Commissioning: Preparing for Energy Metering And Management
Continuing the same train of thought as my January 2009 column, there is benefit to planning for operational energy metering, management, and control in the design phase. As with specifying the BAS to include specific energy performance monitoring points, planning for the measurement of actual energy use (electrical kW and/or kWh, natural gas cubic ft and/or cubic ft/hr, thermal energy Btu and/or Btuh, etc.) also needs the active participation of the future building systems operations/optimization team.
The sooner an energy metering plan can be defined, the sooner that plan can influence design details and be incorporated into the project as inexpensively as possible. With long-term energy conservation in mind, it makes sense to have the metering plan drive the design instead of vice versa. By “design,” I mean the details of how electrical power is distributed to various loads or groups of loads and how chilled water, hot water, gas, and/or steam are piped to their endusers. Waiting until the wiring and piping distribution design is nearly complete before determining what meters can be installed will more often than not limit the owner’s options for effective metering.
Using the plan to save moneyDistribution systems, especially piping, are typically designed to serve their endusers in a manner that minimizes first cost (e.g., limits pipe sizes, pipe lengths, and architectural floor space) while coordinating with architectural features. I recommend also considering the metering plan when designing the most cost-effective piping and wiring systems. A distribution system laid out to minimize size and length may require substantially more meters to meet the owner’s metering requirements than a distribution system designed to accept fewer meters while achieving the same metering goals.
The building owner who is serious about long-term energy monitoring and conservation will include metering goals in the owner’s project requirements (OPR) document. By definition, the OPR precedes the design process. As such, the metering goals cannot be detailed with respect to exactly what will be metered where, but it can be still be quantitative and verifiable. For example, the owner could require that a minimum percentage (25%, 50%, etc.) of a certain type of energy (gas, chilled water, hot water, steam, gas, etc.) be submetered. Another metric might be a requirement that any energy user (e.g., fan, pump, boiler, chiller, heating coil, cooling coil) representing more than a specific percentage of the total load of that energy should be submetered.
Achieving LEED®In order to meet this type of metering requirement, the design team will need to understand how energy will be used in the building. This typically requires at least a rudimentary level of energy modeling. Sophisticated energy modeling is becoming more and more common, because it is a prerequisite for LEED® certification. The energy model used for LEED compliance can also be used to identify all of the building energy users and determine the major users worth submetering.
With detailed information regarding how energy will be consumed by the building systems/equipment, the design team and owner can develop a metering plan to achieve the metering goals. This metering plan then becomes part of the design goals when the design engineers start laying out the distribution systems within the architect’s plans.
This does not mean that the metering plan must take precedence over all other design considerations (cost, aesthetics, etc.), but I believe it should share an equal position in the give-and-take of the design process. If the metering plan needs to be modified in order to meet other project requirements, the owner should be actively involved in making that decision from a life-cycle cost perspective.
It should be the owner’s responsibility to take the lead on defining the metering plan, because the plan needs to be based on how the owner intends to use the data obtained. At a minimum, the metering plan will include regularly trending and monitoring each meter with respect to an established baseline for that meter. This would typically be done through the BAS, so the metering plan will influence the BAS points and trend log specifications as discussed last month.
Some owners may also choose to use the meter data to initiate a load shed program to limit energy demand in their facility. The load shed program could simply require the BAS to issue an alarm when certain energy demand meters exceed set limits. In this case, the building operators would manually stop or curtail selected loads (stop fans or pumps, close valves, adjust setpoints, etc.). Other owners may want the BAS to automatically stop equipment and/or adjust setpoints whenever certain metered limits are reached. Both of these options will require detailed specification during the design phase so that the BAS contractor knows exactly what “load shed” means and the commissioning professional has a sequence of operation to verify during functional testing. ES