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Central Qld Building Products Business

  • Location

    Central Queensland
  • Size

  • Sector

  • Focus area

    • Energy
    • HVAC
    • Variable speed control

7% Proposed
energy savings

An energy assessment for a Queensland cement manufacturer has identified 7% in energy savings through a range of efficiency projects and the installation of a 250 kilowatt (kW) solar photovoltaic (PV) system.

These projects would save the company $68,000 a year in energy costs.  The most energy intensive parts of this 5-day week operation are two natural gas boilers, a compressed air system and a chilled water plant.

Summary of Opportunities

Key Recommendations

Capital Cost

Annual Energy Savings (GJ p.a.)

Annual Energy Cost Savings ($)

Payback Period (Yrs)

GHG Savings (Tonnes of CO2-e)

Compressed air variable speed drive






Heat pump for feedwater






Compressed air line optimisation






Review tariffs






Implement an EMS and reduce standby loads






Thermal battery – 600 litre tank






50 kW / 100 kWh battery






99 kW solar system






250 kW solar system






Variable Output Air Compressor

The manufacturer’s site has two fixed-speed air compressors, both installed around the same time and both still in operation, but each now at the end of its rated life. It’s recommended that the manufacturer consider its asset management framework when deciding whether to extend the operation or replace the air compressors. It was found that retrofitting the lead air compressor with a variable speed drive (VSD) would provide the following advantages over its current configuration:

  • The ability to vary the speed of the compressor to match the requirements would reduce the energy consumption during the loaded state.
  • It would have a reduced capital cost ($20,000) when compared to wholesale replacement of the compressors.
  • It would require less maintenance and have lower operating temperatures, which would save money.

The simple payback period for this option is four years, and it would save 49,643 kWh of energy per annum. It would also help the manufacturer to lower its carbon emissions by 40 tonnes of carbon dioxide equivalent (t CO2-e) each year.

Heat Pump for Feedwater

The curing of concrete using low pressure steam is one of the most energy intensive processes on site. The process cannot solely use electricity as this would be cost-prohibitive, so a low-risk way to electrify part of the curing energy load should be considered. This involves preheating boiler feedwater using a commercially available 80 kW (thermal) air heat pump, powered by renewable energy. It is estimated that a 10.6 kilolitre insulated storage vessel would also be required.

This option presents an opportunity for a sizable reduction in greenhouse gas emissions, with about 41 tonnes of CO2-e in estimated savings. However, it’s not recommended if financial savings are the main goal as the project would have a simple payback period of over 16 years.

Compressed Air Line Optimisation

A site visit uncovered numerous right-angled turns in the compressed air delivery system, which will be causing preventable pressure loss in the system. By simply removing these turns, the site could save $4,090 a year, with a payback period of only six months.

Review Tariffs

This site is currently on a legacy network tariff that will remain in place until at least 2025. It’s recommended that the manufacturer regularly compare tariffs to make sure the legacy tariff remains the right one for the site. Networks tariff change annually, just as a business’ energy consumption patterns change. For these reasons, it’s important for manufacturers to regularly review network tariffs to make sure they’re not paying too much.

Although arrangements beyond 2025 are unclear, it’s likely the site would move to a new tariff, costing an extra $5,900 + GST a year (based on 2019 interval data).

For now, should the manufacturer’s retail contract come up for renewal, there is an opportunity to save $6,701 a year on its retail tariff (the retail component of the site’s tariffs).  

Implement Energy Management System and Reduce Standby Load

Given the size of the site, it’s not unusual for some smaller equipment and lighting to be left on after a shift. The site’s energy consumption could be reduced if these standby loads are eliminated.

Installation of an energy management system (EMS), with appropriate sub-metering, is recommended to easily identify the location and timing at which these loads are on. These loads could be switched off manually or automatically and this would be monitored through the EMS. An EMS integrates a site’s production data with energy consumption so that a business can understand its energy usage in the context of its operation. An EMS can help a business identify issues, find energy savings, track the return on investment, and more.

An additional benefit of an EMS for this manufacturer is that demand response measures could be introduced during peak times. While this is a costly project ($40,000 capex), the energy cost savings would amount to $17,976 per annum, delivering a payback period of just 2.2 years.

Thermal Battery

The site uses a significant amount of chilled water (up to 6,000 litres per day) for batch production. It was discovered that the 112 kW chiller’s cooling load is severely underloaded as it provides about 14 kW of cooling per hour. This type of operation produces extremely large inefficiencies as the chiller is forced to short cycle throughout the day.

This would see the chiller operation automated at night to produce and store 6,000 litres of chilled water in a new insulated tank. The water could then be drawn throughout the day for batch production. This thermal energy storage solution would allow the chiller to operate at its maximum capacity for a short period during the night when electricity pricing is lower. This option has a favourable 1.8-year payback period with cost savings of $5,487 per year.

50 kW / 100 kWh Battery

A 50 kW / 100 kWh battery would provide savings of about $13,000 a year based on 2019 tariffs. This solution would cost over $90,000 to implement, making it unfeasible. This should be reassessed once the site increases its operating capacity, the site shifts to a new network tariff once the legacy tariff that is currently applied discontinues, and/or when the price of batteries has fallen further in coming years.

Choosing the Right Solar PV for the Business

Two options were presented to the manufacturer for consideration: 99 kW and 250 kW solar PV systems. The 99 kW system, which would be eligible for small-scale technology certificates (STCs), is preferred if a short payback period were the priority, however, the larger 250 kW system better meets the company’s objective of greater energy savings and emissions reduction. This is therefore included in the financial summary for this manufacturer.

While it has a longer 13.4-year payback period (compared to 7.7 years for the 99 kW system), the 250 kW system would save over 270,000 kWh per annum compared to more than 130,000 kWh for the 99 kW system. Emissions savings are also double for the larger system.