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Asked And Answered: Decarbonizing The Built Environment

From July 2023 ASHRAE Journal

Asked And Answered: Decarbonizing The Built Environment

Excerpt From Interview With Paul Torcellini, Ph.D., P.E., Fellow ASHRAE

What Are Some of the Technology-Based Solutions That Contribute To Decarbonization?

Let’s start at the top of the energy pie—with the premise that somewhere around 80% of the world’s energy supply is somehow carbon-based today. So, how do we use less of that? And how do we make buildings more efficient? That's where technologies and strategies for avoiding emissions come in, which is where ASHRAE has one of the biggest opportunities—how do we get buildings to use less energy in general?

Fuel going into buildings is scope 1. Fossil fuels burned directly on-site. So there’s a very clear path­way of what you need to make go away if you’re trying to decarbonize. But then the other part of it—and often more than half of it—is electricity. We call these scope 2 and say, “Where’s that electricity being produced and where it’s coming from?” A large fraction of electricity is generated from fossil fuels. And remembering that the biggest part of the energy pie is buildings shows the importance of substantially reducing the energy that buildings use in both new construction and retrofits.

If you look at the Energy Information Administration data,1 you see a leveling off on how much energy buildings are using in the United States (Figure 1). In a flat scenario, we are building buildings at the same rate that we are saving energy in existing buildings. If it is going up, we are not keeping up and the energy pie will continue to grow.

Overall, even if we talk about individual buildings becoming more efficient, we must have a pretty sub­stantial reduction in energy to make this work. And so how is that done? The first place is new buildings. It’s a blank slate, with lots of opportunity to really get energy use intensity (EUI) down to 50% or less of what we kind of consider normal code compliant buildings. The ASHRAE Advanced Energy Design Guide2 series covers this topic and gives EUI targets that can really help consult­ing engineers and designers. We also have good heat pump technologies out there today. With a reduction in loads, air-source and ground-source heat pumps make a lot of sense to heat and cool the building.

Recently, I was cleaning out my mother’s house and I found a brochure put out by Northeast Utilities. It was branded as their 80s and 90s program, which to me implies that it came out in the late 1970s. It’s all about heat pumps. I could reprint this today, and it would still be relevant. Heat pumps have certainly improved. We’ve made them more efficient than what this brochure says. We’ve made them more robust. We certainly can install them, and they come in all kinds of flavors, shapes and sizes. It’s not that it’s a new technology, but it’s a technology that is underuti­lized. We’re also getting better at build­ing envelopes and testing them. This helps the heat pump implementation.

The lighting industry has come leaps and bounds in terms of moving to high efficiency LEDs. Even if you have LEDs that were installed 10 years ago, it’s worth even looking at those because the efficiency has improved so much. A key solution is efficiency, efficiency, efficiency.

What Are Some Decarbonization Considerations Unique to Retrofitting Compared to Newly Constructed Buildings?

The easiest market again is new construction, as it is a blank slate. The retrofit part is a little bit harder because you have all this legacy stuff to tackle. When we build a new building, there’s embodied carbon—that is, carbon released because of the manufacturing and transportation of the products and services to making the new building. In an existing building, the carbon for the construction has already been released—that’s water under the bridge. We don’t have to worry about it. Don't tear down everything and try to build everything new. However, a retrofit takes some careful thinking and planning.

But one of the good things about existing buildings is we spend money on them every day just to maintain them. I would ask the question of whenever you spend money, are you doing it in a way to help reduce carbon? And when I do whatever it is to that building to keep it running, is that helping me on a pathway toward carbon neutrality or taking me away from that pathway?

You might have a steam heating system and pipes keep breaking, so you spend a lot of money to fix the pipes. Well, maybe you could think about how to start shifting that building to a low temperature hot water system. Or if you’re replacing variable air volume (VAV) boxes, designing those boxes so in the future they can accom­modate a lower water temperature. If windows start fail­ing, am I replacing them with low-E windows? If I have to replace the roof on a building, am I beefing up the insulation when I replace that roof? Am I designing the new roof so that it can hold a photovoltaic (PV) system? If I make these changes—how does it downsize the loads such that replacement HVAC down the road matches the improvements? If you have a plan now, you’ve got some mechanism even when something fails to replace it with something that’s better. I call this creating an action plan for the building—a plan to get to carbon neutrality.3

Which Decarbonization Efforts Do You Think Will Be Most Valuable if Prioritized?

Let’s take the pieces that we can do easily. There is no reason that we can’t take new construction and cut its energy 50% and make a dent in that overall curve. We’ve got to get to the point where new buildings do not create additional burden.

And you might say—‘well, new buildings are a small percentage of the overall total.’ That’s true but if you go back 30 or 40 years, it’s almost 50% of the total. You look at the build­ing envelope—get the envelope right, get the envelope tested. How do you really make that thermal envelope? Designing and building a building is about making decisions, and you have the option of always making the right decision. How do we line everybody up to make the right decisions? Set good goals right up front. Much of this also applies to existing buildings—especially major renovations. ASHRAE did that with the new headquarters building project.4 Even though that was a substantial renovation, ASHRAE set some energy targets and set out to meet those targets.


1. U.S. Energy Information Administration. 2023. "Energy Consumption, Residential, Commercial, and Industrial Sectors." U.S. EIA.

2. ASHRAE. "Advanced Energy Design Guides." ASHRAE.

3. U.S. Department of Energy. 2023. "A Guide for Creating a Building-Level Action Plan to Improve Energy Efficiency and Reduce Carbon Emissions." National Renewable Energy Laboratory.

4. ASHRAE. 2021. "ASHRAE Global Headquarters Reaches 'Fully' Net-Zero Energy Milestone." ASHRAE. about/news/2021/ashrae