Air compressors produce a lot of energy. A lot of this is unutilised and will often go to waste. However, by harnessing this energy you can find yourself saving a lot of the costs that come with compressed air production. Let’s have a look at air compressor energy recovery and how it can be used to save you money.
How does air compressor energy recovery work?
The majority of energy used by an oil‐injected screw compressor is transferred as heat into the lubricating oil by the compression process.
By adding an additional heat exchanger into the oil circuit this heat can be recovered by passing water through the heat exchanger providing warm/hot water for other processes.
How much energy from a compressed air system is recoverable?
- 75% of the compressor motor rated kW if running on full load or max. speed, this gives a conservative figure.
Or
- 75% of the compressor shaft power in kW, if known, this will give a more accurate figure and in many cases a higher result.
- Pro-rata for reduced loads / speeds i.e. for 50% loaded use 50% of the 75% figure.
What’s included in the Atlas Copco GA compressor range (integrated energy recovery option)?
- Stainless steel oil/water heat exchanger ‐ Transforms heat from the lubrication oil into warm/hot water.
- Thermostatic valve – Enables the oil to bypass the oil/water heat exchanger when the oil is cold.
- Manual bypass valve – Bypasses the oil/water heat exchanger permanently if energy recovery isn’t required.
- Inlet and outlet water temp. sensors – Enable water temperatures to be displayed on the Elektronikon controller.
- Internal oil and water piping and inlet/outlet water connections.
- Higher rated thermostat – To maintain the oil at a higher temperature and maximise recovered energy.
- Factory filled with a higher grade Roto Xtend Duty Fluid.
What temperature rise and water flow can be achieved?
The temperature rise and water flow are dependent on each other, see the formula opposite.
So with a given recoverable energy figure, which we know from the compressor, we can have either:
- High temperature rise with low water flow
- Low temperature rise with high water flow
Use the formulae below to calculate these.
NOTE:
1) The max water temp. rise & outlet temperature – achievable are 70°C & 90°C respectively.
2) Recoverable energy will fluctuate with the compressor load. If a constant water outlet temp is required the water flow will need to be modulated via either a thermostatic valve or variable speed water pump.
To highlight the value of energy recovery it’s important to calculate the potential energy & CO2 savings. The savings will result from a reduction in the energy consumption of the normal heating source which could be electrical energy, gas or fuel oil.
Typical 2021 energy costs & CO2e factors for used in these calculations:
Electricity ‐ £0.15/kWh – 0.021233 kg CO2e/kWh
Gas ‐ £0.04 / kWh – 0.18316 kg CO2e/kWh
Fuel oil ‐ £0.05 / kWh – 0.26815 kg CO2e/kWh
Watch an expert video on energy saving below.