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.
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 CO
2
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 CO
2
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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