ASHRAE Journal - July 2021 - 27

ROUNDTABLE
It's also necessary that we start to think about the grid
of the future and try to anticipate what those needs are
going to be. As Mark said earlier about installing storage
in the 1980s, we didn't know back then what the
grid was going to look like today. But, if we can project
out 10, 20, 30 years from now what we think that grid
is going to be, we can start to think about what types
of storage we think we need. Today, we can determine
how much storage we are going to need, where it's
going to be, what the requirements are and what systems
to integrate. And I think that's an important piece
that we need to think about as we're developing storage
technologies today.
There's going to be a huge demand on batteries-for
transportation, for grid storage, for building storage.
What are the material limitations for that as we move
forward? And what new materials do we need for battery
storage? And what value does thermal storage have then
if batteries are limited as well?
MacCracken: I may be biased on this, but I think in the
buildings, you're going to have two types of energy storage,
electrical batteries and thermal batteries. I do not
know the exact numbers-obviously it depends where
you are-but it's got to be more than 50% thermal. You're
either heating the building or there's too much energy in
the air in the building, and so you're using energy to get
rid of it to the outside. A tremendous amount is thermalrelated.
It makes sense to use thermal storage to meet
thermal loads, whether heating and cooling, and electrical
storage to meet electrical loads.
An electrical battery can run a screen or a pump or a
motor. Thermal storage can't run those. We'll have the
thermal battery for thermal loads or thermal, the electrical
storage for electrical loads. And conversely, using
electrical storage to run a motor that's running a compressor
that's creating instantaneous cooling makes no
sense. You might as well store the cooling, not the electrons,
because electrons are much more valuable to run
a screen or for things that need electrons.
Narayanamurthy: To continue on Mark's point, how
are we accounting for the EUI impacts of electrical storage
in buildings? Because when we look at the analysis,
let's say a 15% round-trip loss, 85% effi ciency, which is
kind of a good number. To Mark's point of pulling the
electrons in and then sending it back out to run a motor:
are we accounting for that today when we do the EUI calculations
for buildings?
Because if we are, that's going to really kind of emphasize
the importance of keeping electrical storage to
electrical loads and the thermal storage to the thermal
loads or having both of them coexist. Because right now
there's a tendency to say, " Hey, we'll just put in a big battery,
run everything off of it. "
Torcellini: Ram, is that storage coming at an energy
penalty?
Narayanamurthy: Yes.
Torcellini: So it will increase the EUI, but it has a huge
benefi t. And if we're focused solely on EUI, is that the
right metric?
Narayanamurthy: Well, that's the question, right?
Torcellini: Yes.
Narayanamurthy: What is the benefi t of electrical
storage? Resilience? Yes. Carbon reduction? Yes.
MacCracken: For decades, it was all about EUI at the
building, and the amount of kilowatt hours that came
through the meter represented how much energy
you used for that building. It was site energy. And for
decades, the thermal storage industry tried to convince
people that there's a big difference between the effi -
ciency of a power plant during the hot peak of the day
or the cool of night, and a generator uses less energy to
make that same kilowatt hour, even though the meter
read it the same way. So Ram's point is absolutely right
that buildings' EUI, based on the electric meter-which
would be a site measurement-will change with carbon
as the metric.
And you have to remember, like Paul said, any storage
has a penalty because there's going in and coming out.
And thermal storage has been fi ghting this, " Oh, you use
more energy, " forever, but when the electrical batteries
come in no one's pointing toward the round-trip effi -
ciency as a detriment. And it needs to be accounted for,
and like Ram said, it will emphasize that you want to use
storage to meet electrical loads and thermal storage to
meet thermal loads.
Deru: I think obviously we don't want to waste energy,
but what are the metrics that we should be using when
looking at buildings of the future? One of the metrics
I think that is going to be very important is carbon. If
you are looking at reducing carbon emissions, how does
storage help? We need better ways of quantifying the
carbon savings. We're starting to get where we have near
real-time carbon emissions data available, which is defi -
nitely a step forward, but I think we're defi nitely going to
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