HVAC theory questions for the midterm: Book 1, chapter 1: What do you mean by HV
ID: 1718154 • Letter: H
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HVAC theory questions for the midterm: Book 1, chapter 1: What do you mean by HVAC? Write some applications of HVAC. Describe typical air distributon system with schematic diagram. Describe building system design interactions with schematic diagram. Describe HVAC system design process with schematic diagram. Book 3, chapter 2 and book6 chapters 3 & 8: Derive a formula for R of a gas mixture (book 3). Fig 3.19 and 3.20 (book 6): Draw thermal resistance network and find R_ . Explan ton of refrigeration (book 3). Book4, chapter 2 and book 2 chapters 16 & 18: Describe economiser cycle and performance with a schematic diagram and a performance diagram. Describe a CAV and a VAV system of zoned air conditioning with schematic diagrams. What are the factors to be considered for choosing an air conditioning system? Describe the matrix method of choosing a system with an example. Explain a) Dalton's law of partial pressure, b) humidity ratio and, c) relative humidity. Describe 5 psychrometric processes and show them on a symbolic psychrometric chart. Derive equations of by pass factors of heating and cooling coils with a schematic diagram. Describe adiabatic mixing of two air streams and prove that Describe winter/summer/year-round air conditioning system with schematic diagram. Book 1, chapter 7 and book 4 chapter 4: Show the schematic of energy terms for a human and write the energy balance equation. Explain the terms 'do' and 'met'. Name the important air contaminants and their sources. Describe the effects of the contaminants on human health. Describe the methods of controlling indoor air quality. Explain the term MERV. Describe the use of CO_2 to control ventilation rate.Explanation / Answer
1.What is HVAC?
Heating, Ventilating, and Air Conditioning (HVAC) equipment perform heating and/or cooling for residential, commercial or industrial buildings. The HVAC system may also be responsible for providing fresh outdoor air to dilute interior airborne contaminants such as odors from occupants, volatile organic compounds (VOC’s) emitted from interior furnishings, chemicals used for cleaning, etc. A properly designed system will provide a comfortable indoor environment year round when properly maintained.
applications:super charger plate,cooling tower isolation
2.Air distribution system
3.Building system design interaction
4.hvac design system:
2.FORMULA FOR R OF GAS MIXTURE:
R= m1R1+m2R2+m3R3+.../m1+m2+m3
TON OF refigeration:Refrigeration capacity ratings can be confusing, and different industries use different rating
standards. A 50 HP compressor with R-22 refrigerant may have a 50-ton capacity rating at warm RSW
temperatures; however, this decreases very rapidly as operating temperature drops. When used for
freezing this same compressor may only provide 71
/2-tons refrigeration capacity. Compressors also provide
different capacity with different refrigerants.
Technically, capacity ratings are only true at one set of operating conditions—a specific suction
temperature (low pressure), discharge temperature (high pressure), compressor RPM, and refrigerant.
A TON OF REFRIGERATION, or 12,000 BTU per hour capacity, is a term surviving from the day when ice
ruled refrigeration:
A ton of ice melting over 24 hrs. provides a ton of refrigeration each hour.
2,000 lbs. of ice at 144 BTUs per pound = 288,000 BTUs
288,000 ÷ 24 hrs. = 12,000 BTUs per hour, or 1 ton of refrigeration.
3.ECONOMISER CYCLE AND PERFORMANCE:
CAV SYSYEMS:
VAV SYSTEMS:
3.Factors considered for choosing an air conditioning:
An air conditioner is a considerable investment -- one that you don't make very often. You want to make sure that you've spent your money wisely, and your new system will serve you well for years to come. If you're about to buy an air conditioner, it behooves you to keep six considerations in mind:
Your warranty: This is a must. With a warranty, you're protected if something goes wrong. Make sure you know what you need to do to keep the warranty valid. Also keep in mind that warranty coverage for most home-comfort systems requires installation by an HVAC-system contractor. If you do it yourself, your warranty might not be honored.
Budget: Although you might be tempted to purchase the least expensive system available, remember that pricier units tend to have higher efficiencies, which make them less expensive to operate. Spending more up front could save you a wad of cash down the road.
Location: Your outside equipment should be in an area that's relatively free of debris and elaborate landscaping. Check the equipment periodically, and make sure there's nothing around it to restrict airflow. Inside your home, make sure your vents are free of obstructions, such as furniture.
Noise: A loud air conditioner can be an annoyance, causing you to turn up the television and shout in your own family room. More expensive air conditioners tend to run more quietly than less expensive systems. And again, spending a little more up front may be worth it. You can also abate some of the noise by adding curtains, carpeting and other soft elements to your rooms.
Energy efficiency: Today, it's quite easy to find an energy-efficient AC unit. Check the SEER ratings when you're out shopping. The higher the rating, the more efficient the unit. Also make sure that the unit you buy bears the Energy Star logo.
Installation and maintenance: Your best guarantee of problem-free service is to have your system professionally installed. And after that, have it maintained regularly. While you can change the filter and make sure your outside equipment is clean, you should have a professional tune up your system at the start of every cooling season.
4.Daltons law of pressure:
Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.
Humidity ratio:
Humidity ratio can be expressed as the ratio between the actual mass of water vapor present in moist air - to the mass of the dry air. Humidity ratio is normally expressed in kilogram or pounds of water vapor per kilogram or pounds of dry air
Relative humidity:
The amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature.
5.5 phscometric process:
6.Equations for bypass for heating and cooling
8.Winter/year/summer air conditioning system:
Book4:
1.schematic energy terms for a human:
3.What are the common air pollutants around?
Carbon Monoxide (CO)
Pollutants factsFuel combustion from vehicles and engines.
Pollutants factsReduces the amount of oxygen reaching the body’s organs and tissues; aggravates heart disease, resulting in chest pain and other symptoms.
Ground-level Ozone (O3)
Pollutants factsSecondary pollutant formed by chemical reaction of volatile organic compounds (VOCs) and NOx in the presence of sunlight.
Pollutants factsDecreases lung function and causes respiratory symptoms, such as coughing and shortness of breath, and also makes asthma and other lung diseases get worse. More on Ground Level Ozone Here
Lead (Pb)
Pollutants factsSmelters (metal refineries) and other metal industries; combustion of leaded gasoline in piston engine aircraft; waste incinerators (waste burners), and battery manufacturing.
Pollutants factsDamages the developing nervous system, resulting in IQ loss and impacts on learning, memory, and behavior in children. Cardiovascular and renal effects in adults and early effects related to anaemia.
Nitrogen Dioxide (NO2)
Pollutants factsFuel combustion (electric utilities, big industrial boilers, vehicles) and wood burning.
Pollutants factsWorsens lung diseases leading to respiratory symptoms, increased susceptibility to respiratory infection.
Particulate Matter (PM)
Pollutants factsThis is formed through chemical reactions, fuel combustion (e.g., burning coal, wood, diesel), industrial processes, farming (plowing, field burning), and unpaved roads or during road constructions.
Pollutants factsShort-term exposures can worsen heart or lung diseases and cause respiratory problems. Long-term exposures can cause heart or lung disease and sometimes premature deaths.
Sulfur Dioxide (SO2)
Pollutants factsSO2 comes from fuel combustion (especially high-sulfur coal); electric utilities and industrial processes as well as natural occurances like volcanoes.
Pollutants factsAggravates asthma and makes breathing difficult. It also contributes to particle formation with associated health effects.
Effect of contiminants :
4.method to control indoor air quality:
Source control
The most effective method of controlling your indoor air quality is to eliminate or reduce specific sources of pollution. Primary methods of source control include:
Smoking outdoors
Eliminating the use of candles, incense or liquid fuels, which can emit carbon monoxide, VOCs, polycyclic aromatic hydrocarbons and soot as by-products of combustion
Avoiding the use of chemical pesticides
Using natural cleaners instead of chemically-based cleaners
Changing filters in all appliances regularly
5.MERV:
The MERV (Minimum Efficiency Reporting Value) rating of a filter describes the size of the holes in the filter that allow air to pass through. The higher the MERV rating, the smaller the holes in the filter, the higher the efficiency.”
USE OF CO2 TO CONTROL VENTILATION RATE:
There are many ways to use CO2 measurement as the primary or secondary input to automatically control outside air intake rates. CO2 measurement is principally used to estimate the number of occupants in a defined space, based on the mathematical relationship between CO2 respiration and ambient outdoor rates, which are then used to calculate the estimated amount of outside (ventilation) air being supplied to the space.
Because of the added instrumentation costs and offsets by the energy savings expected in variable occupancies (compared to continuous supply of minimum rates for max ), CO2 –based DCV should apply only to dense, unpredictably variable and intermittent occupancies.
Five of the more popular non-proprietary ways include:
Control ventilation directly from interior CO2 concentrations alone;
CO2 Mass Balance;
CO2 Steady-state Concentration Balance (ref. ASHRAE 62-1999 Appdx. D / -2001 Appdx C),
OA Measurement with Reset by DCV (using CO2 or other occupancy input); and,
DCV Control only between Upper/Lower OA design limits, established by direct measurement.
DCV direct control has been attempted using only an indoor concentration measurement, with poor-to-mixed results. Interior concentrations alone have no direct relationship to ventilation rates.
Most methods require CO2 input as the differential (net indoor) concentration calculated from indoor CO2 minus outdoor CO2. This method provides an approximation of human occupancy based on many assumptions, including zero measurement error, constant respiration and production rates. Continuous outdoor CO2 measurement is required as one prerequisite in the conditional use of DCV for compliance with the Ventilation Rate Procedure of ASHRAE 62 and CEC’s Title 24 ventilation code.
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