Energy Glossary

Use our glos­sary to under­stand the tech­ni­cal jar­gon used in the ener­gy indus­try.
Adjustable Speed Dri­ve (ASD)
a con­trol device that varies the shaft speed to the dri­ven load on a motor. One exam­ple is the vari­able fre­quen­cy dri­ve (VFD), some­times called a vari­able speed dri­ve. A VFD con­sists of an elec­tron­ic pow­er con­vert­er that con­verts con­stant fre­quen­cy AC (alter­nat­ing cur­rent) pow­er input into a vari­able fre­quen­cy out­put. The AC motor speed varies in pro­por­tion to the dri­ve out­put fre­quen­cy.
AFUE (annu­al fuel uti­liza­tion effi­cien­cy)
a mea­sure of heat­ing effi­cien­cy on an annu­al basis. AFUE is defined as the heat trans­ferred to the con­di­tioned space divid­ed by the total fuel sup­plied (in Btu) for a giv­en heat­ing sea­son. The high­er the AFUE rat­ing, the greater the effi­cien­cy.
Amp
the basic unit of elec­tric cur­rent, one ampere rep­re­sents the rate of one coulomb of charge per sec­ond. It is defined to be the total net charge flow­ing across a giv­en cross-sec­tion­al area of wire per sec­ond.
Bal­last
all flu­o­res­cent and most met­al halide lamps need bal­lasts to oper­ate. Because the arc gen­er­at­ed in a lamp has almost no elec­tri­cal resis­tance, bal­lasts are pro­vid­ed to reg­u­late the lamp cur­rent. Mag­net­ic bal­lasts con­sist of a coil in series with the lamp, or may also include a capac­i­tor to improve pow­er fac­tor. Elec­tron­ic bal­lasts are more effi­cient and reg­u­late lamp cur­rent by deliv­er­ing high fre­quen­cy puls­es. Elec­tron­ic bal­lasts do not have the large coils and asso­ci­at­ed heat loss of mag­net­ic bal­lasts. They not only oper­ate more effi­cient­ly them­selves, but elec­tron­ic bal­lasts can also improve the effi­ca­cy of the lamp-bal­last sys­tem by 10%-20%.
Bal­last Fac­tor
the bal­last fac­tor is the ratio of the light out­put of a flu­o­res­cent lamp to the light out­put of the same lamp oper­at­ed on a stan­dard (ref­er­ence) bal­last. The bal­last fac­tor is mul­ti­plied by the rat­ed lumens to esti­mate how much light actu­al­ly comes from the tube. T8 elec­tron­ic bal­lasts may have a typ­i­cal bal­last fac­tor of 0.88 to 0.95, but can range from 0.6 to 1.3.
BAS (build­ing automa­tion sys­tem)
opti­mizes the per­for­mance of HVAC equip­ment and alarm sys­tems by automat­ing the inter­ac­tion of build­ing mechan­i­cal sub­sys­tems, improv­ing occu­pant com­fort, low­er­ing ener­gy use and allow­ing off-site build­ing con­trol.
Boil­er
a type of space heat­ing equip­ment con­sist­ing of a ves­sel or tank where heat pro­duced from the com­bus­tion of fuels such as nat­ur­al gas, fuel oil, or coal is used to gen­er­ate steam or hot water. Unlike a fur­nace, air is not forced through the struc­ture; the steam or hot water is cir­cu­lat­ed through pipes to radi­a­tors or base­boards where it warms the sur­round­ing air by con­vec­tion. The two most com­mon boil­er lay­outs are fire­tube and water­tube.
Boil­er Horse­pow­er (bhp)
rate of water evap­o­ra­tion equal to the evap­o­ra­tion per hour of 34.5 pounds of water at a tem­per­a­ture of 100°C (212°F) into steam at 100°C. One boil­er horse­pow­er is about 33,475 Btu per hour (about 9809.5 watts).
Btu
a British Ther­mal Unit is the amount of heat required to raise one pound of water by one degree Fahren­heit. Approx­i­mate­ly equiv­a­lent to the ther­mal ener­gy of a kitchen match.
Can­dela
an SI (Inter­na­tion­al Sys­tem of Units) unit of lumi­nous inten­si­ty. One can­dela is one lumen per stera­di­an, where a stera­di­an is a unit of mea­sure relat­ing the angle sub­tend­ed at the cen­ter of a sphere to the sphere’s sur­face area and radius.
Capac­i­tor
an elec­tri­cal ener­gy stor­age device, con­sist­ing in gen­er­al of two metal­lic plates sep­a­rat­ed and insu­lat­ed from each oth­er by a dielec­tric.
ccf
a com­mon billing term that refers to 100 cubic feet of nat­ur­al gas.
CFC (Chlo­ro­flu­o­ro­car­bon)
a com­pound con­sist­ing of chlo­rine, flu­o­rine, and car­bon. CFCs are very sta­ble in the tro­pos­phere. They move to the stratos­phere and are bro­ken down by strong ultra­vi­o­let light, where they release chlo­rine atoms that then deplete the ozone lay­er. CFCs are com­mon­ly used as refrig­er­ants, sol­vents, and foam blow­ing agents. The most com­mon CFCs are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115.
Chiller
a cool­ing sys­tem that uses mechan­i­cal vapor com­pres­sion (cen­trifu­gal, screw, scroll, or rec­i­p­ro­cat­ing) or absorp­tion to achieve refrig­er­ant phase change. All chillers have evap­o­ra­tors and con­densers, though absorp­tion sys­tems use ther­mal ener­gy to boil a solu­tion to lib­er­ate the refrig­er­ant instead of the elec­tri­cal ener­gy used in a vapor com­pres­sion chiller. Chillers are typ­i­cal­ly found in medi­um to large com­mer­cial and indus­tri­al facil­i­ties, and can range from 25 to 1,500 refrig­er­ant tons.
Coef­fi­cient of Per­for­mance (COP)
rat­ings that are more typ­i­cal­ly found in chiller rat­ings and gas cool­ing equip­ment, as well as in heat pumps. COP is a mea­sure of how effi­cient­ly a heat­ing or cool­ing sys­tem will oper­ate at a sin­gle out­door tem­per­a­ture con­di­tion. As an exam­ple, the com­mon­ly used out­door tem­per­a­ture con­di­tion for a heat pump cal­cu­la­tion in the heat­ing mode is 47ºF. As is also the case for EER and SEER, a high­er COP means high­er effi­cien­cy.
Cogen­er­a­tion
the com­bined pro­duc­tion of pow­er and use­ful heat by the sequen­tial or simul­ta­ne­ous use of ener­gy from one fuel input into a sub­se­quent process. As an exam­ple, steam that is gen­er­at­ed for a man­u­fac­tur­ing process can be used to gen­er­ate elec­tric­i­ty before going to the man­u­fac­tur­ing unit. Wide­ly used in busi­ness­es found in the pulp and paper indus­try, petro­chem­i­cal, met­als, min­ing, and food indus­tries, it is also used on a small­er scale in com­mer­cial build­ings such as hotels, hos­pi­tals, uni­ver­si­ties, and shop­ping cen­ters.
Col­or­ing Ren­der­ing Index (CRI)
a mea­sure­ment of a light source’s abil­i­ty to ren­der col­ors the same as sun­light does. Gen­er­al­ly speak­ing, the CRI indi­cates the abil­i­ty of a lamp to allow indi­vid­ual col­ors to be seen and to dis­tin­guish between these col­ors. On a scale of one to one hun­dred, light sources should have a min­i­mum col­or-ren­der­ing index (CRI) of eighty for most inte­ri­or spaces. Ceram­ic met­al halide lamps, the lat­est “sec­ond gen­er­a­tion” T8 lamps, T5 lamps, and most com­pact flu­o­res­cent lamps have a CRI in the range of eighty-two to eighty-six. Incan­des­cent lamps have a CRI near one hun­dred, because they emit all the col­ors with­in the vis­i­ble col­or spec­trum.
Com­bined Heat and Pow­er (CHP)
also referred to as cogen­er­a­tion because it includes the simul­ta­ne­ous pro­duc­tion of elec­tri­cal and ther­mal ener­gy.
Con­dens­ing Boil­er
a high­ly effi­cient boil­er that is able to recov­er waste heat by cool­ing some of the exhaust gas­es, and then cap­ture the ther­mal ener­gy of the con­den­sate through a heat exchang­er. Con­dens­ing fur­naces and boil­ers require stain­less steel or alu­minum mate­ri­als in their heat exchang­ers to pro­tect them against the mild­ly acidic and cor­ro­sive con­den­sate. Spe­cial­ty plas­tic tub­ing is also com­mon­ly used to return the con­den­sate with­in the heat­ing sys­tem.
Cool­ing Degree Day (CDD)
the mean dai­ly tem­per­a­ture minus 65°F.
Cor­re­lat­ed Col­or Tem­per­a­ture (CCT)
the apparent/perceived col­or of a light source com­pared to the col­or appear­ance of an ide­al incan­des­cent light source at a par­tic­u­lar tem­per­a­ture, expressed in degrees Kelvin (K). The CCT rat­ing is an indi­ca­tion of the warmth or cool­ness of the light, with rat­ings below 3,200°K referred to as warm, and rat­ings above 4,000°K con­sid­ered cool in appear­ance. As CCT increas­es, the appear­ance shifts from red­dish white toward bluish white. Cool light is pre­ferred for visu­al tasks because it pro­duces high­er con­trast than warm light. The col­or tem­per­a­ture of a lamp has noth­ing to do with how hot the lamp will get or how much heat will be giv­en off by the lamp.
Cubic Foot (cf)
as it relates to ener­gy, one cubic foot of nat­ur­al gas at stan­dard tem­per­a­ture and pres­sure (60°F, 14.7 psi) con­tains approx­i­mate­ly 1,030 Btu. Oth­er ener­gy billing units include MCF (1,000 cf, or approx­i­mate­ly 1,030,000 Btu).
Day­light­ing
the use of day­light as a pri­ma­ry source of illu­mi­na­tion in a space. It has become a more impor­tant fea­ture of main­stream con­struc­tion due to its abil­i­ty to low­er ener­gy costs.
Demand (kW demand)
the max­i­mum num­ber of kilo­watt-hours per defined time inter­val used by the cus­tomer. This is typ­i­cal­ly based upon the largest num­ber of kilo­watt-hours used in any half-hour or fif­teen-minute peri­od of the billing peri­od. Demand Charges, a charge per kW or kVA of month­ly billing demand, reflect the elec­tric util­i­ty’s infra­struc­ture cost of pow­er gen­er­a­tion and trans­mis­sion as well as the more expen­sive fuels used in peak­ing plants to meet each cus­tomer’s high­est month­ly pow­er peak.
Dis­trib­uted Gen­er­a­tion (DG)
a mod­u­lar elec­tric­i­ty gen­er­a­tion or stor­age con­cept that involves locat­ing small­er gen­er­a­tors, based on a vari­ety of tech­nolo­gies, clos­er to the elec­tri­cal loads that will be using them. DG has the poten­tial to serve as a reli­able source of stand­by or emer­gency back­up pow­er and, when used with unin­ter­rupt­ible pow­er sup­plies, can offer improved reli­a­bil­i­ty for inter­rup­tion-sen­si­tive equip­ment.
EER (ener­gy effi­cien­cy ratio)
a mea­sure of how effi­cient­ly a cool­ing sys­tem will oper­ate when the out­door tem­per­a­ture is at a spe­cif­ic lev­el (usu­al­ly 95°F). A high­er EER means the sys­tem is more effi­cient. EER = Btu of Cool­ing @ 95°F / Watts used @ 95°F. In the case of a 10 EER, 2 ton air con­di­tion­er: 10 EER = 24,000 Btu Out / 2,400 Watts In.
Effi­ca­cy
the ratio of the light out­put of a lamp (lumens) to its active pow­er (watts), expressed as lumens per watt (LPW). As an exam­ple, an incan­des­cent bulb may pro­vide 1,700 lumens from a 100 watt light bulb, pro­vid­ing an effi­ca­cy of sev­en­teen lumens per watt. Flu­o­res­cent lamps have effi­ca­cies from thir­ty to nine­ty-five lumens per watt, and high inten­si­ty dis­charge lamps (met­al halide, high pres­sure sodi­um, etc.) can have effi­ca­cies exceed­ing 150 lumens per watt.
Elec­tri­cal Ground
an elec­tri­cal means to inten­tion­al­ly cre­ate a low-resis­tance path that con­nects to the earth. This enhances safe­ty and equip­ment pro­tec­tion by pre­vent­ing the buildup of volt­ages that could cause an elec­tri­cal acci­dent or shock­ing haz­ard. Prop­er ground­ing prac­tices are spec­i­fied by the Nation­al Elec­tric Code, IEEE stan­dards, and build­ing codes to insure uni­for­mi­ty and safe­ty in elec­tri­cal sys­tems.
EMS (ener­gy man­age­ment sys­tem)
reduces ener­gy use in build­ings by mon­i­tor­ing con­di­tions and con­trol­ling ener­gy con­sum­ing equip­ment. An EMS is typ­i­cal­ly applied to the largest elec­tri­cal loads, includ­ing HVAC equip­ment, cool­ing tow­ers, pumps, water heaters, and light­ing.
Flu­o­res­cent
a glass tube with elec­trodes at each end and an inside sur­face coat­ed with one or more types of phos­pho­rs. Mer­cury vapor fills the tube at very low pres­sure, along with one or more “buffer” gas­es. Flu­o­res­cent lamps from least effi­cient to most effi­cient include the T12, T8, and T5, where the num­ber rep­re­sents the diam­e­ter of the tube in 1/8″ incre­ments (e.g., a T12 is twelve eighths, or 1–1/2″ diam­e­ter). As the diam­e­ter gets small­er, glare increas­es. There are also high out­put T8 and T5 lamps that pro­duce greater lumen out­put.
Foot-can­dle
the dis­tri­b­u­tion of light on a hor­i­zon­tal sur­face is called its illu­mi­na­tion, which is mea­sured in foot-can­dles. A foot-can­dle of illu­mi­na­tion is a lumen of light dis­trib­uted over a one-square-foot (0.09-square-meter) area. Full sun­light pro­duces an illu­mi­nance of about 10,000 foot-can­dles on a hor­i­zon­tal sur­face. Full moon­light pro­vides an illu­mi­nance of about 0.02 foot-can­dles. Ade­quate illu­mi­na­tion for read­ing is tak­en to be about ten foot-can­dles; machine shop work requires about forty foot-can­dles. One foot-can­dle equals 10.76 lux.
Fur­nace
a type of space heat­ing equip­ment with an enclosed cham­ber where fuel is burned or elec­tri­cal resis­tance is used to heat air direct­ly, with­out using steam or water. The heat­ed air is then blown or forced through­out the build­ing, typ­i­cal­ly via air ducts, where it enters a room through a reg­is­ter in the floor or the wall to pro­vide heat via con­vec­tion. Fur­naces can be pow­ered by a num­ber of dif­fer­ent means, such as elec­tric, gas, fuel oil, coal, or wood.
Halo­gen Incan­des­cent
also called tung­sten halo­gen lamps, the fil­a­ment is sur­round­ed by a hot gas from the halo­gen fam­i­ly (flu­o­rine, chlo­rine, bromine, or iodine) to improve effi­cien­cy. The halo­gen gas­es allow for regen­er­a­tion of the tung­sten fil­a­ment, thus enabling the fil­a­ment tem­per­a­ture to be increased for high­er effi­cien­cy. These lamps are pri­mar­i­ly used com­mer­cial­ly in the­ater, store, and out­door light­ing sys­tems.
Har­mon­ics
non-lin­ear sig­nals inher­ent in elec­tri­cal sys­tems that have motors, vari­able speed dri­ves, capac­i­tors, induc­tive devices or oth­er elec­tri­cal cir­cuit­ry not oper­at­ing in a pure­ly resis­tive or lin­ear mode.
HCFC (Hydrochlo­ro­flu­o­ro­car­bon)
a com­pound con­sist­ing of hydro­gen, chlo­rine, flu­o­rine, and car­bon. Devel­oped as an inter­im bridge between CFC and HFC refrig­er­ants, HCFC pro­duc­tion and con­sump­tion is cur­rent­ly capped in the Unit­ed States. As of 2020, HCFC-123 can no longer be used in new equip­ment and pro­duc­tion will cease in 2030. HCFC-142b and HCFC-22 will be phased out of new equip­ment by 2010. Accord­ing to the EPA, HCFCs con­tain chlo­rine and thus deplete stratos­pher­ic ozone, but to a much less­er extent than CFCs.
Heat Pump
takes advan­tage of under­ground ther­mal ener­gy or out­side air to pro­vide space con­di­tion­ing heat­ing, cool­ing, and humid­i­ty con­trol. Rather than con­vert­ing chem­i­cal ener­gy to heat, as in a fur­nace, a heat pump works by mov­ing heat. Heat pumps pull heat from the air or earth to pro­vide heat in the win­ter. In the sum­mer, the heat pump becomes an air con­di­tion­er that pulls heat from a build­ing by trans­fer­ring it to the earth or the air. Heat pumps can be air source or water source (geot­her­mal), and can also be found in indus­tri­al appli­ca­tions.
Heat­ing Degree Day (HDD)
65°F minus the mean dai­ly tem­per­a­ture.
Heat­ing Sea­son­al Per­for­mance Fac­tor (HSPF)
the ratio of the sea­son­al heat­ing out­put in Btu divid­ed by the sea­son­al pow­er con­sump­tion in watts for a heat pump. Like SEER rat­ings for air con­di­tion­ers, HSPF is a sea­son­al mea­sure. HSPF rat­ings of sev­en to nine are com­mon for air source heat pumps, while geot­her­mal (water source) heat pumps typ­i­cal­ly have HSPF rat­ings greater than ten. As an exam­ple, an HSPF of 8.5 cor­re­lates to 249% effi­cien­cy (8.5 / 3.412 x 100).
Hen­ry Hub
a pop­u­lar pric­ing point for nat­ur­al gas spot and futures con­tracts that is trad­ed on the NYMEX and oth­er exchanges, it is phys­i­cal­ly locat­ed in Louisiana at the inter­sec­tion of nine inter­state and four intrastate nat­ur­al gas pipelines.
HFC (Hydro­flu­o­ro­car­bon)
a com­pound con­sist­ing of hydro­gen, flu­o­rine, and car­bon devel­oped as a class of replace­ments for CFCs. Because they do not con­tain chlo­rine or bromine, they do not deplete the ozone lay­er. All HFCs have an ozone deple­tion poten­tial of zero.
High-Inten­si­ty Dis­charge (HID)
an elec­tric lamp that pro­duces light direct­ly from an arc dis­charge under high pres­sure, such as mer­cury vapor, met­al halide, and high and low-pres­sure sodi­um. There are large dif­fer­ences in effi­cien­cy, col­or ren­der­ing, and oth­er char­ac­ter­is­tics with­in HID lamps. HID lights require start­ing times of between two and fif­teen min­utes before reach­ing full out­put.
High-Pres­sure Sodi­um (HPS)
these lamps use sodi­um as the main light-emit­ting ele­ment, though these lamps also con­tain some mer­cury. Most HPS lamps require an ignit­er, in addi­tion to a bal­last. The ignit­er gen­er­ates high volt­age puls­es for start­ing. The bal­last reg­u­lates the cur­rent after the lamp has been start­ed. Effi­ca­cies can vary from 50 to 150 lumens per watt, and CRIs between twen­ty and eighty-five. Light­ing col­or is yel­low­ish white, with the dis­ad­van­tage that the low­er CRI yel­low­ish light can make it dif­fi­cult to dis­tin­guish the col­ors of objects illu­mi­nat­ed by it.
Horse­pow­er (hp)
a unit of pow­er, typ­i­cal­ly ascribed to motors, equiv­a­lent to work­ing at the rate of 33,000 ft-lb/minute, or 550 ft-lb/sec. One hp = 746 watts. Can be equat­ed to elec­tri­cal pow­er in motors, kW = 0.746 hp / motor effi­cien­cy.
Incan­des­cent
light is emit­ted by a hot glow­ing body, com­mon­ly a tung­sten fil­a­ment. Incan­des­cent light­ing is char­ac­ter­ized by very high CRI, but very low effi­cien­cy.
Infrared (IR)
elec­tro­mag­net­ic radi­a­tion of a wave­length longer than vis­i­ble light, but short­er than microwave radi­a­tion, the name means “below red” (from the Latin infra, “below”). Ener­gy is trans­mit­ted in wave­lengths from an infrared emit­ter direct­ly to the object. Infrared is typ­i­cal­ly divid­ed into three wave­length cat­e­gories — short, medi­um, and long — that fall between 700 nm and 1 mm. An alter­na­tive to con­vec­tion heat­ing, infrared is used in dry­ing and cur­ing for many indus­tri­al appli­ca­tions, includ­ing pulp and paper pro­cess­ing, paint dry­ing and cur­ing, plas­tics, and tex­tile man­u­fac­tur­ing. Fuel source can be either elec­tric or gas.
Ini­tial Light Out­put
a lam­p’s out­put, in lumens, after 100 hours of sea­son­ing.
Instant-start Bal­last
this type of bal­last applies a high-volt­age across the elec­trodes, up to twice as high as with oth­er start­ing meth­ods, to strike the elec­tric arc. The high­er volt­age is nec­es­sary because the elec­trodes are not heat­ed pri­or to start­ing. It is 5%-10% more ener­gy effi­cient than rapid or pre­heat start­ing, but caus­es greater wear on the elec­trodes dur­ing start­ing. New­er, improved designs min­i­mize the degra­da­tion of life caused by fre­quent switch­ing, though it may still be an issue for some types.
Kilo­volt-Ampere (KVA)
a unit of elec­tri­cal pow­er equal to 1,000 volt-amperes.
Kilo­volt-Ampere Reac­tive (KVAR)
the elec­tric util­i­ty must sup­ply more pow­er to account for the loss­es incurred due to exces­sive induc­tance or capac­i­tance. If the use­ful pow­er that the ener­gy user con­sumes is described as “Work­ing Pow­er” or “Real Pow­er” (kW), then the com­po­nent of lost pow­er is some­times referred to as Reac­tive Pow­er, or kilo­volt amps reac­tive (KVAR).
Kilo­watt Demand (kW demand)
the max­i­mum num­ber of kilo­watt-hours per defined time inter­val used by the cus­tomer. This is typ­i­cal­ly based upon the largest num­ber of kilo­watt-hours used in any half-hour or fif­teen-minute peri­od of the billing peri­od. Demand Charges, a charge per kW or kVA of month­ly billing demand, reflect the elec­tric util­i­ty’s infra­struc­ture cost of pow­er gen­er­a­tion and trans­mis­sion, as well as the more expen­sive fuels used in peak­ing plants to meet each cus­tomer’s high­est month­ly pow­er peak.
Kilo­watt-Hours (kWh)
the quan­ti­ty of true pow­er mul­ti­plied by time. 1,000 watts of pow­er used for one-hour equals one kilo­watt-hour. Kilo­watt-hours are referred to as true pow­er because they are a mea­sure of that por­tion of the kilo­volt-ampere hours that can be con­vert­ed from elec­tri­cal ener­gy into some oth­er form of use­ful ener­gy, such as heat, light or motion.
Light
the eye per­ceives vis­i­ble light over a range from 380 nanome­ters (nm) to 780 nm, with a range of 400 to 700 nm quite com­mon. Human eyes typ­i­cal­ly have a max­i­mum sen­si­tiv­i­ty of ~ 555 nm (in the green spec­trum). The eye may, how­ev­er, have some visu­al response at even wider wave­length ranges.
Load Fac­tor
the ratio of the aver­age elec­tri­cal load divid­ed by peak load dur­ing a des­ig­nat­ed peri­od of time. As an exam­ple, if a busi­ness used 10,000 kWh dur­ing one month (720 hours) and had a max­i­mum demand of 25 kW, then the load fac­tor would be 56 per­cent (10,000 kWh x 100)/(720 hours x 25 kW).
Low-Pres­sure Sodi­um (LPS)
sim­i­lar to high-pres­sure sodi­um lamps, except that the effi­ca­cy is high­er at the expense of a low­er CRI. Some com­mer­cial LPS lamps have achieved an effi­ca­cy of 180 lumens per watt, but their CRI is very poor, rang­ing from zero to twen­ty. Low-pres­sure sodi­um bulbs are mono­chro­mat­ic, mak­ing it dif­fi­cult to dis­tin­guish col­or under these lights. Start­ing times of between sev­en and fif­teen min­utes are also required before they reach full out­put. Typ­i­cal appli­ca­tions include high­way and secu­ri­ty light­ing.
Lumen
the lumen is a unit of lumi­nous flux, as defined in terms of the can­dela, which is the foun­da­tion unit for the mea­sure­ment of vis­i­ble light.
Lumen Main­te­nance
a mea­sure of how well a lamp main­tains its light out­put over time. It is the rat­ed mean light out­put as a per­cent­age of rat­ed ini­tial light out­put. It may be expressed numer­i­cal­ly or as a graph of light out­put vs. time. Numer­i­cal lumen main­te­nance num­bers are usu­al­ly a per­cent­age of ini­tial light out­put at 40% of rat­ed life.
Lux
a mea­sure of illu­mi­nance in lumens per square meter. One lux equals 0.093 foot-can­dles.
Medi­um Bi-Pin
a type of con­nec­tor com­mon­ly used on T8 and T12 flu­o­res­cent lamps. Two small pins pro­trude from the lamp ends, which are insert­ed into a sock­et in the fix­ture. T5 flu­o­res­cent lamps use a sim­i­lar but small­er con­nec­tor called a minia­ture Bi-Pin, which is not inter­change­able with a medi­um bi-pin.
Mer­cury
this sub­stance has many desir­able opti­cal prop­er­ties, mak­ing it the pri­ma­ry light-emit­ting vapor used in flu­o­res­cent light­ing. It is also com­mon­ly used in high inten­si­ty dis­charge light­ing. Light is emit­ted when mer­cury atoms relax from their first excit­ed ener­gy lev­el at a wave­length of 254 nanome­ters. Phos­pho­rs con­vert this UV light into vis­i­ble light, and buffer gas­es (argon) can be added to fur­ther improve light­ing qual­i­ty.
Mer­cury Vapor (MV)
the least effi­cient of the HID lamp types, almost all of their light is emit­ted by mer­cury vapors. CRI is on the low end, typ­i­cal­ly in the range of forty to fifty-five. MV lamps com­pete with high-pres­sure sodi­um and met­al halide for out­door light­ing appli­ca­tions where light­ing qual­i­ty is less impor­tant. MV lamps have the longest life of HID-type lamps, but are not very effi­cient — with effi­ca­cies rang­ing from 35 to 65 lumens per watt. Light­ing col­or is in the bluish white spec­trum.
Met­al Halide (MH)
evolved from mer­cury vapor lamps, MH lamps use a vari­ety of met­al vapors, rather than mer­cury vapor alone, to achieve bet­ter light­ing qual­i­ty (CRI rat­ings from six­ty to nine­ty). Met­al halide implies that the addi­tion­al met­als include com­pounds with some of the halo­gen ele­ments (flu­o­rine, chlo­rine, bromine, or iodine). MH lamps are not inter­change­able with mer­cury vapor lamps, except in some small sizes. Effi­ca­cies range from 75 to 125 lumens per watt.
Micro­tur­bine
a small-scale pow­er gen­er­a­tion source approx­i­mate­ly the size of a refrig­er­a­tor, rang­ing typ­i­cal­ly from 25 to 200 kW. Advan­tages include: small num­ber of mov­ing parts, com­pact size, light-weight, greater effi­cien­cy, low­er emis­sions, low­er elec­tric­i­ty costs, and oppor­tu­ni­ties to uti­lize waste fuels. Micro­tur­bine sys­tems are com­prised of a com­pres­sor, com­bus­tor, pow­er tur­bine, gen­er­a­tor, and often a recu­per­a­tor.
Pack­aged Rooftop HVAC
also referred to as pack­aged heat­ing or pack­aged cool­ing equip­ment, these sys­tems con­tain the com­pres­sor, evap­o­ra­tor coil, con­denser, heat­ing unit, sup­ply fan, exhaust fan, and fil­ter in one pre­assem­bled pack­age that can be installed as a self-con­tained unit. A num­ber of sizes and designs are avail­able and most are com­mon­ly found on the rooftops of office build­ings, retail stores, malls, schools, man­u­fac­tur­ing plants, and a host of oth­er com­mer­cial and indus­tri­al facil­i­ties. Can be fueled by gas, elec­tric, fuel oil or a com­bi­na­tion of these fuels.
Phos­pho­rs
used in flu­o­res­cent and HID lamps to improve light­ing qual­i­ty, phos­pho­rs are crys­tals that con­vert the UV light emit­ted by the mer­cury vapor into vis­i­ble light. The make­up of the var­i­ous phos­pho­rs deter­mines the col­or emit­ted by the flu­o­res­cent or HID light.
Pow­er Fac­tor (PF)
a ratio equal to the real pow­er (kW) divid­ed by the appar­ent pow­er (kVA). PF = kW/kVA
Radi­ant Heat­ing
relies on the con­cept of radi­ant heat trans­fer, in which heat pro­duced by the sys­tem radi­ates to near­by objects and sur­faces. Just as the sun heats peo­ple and objects even when the air is cold, radi­ant heat­ing can warm the peo­ple and objects in a room with­out hav­ing to warm the air in the room. The most com­mon form of radi­ant heater is an infrared heater.
Rapid-Start Bal­last
this type of bal­last uti­lizes a method of start­ing flu­o­res­cent lamps in which lamp elec­trodes are heat­ed pri­or to start­ing, using a starter that is an inte­gral part of the bal­last. Heat­ing the elec­trodes before start­ing the lamps reduces the volt­age required to strike the elec­tric arc between the elec­trodes. A rapid-start sys­tem starts smooth­ly, with­out flash­ing.
Reac­tive Pow­er (kVAR)
the quan­ti­ty of non-work­ing pow­er caused by mag­ne­tiz­ing cur­rent. Reac­tive pow­er is mea­sured in kilo­vars or kVARs. Reac­tive pow­er is required for cer­tain devices to oper­ate, but it is not avail­able as use­ful pow­er on the out­put side of the device. Exam­ples of such devices are motors, trans­form­ers, relays, and flu­o­res­cent lights.
Refrig­er­ant
a com­pound used in a heat cycle that under­goes a phase change from a gas to a liq­uid and back. The main uses of refrig­er­ants are in chillers, air con­di­tion­ers, and refrigerators/freezers.
Rel­a­tive Humid­i­ty (RH)
a mea­sure of the amount of water in the air com­pared to the amount of water the air can hold at a par­tic­u­lar tem­per­a­ture. Warmer air has more capac­i­ty to “hold” water vapor than cold­er air. Dew point is a mea­sure of how much water vapor is actu­al­ly in the air.
SEER (sea­son­al ener­gy effi­cien­cy ratio)
a mea­sure of effi­cien­cy over an entire cool­ing sea­son, as opposed to a sin­gle out­door tem­per­a­ture. Res­i­den­tial units are almost always rat­ed in SEER. SEER came into use as a more prac­ti­cal mea­sure, since the tem­per­a­ture out­side is not always 95ºF. Also, the denom­i­na­tor is in watt-hours, not in watts as is the case for EER. The same rela­tion­ship holds true, i.e., a high­er SEER means the sys­tem is more effi­cient. SEER is the total amount of cool­ing the air con­di­tion­er will pro­vide over the entire cool­ing sea­son divid­ed by the total num­ber of watt-hours it will con­sume, or SEER = Sea­son­al Btus of cool­ing / Sea­son­al watt-hours used.
Spark Spread
the dif­fer­ence between the price of elec­tric­i­ty sold by a gen­er­a­tor and the price of the fuel used to gen­er­ate it, adjust­ed for equiv­a­lent units. Some­times it is referred to as the price of elec­tric­i­ty with­out the fuel com­po­nent. Spark spread is often used as a deci­sion fac­tor to deter­mine when to run a gen­er­a­tor, by cal­cu­lat­ing the Btu equiv­a­lent gen­er­a­tion cost for nat­ur­al gas and elec­tric­i­ty based on spe­cif­ic mar­ket con­di­tions.
Stand­by Gen­er­a­tor
sup­plies back­up pow­er to ener­gy users in the event of a pow­er out­age. Typ­i­cal­ly lim­it­ed to appli­ca­tions that require back­up pow­er to an exist­ing pow­er util­i­ty grid, stand­by gen­er­a­tors are not designed to run as prime pow­er or in a con­tin­u­ous appli­ca­tion. They can play a strate­gic role in min­i­miz­ing pow­er costs and max­i­miz­ing pow­er reli­a­bil­i­ty by ensur­ing unin­ter­rupt­ible, onsite stand­by capa­bil­i­ty in the event of pow­er out­ages, both unex­pect­ed or planned.
Steam Trap
auto­mat­ic valves found on the steam dis­tri­b­u­tion lines of a boil­er heat­ing sys­tem to keep the sys­tem oper­at­ing opti­mal­ly by purg­ing con­den­sate and main­tain­ing steam qual­i­ty. The devices typ­i­cal­ly have a float to trap the con­den­sate. Once the steam has con­densed to become hot water, it is removed by the trap and is either returned to the boil­er or dis­charged to the atmos­phere.
Therm
an ener­gy unit equal to 100,000 Btus. A decatherm is equal to 10 therms.
Ther­mog­ra­phy
infrared ther­mog­ra­phy has been used in pre­dic­tive main­te­nance and con­di­tion mon­i­tor­ing of elec­tri­cal and mechan­i­cal equip­ment, as well as build­ing per­for­mance test­ing. Infrared imagers cap­ture infrared radi­a­tion emit­ted from objects and dis­play these invis­i­ble wave­lengths as vis­i­ble light images. They are use­ful in appli­ca­tions where a vari­a­tion in tem­per­a­ture, reflec­tion, sur­face con­di­tion, or mate­r­i­al may cause a dif­fer­ence in the radi­at­ed ener­gy lev­el detect­ed by the equip­ment.
Three-Phase Pow­er (3 phase)
a very effi­cient means of trans­mit­ting elec­tri­cal ener­gy where­by the sequen­tial peaks (of phas­es A, B, and C) are spaced 120° apart to enable a rel­a­tive­ly smooth pow­er curve. The goal of effi­cient­ly deliv­er­ing elec­tri­cal pow­er over a three-phase sys­tem is to either keep the phas­es bal­anced with the same amount of load or in sym­me­try with each oth­er. Motors greater than 10 hp are almost always three-phase pow­er, because they tend to be more effi­cient than sin­gle-phase motors.
Ton (refrig­er­ant ton, RT)
defined as the cool­ing capac­i­ty of an air con­di­tion­ing sys­tem. One ton is equal to the Btu ther­mal con­tent required to melt one ton of ice in a 24-hour peri­od. A 1‑ton air con­di­tion­er is rat­ed at 12,000 Btu, a 2‑ton unit at 24,000 Btu, a 3‑ton unit at 36,000 Btu, and so forth. It takes 144 Btu of heat to melt 1 pound of ice in 24 hours, or 288,000 Btu to melt a ton (2,000 pounds) in 24 hours. Typ­i­cal res­i­den­tial cen­tral heat­ing sys­tems pro­vide from 1 to 5 tons of cool­ing. Com­mer­cial rooftop units are typ­i­cal­ly 3 to 20 tons each. Chillers can range from 15 up to 1,500 tons.
Ultra­vi­o­let (UV)
elec­tro­mag­net­ic radi­a­tion of a wave­length short­er than that of vis­i­ble light, the name means “beyond vio­let” (from Latin ultra, “beyond”), vio­let being the col­or of the short­est wave­length of vis­i­ble light. UV is also called black light, as it is invis­i­ble to the human eye. UV wave­lengths are often sub­di­vid­ed into UV‑A (380–315 nm), UV‑B (315–280 nm), and UV‑C (280–10 nm).
UPS (Unin­ter­rupt­ible Pow­er Sup­ply)
pro­vides back­up pow­er in the event of a pow­er out­age. A UPS can range from a 300 VA unit to pro­tect a sin­gle PC up to 1,000 kVA sys­tem to pro­tect clus­ters of equip­ment or entire facil­i­ties, such as those found in telecom­mu­ni­ca­tions, finan­cial ser­vices, hos­pi­tals, and indus­tri­al sites with mis­sion crit­i­cal process­es. In addi­tion to pro­vid­ing back­up pow­er, UPS sys­tems can also pro­vide “con­di­tioned” pow­er. The three types of UPS sys­tems include off-line, line-inter­ac­tive, and on-line.
Volt
the basic unit of volt­age, or elec­tric poten­tial dif­fer­ence. It is the dif­fer­ence of elec­tri­cal poten­tial between two points of an elec­tron­ic cir­cuit. One help­ful descrip­tion uses a water anal­o­gy, equat­ing volt­age (volts) to the flu­id pres­sure in a water pipe sys­tem, and cur­rent (amps) to the actu­al flow of water.
Watt
a mea­sure of pow­er that is the prod­uct of volt­age (volts) and cur­rent (amps). It is rough­ly equiv­a­lent to 3.412 Btu/hr. One kilo­watt (kW) equals 1,000 watts.

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