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Well worth itA supermarket in Melbourne’s Docklands precinct has operated so efficiently since opening that its electrical meters were checked for accuracy amid concerns they weren’t working properly. As Sean McGowan reports, such is its impact that it might rewrite the rulebook on supermarket design.

Woolworths Victoria Harbour is part of Bovis Lend Lease’s large, mixed-use development located in the heart of Melbourne’s Docklands precinct.

The complex incorporates the 2,600 sq m supermarket, a small atrium, mall and a number of specialist retailers, as well as a childcare centre and 3,000 sq m of Green Star-rated commercial office space above.

Behind the mechanical and electrical systems design of the complex was consulting engineering firm Wood & Grieve Engineers, which went well beyond the standard supermarket design brief to deliver a supermarket that has astounded those involved with its energy efficiency.

“Woolworths were obviously the anchor tenant in the building, and normally when we design a Woolworths we

simply design it in accordance with their technical standards, which have been around for many years,” says David Simpson, Aff. AIRAH, project engineer – director at WGE.

the advantage of Co2 is that it’s an environmentally friendly refrigerant, and by sharing the plant we could actually run the system flat out, so it runs more efficiently.’

“However, this job was different. The site had a green overlay and Woolworths came on board, and that’s why it’s unique.”

Rather than basing the design to the Woolworths technical standards, which

is the standard practice, the green overlay placed on the site by the Docklands Authority (before the introduction of the Green Star Retail tool) meant that WGE would need to meet the Woolworths standards of specification while also ensuring the design met the efficiency required by the precinct.

To address this challenge, WGE was required to push the boundaries of traditional supermarket HVAC&R system design.

“We had this relatively old-fashioned standard, which included running air conditioning systems 24/7, no economy cycles, separate heating systems, and yet a requirement by the precinct authority to achieve high energy efficiency,” recalls Simpson. “So we had to find a way of doing it in a very efficient way.”

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By challenging the status quo, the rulebook for supermarket design in Australia would be rewritten, for the better.

eCoNoMY CYCles AND Co2According to Simpson, the first major diversion was to incorporate the use of CO2 into the store’s air conditioning system.

While Woolworths had already successfully operated cascade CO2-charged refrigeration systems at a number of stores around the country, the same refrigerant had not been applied to the in-store air conditioning system. The team at WGE, with the assistance of Woolworths’ refrigeration engineers, saw this as a two-pronged opportunity to use this refrigerant while achieving high efficiency.

“The advantage of CO2 is that it’s an environmentally friendly refrigerant,” Simpson says, “and by sharing the plant we could actually run the system flat out, so it runs more efficiently.”

Furthermore, the system was air-cooled, reducing Legionella risks.

Don’t expect to see grass on the roof or wind turbines at this supermarket. the environmental innovations are more than just skin deep, and tackle the main contributors to carbon emissions in store: air conditioning and refrigeration.’

To ensure the refrigeration and air conditioning systems operated cooperatively, digital direct control (DDC) was installed on both the store’s refrigeration systems, with a separate DDC for the air conditioning systems. A careful interface was installed between the two.

Simpson says that while this design would see the plant operate more efficiently, the

use of CO2 in the air conditioning system brought with it a secondary issue: the risk that the coils would ice up.

These issues were further compounded by the introduction of economy cycles, something that has long been avoided in Australian supermarkets due to humidification concerns, particularly at night. Yet WGE had calculated a significant payback for its introduction, and designed it into the CO2 refrigeration system.

“What that meant was we could actually use the outside air, rather than running the chillers for the refrigeration plant,” Simpson says. “However, to avoid humidity issues we put split coils in the air conditioning unit, similar to a face-and-bypass arrangement, where you can actually get partial dehumidification by running one out of the four coils for part-load cooling.”

A range of computer simulations was conducted on the night-time conditions at the site, revealing that for a large part of the year the use of economy cycles,

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either alone or together with one or two of the split coils in operation, provided the level of dehumidification required.

Four separate coils, non-interlaced to provide humidity control, were provided in the AHU; however, concerns about the coils freezing required further thought.

“CO2 is a lot colder a refrigerant than, say, chilled water or the standard CFC refrigerant, so we had to be really careful about the possibility of icing up the coils,” explains Simpson. “Therefore we incorporated a range of safety controls, including a pressure-drop sensor across the coils, which would send a signal back to the control system to reduce the cooling, in the event that coils were icing up.”

While the concerns were well founded, he says there has been no incidence of the coils freezing up since commissioning.

Another benefit of the use of economy cycles in the HVAC&R design was the ability to design the spill air path through

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the complex’s atrium at the entrance to the supermarket, where the specialty retailers are located. This design has enabled the store to benefit from free cooling.

For heating, gas radiant heaters were installed overhead, proving the most efficient form of heating for this atrium space.

“Even when the economy cycle is not operating, the fresh air component in the system is also relieved through the atrium,” Simpson explains.

exPoseD MAss AND DisPlACeMeNtAnother simple design element that has contributed significantly to the energy efficiency of this supermarket’s operation is the deliberate use of exposed thermal mass.

The design team identified the concrete floors and ceiling as ideal to expose the store’s thermal mass. Thus floors were left uncovered

and given a simple polished concrete finish, while much of the ceiling, barring food preparation areas, was left exposed.

Another simple design element that has contributed significantly to the energy efficiency of this supermarket’s operation is the deliberate use of exposed thermal mass.’

Air distribution also moved away from standard specification. Normally, conditioned air would be introduced overhead through exposed ductwork and side-blow diffusers. Due to the relatively high ceiling of about 5m, a displacement system was adopted.

“A displacement system here offered a number of advantages,” explains Simpson. “Firstly, it effectively only air conditions the occupied space,

which is to about 2.1m off the floor. Secondly, we were able to lower the air pressure resistance of the system and save on fan power.”

By reducing the air velocity, the system was able to save significant fan energy. Simpson says this same approach was taken to the coils in the air conditioning unit, with reduced air velocity saving significant fan energy while maintaining system performance.

“Remember here that the fan is running 24 hours a day, so it doesn’t take long before these sort of initiatives pay back,” he says.

Although the application of a displacement system offered significant energy savings, the challenge of introducing air at floor level on a concrete slab required an innovative approach using the nature of supermarket layouts.

WGE’s solution was to install overhead ductwork, exposed on the ceiling, feeding conditioned air to all areas of the store.

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This was delivered to floor level via duct droppers, which passed through the gondolas [shelving units], supplying air to the “kicker” in every second aisle. Mesh was installed at each dropper point to reduce air spill and equalise the distribution of air.

“The other advantage with a displacement system is that the supply air temperature can be higher than a traditional system. In this case it was set at 17°C,” says Simpson, adding that the design temperature also had to take into account the incidence of shoppers experiencing coldness near their feet.

“By having a higher supply air temperature, you can also take advantage of economy cycles for greater periods of time,” Simpson says. “The disadvantage, of course, is that you don’t get the right levels of dehumidification, but the split coils helped our cause.”

To further reduce energy consumption, a variable speed drive was installed on the supply air fan, which was particularly effective at night when large quantities of air are not required throughout the supermarket, and loads are lower.

“Here we had a night setback,” Simpson says. “So in other words, your supply air fan would back off, and small saving in air resistance results in a large saving of fan energy.”

HeAt reClAiM BY A NoseIncredibly for a concrete building in Melbourne, Woolworths Victoria Harbour requires very little heating. Whatever heating is required has been supplied by reclaiming the heat rejected from the store’s refrigeration plant.

WGE calculated that the minimum heat output from the around-the-clock operation of the CO2 refrigeration system was slightly in excess of the heating requirement of the store.

After much discussion with the client, it was deemed that the installation of a heat reclaim unit would prove satisfactory and add to the energy efficiency of the store, hence the deletion of a heating boiler.

“It was slightly risky, as every other Woolworths has had heating installed (via gas boiler), and while the differential between the heat output and heat requirement was slim, it has worked,” says Simpson.

Along with these high-efficiency departures from the standard, modern supermarket design, staples such as cold aisle returns and automatic night blinds on refrigeration cases also contributed to the store being hailed as the company’s first “green store” when it opened its doors to customers in May 2008.

We had this relatively old-fashioned standard, which included running air conditioning systems 24/7, no economy cycles, separate heating systems, and yet a requirement by the precinct authority to achieve high energy efficiency. so we had to find a way of doing it in a very efficient way.’

“Don’t expect to see grass on the roof or wind turbines at this supermarket,” said Michael Luscombe, CEO of Woolworths Limited, at the time of the opening. The environmental innovations are more than just skin deep, and tackle the main contributors to carbon emissions in store: air conditioning and refrigeration.”

While the cascade CO2 refrigeration system is said to have reduced the store’s greenhouse gas emissions by around 25 per cent, the performance and energy efficiency of the store has not been revealed publicly.

Yet it is believed the store’s energy performance took even the company’s technical team by surprise during the first few months of operation, so much so that it was thought the store’s kW/hr run meters weren’t working properly.

Following tests for calibration and checks on their accuracy, it was confirmed the meters weren’t telling lies at all. One Woolworths engineer reportedly described the store as “one of the most energy efficient Woolworths in Australia.”

It is among three “green stores” to have been opened by Woolworths to date (the others are in Rouse Hill and Geelong), as the company continues to amend its standards to incorporate many of the features first introduced at Victoria Harbour. ❚

Would you like to know more?

To read more about energy-efficiency in retail environments, go to the publications tab at www.airah.org.au

The November 2008 HVAC&R Nation featured an article, “IGA greens its aisles”.

An article about the award-winning Rouse Hill project, “Retail therapy”, appeared in the August 2009 issue of Ecolibrium.

Air-handling unit with chilled water.