IEEE Technology and Society Magazine - Fall 2014 - 78

For a subset of dwellings,
statistically and economically
significant savings were achieved.
factors, for example neighborhood
networks, engagement campaigns,
and different demographics.
During the project, Knowle West
Media Centre (KWMC) ran a number of workshops with the households participating on a voluntary
basis. The workshops focused on
different objectives, predominantly
discussing how others were reducing
their energy consumption, as well as
advising participants on how to use
the tablet and interface. The level of
participation in the workshops was
relatively low and in general, these
workshops had no long-term effect
on the interface use.

Overhead and Economic
Considerations
While energy monitoring and conservation are truly worthwhile
objectives, it is also of interest to
identify the footprint of the monitoring infrastructure, e.g., some interesting issues worth examining are:
■■

■■

How much energy do the elements in the monitoring infrastructure consume?
How much energy is consumed
by the monitoring infrastructure
as a whole?
How does this compare against
the typical average daily
consumption?
What is the cost of operating
the monitoring infrastructure
at the consumer's premises, on
the data collection side, as well
as for the pilot as a whole?
What are the other costs associated with deploying the monitoring infrastructure in order
to conduct the pilot study, and
how do these compare against
the energy costs?

The ensuing discussion attempts
to elaborate on these issues with
78

the aim of providing a broader perspective on the Bristol city pilot.
Volume of Energy
Monitoring Data
When the server requests measurement information from a dwelling,
the dwelling returns the requested
information as a 64-byte response
comprised of the dwelling identifier, current time, device type/
address,
temperature,
humidity, instantaneous and cumulative
power consumption, and gas meter
reading (in the form of a cumulative pulse). It is worth noting that
since the size of the packet payload is small (64 bytes), this does
not place any significant burden
on the communication technology
required to transport this information. We observed that, for the most
aggressive data collection regime
(once every minute), close to 100
kilobytes (kB) of data is logged per
day, per dwelling at the data collection server. For the Bristol pilot
comprised of roughly a hundred
dwellings, this translates to 10MB
per day and 3650MB per year. In
terms of monetary cost for the storage required to fund this project for
a couple of years, it is estimated to
be roughly £10 (U.S. $17). This is
miniscule in comparison to some
of the other costs, notably the ones
related to deployment.
Energy Consumption of
the Monitoring Infrastructure
and Related Costs
The monitoring infrastructure is
meant to provide data that will lead
to insightful information in order
to help identify avenues for further
reduction. It is of interest to identify
the footprint of this infrastructure.
Fig. 7 shows the energy footprint of
each element of the monitoring infrastructure in a dwelling. Since these

devices are measuring consumption
every minute, it is assumed that all
of these devices remain powered on
all the time. As evident from this
figure, not only is the footprint of
each individual device quite small,
but also the total footprint per day is
miniscule at 0.345 kWh. Examined
over a period of a year, this footprint
figure translates to 127.75 kWh.
For the sake of simplicity, if we
assume a fixed price energy tariff of
10p/kWh, this translates to a monetary cost of £0.035 (U.S. $0.06) per
day (£12.77 (U.S. $21.76) per year),
per dwelling to operate the monitoring infrastructure. Fig. 8 shows the
energy footprint of the monitoring
setup. We observe that the energy
consumption on the server side (per
day) is just over a quarter that of
the total energy consumed for running the monitoring infrastructure
in all the dwellings over a day. This
suggests that if the pilot study were
to be scaled up (i.e., if more dwellings participated), the proportion
of the energy footprint of the server
side would be even smaller in comparison. The value corresponding
to the overall consumption depicted
in Fig. 8 is the total energy spent
on running the pilot study for a
day. Assuming a fixed energy tariff like the one mentioned earlier
(10p/kWh), the energy footprint figure
indicates that it would cost roughly
£4.40 (U.S. $7.50) to run the pilot for
a day (or £1600 (U.S. $27200) to run
the pilot for a year).
We also observed that the average daily consumption increases
with the size of the dwelling and
also with the number of occupants. As one would expect, when
the average daily consumption
increases, the monitoring overhead
decreases. Overall, while monitoring overhead appears to be significantly lower in comparison to
average daily consumption, for
smaller dwellings that save a modest amount of energy (as many did
in this study), the energy/cost burden introduced by the monitoring
infrastructure may be an issue.

IEEE TECHNOLOGY AND SOCIETY MAGAZINE

FALL 2014

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