Case study: replacing R22 large-scale AC systems with NH3 in Australia

In an administrative office building in South East Queensland, Australia, two R22 based large-scale air conditioning systems were replaced with ammonia (NH₃) systems using chilled water as a secondary refrigerant. The new system results in 35-50% annual energy savings as well as a substantial reduction in maintenance costs, with an estimated payback on investment of 8.5 years.

The introduction of the carbon price on synthetic greenhouse gases (SGG) in Australia in July 2012 has triggered an increased interest in natural refrigerants for both existing and new installations. This has also been the case for the Logan City Council in South East Queensland, Australia, which decided to renovate its administration building and replace two R22 air-conditioning units with a new ammonia-based system.

Transitioning to natural refrigerants

When seeking replacement technology for the R22 air-conditioning system, the Logan City Council set out to meet the following criteria:

Elimination of an environmentally harmful refrigerant to meet their overall objective of reducing their carbon footprint
Reduction of power consumption to pave the way for renewable energy supply
Recovery of condenser heat from the new air conditioning system to eliminate/minimise the electric energy input into the building hot water systems

Designed and commissioned by Scantec Refrigeration, the replacement system is comprised of two identical water cooled, low refrigerant-charge units, JCI'c SABROE HeatPAC Water Chillers, employing natural refrigerant ammonia (NH₃). The combined cooling capacity of the two open-type reciprocating compressors is around 1200 kW, controlled by a combination of compressor speed control and cylinder unloading. A sophisticated proprietary control system determines the optimum combination of rotational speed and cylinder unloading ensuring maximum energy efficiency while minimising the probability of resonance frequencies.

New NH₃ system incorporates heat recovery

Both chillers are fitted with a shell and tube type discharge gas desuperheater. These heat exchangers recover heat from the discharge gas leaving the compressors prior to the gas entering the condensers. The heat recovered from the system can be utilised for water heating or various other purposes, which will yet have to be determined by the Council.

35-50% estimated annual energy savings

The total installed cost of the new NH₃ based air-conditioning system was around $1,000,000 (€ 750,000). The estimated emissions reduction is 680 tonnes CO₂eq annually and the predicted annual energy savings around 35-50%. This reduction represents a combination of lowered electrical energy consumption and the elimination of fugitive gases from the existing HCFC22 systems. Based on a carbon price of $23/ton of CO₂eq and a unit electricity charge of $200/MWh, the simple payback period on the investment is 8.5 years.

Some of the key benefits from pursuing this project include:

No HFC Levy because the global warming potential (GWP) of ammonia is zero
Reduction in the loss of fugitive gases – this represents a reduction of around 80 tonnes of CO₂eq annually based on an annual leakage rate from the previous HCFC 22 systems of 9%
Improvement in maximum chiller Coefficient of Performance (COP) from 2.52 to around 3.83 at full load when accounting for the influence of electric motor efficiencies
Through the inclusion of variable frequency drives on the new NH₃ based chillers, the integrated part load value (IPLV) is predicted at 9.51; this is around 60-70% better than status quo
Based on the new NH₃ based chillers providing a total annual cooling energy of 4,200 MWh , the annual reduction in electrical energy consumption is estimated at 500 MWh; using a unit electricity cost of $200/MWh this represents an annual cost saving of $100,000
Potential to drastically reduce the energy consumption associated with the production of hot water in the future