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Cold Air Distribution Design Manual Cold Air Distribution Design Manual
TR-106715
Research Project 3280-39
Final Report, August 1996
Prepared by
Titus, Division of Tomkins Industries
990 Security Row
Richardson, TX 75081
Dan Int-Hout
Reinhard Ratz
Prepared for
Electric Power Research Institute
3412 Hillview Avenue
Palo Alto, California 94304
EPRI Project Managers
M. Khattar
R, Wendland
Commercial Customer Systems Group Contents

Section
Page
Note - Page # likely to change in final print!)
1
Introduction
7
Background
7
Purpose
7
Scope
7
2
Thermal Comfort
9
Comfort Limits Set by ASHRAE Handbook,
10
ASHRAE Standard 55-92, and
ISO Standard 7730-94
Air Diffusion Performance Index (ADPI):
11
Comfort as a Function of Room Air
Velocity and Temperature Difference
Fangers PMV Comfort Index
13
General Comfort Guidelines
14
3
Outlet Types
15
4
Throw and Drop From Outlets
17
Other Diffusers with Cooling
18
5
Typical Air Distribution Characteristics
20
Room Primary Air
20
Total Air
20
Natural Convection Currents
20
Stratification Layers and Zones
20
Return Intake
21
Room Air
21
Temperature Gradient
21
6
Diffuser Selection Methods
22
Method I Selection by Noise Criteria (NC)
22
or alternatively, Room Criteria
Method II Selection by Supply Jets Mapping
26
Method III Selection by Calculating Separation Distance 27
Method IV Selection by Comfort Criteria (ADPI)
29
Method V Integrated Analysis
34
7
Candidates for Cold Air Distribution
35
Conventional Diffusers
35
Cold Air Diffusers
35 8
Psychrometrics (Condensation Issues) and IAQ
37
Condensation
37
Comfort
38
Indoor Air Quality
38
9
Heating Issues
39
10
Diffuser Qualifications
40
11
Summary
42
Appendices
A. 80% ADPI Performance Graphs
A-1
B. Applicable Standards
B-1
C. References Annotated
C-1 Illustrations

Figure
Page
1 Neck Comfort Region
2 Ankle Comfort Region
3 ADPI Comfort Region
4 PMV Plot
5 Buoyancy With Ceiling
6 Buoyancy Without Ceiling
7 NC Chart
8 Draft Temperature Profile
9 ADPI vs. CFM/Sq.Ft.
10 Integrated Step-by-Step Process
Appendix A Figures
A1 4-Way Diffuser Selection
A2 Circular Ceiling pattern
A3 Omni Diffuser, 8 in. Neck
A4 Omni Diffuser, 15 In Neck
A5 TMS Diffuser, 10 in. Inlet
A6 TMS Diffuser, 14 in Inlet
A7 Semicircular Pattern ADPI
A8 PAS Diffuser, 10 Inlet
A9 Cross-Flow pattern ADPI
A10 TDC Diffuser, 14 in Inlet (4 way)
A11 Z-Com Diffuser
A12 OMNI LT Diffuser @ 30
o
T
A13 OMNI-LT Diffuser @ 10
o
T
A14 PSS-LT Diffuser, 30
o
T
A15 PSS-LT Diffuser, 10
o
T
A16 PSS-LTHC Diffuser
A17 Linear Diffuser Areas.
A18 ADPI Range, Linears
A19 1 in Linear Diffuser
A20 Cold Air Linear, 30
o
F T
A21

T Effect, Cold Air Linear Diffusers Tables

Table
Page
1 Velocities and Temperatures
2 Maximum CFM for Comfort
3 Space Effect
4 ADPI Range Abstract

In the selection of diffusers for a building, the engineer has few tools to assist him in
making an informed selection. Often the choice is driven by architectural concerns and
past experience. With Cold Air Distribution (CAD) Systems, however, the choices are
more critical due to concerns over ventilation and comfort at reduced air flows. The EPRI
Design Guide for Cold Air Distribution, recently re-released in 1995, provides a great deal
of information on Cold Air System design. It does not, however, fully describe the process
of diffuser selection when cold air is delivered directly to the space. To assist the engineer
in making these selections, EPRI contracted for the creation of a design manual for cold air
diffuser selection. This manual is in final edit and review at this time.
Selecting and sizing diffusers to be used with cold air systems is an important issue to
todays building industry where optimal design is desired. Concerns over Indoor Air
Quality (IAQ) and occupant comfort, combined with the reduced loads present in many
spaces, leads to designs with very low air supply rates. The economic advantages of
using colder supply air (smaller ducts, fans, etc.) are weighed against the problem of
providing proper air circulation with the even lower air flows that result.
The Cold Air Distribution Manual shows that CAD is not very different from conventional air
delivery systems. The colder air requires a more careful selection of diffusers, as
unwanted drafts can be more objectionable with colder air. The same acceptable design
practices which work for conventional supply systems still apply with air colder than 50
o
.
The process will show that some diffuser types are unsuited for very low air flow rates,
regardless of the supply air temperature. 1
INTRODUCTION

Background
Selecting and sizing diffusers to be used with cold air systems is an important issue to
todays building industry where optimal design is desired. Concerns over Indoor Air
Quality (IAQ) and occupant comfort, combined with the reduced loads present in many
spaces, lead to designs with very low air supply rates. EPRI (1995) has prepared a Cold
Air Distribution Design Guide covering all aspects of the basis for and design of a CAD
system. In this manual, the selection of a diffuser for use with a cold air system is discussed
in detail, along with some of the other issues covered in the EPRI CAD design Guide.
Purpose
The purpose of this manual is to assist engineers in selecting and applying diffusers for
applications involving the distribution of cold air. Cold air is defined, for the purposes of
this manual, as air at temperatures below 52
o
F being delivered directly to the occupied
space.
Scope
This manual is limited to the proper application and selection of diffusers. It is not intended
to be a justification of cold air, nor a design guide for selecting cold air over other systems.
This manual will indicate the issues surrounding how to determine a diffusers acceptability
for cold air, and should be used with the EPRI Cold Air Distribution Design Guide for
a full analysis of Cold Air Distribution (CAD) designs. It will be an extension of the
ASHRAE Fundamentals Chapter 31 diffuser selection process, extended to include cold
air/very high induction diffusers.
The manual has been created to solve two problems: ASHRAEs current guidelines on diffuser selection and Air Diffusion
Performance Index (ADPI) selection are based on diffusers available at the
time (early 1970s). The special very high induction diffusers often employed
now with cold air systems were not available and not included in that
analysis.




Introduction
Engineers need to be certain that diffusers selected for use with Cold Air
Distribution (CAD) will be able to maintain both adequate and acceptable
ventilation within the space over the range of expected air flow.
This manual discusses types of outlets, diffuser types, selection methods, comparison of
diffuser types, Psychrometrics, heating applications, and economics. Often cold air
diffusers will also be used for heating. With these varying conditions, occupant comfort and
ventilation requirements must be considered.
Design parameters include throw, sound pressure drop and zone comfort. Several
methods are detailed outlining the selection and application of diffusers for cold air
applications. Manufacturer catalog data at isothermal conditions can be used with known
temperature conditions to calculate expected performance. At least one manufacturer has
throw and drop already available in catalog tables for cold air diffusers given colder outlet
air.
The use of cold air delivery systems has increased over the past few years. Before the
development and acceptance of direct delivery of cold air with qualified diffusers or with
special cold air diffusers, mixing systems were used to deliver air to spaces at the
traditional 52-55
o
F. These included both series and parallel fan-powered terminals and
air-to-air induction devices. The increased energy required by the fan motors or higher
system static required for induction partially offset energy savings from CAD design.
Direct injection of cold air offers the maximum energy savings resulting from the reduced
air quantities.
A number of studies (See Appendix C) have been conducted into the physical aspects of
cold air emerging from a horizontal diffuser and then mixing with room air. This manual
emphasizes the essential considerations that will allow the consulting engineer to design
and specify an optimum cold air distribution s