Anticipating the Smart Grid

12/13/2013


How the Smart Grid will affect building operators, designers

Now that a basic understanding of how the Smart Grid will eventually operate has been established, and the financial incentives have been identified, an intelligent determination of the features an individual building will need to reach its full potential on the Smart Grid can be explored. Without the preceding background information, the uninformed operator and designer could fall for the next fad touting Smart Grid integration—whether cost- and operationally effective, or not. 

Advanced Metering Infrastructure: AMI is the power industry term for the overall infrastructure including electronic hardware, data management software, and local building smart meters that will allow all the market players to communicate power usage data securely, efficiently, and, most importantly, in real time. For building operators and designers, the component of interest and responsibility is the smart meter. 

For the data that a smart meter collects to be useful upstream, it has to be as targeted as possible. To take advantage of peak demand saving incentives, the peak demand loads must be isolated from all other metered loads. Examples of these peak demand loads include major power consuming HVAC equipment such as chillers, air handlers, and pumps and cooling towers. In larger facilities and campus facilities, these loads should be submetered further to enable determination of power usage, not only by building or area, but also by operational priority. 

Examples of the need to categorize based on operation priority include mission critical servers for financial institutions or major life safety equipment in a larger commercial building that cannot be shunted for any reason regardless of the financial incentive from the utility. If they are on the same power infrastructure as general tenant spaces—or support spaces in the case of owner occupied buildings—the entire power demand of the co-mingled systems is taken off the table for eventual utility incentives. As such, it is imperative for building operators and designers to be able to segregate critical systems from noncritical and support systems. Typically, for most businesses, the cost impact of reduced productivity from even noncritical systems may be too great compared to the potential utility incentives that are being offered. As such, it is important for the entire building management and operations team to establish the true costs and benefits of any DR scheme and agree to cutbacks only where the impact of the reduction makes overall financial sense. After the determination of appropriate systems is made, then only those sub-systems need to be isolated and tracked through the AMI. 

Design, renovation of power distribution: The critical issue at the local building level is the efficacy of the power distribution infrastructure. The promise of the Smart Grid is to allow buildings to help their local utilities manage peak power demand in return for financial incentives. The facility electrical designer has a number of options to implement a smart metering infrastructure into new and existing buildings. The common feature among all solutions involves a central signal from the utility that a curtailment event is required. Typically, this communication component is by the utility and is a part of the actual utility meter. The two general approaches the building owner can implement include a more rigid solution and a more flexible solution. Each has its pros and cons. In the rigid solution approach, the designer provides smart breakers for various power circuits for non-emergency, non-essential loads that he or she can actively disable based on a hierarchy similar to Table 1. This rigid solution, though more invasive to the building’s power infrastructure and thus higher first cost, ensures a higher level of certainty that curtailment loads will meet contractual requirements of a DR agreement. Alternatively, a more flexible solution is to allow the BAS to send signals to various equipment controllers or even to smart panelboards to either raise setpoint temperatures or other parameter settings that will produce the desired demand reduction in HVAC systems, selectively shutting off particular lighting circuits to create step dimming (most economical), or sending a signal to a lighting control panel to dim all or specific lighting fixtures or circuits to achieve desired lighting reductions. The risk to this solution is that the reductions may not always meet the reduction targets based on the intricacies of BAS sequencing, safeties, and overrides. The following describes the general design considerations to implement these options. 

Table 1: Sample building power load classification and prioritization. Courtesy: CCJM Engineers

For the rigid solution, the challenge to implement smart breaker load shedding is the redesign and re-installation of existing power distribution to the extent necessary to allow isolating non-essential power loads at the scale that meet the requirements of the utility offering the DR incentive. The solution is a balancing act. In some situations, it will require selective re-feeding of feeders from comingled panels to dedicated panels that are on the smart metered non-essential feed. In most instances, the most cost-effective solution may be to isolate the non-essential loads, wherever they may be fed from, using smart breakers that have a shared communication protocol—typically wireless—with the smart metering system. This allows the maximum penetration into the building’s power distribution infrastructure and allows multiple levels of control over non-essential and even noncritical loads, depending on the incentives that are being offered. 

For new buildings, it is imperative for electrical designers, building owners, and building operators to establish a hierarchy of specific targeted and critical loads to segregate those that the building owner has determined are “on the table” during eventual DR agreement negotiations. After the loads are classified, the electrical designer can proceed with a power distribution scheme that not just allows originally installed components to be properly segregated, but also anticipates future growth of the loads by category. Table 1 offers an example of the categories and sample loads that may be established to help define the overall power distribution system and provide guidelines for future expansion and renovation within the building. 

Figure 3: This single line diagram shows a typical smart panel and breaker implementation. Courtesy: CCJM EngineersThe flexible solution also requires some level of upgrade to the power distribution. However, most of the curtailment actions can be implemented through modifications to BAS sequence of operations and lighting controller sequencing. In new construction, the designer may choose to include smart panelboards and smart breakers to allow a hybrid solution that includes BAS sequences of operations tailored to lowering power demand through raised thermal setpoints in the cooling season and lowered setpoints in the heating season, and also implementing direct shunting of specific power circuits where it makes more economical sense to isolate non-essential loads and simply turn them off instead of variably reducing capacity. 

Most small commercial HVAC equipment does not have an option to variably reduce performance; it is simply on/off. For those devices, shutting power off through a smart breaker may be the most practical approach. For HID lighting, the only practical load reduction scheme is to segregate a portion of the lighting to specific circuits that can be shut off when required. Fluorescent lighting may be dimmed using dimming ballasts, but the cost of the premium ballasts may outweigh any utility-based financial incentive or extend the payback beyond acceptable limits. The more practical solution is to simply route certain fixtures to dedicated circuits that can be selectively shut off through lighting controller relays or smart breakers to simulate a step dimming solution that is acceptable to the building occupants, life safety requirements, and curtailment requirements (see Figure 3). Alternatively, where light levels must remain more uniform, fixtures may be provided with dual ballasts to reduce a portion of lamps within each fixture in certain coverage areas.

Wireless, smart meter and panel/BAS integration, renewable energy sources, and electric vehicle are technologies on the horizon that will directly affect commercial buildings and are worth further exploration. 



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