In
the main exhibition space, it is expected that for lengthy periods
the required environmental conditions will be met by natural
ventilation alone (this also being used to night cool the building).
Only if temperature and/or CO2 levels breach pre-set limits,
does the Trend BMS bring on the mechanical ventilation and cooling.
When needed,
tempered air is supplied to the main exhibition space by a single
air handling unit, a further seven AHU’s serving the other
public areas. All are closely controlled by the Trend system.
In achieving the desired supply air temperature it makes maximum
use of free heating or cooling by modulating heat exchanger
face and bypass dampers or operating pumped reclaim circuits.
Particularly close control is called for in the museum’s
special exhibitions gallery, where there will be a changing
programme of exhibits. The latter will include items that require
highly stable conditions. The room’s AHU has three control
modes, each corresponding to a different set of temperature
and humidity tolerances. The modes are selectable via the system’s
main operator interface.
Canal
Cooling
The main
exhibition space, special gallery and museum’s restaurant
also have under floor heating and cooling circuits, which are
controlled from sensors in the floor. They have two sources
of ‘coolth’: water from the Manchester Ship Canal
and the buildings two chillers, which also serve the AHU’s.
There is only recourse to the chillers if the canal water is
too warm to satisfy demand.
Water is drawn from the canal through an intake 3.5m below the
surface. After filtration it circulates through a plate heat
exchanger and is discharged back into the canal. The secondary
circuit from the heat exchanger supplies not only the under
floor circuits but also cools the chiller condensers. One of
the Trend system’s tasks is to implement a daily backwash
routine (using rainwater if available) of the duty heat exchanger.
As a further energy saving measure the BMS provides variable
speed control of the primary and secondary pumps using flow
temperature and differential pressure readings.
The museum’s
chiller plant supplies a pair of buffer vessels; a further pair
is fed by its four gas-fired boilers. The system enables and
sequences the plant to maintain the hot and cold water storage
vessel temperatures at 82 degrees C and 5.5 degrees C respectively.
Reverse cycle heat pumps have been installed as back-up energy
source for the special gallery’s AHU. The BMS also brings
these on if the gallery is the only area calling for cooling,
since this is a more energy efficient option than running the
chillers.
1Q251
controllers
The system
incorporates eight network-linked IQ251 intelligent controllers,
which have up to 128 input/output points each. As well as controlling
and monitoring the HVAC services, the IQs control sump pumps,
log utility meter readings and monitor the condition of the
building’s generators and an interceptor device that prevents
petrol from the car park being washed into the canal. A Trend
‘962’ PC-based supervisor is used by the museum’s
FM company for system management and monitoring.
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