Client Example

The Cold storage that saves money while it saves the environment

Cold storage facilities are both expensive to build and to operate, but it is possible to build a facility that is both environmentally friendly and still reduce the operating costs by a significant amount.

In late 2008 Strathbrook Industrial Services installed a freezer complex for Old Fashioned Foods that took advantage of the latest developments in refrigeration technology with the twin aims of reducing the operating cost now and protecting the systems owner from the effects of a Carbon tax in the future.

To achieve these goals a very environmentally friendly Carbon dioxide cascade refrigeration system was designed and installed. The system circulates liquid CO2 through the two 25m x 30m x 8m high freezer rooms in place of the a conventional chemical refrigerant.

The carbon dioxide is much denser than normal refrigerants so the volume that needs to be circulated is up to eight times lower. This allows for the pipes to be much smaller which reduces the install cost and reduces the refrigerant charge.

The CO2 is also considerably cheaper to buy or replace should a leak develop.  The cascade system uses a conventional refrigerant (R134a) to remove the heat from the CO2 once it is returned to the plant room in three special brazed plate heat exchangers, and rejects the heat to atmosphere via a conventional air cooled condenser.  This greatly reduces the volume of R134a and allows the system to operate on a medium temperature refrigerant that operates much more energy efficiently than the conventional freezer gasses can.

 

The power saved by removing the electric elements is calculated to be $15000.00 per year, plus the removal of the maintenance of the contactors, overloads, heaters and cables.

 

Carbon Dioxide is used as the measuring stick against which all global warming chemicals and processes are measures, with one ton of CO2 being the basic unit.

The refrigerants that are most commonly used in commercial freezers and cold storage systems are R404a and R507.  These gasses are highly damaging to the environment with global warming potentials of 3,600 times that of CO2.

With the Gillard government pledging to set a price on carbon, any new tax will hit the refrigeration industry hard, with any new tax being multiplied by the chemicals global warming potential. In the case of R404a for example one kg of refrigerant lost to the atmosphere will do the same amount of damage as 3.6 tons of carbon dioxide released from a power station smoke stack.

This will equate to a carbon tax of 3.6 times to agreed rate. So a $20 per ton tax will add $72.00 per kg to the gas, which will be added to the current price of the gas. Given that the tax rate will almost certainly rise over time, it is worth considering to result of a $50.00 per ton tax levied on a 200kg gas loss.

3.6 x $50 = $180 per kg plus the cost of the gas, say another $50.00 = $230.00 multiplied by 200kg of gas = $46 000.00 plus the cost of the repairs and labor to install the new gas!

The system has four evaporators in each room, each piped back to the CO2 machine in copper tube which is insulated with expanding foam inside a 100mm PVC sleeve.  The PVC sleeve greatly increases the insulation factor of the tube and also provides the highest possible mechanical protection.

 

The system has been calculated to be 25% more energy efficient than a conventional Freon type system

 

The evaporators themselves are specially designed and manufactured to incorporate the new hot glycol defrost system, this not only eliminates the electric element defrost system, it saves power, reduces defrost times, and produces a much drier room.  This is a result of the lower defrost temperatures and the way that the glycol transfers the heat into the evaporators tubes and fins without allowing the water melted off the coil block to boil and escape from the evaporator during the defrost cycle.

The glycol defrost system harvests heat from the hot R134a refrigerant discharge vapor and stores it in an insulated tank.  Every hour one of the evaporators shuts down and goes into a defrost cycle.  The glycol pump pumps hot glycol through special tubes in the coil block.  The frost on the coil melts, cooling the glycol which is returned to the tank.  At the end of the defrost the warm glycol remains static in the tubes in the evaporator and cool to the refrigerant temperature, and assists with the heat transfer, boosting the cooling capacity of the evaporator.

The power saved by removing the electric elements is calculated to be $15000.00 per year, plus the removal of the maintenance of the contactors, overloads, heaters and cables.

The system has been calculated to be 25% more energy efficient than a conventional Freon type system, and can operate on a primary refrigerant that will not attract a carbon tax in the future. The cost of the installation was slightly higher than a conventional installation, with the payback period required to recover the additional outlay being approximately 12 months.

If you are planning on building a cold storage facility in the future, don’t forget to ask your refrigeration supplier about CO2 and hot glycol defrost.

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