Commercial AC installation guide (step by step)

Step by step

1. Step 01

   Site survey and heat load calculation

   An engineer visits the site to measure floor area, ceiling height, window area and orientation, insulation quality, occupancy, IT or kitchen equipment load and existing ventilation. These feed a full CIBSE standard heat load calculation in kW, not a rule of thumb BTU estimate. As a sanity check, offices typically land at 600 to 700 BTU per m² (roughly 180 to 220 W per m²), retail 800 BTU per m², and kitchens and server rooms 1,000 or more. Under-sizing means the system runs constantly and never hits setpoint on hot days. Over-sizing causes short-cycling, poor dehumidification and 15 to 25% higher running costs. AccuTemp's survey report includes the calculation workings so you (or your consultant) can verify the number.

2. Step 02

   System architecture: split, multi-split or VRV/VRF

   Single-split systems (one indoor, one outdoor) suit rooms up to around 50 m² or isolated spaces like server rooms. Multi-split (up to 5 indoors on one outdoor) suits small offices where the indoor units run on similar schedules. VRV/VRF (Variable Refrigerant Volume/Flow) suits anything above around 15 kW total. It varies refrigerant flow to each indoor unit independently, delivers heat recovery between zones (one room heating while another cools), and scales cleanly to 40 or more indoor units on a single outdoor system. Getting this decision right upfront prevents expensive rework. Adding a 6th indoor unit to a multi-split later means replacing the outdoor unit.

3. Step 03

   Indoor unit type: ducted, cassette or wall-mounted

   Ducted units sit above the ceiling void and distribute air through grilles. They are the quietest and most discreet, and best suited to premium offices and hospitality. They require at least 250 mm of ceiling void. 4-way cassettes mount flush in suspended ceiling tiles with 360° airflow, which suits open plan offices and retail. Wall-mounted units are fastest and cheapest to install with no ceiling work, so they are ideal for server rooms, meeting rooms and small back-of-house spaces. Floor-standing and ceiling-suspended units cover the awkward cases, such as Victorian buildings with no ceiling void, or industrial units with exposed structure. Indoor types can be mixed on the same VRV system if the building needs it.

4. Step 04

   Brand, refrigerant and efficiency selection

   AccuTemp specifies Daikin (D1+ Premier Partner), Mitsubishi Electric and Toshiba, all rated for 12 to 16 year commercial lifespans on R32 refrigerant. R32 has 68% lower global warming potential than R410A (675 versus 2,088 GWP) and is now the UK default for new installations. R410A is being phased down under the F-Gas Regulation. Efficiency is measured as SEER (cooling) and SCOP (heating). Part L 2021 sets minimum thresholds, and Daikin's premium ranges (VRV 5, Sky Air Alpha) exceed A+++ in most configurations. Cheaper Chinese and Korean units come in 15 to 25% lower on upfront cost but typically fail at 5 to 7 years with no UK spares network. The whole life cost comparison is rarely close.

5. Step 05

   F-Gas, TM44 and Part L compliance

   Three compliance regimes apply to every UK commercial installation. The F-Gas Regulation requires annual leak checks on any system with refrigerant charge above 5 tonnes CO₂ equivalent (50 tonnes triggers six-monthly, 500 tonnes quarterly), plus an on-site F-Gas register from day one. TM44 inspections apply to buildings with combined cooling capacity above 12 kW and must be carried out every 5 years and lodged on the government's TM44 register. Part L of the Building Regulations sets minimum SEER and SCOP thresholds, minimum controls (zone control, time control, temperature control), and commissioning evidence requirements. AccuTemp handles all three in-house. Our engineers are F-Gas certified, we hold accredited TM44 assessor status, and Part L compliant commissioning documentation is supplied at handover.

6. Step 06

   Installation: pipework, electrical and condensate

   Refrigerant pipework is copper, brazed under nitrogen purge (nitrogen displaces oxygen so no oxides form inside the pipe, which is critical for compressor life), pressure tested to 42 bar for 24 hours, then triple evacuated to 500 microns before charging with R32. Electrical supply is sized to the outdoor unit's MCA (minimum circuit ampacity) with the correct isolator and RCBO. A 15 kW outdoor unit typically needs a 32A three-phase supply. Condensate drainage runs at a minimum 1:100 fall to gravity where possible, or to a condensate pump where the run is too long or the drop insufficient. Every joint, pressure test and vacuum reading is recorded in the commissioning documentation.

7. Step 07

   Controls, BMS integration and zoning

   Modern commercial installations rarely run on a wall-mounted controller alone. AccuTemp specifies Daikin Intelligent Touch Manager or Mitsubishi AE-200 as the central controller for anything above 5 indoor units, covering schedules, setpoint limits, occupancy overrides, energy monitoring and remote diagnostics. For buildings with a BMS (Trend, Tridium, Distech, Priva), we integrate via BACnet or Modbus so HVAC sits alongside lighting, access control and metering. Zoning strategy matters as much as the hardware. Open plan floors get one zone per aspect (north and south differ by 3 to 5°C in summer). Meeting rooms get individual control with 30 minute occupancy timeouts.

8. Step 08

   Commissioning, handover and lifecycle plan

   Commissioning records airflow (m³/s at each grille), temperature differential (target 8 to 12°C across the coil), refrigerant suction and discharge pressures, superheat and subcooling, electrical draw at each unit and controller function on every zone. That baseline is the reference every future service visit compares against. Without it, no engineer can tell whether the system is degrading or performing normally. The handover pack includes O&M manuals, an F-Gas register with initial charge logged, warranty registration (Daikin cover extends to 5 to 7 years for D1+ Premier Partners), Part L commissioning certificate, TM44 lodgement where applicable, and a recommended maintenance schedule. Typically that is two visits per year for standard offices, four for retail, and quarterly for critical cooling.

Frequently asked questions

How long does commercial AC installation take?

Most single-split installations complete in 1 to 2 days on site. Multi-cassette office fit-outs typically run 1 to 3 weeks. Large VRV/VRF systems with significant pipework can run 4 to 8 weeks. AccuTemp confirms exact timings after the free site survey with a written programme by stage.

Do I need planning permission for commercial AC?

Most internal installations do not require planning permission. External condenser units on listed buildings, in conservation areas, or above 0.6 m³ in volume may need permission, as may units visible from a highway on principal elevations. AccuTemp checks planning constraints during the site survey and manages any application on your behalf.

What size air conditioning unit do I need?

Cooling load is calculated in kW (or BTU per hour) from floor area, occupancy, glazing area and orientation, equipment heat load and insulation quality. A typical 30 m² office lands around 5 kW (18,000 BTU). AccuTemp's free site survey produces a full CIBSE standard heat load calculation rather than a rule of thumb estimate, so the specified capacity matches actual peak demand.

How much does commercial air conditioning installation cost in the UK?

Wall-mounted single splits start from £1,400 plus VAT installed. Ceiling cassettes are typically £2,800 to £4,500 per indoor unit. VRV/VRF systems run £1,200 to £1,800 per kW installed at project level. Every AccuTemp quote is fixed price after site survey, with no day rate variations.

What's the difference between ducted, cassette and wall-mounted AC?

Ducted units hide above the ceiling and distribute air through grilles. They are the quietest and most discreet, and need 250 mm of ceiling void. 4-way cassettes mount flush in suspended ceiling tiles with 360° airflow, which suits open plan. Wall-mounted units are fastest and cheapest to install with no ceiling work, which suits server rooms and small offices.

How long does a commercial AC system last?

AccuTemp installations consistently deliver 15 to 16 year lifespans on Daikin equipment when paired with planned maintenance. Generic installations without proper commissioning or a maintenance regime typically fail at 5 to 7 years, usually through compressor damage from refrigerant contamination or ignored condensate faults.

Do you handle F-Gas, TM44 and Part L compliance?

Yes, all three in-house. AccuTemp is F-Gas registered and every installation includes the F-Gas register and initial leak check schedule. TM44 inspections are carried out by our own accredited assessors and lodged on the government register. Part L commissioning certificates are issued at handover with the full evidence pack.

Can you integrate with our BMS?

Yes. AccuTemp integrates Daikin and Mitsubishi systems with all major BMS platforms (Trend, Tridium/Niagara, Distech, Priva and Siemens Desigo) via BACnet/IP, BACnet MS/TP or Modbus. Integration scope is agreed with your BMS integrator during design and commissioned jointly.

Do you offer emergency replacement if our existing system has failed?

Yes. AccuTemp typically has temporary cooling on site within 24 hours for a failed system and a permanent replacement quoted within 48. Emergency replacement projects are prioritised in the workshop and installation programme.

What warranty comes with the installation?

Standard Daikin warranty is 3 years on parts and compressor. As a Daikin D1+ Premier Partner, AccuTemp extends this to 5 years on most ranges and up to 7 years on the premium VRV 5 range. Warranty is registered with Daikin at commissioning so cover is active from day one, with no forms for the customer to complete.