Most operations directors we talk to have a fuzzy sense that their air conditioning is "expensive in summer" and a worse sense of what to do about it. With electricity at the Ofgem-set non-domestic rates and another warm summer behind us, the running-cost question is getting sharper. This is the working maths we use when surveying offices, retail units and restaurants in Kent and South East London — what the bill is actually made of, what swings it, and where the realistic savings live.
How commercial AC running cost is actually calculated
The honest version is one equation:
Cooling cost = (kW cooling load × hours of operation) ÷ SEER × electricity unit rate
Plug realistic numbers in. A 200 m² UK office at typical occupancy loads roughly 60–80 W/m² of cooling at peak — call it 14 kW peak. Modern VRF at SEER 7.5 means it draws around 1.9 kW of electricity to deliver that cooling. At a commercial unit rate around 25–30p/kWh, that's roughly £0.55 per hour at peak. Over a 9-hour cooling day in July, that's around £5 in pure compressor energy, plus a bit for fans and controls. Cool a London office five days a week for the four hot months and you're looking at hundreds of pounds, not thousands.
Where bills get dramatic is in older, oversized, mis-controlled systems where the maths above compounds badly.
What pushes the bill up
- Old kit with SEER 3–4. A 12-year-old fixed-speed split is doing the same cooling job for twice the electricity.
- Oversized systems. An AC unit sized for the wrong load short-cycles, which kills efficiency and shortens compressor life.
- Dirty coils and filters. A 20% drop in airflow at the indoor unit can mean a 10–15% increase in compressor work.
- Setpoint creep. Reducing setpoint from 24°C to 21°C can increase cooling load by 30–50%.
- Doors and windows. Retail units with doors propped open run cooling that's effectively cooling the street.
- Solar gain. South-facing glass with no shading can add 4–5 kW of cooling load to a small office.
Splits, multi-splits and VRF compared
Single splits
One outdoor, one indoor. Cheapest install, simple to maintain, fine for a single meeting room or small shop. Inverter models are decent at part load. Becomes inefficient and ugly when you need more than 2–3 of them on a building.
Multi-splits
One outdoor unit driving 2–5 indoor units. Tidier, slightly cheaper to run than separate splits, but limited zone control — all indoors on the same outdoor must usually be in the same mode (all cooling or all heating).
VRF / VRV
Variable Refrigerant Flow (or VRV in Daikin terminology) is the workhorse for offices and multi-zone buildings. One refrigerant loop feeds 8–30+ indoor units, each independently controlled. Inverter compressors modulate output 10–100%, so part-load performance is excellent. Heat-recovery VRF can simultaneously cool one zone and heat another, using waste heat — brilliant in mixed-use buildings.
Indicative install cost ranges (2026 UK)
Rough budget figures for a typical commercial fit-out, supplied and installed:
- Wall split, 3.5 kW (single room/office): £1,400–£2,400.
- Cassette in a suspended ceiling, 5–7 kW: £2,800–£4,500 per unit installed.
- Small VRF, 8–14 kW, 4–6 indoor units: £14,000–£28,000.
- Mid-size VRF, 28–45 kW, 10–14 indoor units: £35,000–£65,000.
These vary widely with access, builders work, controls, BMS integration and electrical supply upgrades.
Running cost case study: typical Sevenoaks office
Say a 300 m² first-floor office with 18 staff. Peak cooling load around 22 kW. Old multi- split system running at SEER 4. Replaced with a Mitsubishi or Daikin VRF rated SEER 8.2.
- Annual cooling energy use, old system: ~7,000 kWh.
- Annual cooling energy use, new VRF: ~3,400 kWh.
- Saving at 28p/kWh: ~£1,000/year on cooling alone.
- Plus reverse-cycle heating saves further versus gas in shoulder months.
Payback on a system upgrade typically lands in the 6–10 year range, faster if heating is converted off gas in the same job.
Where the easy wins are if you can't replace yet
- Service the system twice a year. Clean coils and filters add 5–15% efficiency back.
- Set a sensible setpoint policy. 23–24°C for cooling, 19–20°C for heating. Lock the controllers.
- Use time clocks or BMS scheduling. Stop cooling empty buildings at 6am and 7pm.
- Refrigerant top-up if it's low. An under-charged system loses cooling capacity fast and works the compressor harder.
- Solar control film on south glass. Knocks 30–50% off solar gain into the space.
- Free cooling. When it's 16°C outside, open the windows or use the MVHR/AHU bypass. Don't run compressors.
F-Gas and TM44 — the non-negotiables
Commercial AC isn't just an energy story — it's a compliance story. Two specifics in the UK in 2026:
- F-Gas regulations require periodic leak checks based on the system's CO⊂2-equivalent refrigerant charge. Most VRF installs in offices fall into the 12-month or 6-month leak-check bands. Logs must be kept for at least 5 years.
- TM44 inspections apply to AC systems over 12 kW combined effective output. Reports are valid for 5 years and inspections must be carried out by an accredited assessor. Non-compliance attracts fines up to £300 per system.
FAQ
How much does it cost to run an office air conditioning system?
As a rough rule, a well-designed modern VRF in a UK office runs at around 30–50p per m² per cooling day. A 200 m² office might cost £60–£100 a day at peak summer load, far less averaged over the year.
Are VRF systems cheaper to run than splits?
Per kW of cooling delivered, yes — VRF inverter compressors modulate to match demand, so part-load efficiency is significantly better than fixed-speed splits. Anything multi-zone almost always wins on VRF.
What is SEER and why does it matter?
SEER (Seasonal Energy Efficiency Ratio) measures cooling output per unit of electricity over a typical year, not just at peak. A SEER of 7+ is good; 8.5+ is excellent. Higher SEER directly cuts running cost for the same cooling delivered.
Can air conditioning be used for heating too?
Yes — most modern commercial systems are heat pumps that reverse cycle and provide heating in winter, often at COP 3–4. For offices and retail, AC heating is usually cheaper than gas in shoulder seasons.
How often should commercial AC be serviced?
Twice yearly is standard — once before cooling season and once before heating. F-Gas leak checks are also legally required at intervals based on the system's CO⊂2-equivalent refrigerant charge.
Office, restaurant or retail unit with a cooling bill you'd like to bring down? We design, install and service commercial AC across Kent and South East London — see our air conditioning capabilities or request a quote and we'll come and measure the building properly before recommending anything.