Energy Efficiency And HVAC Technology
Understanding the interdependence of HVAC technologies with one another, as well as with other electrical loads and maintenance and operations practices, is integral to specifying individual HVAC technologies and whole systems. As with lighting, technologies and possible configurations for HVAC systems are vast and varied.
The following overview offers a quick reference to key considerations with some of the most effective technologies. As with lighting, trial installations are a good idea; so is working with manufacturers and distributors.
Getting the most from HVAC controls
Because a building's performance can be dramatically improved by installing and fully using HVAC controls, it is essential to understand and correctly use those controls. The place to start is with a close look at what is really transpiring in your building, 24 hours a day, seven days a week.
What is happening with each piece of equipment? On holidays? Weekends? As the seasons change, do your operations change? It is important to understand where and how energy is being consumed in order to identify where waste is occurring and where improvements can be implemented. Then it is imperative to ask, "What exactly do I want these controls to do?"
Energy management systems (EMS) are designed to run individual pieces of equipment more efficiently and to permit integration of equipment, enhancing performance of the system. In a typical EMS, sensors monitor parameters such as air and water temperatures, pressures, humidity levels, flow rates, and power consumption. From those performance points, electrical and mechanical equipment run times and setpoints are controlled.
Seven-day scheduling provides hour-to-hour and day-to-day control of HVAC and lighting systems and can account for holidays and seasonal changes. As the name implies, night temperature setback allows for less cooling in summer and less heating in winter during unoccupied hours.
Optimal start/stop enables the entire system to look ahead several hours and, relative to current conditions, make decisions about how to proceed; this allows the system to ramp up slowly, avoiding morning demand spikes or unnecessary run times.
Peak electrical demand can be controlled by sequencing fans and pumps to start up one by one rather than all at once and by shutting off pieces of HVAC equipment for short periods (up to 30 minutes), which should only minimally affect space temperature. Economizers reduce cooling costs by taking advantage of cool outdoor air. Supply-air temperature-reset can prevent excessive reheat and help reduce chiller load.
An EMS can provide an abundance of information about building performance, but someone has to figure out what they want the EMS to do and then give it directions. Calibrating controls, testing and balancing are key to any well-maintained HVAC system, but are especially critical to optimize control efforts.
Variable speed drives and energy-efficient motors
Variable speed drives (VSDs) are nearly always recommended as a reliable and cost-effective upgrade.
VSDs are profitable where equipment is oversized or frequently operates at part-load conditions. Savings of up to 70 percent can be achieved by installing VSDs on fan motors operating at part-load conditions. They may be applied to compressor or pump motors and are generally used in variable air volume (VAV) systems. They are also cost effective in water-side applications. Backward-inclined and airfoiled fans are the best VSD candidates.
Air-handler configurations controlled by variable inlet vanes or outlet dampers squander energy at part-load conditions. Using throttle valves to reduce flow for smaller pumping loads is also inefficient. The efficiency of motors begins to drop off steeply when they run at less than 75 percent of full load; they can consume over twice as much power as the load requires. VSDs operate electronically and continually adjust motor