How to design sustainable HVAC systems

In the past several years, the building industry has seen a significant shift toward sustainability initiatives, such as green rooftops and using electricity for energy

By Chris McDaniel and Sven Peulen June 1, 2023
Courtesy: Jordan & Skala Engineers


Learning Objectives

  • The reader will understand what electrification is and how it applies to the architecture/engineering/construction industry, specifically in rooftop units and HVAC system technologies.
  • The reader will understand both the pros and cons of moving toward sustainable fuel sources and away from fossil fuels for the heating of a building.
  • The reader will learn about the limitations of the power grid and how it will be affected as more electrified buildings come “online.”


Sustainable design insights

  • The architecture/engineering/construction (AEC) industry is shifting toward sustainability and environmental, social and governance (ESG) initiatives, with a trend toward electrification, green rooftops and clean energy.
  • This movement is necessary to reduce negative impacts on the environment and climate change, as younger generations see green practices as critical.
  • The AEC industry is making improvements in sustainability through the electrification of air conditioning units and green rooftop units, as well as by increasing efficiencies of heating and cooling systems to meet stricter energy efficiency mandates in building codes.

Over the past 15 years, the architecture/engineering/construction (AEC) industry has seen a significant shift toward sustainability and environmental, social and governance (ESG) initiatives. As a part of that,This article has been peer-reviewed. there has been a notable trend toward green rooftops, as well as using electricity for energy, rather than traditionally used fossil fuels. The term for this process is called electrification — and over the next decade, the movement toward using sustainable and clean energy will become more prevalent.

As a part of this movement, self-contained units and rooftop units (RTUs) used for heating and cooling a building are moving away from ozone-depleting refrigerants and greenhouse gas-producing fossil fuels to clean, efficient energy. Although the electrification of heating, ventilation and air conditioning (HVAC) systems has many impactful benefits, it doesn’t come without its challenges in terms of cost impact, the required electric infrastructure and adjustment to comfort.

The movement toward sustainable building design and construction is necessary as younger generations, including millennial and Generation Z, see green practices as critical to reducing negative impacts on the environment and climate change. Buildings and developments that are not environmentally friendly will see slower leasing rates and decreased revenue as a result.

Figure 1: Residential and commercial buildings are responsible for 6.9 million tons of greenhouse gas emissions annually. Courtesy: Jordan & Skala Engineers

What Is electrification?

Electrification is the use of electricity — distributed by the local power grid — to power devices that typically require a fossil fuel energy source, such as oil, natural gas and coal. In the AEC industry, electrification is typically seen throughout mechanical equipment and infrastructure, such as in self-contained systems.

Residential and commercial buildings’ contributions to greenhouse gas emissions is a growing global topic. In 2021, a utility provider in British Columbia produced a report citing that 6.9 million tons of B.C.’s greenhouse gas emissions were from buildings and homes. By evaluating how we heat and cool buildings and considering alternative clean energy options, such as renewable electricity, hydrogen fuel cells or hydroelectricity, the AEC industry can significantly reduce these emissions.

It is anticipated that in the nearer future, we will see a national mandate toward electrification. Currently, in most regions of the country, owners and developers have a choice of using current technology to heat and cool their buildings or using electrified RTUs. There are few exceptions to this, as some local jurisdictions — such as Denver and Washington, D.C. — require that buildings designed and constructed moving forward do not use fossil fuels. It is anticipated that more local jurisdictions will follow suit in the nearer future.

Figure 2: As of 2023, the Department of Energy has enacted a new nationwide efficiency mandate for HVAC equipment — referred to as SEER2. It is estimated that 70% of current products in the base tier of HVAC equipment will not meet the 2023 minimum efficiency requirement. Courtesy: Jordan & Skala Engineers


Burning fossil fuels for electricity releases greenhouse gases, primarily carbon dioxide. In turn, these gases trap heat within the atmosphere and cause the planet’s temperature to rise. Improvements in HVAC systems technology are being made in order to reduce ozone-depleting chemical emissions.

Refrigerant, a liquid or gaseous chemical compound required for HVAC systems to cool or heat incoming air has historically contained a significant amount of harmful gas, known as hydrochlorofluorocarbons (R-22) and hydrofluorocarbons (R-410A) that negatively affect the ozone layer. The HVAC manufacturing industry has moved away from the ozone-depleting R-22 (which became illegal to produce in the United States in 2010) to a cleaner and more efficient R-410A.

In recent years, manufacturers have been quickly transitioning to an even cleaner R-454B and R-32, which contains almost zero hydrofluorocarbons and have a very low global warming potential — almost two-thirds the amount of R-410A. Plans to phase out R-410A and transition to R-32 will be complete by 2030.

Improvements in sustainability are also being made by increasingly more stringent energy standards and codes. Energy standards and code, primarily ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and International Energy Conservation Code are recognized benchmarks of the industry. These have become increasingly more stringent regarding energy efficiency minimums requiring HVAC manufactures to innovate equipment design to meet or exceed these minimums.

In addition to the energy code requirements, the U.S. Department of Energy (DOE) mandates minimum system efficiencies although not in concert with the energy standards and code. The DOE mandates a system’s seasonal energy efficiency rating (SEER2, formerly SEER), which is calculated as follows: the total heat removed from the conditioned space during the annual cooling season, British thermal unit (Btu), divided by the total electrical energy, watt-hour, consumed by the air conditioner or heat pump during the same season Btu/watt-hour. The higher the SEER2 rating is, the better the system’s efficiencies.

While SEER ratings have been required by the DOE since 2007, further strides are being made to reduce overall energy consumption. As of Jan. 1, 2023, the DOE has enacted a new nationwide efficiency mandate for HVAC equipment — referred to as the aforementioned SEER2 — based on nationwide regions (ranging from a rating of 14 to 15). It is estimated that 70% of current products in the base tier of HVAC equipment will not meet the 2023 minimum efficiency requirement. This new mandate has pushed manufacturers to develop more efficient equipment.

Heat pumps that exist now are, in general, much more efficient. Systems have chipsets installed that have robust logic and learning abilities with variable speed fans that can increase or decrease airflow based on capacity demand and, in turn, use less energy; legacy mechanical equipment ran at a constant speed without the ability to adjust, potentially using more energy.

Further HVAC system efficiency can be gained by the use of energy recovery equipment that reduces cooling and heating demand by recovering waste heat from the airstream. According to the DOE, energy recovery equipment can provide energy savings of 15% or more.

Figure 3: The control sequence of operations on a smart HVAC system does not incur any additional costs and could save building owners and developers 15% on their overall energy bill. Courtesy: Jordan & Skala Engineers

Energy cost impact

Although electrification has an overall significant positive impact on the environment, there are some cost considerations that building owners and developers should be aware of before design and construction.

In general, electrification is a more expensive method (in terms of upfront capital costs) of heating and cooling a building than using fossil fuels as energy. Currently, electricity rates (specifically on a unit energy cost basis) are significantly higher than that of natural gas, so the overall operating and utility costs of a building are naturally going to be higher with electrified HVAC units.

In addition to the overall increase in the cost of energy, as the heating and cooling manufacturers transition from R-410A to a more efficient and environmentally friendly R-454B or R-32 refrigerant, there are some additional costs that should be considered during the schematic design of a building. Although at an individual level, R-454B and R-32 refrigerant is more energy efficient than both R-410A and R-22, equipment costs will be higher than that of current equipment.

Another significant cost impact will be the increased electrical distribution infrastructure. Because the main electrical room and sub-electrical rooms will be larger throughout a building, there will be increased costs associated with the larger equipment. Consequently, the larger rooms will take away valuable rentable square footage within a development.

How to achieve sustainability

Due to the increased infrastructure requirements and electrical service size, it is important for the design team to understand what type of heating and cooling system will be desired before beginning design. Some additional design considerations for electrified RTUs include that larger transformers will be required on the project site, the number and size of electrical rooms will increase (potentially doubling or tripling) and additional space may be needed on the exterior of the building.

A positive long-term cost impact will be when the property is sold later, the value of an electrified building will be notably higher than that of one that uses fossil fuels for energy, as investors recognize the value in future-proofed developments.

Specifying an intelligent HVAC system can assist with significant energy savings as they relate to the system’s sequence of operations and controls via the building management system. The control sequence of operations — essentially, how the system in place should operate and control a given space — on a smart HVAC system does not incur any additional costs, but could save building owners and developers 15% on their overall energy bill.

By using thermal storage loading and unloading (the opening and closing of a RTU’s valves to use energy that’s been absorbed by the building throughout the day via furniture, windows, walls, etc.), the heating and cooling system can use stored energy before its necessary to power on the system and create additional energy. Smart building controls are automated to maximize and optimize how energy is flowing in and out of the building and, therefore, do not require the tenant to manually adjust the thermostat.

Intelligent thermostats “learn” from historical patterns and “remember” energy requirements from days and weeks prior, allowing the thermostat to adjust which times it runs to reach the desired temperature and deploy temperature setbacks during unoccupied hours. Additionally, smart thermostats can adjust based on a specific floor’s required heating and cooling.

For example, in some building types, because heat rises, the top floor of a building retains more heat than the lower floors and because the top floor may only need 50% of the heat required to maintain temperature as the bottom floor, the extra capacity/energy can be distributed to other floors where needed.

As high-performing and energy-efficiency buildings are increasingly more desirable by millennials and Generation Z, this, in turn, makes an owner/developer’s property more marketable and attractive to potential tenants. Statistically, seven out of 10 millennials agree that prioritizing the climate is key to providing a sustainable planet for future generations — with 81% of millennial adults believing that alternative energy sources should be a national priority.

Additionally, buildings that implement sustainable practices or green building programs (such as U.S. Green Building Council LEED, Fitwel or WELL) benefit from better leasing rates and higher property values over time.

From a marketing perspective, the AEC industry has seen a huge shift in prioritizing energy-efficient buildings. For example, in a large metropolitan area, a LEED certified (or similar) building had a competitive advantage against other similar properties; however, if you do not have a sustainable building, you will rent out significantly more poorly than surrounding properties.

In the current market, sustainability and green initiatives are no longer viewed as a “check box”; environmentally friendly practices, such as electrification and energy-efficient HVAC systems, are both required and expected.

Additionally, developers with sustainable developments as a part of their portfolio are typically more attractive to investors.

Figure 4: Statistically, seven out of 10 millennials agree that prioritizing the climate is key to providing a sustainable planet for future generations — with 81% of millennial adults believing that alternative energy sources should be a national priority. Courtesy: Jordan & Skala Engineers

Electrical infrastructure

Decarbonizing the grid — generating energy from renewable sources — is a primary goal of the Biden administration; a governmental pledge was made to achieve a carbon-free power sector by 2035. Many local governments are offering incentives for developers to electrify their buildings, with some local jurisdictions, such as Washington, D.C., mandating that by 2030, all buildings — new and existing — will need to use an energy source other than natural gas.

Energy generation and power plants will need to be more centralized and all energy will be from a renewable source; everything will be completely reliant on the grid. As more local jurisdictions are moving toward 100% electrification and as local and national energy codes continue toward clean energy, there will be a drastic increase in the usage of the power grid.

The U.S. electrical grid has already experienced an increased strain since 2020 due to a large majority of people working from home due to the COVID-19 pandemic. Additionally, climate change has caused stress on the energy grid, as well. Today, the already-aging grid is increasingly more vulnerable to weather conditions, as temperatures and natural disasters have reached an unprecedented extreme that has not been historically experienced.

One major issue that the energy grid is facing is that the average life of all power lines is approximately 30 years old; therefore, the current electrical grid in totality was designed and built for a very different world than what we live in— one that experienced a stable climate and with significantly less demand and digitization than we experience.

With the aging infrastructure of the grid, increased power demand caused by new building technology — such as air conditioning/RTUs — could result in a power overload causing blackouts. The current electrical grid cannot support 100% of all buildings to be heated and cooled using solely electricity. It will take an improved, more sophisticated power grid with significantly increased reliability and capacity in order to support 100% of all buildings to be electrified.

A recent example of this occurred when a vote against the gas ban occurred within Washington, D.C’s Construction Codes Coordinating Board due to the concern that the electrical grid would not have capacity.” The state — with lobbying from the local power company — had originally anticipated eventually moving to fully electric, but once the study was complete and the statistics were released, it was learned that the entire grid would shut down if only a portion of the buildings achieved this. Maryland decided to take a slow, phased approach in which certain types of facilities can go fully electric during certain time frames in order to stagger the number of buildings coming online at one time to not overwhelm the grid.

Comfort adjustment, impact

Another item that building owners and developers should consider is that occupants of their building will notice a difference between heating produced by a gas furnace versus that of electric heat. In general, people associate the warm feeling and audible hum of a gas furnace with warmth and comfort; overall, heating a building via a natural gas furnace is typically a positive experience for those within the building.

Owners and developers should be aware that there is an educational component to heating using electricity that should be taken into consideration. As more local jurisdictions adopt electrification and more buildings use clean energy, the need to educate will decrease. Tenants will begin to adjust to the standard results of using an electric heating system.

As the AEC industry continues to focus on green and ESG initiatives, it is valuable to consider all sustainable options. Whether you choose to go fully electric or take a hybrid approach with your HVAC systems, future-proofing your client’s building with sustainable systems will help attract tenants and investors, attain an overall healthier environment, as well as potentially achieve a compelling return on investment.

Author Bio: Chris McDaniel, PE, LEED AP, is a principal at Jordan & Skala Engineers, where he oversees all Washington, D.C.-area projects for the firm. He has more than 25 years of proficiency in mechanical engineering and project management, as well as 11 years of mechanical system installation experience. Sven Peulen, PE, LEED AP BD+C, is mechanical discipline leader at Jordan & Skala Engineers. He has been with the company for 12 years and has more than 17 years of mechanical engineering experience.