Despite enormous advances in building-control technologies over recent years, the greatest number of complaints from building occupants still relate to poor comfort. The good news is that this is not a difficult problem to solve. It does, however, require a fundamental change in thinking about how building comfort systems are controlled—and it takes some real effort.
For those ready for the challenge, huge improvements in comfort and building operating efficiency are waiting. Current HVAC control strategies were developed before the era of networked digital controls, and the control of the heating and cooling systems has never been effectively connected to the actual thermal requirements of spaces served. For example, most cooling plants don’t use the control network to determine chilled-water temperature or flow requirements, nor do air systems adjust supply-air temperature and flow based on information from occupied spaces. Instead, a crude system of mechanical devices, valves, and dampers still control HVAC capacity by restricting or diverting flows at part-load conditions. This outdated mechanical means of capacity and distribution control wastes energy and is directly responsible for the problems that most commonly cause occupant discomfort.
The key to more efficient and comfortable buildings is to make the change from current mechanical methods of capacity and distribution control to more efficient and effective methods that fully utilize a control network and its advanced logic.
To improve this obsolete method of comfort system operation requires an important first step: the instrumentation in the building spaces needs to be increased so that the controls can react to space conditions. Dating from the days of pneumatic controls, most buildings continue to incorporate only a single space-temperature sensor for each zone. This was all that could be accommodated with controls of the past, but if we are to improve comfort, it is imperative that the control system “see” the conditions in every occupied space. This requires—at a minimum—a space-temperature sensor in every closed-door office, and multiple sensors in large open spaces. It also requires that the occupancy condition at each temperature sensor location be known.
With modern control systems, this is neither difficult nor expensive to accomplish. Temperature sensors are not expensive, and by integrating occupancy sensor-based lighting controls into the comfort control system, the temperature and occupancy of every occupant location can be determined.
With this information, an entirely new approach to comfort-system control that is far more efficient and effective can be implemented using the same or very similar equipment and configurations now employed. However, instead of generating design day levels of heating and cooling, these systems are regulated at their sources to provide only what is needed to the occupied spaces. Then, the valves and dampers act merely as balancing devices instead of primary-control devices. As a result, the temperature and pressure differences across these devices and the potential for the mechanical control to adversely affect comfort are all greatly reduced. The outcome is a dramatic improvement for both energy performance and comfort.
But, if this approach is so successful and cost effective, why is it not universally applied today? I think the answer may be as simple as this: most in the industry are just unwilling to try new approaches. However, since you are reading this newsletter and have taken the time to read this article, you are probably ready to try new approaches. Take up the challenge. Whether you are a designer, contractor, owner, or operator, you have an opportunity to do something different that will make a big difference for a building, and potentially for our industry. I urge you to seize the opportunity to control for comfort.
I invite your thoughts, comments, and ideas about this article. Please contact me at thc@hartmanco.com
Thomas Hartman, PE, is principal of The Hartman Co., Georgetown, TX. He can be reached at 254/793-0120, or by e-mail at thc@hartmanco.com