Troubleshooting HVAC


HVAC systems provide the Fresh Air requirements for building occupants and make-up to replace air lost from a building from pressurisation or extract systems. In addition, they can provide both the heating and cooling function to offset building fabric and internal component losses or gains. Lastly, in some circumstances the HVAC systems are used to control humidity levels. However, not all HVAC systems are designed correctly or perform in accordance with their intended design.

Each component of HVAC (Heating Ventilation Air Conditioning) systems require detailed selection, assembly in the correct sequence and the application of an appropriate control strategy to enable the system as a whole to operate properly and to achieve the result first envisaged at the design stage. A detailed analysis of building heating and cooling loads, net air balance (pressurisation vs leakage), and net moisture gains/losses is required to determine the correct capacity of each of the elements which make up the HVAC system. If one or more of these components is incorrectly sized the entire system will not function correctly. Even if the system was designed correctly at the design stage there is always the possibility that the components installed do not match the performance requirements of the specification. Lastly, even if the entire system was designed and installed correctly in the first instance, later modifications of the system without due regard to the effects of the modifications on the whole system can lead to a system which performs poorly or not at all.


Common pitfalls:

  • Incorrect allowance for building infiltration/exfiltration and the consequential effect this has on heating/cooling loads and the quantity of Fresh Air required to meet the surplus/deficit.
  • Miscalculation of pressure drops along the index leg of the distribution system resulting in AHU Fan sizes which are too large or too small for the intended load.
  • Lack of understanding of the psychrometric processes inside the Air Handling Plant leading to overly dry buildings in winter or plant dripping with condensation.


Callidus Design provide a troubleshooting service for the HVAC system in question where we will reverse engineer the system components to determine if they are capable of meeting their intended function. This is most easily achieved where there are sufficient records available for the installed system from the O&M (Operation & Maintenance) Manual. Where this information is not available the system can be surveyed and measured to achieve the same end result. If a flaw in the design of one or more components is determined then Callidus Design can provide a subsequent design function to specify the requirements for the rectification of the said components.