THE LIFE SUPPORT THAT BRINGS LIFE TO A BUILDING PART 2

Last month’s publication discussed how an air conditioning system forms the life support of every building and the importance of ensuring that a healthy air quality is maintained within the space.

This edition will discuss how 3 critical design mistakes within the design of a building can negatively impact the performance of an HVAC system and affect the wellbeing of a building.

Mistake # 1 – The condensers on the rooftop must be hidden from the public so a wall must be constructed around the perimeter where the condensers are placed on the rooftop.

The construction of a wall around the perimeter of the condensers may be pleasing to the designer but for the HVAC system, problems will arise when the system is required to operate at its maximum capacity.  

Constructing a wall around the perimeter of the condensers will promote hot air recirculation and cold ambient air will not be drawn over the condenser coils. This will reduce the heat transfer from the refrigerant to the ambient air.

As less heat is rejected on the hot gas side of the refrigerant system, the head pressure will begin to rise. Eventually the head pressure will reach its maximum allowable value and the unit will trip on high pressure. Constant tripping of the unit on high pressure will result in the HVAC system being offline during peak cooling conditions and this will affect the productivity of occupants within the building.

Mistake # 2 – It is okay to construct a wall around the perimeter of the condensers but install louvers in the wall to prevent hot air recirculation.

This comment is a solution and will prevent hot air recirculation around the condenser coils if the condenser fans are able to overcome the pressure drop over the louver and expel the hot air out of the perimeter structure.

Condenser fans are axial type fans that are unable to handle very high pressure drops. Introducing a louver into the system increases the pressure drop which can potentially decrease the airflow that is pulled over the condenser coil.

Decreasing the airflow over the condenser coil will decrease the heat transfer from the refrigerant to the ambient air and will result in the tripping of the cooling unit on high pressure.

Installing louvers in the perimeter wall is a solution provided that the size of the louver is adequate and a small pressure drop exists over the louver. Should such a solution be considered, the designer should consult with the condenser manufacturer and ensure that the condenser fans are able to accommodate the additional pressure drop over the louver.
 Mistake # 3 – Lets extend the existing building and the current HVAC system will have adequate capacity.

The HVAC system can be neglected when performing extensions to an existing building. Additional rooms are added which introduces an additional heat load and increases the fresh air requirements to the existing structure.

Sometimes comments such as “the existing HVAC cooling units have extra capacity so it can handle the additional load.” are made without verification. Making this assumption can be costly as additional plant room space will not be allocated for the installation of new cooling units or inadequate plant room space will be available for the upgrade of the existing cooling units.  
  
The implications of making this assumption will only become apparent once the occupants have moved into the renovated section and experience uncomfortable working conditions.

Rectification of the problem will not be easy as upgrading the existing cooling unit will take the buildings HVAC system offline and trying to find plant room space for the new cooling unit will be problematic if no space is available.

It is important to remember that space should be allocated for the installation of new cooling units should extensions be made onto an existing building. These mistakes can sometimes be overlooked but awareness can help prevent future problems from occurring when constructing a new building or performing renovations onto an existing building.

The HVAC system can often be taken for granted but this is the system that allows occupants to work in a comfortable environment that promotes productivity and happiness.

We have now completed and understand how building constructions can affect the design of an HVAC system. If you would now like to learn what topics you need to discover to become a HVAC expert,  
Wishing you a successful month ahead

ABOUT THE AUTHOR

Michael Young graduated from the University of the Witwatersrand in the field of Mechanical Engineering (B.Sc Mech Eng) in 2008. After he completed his undergraduate studies, he proceeded to work in the HVAC industry whereby he worked in the manufacture, contracting and consulting sector.  

In 2013, Michael qualified as a Professional Engineer (Pr.Eng) with the Engineering Council of South Africa (ECSA) and then founded M&Y Consultants and Trainers (PTY) Ltd whereby he is perusing his passion of helping others within the HVAC&R and Engineering industry through his training courses.

Michael is passionate about helping others and sharing his knowledge and experience that he has gained through working in the industry. 

He is a regular contributor for the Refrigeration and Air Conditioning Africa (RACA) Journal and has also presented technical talks in association with the South African Institute of Mechanical Engineers (SAIMechE), the South African Energy Efficiency Convention (SAEEE) and Data Centre Central Conference.