Commercial HVAC Systems Guide
by Marco Aguirre & Patrick Pease, PE.
Published October 20, 2022.
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.
Let's Get Started!
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.
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Low Performance typically will have the highest EUI and utility bills
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Average Performance will have EUI and utility bills similar to the majority of buildings
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High Performance will have the lowest EUI and utility bills
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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
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Low Cost - typically less than $5.57/ft2 ($60/m2)
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Mid-Range Cost - Typically between $5.57/ft2 to $9.19/ft2 ($60/m2 to $99/m2)
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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:
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Small - Equipment takes the least amount of space, often located on the rooftop [only] or in smaller mechanical rooms.
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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.
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Large - Equipment takes up the most space, and often requires large mechanical rooms or additional ceiling void space.
For Air Systems
Small | Medium | Large |
|---|---|---|
Single Zone Systems | DOAS | VAV Systems |
CAV Systems |
For Heating
Small | Medium | Large |
|---|---|---|
Electric Resistance | Gas Boiler | GSHP |
Furnace | Electric Boiler | VRF |
ASHP |
For 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:
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Simple - limited maintenance required. Typically handled through an annual maintenance contract, with no on-site staff required.
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Average - some regular maintenance required. Typically handled through monthly maintenance contracts or an on-site staff shared by a collection of similar buildings.
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Advanced - frequent maintenance required. Typically full-time operation/facility staff on-site performing maintenance activities daily.
For Air Systems
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 |
For Heating
Simple | Average | Advanced |
|---|---|---|
Furnace | Gas Boiler | ASHP |
Electric Resistance | Electric Boiler | GSHP |
VRF |
For Cooling
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
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Small, Single Story
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Single Zone, with Electric Resistance and Packaged DX
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CAV w/ Reheat, with ASHP and Packaged DX
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CAV w/ Reheat, with ASHP and Water Cooled Chiller
-
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Medium, Low to Mid-Rise
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Single Zone, with Furnace and Packaged DX
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VAV w/ Radiant, with Electric Resistance and Water Cooled Chiller
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VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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DOAS w/ VRF
-
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Large, Mid to High-Rise
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VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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VAV w/ FCU
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VRF Systems
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Education
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Secondary (Middle to High School)
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VAV w/ Radiant, with Gas Boiler, Air Cooled Chiller
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DOAS Systems
-
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Elementary (small, single-story)
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Single Zone, with Electric Resistance and Packaged DX
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Single Zone, with Gas Boiler and Packaged DX
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University (classroom and administration)
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DOAS w/ WSHP, with Gas Boiler and Cooling Tower
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VAV w/ Reheat, with ASHP, and Water Cooled Chiller
-
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University (Campus scale)
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GSHP Systems
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Hospital
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CAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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DOAS w/ FCU, with Gas Boiler and Water Cooled Chiller
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DOAS w/ Induction, with Gas Boiler and Water Cooled Chiller
Outpatient Healthcare
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VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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DOAS w/ VRF
Laboratory
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CAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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DOAS w/ FCU, with Gas Boiler and Water Cooled Chiller
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DOAS w/ Induction, with Gas Boiler and Water Cooled Chiller
Retail
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Small to Medium, single story
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Single Zone, with Electric Resistance and Packaged DX
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Single Zone, with Furnace and Direct Expansion
-
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Large, multi-story
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CAV w/ Reheat, with Gas Boiler and Packaged DX
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VAV w/ Reheat, with Gas Boiler and Water Cooled Chiller
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Apartments/ Multifamily
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Low to Mid-rise
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Natural Vent, with ASHP and Direct Expansion
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Single Zone, with Furnace and Direct Expansion
-
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High-rise
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DOAS w/ WSHP, with Gas Boiler and Cooling Tower
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CAV w/ Radiant, with Electric Resistance and Packaged DX
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DOAS with VRF
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Hotel/ Lodging
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Single Zone, Electric Resistance, Packaged DX
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DOAS w/ FCU, with Gas Boiler and Air Cooled Chiller
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DOAS with VRF
Residential - Read the full article here.
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Split Systems
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Single Zone, with Furnace and Direct Expansion
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Single Zone, with Electric Resistance and Packaged DX
-
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Ductless Mini-Split Systems
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Natural Vent, with ASHP and Direct Expansion
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Natural Vent, with Gas Boiler and Direct Expansion
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Natural Vent, with Electric Boiler and Direct Expansion
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Natural Vent, with Electric Resistance and Direct Expansion
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Packaged Systems
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Single Zone, with Gas Boiler and Packaged DX
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Single Zone, with Electric Boiler and Packaged DX
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Single Zone, with Furnace and Packaged DX
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Single Zone, with Electric Resistance and Packaged DX
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Stadiums, Convention Centers, Courthouse, Performing Arts other assemblies
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VAV w/ Reheat, with Gas or Electric Boiler and Air or Water Cooled Chiller
Fitness Center (Retail Gym)
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Single Zone, with Furnace, and Direct Expansion
Airport Ticketing area or Terminal
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VAV w/ Reheat, with Gas or Electric Boiler and Air or Water Cooled Chiller
Warehouses
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Distribution Center
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Single Zone, with Gas Boiler, and Packaged DX
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Manufacturing or Assembly
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Natural Vent, with Gas Boiler and No Cooling
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Single Zone, with Gas Boiler, and Packaged DX
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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!
by Marco Aguirre & Patrick Pease, PE.
Published October 20, 2022.
Cite: Aguirre, Marco and Pease, Patrick. “Commercial HVAC Systems Guide.” Cove.tool Help Center. Cove Tool, Inc., October 20, 2022. https://help.covetool.com/en/articles/6520562-commercial-hvac-systems-guide.