What is the scope of an air conditioning inspection?

Refrigeration

Refrigeration equipment and its associated heat exchange systems are checked briefly. The inspection looks primarily for indicators of damage or lack of maintenance that would significantly reduce their efficiency from their ‘as new’ state and does not provide high levels of detail.

Effective heat rejection is necessary to maintain the efficiency of the refrigeration system. If outdoor heat rejection equipment is damaged, or its access to adequate flow of air is otherwise reduced by blockage due to dirt or debris, its effectiveness in rejecting heat is reduced and its temperature will be unnecessarily high. This has the effect of reducing refrigeration efficiency and reducing the cooling capacity of the system. It may cause the refrigeration equipment to turn off and on under the action of its own high temperature or pressure cut-out, often without satisfying the building cooling load.

Similarly, effective indoor heat exchange is necessary to maintain the efficiency of the refrigeration system. If this heat exchange equipment is damaged, or its access to adequate airflow is otherwise reduced, its effectiveness in transferring heat to the refrigeration system is reduced and its temperature will be unnecessarily low. This consequentially reduced temperature at the indoor unit increases the temperature difference that the refrigeration system has to maintain, which has the effect of reducing the cooling capacity of the system. It may cause the refrigeration equipment to turn off and on under the action of its low temperature or pressure cut-out, often without satisfying the building cooling load.

Air moving systems

Where installed as part of the system to provide cooling, air moving systems is an important factor in the assessment. The contribution that fans make to the total annual energy consumption of the combined cooling system is likely to be higher than that of the refrigeration plant itself, and there may be a greater potential for improvement.

The effectiveness of how air is delivered can play a part in determining the overall efficiency of the air conditioning system. Where delivery systems are ineffective, a plant that is otherwise efficient may operate for longer periods than necessary. However, the reverse may also be true, in that some delivery systems may interact unfavourably with occupants or control sensors, leading to reduced operation and consequential lack of adequate cooling. Improving some systems, even those operating at good efficiency, could reduce annual energy use.

Important factors to observe are the condition of; damage to; or blockage of filters and heat exchangers, and the fan type and method of control. Ventilation air delivery systems need free access to outdoor air. Where grilles, screens or pre-filters are obscured through damage or by debris, additional energy will be needed to overcome the extra resistance caused by the restriction to air flow, or the system may under-perform in other ways due to reduced air flow rates.

Where systems provide cooled air, admitting air from locations where the local air temperature may be higher than ambient will add to the energy required to achieve cooling to the required temperature. Such locations might include positions near busy roads, in car parks, or where exhaust air from the building could be drawn into the air inlet.

Controls

System controls are assessed in more detail. There could be considerable scope to identify inefficiency due to inappropriate control methods and control settings and poorly located sensors. There may be potential for improvement at low cost. Improving systems might be as simple as adjusting time switches or for cooling or heating thermostats being set correctly. The energy assessor would not reset them, but will report to the building owner or manager.

An investigation of the realised effectiveness of system controls over any significant period of operation would be outside the scope of a simple inspection regime, but a series of physical observations of their layout and operation could give an indication of potential inefficiency, ineffectiveness or misuse.

It might not be possible to investigate some aspects of the layout and operation of controls, particularly in more complex systems. However, enough of the important elements may be accessible for a brief examination. The following important elements of a system’s controls should be assessed during an air conditioning inspection:

• the set temperatures to which the treated spaces are to be conditioned
• the time periods during which they are to be conditioned
• the appropriateness of the control zones, control sensors and their locations
• the potential for cooling to be operated at the same time as heating
• the method of refrigeration capacity control
• the method of air flow rate control

Where systems are controlled by a building management system, it may be necessary for the building manager to arrange for the relevant information to be extracted from the building management system prior to the inspection.

Documentation

The quality, extent and accessibility of relevant information provided before an energy assessor inspects the system has important consequences for the effectiveness and cost of an air conditioning system inspection. Information about the air conditioning systems installed and their operation should be provided to the energy assessor in order for them to be able to carry out the most effective assessment of the system. Incomplete or missing documentation not provided to an energy assessor could reduce the effectiveness of the assessment. It could also increase the cost of the inspection by requiring the energy assessor to locate relevant documentation while on site.

The energy assessor will ask the building owner or manager to provide a list of relevant records; for sight of the principal documents before the site visit; and for site records to be made readily available. Any available documentation must be provided prior to the inspection. This could include, for example, catalogue information and details provided during installation, commissioning and maintenance of the system.

Maintenance

Evidence of any existing planned maintenance schedule or of other recent maintenance activities will be sought. Where documentation clearly shows that equipment and systems are already the subject of regular good practice checking and maintenance procedures, a number of aspects of the inspection and provision of advice may be reduced in scale or omitted.

Advice on improvement options

a) It is likely that an assessment will conclude that the energy efficiency of the system will fall into one of three categories:

• systems where efficiency is clearly impaired due to faults, neglect or misuse
• systems where efficiency is likely to be lower than current accepted minimum provisions due to aspects of design or use
• systems that are acceptably efficient

b) There are three broad levels of advice that the building owner or manager may receive:

• advice on the rectification of faults in the system that are impairing its efficiency as designed
• improvement advice to bring existing systems broadly to a standard of ‘inherent’ efficiency consistent with the current minimum provisions of building regulations or standards
• best practice improvement advice to raise standards even where systems are fully compliant with the current minimum provisions of building regulations or standards

Given the need for simplicity and consistency, the inspection will mainly provide a combination of aspects of a) and b). However, best practice advice may be provided on a generalised basis by referring to other published guidance sources.

A further category of advice which may also be given concerns some systems which may be older and operate with refrigerants which are being phased out, or may have their use and supply restricted under regulations relating to ozone depleting substances. In these cases, the energy assessor may give advice on possible options for future system adaptation to use other refrigerants or for complete replacement. This advice will need to be supplemented by a more detailed assessment when modifications or replacement are to be undertaken.

More detailed information about the inspection process and good practice inspection and maintenance guidance can be found in the CIBSE TM44 guidance (or similar equivalent guidance).