United air conditioning pdf free download

Houma Today July 3, Is air conditioning helping spread coronavirus? In southern states, being indoors may be a factor Bill Bahnfleth. Business Insider July 1, 4 ways to know if you're in a well-ventilated space, reducing the risk of spreading or contracting the coronavirus Bill Bahnfleth. The Washington Post June 26, As America struggles to reopen schools and offices, how to clean coronavirus from the air Bill Bahnfleth.

Fast Company June 6, Will air-conditioning help spread the coronavirus? Probably Not Bill Bahnfleth. Building Readiness PDF. Energy Recovery PDF. This analysis is meant to be able to identify potential issues with ERVs, such as being considered leaky, so that they can be evaluated for operation during an epidemic.

The Exhaust Re-entrainment Guide was created by the Building Readiness Team to identify the concerns and potential methods to evaluate your systems for exhaust re-entrainment. This applies to units with and without ERVs but includes multiple methods to evaluate your systems. In the context of the rapidly evolving state of knowledge regarding transmission of COVID, design professionals may consider interventions that adopt a precautionary principle, taking reasonable actions that reduce risk while awaiting greater scientific certainty.

Therefore, this guidance should be read in conjunction with the relevant government guidance and available research. This material is not a substitute for the advice of a qualified professional. By adopting these recommendations for use, each adopter agrees to accept full responsibility for any personal injury, death, loss, damage or delay arising out of or in connection with their use by or on behalf of such adopter irrespective of the cause or reason therefore and agrees to defend, indemnify and hold harmless ASHRAE and ASHE, the authors and others involved in their publication from any and all liability arising out of or in connection with such use as aforesaid and irrespective of any negligence on the part of those indemnified.

Updated Residential Guidance February 17, Air Force, U. Navy, and Canadian Atmospheric Environment Service. The data are an average of 15 years.

An occurrence of less than 2. This design value is often used for evaporative cooling design. A degree day is the difference between a base temperature and the mean daily outdoor air temperature To.

The human body requires energy for physical and mental activity. This energy comes from the oxidation of food. The metabolic rate depends mainly on the intensity of the physical activity of the human body. Heat is released from the human body by two means: sensible heat exchange and evaporative heat loss.

The physiological and environmental factors that affect the thermal comfort of the occupants in an air-conditioned space are mainly: 1.

Metabolic rate M determines the amount of heat that must be released from the human body. The operating temper- ature To is the weighted sum of Tr and Trad. Trad is defined as the temperature of a uniform black enclosure in which the surrounded occupant would have the same radiative heat exchange as in an actual indoor environment.

Tr affects both the sensible heat exchange and evaporative losses, and Trad affects only sensible heat exchange. Air velocity of the indoor air vr , in fpm, which affects the heat transfer coefficients and therefore the sensible heat exchange and evaporative loss.

Clothing insulation for occupants is typically 0. Regarding the indoor humidity: 1. Many comfort air-conditioning systems are not equipped with humidifiers. Winter indoor relative humidity should not be specified in such circumstances. For air-conditioning systems that use flow rate control in the water cooling coil, space indoor relative humidity may be substantially higher in part load than at full load.

For space served by air-conditioning systems using low- and medium- efficiency air filters, according to the U.

Total particulate concentration. This concentration comprises particles from building materials, combustion products, mineral fibers, and synthetic fibers.

Formaldehyde and organic gases. Formaldehyde is a colorless, pungent-smelling gas. It comes from pressed wood products, building materials, and combustion. Formaldehyde causes eye, nose, and throat irritation as well as coughing, fatigue, and allergic reactions. Formaldehyde may also cause cancer. Other organic gases come from building materials, carpeting, furnishings, cleaning materials, etc.

Radon, a colorless and odorless gas, is released by the decay of uranium from the soil and rock beneath buildings, well water, and building materials. Radon and its decay products travel through pores in soil and rock and infiltrate into buildings along the cracks and other openings in the basement slab and walls.

Radon at high levels causes lung cancer. The estimated national average is 1. These include bacteria, fungi, mold and mildew, viruses, and pollen. They may come from wet and moist walls, carpet furnishings, and poorly maintained dirty air-conditioning systems and may be transmitted by people. Some biological contaminants cause allergic reactions, and some transmit infectious diseases.

Combustion products. These include environmental tobacco smoke, nitrogen dioxide, and carbon monoxide. Environmental tobacco smoke from cigarettes is a discomfort factor to other persons who do not smoke, especially children.

Nicotine and other tobacco smoke components cause lung cancer, heart disease, and many other diseases. Nitrogen dioxide and carbon monoxide are both combustion products from unvented kerosene and gas space heaters, woodstoves, and fireplaces. Nitrogen dioxide NO2 causes eye, nose, and throat irritation; may impair lung function; and increases respiratory infections. Carbon monoxide CO causes fatigue at low concentrations; impaired vision, headache, and confusion at higher concentrations; and is fatal at very high concentrations.

Houses without gas heaters and gas stoves may have CO levels varying from 0. Human bioeffluents. These include the emissions from breath including carbon dioxide exhaled from the lungs, body odors from sweating, and gases emitted as flatus.

There are three basic means of reducing the concentration of indoor air contaminants and improving indoor air quality: 1 eliminate or reduce the source of air pollution, 2 enhance the efficiency of air filtration, and 3 increase the ventilation outdoor air intake. Dilution of the concentrations of indoor contaminants by outdoor ventilation air is often the simple and cheapest way to improve indoor air quality.

The amount of outdoor air required for metabolic oxidation is rather small. Field measurements of daily maximum CO2 levels in office buildings reported by Persily show that most of them were within the range to ppm.

If unusual contaminants or unusually strong sources of contaminants are introduced into the space, or recirculated air is to replace part of the outdoor air supply for occupants, then acceptable indoor air quality is achieved by controlling known and specific contaminants. This is called an indoor air quality procedure.

Clean Rooms Electronic, pharmaceutical, and aerospace industries and operating rooms in hospitals all need strict control of air cleanliness during manufacturing and operations.

Space Pressure Differential Most air-conditioning systems are designed to maintain a slightly higher pressure than the surroundings, a positive pressure, to prevent or reduce infiltration and untreated air entering the space directly. For comfort air-conditioning systems, the recommended pressure differential between the indoor and outdoor air is 0. WG indicates the pressure at the bottom of a top-opened water column of specific inches of height; 1 in. For clean rooms, Federal Standard No.

WG with all entryways closed. When the entryways are open, an outward flow of air is to be maintained to prevent migration of contaminants into the clean room. In comfort systems, the space pressure differential is usually not specified in the design documents. Sound Levels Noise is any unwanted sound.

In air-conditioning systems, noise should be attenuated or masked with another less objectionable sound. Sound power is the capability to radiate power from a sound source exited by an energy input. The intensity of sound power is the output from a sound source expressed in watts W.

The human ear and microphones are sound pressure sensitive. The sound power level of any sound source is a fixed output. It cannot be measured directly; it can only be calculated from the measured sound pressure level. The sound pressure level at any one point is affected by the distance from the source and the characteristics of the surroundings.

For convenience in analysis, sound frequencies are often subdivided into eight octave bands. An octave is a frequency band in which the frequency of the upper limit of the octave is double the frequency of the lower limit.

An octave band is represented by its center frequency, such as 63, , , , , , , and Hz. On Hz the octave band has a higher limit of Hz and a lower limit of Hz. Human ears do not respond in the same way to low frequencies as to high frequencies. The object of noise control in an air conditioned space is to provide background sound low enough that it does not interfere with the acoustical requirements of the occupants. The distribution of background sound should be balanced over a broad range of frequencies, that is, without whistle, hum, rumble, and beats.

The most widely used criteria for sound control are the noise criteria NC curves. The shape of NC curves is similar to the equal-loudness contour representing the response of the human ear. NC curves also intend to indicate the permissible sound pressure level of broad-band noise at various octave bands rated by a single NC curve. NC curves are practical and widely used. RC curves are similar to NC curves except that the shape of the RC curves is a close approximation to a balanced, bland-sounding spectrum.

The A-weighted sound level is a single value and simulates the response of the human ear to sound at low sound pressure levels. If the period is shorter, the dBA level can be slightly higher. Refer to this standard for details. A room is an enclosed or partitioned space that is considered as a single load. An air-conditioned room does not always have an individual zone control system. A zone is a space of a single room or group of rooms having similar loads and operating characteristics.

An air-conditioned zone is always installed with an individual control system. A typical floor in a building may be treated as a single zone space, or a multizone space of perimeter, interior, east, west, south, north, Space and equipment loads can be classified as: 1.

The rate of sensible heat entering the space is called sensible heat gain qes, whereas the rate of latent heat entering the space is called latent heat gain qel. The cooling coil load qcc is the rate of heat removal from the conditioned air by the chilled water or refrigerant inside the coil.

The heating coil load qch is the rate of heat energy addition to the conditioned air by the hot water, steam, or electric elements inside the coil. Convective Heat and Radiative Heat Heat enters a space and transfer to the space air from either an external source or an internal source is mainly in the form of convective heat and radiative heat transfer.

Consider radiative heat transfer, such as solar radiation striking the outer surface of a concrete slab as shown in Figure 9. Most of the radiative heat is absorbed by the slab. Only a small fraction is reflected. After the heat is absorbed, the outer surface temperature of the slab rises. If the slab and space air are in thermal equilibrium before the absorption of radiative heat, heat is convected from the outer surface of the slab to the space air as well as radiated to other surfaces.

At the same time, heat is conducted from the outer surface to the inner part of the slab and stored there when the temperature of the inner part of the slab is lower than that of its outer surface. Heat convected from the outer surface of the concrete slab to the space air within a time interval forms the sensible cooling load. The sensible heat gain entering the conditioned space does not equal the sensible cooling load during the same time interval because of the stored heat in the building envelope.

Only the convective heat becomes cooling load instantaneously. The sum of the convective heats from the outer surfaces, including the outer surfaces of the internal heat gains in a conditioned space, becomes cooling load. This phe- nomenon results in a smaller cooling load than heat gain, as shown in Figure 9. In a load profile, load is always plotted against time.

The load profile depends on the outdoor climate as well as the space operating characteristics. Peak load is the maximum cooling load in a load profile. Block load is the sum of the zone loads and floor loads at a specific time. The sum of the zone peak loads in a typical floor does not equal the block load of that floor because the zone peak loads may all not appear at the same time.

Moisture Transfer in Building Envelope Moisture transfer takes place along two paths: 1. Moisture migrates in the building envelope in both liquid and vapor form. Liquid flow is induced by capillary flow and moisture content gradient. Vapor diffusion is induced by vapor pressure gradients. Moisture content is defined as the ratio of the mass of moisture contained in a solid to the mass of bone- dry solid.

During the migration, the moisture content and the vapor pressure are in equilibrium at a specific temperature and location. Air leakage and its associated water vapor infiltrate or exfiltrate through the cracks, holes, and gaps between joints because of poor construction of the building envelope. The driving potential of this air leakage and associated water vapor is the pressure differential across the building envelope. If the insulating material is of open-cell structure, air leakage and associated water vapor may penetrate the perforated insulating board through cracks and gaps.

Condensation, even freezing, will occur inside the perforated insulation board if the temperature of the board is lower than the dew point of the leaked air or the freezing point of the water. In most comfort air-conditioning systems, usually only the space temperature is controlled within limits. A slight variation of the space relative humidity during the operation of the air system is often acceptable. Therefore, the store effect of moisture is ignored except in conditioned spaces where both temperature and relative humidity need to be controlled or in a hot and humid area where the air system is operated at night shutdown mode.

In most cases, latent heat gain is considered equal to latent cooling load instantaneously. It is also assumed that the superposition principle holds.

When a number of changes occur simultaneously in the conditioned space, they will proceed as if independent of each other. The total change is the sum of the responses caused by the individual changes. The energy analysis program compares the total energy use in a certain period with various alternatives in order to determine the optimum one. Convective heat, latent heat, and sensible heat gains from infiltration are all equal to cooling loads instantaneously.

Space cooling load is a component of the cooling coil load. The Rigorous Approach The rigorous approach to the calculation of the space cooling load consists of 1 finding the inside surface temperatures of the building structures that enclose the conditioned space due to heat balance at time t and 2 calculating the sum of the convective heats transferred from these surfaces as well as from the occupants, lights, appliances, and equipment in the conditioned space at time t.

This conductive heat can be found by solving the partial differential equations or by numerical solutions. The number of inside surfaces i is usually equal to 6, and surface i is different from j so that radiative exchange can proceed.

Using a rigorous approach to find the space cooling load requires numerous computer calculations. It is laborious and time consuming. The rigorous approach is impractical and is suitable for research work only. Coefficients vn and wn are called transfer function coefficients, or weighting factors. Weighting factors are used to weight the importance of the effect of current and previous heat gains as well as the previous space sensible cooling load on the current space sensible cooling load qrs,t.

Mitalas and Stevenson and others developed a method for determining the transfer function coefficients of a zone of given geometry and details of the calculated space heat gains and the previously known space sensible cooling load through rigorous computation or through tests and experiments. In DOE 2. Sowell and Spitler et al.

The space cooling load is calculated directly by multiplying the heat gain qe with CLTD, SCL, or CLF instead of first finding the space heat gains and then converting into space cooling loads through the room transfer function.

Finite Difference Method Since the development of powerful personal computers, the finite difference or numerical solution method can be used to solve transient simultaneous heat and moisture transfer in space cooling load calculations. Wong and Wang emphasized the influence of moisture stored in the building structure on the cool-down load during the night shut-down operating mode in locations where the summer outdoor climate is hot and humid.

The finite difference method is simple and clear in concept as well as more direct in computation than the transfer function method. The conversion of space heat gains to space cooling loads takes place by 1 averaging the radiative heat gains to the current and successive hours according to the mass of the building structure and experience and 2 adding the instantaneous convective fraction and the allocated radiative fraction in that time period.

Conduction Heat Gains Following are the principles and procedures for the calculation of space heat gains and their conversion to space cooling loads by the TFM. The R value, expressed in hr. Sol-air temperature Tsol is a fictitious outdoor air temperature that gives the rate of heat entering the outer surface of walls and roofs due to the combined effect of incident solar radiation, radiative heat exchange with the sky vault and surroundings, and convective heat exchange with the outdoor air.

There are two types of shading devices: indoor shading devices and outdoor shading devices. Indoor shading devices increase the reflectance of incident radiation.

Venetian blinds and draperies are the most widely used indoor shading devices. Most horizontal venetian blinds are made of plastic, aluminum, or rigid woven cloth slats spaced 1 to 2 in. Vertical venetian blinds with wider slats are also used. Draperies are made of fabrics of cotton, rayon, or synthetic fibers.

They are usually loosely hung, wider than the window, often pleated, and can be drawn open and closed as needed. Draperies also increase thermal resistance in winter. External shading devices include overhangs, side fins, louvers, and pattern grilles. They reduce the sunlit area of the window glass effectively and therefore decrease the solar heat gain.

External shading devices are less flexible and are difficult to maintain. Shading Coefficient SC. The shading coefficient is an index indicating the glazing characteristics and the associated indoor shading device to admit solar heat gain.

Heat Gain through Window Glass. It is simple and more convenient if they are calculated separately. Internal Heat Gains Internal heat gains are heat released from the internal sources. Lights Heat gain in the conditioned space because of the electric lights, qe.

The pressure difference is probably caused by wind pressure, stack effect due to outdoor—indoor temperature difference, and the operation of an air system s. Today new commercial buildings have their external windows well sealed. If a positive pressure is maintained in the conditioned space when the air system is operating, infiltration is normally considered as zero.

When exterior windows are not well sealed, the outdoor wind velocity is high at winter design conditions, or there is a door exposed to the outdoors directly, an infiltration rate of 0. When the volume flow rate of infiltration is determined, the sensible heat gain due to infiltration qs. It becomes space cooling load instan- taneously. Ventilation air is often taken at the AHU or PU and becomes sensible and latent coil load components.

RTF is affected by parameters like zone geometry; wall, roof, and window construction; internal shades; zone location; types of building envelope; and air supply density. Space Air Temperature and Heat Extraction Rate At equilibrium, the space sensible heat extraction rate at time t, qxs,t, is approximately equal to the space sensible cooling load, qrs,t, when zero offset proportional plus integral or proportional-integral-derivative control mode is used.

Space air temperature Tr can be considered an average reference temperature within a time interval. It is used to size and select the heating equipment. In heating load calculations, solar heat gain, internal heat gains, and the heat storage effect of the building envelope are usually neglected for reliability and simplicity. An air handling unit AHU handles and conditions the air, controls it to a required state, and provides motive force to transport it.

An AHU is the primary equipment of the air system in a central air- conditioning system. The basic components of an AHU include a supply fan with a fan motor, a water cooling coil, filters, a mixing box except in a makeup AHU unit, dampers, controls, and an outer casing. A return or relief fan, heating coil s , and humidifier are optional depending on requirements. The supply volume flow rate of AHUs varies from to about 60, cfm.

AHUs are classified into the followings groups according to their structure and location. They need more space and are usually for large units.

In vertical units, as shown in Figure 9. They are often comparatively smaller than horizontal units. Air is evenly distributed over the coil section, and the fan discharge can easily be connected to a supply duct of nearly the same air velocity.

In a blow-through unit, as shown in Figure 9. It usually has hot and cold decks with discharge dampers connected to warm and cold ducts, respectively. Factory-Fabricated and Field Built-Up Units Factory-fabricated units are standard in construction and layout, low in cost, of higher quality, and fast in installation.

Field built-up units or custom-built units are more flexible in construction, layout, and dimensions than factory-built standardized units. Rooftop and Indoor Units A rooftop AHU, sometimes called a penthouse unit, is installed on the roof and will be completely weatherproof.

Case Studies. Tower of London. Airedale develops bespoke solution to solve DataCentre challenge. Contact Us to Learn More. Useful Links Accessibility. Contact Us. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. However you may visit Cookie Settings to provide a controlled consent.

Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. In this study, the conference room air was well mixed, which helped transport aerosols to the air cleaners.

In rooms with poor air mixing and potential stagnation zones, air cleaners might be less effective. Airflow patterns in real-world settings such as classrooms will vary among buildings and rooms, and rooms of different dimensions and with different ventilation rates will also have different airflow patterns. Second, the aerosol source manikin in this study was kept in one fixed location. In reality, potentially infectious occupants could be anywhere in the room and might move around the room occasionally.

Third, this study only used one source manikin and three receiver manikins; additional sources and receivers could change the dynamics of aerosol dispersion within a room.

Fourth, the study was limited to aerosol particles of 0. However, particles outside this size range would behave differently. Finally, the study only assessed aerosol exposure; it did not directly examine disease transmission. Although the study provides useful information about the dynamics of respiratory aerosol particles and the effects of HEPA air cleaners and universal masking, many other factors are also important for disease transmission, including the amount of virus in the particles, how long the virus survives in air, and the vaccination status of the room occupants.

Portable HEPA air cleaners offer a simple means to increase the filtration of aerosol particles from a room without modifying the existing building ventilation system 2.

The optimal location for HEPA air cleaners will depend upon the unique conditions in each room, but they are likely to be most effective when they are placed as close to the occupants as is practicable. Larger reductions in exposure occur when air cleaners are used in combination with universal masking. Corresponding author: William G. Lindsley, wlindsley cdc.

All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest.

No potential conflicts of interest were disclosed. HEPA air cleaners are commercially available, relatively inexpensive, and easy to use. The mouth of the speaker receiver was 5 ft 1. The air cleaners were placed either side-by-side in the center of the room on the floor, in the front and back of the room on the floor, on the left and right sides of the room on the floor, or on the left and right sides of the room and elevated 30 in 0.

The room ventilation system air inlets and outlets were located in the ceiling as part of the light fixtures. They place their computers and racks on raised floors, two tiles apart, with their air intakes facing each other. The CRAC cooling system pumps cool air through perforated floor tiles between the racks, the computers and racks intake the cool air and exhaust hot air into the opposing hot aisle. Computer room air conditioning units on the floor then pull in the hot air exhausted into the hot aisles, and release it underneath the floor tiles, completing the cycle.

In this way, a CRAC unit air handler can keep cool air running through the system and help keep a steady airflow through the environment.

It's even become common to take advantage of the space above computers and racks and make another "hot aisle" of the room's ceiling, where heat normally escapes and hovers. To keep the whole computer room cool, technicians advocate turning the area above racks into a hot air plenum by placing ducts and more CRAC units. Hot air escapes into the plenum to be pushed back into the system, below the floor, where it can be cooled and released back into the system.

This works for your computer room by removing hot air from the data center. Bringing in more hot return-air helps the heat exchangers in the CRAC units produce colder air to pump out to the computer room floor.

Of course, monitoring the quality of the air conditioning in the computer room means much more than simply monitoring the CRAC unit components themselves. Even if they're working, there's no guarantee that the cool air they pump into the environment is making it to your equipment. And since there's no guarantee of homogenized equipment across the computer room, it's likely that you'll have hot and cold spots.