 
Technica Integrated Engineering
Co. Ltd.
Unit
10, 22/F., Blk A,
Wah Lok Ind. Centre,
31-41
Shan Mei Street,
Fotan, N.T.,
Hong Kong.
Tel: (852) 5802 2099
Fax: (852) 37554468
email:
info@technica.com.hk
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Central heating, ventilation, and air conditioning
(HVAC) systems regulate temperature, ventilation, and humidity levels to
ensure the physical comfort of occupants in most commercial and industrial
buildings. Central HVAC systems come in a variety of different types;
purchasing a system with a high efficiency rating can save you up to 35
percent on energy costs. In addition, HVAC controls, economizers, thermal
energy storage systems, and other efficient HVAC technologies can save you
even more on energy costs.
Typical Applications
Commercial buildings commonly choose several types of
systems based on the space conditioning needs of different systems. A
constant-volume (CV) system might cool the interior, which has relatively
uniform cooling requirements while a VAV system conditions perimeter areas
which have variable requirements. Where precision control is required
(e.g., hospital operating rooms), custom single-zone air handlers may be
used. In large facilities, which have widely varying requirements,
flexibility is extremely important.
Table 1 shows some typical
applications for various types of systems.
Typical
Applications of Central HVAC System |
Building Type |
Type of System |
Office Buildings (low
rise) |
VAV; or CV in the core, and hydronic at perimeter |
Office Buildings(high
rises) |
Central CV system for core, VAV or hydronic at perimeter; dual duct
is common in existing buildings |
Department Stores |
Multiple CV or VAV air handlers |
Universities |
Central steam boiler and chiller plant with CV, VAV or combined
air-water systems at each building |
Schools |
Central boiler and chiller with CV or VAV air handlers serving
individual common areas, and hydronic or combined air-water systems
in classrooms |
Hospitals |
Large chiller, boiler plant (steam common); separate CV systems for
critical areas; CV or VAV for common areas; hydronic and combined
air-water in patient rooms |
Hotels |
VAV for common areas; fan-coil units in guest rooms for individual
temperature and humidity control |
Assembly Theaters |
Multiple VAV air handlers |
Librabries, Musuems |
Multiple CV air handlers, with precise humidity and temperature
control |
Problems Generally Found in Chiller Plants
Space cooling for buildings in
Hong Kong accounts for a significant part of the energy consumption in
the building sector. Electricity consumption by a central
air-conditioning chiller plant may be up to 30% of the total energy
consumed in a building. Inadequacy in wrongly estimation of building
cooling load or misuse of “safety margin result in oversizing a plant is
also common in Hong Kong. Therefore, setting up a quality monitoring
system for a chiller plant will help plant operators to diagnose
problems and optimize plant performance. Unfortunately, reliable
transducers and metering equipment at are essential to properly maintain
plant and to monitor performance are absent or of inadequate accuracy
for temperature, pressure, water flow rate and electrical input.
Particular attention should be paid to the following parameters for
accurate data to be obtained for energy saving analysis:-
-
Chilled water temperature measurement,
-
Chilled water flow measurement,
-
Flow rate evaluation using centrifugal chilled water pump curves method,
-
Input power measurement.
Tips for Efficient Operation and Maintenance
Regular maintenance is
needed to keep equipment clean and functioning properly and to avoid
wasting energy. The following items should be part of a maintenance
program:
-
Check
controls for proper operation. Linkages should operate smoothly
throughout their full range. Dampers and valves should provide proper
flows. Check time clocks and programmed schedules to see if equipment
run-time can be reduced. If the facility has an energy management
system, use its data tracking (trending) capability to determine whether
components actually operate as they should.
-
Clean
all heat transfer surfaces (coils, heat exchangers). Use efficient
filters.
-
Check
drive efficiency. Align and adjust belts; check motor efficiency.
Service chillers, cooling towers, and boilers
according to manufacturers' procedures.
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