Air Handling Unit (AHU):
Equipment used to distribute the conditioned air to a space; includes heating and cooling coils, fans, ducts, and filters. Packaged systems that do the same thing might go by other names (e.g. rooftop unit), but for the purposes of BRS, can be modeled using the AHU section.
Airflow:
Volumetric flow rate of air in a duct with units of cubic feet per minute (cfm)
Baseline:
An initial performance level established to track improvements over time. For example, a building and its operations prior to any intervention, such as re-tuning, retrofits, performance contracts, etc.
Building Automation System (BAS):
A system of digital controllers, communication architecture, and user interface that monitors and controls a building's mechanical and electrical equipment such as heating, ventilation, and air conditioning (HVAC); lighting; fire protection; vertical transport systems; and irrigation systems. The system can be used to optimize facility operation and reduce energy consumption. Also known as a Building Control System (BCS), Energy Management System (EMS), and Building Management System (BMS).
Building Pressure:
The static pressure of building air relative to ambient outdoor air. Note that building pressure can vary from floor to floor in significant ways for tall buildings during hot and cold weather. This is called the stack effect. The BRS calculates only a single building pressure.
Building Re-tuning:
Defined as a systematic process to identify operation problems by leveraging data collected from the BAS and correcting those problems at no-cost or low-cost.
Calibration:
For energy models, calibration is the process of making modifications to the original baseline building specifications to produce simulated energy consumption that more closely matches metered energy consumption. The modifications are typically made to building and HVAC system parameters that are hard or impossible to determine from an audit or otherwise have higher uncertainty associated with them.
Condenser Coil:
A heat exchange element in the form of a pipe or tube that is used to condense refrigerant from a gas to a liquid.
Constant Speed:
A piece of equipment that is only capable of producing a fixed output flow rate. This most commonly may apply to a pump, fan, chiller, or cooling tower.
Constant volume (CV):
A type of air-distribution system that circulates a constant volume of air to the conditioned space regardless of the demands of the space.
Cooling Coil:
A heat exchange element in the form of a pipe or tube with warm air on the outside and refrigerant on the inside that is used to cool air under forced convection with or without dehumidification. May consist of a single coil section or several coil sections assembled into a bank.
Cooling Plant:
The set of mechanical components and systems responsible for generating a centralized cooling supply (usually chilled water) for a building. The components typically include primary and secondary pumps, chillers or district cooling heat exchangers, cooling towers or dry coolers, valves, connecting piping, and water treatment systems.
Dashboard:
For digital media, a single page that either conveys all of the most useful and salient information about a system or process using graphics and performance metrics. For the BRS, the re-tuning dashboard shows all the baseline control strategies for each of the re-tuning measures, while also allowing the user to make modifications to those controls and initiate a new simulation to investigate the impact of those modifications.
Dedicated Outdoor Air System (DOAS):
An air-handler section that conditions 100% outside air prior to either delivering this conditioned outdoor air directly to building spaces or in some cases, to the outdoor air mixing box of a conventional air-handling unit. A dedicated outdoor air system often, but not always, includes an energy recovery system. The energy recovery system may include either a heat recovery wheel to transfer heat between an outdoor air stream and an exhaust air stream, or a set of coils (one in the outdoor air stream and one in the exhaust air stream) and a pumping system between them. This is referred to as a run-around loop.
Demand-Controlled Ventilation (DCV):
An HVAC control system/strategy that varies the amount of outside air introduced to a building based on the internal concentration of CO2 (an indication of building occupancy) to reduce the energy necessary to heat, cool, and dehumidify ventilation air.
Density (peak loading):
The installed or peak power consumption for lights, electric equipment, or the number of people, in each case normalized by the floor area served [W/ft2] or [People/ft2].
Differential Pressure:
The difference between the pressure measured at two points in either a chilled water or hot water loop, usually the difference in pressure between the outlet of the pumping system and the farthest point in the loop. The differential pressure provides a measure of how much (as a minimum) water pressure will be available to each of the building's coils.
Efficiency:
For a component or system, the ratio of useful output energy to the required input energy.
ENERGY STAR Portfolio Manager Score:
A standard for benchmarking commercial buildings comparing energy performance to comparable buildings, normalized for climate zone and operating characteristics. A score of 50 represents median performance. A higher score is better than average; lower is worse. See
https://www.energystar.gov/buildings/benchmark
Energy Use Intensity (EUI):
A metric of annual energy use per floor area that is commonly used in benchmarking energy-use data. A low EUI generally signifies an energy efficient building. However, certain occupancies use more energy than others by nature of the operations (e.g. hospital vs warehouse).
Heat Pump:
A device that uses the vapor compression refrigeration cycle to move heat from one area to another. It can deliver cooling or heating to a space by reversing the flow of refrigerant.
Heating Coil:
Heat exchanger that heats air under forced convection. May consist of a single coil section or several coil sections assembled into a bank.
Heating Load:
The amount of heat a heating system must provide per unit of time to maintain the indoor design temperature level, typically measured in Btu/hour.
Heating Plant:
The set of mechanical components and systems responsible for generating a centralized heating supply (either hot water or low-pressure steam) for a building. The components typically include primary and (sometimes) secondary pumps, boilers or district steam heat exchangers, valves, connecting piping, water treatment systems and steam condensate return.
Infiltration:
The transfer of outdoor air across the building envelope and into the building through cracks and intentional openings.
Interval Metered Data:
A dedicated building meter that collects utility energy consumption at an hourly or sub-hourly interval according to the customer or transmission and distribution system needs.
Life Cycle Cost Analysis:
A standard form of benefit-cost analysis used to evaluate cost-effectiveness by comparing incremental system costs to the cost savings over the life of the project. The difference between the life cycle cost of the baseline and each alternative is a net present value (NPV) or the net savings offered by that alternative.
Makeup Air:
Any combination of outdoor and transfer air intended to replace exhaust air and air leakage.
Model (building energy):
A simplified representation of a building that can be used to estimate/predict performance and energy consumption for unknown conditions (e.g. system upgrades and control changes). Models are usually most useful in estimating the difference between a baseline and a post-intervention state than in predicting the energy consumption for a new building with unknown consumption.
Monthly Billing Data:
Metered energy consumption data from the utility provider that is provided for the purposes of monthly billing. In the cases of some campuses of buildings, this data may be collected at the campus level and thus not of much use for calibrating building energy models.
Multi-Zone System:
A type of air-distribution system that is similar to a dual-duct system in that two streams of air, hot and cold, are mixed to produce a desired temperature. But whereas dual-duct systems mix the air in individual boxes located at each area or room, multi-zone systems mix air with dampers near the fans, then feed the conditioned air to each zone based on its load.
Optimal Start:
A machine learning algorithm that provides an air-handler with a custom start-up time every morning in response to the outdoor air temperatures, zone temperatures, and time remaining prior to occupancy.
Outdoor Air:
Air outside a building or taken from the outdoors and not previously circulated through the system including ambient air that enters a building through a ventilation system, through intentional openings for natural ventilation, or by infiltration.
Packaged Unit:
A self-contained HVAC unit that provides heating and/or cooling to a building space.
Primary Loop/Primary Pump:
In common building parlance, the primary loop is a water loop that pumps water through the chillers or boilers. It may also be the same loop that serves the building hot water or chilled water coils. In the BRS, the term primary is used only to refer to a set of pumps that are constant speed, serving the boiler or chiller, when there is another set of pumps that serve the rest of the building (secondary loop). In the event of single-loop systems, these should be modeled in the BRS as secondary loop-only systems.
Reheat:
The heating of air that has been previously cooled (by cooling equipment or an economizer) by a heating device, such as a hot water or electric coil, and controlled via a zone thermostat.
Schedule:
This could refer to an actual schedule used for control or building operations, such as an HVAC occupancy schedule, or a building occupancy schedule or it could refer to an operational time-of-use profile that is applied to internal loads (lighting, equipment and people) to help the model estimate how these loads vary as a function of time of day and day type.
Secondary Loop/Secondary Pump:
In common building parlance, the secondary loop is a water loop that pumps water through the building heating or cooling coils and back, and interfaces with a separate primary loop through a decoupler bridge, allowing the two loops to have different flow rates. In the BRS, the term secondary is used only to refer to the loop serving the building heating or cooling loads, regardless of whether this loop also flows through the chillers or not.
Setpoint:
Desired temperature, humidity, or pressure in an area, space, or duct.
Simple Payback:
The measurement of the elapsed time between an initial investment and the point at which accumulated savings are sufficient to offset the initial investment.
Simulation:
The exercising of a model to produce a prediction – in this case about annual energy consumption and utility costs.
Solar Heat Gain Coefficient (SHGC):
The fraction of solar radiation transmitted or absorbed through a window and subsequently released as heat inside the zone.
Static Pressure (SP)/Static Pressure Reset:
The pressure downstream of the supply fan, typically measured 2/3 of the way down the duct, with respect to the zone (building pressure).
Supply Air:
Air delivered by mechanical or natural ventilation to a space that is composed of any combination of outdoor air, recirculated air, or transfer air.
Supply Air Temperature (SAT)/ Discharge Air Temperature (DAT):
The temperature at the outlet of the AHU and the inlet to zone air terminal units.
Temperature Reset:
A strategy for saving energy that adjusts the temperature of either the air or water supplied by an HVAC system based on measurements of the actual load or a proxy for the actual load, such as outdoor air temperature.
Thermal Mass:
Building construction layers, equipment, and furnishings that create thermal inertia. This is reflected numerically as the amount of heat that must be provided to produce a unit change in zone temperature.
U-Factor:
A measure of how much thermal heat (excluding solar transmittance, in the case of windows) is transmitted through a wall or window, as a function of the temperature difference on each side. The U-factor is the inverse of the effective R-Value, so can be roughly estimated by taking the inverse of the insulation R-Value, however this does not take into account thermal breaks and additional thermal resistance provided by other layers of wall construction, including air gaps.
Variable Air Volume (VAV):
A type of air-handling system that provides air at a constant temperature and varies the air quantity to each zone to match the variation in room load.
Variable Speed:
An HVAC component that is capable of adjusting its speed through the use of a variable speed drive to provide a range of flow rates. This designation may apply to pumps, fans, chillers, and cooling towers.
Weather data, TMY (Typical Meteorological Year):
A collation of selected weather data for a specific location, including hourly values of solar radiation, outdoor air temperature and humidity for a one-year period. The full data set includes other weather-related values and measurements that are not used by the BRS. The values are generated from a data bank much longer than a year in duration, at least 12 years. It is specially selected so that it presents the range of weather phenomena for the location in question, while still giving annual averages that are consistent with the long-term averages for the location in question. TMY3 weather data is used in the BRS, with 1,020 U.S. locations and territories that are available for selection by the user.
Zone:
A thermal zone in a building is an area of a building served by a single thermostat and a piece of or set of equipment controlled by that thermostat. It may include a single room, several rooms, or only a fraction of a larger open space. For modeling purposes, the 'zone' may be much larger, encompassing several thermal zones in the actual building. The goal of the modeler is to group several thermal zones with similar loads and characteristics into a single modeled zone for simplicity.