by Ben Gries, PE, LEED AP
Choosing the right HVAC system for your building may not be an easy task, complicated by the fact that there is no “right” answer. There are many types of HVAC systems and all have unique attributes. It is important to consider the application, use and the project’s goals to determine which characteristics, and ultimately which system, is best suited.
The use of the building can drive many aspects, from the architecture to the MEP systems. School buildings are very different from office buildings and hospitals are very different from industrial buildings. It goes even further — Is it a primary school or college building? Is it a private school or public school? Is the hospital a regional medical center or a behavioral health facility? Understanding the use of the building helps narrow down the appropriate HVAC systems for comparison.
Location has a major effect on the HVAC system as well. How does the local climate contribute to the building load? Is the elevation high or low? Is the climate wet or dry? What utilities are available at the site? What are the costs of those utilities? What is the clarity of the sky? What is the normal average windspeed? Are there natural weather events that need to be accommodated? Is the location urban, suburban, rural or isolated? Are there cultural/social norms that need to be accommodated?
Another important aspect is who owns the building and who uses it; frequently these are different people with different expectations. An owner that occupies their building may be interested in total cost of ownership of a system. An owner that leases a building may just be interested in initial costs. A single building owner may prefer a simple system with limited maintenance. A multi-building owner may prefer durable, long-lasting equipment that is consistent from building to building. An occupant may want individual control of their spaces rather than being on a group system. The building owner and user play an important role in determining the system type.
Project goals are very important as well. Is this building pursuing a certification or performance goal? Are there proformas that need to be met to ensure project funding? Does the building need to be flexible, accommodating many different uses, tenants or arrangements? Are their specific temperature or humidity requirements to satisfy occupant needs or specific exhibits that will occupy the space? Is there a specific timeline, energy use, initial cost or maintenance needs that must be accommodated?
Answering all of these questions can be difficult, especially in the initial, conceptual phase of the project, but discussing them can help narrow the HVAC system possibilities. There are many types of HVAC systems — water-cooled, air-cooled, gas-fired, geothermal and even passive systems. What system is right for your building?
Here’s a quick overview of the various types of systems:
Passive systems don’t require the use of energy to operate, such as earth ducts or windows. Passive systems are very attractive when the lowest possible energy use is desired. They may be good for Passive House applications or locations with mild climates and low heating/cooling loads.
The vast majority of buildings require an active HVAC system. Air-cooled HVAC systems are typically lower in initial cost, but use more energy to operate than comparable water-cooled systems. Water-cooled systems have different maintenance requirements than air-cooled systems. Geothermal systems typically use the least energy, but can have significant initial costs. Hot and chilled water systems are typically very reliable with long life and good equipment interchangeability, but system sophistication may be more than the available staff or service groups can accommodate. Packaged systems may be inexpensive, but have comparatively short service life and can significantly affect the aesthetics of the building.
As you can see, there are many system types, and each has many variations. Discussing project requirements and developing an understanding of the building, as well as the owner’s expectations will drive the system choices. Performing a comparison of those system choices that shows an estimate of initial costs, ongoing energy use and maintenance costs, system characteristics with pros and cons for the specific application and an estimate of the total cost of ownership will help the owner decide the best system for the building and set clear expectations for the system performance.