Optim Pro – Bespoke Air Conditioning Engineering
This provides realistic energy usage estimates for common air conditioning system capacities based on modern inverter technology.
All figures reflect:
- Typical UK operating conditions
- Average system efficiency (COP ~3.5)
- Real-world modulation behaviour
How to Read This
- Cooling Capacity (kW) = what the system delivers
- Electrical Input (kW) = what it consumes
- kWh per hour = actual energy used
- Systems rarely run at full load continuously
Energy Usage Table
| System Size | Max Input (kW) | Medium Load (kW) | Low Load (kW) | kWh per hour (range) |
|---|---|---|---|---|
| 2.0 kW | 0.6 | 0.3 | 0.15 | 0.15 – 0.6 |
| 2.5 kW | 0.7 | 0.35 | 0.2 | 0.2 – 0.7 |
| 3.5 kW | 1.0 | 0.5 | 0.25 | 0.25 – 1.0 |
| 5.0 kW | 1.4 | 0.7 | 0.35 | 0.35 – 1.4 |
| 7.0 kW | 2.0 | 1.0 | 0.5 | 0.5 – 2.0 |
| 9.0 kW | 2.6 | 1.3 | 0.65 | 0.65 – 2.6 |
| 10.0 kW | 2.9 | 1.5 | 0.75 | 0.75 – 2.9 |
| 12.0 kW | 3.5 | 1.8 | 0.9 | 0.9 – 3.5 |
Estimated Running Costs (UK Electricity ~27p/kWh)
| System Size | Low Load | Medium Load | Full Load |
|---|---|---|---|
| 2.0 kW | £0.04/hr | £0.08/hr | £0.16/hr |
| 2.5 kW | £0.05/hr | £0.09/hr | £0.19/hr |
| 3.5 kW | £0.07/hr | £0.14/hr | £0.27/hr |
| 5.0 kW | £0.09/hr | £0.19/hr | £0.38/hr |
| 7.0 kW | £0.14/hr | £0.27/hr | £0.54/hr |
| 9.0 kW | £0.18/hr | £0.35/hr | £0.70/hr |
| 10.0 kW | £0.20/hr | £0.41/hr | £0.78/hr |
| 12.0 kW | £0.24/hr | £0.49/hr | £0.95/hr |
Key Engineering Insight (What Most Contractors Don’t Explain)
- Air conditioning does not consume its rated capacity in electricity
- A 10 kW system typically draws ~2.9 kW, not 10 kW
- This is because modern systems move heat, rather than generate it
- Typical systems deliver 3–5x more cooling than electrical input
Real-World Usage Expectation
For most UK applications:
- Residential / offices (well sized systems):
→ Operate 40–70% load most of the time - Typical actual consumption:
→ 0.3 – 1.5 kWh per hour for most rooms - Oversized or poorly maintained systems:
→ Higher energy + reduced lifespan
Commercial Insight (For Decision Makers)
Neglected systems:
- Consume 20–40% more energy
- Fail under peak load (reactive repair scenario)
- Increase lifecycle cost significantly
Well-maintained systems:
- Maintain design efficiency
- Deliver stable running costs
- Reduce emergency callouts
Conclusion
Modern air conditioning is not energy intensive when correctly engineered and maintained.
The real cost driver is:
➡️ Poor design
➡️ Lack of maintenance
➡️ Incorrect system sizing