May 2018 — Establishing and implementing standard operating procedures (SOP) in an effort to improve operations and reduce energy costs can be achieved with little or no layout of capital funds. Numerous studies have been conducted that prove that significant energy savings can be obtained through minor operational changes, such as improved maintenance or repair of malfunctioning equipment.
This article presents guidelines for each of the following types of duct systems:
- Dual-duct systems
- Multizone systems
- Variable air volume systems
- Constant air volume systems
- Steam systems
SOP programs can be developed virtually overnight, but their implementation is continuous. For example, filters have to be changed routinely, HVAC system coils must be kept clean, motor and fan bearings must be lubricated, and lighting fixtures must be cleaned. All of these tasks are essential steps that are included in SOP programs. These programs will form an ongoing process to ensure that equipment operates at peak performance.
The following guidelines will help you to design a comprehensive SOP program for ductwork systems, including dual-duct systems, multizone systems, variable air volume (VAV) systems, constant air volume (CAV) systems, and steam systems. The scope of these guidelines is broad, as many diverse and alternative mechanical systems exist in any given building or facility. Although some of these procedures may not be applicable in your facility, the majority of items listed will be helpful points of reference as you develop and implement your own SOP programs.
While these guidelines are intended to be applicable to facilities across the country, be sure to consult your local building standards and codes for additional details and requirements.
The central unit of a dual-duct system provides both heated and cooled air, each at a constant temperature. Each space is served by two ducts: one duct carries hot air, and the other carries cold air. The ducts feed into a mixing box in each space which, by means of dampers, mixes the hot and cold air to achieve the specific air temperature required to meet load conditions in the space or zone involved. Methods for improving the energy consumption characteristics of this system include the following strategies:
- Lower hot deck temperature and raise cold deck temperature.
- Reduce airflow to all boxes to a minimally acceptable level.
- When no cooling loads are present, close off cold ducts and shut down the cooling system. Reset the hot deck according to heating loads and operate as a single-duct system. When no heating loads are present, follow the same procedure for heating ducts and hot decks. It should be noted that operating a dual-duct system as a single-duct system reduces airflow, resulting in increased energy savings through a lowered fan speed requirement.
- Consider converting to a VAV system when an energy and economic analysis to do so is favorable.
A multizone system heats and cools several zones—each with different load requirements—from a single, central unit. A thermostat in each zone controls dampers at the unit that mix the hot and cold air to meet the varying load requirements of the zone involved. The following steps can be taken to improve energy efficiency of multizone systems:
- Reduce hot deck temperatures and increase cold deck temperatures. While this will lower energy consumption, it also will reduce the system’s heating and cooling capabilities.
- Consider installing demand reset controls, which will regulate hot and cold deck temperatures according to demand. When properly installed and with all hot deck or cold deck dampers partially closed, the control will reduce the hot deck and raise the cold deck temperature progressively until one or more zone dampers is fully open.
- Consider converting systems servicing interior zones to variable volume. Conversion is performed by blanking off the hot deck, removing or disconnecting mixing dampers, and adding low-pressure VAV terminals and pressure bypass.
Variable Air Volume Systems
A VAV system provides heated or cooled air at a constant temperature to all zones served. VAV boxes located in each zone or in each space adjust the quantity of air reaching each zone or space depending on its load requirements. This system automatically reduces the volume of air when space requirements are satisfied. Conserving energy consumed by this system through any of the following ways:
- Lower hot water temperature and raise chilled water temperature in accordance with space requirements.
- Raise air supply temperature to the point at which the VAV box serving the space with the most extreme load is fully open.
- Consider installing static pressure controls for more effective regulation of pressure bypass (inlet) dampers.
- Consider installing fan inlet damper control systems if your system is not presently equipped with this feature.
Constant Air Volume Systems
Most CAV systems are either part of another system, such as a dual-duct system, or serve to provide precise air supply at a constant volume. Opportunities for conserving energy consumed by such systems include the following measures:
- Determine the minimum amount of airflow that is satisfactory and reset the constant volume device accordingly.
- Investigate the possibility of converting the system to variable (step controlled) constant volume operation by adding the necessary controls.
Steam systems use steam as a heat source. The steam can be provided either by an on-site boiler or by district steam. Methods for modifying the steam distribution system are listed below:
- Install insulation on all mains, risers, branches, economizers, water heaters, and condensate receiver tanks where this equipment is not currently in place.
- Add additional shut-off valves for more efficient zone control.
- Install recorder pressure gauges and thermometers to enable continual monitoring of the system.
- Modify equipment as necessary to recover heat going to the sewer. Such reclaimed heat from blowdown can be used for boiler feedwater heating, to heat a portion of the building, to preheat water being supplied to the domestic hot water heater, or to be returned to the boilers.
This article is adapted from BOMI International’s Energy Management and Controls course, part of the SMA and SMT designation programs. More information regarding this course or BOMI International’s new High-Performance Sustainable Buildings credential (BOMI-HP™) is available by calling 1-800-235-2664. Visit BOMI International’s website, www.bomi.org.