Rotary screw compressors reject a large amount of heat while producing compressed air. Where there is a genuine use for that heat, a properly designed recovery system can redirect it into space heating, water heating or suitable industrial processes instead of simply exhausting it outdoors.
Almost all of the electrical energy entering an oil-injected rotary screw compressor ultimately appears as heat somewhere in the compressor system. Manufacturer heat-recovery literature commonly identifies a large proportion of that energy as potentially reusable under suitable conditions; for example, Fini documentation states that up to 90% can be reusable in a suitable oil-injected screw installation.
That does not mean every workshop can recover 90% of its compressor electricity bill as cash savings. The amount that is genuinely useful depends on compressor load, operating hours, recovery method, pipework or duct losses, seasonal heating demand and what existing heat source is being displaced.
The simplest approach is often to use the compressor's warm cooling air for space heating. Ductwork can direct warm discharge air into a workshop or adjoining area during the heating season, with a suitable arrangement to reject heat outdoors when it is not needed.
On suitable screw compressors, a manufacturer-approved heat exchanger can transfer heat from the compressor's oil circuit into a water circuit. The recovered heat may then support compatible process-water or heating applications.
Heat recovery is most attractive where the compressor runs for meaningful periods and there is a nearby, regular demand for heat at the same time.
A simple calculation based only on compressor kW, annual hours, an assumed recovery percentage and the electricity price can substantially overstate the financial benefit. It may assume all recovered heat is useful and that it replaces energy at the same unit cost.
A more realistic assessment separates recoverable heat, useful heat and avoided heating cost.
| Step | What to Establish | Why It Matters |
|---|---|---|
| 1. Compressor Input & Load | Measured or well-supported compressor power, loaded hours and operating profile | A 22 kW compressor does not necessarily draw 22 kW at full load for every operating hour. |
| 2. Recoverable Thermal Output | Manufacturer or engineering data for the exact recovery arrangement | Different machines and recovery systems make different amounts of heat practically available. |
| 3. Heat Utilisation | How much of that heat can actually be used when it is available | Summer operation, shutdown periods and mismatched heating schedules can reduce utilisation. |
| 4. Displaced Heating Source | Gas, electric resistance, heat pump, oil or another source | The financial value of a recovered kWh of heat depends on the heat source it replaces and that system's efficiency. |
| 5. Project Cost | Ducting, heat exchanger, pumps, valves, controls, insulation, installation and commissioning | Simple payback should use the complete installed cost, not only the price of one component. |
For an air-cooled screw compressor, the cooling fan already moves warm air away from the compressor. Where the plant-room layout is suitable, carefully designed ductwork can redirect that air to a useful space during cold weather.
Excessive duct resistance can reduce cooling airflow and cause the compressor to run hot. Duct dimensions, bends, grille area and any additional fans need to be checked against the compressor manufacturer's permitted external pressure or ventilation requirements.
The compressor will continue to generate heat when the building does not need space heating. A bypass or damper arrangement should allow warm air to be discharged safely elsewhere without compromising compressor-room ventilation.
Recovering heat into water is attractive where the site has a stable water-heating or process-heating load, but it should not be treated as a universal bolt-on accessory. The exact compressor, cooling circuit and manufacturer's approved options need to be checked first.
A variable-speed compressor changes output to follow changing compressed-air demand, so the amount of heat produced also changes with compressor load. That does not inherently make heat recovery more efficient; it simply means the available heat will vary with the operating profile.
For a heat-recovery project, what matters is whether there is enough useful compressor load at the same time as the site needs heat. A fixed-speed or variable-speed screw compressor may both be suitable depending on the installation and manufacturer options.
Tanair variable-speed equipment and the Power Systems NOBEL range are relevant routes to consider. Heat-recovery compatibility must be confirmed for the exact compressor model rather than assumed across an entire range.
A recovery system should never compromise the compressor's cooling, access or servicing. Any dampers, heat exchangers, pumps, valves, filters or controls added to the installation need to remain maintainable.
Heat recovery does not make the compressor consume no electricity. It increases the value you obtain from energy that would otherwise leave the compressor as waste heat.
Separately, the compressed-air system itself may have opportunities to reduce electrical consumption through pressure optimisation, leak reduction, correctly sized equipment, improved controls or variable-speed operation where the load profile supports it.
Do not assume that a heat-recovery project automatically qualifies for a particular UK grant, capital allowance or incentive. Schemes, qualifying technologies and tax treatment can change, and eligibility depends on the business and the exact expenditure.
If funding or tax treatment affects the investment decision, check the current government scheme rules and take appropriate professional tax or accounting advice before committing to the project.
A large proportion of compressor input energy ultimately becomes heat. Manufacturer literature for suitable oil-injected screw systems can quote recoverable proportions as high as around 90%, but actual useful recovery depends on the exact compressor, recovery equipment, operating load and whether the site can use the heat when it is available.
It can on some sites, particularly where larger compressors run for many hours and recovered heat displaces a significant paid-for heating load. It should not be promised without knowing compressor load, operating hours, useful heat demand and the cost of the heating source being displaced.
Potentially, yes. Warm cooling air from a suitable air-cooled compressor can sometimes be ducted into a workshop, provided the ducting does not restrict compressor cooling and there is a safe alternative heat-rejection route when heating is not required.
Some oil-injected screw compressors can use approved heat-recovery equipment to transfer heat from the cooling circuit into water. Check manufacturer compatibility and the required water temperatures before specifying a system.
Not automatically. A VSD compressor changes its output with air demand, so available heat also varies with load. Heat-recovery value depends on the overlap between compressor operation and the site's demand for heat.
No. Simple warm-air ducting may be possible on many suitable air-cooled screw compressors, while water heat recovery normally requires an approved exchanger and compatible cooling circuit. The exact model should be checked first.
Estimate the amount of heat that can genuinely be recovered and used, then value that heat against the heating fuel or electricity it will actually replace. Include heating-system efficiency and the complete installed project cost when assessing payback.
No. Payback varies with compressor utilisation, heat demand, heating energy prices, project complexity and installed cost. A simple air-to-air system may have a very different payback from an engineered water-recovery installation.
Tell us the compressor make and model, motor size, operating hours and how your workshop or process is currently heated. We can help identify whether heat recovery is worth assessing further.
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