| Application Considerations
Index — Application Considerations
| Item |
Page(s) |
| Access/Blank Module |
23 |
| Acoustics |
19, 25 |
| Air Blender Module |
22 |
| Air Handling Unit Layout |
|
Single Path
|
15 |
Dual Path
|
16 |
| ASHRAE Standard 62 |
12-15 |
| Building Pressurization |
10 |
| Blow-thru Units |
7 |
| Coil Module |
23 |
| Condensate Trapping |
14 |
| Coupled Units |
17 |
| Draw-thru Units |
16 |
| Diffuser Module |
26 |
| Economize |
22 |
| Energy Recovery |
12, 21 |
| Exhaust Fan Economizer |
11 |
| Face and Bypas |
24-25 |
| Fan Module |
25-26 |
| Filtration |
12-13, 23 |
| Freeze Protection |
12, 24 |
| Humidification Module |
26 |
| Intake Module |
20 |
| Mixing Box Module |
20 |
| Moisture Eliminator Module |
20 |
| Plenums |
26 |
| Return Fan Economizer |
11 |
| Stacked Units |
17-18 |
| Traq Dampers |
12, 20 |
| Turning Module |
26 |
| Water Management |
14 |
In essence, an "air handling unit" or "AHU" is no more than its name implies: a device that "handles" — that is, moves and/or conditions — air. How it
accomplishes this mission is determined by the
functions it must perform in a given application and
the arrangement of the components needed to perform those functions.
The "building-block" design of the Modular
Climate Changer® affords an extraordinary degree of
flexibility. But to successfully exploit that
flexibility to satisfy each job’s unique
requirements, the designer must:
- Apply the Modular Climate Changer air handler in a manner consistent with good HVAC design practices.
- Understand the impact of ASHRAE Standard 62, "Ventilation for Acceptable
Indoor Air Quality," on air- handler function and
layout.
- Know how specific Modular Climate Changer modules can address design requirements
in arrangements optimized for available space, energy
costs and acoustical performance.
With these objectives in mind, this section is divided into four topics that present application considerations for effective
Modular Climate Changer design: air handler
functions, layouts, arrangements and
components. Use it in conjunction with the
Microsoft® Windows™ -based Modular Climate Changer
selection program and the Designing an
"IAQ-Ready" Air Handler System manual
(Trane publication number SYS-AM-14). Be sure to
consult your local Trane sales engineer as well for additional application assistance.
AHU Functions
To properly lay out an air handling unit, the designer
must first understand its function(s) in the context of
the application. Those "functions" are
primarily governed by outdoor air (OA) requirements which, in turn, depend on the condition of the outdoor air (i.e., its sensible
temperature, relative humidity and cleanliness).
Figure A-1 summarizes the procedure for establishing a
particular application’s OA requirements:
1
Calculate total system supply airflow using accepted HVAC design practices. Base this calculation on space load and the
temperature difference between space and supply air.
2
Then, determine the amount of outdoor air needed: either the amount required
to comply with the ventilation requirements of ASHRAE
Standard 62 or to "make up" for air leaving
the building via fixed exhausts (e.g., lavatory fans, lab hoods, exfiltration, and any air used for indoor combustion processes)
— whichever is larger. In most cases, outdoor air
volume should equal exhaust air volume to maintain
proper building pressurization and air volume.
3
Finally, having established the amount of outdoor air and total supply air required, quantify the return air volume and
percentage of outdoor air.
Together, these airflow requirements dictate the type
of air handler(s) needed and the tasks that must be
performed.
Steps:
1.Determine space load and deltat
2.Calculate Total CFM : Total
CFM=spaceload/1,085 X delta t
3.Determine minimum outside air(OA)
requirments
4.Ditermined fire exhaust air (EA) requirments
5.Calculate OA and EA.
6.Calculate RA (RA=Total CFM -OA) and
%OA(%OA=OA/Total CFM)
*Based on current industry practice
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