Basics of Psychrometrics Practical Heat Load Calculation

Total Page:16

File Type:pdf, Size:1020Kb

Basics of Psychrometrics Practical Heat Load Calculation Basics of Psychrometrics Practical Heat Load Calculation Webinar 30 April 2020 Vikram Murthy ASHRAE Mumbai Chapter Sessions ►Basics of Psychrometrics ►All about Heat ►Practical Heat Load (Cooling Load) Calculation ( Using the E 20 , CLTD - Cooling Load Temperature Difference Method ) Psychrometric basics Psychrometrics ► A hundred and eighteen years ago, Willis Carrier, developed a method that allows us to visualize two of the variables -- the combination of air temperature and humidity that exist in a space. The tool he developed is called the Psychrometric Chart. ► Psychrometrics, which Willis Carrier developed, is the study of the mixture of dry air and water , and is the scientific basis of Air conditioning . Willis Carrier Willis began his first job at the Buffalo Forge Company . Solving a Problem at the Sackett Wilhelm Lithographing Company in Brooklyn, he formulated the Laws of Psychrometrics . Willis Carrier laid down the Equations of Psychrometrics in 1902 . The Carrier Company he founded developed the Centrifugal Chiller and the Weathermaker, that we call an Air Handling Unit or AHU . Purpose Of Comfort Airconditioning ►To Cool or Heat ►To Dehumidify or Humidify (remove or add moisture) ►To remove odours ►To remove particulate & microbial pollutants Definitions Of Air ► Air is a vital component of our everyday lives. ► Psychrometrics refers to the properties of moist air. ► Dry air ► Moist air ► Moist air and atmospheric air can be considered to mean the same Units ► We work in INCH POUND system of units, IP units. (The other unit system in use is SI units) Units of length: ft, inches. Units of area: sq.ft Units of volume: cu.ft. Weight: pound, lb. Moisture: grains. 7000 grains = 1 lb. Units ► Temperature: Deg F Ice = 32 deg F (0 deg C) ► Boiling water = 212 deg F (100 deg C) Body temp.: = 98.6 deg F ( 37 deg C) Karachi Summer temp = 99 deg F (37.1 deg C) Heat: (sensible and latent) Btu Specific Heat: btu/lb per deg F Specific Heat of dry air: Btu/lb per deg F Specific Heat of water vapour: Btu/lb per deg F W = humidity ratio, lbs of water per pound of dry air Units ► Rate of heat flow: Btu/Hr 1 watt = 3.41 BTU/Hr 1 kW = 3410 BTU/Hr 1 H.P. = 2545 BTU/Hr 1 Ton of Refrigeration = 12,000 BTU/Hr K value: BTU/Hr/Sq.ft/Inch thickness/deg F U value: BTU/Hr/Sq.ft/deg F Air quantity: cuft per minute, Cfm Psychrometry ►Air conditioning, by its very name means treating air. ►How would Air behave when it is subjected to cooling, heating, humidifying or de- humidifying processes. ►A study of the properties of Air at normal atmospheric pressure. ►Such a study is what is called Psychrometry. Psychrometry ►Psychrometry is the science of studying the thermodynamic properties of moist air and the use of these properties to analyze conditions and processes involving moist air. Psychrometry (from the Greek word : psukhros which means cold) , is the study of moist air (which is mostly oxygen, nitrogen and water vapor) and of the changes in its condition. an energy or heat graph ►Any point on the psychrometric chart represents air in a specific condition containing a certain amount of heat. The following can be determined by using a Psychrometric Chart : ►dry-bulb temperature ►wet-bulb temperature ►relative humidity (RH) ►humidity ratio ►specific volume ►dew point temperature ►enthalpy Dry Bulb Temperature ►air temperature ►indicated by a thermometer ►measured using a normal thermometer ►degrees Fahrenheit (oF) ►an indicator of heat content ►Constant dry bulb temperatures ►appear as vertical lines Dry Bulb Lines ►Any vertical line is a line of constant temperature. ►condition of air represented by any point on this line will have the temperature corresponding to this vertical line. ►the temperature as recorded by a thermometer which is dry. Dry Bulb Temperatures Dry-bulb Temperature - The temperature of air as registered by an ordinary thermometer. The horizontal X-axis denotes dry bulb temperature (DBT) scale. Vertical lines indicate constant dry bulb temperature. DBT is the air temperature measured in °C or °F and determined by an ordinary thermometer. Typical DB Line Humidity Ratio / Absolute Humidity Y-axis indicates humidity ratio or absolute humidity, which is the weight of the water, contained in the air per unit of dry air. This is often expressed as pounds of moisture per pound of dry air. Humidity ratio is found on the vertical, y-axis with lines of constant humidity ratio running horizontally across the chart. Humidity Ratio / Absolute Humidity The Y axis shows the water vapor component and is generally shown in lbs of water vapor. Sometimes the vapor content is also shown in grains of water vapor. One pound of water vapor =7000 grains of water vapor Moisture is indicated in either Lbs of water vapor or grains of water vapor, per pound of dry air Typical Absolute Humidity Line Wet Bulb Lines ►There are number of parallel slant lines which are called wet bulb lines. ►temperature of the air as recorded by a thermometer with a wet wick on its bulb. ►air having a certain wet bulb temperature will have a definite heat content although its dry bulb temperature may be anything. Wet Bulb Lines Wet Bulb Temperatures Wet Bulb Temperature (WBT) is defined as the temperature at which water, by evaporating into air, can bring the air W e to saturation at the same t B ul b temperature Li ne Inherent in this definition is an assumption that no heat is lost or gained by the air. MEASURING THE WET BULB TEMPERATURE The wet-bulb thermometer is wrapped in a cotton wick; when the wick is completely wet, swing the thermometer around, and the water evaporating at the wick pulls the wet- bulb thermometer’s temperature down in direct proportion to the water content of the air around it. The drier the air, the more water evaporates at the wick and the lower the wet-bulb temperature gets MEASURING THE WET BULB TEMPERATURE The wet-bulb thermometer tells us the relative humidity-the moisture content of the air compared with how much moisture it can hold. When the dry- and wet-bulb temperatures are equal it means that the air is holding as much moisture as it possibly can- i.e. air is at 100% relative humidity. Relative Humidity Lines ►When the air contains its maximum moisture content, we call it saturated air. ►when it contains anything less than this maximum limit then it is not saturated air. ►We, therefore, say that such air is 50% saturated or 60% saturated. ►the percentage saturation is "relative humidity" Relative Humidity The Condition of Air at Point T is plotted on the chart and its saturated moisture content is then 2 checked We find that the T 1 saturated condition moisture content is indicated by Point 2 The moisture condition at condition T is indicated by Point 1 Relative Humidity The relative Humidity of 2 air at condition T is the ratio of Moisture content T at saturation, to the 1 Moisture condition of air at the specific condition RH = Specific Moisture value ( Point1) Specific Moisture value ( Point 2 Relative Humidity Relative Humidity, is an expression of the moisture content of a given atmosphere as a percentage of the saturation humidity at the same temperature. The RH lines are shown on the chart Saturation Line ►The curved line on the extreme left-hand side of the chart is what is called the saturation line. ►condition of air represented by any point on this line is said to be saturated air. ►the air is having the maximum possible content in it. It cannot hold any further moisture. Relative Humidity The air is 100% saturated when the moisture content in the air is at its maximum possible and the saturation line is shown on the chart Dew Point ►The Dew Point is the temperature at which water vapor starts to condense out of the air. ►Move horizontally on the psychrometric chart and read the temperature where you intersect the saturation line. ►It is the moisture content which determines the dew point. Dew Point Dew Point Temperatures When air, at a certain dry bulb temperature and relative humidity, is cooled up to saturation condition, from point R to Saturation, it reaches its DEW POINT CONDITION R Condensation occurs on surfaces, which are at or below the dew-point temperature, and which are in contact with the air DEW POINT at condition R Dew Point ► If the dew-point temperature is close to the air temperature, the relative humidity is high. ► if the dew point is well below the air temperature, the relative humidity is low. ► If moisture condensates on a cold bottle from the refrigerator, the dew-point temperature of the air is above the temperature in the refrigerator. ► The Dew Point is given by the saturation line in the psychrometric chart. Enthalpy ►Wet Bulb Lines as lines of constant heat content of air. ►Enthalpy is just another term used in place of "heat content". Enthalpy ►At any temperature there is a limit to the maximum moisture holding capacity of air. ►At higher and higher atmospheric pressure, the moisture holding capacity at any given temperature becomes less and less. ►The enthalpy of moist and humid air consist of sensible heat and latent heat. ENTHALPY Enthalpy (E) is the heat energy content of moist air. It is expressed in Btu per Enthalpy scale pound of dry air and represents the heat energy due to temperature and moisture in the air. Lines of constant enthalpy run diagonally downward from left to right across the chart ( As shown).
Recommended publications
  • Wind- Chimney
    WIND-CHIMNEY Integrating the Principles of a Wind-Catcher and a Solar-Chimney to Provide Natural Ventilation A Thesis presented to the Faculty of California Polytechnic State University, San Luis Obispo In Partial Fulfillment of the Requirements for the Degree Master of Science in Architecture by Fereshteh Tavakolinia December 2011 WIND-CHIMNEY Integrating the Principles of a Wind-Catcher and a Solar-Chimney to Provide Natural Ventilation © 2011 Fereshteh Tavakolinia ALL RIGHTS RESERVED ii COMMITTEE MEMBERSHIP TITLE: WIND-CHIMNEY Integrating the Principles of a Wind-Catcher and a Solar-Chimney to Provide Natural Ventilation AUTHOR: Fereshteh Tavakolinia DATE SUBMITTED: December 2011 COMMITTEE CHAIR: James A. Doerfler, Associate Department Head COMMITTEE MEMBER: Jacob Feldman, Professor iii WIND-CHIMNEY Integrating the principles of a wind-catcher and a solar chimney to provide natural ventilation Fereshteh Tavakolinia Abstract This paper suggests using a wind-catcher integrated with a solar-chimney in a single story building so that the resident might benefit from natural ventilation, a passive cooling system, and heating strategies; it would also help to decrease energy use, CO2 emissions, and pollution. This system is able to remove undesirable interior heat pollution from a building and provide thermal comfort for the occupant. The present study introduces the use of a solar-chimney with an underground air channel combined with a wind-catcher, all as part of one device. Both the wind-catcher and solar chimney concepts used for improving a room’s natural ventilation are individually and analytically studied. This paper shows that the solar-chimney can be completely used to control and improve the underground cooling system during the day without any electricity.
    [Show full text]
  • Mathematical Reference
    TRNSYS 16 a TRaNsient SYstem S imulation program Volume 5 Mathematical Reference Solar Energy Laboratory, Univ. of Wisconsin-Madison http://sel.me.wisc.edu/trnsys TRANSSOLAR Energietechnik GmbH http://www.transsolar.com CSTB – Centre Scientifique et Technique du Bâtiment http://software.cstb.fr TESS – Thermal Energy Systems Specialists http://www.tess-inc.com TRNSYS 16 – Mathematical Reference About This Manual The information presented in this manual is intended to provide a detailed mathematical reference for the Standard Component Library in TRNSYS 16. This manual is not intended to provide detailed reference information about the TRNSYS simulation software and its utility programs. More details can be found in other parts of the TRNSYS documentation set. The latest version of this manual is always available for registered users on the TRNSYS website (see here below). Revision history • 2004-09 For TRNSYS 16.00.0000 • 2005-02 For TRNSYS 16.00.0037 • 2006-03 For TRNSYS 16.01.0000 • 2007-03 For TRNSYS 16.01.0003 Where to find more information Further information about the program and its availability can be obtained from the TRNSYS website or from the TRNSYS coordinator at the Solar Energy Lab: TRNSYS Coordinator Email: [email protected] Solar Energy Laboratory, University of Wisconsin-Madison Phone: +1 (608) 263 1586 1500 Engineering Drive, 1303 Engineering Research Building Fax: +1 (608) 262 8464 Madison, WI 53706 – U.S.A. TRNSYS website: http://sel.me.wisc.edu/trnsys Notice This report was prepared as an account of work partially
    [Show full text]
  • Passive and Low Energy Cooling Survey
    Environmental Building News - Marc Rosenbaum's Passive and Low Energy Cooling Summary... Page 1 of 14 Home Search Subscribe Features Product Reviews Other Stories Passive and Low Energy Cooling Survey by Marc Rosenbaum, P.E. Marc's other articles 1.0 Comfort 2.0 Psychrometrics 3.0 Conventional Mechanical Cooling Using Vapor Compression 4.0 Loads 5.0 Climate 6.0 Distribution Options 7.0 Dehumidification 8.0 Ventilative Cooling 9.0 Nocturnal Ventilative Cooling 10.0 Night Sky Radiational Cooling 11.0 Evaporative Cooling 12.0 Earth-coupled Cooling 13.0 System Strategies This report documents a survey I made of passive and low energy cooling techniques. It begins with an overview of general cooling issues. The topics covered in the sections following are: comfort, psychrometrics, an overview of mechanical cooling, loads, climate data, distribution options, dehumidification, ventilative cooling, nocturnal ventilative cooling, radiant cooling, evaporative cooling, earth-coupled cooling, and combined system strategies. Principal references were Passive Cooling, edited by Jeffrey Cook, and Passive and Low Energy Cooling of Buildings, by Baruch Givoni. Both books are primarily academic in nature, but Givoni in particular provides plenty of actual field data. These books don't necessarily represent the state- of-the-art: Cook was published in 1989, and Givoni in 1994. As we decide which direction to pursue, we will seek more current information. The physics are unlikely to change much, however. The usual caveat applies: I am not expert in any of these applications, and all errors herein are mine. 1.0 Comfort Buildings are cooled primarily to enhance human comfort.
    [Show full text]
  • Psychrometrics Outline
    Psychrometrics Outline • What is psychrometrics? • Psychrometrics in daily life and food industry • Psychrometric chart – Dry bulb temperature, wet bulb temperature, absolute humidity, relative humidity, specific volume, enthalpy – Dew point temperature • Mixing two streams of air • Heating of air and using it to dry a product 2 Psychrometrics • Psychrometrics is the study of properties of mixtures of air and water vapor • Water vapor – Superheated steam (unsaturated steam) at low pressure – Superheated steam tables are on page 817 of textbook – Properties of dry air are on page 818 of textbook – Psychrometric charts are on page 819 & 820 of textbook • What are these properties of interest and why do we need to know these properties? 3 Psychrometrics in Daily Life • Sea breeze and land breeze – When and why do we get them? • How do thunderstorms, hurricanes, and tornadoes form? • What are dew, fog, mist, and frost and when do they form? • When and why does the windshield of a car fog up? – How do you de-fog it? Is it better to blow hot air or cold air? Why? • Why do you feel dry in a heated room? – Is the moisture content of hot air lower than that of cold air? • How does a fan provide relief from sweating? • How does an air conditioner provide relief from sweating? • When does a soda can “sweat”? • When and why do we “see” our breath? • Do sailboats perform better at high or low relative humidity? Key factors: Temperature, Pressure, and Moisture Content of Air 4 Do Sailboats Perform Better at low or High RH? • Does dry air or moist air provide more thrust against the sail? • Which is denser – humid air or dry air? – Avogadro’s law: At the same temperature and pressure, the no.
    [Show full text]
  • Performance of Rotary Enthalpy Exchangers
    PERFORMANCE OF ROTARY ENTHALPY EXCHANGERS by GUNNAR STIESCH A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE (Mechanical Engineering) at the UNIVERSITY OF WISCONSIN-MADISON 1994 ABSTRACT Rotary regenerative heat and mass exchangers allow energy savings in the heating and cooling of ventilated buildings by recovering energy from the exhaust air and transferring it to the supply air stream. In this study the adsorption isotherms and the specific heat capacity of a desiccant used in a commercially available enthalpy exchanger are investigated experimentally, and the measured property data are used to simulate the regenerator performance and to analyze the device in terms of both energy recovery and economic profitability. Based on numerical solutions for the mechanism of combined heat and mass transfer obtained with the computer program MOSHMX for various operating conditions, a computationally simple model is developed that estimates the performance of the particular enthalpy exchanger and also of a comparable sensible heat exchanger as a function of the air inlet conditions and the matrix rotation speed. The model is built into the transient simulation program TRNSYS, and annual regenerator performance simulations are executed. The integrated energy savings over this period are determined for the case of a ventilation system for a 200 people office building (approx. 2 m3/s) for three different locations in the United States, each representing a different climate. Life cycle savings that take into account the initial cost of the space-conditioning system as well as the operating savings achieved by the regenerator are evaluated for both the enthalpy exchanger and the sensible heat exchanger over a system life time of 15 years.
    [Show full text]
  • Teaching Psychrometry to Undergraduates
    AC 2007-195: TEACHING PSYCHROMETRY TO UNDERGRADUATES Michael Maixner, U.S. Air Force Academy James Baughn, University of California-Davis Michael Rex Maixner graduated with distinction from the U. S. Naval Academy, and served as a commissioned officer in the USN for 25 years; his first 12 years were spent as a shipboard officer, while his remaining service was spent strictly in engineering assignments. He received his Ocean Engineer and SMME degrees from MIT, and his Ph.D. in mechanical engineering from the Naval Postgraduate School. He served as an Instructor at the Naval Postgraduate School and as a Professor of Engineering at Maine Maritime Academy; he is currently a member of the Department of Engineering Mechanics at the U.S. Air Force Academy. James W. Baughn is a graduate of the University of California, Berkeley (B.S.) and of Stanford University (M.S. and PhD) in Mechanical Engineering. He spent eight years in the Aerospace Industry and served as a faculty member at the University of California, Davis from 1973 until his retirement in 2006. He is a Fellow of the American Society of Mechanical Engineering, a recipient of the UCDavis Academic Senate Distinguished Teaching Award and the author of numerous publications. He recently completed an assignment to the USAF Academy in Colorado Springs as the Distinguished Visiting Professor of Aeronautics for the 2004-2005 and 2005-2006 academic years. Page 12.1369.1 Page © American Society for Engineering Education, 2007 Teaching Psychrometry to Undergraduates by Michael R. Maixner United States Air Force Academy and James W. Baughn University of California at Davis Abstract A mutli-faceted approach (lecture, spreadsheet and laboratory) used to teach introductory psychrometric concepts and processes is reviewed.
    [Show full text]
  • Understanding Psychrometrics, Third Edition It’S Really a Mine of Information
    Gatley The Comprehensive Guide to Psychrometrics Understanding Psychrometrics serves as a lifetime reference manual and basic refresher course for those who use psychrometrics on a recurring basis and provides a four- to six-hour psychrometrics learning module to students; air- conditioning designers; agricultural, food process, and industrial process engineers; Understanding Psychrometrics meteorologists and others. Understanding Psychrometrics Third Edition New in the Third Edition • Revised chapters for wet-bulb temperature and relative humidity and a revised Appendix V that includes a summary of ASHRAE Research Project RP-1485. • New constants for the universal gas constant based on CODATA and a revised molar mass of dry air to account for the increase of CO2 in Earth’s atmosphere. • New IAPWS models for the calculation of water properties above and below freezing. • New tables based on the ASHRAE RP-1485 real moist-air numerical model using the ASHRAE LibHuAirProp add-ins for Excel®, MATLAB®, Mathcad®, and EES®. Includes Access to Bonus Materials and Sample Software • PDF files of 13 ultra-high-pressure and 12 existing ASHRAE psychrometric charts plus three new 0ºC to 400ºC charts. • A limited demonstration version of the ASHRAE LibHuAirProp add-in that allows users to duplicate portions of the real moist-air psychrometric tables in the ASHRAE Handbook—Fundamentals for both standard sea level atmospheric pressure and pressures from 5 to 10,000 kPa. • The hw.exe program from the second edition, included to enable users to compare the 2009 ASHRAE numerical model real moist-air psychrometric properties with the 1983 ASHRAE-Hyland-Wexler properties. Praise for Understanding Psychrometrics, Third Edition It’s really a mine of information.
    [Show full text]
  • Improving Stack Effect in Hot Humid Building Interiors with Hybrid Turbine Ventilator(S)
    MAT EC Web of Conferences 17, 01012 (2014) DOI: 10.1051/matecconf/20141701012 C Owned by the authors, published by EDP Sciences, 2014 Improving Stack Effect in Hot Humid Building Interiors with Hybrid Turbine Ventilator(s) Radia Tashkina Rifa1, Karam M. Al-Obaidi2 , Abdul Malek Abdul Rahman3,a 1,2,3School of Housing, Building and Planning, Universiti Sains Malaysia, 11800, Penang, Malaysia Abstract. Natural ventilation strategies have been applied through the ages to offer thermal comfort. At present, these techniques could be employed as one of the methods to overcome the electric consumption that comes from the burning of disproportionate fossil fuel to operate air conditioners. This air conditioning process is the main contributor of CO2 emissions. This paper focuses on the efficiency of stack ventilation which is one of the natural ventilation strategies, and at the same time attempts to overcome the problem of erratic wind flow and the low indoor/outdoor temperature difference in the hot, humid Malaysian climate. Wind flow and sufficient pressure difference are essential for stack ventilation, and as such the irregularity can be overcome with the use of the Hybrid Turbine Ventilator (HTV) which extracts hot air from the interior of the building via the roof level. The extraction of hot air is constant and consistent throughout the day time as long as there is sunlight falling on the solar panel for solar electricity. The aim of this paper is to explore the different HTV strategies and find out which building dimensions is most expected to reduce maximum indoor air temperature of a given room in a real weather condition.
    [Show full text]
  • The Wind-Catcher, a Traditional Solution for a Modern Problem Narguess
    THE WIND-CATCHER, A TRADITIONAL SOLUTION FOR A MODERN PROBLEM NARGUESS KHATAMI A submission presented in partial fulfilment of the requirements of the University of Glamorgan/ Prifysgol Morgannwg for the degree of Master of Philosophy August 2009 I R11 1 Certificate of Research This is to certify that, except where specific reference is made, the work described in this thesis is the result of the candidate’s research. Neither this thesis, nor any part of it, has been presented, or is currently submitted, in candidature for any degree at any other University. Signed ……………………………………… Candidate 11/10/2009 Date …………………………………....... Signed ……………………………………… Director of Studies 11/10/2009 Date ……………………………………… II Abstract This study investigated the ability of wind-catcher as an environmentally friendly component to provide natural ventilation for indoor environments and intended to improve the overall efficiency of the existing designs of modern wind-catchers. In fact this thesis attempts to answer this question as to if it is possible to apply traditional design of wind-catchers to enhance the design of modern wind-catchers. Wind-catchers are vertical towers which are installed above buildings to catch and introduce fresh and cool air into the indoor environment and exhaust inside polluted and hot air to the outside. In order to improve overall efficacy of contemporary wind-catchers the study focuses on the effects of applying vertical louvres, which have been used in traditional systems, and horizontal louvres, which are applied in contemporary wind-catchers. The aims are therefore to compare the performance of these two types of louvres in the system. For this reason, a Computational Fluid Dynamic (CFD) model was chosen to simulate and study the air movement in and around a wind-catcher when using vertical and horizontal louvres.
    [Show full text]
  • Solar Chimneys for Residential Ventilation
    SOLAR CHIMNEYS FOR RESIDENTIAL VENTILATION Pavel Charvat, Miroslav Jicha and Josef Stetina Department of Thermodynamics and Environmental Engineering Faculty of Mechanical Engineering Brno University of Technology Technicka 2, 616 69 Brno, Czech Republic ABSTRACT An increasing impact of ventilation and air-conditioning to the total energy consumption of buildings has drawn attention to natural ventilation and passive cooling. The very common way of natural ventilation in residential buildings is passive stack ventilation. The passive stack ventilation relies on the stack effect created by the temperature difference between air temperature inside and outside a building. A solar chimney represents an option how to improve the performance of passive stack ventilation on hot sunny days, when there is a small difference between indoor and outdoor air temperature. The full-scale solar chimneys have been built and tested at the Department of Thermodynamics and Environmental Engineering at the Brno University of Technology. The main goal of the experiments is to investigate performance of solar chimneys under the climatic conditions of the Czech Republic. Two different constructions of a solar chimney have been tested; a light weight construction and the construction with thermal mass. KEYWORDS solar chimney, residential ventilation, passive cooling PRINCIPLE OF SOLAR CHIMNEY VENTILATION A solar chimney is a natural-draft device that uses solar radiation to move air upward, thus converting solar energy (heat) into kinetic energy (motion) of air. At constant pressure air density decreases with increasing temperature. It means that air with higher temperature than ambient air is driven upwards by the buoyancy force. A solar chimney exploits this physical phenomenon and uses solar energy to heat air up.
    [Show full text]
  • Indoor Air Quality, the House As a System and Vented Combustion
    Michael J. Van Buren, P.E. Blazing Design, Inc. 49 Commerce Ave, 6A S. Burlington, Vermont 05403 (p) 802-318-6973 Email – [email protected] Fireplace Design “The House as a System” House as a System What does it mean, The “House as a System”? The house as a system refers to how air moves in, out and around a house. Air moves in and out of a house through the “building envelope”. Why Consider the “House as a System”? Many chimneys fail to operate because of aspects of the house and its surroundings. If air flows out of a house, air must flow back into the house Pressure Differences, What Pressure Differences? My Ears Don’t Even Pop! 1 Pound per square inch (Psi) = 27.71 inches of water column (W.C.) 0.1 inch water column (W.C.) = 25 Pascals (PA) House pressures range from 5 to –25 PA What Causes These Air Pressure Differences? Appliances that take air out of the house Exhaust fans – bathrooms, kitchens Clothes dryers Furnaces Atmospherically vented combustion appliances; fireplaces, furnaces, boilers, hot water heaters. Typical Air Flows of Exhaust Fans Device Air Flow (CFM) Bathroom Fan 32-64 Standard Kitchen Fan 85-127 Downdraft Kitchen Fan 210-425 Clothes Dryer 85-160 Central Vacuum 50-110 When air goes out - more air must come in! Fireplace Needs Other Causes affecting Air Pressure Differences The Not-So Obvious Reasons Buoyancy of warm air – “Stack Effect” Wind Furnaces Buoyancy of Warm Air? Everyone knows hot air rises – Why? Hot air is lighter than cold air (air expands when it is heated) That’s why candle flames go up That’s why hot air goes up a chimney Buoyancy of hot air causes a pressure difference in the house relative to the outside pressure which is called “Stack Effect” Stack Effect? Stack Effect - The pressure difference created between the warmer air in a building and the colder air outside.
    [Show full text]
  • Factors Affecting Indoor Air Quality
    Factors Affecting Indoor Air Quality The indoor environment in any building the categories that follow. The examples is a result of the interaction between the given for each category are not intended to site, climate, building system (original be a complete list. 2 design and later modifications in the Sources Outside Building structure and mechanical systems), con- struction techniques, contaminant sources Contaminated outdoor air (building materials and furnishings, n pollen, dust, fungal spores moisture, processes and activities within the n industrial pollutants building, and outdoor sources), and n general vehicle exhaust building occupants. Emissions from nearby sources The following four elements are involved n exhaust from vehicles on nearby roads Four elements— in the development of indoor air quality or in parking lots, or garages sources, the HVAC n loading docks problems: system, pollutant n odors from dumpsters Source: there is a source of contamination pathways, and or discomfort indoors, outdoors, or within n re-entrained (drawn back into the occupants—are the mechanical systems of the building. building) exhaust from the building itself or from neighboring buildings involved in the HVAC: the HVAC system is not able to n unsanitary debris near the outdoor air development of IAQ control existing air contaminants and ensure intake thermal comfort (temperature and humidity problems. conditions that are comfortable for most Soil gas occupants). n radon n leakage from underground fuel tanks Pathways: one or more pollutant pathways n contaminants from previous uses of the connect the pollutant source to the occu- site (e.g., landfills) pants and a driving force exists to move n pesticides pollutants along the pathway(s).
    [Show full text]