MEP Flashcards
Enthalpy
a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.
Demand control ventilation
A system designed to adjust the amount of ventilation air provided to a space based on the extent of occupancy, the system normally uses carbon dioxide sensors but may also use occupancy sensors or air quality sensors.
Light Shelf
A horizontal element positioned above eye level and designed to reflect daylight on the ceiling for improved daylight effectiveness.
Shading coefficient (SC)
The ratio of solar heat gain through a glazing product to the solar heat gain through an unshaded 1/8 inch thick, clear, double strength glass, under the same set of conditions.
SHGC
Solar Heat Gain Coefficient.
The ratio of solar heat gain through a fence station to the total solar radiation incident on glazing. Solar heat gain includes directly transmitted solar heat absorbed solar radiation, which is then re-radiated, conducted, or convected into the space.
Solar time
This time is defined by the sun in its position relative to earth. Because the length of the solar day varies, most references use the mean solar day as a basis for time keeping, this is the average length of a solar day.
Graywater recycling
The collection, treatment, storage, and distribution of wastewater from sources that do not contain human waste such as showers & sinks.
Analemma
The figure-eight curve that represents the angular offset of the sun from its mean position as viewed from the earth. At any given point on the earth, if the position of the sun is noted at the same time every day for a year, the figure of the analemma is produced.
balance-point temperature
The outdoor temperature at which a building makes a transition from a heating need to a cooling need.
daylight autonomy (DA)
Also referred to as spatial daylight autonomy (sDA). The percentage of an area that meets a minimum daylight illuminance level for a specified fraction of the operating hours per year (e.g., 300 lux for 50% of the time). It is one of the options for receiving LEED credit in the Daylight category.
equation of time
The factor used to account for the difference between solar time and clock time. Solar time is based on the position of the sun. Its basic unit is the solar day, the time the earth takes to make one complete rotation on its axis. A solar day may be slightly more than or less than 24 hours by clock time; its exact length changes from day to day due to the earth’s elliptical orbit around the sun and the tilt of the earth’s axis. Depending on the time of year, solar days may pass more quickly or more slowly than days on the clock. As the small differences accumulate, solar time can be ahead or behind clock time by as much as about 161 2 minutes. The equation of time is also expressed in the analemma. The dif- ference between solar time and clock time is also affected by one’s position east or west within a time zone; this is a separate factor from the equation of time.
glazing factor
A LEED-based number calculated by taking into account window area, floor area, a win- dow geometry factor, light transmission, and a window height factor.
ground light
Visible light from the sun and sky, reflected by exterior surfaces below the plane of the horizon.
net metering
The requirement that a utility pay and charge equal rates regardless of which way electricity flows as part of the utility grid. Thus, excess electricity generated with photovoltaics or wind systems can be sold back to the utility.
radiation spectrum
The entire range of electromagnetic radiation extending from 0 Hz to about 1023 Hz. This includes visible light as well as infrared radiation, radio waves, and gamma rays, among others.
radiative cooling
Also known as nocturnal cooling or night-cooled mass. A passive or active design strategy that uses thermal mass to collect and store heat during the day for release at night. This works best in climates where there is a significant difference between daytime and nighttime temperatures, such as the southwest and temperate climates.
solar constant
The amount of solar energy that falls in a unit time on a unit area that is 93,000,000 miles from the sun and oriented on a plane perpendicular to the sun’s rays. The mean value of the solar con- stant is 433 Btu/hr-ft2. Some of this energy is lost as the energy travels through the earth’s atmosphere.
solar savings fraction
The fraction of the total energy used by a system that is provided by a solar technology. The solar savings fraction, represented by the variable f, is a decimal fraction from zero (where no solar energy is used) to one (where all energy used by a system is solar energy).
VLT
visible light transmittance
The fraction of visible light that passes through a glazing material.
workplane
The assumed height at which work is performed, usually considered to be at desk height, 30 in above the floor.
Met
Energy produced per unit of service area per hour by a seated person at rest, one minute is 18.4 BTU/hr-ft².
Convection
The transfer of heat through movement of a gas or liquid. This occurs when the air temperature surrounding an object is less than the surface temperature of the object.
Evaporation
Moisture changing to a vapor.
Radiation
Transfer of heat energy through electromagnetic waves from a surface to a colder surface.
Conduction
Transfer of heat through direct contact between two objects of different temperatures.
Design heating day
A hypothetical but typical very cold day that is used to calculate the maximum heating needs of a space.
Effective temperature (ET)
A derived value that combines the effects of air temperature humidity an air movement.
Dry bulb
The Dry Bulb Temperature refers basically to the ambient air temperature.
Wet bulb
The wet-bulb temperature is the lowest temperature that may be achieved by evaporative cooling of a water-wetted, ventilated surface.
Sling psychometer
A device that consists of a thermometer with a moist cloth around the bulb. The thermometer is swung rapidly in the air, causing the moisture in the cloth to evaporate.
Relative humidity
The ratio of the percentage of moisture in the air to the maximum amount of moisture that the air can hold at a given temperature without condensing.
Emissivity
A measure of an objects ability to absorb And then radiate heat. .The emittance of an object is the ratio of the radiation emitted by a given object or material to that emitted by a black object at the same temperature.
Mean Radiant Temperature (MRT)
The weighted average of the various surface temperatures in a room and angle of exposure of the occupant to these surfaces, as well as of any sunlight present.
Globe thermometer
Measures the operative temperature of a space.
Ventilation required in addict and call spaces.
Crawl spaces: 1/150 or 1/1500 (w/ class I vapor retarder)
Atticks: 1/150 or 1/300 (w/ passive vents & vapor barrier at warm side)
