December 2017 — Submetering is a method building operators use to benchmark energy performance of specific equipment, building systems, tenant spaces, and other end uses. Building operators can use submetering to gain insight into how different segments of the building are performing. Submeters can provide the following energy information:
- Usage analysis and peak demand identification
- Time-of-use metering of electricity, gas, water, steam, chilled water, and other utilities
- Cost allocation for tenant billing
- Load comparisons
- Threshold alarming and notification
- Multi-site load aggregation and real-time historical monitoring of energy consumption and performance patterns
Virtually any system can be submetered using readily available technology. It is important to conduct a cost-benefit analysis (CBA) to determine whether to install a submeter on a particular system. Because prices for submeters range from a few hundred to thousands of dollars, it is often necessary to develop a submetering plan before pursuing this strategy to impact operational performance.
Common building systems that can be submetered include:
- Chilled water production and distribution
- Hot water or steam production and distribution
- Air handling and distribution systems
Common equipment that can be submetered includes:
- Cooling towers (electrical and water consumption)
- Air handling units (fan coils, heat pumps, VAVs, etc.)
- Unit heaters
Submetering can also be done in the occupant space. End-user categories that can be measured through submetering include:
- Lighting loads
- Data centers
- Retail areas (if applicable)
- Plug loads
Submetering can provide building owners and operators with a significant amount of data that can help improve building operations and maintenance scheduling, strategic planning, and occupant comfort.
The reasons to submeter are varied, but the goal is usually the same: to gain information about building and system performance that can help increase efficiencies. Beyond the obvious quantitative benefits, submetering can yield a number of positive qualitative outcomes, such as increased occupant productivity and comfort levels, as well as improved decision making regarding building operations and performance. Some building owners may choose to invest in submeters to fulfill organizational strategic goals focused on energy conservation.
Achieving Efficiencies through Submetering
Submetering can isolate use by tenants in a multifamily residential setting or by retail space in a commercial setting. Often, especially in older buildings, it is not feasible to allocate utility usage by tenants. Securing this type of data can enable building owners to more accurately understand usage by tenant space and provide a degree of fairness to tenants—individual or retail—by charging them only for their portion of the utility bill. Additional benefits include identifying and correcting sources of resource waste, which can lead to improved comfort and performance, as well as longer equipment life.
Equipment on/off time
The easiest way to save energy is to ensure that when equipment is scheduled to be off, it remains off. Building operators who have installed submeters often realize that equipment that is supposed to be off is, in fact, remaining on. This can be caused by a variety of factors, including faulty controllers, service contractors who unknowingly change settings while trying to address other problems, and simple wear and tear on equipment. Regardless, submetering allows building operators to capture the data necessary to verify system operation.
Peak demand is the maximum amount of energy used over a given time period, typically one month. In many parts of the country, peak demand (or maximum demand, as it is sometimes known) plays a big role in increasing utility bills’ overall cost. In some states, as much as one-third of the utility bill can be attributed to this peak demand charge. Some utilities charge more than $20 dollars per kW for this peak demand.
Submetering allows building operators to track and manage peak demand more effectively. In an effort to increase efficiency, building owners will often set equipment to shut down at night and come back on early in the morning before the building is occupied. However, the combination of multiple systems starting up together can cause an undesired coincident demand, which can sometimes occur early in the morning during building start-up, and at a much higher level than if the building systems were scheduled to come on gradually. For example, it is wiser to set peak demand for the middle of a hot July afternoon than at start-up on a July morning.
Irregularities in Performance
Submetering also provides the data needed to track irregularities in building performance. Fans short-cycling, simultaneous heating/cooling, and poor occupancy sensor calibration are examples of the types of irregularities that can be identified and remedied as a result of submetering.
Trending Equipment Efficiency
Comparing operational use curves to benchmarked conditions will allow the operator to determine and trend the efficiency of systems. This information can be used to track maintenance schedules and predict capital expenditures and equipment replacement.
Interaction among Building Systems
Multiple data points can be used to balance equipment performance and ensure systems are tuned to perform as efficiently as possible. This could include adjusting the sequence of operation based on building load and environmental conditions, tuning variable frequency drives on fans and pumps, and adjusting set points on water loops to loads within the building to rely on more efficient machines.
The first step in developing a submetering plan is to establish the overall submetering objective. This can be done in a number of ways, including looking at annual utility costs, identifying primary energy users, looking at poorly designed or improperly operating equipment, or conducting building audits. Once the objectives are established, collection methodologies, data, and equipment types need to be considered and evaluated with a cost-benefit analysis to determine the feasibility.
Submetering plans require thorough formulation as they can take several years to implement. When working through this planning process, know that no single approach will work for every building. As such, the following considerations may need to be addressed:
- Can this work be done in-house, or will it require hiring a trained professional?
- What are the key milestones?
- How should you obtain and maintain stakeholder buy-in?
- What are the details of the equipment monitored: location, type, model, quantity?
- What is the duration, frequency, interval, and other measurements?
- Who will provide, install, and maintain metering equipment?
- What are the specifications, accuracy, calibration procedures of metering equipment?
- How will data be collected, maintained, and reported?
- What are the accuracy and quality assurance procedures?
- What evaluation criteria will be developed and applied?
- Which reporting software and dashboards will be used?
- What are the current and future metering needs?
This article is adapted from BOMI International’s High-Performance Sustainable Building Practices, part of the new High-Performance Sustainable Buildings credential (BOMI-HP™). More information regarding this course or the BOMI-HP™ credential is available by calling 1-800-235-2664. Visit BOMI International’s website, www.bomi.org.