ASHRAE Journal - July 2021 - 31

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equipment size and the wire size. It is a cost optimization
done between the size of the tank, the size of the
wire and the size of the compressor. Do you see that in
other applications as well, or can you validate what I
just stated?
MacCracken: Absolutely right. In my early days I
used to use the water heater as an example. When you
take a shower with a low-fl ow showerhead, that's 18
kilowatts of electricity you would have to use to instantaneously
heat that water. Yet the largest element that
you normally see in an electric hot water heater is 3.5
kilowatts. It's a quarter or a fi fth of the amount of wire
that you need-amount of demand it's going to pull-
because you're averaging it out over time and storing
the energy.
It's similar for cooling of a building. It's going to be very
similar now for heat pumps when we use thermal storage
on the heating side of things. Engineers will be able
to downsize the plant because you're looking at the average
load over 24 hours versus the peak instantaneous
loads.
Torcellini: Is there an analogy on the battery side to
the same?
MacCracken: Not really. I don't think so. For instance,
when you're putting in a thermal storage system for
cooling, if you have a thousand-ton building, if it's a
commercial building use, you can put in a 500 or a 600
ton chiller along with storage and charge it up at night
with that 500 or 600 ton chiller. Then, during the day,
you run the 500 or 600 ton chiller, and you use the storage
to meet the load. You have downsized the chiller
plant. I don't think putting a battery on the building is
downsizing anything, because you're not creating the
electrons at the building.
Narayanamurthy: I think as we go along, especially
with electrifi cation, there's going to be a big impact. In
fact, where we see a huge need for storage is on the edge
of the grid on the distribution circuits. That goes back
to Mark's comment on storage, integrated system and
demand limiting of systems. I think that's going to be
where there's a huge value that has not been quantifi ed.
We see that over and over again when we do building
retrofi ts. How do we look at storage as a way to minimize
demand from a building or from a piece of equipment?
It's going to have a huge impact on distribution planning.
Again, that's another reason to think about passive
storage because, for distribution planners, the wires are
a 50-year asset. They are very concerned. For them a battery
is a load because you can change the controls of the
battery and suddenly create a new peak on the distribution
system. That's something to really think about-how
do you create that assurance for distribution planners
that you have that storage that's going to permanently
reduce your load?
Torcellini: What do you think the future of storage
should look like? Where do you want to see this go?
Again, I go back to the beginning of the discussion with
Mark's comment that we already have storage. It's sitting
in coal piles and in fossil-fuel reservoirs. As we see
a shift, we need to shift what that storage looks like.
What do you think it needs to look like in the future?
Lowe: Do we need storage, or do we need fl exibility?
Does storage then drive fl exibility? Because, I think, at
the end of the day, we're all after chasing lower emissions,
and that requires a new energy mix, some of
which is unpredictable. The goal is to match the building
consumption to the production of these grid scale intermittent
resources. Batteries or thermal storage can help
with that.
But I also think dynamic load, the inverse of
demand response, is something that's really important
to think about. I know we're here to talk about
storage and what it will take, but I'm wondering if
maybe reframing toward better integrating renewables,
making sure the grid is balanced and being
more dynamic on having more fl exible consumption
of which storage can play a part, is really the answer. I
think the other challenge is making sure we're getting
the right price signals so these assets are really being
compensated for; there's some sort of economics
really driving this as well.
MacCracken: I would say that in residential there has
been very little economic driver to put in storage. There's
no off-peak electric rates. You won't see small systems
being developed unless there is some economic driver
making that happen.
What I see in the future are buildings that have two
types of storage. They'll have electrical batteries and
they'll have thermal batteries. They may have fossil fuel
in the ground as backup, for a backup generation of
some sort. The combination of electrical and thermal are
going to be able to make the building responsive to the
changes of the grid as we move forward.
We can get to a lower cost with an integrated
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