Increasing a Building’s Energy System Efficiency Via the Rooftop: Past, Present, and Future

With so much understandable focus on transitioning energy generation from fossil fuels to clean energy, stakeholders must not overlook some of the lowest hanging fruit in the energy realm: energy efficiency. Well-planned energy efficiency programs and technologies represent one of the most critical and natural win-wins out there. Energy efficiency allows for conserving of energy without sacrificing output, meaning buildings and customers cut costs, power providers minimize how much demand they need to reach, and fewer greenhouse gases are spilled into the atmosphere. 

When looking at the buildings sector, HVAC (heating, ventilation, and air conditioning) accounts for a whopping 40% of energy use. Because of that fact, finding ways to minimize heating and cooling needs can have a greater effect on utility bills and environmental impact than some of the more commonly discussed options like turning off lights or buying more efficient appliances. 

For building owners and facility managers seeking out their unique opportunities to get efficient in the heating and cooling department, they should simply tilt their heads to look up to the rooftop. While rooftops are commonly thought of in the energy world as the avenue for solar panels for those trying to be green, not all buildings are suitable for solar energy. A building could be in a region with poor solar irradiance, it could have a roof that doesn’t face the sun during prime solar hours, it could find itself in the shadow of taller buildings, or it could simply be too costly to install solar panels. However, all buildings can benefit from potential efficiency solutions instead, and these efficiency solutions have looked different in the past from today, and looking forward there are emerging technologies that provide new reasons for excitement. 

Looking at the past, present, and future, rooftops can be a tool for energy efficiency: 

Rooftops Past

Early ways to get air conditioning to commercial buildings typically included multiple units on different floors or in different rooms. These systems would send the cool air where it was needed in the summer months, and full HVAC units would do the same with warm air during the winter. This equipment revolutionized the buildings sector, but they did so by adding the greatest amount of aggregate energy demand ever experienced for a single technological advancement (at least until electric vehicles reach their tipping point). 

To feed this addiction to building heating and cooling in a way that didn’t require increasingly great demand loads, high-efficiency rooftop air conditioning units were developed. Putting these units on the rooftop in batch form allowed for greater size units that could thus increase the total equipment efficiency, and modern advances since the turn of the 21st century allowed for improvements on the level of 40 to 50% in just the past decade

Improving building heating and cooling efficiency with larger but more efficient equipment is a helpful, but not very elegant solution. By attacking the sector with a brute force solution, it costs building owners a lot of money to buy into these solutions. Higher efficiency rooftop HVAC units also risk falling under Jevon’s Paradox where building occupants who know they have more efficient equipment may feel license to use the heating/cooling functions more liberally and actually increase total energy demand. Lastly, advancements in the efficiency of these units have slowed in recent years, as the low-hanging fruit of this efficiency solution of yesterday have been picked and resulted in a stall out of further progress. 

 

Rooftops Present

On rooftops of today, however, some more nuanced and clever solutions have started to take hold in the form of how rooftops are designed. On one side, green rooftops have become a common trend in commercial buildings today. A green roof, according to the U.S. Environmental Protection Agency, is “a vegetative layer grown on a rooftop,” meaning the roof is literally green with plant life like small trees, shrubs, grass, or other plants. The goal of a green roof is to reduce the amount of heat that gets transferred into a building over the course of sun-drenched days. This goal is accomplished as the plant life can provide literal shade, acting as insulators to prevent temperature exchange between the building and air, and generally ensure reduce the need to tap into HVAC systems to regulate a building’s temperature. Upon installation of a green roof, a building can experience 15-25% energy savings on summer energy costs by reducing heat transfer from building exterior to interior by up to 72%. At the same time, green rooftops can be more attractive, engaging for occupants, and even reduce the risk of urban heat islands that increase the more the climate changes. 

In a similar vein, cool roofs (sometimes known as white roofs) are a similar solution that comes with buildings designing their rooftops to be painted white. Because dark rooftops, which have architecturally been the norm, trap heat on them and transfer that heat into the building, HVAC systems must work overtime to regulate the temperature during sunny days in the hot months. By simply painting rooftops white, though, rooftops will reflect up to 90% of sunlight (compared with 4% of black asphalt). Reflecting that sunlight, and thus heat, away from the building has a similar impact as green roofs, eliminating how hard air conditioning units need to work to keep the temperature inside a building comfortable, and this goal is accomplished simply at the cost of the white coat of paint. Studies who look at the energy use of a building before and after that coat of paint find energy savings of 8% all the way up to 40%,  making the investment pretty obvious. 

 

Rooftops Future

Technology is always advancing, and given that the building stock accounts for 40% of energy use and greenhouse gas emissions, retrofitting existing buildings and constructing new buildings with the best energy efficiency technologies is of paramount importance.  

A few specific rooftop efficiency trends to keep an eye on in the coming years include:

  • Cool rooftops can be taken to the next level with this recent development from Purdue University of the ‘world’s whitest paint.’ Painting a rooftop with this technical marvel could create 10 kilowatts of cooling power on its own, which could revolutionize building efficiency. 
  • Whereas the efficiency of air conditioner units on rooftops is plateauing, artificial intelligence and machine learning are unlocking new opportunities to use sensors, tracking, and data to optimize how and when the equipment is used. Smart technology will highlight where energy is being wasted without building owners even being aware. 

And scientists and engineers are sure to identify further opportunities all the time, so keep an eye on this space! As they say, the cheapest unit of energy out there is the energy that’s not used, so keep looking for ways to optimize efficiency first and foremost. If you don’t know where to start with efficiency, you can turn to your power provider as they’ll likely have programs to help you embrace efficiency (having your energy use managed and limited helps the utility just as much as the customer). For example, Atlantic Energy works to educate our customers on the best ways they can save energy, including the use of our smart device packages with smart LED lights and smart plugs. Get started today by enrolling with us.

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