5.1.4 Energy efficient controls
An accurate and reliable automatic control system is essential to achieve energy saving. Common control problems such
as over-cooling and system hunting will substantially affect the operation of air conditioning systems and lead to a waste
of energy.
One common problem for shopping malls in Hong Kong is the over-cooling of space. This is attributed to incorrect
settings of thermostats as well as the loss of accuracy of sensing elements over time. In view of this, the design of
automatic control systems should incorporate the necessary maintenance provision to enable calibration of control
systems annually. Facilities, such as test holes, tap points, pressure gauges, thermometers, should be provided to enable
verification of control settings.
Nowadays, the technology of
(DDC) system enables remote adjustment of settings through the
central workstations. To minimise the possibility of incorrect settings, it is recommended that shopping malls should adopt
full DDC as the automatic control system for air conditioning systems in the future planning. Through the DDC, annual
calibration will become much easier. Proper testing and commissioning should be carried out on a regular basis.
5.1.5 Metering for energy audit
Effective measurement and verification (M&V) equipment is essential for performing
for retail areas in the
future. The prime purpose of an
is to identify the demand pattern so that an energy management scheme
can be implemented.
With the wider application of DDC, the M&V equipment could also link up with the DDC system so that trend logging of
data becomes possible. Examples of the M&V equipment for air conditioning applications include:
1
Electromagnetic
flow meter
2
Temperature sensor
3
Pressure sensor
4
Humidity sensor
5
kWh meter
Major air conditioning equipment, such as chillers, A/C pumps and
should be
provided with separate M&V equipment for energy measurement. If the budget is limited, group
metering could be considered as an alternative.
M&V equipment for chiller plant is particularly important. In accordance with the Building
Services Research and Information Association (BSRIA) Technical Notes, the monitoring
equipment should record the input and output energy use of each chiller so that the depreciation
rate can be determined, and to alert the facility management staff when to carry out
maintenance.
5.1.6 Other design considerations
To avoid over-sizing of equipment, appropriate outdoor and indoor air conditioning criteria should be adopted in the
system design and selection of equipment. For outdoor design criteria, these are readily available from the Hong Kong
Observatory as well as international design guides (such as ASHRAE handbook) and the BEC.
For indoor criteria in shopping malls, the target is to maintain human comfort under the activities level. There are
international standards and guidelines available (such as AHSRAE Standard 55) and designers can refer to these
guidelines to determine proper indoor criteria without over-cooling.
To minimise the fan energy against friction loss, air conditioning pipe and duct routes should be arranged according to
the shortest horizontal distance, and should be self-balancing to avoid excessive pumping energy. Whenever possible,
standard fitting should be used. The central air conditioning equipment should be located near to the load centre to
reduce the length of the distribution pipe/duct, as well as energy consumption.
In the overall planning of shopping malls, shops with similar trading and business hours should be grouped together
if possible in order to facilitate energy management. For example, the chilled water supply for an entire zone could be
shut off after business hours to save pumping and cooling energy. Furthermore, the zone AHU serving the public space
associated with the shops cluster can be re-adjusted to lower the fan speed or to raise the temperature setting to save
fan power or cooling energy, respectively.
5
Energy efficient building systems for shopping malls and shop spaces
5.1
Heating, ventilation and air-conditioning (HVAC)
Hong Kong Green Building Council 129
