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.


Path 1: Use PNNL Prototype models as a reference

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:

PNNL Building Type

Equivalent System Type

High-Performance Alternative System Type:

Small Office
1 story, 5,500 ft2 (510 m2)

Single Zone, with Furnace, and Direct Expansion

Single Zone, with Air Source Heat Pump

Medium Office
3 stories, 53,600 ft2 (4,979 m2)

Single Zone, with Furnace, and Packaged DX

VAV w/ Reheat, with Gas Boiler, and Packaged DX

Large Office
12 stories, 498,600 ft2 (46,321 m2)

VAV w/ Reheat, with Gas Boiler, and Water Cooled Chiller

VAV w/ Reheat, with ASHP, and Water Cooled Chiller

Stand-alone Retail
1 story, 24,695 ft2 (2,294 m2)

Single Zone, with Furnace, and Packaged DX

Single Zone, with Air Source Heat Pump

Strip Mall
1 story, 22,500 ft2 (2,090 m2)

Single Zone, with Furnace, and Packaged DX

Single Zone, with Air Source Heat Pump

Primary School
1 story, 73,960 ft2 (6,871 m2)

Single Zone, with Furnace, and Packaged DX

VAV w/ Reheat, with A)SHP, and Packaged DX

Secondary School
2 stories, 210,900 ft2 (19,593 m2)

Single Zone, with Furnace, and Packaged DX

VAV w/ Reheat, with ASHP, and Air Cooled Chiller

Outpatient Healthcare
3 stories, 40,950 ft2 (3,804 m2)

VAV w/ Reheat, with Gas Boiler, and Packaged DX

VAV w/ Reheat, with ASHP, and Packaged DX

Hospital
5 stories, 241,410 ft2 (22,427 m2)

VAV w/ Reheat, with Gas Boiler, and Water Cooled Chiller

VAV w/ Reheat, with ASHP, and Water Cooled Chiller

Small Hotel
4 stories, 43,200 ft2 (4,013 m2)

Single Zone, with Electric Boiler, and Packaged DX

Single Zone, with Air Source Heat Pump

Large Hotel
6 stories plus basement, 122,132 ft2 (11,346 m2)

VAV w/ Reheat, with Gas Boiler, and Air Cooled Chiller

VAV w/ Reheat, with ASHP, and Air Cooled Chiller

Warehouse (non-refrigerated)
1 story, 49,495 ft2 (4,598 m2)

Single Zone, with Furnace, and Packaged DX

Single Zone, with Furnace, and Packaged DX

Quick Service Restaurant
1 story, 5,502 ft2 (511 m2)

Single Zone, with Furnace, and Packaged DX

Single Zone, with Air Source Heat Pump

Full-Service Restaurant
1 story plus attic, 5,502 ft2 (511 m2)

Single Zone, with Furnace, and Packaged DX

Single Zone, with Air Source Heat Pump

Mid-rise Apartment
4 stories, 33,700 ft2 (3,130 m2)

,,Single Zone, with Furnace, and Direct Expansion

Single Zone, with Air Source Heat Pump

High-rise Apartment
10 stories, 84,360 ft2 (7,837 m2)

DOAS w/ WSHP, with Gas Boiler, and Cooling Tower

DOAS w/ VRF


Path 2. Project Scope Factors

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.

  • Low Performance typically will have the highest EUI and utility bills

  • Average Performance will have EUI and utility bills similar to the majority of buildings

  • High Performance will have the lowest EUI and utility bills

  • Variable Performance means that other factors make it difficult to predict performance

For Air Systems

Low Performance

Average Performance

High Performance

Variable Performance

Single-Zone

VAV w/ Reheat

All DOAS options

Natural Ventilation

CAV w/ Radiant

VAV w/ Radiant

CAV w/ Reheat

For Heating

Low Performance

Average Performance

High Performance

Electric Boiler

Gas Boiler

GSHP

Furnace

Electric Resistance

VRF

ASHP

For Cooling

Average Performance

High Performance

Variable Performance

Air Cooled Chiller

Water Cooled Chiller

Cooling Tower

Packaged DX

GSHP

Direct Expansion (DX)

VRF

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.

  • Low Cost - typically less than $5.57/ft2 ($60/m2)

  • Mid-Range Cost - Typically between $5.57/ft2 to $9.19/ft2 ($60/m2 to $99/m2)

  • High-Range Cost - Typically over $9.29/ft2 ($100/m2)

Low Cost

Mid-Range Cost

High-range Cost

Natural Ventilation

DOAS w/ FCU, with Gas Boiler and Air/Water Cooled Chiller

CAV or VAV w/ Reheat, with ASHP and Packaged DX

Any Single Zone Systems

CAV w/ Reheat, with Electric Resistance and Air/Water Cooled Chiller

CAV or VAV w/ Reheat or w/ Reheat, with ASHP and Water Cooled Chiller

DOAS w/ WSHP, with Gas Boiler and Cooling Tower

VAV w/ Radiant, with Electric Resistance and Water Cooled Chiller

DOAS w/ VRF, with Electric Boiler and Cooling Tower

DOAS w/ Induction, with Electric Resistance and Water Cooled Chiller

DOAS w/ VRF, with Ground Source

DOAS w/ VRF

Any GSHP System

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.

Gas Heating Source

Electric Heating Source

Gas Boilers

Electric Boiler

Furnace

Electric Resistance

Ground Source Heat Pump (GSHP)

Variable Refrigerant Flow (VRF)

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:

  • Small - Equipment takes the least amount of space, often located on the rooftop [only] or in smaller mechanical rooms.

  • Medium - Equipment takes up a typical amount of space in the building, and often requires dedicated mechanical rooms or a large portion of the rooftop.

  • Large - Equipment takes up the most space, and often requires large mechanical rooms or additional ceiling void space.

Air Systems

Small

Medium

Large

Single Zone Systems

DOAS

VAV Systems

CAV Systems

Heating

Small

Medium

Large

Electric Resistance

Gas Boiler

GSHP

Furnace

Electric Boiler

VRF

ASHP

Cooling

Small

Medium

Large

Direct Expansion (DX

Packaged DX

Water Cooled Chiller

Cooling Tower

Air Cooled Chiller

VRF

GSHP

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:

  • Simple - limited maintenance required. Typically handled through an annual maintenance contract, with no on-site staff required.

  • Average - some regular maintenance required. Typically handled through monthly maintenance contracts or an on-site staff shared by a collection of similar buildings.

  • Advanced - frequent maintenance required. Typically full-time operation/facility staff on-site performing maintenance activities daily.

Air System

Simple

Average

Advanced

Single Zone Systems

VAV and CAV Systems

DOAS w/ FCU

Natural Ventilation

DOAS w/ VRF

DOAS W/ WSHP

DOAS w/ Radiant

DOAS w/ Induction

Heating Systems

Simple

Average

Advanced

Furnace

Gas Boiler

ASHP

Electric Resistance

Electric Boiler

GSHP

VRF

Cooling Systems

Simple

Average

Advanced

Direct Expansion

Packaged DX

Water Cooled Chiller

VRF

Cooling Tower

GSHP

Air Cooled Chiller


Path 3. Conventional System Selections by Use-types

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

  • Small, Single Story

    • Single Zone, with Electric Resistance and Packaged DX

    • CAV w/ Reheat, with ASHP and Packaged DX

    • CAV w/ Reheat, with ASHP and Water Cooled Chiller

  • Medium, Low to Mid-Rise

    • Single Zone, with Furnace and Packaged DX

    • VAV w/ Radiant, with Electric Resistance and Water Cooled Chiller

    • VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

    • DOAS w/ VRF

  • Large, Mid to High-Rise

    • VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

    • VAV w/ FCU

    • VRF Systems

Education

  • Secondary (Middle to High School)

    • VAV w/ Radiant, with Gas Boiler, Air Cooled Chiller

    • DOAS Systems

  • Elementary (small, single-story)

    • Single Zone, with Electric Resistance and Packaged DX

    • Single Zone, with Gas Boiler and Packaged DX

  • University (classroom and administration)

    • DOAS w/ WSHP, with Gas Boiler and Cooling Tower

    • VAV w/ Reheat, with ASHP, and Water Cooled Chiller

  • University (Campus scale)

    • GSHP Systems

Hospital

  • CAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

  • VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

  • DOAS w/ FCU, with Gas Boiler and Water Cooled Chiller

  • DOAS w/ Induction, with Gas Boiler and Water Cooled Chiller

Outpatient Healthcare

  • VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

  • DOAS w/ VRF

Laboratory

  • CAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

  • VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

  • DOAS w/ FCU, with Gas Boiler and Water Cooled Chiller

  • DOAS w/ Induction, with Gas Boiler and Water Cooled Chiller

Retail

  • Small to Medium, single story

    • Single Zone, with Electric Resistance and Packaged DX

    • Single Zone, with Furnace and Direct Expansion

  • Large, multi-story

    • CAV w/ Reheat, with Gas Boiler and Packaged DX

    • VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller

Apartments/ Multifamily

  • Low to Mid-rise

    • Natural Vent, with ASHP and Direct Expansion

    • Single Zone, with Furnace and Direct Expansion

  • High-rise

    • DOAS w/ WSHP, with Gas Boiler and Cooling Tower

    • CAV w/ Radiant, with Electric Resistance and Packaged DX

    • DOAS with VRF

Hotel/ Lodging

  • Single Zone, Electric Resistance, Packaged DX

  • DOAS w/ FCU, with Gas Boiler and Air Cooled Chiller

  • DOAS with VRF

Residential - Read the full article here.

  • Split Systems

    • Single Zone, with Furnace and Direct Expansion

    • Single Zone, with Electric Resistance and Packaged DX

  • Ductless Mini-Split Systems

    • Natural Vent, with ASHP and Direct Expansion

    • Natural Vent, with Gas Boiler and Direct Expansion

    • Natural Vent, with Electric Boiler and Direct Expansion

    • Natural Vent, with Electric Resistance and Direct Expansion

  • Packaged Systems

    • Single Zone, with Gas Boiler and Packaged DX

    • Single Zone, with Electric Boiler and Packaged DX

    • Single Zone, with Furnace and Packaged DX

    • Single Zone, with Electric Resistance and Packaged DX

Stadiums, Convention Centers, Courthouse, Performing Arts other assemblies

  • VAV w/ Reheat, with Gas or Electric Boiler and Air or Water Cooled Chiller

Fitness Center (Retail Gym)

  • Single Zone, with Furnace, and Direct Expansion

Airport Ticketing area or Terminal

  • VAV w/ Reheat, with Gas or Electric Boiler and Air or Water Cooled Chiller

Warehouses

  • Distribution Center

    • Single Zone, with Gas Boiler, and Packaged DX

  • Manufacturing or Assembly

    • Natural Vent, with Gas Boiler and No Cooling

    • Single Zone, with Gas Boiler, and Packaged DX


Other HVAC System Studies

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!


Related Articles

Did this answer your question?