Technical Glossary

Air Changes per Hour

How many times the room's air volume is replaced per hour due to leakage or ventilation. ACH 0.5 means half the air volume is replaced each hour.

Comfort Zone Coverage

The percentage of floor area with SET below the comfort target (25°C). 60%+ comfort area means most of the room feels cool.

ANSI/ASHRAE Standard 55

International standard for thermal environmental conditions for human occupancy, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

External Heat Gain

Heat entering from outside through walls, roof, and windows (radiation + conduction). Influenced by building orientation and sun intensity.

Internal Heat Gain

Heat generated inside the room by occupants, lights, and electronic equipment.

Cooling Load

Total heat that must be removed from a room by the AC to maintain the setpoint temperature. Calculated from wall, roof, window, occupant, lighting, and equipment heat.

British Thermal Unit per hour

A unit of cooling capacity for air conditioners. 1 BTU/hr = 0.293 Watts. Higher BTU/hr means greater cooling ability.

Computational Fluid Dynamics

Numerical simulation of fluid flow (air/water) using computers. In HVAC, CFD is used to visualize air and temperature distribution inside rooms.

Cubic Feet per Minute

A unit of fan airflow rate. Higher CFM means more air is moved. 1 CFM ≈ 1.699 m³/h.

Clothing Insulation Unit

A measure of thermal insulation of clothing. 0 clo = naked, 0.3 clo = thin shirt + shorts (tropical home), 1.0 clo = business suit.

Cooling Load Temperature Difference

An equivalent temperature difference used to calculate cooling load through walls and roofs. The value accounts for building thermal mass effects and peak solar radiation.

Coincident Design Condition

A condition where multiple extreme parameters (temperature, humidity) occur simultaneously. '2% coincident' means conditions occurring 2% of total hours in a year.

Coefficient of Performance

The ratio of cooling energy produced to electrical energy consumed. COP = 3 means 1 Watt of electricity produces 3 Watts of cooling.

Cooling Seasonal Performance Factor

The seasonal efficiency ratio for inverter ACs: total cooling (Wh) divided by total electricity (Wh) over one season. Higher CSPF means lower electricity consumption.

Thermostat Deadband

The temperature range around the setpoint where the compressor doesn't need to run. For example, setpoint 25°C with ±1°C deadband: compressor turns off at 24°C, back on at 26°C.

Outdoor Design Temperature

The extreme outdoor air temperature used as a reference for cooling load calculations. Typically taken from the 2nd or 0.4th percentile of historical climate data.

The process of eliminating temperature layers (stratification) in tall rooms. A ceiling fan rotating slowly clockwise pulls warm air up and redistributes it.

Temperature Distribution

The pattern of perceived temperature spread across the room. A good fan produces even distribution, not just cooling in one spot.

Dry Bulb Temperature

The ordinary air temperature shown by a standard thermometer. Called 'dry bulb' to distinguish from 'wet bulb'. This is the temperature we feel daily.

Energy Efficiency Ratio

The efficiency ratio for non-inverter ACs: cooling capacity (BTU/hr) divided by input power (Watts). EER > 10 is considered efficient.

Ministry of Energy and Mineral Resources

Energy efficiency certification from Indonesia's Ministry of ESDM. Fans with ESDM label have passed minimum efficiency tests per Ministerial Decree No. 114.K/EK.07/DJE/2021.

Evaporative Cooling

The process of cooling air through water evaporation. Water absorbs heat when evaporating, lowering air temperature. Most effective in dry climates (RH < 40%).

Heating, Ventilation, and Air Conditioning

Systems that regulate temperature, humidity, and air quality inside buildings.

Air Infiltration

Hot and humid outside air entering through gaps in doors, windows, and other small openings. Carries both sensible and latent heat loads.

Cooling Capacity

The maximum ability of an AC to absorb heat from a room, measured in Watts or BTU/hr. Must be greater than the cooling load.

Air Velocity

The speed of fan airflow in meters per second (m/s). Speeds of 0.5–1.5 m/s feel comfortable. Above 2 m/s may feel too strong.

Relative Humidity (RH)

The ratio of actual water vapor to maximum vapor capacity at that temperature, in percent. RH 60–80% is common in tropical regions. High RH makes it harder for the body to sweat.

Thermal Comfort

A condition of mind expressing satisfaction with the thermal environment (ASHRAE 55). Influenced by 6 factors: air temperature, radiant temperature, humidity, air speed, clothing, and activity.

Thermal Conduction

Heat transfer through solid materials (walls, glass) from the hot side to the cold side. Thicker and more insulating walls reduce conduction.

Kilowatt-hour

A unit of electrical energy used by power companies for billing. 1 kWh = 1,000 Watts of power for 1 hour.

Metabolic Equivalent of Task

A measure of body heat production rate. 1 MET = 58.2 W/m² (sitting quietly). Typing ≈ 1.1 MET, casual walking ≈ 2.0 MET.

Percentage Experiencing Draught

The percentage of people who feel discomfort from excessive air movement (draught). PED > 15% indicates a risk of discomfort from too much airflow.

Paardekracht (Horse Power)

An AC capacity unit commonly used in Indonesia. 1 PK ≈ 9,000 BTU/hr. Small rooms (~10 m²) typically need ½ PK, medium rooms (~15–20 m²) need 1–1.5 PK.

Thermal Radiation

Heat transfer through electromagnetic waves (without a medium). Sunlight passing through window glass is an example of radiation load.

Compressor Runtime Fraction

The percentage of time the AC compressor actually runs in one hour. 60% runtime means the compressor works 36 minutes per hour.

Building Envelope

The physical boundary between air-conditioned space and the outdoor environment: walls, roof, floor, windows, and doors. Envelope quality determines external heat gain.

Sensible & Latent Heat

Sensible heat raises air temperature (felt by a thermometer). Latent heat adds moisture without raising temperature. AC must handle both.

Standard Effective Temperature

A standard environmental temperature that provides the same thermal sensation as actual conditions. Accounts for temperature, humidity, air speed, clothing, and metabolic activity.

Setpoint Temperature

The target temperature set on the AC remote. The compressor runs until the room reaches the setpoint, then stops or slows down (inverter).

Safety Factor

A multiplier to add reserve AC capacity. SF 1.15 (15%) for normal rooms, SF 1.20 (20%) for top floors exposed to roof heat.

Indonesian National Standard 6390:2020

Energy conservation standard for HVAC systems in Indonesian buildings. Regulates minimum AC efficiency and cooling load calculation methods.

Effective Temperature

The temperature actually felt by the body, not the thermometer reading. A fan blowing at 2 m/s can lower perceived temperature by 3–5°C without changing room temperature.

Overall Heat Transfer Coefficient

The total heat transfer coefficient of a construction, in W/(m²·K). Lower U-value means better insulation. Plastered brick wall ≈ 2.0; clear glass ≈ 5.8.

Watt (W)

A unit of electrical power. For AC, Watt indicates input power (electricity consumed). For fans, Watt indicates motor power consumption.

Wet Bulb Temperature

The lowest temperature water can reach through evaporation. Measured with a thermometer whose sensor is wrapped in a wet cloth. Determines evaporative cooler effectiveness.