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Sustainable Construction: 5 Ways to Make Greener HVAC Systems

A commercial HVAC system on roof beside rows of solar panels

As the summers get hotter, winters colder, and weather events get more extreme due to climate change, people all over the world will increasingly turn to the thermostat to make their homes and businesses a refuge from the inhospitable temperatures outside.   

The problem is that most heating and cooling systems are, well, part of the problem.  

In fact, air conditioners are one of the biggest drivers of climate change, accounting for 20% of the entire planet’s electricity use, most of which is still generated by the burning of fossil fuels. In addition to contributing to global warming in a major way, the rising need for HVAC systems in the developing world is adding strain to our already overburdened electrical grids. The International Energy Administration (IEA) estimates the demand for cooling alone will more than triple by 2050, devouring as much power as is currently consumed by India and China combined. And despite improved efficiency standards, even modern HVAC systems can be wasteful and expensive to run.  

As recent history shows, we are entangled in a deadly cycle between the changing climate, our outdated energy grids, and conventional approaches to heating and cooling. In the summer of 2020, millions of Californians cranked the dial on their air-conditioners in response to a series of record-breaking heat waves. The Golden State’s aging electrical grid buckled under the surge in demand and millions of people were left to bake in the sweltering heat without air conditioning. Researchers estimate that between 350 to 450 people died from the heat during the summer’s blackouts. A similar scenario played out in Texas this past winter, only in reverse. A freakish cold snap shutdown the state’s ill-prepared power grid, leaving millions shivering in their homes without heat or electricity. A new report estimates that 700 people died during the winter storm while thousands more were saddled with shockingly high heat bills.  

This isn’t a problem we can ignore. Thankfully, the solution is within our reach. We already have the technology, the knowledge, and the specially trained HVAC technicians to build sustainable heating and cooling systems that save money, are less reliant on fossil fuels, and are significantly less harmful to the environment.  

Explore more Sustainable Construction Examples! 

Sustainable Heating and Cooling Systems  

So, how can we make HVAC more sustainable? From design to implementation, there are plenty of eco-friendly approaches to heating and cooling. Here are 5 sustainable HVAC systems worth a look. 

Sustainable HVAC System #1: Geothermal Heat Pumps 

According to the Environmental Protection Agency, geothermal heat pumps are the number one most energy efficient, eco-friendly, and inexpensive heating and cooling systems in existence.  

A geothermal heat pump works by drawing ambient energy from the earth and using it to heat homes during the winter and cool them during the summer. To accomplish this, you’re going to need to start digging. About five to 10 feet down ought to do it, until you get past the frostline, where the earth’s temperature hovers at a constant of about 40° to 70°F year-round. Next, you’ll need to bury some pipes to form a series of subterranean loops, which are then filled with water or a mixture of water and antifreeze. This liquid solution circulates through the loops underground and up through a heat exchanger.

An illustration of geothermal heat pumps in an HVAC system

This process allows a geothermal pump to draw enough renewable energy from the earth to heat or cool a home at the flip of a switch. It’s actually the same way a refrigerator works. There are many different types of geothermal heat pumps, but most are based on this same technological principle.

Geothermal heat pumps are vastly more energy efficient than traditional HVAC systems. Depending on the setup, a geothermal heat pump can operate at an astonishing 400% efficiency. In other words, the pump outputs four units of heat for every one unit of electricity it spends. For comparison, even the most energy efficient traditional heating systems only operate at 90 to 98.5% efficiency—56 to 70% for older systems. 

Traditional heating and cooling systems eat up more than 50% of an average American household’s yearly energy use. Sustainability experts estimate this adds up to about $875 a year per household, or about $92 billion a year nationwide. Since it requires substantially less electricity to run, a geothermal heat pump could shave as much as 70% off an average household’s energy bill while also dramatically reducing its carbon footprint. Unlike a natural gas furnace, a geothermal heat pump doesn’t need to burn fossil fuels to get the job done, though it does still require some juice from the electrical grid to keep the heat exchange circulating. 

That is unless you get your electricity from the sun. 

“If there were ever a marriage made in heaven, it would be to pair a geothermal heat pump with a solar-electric installation,” writes Donal Blaise Lloyd, author of Geopower, a primer on geothermal heating and cooling systems. “They both use nature as an energy source.” 

There are downsides, of course. Geothermal heat pumps are expensive to install, with an upfront cost between $10,000 and $30,000. They’re also not viable options for some homes, depending on their location and the terrain on which they're built. Then again, up to 26% of the price tag of a geothermal heat pump can be rebated with the Renewable Energy Tax Credit, and some states offer their own incentives as well. 

So, if your home is well positioned for it and you can get the math to work in your favor, investing in a geothermal heat pump can pay dividends toward the environment and your pocketbook for years to come.  

“When thinking long-term, you will see that a (geothermal heat pump) saves a lot of money,” Lloyd writes. “The added cost will be more than repaid and there is no pollution. Is there any better way to invest money with such a high return coupled with such low risk?” 

Sustainable HVAC System #2: DeVap (Green Air Conditioning) 

Knowing that DeVap stands for Desiccant Enhanced Evaporative doesn’t get you much closer to understanding what exactly it is. The name sounds like a brand of vape pen, a kind of bug zapper, or maybe an over-the-counter cough medication. In actuality, DeVap is a revolutionary air-conditioning technology that’s lightyears more eco-friendly, energy efficient, and cost effective than conventional cooling systems.   

Invented in 2011 by the US National Renewable Energy Lab, DeVap green air conditioner systems run on desiccant, a type of substance that soaks up humidity and increases dryness in the surrounding environment. Those little silica gel packets marked “Don’t Eat” when you open up a box of new shoes? That’s desiccant.  

These environmentally friendly air conditioners work by moving air through a liquid desiccant heat exchanger, which dehumidifies the air before it flows through an evaporative cooler, and then emits dry and cool air throughout a building’s ventilation system. The DeVap process doesn’t involve chlorofluorocarbons or hydrofluorocarbons, refrigerant chemicals present in traditional air conditioners that cause enormous damage to the ozone layer. DeVap air conditioners are also remarkably more energy efficient than traditional cooling systems, with some estimates showing that they use up to 90% less electricity. Energy reductions of that scale would go a long way toward easing the strain on our electrical grids and averting the “cold crunch” that the IEA predicts for 2050.  

DeVap air conditioning systems aren’t yet in wide use and due to their scale, are only aimed at the commercial market for the time being. If developers can successfully finetune the technology however, your home may someday be cooled by those little packets that came with that brand new pair of self-lacing Nikes. 

Sustainable HVAC System #3: Hydronic Radiant Heating and Cooling 

This next piece of technology isn’t anything new. Human beings have been warming themselves by heat channeled through the floors of their dwellings since ancient times. The Roman aristocracy did it with something called a hypocaust, and Korean architecture has integrated a radiant floor heating system called ondol (온돌;溫突) as far back as the Neolithic period. Those older methods required the burning of wood or other fuels to generate heat. A hydronic radiant floor heating system differs in one key respect: it uses water instead of fire.  

Hydronic radiant heating works by pumping heated water or a mixture of water and antifreeze through tubes—most modern systems use half inch PEX piping—arrayed in a switchback pattern beneath the floor.

An artist rendering shows hydronic radiant heating and cooling lines beneath hardwood floor

The energy then radiates upward, resulting in a gentler, much more comfortable, and evenly distributed heat compared to what’s produced by forced-air HVAC systems. Depending on how well insulated a home is, hydronic radiant heating is about 30% more energy efficient than traditional systems. The process is compatible with natural gas boilers, though hydronic radiant heating systems can also be coupled with more sustainable options like geothermal heat pumps or solar thermal arrays to unlock even greater benefits to the environment and your energy bill.  

Radiant cooling is similar, but instead of hot water in the floor it involves the piping of cold water through specially insulated panels in the ceiling. The technology isn’t as popular as hydronic radiant heating yet, but that may be about to change. Researchers at Princeton recently succeeded in developing an outdoor hydronic radiant cooling system in Singapore that’s up to 50% more energy efficient than traditional air conditioning units. 

As is the case with many other sustainable HVAC options, replacing your current system with hydronic radiant heating and cooling isn’t cheap. Of course, if you’re the kind of person who’s interested in sustainable living alternatives, money isn’t the only consideration.  

“A lot of people who do make the decision to replace…they don’t look at it from the standpoint of return on investment,” said industry expert Keefer Rader in an interview with the Air Conditioning Heating Refrigeration News. “They’re looking at doing the right thing for the environment, for their children’s future.” 

Sustainable HVAC System #4: Passive Solar Heating 

The power of the sun isn’t just useful for generating electricity. You can also harness it to serve as a direct source of heat for your home. That’s what passive solar heating is in a nutshell. No electricity. No moving parts or futuristic materials. Just a house and the sun shining down on it.  Pretty straightforward, right?  

Of course, it’s not quite as simple as that. The sun isn’t a reliable source of passive heat without expert design as well as extensive knowledge of how sunlight changes from day to day and season to season. Ideally, you’re going to start with a location with lots of unobstructed access to direct sunlight. Next, you’re going to need a home with a lot of southward facing windows through which the sun can shine.

The sunlight is then absorbed either by an interior wall, the floor, or another optimally positioned surface. Once the heat has been soaked up by the absorber, it can be stored in a thermal mass below. This is usually a water tank, or a slab made of stone, brick, concrete, or ceramic tiles. Depending on the design, a thermal mass can even retain heat when the sun isn’t shining.  

The heat in the thermal mass then either naturally radiates throughout the house, is blown through the ventilation system with fans, or is distributed by other means. Finally, the level of heat can be adjusted up or down with a series of shutters or other control elements.  

Passive solar heating has a lot of advantages. Similar to geothermal pumps, this process utilizes a free and renewable source of energy that occurs naturally, making it far more cost effective and environmentally friendly than traditional heating systems. The main disadvantage is how much passive solar heating lives or dies based on very specific design elements. Not everyone lives in a home with southward facing windows and a thermal mass that receives sufficient sunlight throughout the day, let alone can afford to design and build (or retrofit) one that does.   

But make no mistake, the principle is tried and true. One need only visit the solar furnace at Mont-Louis in the French Pyrenees for a powerful example of how effective a carefully thought out passive solar heating system can be. Composed of 10,000 glittering mirrors, the citadel’s furnace can concentrate sunlight into a 5,432°F beam of energy capable of melting steel.  

Maybe a tad hot for your average home heating needs. But that’s what the thermostat’s for. 

Sustainable HVAC System #5: Smart Thermostats + Other Sustainability Tips 

Maybe installing a geothermal heat pump or hydronic radiant heating and cooling system isn’t a viable option for you right now. If so, don’t sweat it: there’s still plenty you can do to make your home’s current HVAC system more energy efficient and eco-friendly. 

For those seeking a technological assist at getting a handle on their energy use, smart thermostats are a fantastic place to start. Wi-Fi enabled and accessible from your mobile device, smart thermostats allow you to monitor and adjust the temperature of your home remotely, whether you’re down the block or halfway across the world.

A woman in green sweater uses smart phone beside smart thermostat to adjust temperature

Many also come with sensors that will automatically adjust the temperature of individual rooms based on whether or not they’re occupied. Smart thermostats can also be programmed to automatically reduce your home’s temperature at certain hours of the day. Different companies report that consumers who equip their homes with smart thermostats can save between 15 to 23% on their energy bills. 

Another thing you can do is replace your heating and cooling appliances with Energy Star certified alternatives. Energy Star is a program backed by the US government whose purpose is to encourage the adoption of more energy efficient products and approach the environment with sustainability in mind. You can search for and learn more about a wide variety of more eco-friendly heating and cooling systems on the group’s website. 

And if these options also aren’t within your reach, you can still make your home more sustainable by changing up a few things. An easy place to start is to make sure you replace your air filter every three months. Air can’t pass as easily through a dirty filter, making your HVAC system have to work extra hard. Leaky ducts also waste a ton of energy, so make sure they’re properly sealed and insulated. In fact, it’s estimated that sealing and insulating your ventilation system can increase your home’s energy efficiency by as much as 20%. Finally, a home energy audit—either done by yourself or a professional—can help you understand exactly what your home’s energy use is going toward and identify opportunities for increased efficiency. 

Bottom Line

The challenges presented by climate change aren’t going to evaporate overnight. It’s going to take more than individual choices to heal our relationship with the environment. If we as a society choose to seriously invest in renewable HVAC technologies now, the IEA estimates we can cut the future energy demand in half and save as much as $3 trillion in energy costs over the next several decades. In reimagining how we heat and cool our homes, we have the exciting opportunity—some would even say the obligation—to put a tremendous dent in carbon emissions and take a giant leap into the rarefied air of a more sustainable future.  

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