Heat recovery for oil-free compressors
Turn up to 94% of compressor input power into usable hot water.
Overview
Almost all the electrical energy a compressor consumes turns into heat. In most plants that heat is thrown away through a cooler and, in air-conditioned buildings, paid for a second time to remove it.
A heat recovery package puts a heat exchanger in the cooling circuit and gives you hot water at 70 – 90 °C instead. On a water-cooled oil-free machine, up to 94% of the input energy can be recovered, because there is no oil circuit to complicate the heat path.
Key benefits
Up to 94% recovery
On water-cooled two-stage oil-free machines, most of the input energy comes back as usable hot water.
Real payback
Where the site already burns gas or diesel for process hot water, payback is often under two years.
Retrofittable
Can be added to installed Green Air oil-free machines without replacing the compressor.
No contamination risk
Double-wall heat exchangers available where the recovered water touches a food or pharma process.
How it works
Almost all the electricity a compressor draws leaves it as heat. Recovery does not create anything, it simply catches that heat on its way out and puts it somewhere useful instead of into the plant room.
On an oil free machine the heat is taken from the intercooler and the aftercooler, where the air is hottest and the exchange is cleanest. There is no oil circuit in between, so the water side stays uncontaminated.
What you get back is hot water at up to ninety degrees, which is the temperature that makes it useful for washing, for process heating and for feeding a boiler rather than merely warming a room.
- Up to ninety per cent of input energy recovered
- Hot water at up to ninety degrees
- Heat taken from intercooler and aftercooler
- No oil circuit between air and water
- Fits new machines and existing ones
- Plate exchanger or shell and tube
- Plant room stays cooler as well
- Payback usually measured in months
Is it worth it on your plant
The question is not whether the heat is there. It is whether you have somewhere to put it. A plant that already buys hot water or steam has an immediate answer, and a plant that does not should not be sold this.
We work it out from your running hours, your compressor power and the cost of the fuel you currently burn for hot water. If the arithmetic does not work we will say so.
The second benefit is one people forget. Heat taken out through the recovery circuit is heat the plant room ventilation no longer has to remove, and in a Gulf summer that is worth money on its own.
- Worked out from your running hours and fuel cost
- Needs an existing hot water or heating demand
- Arithmetic shown before you commit
- Plant room cooling load reduced as well
- Retrofit to machines already installed
- Metered so the saving is measured, not claimed
- Sized to your demand, not the compressor
- Installed by our own team
Parts and service
A recovery circuit is a heat exchanger, a pump and some controls. The exchanger is the item that needs attention and water quality is what decides how often.
Scaling reduces recovery quietly. Nothing fails, the water is simply less hot, and without a meter nobody notices that the saving has gone.
We record recovered energy at every service so the system is proved to still be doing what it was bought for.
- Exchanger cleaning on the schedule
- Water quality checked at every visit
- Recovered energy metered and recorded
- Pump and control service included
- Serviced with the compressor on one visit
- Parts held in local stock
- Performance reported after every service
- Fixed price under a service plan
Frequently asked questions
How much heat can I actually recover?
Up to 94% of the electrical input on a water-cooled oil-free machine, because there is no oil circuit complicating the heat path. Air-cooled machines recover less.
What temperature water do I get?
70 to 90 °C, which is hot enough for boiler feed pre-heating, clean-in-place water and most process washing duties.
How much hot water is that in practice?
As a guide, a 75 kW compressor running loaded delivers roughly 1,100 litres an hour raised by 40 °C. We calculate your figures from actual running hours and inlet water temperature.
When does it pay back?
Usually under two years where the site already burns gas or diesel for process hot water. Where there is no hot water demand there is nothing to recover into and it does not pay at all.
Can it be added to a machine I already have?
Yes, if it is a Green Air oil-free unit. The heat exchanger goes into the cooling circuit without replacing the compressor.
Is there any contamination risk to my process water?
Double-wall heat exchangers are available where the recovered water touches food or pharmaceutical processes, so a single failure cannot cross-contaminate.
Does it affect compressor performance?
No, provided the recovery circuit is sized correctly. The compressor still needs to reject its heat. Recovery just sends it somewhere useful instead of a cooling tower.
What happens in summer when I do not need the heat?
The system switches back to the normal cooling circuit automatically. You are not obliged to take the heat when there is no demand for it.
Which industries benefit most?
Textile dye houses, dairies, food processing and anywhere with clean-in-place hot water. Plants that already have a continuous thermal demand.
Do you do a feasibility study first?
Yes, we measure the available heat and the required sink before quoting, because the answer is sometimes that it will not pay on your site.
Related products
Water lubricated oil free compressors
Water seals and cools the rotors instead of oil. Class 0 air, 5.5 to 160 kW.
- Free air delivery
- 0.3 – 27.0 m³/min
- Working pressure
- 7 – 10 bar g
- Motor power
- 6 – 160 kW
Oil free scroll compressors
Quiet, small, genuinely oil free. 7.5 to 37 kW at 8 bar g.
- Free air delivery
- 0.8 – 4.0 m³/min
- Working pressure
- 8 bar g
- Motor power
- 8 – 37 kW
Oil-free rotary screw compressors
Class 0 air with no oil anywhere in the compression chamber.
- Free air delivery
- 0.3 – 6.9 m³/min
- Working pressure
- 5 – 10 bar g
- Motor power
- 15 – 37 kW
Two-stage oil-free compressors 37 – 75 kW
Two compression stages with intercooling for lower energy per m³.
- Free air delivery
- 5.1 – 12.7 m³/min
- Working pressure
- 7 – 10 bar g
- Motor power
- 37 – 75 kW
Not sure which model you need?
Send us your air demand, working pressure and running hours. Our engineers will size the machine and send a written recommendation, no cost, no obligation.