BMS or PLC? Controlling the Regulated Environment

Published on: 
BioPharm International, BioPharm International-09-01-2004, Volume 17, Issue 9

If the system is not 21 CFR Part 11-capable or the network configuration is not appropriate, cost is immaterial.

In the ever-changing world of pharmaceutical facilities delivery, there appears to be a growing interest in the utilization of programmable logic controller (PLC) technology and process systems to control HVAC applications.

Jeff Bredeson

Background Information

Until recently, HVAC equipment and building management systems (BMS) were thought of primarily as non-impact or indirect impact systems to most regulated facility owners. The last decade or so has truly marked the evolution of quality management in the life sciences industry. Companies, as well as the various regulatory agencies (FDA, HPB, MCA, etc.), have realized that there is a direct link between the temperature, humidity, pressure, or particulate count in a space and the quality of the product being manufactured, studied, manipulated, or stored in that space. The logic is that an excursion of these variables caused by a malfunction of the system controlling these points of data — the BMS system — has "direct impact" on product quality, and, therefore, these systems should be qualified and must pass regulatory muster. As companies are starting to embrace a risk-based approach to validation and to assess systems and component criticality, they are finding the environment is an important part of the quality equation in a regulated facility.

Now that the criticality of these systems is recognized, the discussion turns to finding the right control solutions for regulated environments. Historically, commercial BMS systems, the same systems used in schools, office buildings, and hospitals, were utilized in critical industrial areas. Today, many BMS manufacturers are improving, hardening, and securing these systems to make them more industrial in appearance and operation. At the same time, some owners of regulated facilities are looking at other ways to meet their needs. One of the solutions being explored and tested is applying programmable logic controller (PLC) technology to HVAC applications. This article identifies and compares the advantages of each approach from a pragmatic perspective.

Before the advantages of each system are individually addressed, let's examine the critical issues more closely from the building owner's perspective.

Risk Mitigation and Compliance

Risk mitigation and compliance are critical because the penalty for non-compliance is so great, as many companies are learning. The ability to procure robust technology that enables the attainment and maintenance of compliance is not just "nice to have;" rather, it is the proverbial "ticket to the dance." Companies must have a product that can be applied with compliance in mind and meet the relevant regulations — Title 21 CFR Part 210, 211, 820, and 58, as well as Title 21 CFR Part 11. From a system purchaser's perspective, there are several considerations. First, is the vendor's solution compliant? Further, is the validation process in line with company standards and procedures? Is there precedence of the solution being validated? Finally, is the cost of compliance within reason?

Companies now view facility automation systems and component criticality as part of the quality equation.

Many system providers claim that their products are compliant with FDA regulations. In reality, when it comes to systems that include hardware and software, compliance must be built into the product to assure the result. There are very few off-the-shelf systems that are compliant out of the box. In fact, compliance always includes some level of procedural action on the part of the owner. This fact stresses the need to work with a solution provider (PLC or BMS) that understands the regulations that apply to their area of the facility and can provide references of successfully validated solutions. If you are asking a solution provider to apply a technology to an area of the facility that is not their core competency, then you are asking for an unpredictable outcome.

Speed to Market

Business drivers can be different for each project you consider. However, in most pharmaceutical applications the main drivers to success are schedule and compliance. In regards to schedule, the longer it takes to get the facility up and running, the more money it costs and the greater the loss of revenue from delaying production. When schedule is the major business driver, the solution that provides the most predictable outcome should be selected. If your schedule forces you to emphasize predictability of outcome, the solution that is fit for purpose and can be validated may be the right answer.


Another issue, which may seem less important issue but always comes to the surface, is cost. When you compare the price per point of a PLC with a BMS, there are several issues that must be addressed. First, can the system be validated? If the system is not 21 CFR Part 11-capable or the network configuration is not appropriate, cost is immaterial. Of course, there are many different levels of cost associated with a system — material cost, installed cost, validated cost, operational (lifecycle) cost. For the purpose of this discussion, we will focus on the turnkey, validated cost. If you are working with a reputable BMS solution provider with a reference list of clients for whom they have delivered validated solutions, BMS and PLC systems can be compared directly. This issue is discussed further under "BMS Systems on HVAC Applications."

An intelligent operator's interface can control, report, integrate, and manage production environments while helping maintain compliance.

Building Operation and Maintenance

A final business driver that needs to be mentioned is serviceability and support. This is crucial to the long-term success of the facility. Does the solution provider offer local service and support that will meet the owner's needs? Often the owner will claim that if a PLC system is used, it can be supported using internal process automation teams. This raises two issues. First, the manpower on the production floor is always in demand, and, if there are process issues and HVAC issues occurring simultaneously, the process issues will most likely take precedence. There are instances, however, where HVAC-related problems compare in priority to process-related excursions. For example, a fan failing to start in a critical environment is a high-priority issue. To stress the point, if a critical temperature in a production area falls out of specification during production due to that fan failure and the system documents this condition through trended data, the life sciences company is taking the same compliance risk as it would if a production parameter was out of spec during production. Second, the skillsets required to maintain and troubleshoot a process control system and a building management system are different and typically require two separate system-focused groups. With this in mind, let's compare the advantages and disadvantages of BMS and PLC systems as applied to HVAC applications.

BMS Systems on HVAC Applications

First, let's explore the reasons BMS systems are currently the predominant solution for environmental control in regulated environments. The central advantages are in the following areas:

  • Fit for purpose
  • Validation
  • Cost effectiveness
  • HVAC integration
  • Distributed control.

Fit for purpose. The first reason that BMS systems are the choice of the majority of regulated facility owners is that they were originally designed specifically with HVAC applications in mind. This may seem trivial, but it is really a crucial piece in this discussion. Since BMS systems were designed for HVAC applications, many of the most common and frequent applications (such as lead/lag of chillers, rotation of pumps based on totalized runtime, and ramping of modulating output devices), which can be difficult with other systems, are simple to accomplish. This is due to the object-oriented design of most BMS systems.

The concept behind object-oriented design is to create objects (pre-designed and tested pieces of software) that represent the majority of the common HVAC equipment and applications. These software objects are then used as templates in the construction of the system application program. This approach allows a major reduction in programming time since the objects require only configuration rather than programming, which subsequently encourages consistency in programming and system operation from facility to facility.

Figure 1. Architecture of Typical PLC and BMS Systems

Another area where this advantage is apparent is specialized applications such as VAV or pumping packages. BMS systems have stand-alone controllers that are specifically designed to collect data from these devices. PLC systems require remote input and output (I/O) devices, which are not stand-alone, to provide control for these specialized applications. In other words, the brains that run the equipment are not local but are centralized at the PLC. Additionally most BMS solutions include diagnostics and operational algorithms that are built into the software, offering real advantages to the owner. A good example of this is the diagnostics built into most VAV terminal box controllers. At the press of a button, the software will test for connectivity, show the flow through the box, show the room temperature, indicate the reheat status, and calibrate the damper. The amount of work required to get a PLC to provide this type of functionality is staggering.

An important distinction to make here is that the BMS comes from the manufacturer with these objects and HVAC templates already fully tested and installed. These objects merely require configuration for the application rather than the full programming required for the PLC. Conversely, PLCs come from the manufacturer as empty vessels ready for a programmer to create an application using ladder logic. This makes PLCs very flexible, but it also requires more programming time and an in-depth knowledge of the process to get them online. It also makes it harder to assure consistent programming and operation from facility to facility.

Challenge: The disadvantage of a fit-for-purpose design is that it may make the BMS solution less flexible and less customizable than a PLC solution.

Validation. From a validation perspective, object-oriented design allows the BMS solution provider to wrap validation protocols around finished objects and set them on a virtual "software shelf" for use on future HVAC applications for regulated environments. This offers substantial benefits to the facility owner through a reduction in time and cost of validating the BMS system.

Additionally, the industry-leading BMS solution providers have invested significant amounts of time and money to improve their products and implement solutions that are 21 CFR Part 11 capable. These same solution providers are investing in employees and businesses that provide quality project documentation and validation protocol creation for the systems that they produce. These investments should indicate to the industry that BMS manufacturers are committed to the industry and are committed to providing domain expertise that will lead the facility owner successfully through the validation maze.

Figure 2. Event-Based Systems vs. Polling Systems

Challenge: Most of the BMS solution providers are highly specialized, which can limit their validation capabilities to HVAC applications. They may not have the range of experience or understanding of other processes to be able to validate traditional process solutions.

Cost effectiveness. As BMS solution providers expand their capabilities and offer new services, they tend to increase their price. For example, 10 years ago, XYZ BMS Company would have offered to ABC Pharmaceutical Company the identical solution offered to a school or an office building. As XYZ learned more about the differentiated needs of the life sciences industry, they would create products and solutions specific to the needs of that customer. This specialized product, although it still offered HVAC control, had features that made it applicable to the life sciences industry, such as more robust architecture, no single point of failure in the system, multiple networking capabilities, increased data integration capabilities, increased system security, and embedded audit trails to provide accountability. These features are valuable to the industry, so the solution's price increased.

Now, ABC Pharmaceutical Company asks XYZ to provide a turnkey, validated system, which dramatically increases the scope of work that XYZ provides (typically adding functional specification, detailed design specification, some factory acceptance testing, some site acceptance testing, installation qualification, and operational qualification). XYZ, after researching and establishing a market for validated systems, decides to invest in validation engineers and technical writers so they can provide the validated system. This increase in service also increases the cost of the system, but the value of a turnkey system to the customer is greater than or equal to the cost of the solution.

Research and experience indicate that the price per point of BMS systems is rising primarily due to the owner's higher expectations and increasing demand for deliverables. Despite the cost increase of BMS systems, research suggests the installed cost of a fully implemented and validated BMS system is still about one-half the installed cost of a fully implemented and validated PLC system. As a general rule, a fully validated, turnkey PLC system with supervisory control and data acquisition (SCADA) costs between $7,000 and $9,000 per point. This includes the engineering required to apply the system, installation of the system, commissioning and validation protocol generation, and execution. A similar fully validated, turnkey BMS system costs between $2,500 and $4,000 per point with identical delivery. (The range in cost for each solution is due to the variable scope of work and cost of instrumentation).

Challenge: This cost advantage holds true for all but the largest and most complex systems. As projects grow in point count, process control solutions are more cost efficient. BMS systems may lose cost efficiency due to scalability issues when systems go above a certain number of points (exactly where this occurs is debatable and should be compared on a project-by-project basis). PLCs are more scalable and more cost effective with larger systems.

Integration. Several years ago, the commercial BMS market started to embrace the concept of integrated buildings. System integration involves creating connections between the different systems in a facility so that data can seamlessly pass between the systems. This allows easier operation — visualization of multiple systems on a single human-machine interface (HMI) — and better control throughout the facility (more effective data passing makes intra-system control possible).

There are several levels of system integration to be considered. Systems can integrate anywhere from the field bus level (level 0 in S95 architecture) all the way up to enterprise level (level 3 in S95 architecture). BMS systems are designed to talk with other facility systems and to packaged equipment. All the leading BMS providers can integrate the BMS system with fire alarm systems, access control and security systems, and utilities systems (chillers, boilers, pumps, etc.). Industry-leading BMS providers can also provide high-level database integration through the use of industry standard protocols (OPC, XML, BACNet, and others) that allow data aggregation and access from multiple systems through a single database. Integration makes it easier to operate multiple systems while reducing training time for operators.

Challenge: PLC systems, although not as good at integrating with other facility systems, are very good at offering high-level database integrations through industry standard protocols (OPC, ABDH, and others). They are also effective in integrating other process control systems (ModBus, ProfiBus, and others). Difficulties arise when you try to integrate a PLC system with a BMS system, as the standard protocols for these two systems are typically different.

Distributed control. When comparing BMS to PLC, you are comparing a distributed control system (BMS) to a centralized control system (PLC). This means that the BMS distributes its processors down to the point level while PLCs generally keep their processors at a higher level and use remote (I/O) devices to pick up the field instrumentation. The advantages of distributed control include the following:

  • It is less expensive to install. With a BMS system, you can pull a two-wire communications bus back to a supervisory control panel. With a PLC system, you may have to wire each point back to a PLC.
  • It has more robust architecture. If a stand-alone controller in a BMS system loses communication with the rest of the system, it will continue to control the equipment to which it is attached. If a PLC remote I/O loses communication with the PLC, control is lost.
  • Distributed controllers simplify validation boundary assignments during risk assessments, allowing for smaller logical boundaries and, therefore, lower cost.

Another advantage to most distributed control systems is that they are event-based. Event-based control implies that the stand-alone controllers retain the data they are collecting (trend data, audit trail data, schedules, etc.) and send it to the HMI on a timed basis (Figure 1). This makes the HMI a passive device in the system. In reality, a BMS HMI is just a window into the system. The software does not initiate control; it only allows operators to view the system and gives them a graphical tool to make adjustments to the system as required. The controllers send data as they retrieve it, and the individual points are updated on the HMI as the controllers send the data.

Conversely, PLC systems are typically set up as polling systems. In polling systems, the HMI (a SCADA) is an active device in the system. The SCADA will often be connected to many viewer nodes that offer a window into the system, but, in the case of a polling system, the software will initiate data acquisition (Figure 1). The SCADA, on a timed basis, will poll each of the PLCs in the network and request any new data from them. The SCADA will then refresh the entire screen after each poll. The big difference that this creates is in system reliability. If a BMS HMI goes down, the system continues to work and the controllers simply retain the data they are gathering in their buffers until the HMI comes back to life. If a SCADA goes down, certain functions of the system stop, and, more importantly, data cannot be gathered and may be permanently lost. Additionally, since the HMI reaches down into the system to retrieve data, if the polling scan rate is too broad critical data can be missed (Figure 2).

Challenge: PLC systems can be distributed by putting a PLC near each major piece of mechanical equipment or by utilizing "smart sensing" devices. This solution can be cost-prohibitive.

PLCs on HVAC Applications

Now let's consider the reasons that PLC systems are being considered for HVAC. There are five main advantages of PLC systems for HVAC:

  • a single platform
  • a single system validation package across the GxP area
  • the ability to leverage existing process control knowledge
  • flexibility in use and programming tools
  • speed of processing.

Single platform. If a consistent platform is used across the entire facility, a PLC solution makes sense. The owner can simplify the architecture and utilize the same platform across the entire GxP area. The advantages are numerous. The owner can get better economies of scale for price leveraging, train their staff on a single technology, visualize the data anywhere in the facility from a single HMI, and potentially reduce the cost of validation through standardization.

Challenge: The key to making the right decision here is in properly evaluating the business drivers and critical decision criteria. A single technology platform may be important and nice to have, but does it outweigh the predictability of outcome? Only the owner can evaluate this and make the right decision.

Single system validation package. A single system validation package across a campus makes sense. The validation package typically represents between 20 to 30% of the system's cost. It is a crucial part of the puzzle. The regulations must be met, and the documentation is the key to convincing the regulating authorities that ample thought and consideration were given to the regulations. Rolling the entire automation strategy for the facility into a single package can save time by duplicating documents for identical systems. It also has potential to reduce the number of validation protocol providers onsite.

If a single system validation package is desired, a PLC-based process control system is the only choice. As mentioned earlier, BMS systems are not designed for process control. There are a two central reasons for this:

  • speed of processes (BMS systems have limited input and output speeds since the rate of change of HVAC processes is generally much slower than that of production processes)
  • lack of programming flexibility (the object-oriented design of BMS systems make them less flexible).

Challenge: Most facilities require more than one system because very few are used exclusively for production. Most buildings have areas where production issues are not in play — restrooms, hallways, interstitial spaces, and offices. PLC systems, due to their cost structure and scalability, are difficult to deploy in these areas.

Leveraging process control knowledge. There is little question that the most important system in a production facility is the process control system. Revenues earned from production are the reason that the facility was built, and the process control system allows production to be as efficient as possible. Based on that fact, most owners utilize full-time employees to operate and maintain their process control systems. This ensures that system downtime that can affect their ability to produce is held to a minimum. This inhouse knowledge of the process control system can be utilized on the HVAC side as well, if a PLC system is used in the facility.

Challenge: In order for this advantage to be realized, the owner must have adequate, knowledgeable staff to cover both systems. Too often, the owner will limit the staff, citing economies of scale inherited by utilizing a single system across the facility. The result is that the process control system gets the attention it needs while the HVAC system only gets attention when a failure that immediately affects product quality occurs. Additionally, most process control technicians do not understand HVAC applications. Making sure that the staff is cross-trained on HVAC is key before considering this approach.

Flexibility in use and programming. PLCs offer flexibility that is unrivaled in the HVAC controls industry. High levels of flexibility appear throughout PLC solutions, including:

  • the ability to use several different programming tools and languages
  • flexibility in networking protocols
  • support for multiple databases
  • support for multiple HMIs and SCADAs
  • very diverse application capabilities.

PLCs are highly flexible devices. This is one of the most desirable attributes of PLCs, and the main reason why they are still widely available in the market. The ability to use common programming languages such as ladder logic to program PLC devices also offers a large pool of competent programmers from which to hire.

Challenge: Ensure that flexibility is required in your specific application. Don't pay more for better technology than is required by the application, and don't get sentimental about technology. Remember, technology is a means to an end.

Speed of processing. One of the key differences between process applications and HVAC applications is the speed of the process. Many process applications require sub-second data acquisition and processing times to accommodate the needs of the process. In the case of HVAC, the processes are much slower, and therefore, the control system does not need to respond as quickly.

PLCs offer the ability to obtain and process data very quickly making them ideal for stand-alone process control applications.

Challenge: The typical HVAC process does not require the fast response times possible with PLC systems, so the speed advantage of PLC systems is moot when it comes to controlling HVAC systems in the regulated environment. Pressure control can be the exception to this rule, since dramatic deltas in pressure can occur fairly rapidly.

When Is a BMS System Better?

Assuming you are working with a reputable BMS solution provider with a focus on the life sciences market, a solution that can be validated, references of validated solutions, and an understanding of the regulations and the need for risk mitigation, the following aspects of BMS systems are advantages:

  • The systems (hardware and software) are made specifically to work on HVAC applications in critical environments.
  • The programming objects are made to work like the mechanical devices they control.
  • The objects that are used to program the system are not unique. They are tested and can be validated (even prior to use).
  • The solution providers are experts in HVAC systems and critical environments (domain expertise).
  • Price per point is generally one-half the cost of a similar PLC solution.
  • BMS systems are designed for facility integration.
  • Distributed control has advantages over centralized control.
  • The same group that applies the technology can provide system documentation and protocols.
  • The solution is not unique, and the solution provider can support the applications locally.

When Is a PLC System Better?

Again, assuming that you are working with a reputable PLC solution provider that has successfully applied the product to an HVAC application, has a solution that can be validated, has references of validated HVAC solutions, and understands the regulations and the need for risk mitigation, the following aspects of PLC systems are advantages:

  • A single platform can provide process control and HVAC control across the facility.
  • A single platform allows for a single system validation package across the entire facility.
  • Inhouse control knowledge can be leveraged to maintain the HVAC system.
  • It is highly flexible.
  • The solution providers are experts in critical environments and their solution set.
  • The solution provider can support the applications locally.


Choosing the appropriate automation solution for HVAC control requires careful consideration. Those who approach the debate in an unbiased fashion admit that it is not a "one size fits all" argument. The following steps will help you reach the right decision for your facility:

  • Start with a risk assessment to determine the system criticality.
  • Clearly define the business drivers that are critical to project success.
  • Prioritize the identified business drivers.
  • Check decision criteria against: fitness for purpose, predictability of outcome, first cost, ease of implementation, ease of validation, ease of operation, ease of support, total lifecycle cost.

Understanding each system's advantages and clearly defining your project goals and drivers is the key to a best-in-class solution. Ultimately, this will help ensure that dollars are spent diligently and with the greatest possible return on investment.