Commercial Air Conditioning Installation: what a proper job looks like

Stage 1 — the survey, and what it should actually measure

A survey that consists of counting rooms and taking a photograph of the car park is not a survey. A useful one records the things that drive the load and the things that constrain the installation.

On the load side: room dimensions and volumes, glazing area and orientation, any existing shading, occupancy at peak, lighting type and connected load, and the real IT and equipment load — measured or metered where it matters, because nameplate ratings on IT kit are routinely double the actual draw and designing to nameplate is a classic oversizing route. On the constraint side: where plant can physically sit, what the roof or wall will structurally carry, where refrigerant pipe and condensate can run, where the electrical intake is and what spare capacity it has, and how any of it gets into the building without shutting you down.

Ask to see the output. A survey should produce a written record you can hand to a second bidder so you are comparing like with like.

Stage 2 — load calculation and system selection

The heat load is calculated per zone, not per building, because zones behave differently. A south-facing meeting room with full-height glass and twelve people in it has a completely different profile from the north-facing open-plan area next door, and the system has to serve both simultaneously without one stealing capacity from the other.

This is where the system family gets chosen — split, VRF, chilled water or close control — and the reasoning should be explainable in a sentence. If the answer to "why VRF here?" is "it's what we usually fit", that is not a design. The commercial air conditioning overview sets out when each family genuinely wins.

Diversity is the subtlety worth knowing about. Not every zone peaks at once, so the central plant does not need to equal the sum of the zone loads. Applying diversity sensibly saves real money; applying it too aggressively produces a system that cannot cope on the hottest week of the year. A designer should be able to tell you what diversity factor they used and why.

Stage 3 — electrical capacity, and the DNO question

This is the most common cause of a programme slipping, and it is worth resolving early because it sits outside your contractor's control. Commercial AC is a substantial electrical load. Before anything is ordered, someone needs to establish the existing incoming supply capacity, the current maximum demand, and whether the new plant fits inside the headroom.

If it does not, you are into an application to the Distribution Network Operator for a supply upgrade. Those have their own timescales and their own costs, and they are not fast. Finding this out in week two of a project is an inconvenience; finding out the week before commissioning is a serious problem. Where headroom is genuinely tight, options include staging the installation, adding local load management, or selecting equipment with a lower starting current.

Stage 4 — installation, in a building that is still working

Most commercial AC goes into occupied buildings, which makes sequencing as much of the design as the pipework. The practical questions: which areas can be handed over to the installer and when, what work has to happen out of hours, how noise and dust are contained, how fire compartmentation is maintained while penetrations are open, and what the fallback is if a zone loses cooling mid-installation.

The physical work itself covers refrigerant pipework — brazed under an inert gas purge, pressure-tested and evacuated to a proper vacuum before charging, because moisture left in a system is a slow-motion failure — electrical containment and isolation, condensate drainage with adequate falls and traps, structural support for external plant, and fire stopping at every penetration. Condensate is worth singling out: a surprising share of "the air conditioning is leaking" callouts are a blocked or badly-fallen condensate drain rather than a refrigerant issue at all.

External plant noise deserves attention before installation, not after a complaint. A BS 4142 assessment compares the plant's rating level against the existing background at the nearest noise-sensitive receptor. If there are residential neighbours, this can dictate condenser location, attenuation or night-time operating limits, and it is far cheaper to design around than to retrofit acoustic treatment.

Stage 5 — refrigerant safety and charge limits

The move to lower-GWP refrigerants has brought a design constraint that did not used to bite. R32 and R454B are classified A2L — mildly flammable — and BS EN 378 sets maximum refrigerant charge relative to the volume of the smallest room a system serves.

In practice this means a system serving several small rooms may not legally take the charge that the same duty would need in one large space. The mitigations are real engineering decisions: splitting the system, relocating indoor units, adding ventilation or leak detection, or choosing a different system architecture entirely. This is also why a like-for-like swap of an old R410A system is not always permissible — see air conditioning replacement. Where R290 (propane) is used, DSEAR applies as well.

Stage 6 — commissioning, and why it is not a formality

Commissioning is where a correctly-designed, correctly-installed system is turned into one that actually delivers. It covers verifying the refrigerant charge by superheat and subcooling rather than by weight alone, setting and measuring airflows at each terminal, balancing zones against each other, configuring and testing the controls including schedules and setpoint limits, and running the system through both heating and cooling modes to prove changeover.

You should receive a commissioning record with measured figures in it — not a tick sheet. If the document says "airflow: satisfactory" rather than giving a number, it is not evidence of anything. Make this record a contractual deliverable up front; it is the single best protection against a system that quietly underperforms for a decade.

Stage 7 — handover, and starting the compliance clock

At handover you should get O&M manuals, as-installed drawings, the commissioning record, warranty documentation with its conditions clearly stated, and — importantly — the F-Gas record started. That record is your legal responsibility as operator from the day the system is charged, not from the first service visit.

Two things to settle before the installer leaves. First, the maintenance regime: warranties on commercial plant are routinely conditional on documented planned maintenance, and a warranty claim refused because there is no service history is an expensive way to learn that. Second, if the installed effective rated output takes the building above 12 kW — including by aggregation with AC that was already there — the TM44 inspection duty applies and the clock is running. Both are covered on the servicing and TM44 page.

What drives the installed price

Equipment is the visible cost and rarely the variable one. What actually moves an installation quote:

• Access. Ground-level plant versus a rooftop lift with a crane, a road closure and a permit is a large swing on an otherwise identical system.
• Pipe and cable routes. Long or awkward runs through occupied floors add labour, containment and making good.
• Electrical work. Anything from a new sub-main to a full DNO upgrade.
• Out-of-hours working. Common in retail and hospitality, and it carries a premium.
• Builder's work. Penetrations, fire stopping, structural support, decoration.
• Acoustic mitigation where BS 4142 requires it.

Indicative figures are on the AC cost guide, and the funding page covers the capital-allowance routes for plant and machinery.

Frequently asked questions

How long does a commercial air conditioning installation take?

A single split is usually a one to two day job. A small multi-split suite is typically a week. A multi-zone VRF floor commonly runs two to eight weeks depending on zone count, access and whether work is restricted to out-of-hours. The critical path is normally electrical capacity or craneage rather than the mechanical work itself.

Do I need planning permission for external air conditioning units?

Often not, but it depends on the building and the location — listed buildings, conservation areas and units visible from a highway are the usual triggers, and some local authorities treat larger external plant differently. Noise is assessed separately under BS 4142 where there are nearby noise-sensitive properties. Check with your local planning authority before committing to a condenser position.

Will my electrical supply take a new air conditioning system?

It needs checking before equipment is ordered. Establish the incoming supply capacity and existing maximum demand, then compare against the new load. If there is not enough headroom you may need a DNO supply upgrade, which has its own lead time and cost, so this should be resolved at design stage rather than discovered late.

Can you install air conditioning while we stay open?

Usually yes, with sequencing. The work is broken into zones, noisy or disruptive activities are moved out of hours, and fire compartmentation is maintained while penetrations are open. It is worth agreeing the zone-by-zone programme and the out-of-hours element up front, because both affect the price.

What should I get at handover?

O&M manuals, as-installed drawings, a commissioning record containing measured figures rather than tick boxes, warranty documentation with its conditions stated, and the F-Gas record started. If the effective rated output puts the building over 12 kW you should also be told that the TM44 inspection duty now applies.

We install VRF and VRV, split and multi-split, chilled-water and close-control systems across the UK. See the commercial air conditioning overview, the cost guide, or request a quote.