HVAC Knowledge

8/12/2019 HVAC Knowledge

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The speed of a belt driven Blower can be calculated byRpm of Driven pulley = (driver pulley diameter/ driven pulley diameter) x driver pulley Rpm

for ex : if d=4inch diameter and rpm of 1500: and D=12inch diameterRpm of D=(4/12)1500 = 500

What is the difference between Alcohol Thermometer and Mercury Thermometer? Mercury thermometer has mercury inside the bulb as the temperature sensitive fluid, and in alcohol thermometers, it is an alcohol. Since alcohol is non toxic, alcohol thermometers are much safer to use than the mercury thermometers. Alcohol thermometers can be used to measure very low temperatures. Since mercury has a higher boiling point than alcohol,mercury thermometer can be used to measure high temperatures.

CRYOGENIC PLUGGINGThe cryogenic plugging process consists in locally freezing the liquid contained in the pipeline by using the effects of a cryogenic fluid.

The most commonly used freezing fluid is liquid nitrogen (-196C at atmospheric pressure).

Implementation:A box suited to the tube's external diameter forms the cooling envelope. This box is made from stainless steel or polystyrene for smalldiameters.

The box is installed after having locally stripped the pipeline of its covering or insulation.

The freezing box is filled with liquid nitrogen until the top generatrix of the tube is covered. This level must be maintained for the whole durationof the intervention. The ice plug then forms with annular growth, developing from the tube wall towards the pipeline's axis.

When the ice plug has formed, the supply of nitrogen to the envelope is limited to maintaining sufficient level.
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elcetronic expansion valve used in smaller capacity split units

HANDLING POE OILSPOE oils are more hygroscopic than mineral oils, so exposing POE oils to air will result in their absorbing moisture more quickly than

mineral oils. When POE oils are exposed to moisture and heat, they may react, forming acid that is harmful to the system. If a POEsystem is open for the same amount of time service technicians are used to having mineral oil systems open, there is a much greaterchance of moisture contamination of the oil and, consequently, downstream system concerns.
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There are many types and grades of POE oils, so it is important to understand that not all POE oils are the same. Areas of differences includelubricity, miscibility with refrigerants, viscosity, additive packages, pour point, and moisture content. Always check with the compressormanufacturer or system OEM to find the grade of POE oil recommended before adding or changing the oil.

Inline duct exhaust fan

HEPA filter"high efficiency particulate air filter" are routinely used in modern buildings,hospitals in order to control the spread of airborneparticulates and toxic or infectious agents.A True HEPA filter must be at least 99.997% efficient - allowing no more than 3 particles in10,000 to penetrate the filtration media.


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Thermistor is a device which takes temperature inputs and gives output in resistance values

How does a refrigerant distributor function?Distributors are used on multi-circuited evaporator coils. By using multiple circuits in evaporators, the pressure drop through theevaporator is minimized. The purpose of the distributor is to provide equal feeding of the refrigerant to each individual circuit. Becauseof this, its important for each connecting tube from the distributor to the evaporator to be of equal size and length. Also, itsrecommended that distributors be installed in a vertical position, to maintain equal flow under low load.
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Hydrometer used to measure the specific gravity of brine solution in HVAC field

Coefficient of Performance, COPThe COP is a measure of the amount of power input to a system compared to the amount of power output by that system:2Equation 1. Coefficient of performance equals the power output divided by the power input.A cop taking notes on a body outline.The COP is therefore a measurement of efficiency; the higher the number, the more efficient the system is. The COP is dimensionless becausethe input power and output power are measured in Watt. The COP is also an instantaneous measurement in that the units are power which canbe measured at one point in time.Consider a simple electric heater. All of the electricity that is input to the unit is converted to heat. There is no waste and the power output (inheat) equals the power input (in electricity), so the COP is one. The COP can be used to describe any system, not just heating and cooling.

What is a VFD?
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A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and vol tage supplied tothe electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive,and inverter.

Frequency (or hertz) is directly related to the motors speed (RPMs). In other words, the faster the frequency, the faster th e RPMs go. If anapplication does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet therequirements of the electric motors load. As the applications motor speed requirements change, the VFD can simply turn up or down themotor speed to meet the speed requirement.

HOW FLIGHT AIR-CONDITIONER WORKSBell-Coleman CycleThis cooling process uses air instead of a phase changing material such as Freon in the gas cycle. No condensation or evaporationof a refrigerant is involved.This is also known as the Air-Standard Refrigeration Cycle or Reverse Brayton Cycle. This 4-processrefrigeration cycle involves isentropic compression, followed by isobarric heat rejection, then isentropic expansion (usually by aturboexpander), and finally isobarric heat intake. This cycle is commonly used in jet aircraft, using engine bleed air for compressionand venting to the atmosphere. It is also commonly used in commercial air liquification plants
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HOW A TXV WORKS ?

common used refrigerants with molecular namesR-22 Monochlorodifluoromethane

R-12 Dichlorodifluoromethane

R-134a Tetrafluoroethane

R-600a Isobutane (2-Methyl propane)

R-407c Difluoromethane/

pentafluoroethane/

1,1,1,2-Tetrafluoroethane

what is the use of this instrument in airconditioning ?
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Instrument used to check the velocity of air

how expansion vessel works

R-407c ALTERNATE FOR R-22Best capacity and efficiency match to R-22


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The most efficient R-22 retrofit option in the marketplaceA change to POE lubricant is recommended. If existing MO is used, the addition of somePOE to the system is required for proper oil returnRequires a minimum of 20% POE for close-coupled A/C systemsNo TXV change requiredLowest GWP (1774) among R-22 replacementsLower discharge temperatures than R-22

BRAZED TYPE PLATE HEAT EXHANGER

HERMETIC RECIPROCATING COMPRESSOR


10/12

Frozen coils are caused by either low freon levels or a lack of air flow.You can 1) check for dirty filter 2) check the duct work for acrush 3) is there something that is restricting the air flow at the return vent 4) does the fan work? 5) check for dirty coils ,6) check filterdrier.

SILICA GELSilica gel is an amorphous form of silicon dioxide, which is synthetically produced in the form of hardirregular granules (having the appearance of crystals) or hard irregular beads. A microporous structureof interlocking cavities gives a very high surface area (800 square meters per gram). It is this structure thatmakes silica gel a high capacity desiccant. Water molecules adhere to the gels surface because it exhibitsa lower vapour pressure than the surrounding air. When an equilibrium of equal pressure is reached,no more adsorption occurs. Thus the higher the humidity of the surrounding air, the greater the amount ofwater that is adsorbed before equilibrium is reached. It is in these higher humidity conditions (above 50%Relative Humidity) that stored or in-transit items are susceptible to damage.The beauty of silica gel is the physical adsorption of water vapour into its internal pores. There is nochemical reaction, no by products or side effects. Even when saturated with water vapour, silica gelstill has the appearance of a dry product, its shape unchanged.


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USES OF TANDEM CONNECTIONSefficient capacity control - through cycling one or two compressor(s),increased reliability - fewer starts/stops than a single large compressor,reduced load starting, whereby individual compressors can be started up with a time delay between them,redundancy - part load capacity if one or two compressor fail, reduced replacement costs

why oil pressure switch is provided with time delay heater ?When the compressor starts, often the pump doesn't generate the needed oil pressure immediately.

Refrigerant mixed in the oil can boil out and the pump slowly build the necessary pressure.

Without the time delay, the compressor would stop prematurely creating nuisance service calls. so a 120 seconddelay provided on the oil pressure control.


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Date post:	03-Jun-2018
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