A
recent survey of the Trend building energy management system and the
plant it controls at Bridgewater Place, Leeds, is expected to lead
to significant energy savings in what is Yorkshire’s tallest
building. The audit was conducted by Trend at the request of the
site’s property managers Jones Lang LaSalle and involved close
collaboration with the building’s M&E maintenance provider Norland
Managed Services. The £3500 cost of carrying it out was recouped in
a matter of weeks as a result of system changes made during the
audit itself. The latter also identified a further £35,700/yr of
savings that could be achieved through additional investment in the
BEMS, which is now going ahead.
Dubbed the ‘Dalek’ by critics of its distinctive architecture,
Bridgewater Place stands 32-storeys (110m) high and dominates the
Leeds city centre skyline. Completed in 2007, it is a mixed-use
development comprising some 23,000m2 of commercial office
accommodation, 200 luxury apartments and 1400m2 of retail space at
ground level. The apartments occupy the building’s upper 22 storeys;
the offices are spread over three wings that are connected by an
8-storey glass atrium.
Each office wing is served by a main air handler with heat
recuperation and there are some 650 fan coil units providing local
air conditioning. Control and monitoring of the commercial area’s
HVAC services are performed by a Trend BEMS comprising IQ3xcite
controllers on the main plant and a dedicated IQL controller on each
fan coil unit. All the IQs are network-linked and the main point of
system access is a Trend 963 Supervisor.
Norland Managed Services, who took over responsibility for
maintaining the HVAC plant and BEMS earlier this year, felt there
was considerable scope to save energy through optimisation of the
controls. They and Trend thus approached Jonathan Ward, Jones Lang
LaSalle’s recently appointed Facilities Manager at Bridgewater
Place, and proposed an energy audit. Mr Ward has considerable
experience of BEMS and, seeing the potential benefits to the
building’s commercial tenants, quickly gave the green light.
The Trend engineer who conducted the audit spent three days on site
reviewing the operation and control of the HVAC plant. Importantly,
his first task was to talk to Mr Ward and the on-site maintenance
engineer from Norland. These discussions were crucial as they
enabled him to gain a better understanding of the building and the
issues relating to its services.
Before leaving site the engineer made a number of changes to system
control settings and strategy. One of these involved resetting the
building occupation times, which govern when the air conditioning is
turned on and off. These times were reduced in all 25 office ‘zones’
– typically by 3hrs/day – to more accurately reflect actual
occupancy. This change, together with the introduction of optimum
start/stop control in every zone, has reduced unnecessary running of
the air handlers and fan coil units. In addition, the boilers and
chillers are now enabled for just 50hrs/week, not 67hrs as
previously.
The boilers’ running hours have been further reduced by adjusting
the outside air temperature economy setpoint, which if exceeded
prevents them from operating. This was lowered from 24oC to 17oC.
The supply air setpoint for all three AHUs was also trimmed back,
from 19oC to 180oC, in order to increase the use of ‘free’ fresh air
cooling and thereby cut the chilled water demand of the fan coil
units. A final action taken at the time of the audit entailed
implementing a simple staging strategy to stop there always being
two chilled water pumps running irrespective of demand.
The audit also recommended a number of additional measures involving
the installation of new hardware and some major reconfiguring of
system control strategies. Jones Lang LaSalle has now confirmed its
intention to have all of these implemented. The cost of doing so is
put at £39,500 with payback being achieved in a little over a year –
based on an estimated annual cut in gas and electricity consumption
of 518,130kWh, equivalent to a saving of £35,700.
The work is to be carried out in stages over a period of 15 months
and orders for the first elements of the project have already been
placed.
A large part of the savings will come from fitting variable speed
drives on the air handlers’ supply and extract fans. Their speed
will be controlled on the basis of occupancy - as indicated by CO2
sensors – and they will consequently no longer run flat out at all
times. VSDs will also be installed on the chilled water pumps so
their speed too can be matched to demand.
Once all the proposed changes have been completed, the building’s
commercial area could be using over 10% less energy than it was
before the audit.
Yet as Jonathan Ward points out, lower energy consumption is not the
whole story: The building’s tenants will naturally gain from any
fall in our energy spend. But they and we will also benefit from
reduced wear and tear on the HVAC plant - and its longer life – as a
consequence of it running less frequently. Since the building will
have a smaller carbon footprint, there will be an environmental
benefit too.”
In order to keep its BEMS operating effectively and maintain energy
savings, Jones Lang LaSalle has invested in a Trend IQEye, an
automatic monitoring and reporting package that continuously checks
the system and highlights possible problems.
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