, Volume 26, No. 2, February, 1979.

42
NBS>n4A 'REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-2065

5. No.

4. TITLE AND SUBTITLE

MICROPROCESSOR APPLICATIONS AND BUILDING CONTIlOL SYSTEMS

5. Publication Date

July 1980

TO ACHIEVE ENERGY CONSERVATION i. Performing Organization Code

742.05

7. AUTHOR(S)

' “

Yui-May L. Chang and James Y. Shih

8. Performing Organ. Report No. NBSIR 80-2065

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

iC Project;^ask/Work Onit No.

^ ;

742 4482

11 . Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fSfreer. City, State, ZIP) 13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or teas {actual summary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.) A well insulated building may be considered a thermally efficient building. However,

the systems and controls within the building must also be energy efficient in order

to conserve energy. Thus, building controls is an important subject in energy

conservation. In recent years, building control engineers have been developing

energy conserving control methodologies. The availability of microprocessors and

minicomputers has made it possible to apply many control strategies requiring

extensive computations. Since a large segment of energy is consumed in buildings,

the enhancement of control methodologies will help achieve national energy goals.

This report is mainly to investigate the capabilities of microprocessors in building

control applications so that requirements to expedite these applications may be

developed. Microprocessor applications in both conventional control systems and in

local-loop energy conservation devices are examined. In addition, special applications of microprocessors in buildings are explored. The development of microprocessor

technology is also discussed.

17. KEY WORDS (six to twelve entries/ elphebeticel order/ cspi telize only the first letter of the first key word unless a proper name;

| separated by semicolons)

Building automation; building energy management systems; building controls; chiller

controls; distributed control systems; energy conservation; energy conservation devices;

microcomputers and minicomputers; microprocessor applications; programmable controllers.

~18. AVAILABILITY QUnlimited

I I For Official Distribution. Do Not Release to NTIS

[7 ; Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

[X] Order From National Technical Information Service (NTIS), Springfield,

VA. 22161

19. SECURITY CLASS 21. NO. OF

(THIS REPORT) PRINTED PAGES

UNCLASSIFIED 46

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