In this subsection some energy conservation measures (ECMs) commonly recommended for commercial and industrial facilities are briefly discussed. It should be noted that the list of ECMs presented below does not pretend to be exhaustive nor comprehensive. It is provided merely to indicate some of the options that the energy auditor can consider when performing an energy analysis of a commercial or an industrial facility. However, it is strongly advised that the energy auditor keeps abreast of any new technologies that can improve the facility energy efficiency. Moreover, the energy auditor should recommend the ECMs only after he performs an economical analysis for each ECM.
1. Building Envelope
For some buildings, the envelope (i.e., walls, roofs, floors, windows, and doors) can have an important impact on the energy used to condition the facility. The energy auditor should determine the actual characteristics of the building envelope. During the survey, a sheet for the building envelope should be established to include information such as materials of construction (for instance, the level of insulation in walls, floors, and roofs) and the area and number of various assemblies of the envelope (for instance, the type and the number of panes for the windows should be noted). In addition, comments on the repair needs and recent replacement should be noted during the survey.
Some of the commonly recommended energy conservation measures to improve the thermal performance of building envelope are:
1.1. Addition of Thermal Insulation.
For building surfaces without any thermal insulation, this measure can be cost effective.
1.2. Replacement of Windows.
When windows represent a significant portion of the exposed building surfaces, using more energy-efficient windows (high R-value, low-emissivity glazing, airtight, etc.) can be beneficial in both reducing the energy use and improving the indoor comfort level.
1.3. Reduction of Air Leakage.
When the infiltration load is significant, leakage areas of the building envelope can be reduced by simple and inexpensive weather-stripping techniques. The energy audit of the envelope is especially important for residential buildings. Indeed, the energy use from residential buildings is dominated by weather since heat gain and/or loss from direct conduction of heat or from air infiltration/exfiltration through building surfaces accounts for a major portion (50 to 80%) of the energy consumption. For commercial buildings, improvements to the building envelope are often not cost-effective due to the fact that modifications to the building envelope (replacing windows, adding thermal insulation in walls) typically are very expensive. However, it is recommended to systematically audit the envelope components not only to determine the potential for energy savings but also to ensure the integrity of its overall condition. For instance, thermal bridges, if present, can lead to heat transfer increase and to moisture condensation. The moisture condensation is often more damaging and costly than the increase in heat transfer since it can affect the structural integrity of the building envelope.
2. Electrical Systems
For most commercial buildings and a large number of industrial facilities, electrical energy cost constitutes the dominant part of the utility bill. Lighting, office equipment, and motors are the electrical systems that consume the major part of energy usage in commercial and industrial buildings.
Lighting for a typical office building represents, on average, 40% of the total electrical energy use. There are a variety of simple and inexpensive measures to improve the efficiency of lighting systems. These measures include the use of energy-efficient lighting lamps and ballasts, the addition of reflective devices, de-lamping (when the luminance levels are above the recommended levels by the standards), and the use of day lighting controls. Most lighting measures are especially cost-effective for office buildings for which payback periods are less than 1 year.
2.2. Office Equipment.
Office equipment constitutes the fastest growing part of the electrical loads, especially in commercial buildings. Office equipment includes computers, fax machines, printers, and copiers. Today, there are several manufacturers that provide energy efficient office equipment such as those that comply with U.S. EPA Energy Star specifications). For instance, energy efficient computers automatically switch to a low-power “sleep” mode or off mode when not in use.
The energy cost to operate electric motors is a significant part of the operating budget of any commercial and industrial building. Measures to reduce the energy cost of using motors include reducing operating time (turning off unnecessary equipment), optimizing motor systems, using controls to match motor output with demand, using variable speed drives for air and water distribution, and installing energy-efficient motors. Table 4.6.3 provides typical efficiencies for several motor sizes.
In addition to the reduction in the total facility electrical energy use, retrofits of the electrical systems decrease the cooling loads and, therefore, further reduce the electrical energy use in the building. These cooling energy reductions, as well as possible increases in thermal energy use (for space heating), should be accounted for when evaluating the cost-effectiveness of improvements in lighting and office equipment.
3 HVAC Systems
The energy use due to HVAC systems can represent 40% of the total energy consumed by a typical commercial building. The energy auditor should obtain the characteristics of major HVAC equipment to determine the condition of the equipment, its operating schedule, its quality of maintenance, and its control procedures. A large number of measures can be considered to improve the energy performance of both primary and secondary HVAC systems. Some of these measures are listed below:
3.1. Setting up/back thermostat temperatures.
When appropriate, set-back of heating temperatures can be recommended during unoccupied periods. Similarly, set-up of cooling temperatures can be considered.
3.2. Retrofit of constant air volume systems.
For commercial buildings, variable air volume (VAV) systems should be considered when the existing HVAC systems rely on constant-volume fans to condition part or the entire building.
Fig 4.3.1: Variable Air Volume System (VAV)
3.3. Installation of heat recovery systems.
Heat can be recovered from some HVAC equipment. For instance, heat exchangers can be installed to recover heat from air handling unit (AHU) exhaust air streams and from boiler stacks.
3.4. Retrofit of central heating plants.
The efficiency of a boiler can be drastically improved by adjusting the fuel-air ratio for proper combustion. In addition, installation of new energy-efficient boilers can be economically justified when old boilers are to be replaced.
3.5. Retrofit of central cooling plants:
Currently, there are several chillers that are energy efficient and easy to control and operate and are suitable for retrofit projects.
It should be noted that there is a strong interaction between various components of a heating and cooling system. Therefore, a whole-system analysis approach should be followed when retrofitting a building HVAC system. Optimizing the energy use of a central cooling plant (which may include chillers, pumps, and cooling towers) is one example of using a whole-system approach to reduce the energy use for heating and cooling buildings.
4 Compressed Air Systems
Compressed air has become an indispensable tool for most manufacturing facilities. Its uses range from air-powered hand tools and actuators to sophisticated pneumatic robotics. Unfortunately, staggering amounts of compressed air are wasted in a large number of facilities. It is estimated that only about 20 to 25% of input electrical energy is delivered as useful compressed air energy. Leaks are reported to account for 10 to 50% of the waste while misapplication accounts for 5 to 40% of the loss of compressed air. To improve the efficiency of compressed air systems, the auditor can consider several issues including whether compressed air is the right tool for the job (for instance, electric motors are more energy efficient than air-driven rotary devices), how the compressed air is applied (for instance, lower pressures can be used to supply pneumatic tools), how it is delivered and controlled (for instance, the compressed air needs to be turned off when the process is not running), and how the compressed air system is managed (for each machine or process, the cost of compressed air needs to be known to identify energy and cost savings opportunities).
5 Energy Management Controls
Because of the steady decrease in the cost of computer technology, automated control of a wide range of energy systems within commercial and industrial buildings is becoming increasingly popular and cost effective. An energy management and control system (EMCS) can be designed to control and reduce the building energy consumption within a facility by continuously monitoring the energy use of various equipment and making appropriate adjustments. For instance, an EMCS can automatically monitor and adjust indoor ambient temperatures, set fan speeds, open and close air handling unit dampers, and control lighting systems. If an EMCS is already installed in the building, it is important to recommend a system tune-up to ensure that the controls are operating properly. For instance, the sensors should be calibrated regularly in accordance with manufacturers’ specifications. Poorly calibrated sensors may cause an increase in heating and cooling loads and may reduce occupant comfort.
6 Indoor Water Management
Water and energy savings can be achieved in buildings by using water-saving equipment instead of the conventional fixtures for toilets, faucets, shower heads, dishwashers, and clothes washers. Savings can also be achieved by eliminating leaks in pipes and fixtures. Table 4.6.4 provides the typical water usage of conventional and water-efficient fixtures. In addition, Table 4.6.4 indicates the hot water consumption by each fixture as a fraction of the total water usage. With water-efficient fixtures, a savings of 50% of water use can be achieved.