Integrating direct digital controls
Learn about control system attributes, and how integrated control systems can be designed for various building systems
- Understand basic building control system attributes.
- Review control system codes and standards.
- Integrate mechanical, electrical and plumbing systems into a single control system interface.
- Learn about commissioning of control systems.
Mechanical engineers, electrical engineers, plumbing engineers, fire protection engineers, lighting designers and control system engineers all deal with control systems in their daily work activities. Some of these building professionals, except maybe those that deal with control systems on a daily basis, may not good at specifying control systems.
A number of projects use performance-based specifications as a solution to specifying controls for a particular solution or include statements about expanding existing systems in order to match what is existing. Many times, these practices result in inferior control system solutions. The lack of a strong and well–written control system specification may result in disappoint by the design team and owner.
Experienced engineers, contractors and commissioning agents must ensure that project specifications include detailed requirements for system architecture, performance, interface and verification in order to achieve fully capable control system solutions.
Many designers have their own master specification document sections that cover control systems, from the parts and pieces to the sequence of operations. Control system specifications frequently are an afterthought on a project, relegated to the very last thing that is completed before a project goes out the door. Other times, a control system specification is weak because the author of the section is not experienced or lacks a complete understanding of the project requirements.
Building control system types
Design processes must start by identifying the goals of the activity. Creating an outline listing the ultimate goal and the steps to achieve that goal are the best way a project specific control specification will provide the capabilities desired. This process is so much more important in identifying control system requirements when multiple systems are planned to be connected to the same user interface, workstation or web-based than if it was just a single control system for HVAC, lighting or another building system.
The opportunity for failure in a control system to control a single building system is high enough on a typical project that the complication of integrating multiple systems in a single platform may seem daunting or downright unintelligent. The opportunity for failure follows an exponential curve when multiple systems with many different needs and control priorities are mixed into a single data automatic control system capable of human override, especially a single control platform specified by an inexperienced engineer and installed by an inexperienced contractor.
Current building control systems are based on the first direct digital control systems put into mainstream use in commercial buildings in the early 2000s. Those systems were preceded by years of pneumatic control systems, and before that manual control. Many buildings use all three of those types of control systems: manual, pneumatic and DDC. This may be due to the cost of upgrading the entire system, the comfort level of the building owner/operator or because the building has been around for many years. These systems existing in many buildings due to replacement cost, operational needs and user familiarity.
Specifying DDC systems
The purpose of DDC system typically is to increase the user comfort and decrease operating costs. Integration of these systems also may benefit the user or occupants through additional security, safety and peak operational efficiency. The use of DDC systems has allowed building engineers and operators to focus on a multitude of data points and performance that are important to their individual needs.
For example, a building owner may be focused on total energy used in a building and which equipment is driving up operating costs. A building operator may be focus on monitoring performance trends of a specific piece of equipment or temperatures in a constantly struggling space to maintain temperature setpoint, in an attempt to get in front of occupant complaints or equipment downtime. A design engineer may be looking for confirmation that the systems they designed are operating to the level anticipated. Finally, a commissioning agent may want to use a DDC system to first confirm performance and then test systems for reliability and conformance to the construction documents.
Today’s control systems are based on standards and codes developed over time to address energy performance of systems, standardization of systems and interoperability of systems. Many of the “performance” requirements listed in DDC control specifications for HVAC and lighting are driven by requirements in the International Code Council. The ICC organization develops model codes and standards used in design and construction industry. It also established baselines for compliance processes for the building industry. These standards and guidelines provide standardized solutions to control systems, including integration, operation and ability to verify baseline operation.
The codes developed by ICC are adopted by many authorities having jurisdiction in the U.S. These are the officials that review design documents and perform building inspections. Some of the most commonly used codes related to the development of DDC systems are the International Energy Conservation Code and International Mechanical Code. These codes provide codified language on the minimum requirements for control systems to operate HVAC systems, lighting and electrical systems. The IECC code includes requirements for systems to have automatic features for economizer fault detection, hydronic temperature reset, air and hydronic system pressure reset and daylighting automatic response, as well as other items. The IMC code is achieved by using DDC control system for activation of requirement HVAC equipment.
ASHRAE provides standards for control systems through standards and guidelines. ASHRAE’s goal is “to advance the arts and sciences of heating, ventilating, air conditioning and refrigerating to serve humanity and promote a sustainable world.”
ASHRAE standards and guidelines related to control systems operation, performance and design include ASHRAE Standards 0, 13, 36, 55, 62.1, 90.1, 135, 189.1 and 202, among many others with references to functionality and interoperability of systems. Some ASHRAE standards and guidelines are written to be codified and may be adopted in some locations in the U.S. at this time.
NFPA standards include NFPA 3: Standard for Commissioning of Fire Protection and Life Safety Systems, NFPA 4: Standard for Integrated Fire Protection and Life Safety System Testing and NFPA 72: National Fire Alarm and Signaling Code, among others specifically relate to control and testing of building systems. The NFPA standards are generally guidelines that should be followed as best practice, expect where there are conflicts with other adopted codes. Many locations in the use various NFPA standards as enforceable codes.
DDC systems are based on various frameworks established by BACnet, LonWorks and others. These frameworks for control system architecture establish industry standards used in many building systems. Besides these frameworks, other DDC system critical attributes include cybersecurity, such as the ASHRAE Standard 13: Specifying Building Automation Systems, as well as how systems are updated and maintained in the future.
The ability to integrate various control systems into a single platform provides an opportunity for energy efficiency, standardization, simplicity of interface and communication to interested parties. Once the HVAC system DDC systems are fully established through specifications, there should be limited barriers to integration of other systems. An HVAC DDC system commonly integrates variable frequency drives, chiller controls, boiler controls and rooftop unit controllers. These systems require a DDC system to navigate the influx of hundreds or thousands of additional data points that may be read–only, monitor or writable data code. The ability of an HVAC DDC system to accept this vast volume of data creates a strong platform for expansion.
The ability to make future modifications and updates to any DDC system is an important part of the design/specification of these systems. Many mainstream DDC systems are BACnet–based. Systems offered by DDC manufacturers have a wide range of future adaptability once installed. Some systems have “canned” functions and limited capability for future system modifications or adjustments to sequence of operations. These systems have been established by manufacturers and offered by vendors to serve a highly cost-effective purpose.
Other DDC systems are capable of being programmed to do whatever someone needs, but those capabilities come at a cost. There are many variations in between these extremes that are seen in buildings constructed today. Sometimes an engineer and building owner end up with a system that is too complicated (seemingly unlimited control functions) or too simplistic (Why can’t I add one more variable air volume box to an existing system?). It is important that these various options of control system capabilities are discussed during the design phase as the overall functionality of the building will be affected by this design phase decision process.
These issues, too much or too little, are amplified when other control platforms, such as lighting, security, access control, elevators or fire and life safety are added to a mix of building systems in a single interface. Limited functionality for an HVAC control system to be adapted for a different building use or adding a few pieces of equipment can be something that an operator may be able to live with.
Once an operator decides to accept the limited functionality of other systems — such as a fire alarm interface cannot send data to the operator, which indicates the actual zone in alarm or type of alarm. This situation begins to add a level of frustration that a single interface control system cannot do what the operator needs for daily functionality. An operator may say, “We live in a digital world, don’t tell me that one thing cannot be integrated into this operating system that I just paid a boatload of money for one year ago.”
The ability to integrate HVAC, fire alarm, lighting and electrical systems is further complicated by years of development inside each of these industries to establish highly efficient and reliable operating schemes, each for its own purpose. These systems were never designed to work together in a collaborative or integrated environment. In some jurisdictions, these systems are not allowed by the AHJ to be integrated. However, the ability of digital–based control systems allows for software programming to overcome these changes when allowed by the AHJ. Typically, this programming is performed by an experienced HVAC DDC system contractor.
Integration of these systems is the ultimate goal for some building operators, and engineers want to provide the solution. The process of clearly understanding an operator’s goals, various DDC system capabilities and verifying system operation requires a well–written specification, close design and construction team communication and capable project team members from design to construction to ownership.
Commissioning and control systems
The opportunity to use the commissioning process for verification of proper and complete integration of multiple building systems has resulted in positive outcomes on numerous past projects for GRAEF. The commissioning process is the final tool needed once a DDC system for multiple systems has been properly specified, designed and installed. A building commissioning professional is typically a third party that is not influenced by the design or construction team, but works on the owner’s behalf to ensure all systems, including control systems, are functioning as specified. One of the commissioning professional’s tasks is to test the sequence of operations of mechanical, plumbing and electrical control systems. Typically, building commissioning professionals are very knowledgeable in control systems with many having a background in control system contracting.
GRAEF’s experience as a third-party commissioning firm has been used in many situations to provide insurance to a design or construction team by commissioning what was designed by the engineer of record, as well as confirm for the entire project team, including the owner, that the DDC system is fully functional as anticipated by all.
An important part of this commissioning process is the relationship that exists amongst the commissioning professional, design engineer, control system engineers, control system contractors and mechanical contractor. Commissioning of a control system sometimes uncovers unique situations that require input from both a design and testing standpoint. It is imperative that a building commissioning professional’s opinion and preferences are used only for problem-solving as the testing is to be per the construction documents. It is however that base knowledge carried by many commissioning professionals that is most useful with integrated control system projects.
Testing of DDC systems brings with it a variety of complications, including the type of interface, capabilities of the installed system to override specific points, system response times and to what level all systems on the DDC platform are integrated. This testing of control system reactions uncovers the failures of systems to work together, such as when a duct smoke detector is wired to alarm in a fire alarm system, but does not shut down the local air handling unit. Another scenario: When an occupancy schedule that controls both HVAC occupancy and lighting is only used for one and a default program for the other. These examples may relate to life safety issues or energy inefficient operation.
The process for specifying and successfully implementing integration of various building systems into a single DDC–based platform is achievable and very possible. The solutions discussed provide examples from real–life situations that have resulted in a positive outcome. Other actions to consider for a confident result:
- Establish the project goals before design begins so a clear path is determined early and not influenced along the way.
- Don’t forget about keeping it simple.
- Commissioning, commissioning, commissioning.
- Write a great control system specification.
- Incorporate control system requirements across all specification divisions that are required to “work together.” This should include how trade contractors in the field work together and the requirements for electronic control systems operating on a network.