The scope of an inspection
Posted by Mike Gordon on 22 July 2015 12:25 PM
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 level 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 consequent 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, 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 consequent lack of adequate cooling. Improving some systems, even at good efficiency, could increase 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 by damage or debris, additional energy will be needed to overcome the extra resistance caused by the restriction to 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.
System controls are assessed in more detail. There could be considerable scope to identify inefficiency due to inappropriate control methods, incorrect control settings and poorly located sensors, and there could be much potential for improvement at low cost. Although discovered faults might be as simple as time switches or cooling or heating thermostats being incorrectly set, 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, sufficient of the following important issues should be accessible to a brief examination:
Where systems are controlled by a building management system, it may be necessary for the building manager to arrange for relevant aspects of this information to be extracted from the building management system prior to the inspection.
The quality, extent and accessibility of relevant information provided before an air conditioning energy assessor visits an installation has important consequences for the effectiveness and may increase the cost of the inspection. Experience has shown this information is often missed and energy assessors have to spend time trying to locate relevant documentation. This is not effective use of the assessor’s time on site and without the information it is difficult to properly estimate the cost of an inspection.
The air conditioning energy assessor will ask the building owner or manager to provide a list of relevant records, sight of the principle ones before visiting the site and for site records to be made readily available. Any available documentation for the air conditioning system 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. The quality and accessibility of relevant information provided before an inspection takes place may reduce the time taken to complete the inspection and may reduce the cost of an inspection.
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 energy inspection and provision of advice may be reduced in scale or omitted.
Advice on improvement options
Three levels of energy efficiency are likely to be found when systems
Correspondingly to these, there are three broad levels of advice that the building owner or manager may receive:
Given the need for simplicity and consistency, the inspection will mostly provide a combination of aspects of a) and b) only. However, best practice aspects may be provided on a generalised basis by providing reference 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 having their use and supply restricted, under regulations relating to ozone depleting substances. In these cases the assessor may give advice on possible options for future system adaptation to use other refrigerants, or 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 Chartered Institution of Building Service Engineers TM44 guidance: Inspection of air conditioning systems - a guide to Energy Performance of Buildings Directive compliance, or similar equivalent guidance.