9~9{C;Ag^vk3$(?A)?~Xsu0)j a?z
pVi.?m}{0N?,tF(C 8bai39b jp=!jsbW ?|!>HM424_EIJPZ=ANU
?nGq?VKQ`=QvpGfsf\ B'd4ske{V_ 0`z'xU?+P&. They are equipped to provide the treatment of air - cooling, heating or both - by passing air over finned tubes which contain a conditioning medium. 
Manufacturers of Indoor Central-Station Air-Handling Units. Both parallel- or opposed-blade dampers can be used for controlling the overall proportions of the airstreams, but pressure relationships and sizing for wide-open and/or modulating pressure drops needs to be considered. Due to the installed flow characteristics of a damper, they are somewhat linear between 10% and 80%. Fan and blower coils above are typical examples. There are numerous articles and reviews regarding HVAC design. There also may be several other components used such as energy recovery devices that could be employed to assist in the processes. Filters should also be Underwriters Laboratories Inc. (UL) classified. % with an appropriate type fastener to meet or exceed the face area specified by the AHU schedule. Custom air handlers are generally used in large systems over 50,000 cfm. In addition, steam coils must be pitched to the return end of the coil. hm0y?$M6
\mp1:"J7i|SKpH=$[" iJ} (gUFvP p bet}1ifZ93sW[
driw/m'r;dDS\:9"/tlBk A-:
%~_% p/-#8Ai,N{]oBx3(V0{)be S&mUz[_Tg Secondly, all water coils should be fed from a bottom connection so once the header piping is full, and the air is bled out of the system, every tube in the coil will be fed evenly with water. The result of performing a variety of these HVAC processes is the delivery of properly conditioned supply air to the spaces it serves. Many designers prefer this arrangement for a better air distribution over the coils. Fan efficiencies, sound levels, and redundancies are also considerations in fan selections. KA units can be modified to fit into almost any space. hbbd``b`fS56 g+Zb" +$aL S 3$0 $
endstream
endobj
386 0 obj
<>stream
Again, AMCA is involved with ratings standards: AMCA 610 Laboratory Methods of Testing Airflow Measurement Stations for Performance Rating, and AMCA 611 Product Rating Manual for Airflow Measurement Stations. b]&cG7>q|M_m%%./8 pS mzdl
The next level of AHUs could be considered semi-custom, highly flexible, but cataloged, AHUs that can be selected to meet most any commercial, institutional, or even industrial applications. The sides or wall panels can be single or double skin insulated metal panels. Referring again to Figure 4, there is both a heating and cooling coil in the center of the horizontal section. For cooling coils, they are built to be piped in a counter-flow arrangement; or, the air flows in the opposite direction as the chilled water (CHW), and/or the refrigerant in DX coils. The OA damper can be one size and equal to the OA intake louver or ductwork for use in the 100% economizer operation; or, as a better option, can be split into a smaller minimum OA damper and another larger one to accommodate the additional OA needed for 100% intake. In colder climates, another problem when condensate builds up in the coil and steam is unable to move through the top portion of the tubes, the coil could freeze and break. endstream
endobj
383 0 obj
<>/Metadata 45 0 R/Pages 380 0 R/StructTreeRoot 61 0 R/Type/Catalog/ViewerPreferences 397 0 R>>
endobj
384 0 obj
<>/MediaBox[0 0 612 792]/Parent 380 0 R/Resources<>/Font<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI]>>/Rotate 0/StructParents 0/Tabs/S/Type/Page>>
endobj
385 0 obj
<>stream
The HVAC load capabilities of these units generally range from a few thousand cfm to tens of thousands. The casing interior is smooth, all exposed interior integrated elements have a smooth edge finish or rounded edges. These units typically use a building-block or modular construction methodology to allow for a wide range of standard and custom engineered modules. This mixing plenum and/or filter section of the AHU should have service access door(s) as well as differential pressure devices across filter assemblies for indication when the filters are dirty. Designers should pay close attention to the location of the fan in relation to the AHU coils. sized to condition and move a designed volume of air through a duct distribution system. These cookies do not store any personal information. ASHRAE states The basic all-air system concept is to supply air to the room at conditions such that the sensible and latent heat gains in the space, when absorbed by supply air flowing through the space, will bring the air to the desired room conditions.. AHRI uses cookies to ensure that we give you the best experience on our website. These small, terminal-type AHUs are referred to as fan coil units (FCUs) or blower coil units (BCUs), based on size and capacity. Likewise, an interior area comprised of multiple work spaces or cubicles within the building also could be considered a larger HVAC zone. endstream
endobj
startxref
An HVAC systems AHU may contain other components necessary to perform a combination of the four basic psychrometric processes of cooling, heating, dehumidification, and humidification. deep type, based upon the application for which they are needed in the AHU. Available in several executions such as standard, hygienic and corrosion resistant for indoor and outdoor installation with fully factory integrated control system. Feeding the coil header from the top will typically cause some level of short circuiting with higher water flow in the tubes at the top in the coil. download their free cad drawing, revit BIM files, specifications and Although not universal, typical load capabilities for FCUs are 200 to 1200 cfm while BCUs might range from 400 to 3,000 cfm. Necessary cookies are absolutely essential for the website to function properly. Review our, 2016 ASHRAE Handbook HVAC Systems and Equipment, Air-Conditioning, Heating, and Refrigeration Institute (AHRI), AHRI 106 Performance Rating of Air-to-Air Exchangers for Energy Recovery Ventilation Equipment, ASHRAE Standard 84-2013 Method of Testing Air-to-Air Heat/Energy Exchangers (ANSI Approved), ASHRAE Guideline 16 2014 Selecting Outdoor, Return, and Relief Dampers for Air-Side Economizer Systems, AMCA 511 Certified Ratings Program Product Rating Manual for Air Control Devices, ANSI/AMCA STANDARD 500-D-2012, Laboratory Methods of Testing Dampers for Rating, AMCA (Air Movement and Control Association International Inc.), AMCA 610 Laboratory Methods of Testing Airflow Measurement Stations for Performance Rating, and AMCA 611 Product Rating Manual for Airflow Measurement Stations, ASHRAE Standard 62.1-2013: Ventilation for Acceptable Indoor Air Quality, ANSI/AMCA 210 Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating, AMCA 300 Reverberant Room Method for Sound Testing of Fans, 2016 ASHRAE Handbook HVAC Systems and Equipment, Chapter 21, Fans, 2016 ASHRAE Handbook HVAC Systems and Equipment, Chapters 23 and 27, AHRI Standard 410 Forced-Circulation Air-Cooling and Air-Heating Coils, ASHRAE 33 Methods of Testing Forced-Circulation Air-Cooling and Air-Heating Coils, Exploring sustainable grocery refrigeration systems, Webcast: How to specify HVAC motors, drives to meet energy goals, Trends, changes in data center HVAC design, Webcast: Pairing VRF with applied HVAC solutions. 2018 ConstructConnect, Inc. All rights reserved. %PDF-1.4 Dependent upon the application, if this heating coil were located to the OA inlet ductwork near (A) it could be referred to as a pre-heat coil; or, if moved downstream of the cooling coil closer to (C) referred to as a reheat coil. AHRI uses cookies to ensure that we give you the best experience on our website. r ()E e[5egm 2U1U Much of the metal for the AHUs is galvanized, or of aluminum or similar construction as necessary, for long-term protection and strength and typically can be painted as required. The RA damper is then selected on the difference between the total design supply air and the minimum OA flow rate, and considered the maximum RA flow rate. Intermediate and/or final filters, where provided, will be of varying grades of filtration or efficiency to assist in removing smaller and smaller contaminants. In these cases the units are frequently "built up". Mechanical properties in accordance with EN 1886: KA units are equipped with advanced and factory tested components such as fans (plug fans with EC or AC motors), heat exchangers (plate heat exchangers in cross and counter flow version, rotary incondensation, sorption and enthalpy versions, run-around coil), heating coils(water, electric, indirect gas), cooling coils(water, evaporative - DX), filters(from Coarse 65% (G4) up to ePM1 85% (F9) according to EN ISO 16890), protection equipment, control system, etc.. A Central Station Air-Handling Unit is factory-made encased assembly consisting of a fan or fans and other necessary equipment to perform one or more of the functions of circulating, cleaning, heating, cooling, humidifying, dehumidifying and mixing of air. Many optional components can also be added and may include: air-to-air, fixed-plate heat exchangers, sensible and total energy wheels, and face-and-bypass dampers. The roof can be like the sides of the AHU unless its in an outdoor application where additional weatherproofing and joint sealing may be required. H]k0
e7,YB62c(p%plQ;'P:fYa_yutQ'f81./r Slightly larger AHUs selected for outdoor use, located on grade outside or on the roof, are usually referred to as packaged units or rooftop units (RTUs), respectively. These modules can be stacked or arranged in a variety of configurations to address a projects constraints (i.e. The 2016 ASHRAE Handbook HVAC Systems and Equipment, Chapter 21, Fans, provides information on fans and helps in understanding selection criteria. dJ@ql`~?f:nAw{o= #0!n.;cx@.t@kP::2 LZcw`+e"*GJ$@ @+Kb'grB}C#SBPr,\e+
"]G:ab@QE9+RW%GxqprifZTxF7_K2tr$^(g,.!>R];^T+(:XqAq7%#^_ RX
The first set of filters are typically the cheapest to replace and thus maintain, while succeeding sets are more expensive to replace. In other words, individual components are brought to the job site where they are "built up" into the custom air handler. Typically, the HVAC ductwork system returns some, if not all, of the return air (RA) back to the AHU; however, AHUs can simply supply and return air directly to and from the space they serve with very little or no ductwork. Nearly all AHUs will have a MERV 7 or 8 filter assembly that have dust spot efficiencies of 25% to 30% or 30% to 35%, respectively. These cookies will be stored in your browser only with your consent. Some information can be found in the 2016 ASHRAE Handbook HVAC Systems and Equipment, Chapter 4, Air Handling and Distribution. [U^Adb8+q*tp0|V*BxL(m~ \LN[/M5bmtd+Z~Ye5)E,Dbbv ZfRNzzQDT-J$yf;|W.T3G/CO|S]o'Q?l{d '#W/x]9xY ?fnb%pT[=6o~csn The AHU shall have a maximum design external static pressure (ESP) greater than 1.0 in H2O [0.25 kPa]. Do you have experience and expertise with the topics mentioned in this content? Based upon the application, filters may be arranged in one or more layers, or sets. Cooling capacity may also be stated in tons (where 1 ton equals 12,000 Btu/h), with typical applications ranging from 3 to 10 tons or more. Filters are rated by ASHRAE Standard 52.2 2012 test methods and classified by minimum efficiency reporting value (MERV). 2424-in. The desire of every user is a fully automatic operation of the air handling unit according to their needs. An HVAC systems AHU may connect to a corresponding ductwork system that distributes the conditioned discharge or supply air to a section or HVAC zone of the building. No matter if the option you choose is standard, hygienic, corrosion resistant or totally custom-made. For a 4-row coil, the air would pass through rows 1-4 at the same time the CHW or refrigerant is flowing through rows 4-1. As HVAC designers, providing a system that can meet the building comfort requirements at a reasonable cost while minimizing maintenance costs and energy use, is the primary goal. Custom AHUs are often used in applications such as laboratories, large industrial and manufacturing facilities, or in renovations where a semi-custom unit cannot fit. Chilled water and refrigerants for cooling, and hot water, steam and even refrigerants (e.g, hot gas reheat, variable refrigerant flow systems) for heating, are typically used for various psychrometric applications, respectively. By most definitions, an HVAC zone has very similar occupancy and similar HVAC thermal characteristics but does not necessarily have a defined area or size.
In applications with more than one set of filters, a preliminary or rough grade filter would be provided first in the direction of airflow. Refer to Figure 4, a typical AHU schematic which illustrates multiple options for component positions within an AHU. H]o0#?K:ivLU%RcvAw'XASTyH ysH$ \/
Opposed-blade dampers typically have lower pressure drops when modulating. For heating, these components could be steam or heating-hot water coils, direct or indirect gas fired heat exchangers, or even electric strip heat coils. There are several basic things to know about coils. The 2016 ASHRAE Handbook HVAC Systems and Equipment, Chapters 23 and 27 provide more information on coils. Many of these articles and other technical information can be found through ASHRAE, a global society for heating, refrigeration, and air conditioning engineers. Components, such as electric cabinet, control and measuring devices (sensors, motor drives, differential pressure switches, thermostats, etc. or 1224-in.) It is mandatory to procure user consent prior to running these cookies on your website. ASHRAE Guideline 16 2014 Selecting Outdoor, Return, and Relief Dampers for Air-Side Economizer Systems can be referenced for input on these dampers as well as for relief dampers during economizer mode of operation. The specific Standard listed above details the technical requirements for rating and publishing your product performance, the AHRI General Operations Manual (OM) details the program operational rules that are generic to all of AHRIs certification programs and lastly, the Product-specific Operations Manual provides the operational rules that are specific to this program along with the required documents and fees. document.write(new Date().getFullYear()) Air Conditioning, Heating, and Refrigeration Institute 2311 Wilson Blvd, Suite 400, Arlington, VA 22201 | Phone: (703) 524-8800 | Site Map | Privacy Policy Do not sell my information Out of these, 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. Filters are typically placed in the section of an AHU ahead of other components, such as fans, coils, etc.