This article is an attempt to provide guidance for architects to choose an HVAC system in the early stages of design, typically before a mechanical engineer is involved in the project. However, it is always recommended that once one is involved, the project's mechanical engineer should review these options and inputs to confirm they match the specific design intent of each project.

Disclaimer

As there is no well-established guide or widely agreed-upon standard that provides information for architects to choose an HVAC system based on limited information at the beginning of the project, this article will do its best to become that source. The conventions listed in this article are based on years of industry experience of cove.tool's mechanical engineering and research team. If later in the project's life cycle, an engineer becomes involved and chooses a different system, that should be a known possibility. The hope of this article is to inspire confidence in a project team, as the uncertainty around selecting an HVAC system is typically listed as the top deterrence for why architects don't run energy models. Share any feedback you have on this article, so we can continue to improve HVAC literacy across the AEC industry.

How to choose an HVAC system?

Choosing the right HVAC system for your proposed design is really important since it has a direct impact on building efficiency, utility bills, and the level of comfort of the occupants. This task is typically in the mechanical engineer's scope to decide, however in the case where one has yet to be hired, there are some conventions we can follow to make an educated guess. This article has 3 paths to choosing a system:

Note: HVAC Systems include a lot of individual equipment. To help capture each unique piece we break these down into the Air System, Heating System, and Cooling System. More information on how HVAC systems are defined can be found in this article.

The Pacific Northwest National Laboratory (PNNL) is one of the US DOE national laboratories. Among other areas of research, a team here is responsible for reviewing programs that develop frameworks for energy efficiency. The research done at PNNL, specifically around the prototype building models, is used by the DOE's Building Energy Codes Program to evaluate published versions of the energy code, as well as in developing proposed code changes. At cove.tool, we use the PNNL prototype building models for input automation when energy codes do not define all the prescriptive values needed to run an energy analysis.

The PNNL prototype models only include 16 commercial building types with fixed parameters which may vastly differ from your own project. To see a full summary of the building description and other key modeling input information, download the scorecards from PNNL. In section 3, we will attempt to expand the list of typologies based on Industry best practices, so make sure to also cross-reference the other paths listed in this article when choosing an HVAC system.

The following table states the assigned system type for each PNNL prototype model. Since these systems are based on minimum standards and typical practices in the industry, a higher-performing alternative is also provided. This alternative can be explored for projects aiming to go above and beyond minimum performance requirements to save owners' operating costs:

Choice of HVAC system for any project is best done by the mechanical engineer who will consider a wide range of parameters, including Performance, Capital Cost, Heating Source, Space Requirements, and Ease of Maintenance. This is also an effective method for architects to shortlist a system based on the parameters of the project.

Performance - How energy efficient is the system?

We have broken the components of HVAC systems into four performance tiers.

For Air Systems

For Heating

For Cooling

Capital Cost for Mechanical Systems - Is it within budget?

We have broken components of the HVAC system into three capital cost tiers and ranked various systems into each. This is a non-exhaustive list, however, it provides a good framework to think about when considering system type and project budget.

Heating Source - Is the source gas or electric?

The source used to deliver heat to a project has a large impact on the operational carbon and utility costs of the project. Here we define each heating system and the source it utilizes.

Space Requirements - Will the system fit?

Mechanical equipment can take up a lot of space. When planning the HVAC system considering the space required is important when balancing other requirements for space within a building. We have broken the space requirements into three tiers:

Air Systems

Heating

Cooling

Ease of Maintenance - Who will operate and maintain the system?

Every system must be maintained to ensure it is operating correctly and delivering the designed indoor environment. We have broken systems into three tiers for Ease of Maintenance:

Air System

Heating Systems

Cooling Systems

Buildings can be classified according to their principal activity, which is the primary business, commerce, or function carried on within each building. Because similar activities have consistent building loads, and indoor environment requirements they can be served by similar HVAC systems. Here is a non-exhaustive guide to building types and the typical HVAC system that would serve them.

Office

Education

Hospital

Outpatient Healthcare

Laboratory

Retail

Apartments/ Multifamily

Hotel/ Lodging

Residential - Read the full article here.

Stadiums, Convention Centers, Courthouse, Performing Arts other assemblies

Fitness Center (Retail Gym)

Airport Ticketing area or Terminal

Warehouses

System Type Comparison

To see the impact of different mechanical systems on the project, generate a system type comparison. To create a comparison report, create copies of the project and select the systems for the analysis from the 'System Type' drop-down from the 'Building System' tab on the 'Baseline Energy' page. For a side-by-side comparison of the projects with different systems, the users can utilize the compare feature.

Using Optimization

With the optimization feature, users can explore hundreds of system type combinations in a design to make cost-conscious and performance-driven decisions as quickly and often as possible. Learn more about the optimization tool here.

Examples

There are many impacts on a project's performance when picking different HVAC Systems. Here is one example of comparing four different systems using the platform. Here we are able to show the performance improvement after switching to a VRF system.

Here is another study that compares the PNNL Large Office building prototype in Atlanta, GA with 8 different systems. All of these studies can help teams decide on the best option for their projects!

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