When designing a building, there are some things that are pretty straightforward: plumbing fixtures need water supply and drain; you need lighting to see; power for that lighting and other equipment; and you may also want some telecommunications and life safety/security systems – the things that Make Buildings Work. The fixture types that you choose are covered in the details of the project design, but the big rock stuff is pretty standard.
You also must heat, ventilate and cool the building. Do you know how many systems types there are available to accomplish that? Systems can range from unitary equipment in each space to central plant equipment with extensive distribution systems. To assist in this important big rock decision-making, you should consider more than just first cost and even life cycle cost. The following questions need to be answered to select the HVAC system that will work the best for you during the lifespan of the building:
This is usually the first question. What is the probable initial installation cost for the system and does it fit into my overall project budget? Remember, you get what you pay for so lowest cost isn’t always best for the life of the building.
How long will the system operate efficiently and reliably before you must consider system replacement? Some components of systems have 15-year life expectancies while others have distribution life expectancies of up to 50 years.
Does the system have the flexibility to accommodate floor plan changes and system modifications in the future? Some systems require a complete shutdown that could affect adjacent occupied spaces during minor renovations.
How much individual room temperature control is required and does the selected system accommodate that? Grouping similarly-occupied spaces with common exterior exposures is not possible with all systems, or may not be economically feasible.
Are there areas of the building that must maintain minimum, or even maximum space humidity limits? Not all HVAC systems can provide individual, or even any humidity control.
Where will equipment be located and will it be visually acceptable? Sometimes equipment can be hidden in mechanical spaces or screened on the roof, but these measures add cost to the project.
How difficult will it be to perform annual or bi-annual maintenance if equipment is located on the roof or central in a mechanical rooms versus being distributed and located above accessible ceilings or in small closets? Make sure that the design allows clearance space around equipment to perform this maintenance.
Is the equipment noisy and can it be located remote from sound-sensitive spaces? Noise-generating compressors, high velocity fans, and vibrating pumps are best located outdoors or in mechanical rooms with proper screening and acoustical control.
A life cycle cost model can be done to aid in making these decisions, but it cannot address every decision factor listed above — and there may be more factors that are important to you as the building owner.
Sometimes, the people who are responsible for maintaining the building systems are simply more comfortable with one system over the other due to past experiences, which could be a cost savings if extensive training or outside expertise is not required. Your mechanical engineer should discuss these options with you to select the HVAC system that is best you.