CEM key terms

The ratio of average load over a period to the peak load in that same period. A high load factor means equipment and purchased capacity are used steadily rather than in short, expensive bursts.

A monthly utility charge based on the highest power draw (kW) recorded during the billing period, separate from energy charges. It recovers the cost of capacity the utility must keep available for the customer's peak.

The maximum rate of energy use, in kilowatts, reached during a defined interval such as 15 or 30 minutes. Utilities meter it with interval averaging so brief spikes are smoothed.

A tariff where the price per kilowatt-hour varies by time block, typically higher on weekday afternoons and lower at night. It signals when to shift flexible loads to cut cost.

A tariff in which the energy price changes hourly or at short intervals, reflecting wholesale market conditions. Customers need automation or forecasting to manage cost exposure.

The ratio of real power (kW) to apparent power (kVA) in an alternating-current circuit. Low power factor means more current flows for the same useful work and can trigger utility penalties.

Deliberate, temporary reduction of electrical load in response to a utility signal, price spike, or grid event, usually for payment. It can be automated through the building control system.

Moving a flexible load, such as thermal storage or a batch process, from a high-cost period to a low-cost one without reducing total energy use. It lowers cost rather than consumption.

Annual energy consumed per unit of floor area, such as kBtu per square foot or kWh per square meter. It allows comparison of buildings of different size and is the basis of benchmarking.

Comparing a building's energy performance against similar buildings or a historical baseline, often using a normalized score. It identifies candidates for audit and tracks improvement over time.

Adjusting measured energy use for differences in outdoor temperature and other weather variables so that different periods or buildings can be compared fairly.

A measure of heating or cooling demand obtained from the difference between a reference temperature and the daily mean outdoor temperature, summed over a period.

A systematic study of how and where a facility uses energy, identifying conservation measures and estimating their cost and savings. Its depth ranges from a walk-through survey to a detailed investment-grade analysis.

The process of quantifying actual savings from an efficiency project by comparing measured post-installation use against an adjusted baseline. It follows a documented protocol so savings claims are defensible.

The initial project cost divided by annual savings, giving the number of years until savings repay the investment. It ignores the time value of money and cash flows after payback.

Comparing alternatives by discounting all costs and savings over the equipment's life, including capital, energy, maintenance, and replacement. It reveals options that a simple payback screen would wrongly reject.

The interest rate used to convert future cash flows into present value. A higher rate penalizes long-payback measures and favors low-capital, quick-return options.

The ratio of useful heating or cooling output to energy input, in consistent units. A heat pump with a coefficient above one delivers more heat energy than it consumes in electricity.

A cooling efficiency rating for unitary air conditioners and heat pumps, calculated as seasonal cooling output in Btu divided by seasonal electrical input in watt-hours.

A control strategy or damper assembly that brings in cool outdoor air to satisfy cooling load when conditions allow, reducing mechanical refrigeration. It is a common source of energy waste when sensors drift.

A failure such as a stuck damper, faulty temperature sensor, or incorrect changeover setting that prevents free cooling or causes simultaneous heating and cooling. Detection is a standard part of commissioning.

Applying the commissioning process to an existing building to find and fix operational problems, without new capital equipment. Savings often come from correcting controls, schedules, and simultaneous heating and cooling.

A quality-focused process that verifies building systems and assemblies are designed, installed, and function according to the owner's requirements and the design intent.

A networked control system that monitors and schedules HVAC, lighting, and other equipment, collects trend data, and applies sequences of operation from a central or cloud interface.

Automated analysis of sensor and trend data to identify equipment problems and their likely causes, such as a failing valve or biased sensor, before occupants notice.

A scheduled relaxation of a temperature setpoint during unoccupied hours to reduce heating or cooling energy. The savings depend on building mass, recovery time, and equipment capacity.

An electronic device that varies the speed of an alternating-current motor to match load instead of running it at full speed with throttling. Affinity laws make reduced speed cut power sharply.

Relationships stating that airflow varies with fan speed, pressure with the square of speed, and shaft power with the cube of speed. A small speed reduction yields a large power reduction.

Installed lighting wattage divided by floor area, used by energy codes to cap lighting energy. It is calculated separately for space types and checked during permit review.

The amount of visible light produced per unit of electrical power, expressed in lumens per watt. Higher values indicate a more efficient lamp or luminaire.

A legally adopted set of minimum requirements for building envelope, lighting, HVAC, and service systems, intended to limit energy use. Compliance is typically shown by prescriptive or performance paths.

A path where highly conductive material such as steel framing or a slab edge bypasses insulation, increasing heat flow. It lowers effective envelope performance and can cause condensation.

The capacity of building materials to absorb, store, and later release heat, which damps indoor temperature swings. It affects how quickly a space responds to setback and to passive solar gain.

Storing cooling or heating capacity, for example in chilled water or ice, for use during peak periods. It shifts electrical demand and can reduce demand charges and time-of-use cost.

The amount of energy currently stored in a battery expressed as a percentage of its rated capacity. Controls use it to limit charging and discharging within safe operating bounds.

The share of electrical energy put into a storage system that is delivered back on discharge, after conversion and standby losses. It directly affects the cost of shifting energy.

Generating electricity on site while capturing waste heat for space heating, domestic hot water, or process use. High overall efficiency depends on matching heat and power loads year-round.

A billing arrangement where exported electricity from an on-site generator offsets imported consumption, often at the retail rate. Rules on credit value and expiry vary by jurisdiction.

The share of fuel energy transferred to steam or hot water, measured on a higher or lower heating value basis. Stack losses and blowdown are major determinants of real performance.

Heat carried out of a boiler or furnace in the exhaust gas, driven mainly by flue temperature and excess air. Reducing excess air or adding an economizer recovers some of this loss.

Deliberate draining of boiler water to control dissolved solids and prevent scale and foaming. Excessive blowdown wastes energy; conductivity-based control keeps it to the necessary minimum.

An unintended escape of pressurized air from a joint, hose, or fitting in an industrial air system. Leaks are a leading waste source because they persist and are often inaudible in noisy plants.

The electrical power required to produce a unit of compressed air flow, such as kW per 100 cubic feet per minute. It allows comparison of compressor efficiency at a given pressure.

Matching pump output to demand by changing motor speed rather than throttling a valve or bypassing flow. It captures the cube-law power reduction that throttling cannot achieve.

Adding capacitors or active equipment to reduce reactive power so the power factor approaches unity. It avoids utility penalties and frees transformer and conductor capacity.