HVAC product selection is not as easy as it sometimes seems. For sure, the key part of engineering is the KIS principle (Keep It Simple). However, the KID principle (Keep It Defendable) is even more important in today’s litigious construction industry where there are increasingly more demanding codes and standards that apply to integrated building design, construction, operation, and maintenance. One example is the basic selection and installation of life safety dampers that must be cycled periodically to prove they will indeed operate and provide the life safety features the codes require. Engineers and architects who fail to provide integrated design to allow for the maintenance access to life safety dampers may indeed find themselves liable for a loss of property or life occurrences.

Engineers who consider themselves high-level, “system” concept thinkers must also think about the details of product selection. HVAC engineering involves HVAC systems design. HVAC systems are made up of products. Products are made up of components with features. Features perform functions. These functions are integrated and combined to provide benefits to the end user as part of the HVAC system. Understanding the functional requirements of an HVAC product is essential to the product selection and specification process. Without this understanding it is possible the product selection and specification will not be fully defendable when challenged by those who may be harmed in some way by the product’s functionality.

The term “value” is a term used in many marketing campaigns by professional engineers, contractors, and HVAC product manufacturers. The claim is generally meant to convey that the company provides value in their approach. Value is a good thing. Providing value for a client and building owner implies the engineer, contractor, or equipment manufacturer is indeed being prudent on behalf of the owner. These systems and products in the design and installation give the end user and building owner good use of their funds from the first cost of the building through the life cycle cost of the building.

However, value can be deceptive when combined loosely with a term such as “value engineering,” which many times is used when a project comes in over budget. Many times, value engineering is simply cost cutting with no regard to whether the original criteria by which systems and products that were part of the contract documents are being maintained for the owner. Indeed, sometimes “value engineering” becomes a devaluing of the HVAC system and products the owner of the building first thought they would be receiving.


HVAC System Selection

Before any HVAC product is ever selected there is a process early in the design phase of a project wherein the HVAC system is determined. There are many criteria that are taken into account to make this decision. First and foremost, the building code is setting the minimum requirement. This process also takes into account many functions of the HVAC system that relate directly to industry standards written by organizations such as ASHRAE, the U.S. Green Building Council (USGBC), Sheet Metal and Air Conditioning Contractors’ National Association (SMANCA), National Fire Protection Association (NFPA), UL, etc. The code is the minimum requirement but not always the best value for the owner of the building. Added value can come with an incremental investment by the building owner that goes above and beyond what a code may require.

One good source of a logical process for selecting an HVAC system is outlined in the 2016 ASHRAE Handbook — HVAC Systems and Equipment. In chapter 1, “HVAC System Analysis and Selection,” there is a process that takes into account many criteria. This process is a good starting point for every project and may be good to use as documentation in an initial meeting with an architect and facility owner to ensure everyone is clear regarding the engineering objective of the HVAC professional engineer of record on the project. In cases where a contractor is involved at the beginning of a project, whether it’s a design-build project or a joint-venture project, it’s wise to have the input of the contractor regarding cost, constructability, and maintainability. In addition, it’s essential to have the facility owner’s maintenance and building facility management team (whether internal or contracted to an external firm) involved in the system selection process as well.

As an extension of this article, it may be wise to take time to read this material in the ASHRAE Handbook and develop a document to be used on projects to help clarify and document the HVAC system design intent for the benefit of all team members. Sometimes a project can start with good intentions, but as the project develops through the conceptual design phase to the schematic design to the design development to the contract document phases of the design, the original design intent is forgotten and sacrificed as other perceived, or real, higher priorities are embraced by the team without the knowledge of the facility owner, who is generally the client.


HVAC Product Selection

HVAC product selections are done to fit in the HVAC system. Each product has components with features and benefits that come at various costs to the facility owner either in first cost, maintenance cost, energy cost, or possibly even disposal cost. The tendency in just about every project is to focus on the first cost of a product at the time of bidding when contractors are competing for the project as a part of their general business practice.

One of the best resources in the industry is almost one of its best kept secrets when it comes to a logical process documented for HVAC product selection and specification. This is the Construction Specifications Institute’s (CSI) The Project Resource Manual (PRM). The PRM is the book that is the basis from which an engineer can become a Certified Construction Specifier (CCS).

The PRM not only has a section titled “Product Evaluation and Selection,” but it also has sections that relate to the entire project delivery process, including contract types, contract documents, and what to expect from a professional Certified Construction Product Representative (CCPR). The PRM essentially is the authoritative resource for the organization, preparation, use, and interpretation of construction documents encompassing the entire life cycle of a facility and the systems and equipment within the facility.

According to the CSI PRM, there are four general categories of products. These are commodities, standard products, custom products, and proprietary products. Understanding these categories is helpful when making product selection decisions and when specifying the HVAC products. This includes products perceived as commodities like plaque diffusers (Figure 1) and VAV box inlet sensors (Figure 2). With this in mind, the CSI PRM outlines a multi-step process for product selection. First, there is establishing the product’s functional requirements. Next, there is the identification of possible products that are available or may be required to be developed. Next, there is the evaluation of the products based on meeting the product’s functional requirements. Lastly, in the design process, is the incorporation of the products into the drawings and specifications as part of the contract documents that become part of the owner-contractor agreement.

The ASHRAE Handbook does not have an overall general HVAC product selection process outline like it does for the HVAC systems. However, there are several criteria, features, and benefits discussed throughout the four-volume ASHRAE Handbook set for various specific products. There is a lot more to selecting HVAC products than simply listening to the most recent sales pitch by a product representative who happens to come to an engineering firm’s office to give a lunch-and-learn explaining why their products are the newest and best on the market.

Just as with an HVAC system selection process, the lowest common denominator of any HVAC product selection is whether it meets all of the current codes and standards that are in effect in the municipality in which the products will be installed. Beyond that there are many, many, many criteria to take into consideration based on what the owner needs or wants and is willing to pay for.

Documentation of the product selection process is essential for many reasons throughout the building design and construction and operation process. ASHRAE’s terminology definition of the “basis-of-design“(BOD) is as follows and includes product selections: “a document that records the concepts, calculations, decisions, and product selections used to meet the Owner’s Project Requirements and to satisfy applicable regulatory requirements, standards, and guidelines. The document includes both narrative descriptions and lists of individual items that support the design process.” The key point here is “records” (document) the process. Remember — KID.

This is important to understand and embrace professionally by all team members but most importantly by the professional engineer-of-record of record who applies his or her personal seal to the set of contract documents, which are the documents incorporated into the owner-contractor agreement. Yes, the product selections and documentation thereof are part of a legal document. Although many, or maybe even most, HVAC engineers are not educated in legal contract documents, the profession they are in does indeed include writing specifications that are part of a legal contract.

According to ASHRAE terminology, the question of when product selection begins can be answered when looking at the definition of “Design Intent:” “an initial version of the operating manual developed in the conceptual design stage. It contains a description of the building functions for which the design is intended, lists the design parameters of systems to perform these functions, and provides a brief description of the operating routines that are to be followed to comply with the functional requirements of the building.”

A product is made up of components that provide features and benefits that are integrated into the overall HVAC and other building systems to accomplish the functional “design intent.” Thus, the product selection begins at the beginning phase of a project and remains an integral part of the HVAC system selection process.

One tool that has been used by some engineers, and is a great way to document HVAC systems and product selections, is a feature/benefits analysis matrix. This tool can be used as a subjective evaluation of a product, as an objective evaluation, or a combination of both. The tool allows for early discussion, conversation, and brainstorming with the facility owner and managers to ensure everyone’s concerns are addressed from the beginning of a project. A features/benefits analysis matrix can be setup for any HVAC system and product within the system. It can also be great documentation that a thorough engineering process was completed to make the final system and product selection.


Product Specifications

There is no doubt that the documentation within the contract documents regarding the desired characteristics of HVAC products is essential to getting the best value on bid day. If there is vagueness in the contract documents, then the bidding will not provide the best value as contractors will attempt to cover their potential risks based on the uncertainty in the contract documents.

It’s always good to have a definition of a term used in construction. What is a specification? The term specification has these two definitions to keep in mind:

1) Specification according to ASHRAE terminology: “statement of a set of requirements to be satisfied by a material, product, system, or service that indicates the procedures for determining whether each of the requirements is satisfied.”

2) Specification according to CSI PRM: “Define the qualitative requirements for products, materials, workmanship, and administrative requirements upon which the project is based

According to CSI, effective communication within a legally enforceable set of contract documents demands the construction specification language is to be clear, concise, complete, and correct. There is not a lot of wiggle room in this statement when it comes to the legal standard of care in the profession of engineering. The engineer of record has a due diligence responsibility to ensure the specification is  clear, concise, complete, and correct according to CSI.

This article won’t get into all of the methods of specifying that are outlined and explained in the CSI PRM; however, it would be of value to every professional engineer, contractor, and facility owner and manager to research and understand these methods. They are: descriptive, performance, reference standard, and proprietary (open and closed). These methods of specification can be used alone or integrated within a set of contract documents and also within one section of a product specification. It is essential to understand which method applies to each and every statement within a specification.


Bidding and Submittals — Holding the Spec

Ultimately, product selection by the professional engineer of record gets communicated in the contract document drawings and specifications that are used by the bidding contractor. After the contract is awarded by the owner to a contractor, documentation of the product that was used in the bid, or ultimately negotiated to be used, is submitted to the engineer for “approval.” If accepted, it may be purchased and installed. This article won’t get into what “approval” of a submittal means, but suffice it to say, a product submittal is not a change to the contract between the owner and the contractor. The contractor is accountable to comply with the contract document requirements of the product specification per the owner-contractor agreement.

Unfortunately, over the past several years, the pre-bid request for information (RFI) process has fallen off dramatically in the HVAC industry. Also, multiple late addendums  by architects and engineers cause wasted bidding time. This is partially because of the speed of the industry. Contractors have been conditioned to wait until the last possible minute to get addendums. Addendums require extra time to rework bids that might otherwise have been completed in a timely manner with time for RFIs.

One of the challenges for contractors and equipment suppliers is knowing if the professional engineer of record will “hold the spec.” What? Does the engineer of record have the authority to not “hold the spec?” Isn’t the specification of a product part of the owner-contractor agreement, and this contract does not include the engineer of record changing his or her mind without the owner’s awareness and approved change order? This is unfortunately one of the age-old issues even today in this sophisticated construction industry. Many in the industry do not understand the basic legalities of a submittal process. This is indeed worth every business in this industry having a clear understanding. There are experts in the industry who can come talk to any company that wants to minimize its risk that is involved with “holding the spec” by a professional engineer-of-record and what authority he or she has (and doesn’t have) regarding “holding the spec,” which is part of the owner-contractor agreement. Suffice it to say, know the risk of not complying with the contract documents even if the engineer of record “approves” a submittal of a product that does not comply. This is often misunderstood by contractors and suppliers that do not have direct contracts with the engineer but still assume the engineer-of-record is always able to speak on behalf of the owner. This is not always true but can be under certain contractual relationships between the owner and the engineer. Many in the industry do not take time to read what “approved” means nor understand the underlying requirement to ensure compliance with the owner-contractor agreement, which is based on the contract documents, not the a submittal review.


Air Distribution and VAV Systems

In a building where the air distribution has been selected to be a VAV system, there are many factors to consider in product selection and specifications. Taking into account ASHRAE Standards 55, 62, and 90.1 (comfort, ventilation, and energy, respectively), there are many challenges. Seemingly simple products like a plaque diffuser and a crossflow sensor in a VAV box require thought regarding properly specifying their performance.

Many times, the energy aspect of a VAV system is well understood and accomplished with good turn-down ratios of the cooling and heating primary and secondary system product selections and controls. A full analysis of when a building will be at various load profiles may not always be required; however, there is a general understanding of how and why reducing airflow in a VAV system will save energy and can meet the intent of ASHRAE Standard 90.1, whether calculated or not.

 Meeting the requirements of ASHRAE 62 gets to be more challenging when the selection of the supply air diffusers in a space are selected. Probably too many supply air diffuser selections are done using what is assumed to be the tried-and-true rule-of-thumb technique of selecting the diffuser at peak cfm in a space based on the terminal velocity. This technique has been used for years and is generally the performance documentation every diffuser manufacturer gives with regard to terminal velocity distances of 50/100/150 FPM at isothermal conditions. Depending on the space, an engineer may use one of those terminal velocities at the peak cfm to select the basis-of-design supply air diffuser; however, that is only one point of operation and may be a very small part of the space load profile in both heating and cooling. What about the other times when the space is not at peak cfm? How is the supply air diffuser performance analyzed by the engineer, and how is that documented in the contract documents to ensure the product provided meets those performance functional requirements? In reality, the industry is actually still struggling to give engineers the tools to make this analysis with current product performance documentation. It’s the last physical product that supply air passes through before entering a space, yet the selection tools are not available to make a defendable selection at all points of performance. Is the air diffusion performance index (ADPI) selection process totally defendable to show compliance with ASHRAE standards and codes? There is not available information for heated air entering spaces or cooling air above tested ceiling heights. There may be some industry information, but how defendable is it when “experts” start explaining the manner in which the data is limited in the testing and how the ASHRAE standards are consensus standards with some likely biased opinions by vested participants in the industry?

Comfort? Yes, comfort. The generally accepted assumption is that the HVAC engineer will select air devices that will maintain comfort in a space at all flow conditions. ASHRAE Standard 55 has some very challenging requirements regarding comfort, requirements that include not only airflow terminal velocity parameters in a space but also temperature and humidity. Can VAV systems be designed without humidification controls and still be able to comply with ASHRAE Standard 55 in a VAV system? Is the data provided by the supply air device manufacturers sufficient to use at the design phase of a project to show compliance with the codes and ASHRAE Standard 55? A point to ponder for sure when the KID principle is applied.

Air distribution and VAV systems seem so simple. They have been utilized in buildings for many years — some with no problems and others with problems, such as dumping of supply air, which can be a good thing, too. It might be asked how problems can still happen after all these years of using VAV systems. Are some of these systems designed by rule-of-thumb techniques and not fully analyzed and engineered? Could it be that the product selection process in air distribution systems, and VAV systems in particular, needs to be re-evaluated by ASHRAE and manufacturers of those products? Are the hole covers known as supply air diffusers really evaluated well enough in the selection process? Is the testing of supply air devices really sufficient by air device manufacturers to give the full data needed for an engineer to make selections that meet the codes and standards? Points to ponder for sure.

Another specifiable component in every VAV system is the pressure measuring device in the inlet of a VAV box. Some are more accurate than others. Some are metal, and some are not. Some have center averaging characteristics, while others don’t. It’s good to look at specifications and understand the performance differences of the products in the specifications. Performance specifications are good to comply with the KID principle.



Product selection is not as easy as it sometimes seems. The KID principle is more important than ever as professional engineers work within a project design team to not only make product selections that provide value for the facility owner but also meet all applicable codes and standards.

Both ASHRAE and CSI have resources that can be used to help in the documentation of proper HVAC system and product selections. It would be beneficial for professional engineers to consider obtaining their CCS. A CCS ensures that the professional engineer-of-record  not only has his or her professional engineering credentials through formal education and training but also has a working knowledge of understanding contracts that incorporate the drawings and specifications included in the owner-contractor agreement. 

A basic VAV air distribution system has many components, products, and controls that need to be evaluated and documented into the contract documents. The process may not be as simple as the industry allows it to be when full documentation is done to ensure the owner gets what is generally accepted as the design intent to meet current codes and standards that are becoming more and more challenging. Keeping the product selection process and documentation truly defendable is why the engineer of record is not just “designing” a system.

Always remember the KID principle. It really is more important than the KIS principle in the building sciences industry in this litigious construction industry. Finally, note that this author is available to provide presentations on this subject at private corporations or organizations.

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