Heat Recovery for Air Compressors
Compressed air is the “fourth utility” of UK industry. It is essential, but it is thermodynamically inefficient. A standard air compressor converts approximately 80% to 94% of its electrical input energy into heat.
Without heat recovery, this energy is lost through the cooling system. You pay for this heat whether you use it or not.
A compressor behaves like a constantly boiling kettle. Standard systems vent the steam (heat) out the window. Heat recovery captures this heat instead of venting it. We pipe this thermal energy directly to your boiler feed, process water, or radiators. This provides hot water and space heating using energy you have already purchased.
Design Air (Scotland) Ltd delivers heat recovery solutions across Glasgow, Edinburgh, and the Central Belt. We engineer systems that turn waste heat into a financial asset.
What is Heat Recovery and How Does it Work?
Heat recovery is the engineering process of intercepting waste heat from compression. We transfer this heat to a usable medium, such as water or air.
The compressor becomes a thermal generation asset rather than just an air source.
Energy Breakdown: Where is the Heat?
For a typical oil-injected screw compressor, the heat distributes as follows:
- 72–76%: Oil Cooler (recoverable via water)
- 13–15%: Aftercooler (recoverable via water or air)
- 4–10%: Compressed Air (latent heat)
- 2–5%: Radiation from the motor and canopy
Oil-Injected Rotary Screw Systems
Most industrial sites in Scotland operate oil-injected compressors, such as the Atlas Copco GA VSD⁺ series. We install a stainless steel brazed plate heat exchanger within the oil circuit. Hot oil (approx. 80–90°C) passes through one side. Cold facility water flows through the other. This produces hot water at temperatures between 70°C and 80°C.
Engineering Criticality: Preventing Bearing Failure
A thermostatic mixing valve is mandatory in these systems. It prevents “overcooling.”
If oil temperature drops below the pressure dew point, moisture condenses inside the compressor element. Water contamination leads to oil emulsification and catastrophic air end damage. The valve modulates flow to strictly maintain minimum operating temperatures.
Oil-Free Water-Cooled Systems
Oil-free compressors (Atlas Copco ZR/ZT series) offer the highest recovery potential. They operate at higher internal temperatures. They use separate water circuits. These systems routinely produce high-grade hot water up to 90°C.
Integrated Energy Recovery (ER) units, such as the Atlas Copco ER 90–900, differ from standard exchangers. They automatically modulate water flow to target a specific discharge temperature. They prevent thermal shock on start-up. They ensure the compressor’s cooling requirements are met before harvesting heat.
Air-Cooled Ducted Recovery
For facilities without hydronic heating needs, we install ducting with thermostatic dampers on the cooling exhaust.
- Winter Mode: Dampers direct hot air (50–70°C) into workshops or warehouses.
- Summer Mode: Dampers exhaust heat outdoors to prevent building overheating.
Ducted recovery captures almost all fan-exhaust heat. This typically represents 96% of the energy not used for compression.
See our technical guide for full definitions: What is Air Compressor Heat Recovery?
How Much Energy Can You Recover?
System efficiency depends on compressor type and integration method.
- Integrated Systems (Atlas Copco GA/Z): Recover 90–94% of electrical input energy.
- Retrofit Kits (Mixed Fleet): Recover 50–80% of available heat depending on cooling architecture.
Design Air provides systems compliant with ISO 11011 standards for compressed air energy efficiency assessments.
Why Should Scottish Businesses Invest?
Financial return is the primary driver. Heat recovery shifts focus from maintenance costs to energy savings.
Reduce Heating Bills
Recovered heat displaces gas or heating oil. Electricity is more expensive than gas. Using “free” electrical waste heat to offset gas consumption yields high savings. Scottish facilities typically reduce heating bills by 30% or more.
Return on Investment (ROI)
Payback periods are short. Recovered heat displaces gas, a major operational cost. Most installations see a full ROI in 1–2 years.
ROI Example Calculation
- Compressor: 100 kW running 4,000 hours/year
- Energy Cost: ~£60,000 electricity
- Recoverable Heat: Equivalent to ~300,000 kWh of gas
- Savings: Displacing gas saves approximately £17,000/year
- Payback: A £20,000 installation pays for itself in ~14 months
Compliance: SECR & ESOS
Recovered heat counts directly toward energy reduction targets. This supports compliance with SECR (Streamlined Energy and Carbon Reporting) and ESOS (Energy Savings Opportunity Scheme). It reduces Scope 1 carbon emissions by lowering on-site fossil fuel usage.
Financial Incentives
- Full Expensing: Claim 100% first-year capital allowances on equipment.
- Scottish SME Loan: Access interest-free loans and cashback grants for energy efficiency.
IETF Phase 3: Grant funding for complex industrial heat recovery projects.
What Are the Practical Applications?
Constant-load applications deliver the quickest ROI.
High-Value Applications (Year-Round)
- Boiler Feed Water: Pre-heating make-up water from 10°C to 70°C.
- Process Washing: Hot water for Clean-In-Place (CIP) systems.
- Industrial Cleaning: Parts washing and degreasing.
- Pharma: Temperature maintenance for jacketed vessels.
Seasonal Applications
- Space Heating: Highly effective in winter. Offers little value during Scotland’s warmer months. We prioritise water-based recovery where year-round demand exists.
Safety Note: Potable Water
Recovering heat for showers or washrooms requires legal compliance. We install double-wall vented heat exchangers. If a plate cracks, fluid leaks externally to a safety gap. This prevents oil from contaminating the water supply.
Which Atlas Copco Systems Support Heat Recovery?
As an authorised distributor, Design Air supplies Energy-Efficient Air Compressors engineered for heat recovery.
GA VSD⁺ and VSDˢ Models
Variable Speed Drive technology ensures stable oil temperatures. This guarantees consistent heat transfer to the water circuit.
ZR/ZT Oil-Free Range
Pairs with Atlas Copco ER 90–900 units. These are fully integrated modules. They control water flow and temperature automatically.
SMARTLINK Connectivity
Remote monitoring tracks energy performance. It monitors the temperature difference ($\Delta T$) across the heat exchanger. A drop in $\Delta T$ triggers a service alert for cleaning. This prevents efficiency loss.
Mixed-Fleet Retrofits
We retrofit systems from Kaeser, Ingersoll Rand, CompAir, and Gardner Denver. We use universal kits from manufacturers like Bowman and Thermotech. We design modular solutions that integrate with legacy boiler circuits.
Common Challenges and Solutions
Proper engineering prevents system failure. Design Air addresses common risks during the survey phase.
| Challenge | Cause | Solution |
| Low Output | Incorrect sizing | Accurate thermal load survey |
| Overheating | No bypass installed | Install thermostatic diversions |
| Scale Buildup | Hard water | Filtration and water softeners |
| Oil Contamination | Single-wall exchanger failure | Use double-wall vented exchangers |
| Integration Issues | Legacy heating circuits | Modular retrofit kits |
How Design Air Supports Heat Recovery Projects
Design Air (Scotland) Ltd is based in Airdrie. We serve Glasgow, Edinburgh, Dundee, Fife, Stirling, and Perth.
We provide a complete turnkey solution:
- Survey: We conduct a Compressed Air Energy Audit to quantify available heat.
- Water Testing: We analyse water hardness to prevent scaling.
- Design: We calculate thermal loads and select exchanger sizes.
- Installation: We install pipework, valves, and safety controls.
- Maintenance: We include heat exchanger cleaning and valve inspection in service plans.
Frequently Asked Questions (FAQ)
No. A correctly sized system with a thermostatic bypass improves performance. It reduces the thermal load on the compressor’s standard cooling fans.
Yes. Retrofit kits are available for most oil-injected screw compressors. The machine must have sufficient remaining service life to justify the investment.
The system automatically bypasses the heat exchanger. The compressor reverts to its standard cooling radiator. This ensures continuous operation regardless of heat demand.
Contact Us
Most Scottish sites recover their investment in under two years.
Contact Design Air (Scotland) Ltd today to book a no-obligation heat recovery survey.