The ultimate objective of any serious energy-conservation program is a central, computer-automated electronic controls system. This integrated system of remote sensors and control devices permits the optimum use of energy in all areas while simultaneously providing the best environment for building occupants. The equipment that should be included in this electronic harness can be divided into five major categories:
1. Air-handling units
2. Hot-water heaters
3. Cooling towers
4. Chillers
5. Boilers
Noteworthy features of each of these categories have been discussed in previous chapters, along with the means to make optimum use of available energy. These energy-conserving projects sometimes have controls, in the form of timers or on/off features, able to operate independently of a central system. Where computer hardware or programming is needed it’s often integral to the controlling device.
In most of the cases discussed heretofore, local control is preferable to a centralized control. It’s also acceptable to employ mechanical and pneumatic devices, especially in circumstances where mechanical vibration, temperature extremes, or limited accessibility are an issue. The staff expertise is another overriding consideration, assuming they can troubleshoot mechanical and pneumatic equipment, and not electronic devices. So, with independent, local nonelectronic control loops already in
place to provide a reasonable degree of energy efficiency, the system will not lose its efficiency and effectiveness if an EMS network malfunctions for any reason.
This is not to advise against the installation of quality electronics, it’s only a reasonable evaluation of the state of the art. Electronic controls look good on paper but do not always work as planned, because of the equipment as well as the operators. If reducing the utility bills is a priority at a facility, then there’s a limit to the exuberance that should be practiced in the pursuit of energy conservation. That limit might aptly be symbolized by the demand portion of the electric bill; it’s this billing that electronic controls are most effective in reducing.
To understand the whole picture better, consider a complete building system, in which all of the equipment is controlled by a central computer. Any computer problem can cause a portion of the system to run wild. More energy than usual may then be used to maintain service to all spaces. This results in a higher peak for that day. This, in turn, affects the electric bill for the entire month—sometimes for the whole year—depending on the billing scheme predicated by the local utility. The smaller the business, typically, the more drastic the effect of any deviation on the demand-use bill. If this happens just once a year, then all the gains from all the projects have been voided in one fell swoop.
The advantage of retaining a degree of local control for each system is that when the network goes down, the system continues to operate at a reasonable level of efficiency This is particularly important at locations remote from a maintenance center or with a minimal (e.g., part-time) engineering staff available to troubleshoot. Indeed, a fail-safe feature is a selling point to such installations, as it reduces the risk inherent in a new energy-management system, making it more feasible to justify the investment to management.
Returning to the issue of the EMS itself, a building with an expected useful lifetime of 10 or more years can very well benefit from a long-range plan that includes the installation of a complete EMS at some point. This decision should be made before beginning any energy-conservation projects, because it affects the selection of any new equipment that is to be installed. For example, most timers and local controls devices come in two varieties: inexpensive stand-alone units and, for a little more money, devices that can be tied directly to an EMS. If a centralized system is foreseen, then spending a little more now for equipment that can be controlled by the EMS later reduces the total cost of the EMS, since some of the new controls will not have to be included in that package.
The following series of projects is a practical sequence of individual projects that leads to a full EMS capable of using the centralized control to the best advantage.
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Excerpt from Energy Conservation Projects.