8/13/2019 BMS 23 aug

1/11

CONTROL SYSTEMS

8/13/2019 BMS 23 aug

2/11

Contents

Why use building control systems ?

Basic Control Terminology

Open and Closed Loop Control

Types of Controls

Control by Time

Occupancy

Physical Conditions

8/13/2019 BMS 23 aug

3/11

WHY USE BUILDING CONTROLS?

When installed correctly and when working properly, buildingcontrols have a range of benefits. They can:

Minimize running costs, energy consumption and pollution associated withenergy use.

Improve comfort for building users.

Limit excessive wear and tear on building systems and plant.

8/13/2019 BMS 23 aug

4/11

BASIC CONTROL TERMINOLOGY

A control system consists of three basic elements: a sensor a controller and a controlled device.

The sensor measures a variable, such as temperature, and transmits its value tothe controller.

The controller uses this value to compute an output signal, which is transmittedto the controlled device.

When the signal is transmitted, the controlled device changes the output of theload.

8/13/2019 BMS 23 aug

5/11

8/13/2019 BMS 23 aug

6/11

8/13/2019 BMS 23 aug

7/11

Use occupancy sensors to control lighting, heating and cooling according tomotion detected within an intermittently occupied area.There are three basicsensor technologies:

Infrared, Ultrasonic, and Acoustic.

Infrared Sensors :

Infrared (IR) technology senses body heat.

IR requires a straight line -of- sight in order to operate properly.

IR is ideal for small offices and other regularly shaped rooms as well as high

spaces (auditoriums, open classrooms, large open offices with low or nopartitions, factories and other large work facilities)

CONTROL BY OCCUPANCY

8/13/2019 BMS 23 aug

8/11

Ultrasonic sensors : Ultrasonic (US) technology emits a high-frequency sound that reflects off roomsurfaces. US sensors have good sensitivity and range where small motions must bedetected. They suit irregularly shaped spaces and room obstructions such as medium tohigh partitions, large furniture or structural columns.

Acoustic Sensors :

Acoustic or audible sensors rely on voices, machinery sounds, keyboard tappingand other typical daily noises. This technology works well in areas with high partitions or other obstructions, orhigh air movement within the space during unoccupied periods, such as kitchensand large washrooms.

8/13/2019 BMS 23 aug

9/11

CONTROL BY DAYLIGHT LEVEL

Light sensors or photocells are most commonly used to control artificiallighting when there is sufficient natural daylight.

As daylight hours vary throughout the year, sensors help to provide closer

control and can achieve substantial savings.

Where high-frequency fluorescent lighting is installed, these controls can dimthe light output when daylight is adequate.

Photocell control can be combined with occupancy control systems to reducelight output when day-lighting levels are adequate, and switch lighting offwhen the space is unoccupied.

8/13/2019 BMS 23 aug

10/11

A photosensor should be assigned to each lighting zone. There are two main types of daylight controls, closed loop and open loop .

In a closed-loop system the sensor is located in the controlled space.

best for classrooms, open offices, concourses, lobbies, malls, factories andother large open areas.

In an open loop system the photosensor is located outside the space(s) itcontrols, and is not affected by the electric light contribution. small offices or rooms, outdoor lighting, atria, and other daylighting features.

8/13/2019 BMS 23 aug

11/11

CONTROL BY ZONINGSome areas in large buildings require different levels of heating, lighting, coolingand ventilation.

A solution to this is to create zones in the building where separate time,temperature and occupancy controls are installed for individual areas. Zoned areas will provide closer, more efficient control. This can improve localconditions and save on costs. Zoning should be considered when there are:

Different occupancy patterns Different temperature requirements Different activities taking place A number of floors .