Building Energy Management » Building Energy Management systems

Technique

A monitoring and controller unit of a BEM system is responsible for receiving the signal from a sensor, analysing the signal and sending an appropriate control action to the actuator to perform. The data from various points in the system such as sensor and meters with data loggers can be observed from this control unit through display units. This process of controlling can be automated or can be overridden by manual controls based on the real time data. The data collected is then analysed and measures for optimizing energy consumption are considered.

Instruments for measurement and metering

Sensors
Various kinds of sensory equipment along with data loggers are deployed at various points of a BEM system. Their function is to measure temperature, electrical power, air movement and quality, water flow, relative humidity, occupancy, light levels etc. at various points in the building and service systems.

Sensory	Typical equipment used	Location/usage in a building or service systems
Temperature	Thermo couples, thermistors and resistance thermometers	Indoor temperature, outdoor temperature, surface temperature, radiant temperature, fluid temperature in pipes and ducts etc.
Electrical power	Current clamps (generally used when sub-metering to dedicated end uses is absent; sub-metering, however, is preferable)	Used to gauge electrical energy consumed for lighting, equipment and appliances, fans, pumps, lifts and escalators, machine tools, compressors etc.
Air movement	Rotating vane anemometer, hot wire anemometer, pilot tubes	To measure indoor and outdoor air movement, ventilation or infiltration rates, air movement through ducts etc.
Indoor air quality (CO₂ sensors)	Non-dispersive Infrared sensors, chemical sensors	Used to measure CO₂ build up in the space to enhance ventilation
Water flow	Impeller type rotary mechanism	Water flow in pipes connected to chillers, boilers, AHUs etc.
Relative humidity	Capacitive sensors, resistive sensors, thermal conductivity humidity sensors, wet-and-dry bulb humidity sensors	To measure Indoor and outdoor humidity levels, to predict chances of condensation
Occupancy/motion sensors	Infrared sensors, ultrasonic sensors	Detects presence of occupants within the space
Daylight sensors	Photodiode sensors, analogue photo sensor	Determines lighting levels in space

Meters
The simplest way of monitoring energy consumption in a building is to note consumption data from the utility meters. Typical utility meters consist of electricity, natural gas, steam, water and condensate, compressed air meters and data loggers. However, a single utility meter per fuel source cannot be able to give a breakdown of energy use per end use. Therefore, adopting a measurement and verification plan with sub-meters helps in identifying areas of energy wastage, make improvements and measure the savings incurred due to improvements.

Besides sensors, a sophisticated BEM system also employs an appropriate measurement and verification plan (M&V plan, as per IPMVP) and involves deploying of sub-meters and data loggers for various groups of end uses. For example, in a medium office building, electrical sub metering includes installing separate meters for lighting, HVAC, office equipment, hot water, parking etc. These meters can be further grouped per floor, or per block or per user group etc. based on the M&V plan. All the data from the data loggers from the meters is fed into the monitoring unit of the BEM system.

In addition to normal meters, Advanced Metering Infrastructure (AMI) or smart meters enabled with information technology communicates not only with local building networks but also with the utility provider giving real-time information on demand. Steps are being taken towards promoting the use of smart energy meters and devices by public bodies. A Public Utility Commission of Texas report to the Legislature on Advanced Metering encourages the use smart meters with the capability to communicate with devices inside the premises, including usage monitoring devices, load control devices, and prepayment systems through a Home Area Network (HAN) based on open standards and protocols that comply with nationally recognized non-proprietary standards such as ZigBee, Home-Plug or the equivalent (Public Utility Commission of Texas, 2010).

Networking and communications protocols

A central monitoring and control unit is responsible for monitoring and measurement in a BEM system. It consists of IT networking and corresponding hardware elements such as bus units and sub-meters linking to various end uses (both sensors and actuators) such as HVAC, lighting, hot water, security, etc.

Hardware
Controller unit usually consists of a pre programmed microprocessor device capable of carrying out the relay transmissions by using modular bus units with digital and analogue input/output channels. The bus devices are configured as per the desired application into bus couplers and bus terminal controllers with embedded PC. The bus terminal controllers communicate with room controller units. Room controller units typically receive analogue input to sense temperature, air flow and quality, lighting levels and send out analogue output to the control devices such as fans, heater elements, flow control dampers, window shutters etc. to initiate necessary action.

Depending upon the complexity they are configured in various hierarchal levels. Simplest of the systems have field level room controllers directly connected to bus terminals with embedded PCs with or without display devices. Complex systems have field level room controllers connected to bus terminals at floor or system level (central HVAC), which in turn are connected to a central building management system with sophisticated display units and control features. In complex systems controls are available at both local level and central level. The hierarchy of operation depends on the configuration of the automation systems to suit building usage.

Data transfer
The input and output data transfer between sensors to controllers and controllers to devices takes place in a single or different standards such as DALI, Zigbee, EnOcean, LONWorks, KNX, MODBUS etc. This includes both wired and wireless connections. When multiple standards are used within a system, it is bridged using bus couplers within a network.

The data communication between various bus terminal controllers and bus couplers take place in standard platforms such as BACnet, DMX, PROFINET, and Ethernet etc. The latest technologies also use Internet Protocol based control systems that work in conjunction with multiple Building Automation Control (BAC) platforms.

In residential buildings electrical appliances, lighting devices, HVAC systems with built-in sensors and actuators (Anastasi, Corucci, & Marcelloni, 2011) enable real-time energy consumption monitoring through Home Area Network (HAN) which provides real time hourly (or sub hourly) time step data to the home-owner on the energy consumption of various end uses. HAN is a network within the home that enables communication between “smart” devices including HVAC, security, lighting, and appliances. This also provides the home user with ability to remotely control devices within the HAN (such as adjusting a thermostat or turning off lights). This helps consumers to better manage consumption and cost, and utilities to better manage supply and demand, and to react quickly during emergencies.

All the data from various modular bus units is relayed to a central building management and automation system. There are a variety of building energy management software that comprehends the data received from bus units (in single or multiple standards) and represents it in a user-friendly environment facilitating monitoring and controlling.

Analysis and optimization

The energy consumption output data that is available from monitoring and measurement can be analysed periodically. The analysis typically takes into account external weather data, occupancy schedules, automation schedules, user behaviour data and system performance. Periodical (typically monthly or weekly or hourly or seasonal) breakdown of some of the important data obtained from BEMs systems is recommended as follows:

Data	Example	Analysis and target action
Break down of energy consumption by end use	Equipment, lighting, HVAC, Hot water, refrigeration etc.	Identifying pockets for saving energy by comparing the data to best practice consumption level targets. E.g., through scheduling and automation
Break down of energy consumption by space function	Offices, Kitchen, meeting rooms, living room, bedroom, cafeteria etc.,	Identifying pockets for saving energy by comparing the data to best practice consumption level targets. E.g., through scheduling and automation
Break down of energy consumption by plant and mechanical systems	Fans, pumps, Cooling tower, chiller, boiler, steam generation, refrigeration etc.	Matching demand and schedules to optimize energy consumption. Scope for retrofitting and upgrading equipment can be identified.
Break down of energy consumption by fuel	Electricity, Oil, Gas, Renewables etc.	Shifting to more efficient fuels
Break down of utility cost by fuel	Cost of Electricity, Oil, Gas, Renewables etc.	Shifting to more cost effective fuels
Break down of energy consumption by time	Occupancy and non occupancy hours, daytime and night-time, seasonal etc.	Revise scheduling and automation and adapt plant operation and user behaviour to achieve energy consumption targets
Load or demand profiles of various end uses	Equipment, lighting, HVAC, Hot water, refrigeration etc.	Arrive at optimum load management patterns through load shifting and minimizing peak demand
Load or demand profiles of various plant and mechanical systems	Fans, pumps, Cooling tower, chiller, boiler, steam generation, refrigeration etc.	Arrive at optimum load management patterns through load shifting and minimizing peak demand

Based on this data a schematic step-by-step approach is followed in order to optimize one or all of the above described parameters in conjunction or in isolation. In some cases the systems can be optimized by just recalibrating and adjusting the controls to suit updated user behaviour patterns. The energy usage data for various end uses can be compared to various parameters like weather conditions, user behaviour, occupancy patterns etc. the potential pockets of energy wastage can be identified and rectified accordingly. Based on the performance indicators from the data obtained tangible energy saving targets can be set periodically.

In commercial and office buildings with large and complex systems IPMVP guide provides guidelines on how to optimize energy consumption based on the monitored data. Energy conservation measures (ECMs) covered in the IPMVP include fuel saving measures, water efficiency measures, load shifting and energy reductions through installation or retrofit of equipment, and/or modification of operating procedures.

Modern day equipment in residential buildings is fitted with sensors and transmits data wirelessly making it less hassle for homeowners. The collected data is presented with a graphic user interface on TVs, computers and smartphones and can be remotely controlled using multipurpose remote controls or using Internet through laptops and smart devices. This makes it cost effective and easy to use approach for saving energy for both new and existing buildings. The output data from the BEM system is both in the form of readable graphical format as well as text and CSV format depending on the system employed.

The following selection of key target actions can be revised periodically based on the data available from BEM systems.

Corrective measure	Description
Scheduling and automation	The controls need to be scheduled and automated to ensure comfort while reducing energy wastage. Systems can be completely automated or a manual override can be provided to best suit the occupancy schedules and usage patterns of the inmates. Building Controls Industry Association (BCIA) suggests a manual on and auto-off approach while programming so that only services that people need, can be turned on at a time and turned off automatically when unoccupied.
Load management	Load shifting and other better load management techniques can optimize peak load or demand of various mechanical systems or end uses. This can help in reduction of the utility tariffs by responding to demand charges efficiently.
Optimum start up	Optimizing system start-up timings and night setback temperatures can be optimized for different seasons or as per the external weather conditions to save considerable energy.
User behaviour modi-fication	Besides all other energy saving strategies, this is the most important and relatively easier to achieve. As they say, buildings do not consume energy, people do. Educat-ing and informing the building users about energy saving techniques and motivating them with easily comprehendible graphical analysis will help energy wastage. An example is the ‘mission E campaign’ presented as a good practice example in the bigEE Policy Guide.

Implementation

Different kind of controls can be implemented at various systems and sub system levels of HVAC systems, lighting, equipment, etc. Some of the important control functions have been listed here.

HVAC controls

Heating, ventilation and Air conditioning (HVAC) controls are used to precisely control space temperature and ventilation airflow. Using specialized sensors and controls that respond to space demand and external weather conditions save considerable energy. Studies have shown that by the use of building automation and control systems the potential savings for heating energy would be approximately 5-50% and for cooling it would be about 10-80% (Becker, Bollin & Eicker, 2010).

HVAC controls consist of a series of sensors and controllers relaying information over a network. Sensors are typically equipped to measure temperature, humidity, air flow and air quality at various points in the building, within the thermal and air distribution network, heating and cooling plants (e.g., chillers and boilers) and also on the exterior of the building. The information from the sensors is relayed to the automation system and appropriate control sequences are activated.

HVAC systems can be divided into two components, the supply side and the demand side. The main control purpose on the demand side is to sense and maintain the room set point temperature, humidity and minimum level of fresh air. The demand side needs to identify the load on the supply side system and operate to meet the load.

The demand side typically consists of all air systems or air water systems. Sensors are placed to monitor the room air set point temperature, humidity and ventilation levels at the zone level. In all air systems corresponding controls are located at the AHU level. Chilled water or hot water supply temperature, flow and mixing or air is thus controlled at the AHU level to meet the zone requirements. Flow valves are controlled by the use of dampers and by regulating fan speed by the use of variable speed drive attached to the fan motor. Air water systems correspondingly regulate the flow of refrigerant or chilled or hot water to the zone terminal units.

The supply side consists of three major components, Chiller or boiler, distribution system (consisting of pumps) and a heat rejection device (condenser) in case of chiller. Chiller operation should meet the chilled water demand while operating at maximum efficiency. There are various techniques to achieve capacity control in chillers so that chiller can work only to meet the demand and thus reducing excess load on the chiller. This is done by a thermostatic expansion valve, inlet guide vane, hot gas bypass, variable speed driver or a slide valve depending on the kind of chiller and its compatibility with the control technology. The most efficient and popular among the control techniques is the variable speed drive, which is attached to the chiller and regulates the chiller speed according to varying demand. In case multiple chillers or boliers are connected to each other then sequential operating of chillers or boilers is very important for optimal efficiency. It has to be ensured that any given chiller is operated at its maximum COP (every boiler at maximum efficiency) most of the time (Wang, 2010).

Adjustable thermostats
The US Environmental Protection Agency reports that homeowners can save about €130 a year by properly setting their programmable thermostats and maintaining those settings. It is noticed that by reducing the room temperature by 1 °C, 6% of heating energy is saved (ABB, 2009). Residential units typically have a central hot water unit with radiators in individual rooms or heat pumps for heating and split Air conditioners with an indoor unit evaporator and an out-door condensing unit.

By having individual room sensors and programmable thermostats (PT) it is possible to maintain different temperature in the different rooms. Programmable thermostats allow functions like cooling or heating the space just before occupancy and shifting the temperature to setback limits or turning off the system during standby or unoccupied periods. PT can be set for different modes as discussed in later section (AFMCS/start-up controllers) and can also have a temporary override or hold function to manually control it when necessary. However, care needs to be taken that the user is in full control and fully aware of the functions of the programmable thermostats. Studies have shown that if the user if not in aware of the control settings it is more likely to result in higher energy consumption than normal (Meier, et al.). Iconography, ease of use and clarity are the important features that govern the appropriate use of a thermostat. Organizations like Building Controls Industry Association (BCIA) have studies on the psychology of the end user and studies on different kind of thermostat controls. Thereby they made recommendations on the appropriate iconography and checklists for building designers, manufacturers and suppliers and control installers so that the controls achieve the desired results in the form of energy savings and increased comfort (Bordass, Leaman, & Bunn, 2007).

Demand controlled ventilation
Minimum levels of ventilation are required in space for fresh air requirements both for breathing and to maintain optimum humidity levels. Various standards and guides like ASHRAE 62.1-2010, CIBSE Guide E, describe the minimum acceptable ventilation levels. Ventilation in the building can be optimized ef-fectively through a strategy known as demand control. This strategy calculates the amount of required ventilation by sensing the amount of carbon dioxide (CO₂) and humidity in the space. CO₂ sensors and humidity sensors are placed either in the space or in the return air duct. They measure the amount of CO₂ and humidity present in the space and thereby adjust the ventilation rate accordingly. This enables reduction in the conditioned load of the fresh air by reducing the fresh air quantity and at the same time maintaining minimum fresh air levels. Studies show that by employing demand control ventilation energy savings of up to 40% can be obtained (Becker, Bollin, & Eicker, 2010).

Cooling tower with fans enabled with Variable Speed Drive
The main aim of the heat rejection device is to reduce the Entering Condensing Water Temperature of the chiller. The heat rejection device is generally either air-cooled or water-cooled and consists of a cooling tower with fans to dissipate heat to atmosphere. Cooling tower fans with variable speed technology achieves energy savings by optimizing the fan speed with varying load conditions.

Water-side economizer control in water cooled condensers
Water side economizer can help reduce load on the chiller by passing the chilled water from refrigerant and cool it directly by the condenser water from the cooling tower in seasons of low humidity and low temperature. Chiller load can be considerably reduced or completely bypassed during favourable ambient conditions. This can be achieved by using chilled water produced by evaporation or by heat exchanger between condenser water, which is cooled by evaporation, and chilled water.

Pumps with variable speed drive
The distribution system is driven by pumps and it works in different configurations, Constant primary only, constant primary and variable secondary, and variable primary only. Of late there have been arguments that constant speed pumps should be done away with totally and only variable pumps should be used in order to achieve actual energy efficiency both in order to reduce pumping energy and also to increasing chiller efficiency. In heating systems, up to 18 % of savings in pumping energy have been demonstrated through system optimization (Adhikari et al., 2012).

Airside economizer control
Economizer on the supply side can significantly reduce the energy use by using a technique called free cooling. An economizer control added to an Air Handling Unit (AHU) enables the direct outdoor air to cool the space when the outdoor air temperature is lower than the return (mixed) air temperature and thus reduces or eliminates the cooling load on the system. ASHRAE 90.1 a standard on energy efficient buildings mandates the use of airside economizer in particular climate zones where it has significant energy savings.

Energy recovery ventilation control
Energy recovery ventilator transfers heat and moisture from the exhaust air stream to the incoming air stream and thus precools or preheats intake air. However, ERVs consume energy to operate. In case the operational energy for ERV exceeds the cooling or heating energy saved the ERV function should be stalled. Controls are therefore required to operate ERVs only when there is considerable heating or cooling energy savings.

Lighting controls

Lighting in buildings consumes approximately 10-30% of total energy in office buildings, to a lesser extent in residential buildings (approximately 5-25%) and much higher in specialised retail buildings (approximately 20-50%). The savings incurred by using efficient lighting (e.g., LEDs) can be further optimized by the use of different kinds of lighting controls available. Lighting control ensures the light is provided where and when it is needed in the right amount while maximizing the use of daylight and minimizing the lighting energy wastage. Lighting controls typically include occupancy sensors, daylight sensors, dimmers etc. and save approximately of 20-50% of total lighting energy consumption. In typical office buildings the payback period for wireless lighting controls is approximately 2.3 years (enocean alliance, 2011).

Lighting control systems consists of hardware such as sensors and, relay switches controllers which work using various communication protocols like DALI, enocean etc. DALI is an acronym for Digital Addressable Lighting Interface and is targeted to suit commercial architectural requirements (DALI). DALI is specifically developed for ballasts and relay switches. Lighting communication protocols can be used as a stand-alone lighting control system or integrate with other building automation systems using protocol translation with systems like BACnet, LonWorks etc.

Daylight sensors
Buildings should be appropriately designed for effective distribution of daylight. Daylight sensors sense the amount of daylight illumination available in the space and accordingly reduce the artificial lighting either by turning off or reducing the intensity of lighting through the use of dimmers. Typical lighting sensors used nowadays are based on silicon photo diodes. Photodiodes are photo sensors that generate a current or voltage when the semiconductor is irradiated by light. Commercial sensors are made up of Photo ICs and they combine photosensitive section and a signal processing circuit into one package (Hammamatsu, 2013). Photo IC detect the varying levels of illuminance in the space and relay a signal to a control section, which thereby controls the intensity of the lighting device. Daylight sensors are placed in the perimeter zone of a building till a point where the daylight penetration is possible. Care needs to be taken while placing the sensor. The effectiveness of the sensor depends on the task location, the algorithm that controls the daylight, the lighting system used and the sensor field of view (LBNL, 2011).

Occupancy sensor
Occupancy sensors detect the presence of people in the space and thereby turn on and off the lights accordingly. It is recommended that a manual on and auto off approach should be employed. This increases occupant satisfaction by giving the occupant direct control on the environment while ensuring that the lights turn off automatically while there is no occupancy in the space, thereby minimizing lighting energy wastage due to negligence. An electronic presence detector forms the core-sensing element of an occupancy sensor. Typical presence sensors available are passive infrared sensors known as PIR and active ultrasonic or microwave sensors. Occupancy sensors serve multipurpose functions by not only enabling lighting control, but also they can be integrated with HVAC and security systems. Care needs to be taken while choosing the type of sensor and also placing the sensors so that they maximise the detectable area while reducing the probability of false alarm.

All these controls can be programmed to suit the user behaviour and can be overridden any time. Automatic window blind control devices can be used to allow desirable amount of light into the space and also avoid glare. Studies conducted by the LBNL estimates average lighting energy savings potential are 24 % for occupancy, 28 % for daylighting, 31 % for personal tuning (flexibility of controls lies with the users), 36 % for institutional tuning (lighting control strategies follow central control/policies) and 38 % for multiple approaches (LBNL, 2011).

Shading control devices
Shading devices like fixed shades, internal and external blinds, louvers etc. are necessary in passive building design for controlling heat gain and amount of daylight in the space. Automatic window blinds/louver control devices can be used to allow desirable amount of light into the space and also avoid glare. They can be automatically regulated by fixed schedules depending on the Sun path of the place and prevailing ambient light conditions on the outside and can also be manually overridden.

Switches
A simple switch operates on the binary function on/off. A switch can be used to control the lighting using occupancy detectors. It also can be operated based on the schedules of building occupancy and connected to the central BMS system or can operate locally on the basis of manual on and auto off principle. Turning off the lights when not required is the most simple and effective way of conserving energy.

Dimmers
Dimmers control the brightness of the lamp by the use of dimmable ballasts. Unlike old dimmable ballasts that use resistance, reactor and transformer dimmers and loose energy as heat, modern dimmers are based on thyristors, transistors or silicon-controlled rectifiers (SCR) (Wang, 2010).

The selection of control devices depends on the space layout and the availability of daylight. Energy savings and cost analysis has to be carried out before choosing a particular or a combination of technologies. It has to be noted that dimming is still expensive compared to switching technology and only suits a well daylit area. However, in abundant daylit areas dimming has an advantage as the occupants less perceive the changes caused in lighting levels used by dimmers and thus they are least disturbing (LBNL, 2011).

Advanced Facility Monitoring and Control Systems (AFMCS)

In addition, to be able to optimize individual components the function of centralized control is important to regulate all the individual components of the system, i.e. supply side, demand side, distribution system and heat rejection device in conjunction to each other deepening on the varying loads to reap all the benefits of energy efficiency. Complex functions like night purge ventilation; pre cooling and heating, load cycling, maximum demand control and monitoring can be sophisticatedly controlled by automated process (Savage, 2009). Many energy saving measures typically used in advanced energy efficient buildings also tend to underperform because of the absence of corresponding control systems (New Buildings Institute, 2009).

Optimum start up controllers
Office buildings typically have a fixed occupancy pattern. However, a challenging aspect in office spaces is that the HVAC system schedules are not only a function of the occupancy but are also dependent on outside ambient temperature, system operation sequences, thermal inertial of the building and their efficiencies while meeting the zone set points. Optimum start-up controllers, through intelligent algorithms, ensure the building reaches the desired indoor temperature by the time it is occupied by turning on the HVAC systems at an appropriate time depending on the external weather conditions (or seasons). This eliminates the unnecessary energy waste that is occurred otherwise by starting up the systems too early or cause discomfort by starting them too late. System start-up timings and night setback temperatures can be optimized for different seasons or as per the external weather conditions to save considerable energy.