AC CL 1.7 - Sampling Rules
Posted by Mike Gordon on 22 July 2015 12:00 PM


NOS level: 3 & 4

Scope: England & Wales and Northern Ireland


Air Conditioning Inspections Sampling Rules

With regard to onsite sampling, the minimum number of units sampled on site needs a more detailed clarification to both Energy Assessors (EA) and auditors. On consideration the key requirement is to clearly define a minimum sample depending on what type of system components are present.


To revise the text of CIBSE TM44 section 1.7.2 on sampling. The following text replaces the text in the printed edition of TM44.

Revised text for TM44 section on sampling.

1.7.2 Sampling

The primary purpose of the air conditioning inspection is to assess the relative energy efficiency of the installation, and to identify where there may be scope for energy savings. For larger installations it is not cost effective to inspect every component, and so in these cases it may be appropriate to inspect a sample number of components of certain types.

The following rules apply to the preparation of any sampling programme for any air conditioning installation.

Central Plant

All central chiller plant must be inspected.

For central air handling plant a minimum of ten units or 30%, whichever number is the greater, must be inspected. The requirement also applies to any central air handling plant which does not directly deliver cooling but which is a part of a system which is capable of delivering cooling.

Wherever possible, the air volume and set points should be determined for all air handling units, and sampling is not permitted.

Packaged systems

Where an installed system consists of a series of packaged cooling plant components (including ‘Versatemp’ type units), then a 10% sample of the total number of outdoor units must be inspected, with a minimum of 3 units being sampled. In addition an equal number of indoor units must be inspected.

Indoor units for packaged systems may include fan coil units and cassettes.

Terminal Units for Centralised Systems

A 2% sample of the total number of terminal units must be inspected, with a minimum of 5. For very large systems where consistent conditions are found a maximum of 20 units

may be applied.

Terminal units for centralised systems may include VAV terminals, fan coil units or chilled beams, local heat recovery and ventilation units.

An air conditioning EA must take a representative sample of the installation on site, having regard to the age and size/capacity of the components. While the minimum number of components must always be inspected, an EA may choose to include a larger sample to improve the quality of the Air Conditioning Inspection Report being provided.

If different makes of units are present on site then at least one of each make must be inspected.

If observations of any unit type are found to be inconclusive (where the inspection has identified a problem or area of concern) then further units must be sampled where more units of that type are available.

These sampling rules should ensure that a reasonable minimum number of plant items are inspected. The sampling required for larger items of plant is more stringent, reflecting the fact that these items of plant will demand a greater proportion of the energy used and are also more likely to contain more refrigerant, depending upon the nature of the equipment.

The EA must confirm the sampling size chosen, the reasons for selecting that sample size and that a representative inspection has been carried out. A clear record of the sampling applied and the justification for any selections should be prepared by the EA and will be used in an audit of their work. Where a sample inspection has been carried out this must be recorded in the Air Conditioning Inspection Report Certificate.