NATE Senior Efficiency Analyst key terms

The fraction of total cooling capacity used to remove sensible heat rather than latent heat. It equals sensible capacity divided by total capacity and shapes how a system handles both temperature and humidity loads.

Energy absorbed or released when moisture changes state without changing temperature, such as water vapor condensing on a coil. In air conditioning it represents the dehumidification portion of the load.

The combined sensible and latent heat removal rate of a system, usually stated in Btu/h or tons. It is the sum of sensible and latent components at specific entering air and outdoor conditions.

The rated capacity label assigned to equipment, where one ton equals 12,000 Btu/h. Actual delivered capacity differs with entering wet-bulb, outdoor temperature, and airflow, so nominal values are not performance guarantees.

A multiplier or correction applied to rated capacity to reflect real operating conditions such as altitude, high outdoor temperature, or reduced airflow. It converts laboratory ratings into realistic expected performance.

Manufacturer data showing capacity and power across ranges of entering air conditions, outdoor temperature, and airflow. Analysts use it to predict how equipment behaves outside the single rated point.

The actual load divided by the equipment's full-load capacity at the same conditions. It indicates how far below maximum output a system operates and influences cycling losses and efficiency.

A weighted efficiency metric combining full-load and part-load performance across a specified load spectrum. It rewards equipment that runs efficiently at low loads, where most operating hours occur.

A single-number rating derived from efficiency at several part-load points, weighted by typical time spent at each. It is used mainly for larger unitary and chiller equipment comparisons.

A seasonal efficiency rating for cooling equipment that weights performance across a range of outdoor temperatures and load conditions. Higher values indicate less energy used per unit of cooling over a season.

Cooling capacity in Btu/h divided by electrical input in watts at a single specified rating condition. It allows direct comparison of equipment at full load and a defined outdoor temperature.

Useful heating or cooling output divided by energy input, expressed in consistent units so it is dimensionless. COP above one is normal for heat pumps because they move heat rather than create it.

A seasonal heating efficiency rating for heat pumps that accounts for output and input across varying outdoor temperatures and defrost cycles. It reflects real winter performance better than a single-point rating.

The outdoor temperature at which a heat pump's heating capacity exactly equals the building's heat loss. Below it, supplementary heating is needed to maintain indoor temperature.

Supplemental heating, often electric resistance, that operates when a heat pump cannot meet the load alone. Excessive use signals sizing, balance point, or control problems and raises energy use sharply.

A set outdoor temperature at which a control disables a stage or component, such as electric resistance heat or the compressor. Proper settings prevent wasteful simultaneous heating and cooling.

Efficiency penalty from repeated startup and shutdown, when equipment runs inefficiently during brief on periods and may not stabilize before stopping. It grows as part-load ratio falls in single-stage systems.

The outward force per unit area exerted by air on duct walls, measured in inches of water column. It represents resistance to airflow and is used to judge whether a duct system is restrictive.

The pressure associated with air speed in a duct, equal to total pressure minus static pressure. It is used with pitot-tube readings to calculate air velocity and volume flow.

The pressure difference the blower must overcome across the equipment and its attached ductwork, excluding internal components like coils and filters. High values indicate restrictive ducts or undersized returns.

The loss of pressure as air moves through a filter, coil, damper, or fitting. Each component adds resistance that the blower must overcome, and large drops reduce delivered airflow.

Pressure loss per unit length of duct, typically inches of water per 100 feet. It guides duct sizing and reveals whether runs are oversized or too restrictive for the available blower pressure.

The straight-duct length that would produce the same pressure loss as a fitting such as an elbow or tee. It converts fitting resistance into added duct length for friction calculations.

A dimensionless number describing how much pressure a specific fitting loses relative to its velocity pressure. Sharp turns and abrupt transitions have higher coefficients and should be minimized.

The volume of air moved per minute, usually measured in cubic feet per minute. Correct airflow is essential because capacity, charge behavior, and temperature split all depend on it.

A measurement method using multiple pitot-tube readings across a duct cross section to determine average velocity and calculate airflow. It requires a straight duct section and careful probe placement.

The difference between return and supply air temperatures across operating equipment. It is a quick indicator of airflow and capacity, but only meaningful when airflow and load conditions are known.

The temperature difference between two measurement points, such as entering and leaving air or liquid. Analysts compare measured delta T with expected values to detect airflow or capacity problems.

Conditioned air escaping through joints, seams, or holes before reaching occupied spaces. It wastes energy, can pressurize or depressurize zones, and is quantified by leakage testing at a specified pressure.

The process of closing leaks with mastic, tape, or aerosol methods to reduce air loss. Effective sealing improves delivered airflow and reduces energy waste, especially in unconditioned spaces.

Thermal wrapping or lining that limits heat gain or loss through duct surfaces. Missing or damaged insulation raises supply air temperature and reduces effective capacity at the registers.

The temperature of refrigerant vapor above its saturation temperature at the measured pressure. It confirms that liquid has fully boiled off before the compressor and is used to verify charge in fixed-orifice systems.

The temperature of liquid refrigerant below its saturation temperature at the measured pressure. It indicates how much liquid remains in the condenser and is the primary charge check for thermostatic expansion valve systems.

The temperature at which refrigerant changes state at a given pressure. Comparing it with measured line temperatures reveals superheat, subcooling, and whether the system is operating as designed.

A modulating metering device that regulates refrigerant flow to maintain a target superheat at the evaporator outlet. Its operation makes subcooling the preferred charge indicator.

The difference between the leaving fluid or air temperature and the refrigerant saturation temperature in a heat exchanger. A growing approach suggests fouling, scaling, or reduced heat transfer effectiveness.

Accumulation of dirt, scale, or debris on condenser surfaces that impedes heat rejection. It raises condensing temperature and pressure, increasing compressor power and reducing capacity.

The saturation temperature of refrigerant in the condenser at the existing discharge pressure. Higher values mean the compressor works harder to reject heat, lowering efficiency.

Discharge pressure divided by suction pressure, both absolute. High ratios increase compressor stress and discharge temperature and often signal low suction pressure or high condensing pressure.

The ratio of real power in watts to apparent power in volt-amperes in an alternating-current circuit. Low values indicate poor utilization and can affect demand charges and motor efficiency.

A utility billing component based on the highest average power draw during a billing period. Reducing peak demand can lower bills even when total energy consumption is unchanged.

A record of energy use over time, showing how demand varies by hour, day, or season. It helps identify peak periods and opportunities for controls or scheduling improvements.

Energy consumed per unit of floor area over a period, commonly kBtu per square foot per year. It allows comparison of buildings of different sizes and tracking of improvement over time.

A reference representation of expected energy use under defined conditions, used to measure savings from changes. It must be adjusted for variables like weather and occupancy to stay valid.

A structured process for quantifying savings from efficiency measures using metered data and agreed methods. It separates real savings from changes caused by weather, occupancy, or operations.