You don’t have to live in a large city or be in the middle of summer to experience the heat island effect. Janelle Penny, editor-in-chief of Buildings, shares what this is and what you can do to lower the impact it has on your facility. (This was a previously live-recorded FM Friday episode.) Listen now >>
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This is Janelle Penny, I’m the editor-in-chief of BUILDINGS media and I’m here with another FM Friday broadcast.
I wanted to talk about urban heat islands and some of the things that individual building owners can do.
Of course, urban heat islands aren’t created by one building. It’s a phenomenon that can cover large areas and cities and you can’t resolve the problem just by yourself. But some of the tactics out there can be really useful for at least keeping your building more comfortable and doing your part to reduce the formulation of those heat islands.
If you’re not familiar with the phenomenon, an urban heat island is just a hotter area that tends to exist in places with a lot of densely placed buildings and a lot of paved surfaces that are absorbing extra heat from the sun. It makes the area several degrees hotter than a rural area or even less dense places in a city.
And because of that extra sun absorption, it then creates hotter temperatures indoors, which makes your occupants uncomfortable. To try to keep them comfortable, you’re stressing your HVAC system with the extra demand and ultimately paying more in energy bills.
And you know as well as I do this is prime time for high energy bills.
Specifically, some of the things that contribute to heat islands forming are, like I said before, paved surfaces, but also impermeable ones. So, think of walkways, roads, big parking lots or parking structures, all those things are absorbing that solar radiation as heat.
And the fact that they’re impermeable isn’t contributing directly to the heat island formation, but it is contributing indirectly because water runoff is just flowing right off of those surfaces and ending up in the stormwater system instead of being absorbed by green spaces or even other bodies of water that would help cool the area through evaporation and evapotranspiration.
So, that can cause a lot of problems.
Dark surfaces, of course, especially roofs, are a big one in areas that have more cooling days than heating ones. Roofs and also blacktop absorb a lot of sun and then radiate that back out. So, those are pretty big contributors to heat islands.
Thermal mass, which is just the ability of a material to absorb and store heat energy is a big contributor. That’s specifically a problem with a lot of high-density materials like concrete or bricks—in other words, the most popular building materials—have high thermal mass, whereas things like timber don’t have as much.
And the thing about dense materials and thermal mass just means that they store a lot of heat during the day, and so they slowly release it overnight, which then contributes to those higher temperatures in that area we’re talking about.
A lack of vegetation, this kind of goes back to that impermeable surfaces problem, plants and trees can create shade and also they cool the air through evapotranspiration again, by if you have a lot of paved surfaces, there’s not many places to plant, or not as many places to have green space.
So, that can contribute, and the lack of plants makes it really difficult to cool that area back down.
Waste heat, anyone who has mechanical air conditioning is exhausting heat into the environment, which is a direct contributor to the problem, of course, because you’re literally adding heat into the hot environment.
And finally, the changing climate, just the fact that it’s changing contributes to the urban heat island formation and the heat islands exacerbate the changes in the climate, so it’s kind of creating a cycle of feeding on itself.
There are a few things that you can do to at least offset that effect and its affect on your building a little bit. Tracking of the existence of these islands is usually something that your city or community organization will do. So, that might be a good place to start to get a hold of how big the problem is.
But even if you don’t have that data, there are still plenty of things you can do to both reduce your individual contribution and try to keep your building cooler in the meantime.
One place that you probably want to start is checking with your local jurisdiction. They might be thinking about adopting a newer version of the building code or even just conducting some community outreach. And if you’re lucky, they might even have some rebates for implementing some kind of mitigation technology. So, that’s a place to start.
Then you can look at your own building and see what you can do. Of course, if you can get a rebate for something, that would be the top priority, right?
But then you can start looking at other strategies you can implement. And some of them will deliver you other benefits beyond just producing your individual contribution to the urban heat island effect.
Let’s say you’re noticing your parking lot has a lot of cracks in it. It’s about time to repave it anyway. You can maybe think about spending a little more upfront and installing that permeable pavement and it will allow water runoff to flow through it instead of ending up in the stormwater system like we were talking about earlier.
So, it can be absorbed by plants or other bodies of water. That stuff helps cool the area and it also reduces your stormwater bills if you live in a place that charges for stormwater fees. That’s one to think about.
Reflective roofing, to look at that dark roof problem, of course, if you live in an area like I live in where we have many more cooling days than we have heating days, I’m sure you know all about cool roofing already.
But it is one to think about, especially now that you can get so many coatings and retrofits, where you don’t have to redo the whole roof just to make it lighter colored or more reflective.
The more reflective a roof is, the more effective it will be in reducing that temperature, which then reduces that heat gain and reduces your energy bills. And adding the coating can also lengthen the life of the roof under it, because the roof itself is no longer exposed to quite as much weathering, which can then save you money in the long run.
So, that’s another example of how some of these strategies can not only reduce your contribution to urban heat islands, but also save you some time or money or headaches in the long run. So, that can be useful.
There are some really interesting new innovations in cool roofing technology that are really giving people some more options in this area. Specifically, it doesn’t really have to be white anymore.
There are some really interesting cool colors being developed at Lawrence Berkley National Lab right now that have reflective qualities that are pretty similar to the typical white roof or light colored roof, but they’re dark appearing and they range from royal blue, there’s a deep brown or even a black one that have reflectivity ratings that are up to 10 times higher than the same color in a non-reflective formulation, even though it looks the same visually.
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So, a product that looks the same to our eyes, that it’s reflecting a greater amount of that inferred heat that’s really driving up the cooling energy in your building. Hopefully will be an option pretty soon.
In the meantime, you also want to investigate products that are currently on the market since those particular colors are still in development. I spoke to someone from the Cool Roof Rating Council who let me know that they have a very stringent rating process that tests all these different roofing products for solar reflectance and thermal emittance.
Both of those are important and you want to ask vendors about both of them. But in short, solar reflectance is how much solar radiation is reflected away from the roof.
And thermal emittance is how efficiently the roof can get rid of heat that is absorbed. So, that goes back to what we’re talking about, high-density building materials, they absorb a lot of heat and then slowly radiate it out all night once the sun is gone.
Something with a high thermal emittance rating would be able to get rid of it quickly. So, that’s something to look for. And the Cool Roof Rating Council actually has this super handy thing called the Rated Products Directory. I think there are around 3,000 roofing products in it.
But you can look up solar reflectance, thermal emittance values and also the solar reflectance index score, the SRI, which kind of combines those other two values into a 0-100 rating so it’s easier to just compare apples to apples that way.
And that can be a really useful tool if you’re thinking about tackling a roof specifically. Some other things that you can do are more vegetation if you’re able.
I know a green roof retrofit is a big undertaking, but if that’s not possible, can you think about perhaps increasing the green space on the ground or on a terrace if you have one?
There are a lot of different options for you out there, but anything you can do to tackle any of those six contributors to heat island formation will at least reduce your building’s contribution to the effect.
And in the meantime, as you’re working on reducing the heat island, at least give you some savings on energy, air conditioning and hopefully financial savings.
So, those are just a few of the things that you can do about urban heat island formation.
And that’s all for this week. I’m really looing forward to sharing more stories with you next week. So, if there’s a topic you’d like us to cover on the next FM Friday, please tweet us @BuildingsMedia or reach out to us on any of our other channels, on Facebook or LinkedIn.
Until next week, this is Janelle Penny. I’m the editor-in-chief for BUILDINGS media. And I’m signing off. You have a great weekend.
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