A Practical Guide to Deep Carbon Reduction Retrofits Eliminating the bulk of emissions from existing buildings poses unique challenges, but bringing an in-depth understanding of building operations into the design process offers a path forward.

Brad White P.Eng, MASc President, SES Consulting Inc. Contributing Editor

Eliminating the bulk of emissions from existing buildings poses unique challenges, but bringing an in-depth understanding of building operations into the design process offers a path forward.  

When we think of high-performance buildings, something like this usually comes to mind: 

However, if we’re going to achieve meaningful reductions in carbon emissions from commercial real estate (CRE), then we really need to focus on buildings like these:

The vast majority of commercial real estate in North America was built between 1960 and 2000. These humble buildings are the workhorse of the sector and, not coincidentally, responsible for the majority of emissions. Deep retrofits of these existing buildings are a must if we’re going to achieve the kinds of emissions reductions that are being targeted in the next 10-30 years. Now, you could just gut the existing buildings and completely redo the envelope and mechanical systems to meet low carbon standards like Passive House, LEED Zero, etc. This may be the right solution for some buildings, but it’s disruptive, expensive and, as this article will hopefully convince you, not the only way. 

Before we dive into how we need to discuss the what. What are we actually trying to achieve when we talk about decarbonizing a building? Location matters when it comes to emissions, but there are some significant developments when it comes to energy supplies that are providing clarity on the best path to low-carbon buildings. Many previously “dirty” grids are looking to drastically reduce their reliance on coal power in favor of renewables in the coming years. We’re already seeing this happen in a big way. In the US, electricity-related CO2 emissions have fallen by a third from their peak in 2005, while overall electricity consumption has remained constant. Even in jurisdictions where the electricity emissions factor remains relatively high, there is often the option to purchase 100% renewable energy for a premium. A premium that is becoming more modest all the time. Supplies of carbon-neutral fuels, such as bio-gas, are also increasingly available, but in much more limited quantities compared to renewable electricity.  

Based on these trends, there is a growing consensus that decarbonizing buildings means electrification of heating and hot water systems. Alternatives such as biomass and renewable natural gas will play a role as well but, wherever possible, this will mean the adoption of heat pumps as a cost-effective use of electricity for heating. But while the end goal for our buildings may be increasingly clear, how to get there in the most cost-effective manner poses some real challenges. The solution is to dive deep into understanding exactly how the building systems are operating and the adjustments and optimizations that need to be made to effectively use heat pumps and other low-carbon heating sources.  

The journey to net-zero begins with efficiency. The goal here is certainly to reduce energy consumption and associated costs. But, to further the goal of decarbonization, we’re also looking to reduce the heating loads in order to minimize the amount that needs to be shifted to electricity. We’re also looking to reduce electricity consumption and demand to free up service capacity to handle the shifted heating load. However, keeping in mind our goal of finding the most cost-effective path to decarbonization, the efficiency measures undertaken as a first step should be ones that make good financial sense. Major equipment replacements or upgrades should also be avoided at this early stage as well, those will come later. Things like BAS upgrades control recommissioning, lighting upgrades, adding variable speed drives to fans, etc. should be the focus here.  In particular, the investment made into building automation and controls at this stage are essential for accomplishing the rest of the low carbon conversion. 

That was the easy part. The next step of this process is the crucial one, and where we start to deviate from the usual design process. We need to figure out what it’s going to make the building compatible with low carbon heating technologies. The lynchpin of our decarbonization strategy is the switch from natural gas heating to heat pumps. When it comes to hydronic systems, most heat pumps that are practical to use in this application have a maximum output temperature of ~130°F. This can pose some challenges in a building that’s used to ~170°F heating water.  Fortunately, our experience has shown that most buildings can cope with heating water temperatures that are much lower than originally designed for without major modification to terminal equipment over a range of conditions. 

The main challenge here is figuring out exactly what that range is for your building, and whether that gives you the emissions reduction you’re looking for. This isn’t something that can be entirely figured out from models, it requires reviewing and analyzing available operating data to understand the building loads, and empirical testing to evaluate how the building will respond to different operating conditions. This is where having a robust BAS is crucial. To start, we’ll often construct a chart like the one below, so that we can understand exactly what the heating loads look like across a range of temperatures. This particular load chart was constructed using a virtual meter based on archived BAS data. Since we’re interested in emissions reductions, we’re looking here at the total energy use, rather than the instantaneous BTU requirements. We can clearly see that for this high-rise office building located in Vancouver, the bulk of the heating energy, and associated CO2 emissions, occur above 2°C. 

We created a similar virtual meter for recoverable heat from cooling systems that we can use water to water heat recovery chillers to extract. The remaining energy (where the heat load exceeds recoverable heat) is the energy that we need to provide by some other means, in this case likely an air to water heat pump. Efficiency measures will bring this heating load down to some extent, but our goal would be to use our heat pump to deliver the remaining heat needed above ~2°C. 

This leads us to our next key question; can a heat pump give us hot enough water to keep the spaces satisfied at 2°C? Here’s where the empirical testing comes in. Rather than trying to use heat loss models to determine this result, we test it in the real world. We would lower the building heating water setpoint to heat pump temperatures during cold weather and see what happens. You need to be careful not to operate non-condensing heating equipment at condensing temperatures for extended periods of time, and you’ll be keeping a close eye on cold complaints, but even a few hours of testing can provide invaluable data. 

Based on how these tests turn out, you’ll have a much better idea of where you go from here. Possible next steps include (in order of how much they’re going to cost to address): 

• Tests went great, You’re Good!

• You have problem zones that need to be addressed. Sometimes the fix may be as simple as adding some supplemental heating or cooling, resizing reheat coils, or as complicated as having to correct underlying flaws in the HVAC system

• You have major problems and need a different heating solution (e.g. more expensive heat pump capable of higher hot water temps or a hybrid heat pump/boiler design),
  significant upgrades to mechanical systems, building envelope upgrades, or all of the above. The more extreme your climate, the more likely this last scenario is.
  

Once you’re through this stage, the last step is figuring the right mix of low-carbon heat sources for your building. For this part of the upgrade, you want to look for synergies with required boiler/chiller upgrades for end-of-life equipment to greatly improve the economics. 

Looking for opportunities to recover waste heat from within the building using a heat recovery chiller (HRC) should be the first option considered. Examples of potential heat sources include any chilled water loads, condenser loops, eliminating free cooling, exhaust fans, etc. HRCs typically operate with a very high efficiency. Because they can be used in place of conventional chillers and other mechanical cooling equipment, their use often comes with no increase in electrical load, leading to very good ROIs. In buildings that have significant year-round cooling loads, heat recovery chillers can actually provide the majority of space heating needs. We have a several excellent examples of this outcome Vancity Credit Union Headquarters and Park Place and Coquitlam Centre Mall. 

If there is a significant heating load remaining, then you’d next look at installing an air source or ground source heat pump, depending on the climate. This is the phase where you’re most likely to get into electrical or structural upgrades to accommodate the new equipment. Depending on your GHG reduction target, you could stop here, having offset the vast majority of your combustion-related emissions. What remains is usually the peak heating load which is actually an excellent application for natural gas heating equipment. This peak load is expensive to offset with heat pumps or electric boilers and contributes relatively little to emissions reduction. However, if you are aiming for zero emissions then bio-fuels (depending on availability) or installing electric boilers are among the best options.  

The roadmap to deep carbon retrofits in an existing building then looks something like this:

Example Pathway to Elimination of Combustion Emissions in an Existing Building

You should plan for this to be a process that takes a few years. Aside from spreading out the expenditure, this length of time is recommended so that you can collect the data and properly analyze the impact of your changes before moving to the next step. Buildings are complicated and rarely are the results exactly as we predict them to be, let the building data and real-world performance be your guide. 

I started out describing this as a practical approach to decarbonization, but please don’t confuse practicality with cost-effectiveness. In most cases, getting a building to an 80%+ carbon reduction is not a cost-effective exercise in the sense you should expect an attractive financial ROI. There are exceptions to this, usually where there is a big source of waste heat that is easily harnessed but, for the most part, you will spend a bunch of money and operating costs will not be significantly reduced, they may even be higher. Beyond Step 4, there is rarely a viable financial payback. Steps 5 and 6 are for those that have made the decision to achieve deep carbon retrofits for reasons that are not financial. Among our clients, common motivations for pursuing deep carbon reductions are things like corporate GHG reduction targets, internal carbon pricing, hedging against future carbon taxes, or carbon intensity regulations, to name a few. As a result, I do believe there is a lot of value in identifying the most cost-effective pathway to low carbon by following a pathway something like I’ve described above. It could be the difference between spending $2M and $5M to achieve a similar outcome. 

Our future is low carbon, by taking steps today to efficiently electrify our buildings and purchase renewable electricity wherever possible, our existing buildings can meet even the most ambitious carbon reduction targets.

More from Brad here   Data Driven Design – Retrofitting for a Low Carbon Future How we design and size equipment needs a modern approach as we retrofit with low carbon heating systems. All of that BAS data you’ve been archiving can help.

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