HVAC & Controls
Building Management Systems (BMS)
Building management systems are central computerised systems used to manage a building’s operation.
Systems that may be connected to a building management system include heating, ventilation, air conditioning, lighting, security, fire services, plumbing and building access. A building management system can contribute to reductions in energy usage by automatically adjusting a building’s systems, turning them off when they are not required or optimising their running cycles.
Chillers & Boilers
HVAC systems are the greatest energy consumers in most commercial buildings, and most of these air conditioning systems vary according to the application, but they all have similar attributes.
Outside of a good control automation system, the chiller, boiler and motors have the greatest potential to capitalize on energy efficiency and offer the best return on investment.
Generally, chillers are the primary consumer of energy in most building systems. So, even small changes in operating efficiency can affect energy costs. Chillers are typically meant to carry the largest cooling load during an ordinary year in the facility, even though that load may only happen for a few hours. For the remainder of the time, the chiller system works at a lesser load, occasionally an even greatly reduced load.
Unfortunately, chillers run at their highest efficiency when they run at or near full-load settings. So, as the load on the chiller declines, the efficiency of the chiller also declines.
Combustion efficiency for air and fuel mixtures is vital to proper boiler operation. Too much oxygen reduces the operating efficiency of the boiler and causes undesirable pollutants.
Likewise, too little oxygen will result in fuel not completely combusting and will create a build-up of soot, clogging surfaces and reducing boiler efficiency. Therefore, some excess oxygen is necessary to ensure complete combustion and prevent damage from soot build-up.
Fine-tuning the boiler’s combustion controls will limit the excess air introduced into the boiler and, consequently, increase its periodic operating efficiency.
An air handler, or air handling unit (often abbreviated to AHU), is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. Usually, an air handler is a large metal box containing a blower, heating and/or cooling elements filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork that distributes the conditioned air through the building, and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served, without ductwork.
As part of the HVAC system, AHU’s and Air Extraction units are also consumers of energy and part of the NuGreen audit process we assess the load they use in undertaking their function.
Variable Speed Drives (VSD)
Traditionally, air conditioning system components such as fans and pumps have used constant speed drives (motors) – they operate at a fixed speed and can only be switched on or off.
Variable speed drives allow these components to modify the speed they operate at to better match the load that is being put on them. This can allow for significant energy savings, depending on the system. Variable speed drives also tend to require less maintenance as their ‘soft start’ capability reduces start up wear compared to fixed speed drives.
Variable speed drives aren’t necessarily a direct replacement for fixed speed drives though. System changes will probably be required to allow variable speed drives to be used and realise their full potential, as changing one or more drives from fixed to variable speed will have an effect on other system components and efficiencies.
Direct Digital Controls – Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, setpoints, controllers, logic, timers, trend logs, and alarms.
The unit controllers typically have analog and digital inputs that allow measurement of the variable (temperature, humidity, or pressure) and analog and digital outputs for control of the transport medium (hot/cold water and/or steam). Digital inputs are typically (dry) contacts from a control device, and analog inputs are typically a voltage or current measurement from a variable (temperature, humidity, velocity, or pressure) sensing device. Digital outputs are typically relay contacts used to start and stop equipment, and analog outputs are typically voltage or current signals to control the movement of the medium (air/water/steam) control devices such as valves, dampers, and motors.
Groups of DDC controllers, networked or not, form a layer of system themselves. This “subsystem” is vital to the performance and basic operation of the overall HVAC system. The DDC system is the “brain” of the HVAC system. It dictates the position of every damper and valve in a system. It determines which fans, pumps, and chiller run and at what speed or capacity. With this configurable intelligence in this “brain”, we are moving to the concept of building automation.
More complex HVAC systems can interface to Building Automation System (BAS) to allow the building owners to have more control over the heating or cooling units. The building owner can monitor the system and respond to alarms generated by the system from local or remote locations. The system can be scheduled for occupancy or the configuration can be changed from the BAS. Sometimes the BAS is directly controlling the HVAC components. Depending on the BAS different interfaces can be used.
NuGreen Solutions provide a number of services which can improve the energy efficiency of a building by better managing and optimising the controls and BMS of a facility.
Tuning & Commissioning
Optimisation of energy saving features and ensuring safe operation of a new facility requires a combination of good design, quality installation, thorough commissioning and ongoing tuning of operating systems. Often commissioning quality is adversely aff¬ected by construction program pressures and shortfalls in understanding the integrated function of systems.
Recommissioning occurs when a building that has already been commissioned undergoes another commissioning process using the same tests used in the original commissioning process.
Recommissioning of existing buildings is undertaken with the aim to improve the performance of building services and energy efficiency.
Recommissioning is made easier if existing commissioning data and operations and maintenance manuals are made available to commissioning staff¬. This information provides an overview of the systems, relative performance benchmarks, how they have performed in the past and what systems have been modified.
NuGreen has in-house commissioning and building tuning teams that undertake full tuning and commissioning as part of the implementation phase of a project.