Feature
Stockland Wendouree Shopping Centre in Ballarat, Victoria.
HOW IT WORKS
The prototype unit has been sized to deliver
1100m³/hr airflow, capable of providing 10kW
of cooling at rated conditions.
The two-stage desiccant air conditioning
system functions either in the desiccant cooling
mode, or in IEC cooling mode based on ambient
humidity (>40% RH) and storage tank temperature
(>140°C at the top of the tank) set points.
The system consists of two desiccant wheels
to provide maximum dehumidification of
the process air. A closed-loop solar-heat-driven
high-temperature airstream is used for regeneration
of the low-temperature wheel. Heat for the
low-temperature regeneration is provided firstly
through a heat-recovery wheel in the process
air stream, and secondly via heat recovered from
the closed loop.
EFFICIENT COOLING
To simplify the design, moist air has been used
rather than superheated steam as the regeneration
medium in the closed high-temperature loop.
The desiccant air conditioning system has delivered
between 10 and 12kW of cooling when operating in
the desiccant cooling mode, and 5 to 6kW of cooling
when operating in IEC mode.
Sensible cooling of the process air is achieved when
air goes through an indirect evaporative cooler (IEC).
Due to the closed-loop regeneration and
heat-cascading design, the unit is expected to
provide a high thermal coefficient of performance
(COP) – the ratio of cooling provided per unit of
heat input – compared to a conventional single-stage
desiccant air conditioning system.
Solar heat is achieved from concentrating trough
collectors installed on the centre’s rooftop, capable
of providing 70kW of heat at rated conditions.
This heat is stored in a 2000L thermal oil tank.
Both systems were installed and integrated with
the site’s space-heating system to allow the solar heat
to be utilised throughout the year.
Operational data has shown the system to effectively
produce air conditioning and heating to the shopping
centre, with the installed solar collectors delivering
over 1MWh of solar heat per month. During winter
months, more than 50 per cent of heat delivered
from the collectors has been used for space heating.
Typical desiccant mode operational data shows
the performance of the two-stage desiccant system
is as expected. It has a mean thermal COP of 0.66,
and an electrical COP of 7 in desiccant mode
and 10 in IEC mode.
According to the CSIRO, the IEC component
of the unit has been functioning consistently.
It has provided the expected cooling to the building,
with wet-bulb efficiencies of 80 to 100 per cent.
The high-temperature heat delivered to the
closed regeneration loop has been successfully
used for drying the high-temperature wheel.
The low-temperature wheel has been regenerated
using a regeneration air stream delivering
50–60°C heat without an external heat source.
By cascading heat from the high-temperature side
to perform the low-temperature wheel regeneration,
a higher thermal COP has been achieved. CSIRO
says that with further development, the thermal COP
of the system could potentially be increased to 1.
Though the unit installed at Stockland Wendouree
is a “proof of concept” demonstration with a rated
cooling capacity of 10kW, the design can be scaled
to higher capacities. It is envisaged that once
commercialised, systems will target capacities
in the range of 50–100kW of cooling capacity, making
them suitable for large-scale commercial buildings.
Key project facts
Host site
Stockland Wendouree
Shopping Centre, Ballarat
Project partners
CSIRO, Stockland Group
and NEP Solar
Cost
$1.2 million ($520,000
funded by ARENA)
Cooling capacity
10–12kW in desiccant
mode, 5–6kW in IEC mode
Thermal COP
0.66
Solar thermal
collectors
70kW heat at rated capacity
(1MWh per month)
Solar
temperatures
150°C to 200°C
August 2016 | www.hvacrnation.com.au | HVAC&R Nation | 21