Demand charge
The part of a commercial electric bill priced on your peak rate of use, in kilowatts, rather than your total use in kilowatt-hours. Con Ed bills it on the highest 30-minute integrated demand recorded in the month, so one sustained half-hour of high draw sets a charge that applies to the whole billing period. On Con Ed's SC9 large commercial rate the charge is $44.05 per kW per month in summer and $34.50 the rest of the year, and on real NYC bills demand can be the majority of the total. Degraded HVAC equipment raises both halves of the bill at once: more kilowatt-hours and a higher peak. The full walkthrough, on a real bill, is in Demand charges, explained for building owners.
Delta-T
The temperature difference across a heat exchanger, most often measured between the air entering and the air leaving an evaporator coil. A healthy unit produces a stable delta-T for a given set of conditions, because it is moving heat at the rate it was designed to. When delta-T narrows, the unit is moving less heat per pass: the classic early symptoms are restricted airflow (a clogged filter), a refrigerant problem, or a fouled coil. The space still reaches setpoint because the unit compensates by running longer, so occupants feel nothing. Delta-T is one of the signals AirPulse baselines per unit and per weather band, which is how a fault shows up in the data weeks before anyone feels it.
Short cycling
A pattern where equipment starts, runs briefly, stops, and starts again in rapid succession instead of completing normal cycles. Starting is the hardest thing a compressor does; a unit that starts many times an hour is spending its mechanical life at the worst part of the curve while delivering poor comfort and poor dehumidification. Short cycling is almost always a symptom of something else: an oversized unit, a failing control or sensor, refrigerant trouble, or an iced coil. Because it is a change in cycling behavior rather than temperature, a thermostat hides it and occupants rarely notice. Cycling pattern is one of the core signals in an AirPulse baseline, and a cycling change against the same weather is a common first alert. See How it works.
Baseline
As AirPulse uses the term: a statistical model of one specific unit's normal, built from its own runtime, temperatures, cycling, and power draw, bucketed by outdoor conditions, because normal at 95°F is nothing like normal at 70°F. The baseline takes about 30 days to form and keeps refining across seasons. Every new hour of operation is scored against the matching weather band, so a deviation means the unit changed, not the weather. This is deliberately explainable statistics (per-band mean and variance), not a black box, and it is the difference between an alert that says “something looks off” and one that says how far off, since when, and what it is costing. The full pipeline is on How it works.
Load factor
Average electric demand divided by peak demand over a billing period, expressed as a percentage. A load factor near 100% means steady, flat consumption. A low load factor means a spiky load: the building uses little energy overall but hits a high peak, and on a demand-billed meter that spike is what sets the demand charge. That combination is expensive. On a real NYC commercial bill we analyzed, an 18% load factor helped push demand-related charges to about 70% of the total and the effective rate to $0.694 per kWh. HVAC-driven buildings commonly run low load factors, which is why the same kilowatt-hour costs a spiky building several times what it costs a flat one. The walkthrough is in Demand charges, explained.
PTAC
Packaged terminal air conditioner: the self-contained, through-wall heating and cooling unit under the window of most hotel rooms and many hospital and apartment buildings. Each PTAC serves one room and stands alone, so a building does not have one HVAC system, it has a fleet of dozens or hundreds of small ones, usually with no central visibility at all. That structure is what makes PTAC buildings distinctive: no single unit matters much, but faults multiply across the fleet, and a failed unit is discovered by the guest or tenant standing in the hot room. Fleet-scale monitoring flips that: every unit reports, failures surface before check-in, and maintenance goes to the units that need it. See pricing for fleet volume tiers.
BAS (building automation system)
A building automation system: centralized control for a building's mechanical and electrical plant, the domain of large commercial properties with engineered points lists, controls contractors, and a front-end in the engineer's office. A BAS is built to controlequipment: schedules, setpoints, sequences, interlocks. It is not typically built to learn each unit's normal, detect slow degradation against weather-matched history, or price a deviation in dollars, and most small and mid-size buildings have no BAS at all. Equipment intelligence is not a BAS replacement; it attaches per unit, with no points list or site engineering, and answers a different question: not “is the unit on?” but “is the unit still healthy, and what is it costing?” See How it works.
Equipment intelligence
The category AirPulse builds in: continuous per-unit monitoring of HVAC equipment, combined with learned baselines for each machine and alerts priced in dollars. A thermostat knows the room. A BAS controls the plant. Equipment intelligence knows the machine: what this specific unit's normal looks like in this weather, when it starts drifting from that normal, and roughly what the drift costs per month, so the fix can be scheduled while it is still small. The dollar figure is the point, because equipment problems are budget problems long before they are comfort problems; the waste is documented (a dirty filter alone is 5 to 15% of a unit's energy, per the U.S. DOE), and the sourcing rules behind every such number are in How we make claims.
Go deeper
These terms do their work in the articles: What HVAC really costs a NYC building per year, Demand charges, explained, What a dirty filter actually costs you, and the sourcing rules in How we make claims. For your own building, start at buildings or pricing.