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B. SYSTEMS HANDLING SPECIAL GASES
trols, heat exchangers, and auxiliary heaters must be
effectively integrated. Unlike the selection of a furnace or boiler, a solar space heating system may be
sized to provide a selected portion of the annual heating load. Generally 30 to 70 percent is reasonable.
The size of the solar system basically depends on
the collector area. The collector area then determines
the quantity of solar heat delivery or the amount of
fossil fuel savings.
Guidelines for sizing components of integrated airbased solar systems for space and potable water
heating are listed in Table 13-1. A typical arrangement
for which the guidelines apply is shown in Figure 131.
2. Duct System Layout
A layout of the duct distribution system should be
prepared and sizing of all ductwork should be accom-
plished using the method that the designer is most
comfortable with for the air volume required. However, the designer shall be responsible for correctly
sizing the duct system so that its total external static
pressure (ESP) shall not exceed the manufacturer's
ESP rating for the air handling equipment.
Ducts connecting solar air collector inlets and outlets
shall be sized to meet the air quantities that are required by the airflow characteristics of the collector.
Review the collector manufacturer's literature to determine the correct flow rates. Connections to the
collectors shall be in accordance with the manufacturer's recommendations.
When auxiliary heating equipment is used, the airflow
volume of the duct distribution system must provide
an air temperature rise through the equipment that is
below the maximum temperature rise noted on the
Table 13-1 GUIDELINES FOR SIZING COMPONENTS OF AIR-BASED SOLAR SYSTEMS
FOR SPACE AND POTABLE WATER HEATING
*For potable water heating only the collector slope should be at latitude angle, and the recommended range is
Lat - 5° to Lat + 5°
**For potable water heating only systems, pebble bed storage is not required.
Figure 13-1 TYPICAL AIR-HEATING SYSTEM
3. Solar Collecting Systems
The duct system between the solar collectors and the
thermal storage containers, and the ductwork connecting to the space distribution system shall be
known as the primary solar duct system (PSDA). The
PSDA shall be designed using the criteria described
above. Care shall be used to assure balanced airflow
in the PSDS for the various operational modes of the
All ducts and duct linings composing the PSDS shall
be installed in strict conformance with the SMACNA
HVAC Duct Construction Standards and Fibrous
Glass Duct Construction Standards. All materials
used in the PSDS shall be able to withstand temperatures up to 250°F (121°C) without degradation or
release of odor-causing or noxious gasses.
Air leakage from PSDS should not exceed 5 percent.
It is not the intent of these Standards to test the PSDS
for compliance with the 5 percent duct leakage requirement, but simply to assure construction stan-
dards which will essentially provide the required degree of air tightness in the PSDS.
Ducts may be sealed using mastic, or mastic plus
tape or gasketing as appropriate. The selection of the
most appropriate sealant depends on joint configuration, clearances, surface conditions, temperature,
the direction of pressure and preassembly or post
assembly placement. Tapes should not be applied to
bare metal nor to dry sealant. Foil tapes are not suitable. Liquids and mastics should be used in wellventilated areas and the precautions of manufacturers followed. Oil base caulking and glazing compounds should not be used. Gasketing should be material with long life and suitable for the service.
4. Solar System Dampers
a. CONTROL DAMPERS (Motorized)
Dampers that open or close to divert, direct, or shutoff airflow in the Primary Solar Duct System shall
have "sealing" edges on the blades with a suitable
material such as felt, rubber, etc., to insure tight cutoff
of the air stream when closed.
b. SHUT-OFF DAMPERS
Shut-off dampers installed to prevent air flow, as in
the summer by-pass duct in the Primary Solar Duct
System, shall be sealed tightly to prevent air flow
when pressurized from either side of the damper.
Slide dampers shall have suitable seals on the guides
to prevent leakage around the blade and through the
Table 13-2 SOLAR AIR DISTRIBUTION SYSTEMS
c. VOLUME DAMPERS
Volume control of balancing dampers shall be installed in each branch or zone duct. Single leaf dampers which are a part of a manufactured air grille do
not meet the requirements of the SMACNA solar installation standards found in the SMACNA "Installation Standards for Residential Heating and Air Conditioning Systems." Opposed blade dampers which
are a part of a manufactured air grille meet the requirements of the Standards if sufficient space is provided behind the grille face for proper operation of the
Where space prohibits the use of an opposed blade
damper behind the grille face, an opposed blade
damper may be installed in the register stack at a
location where it is accessible from the grille opening.
Volume dampers installed in branch ducts where the
total estimated system static pressure is less than
0.5 in. w.g. (125 Pa) should be of a single leaf type.
Volume dampers installed in ductwork where the total
estimated system static pressure exceeds 0.5 in. w.g.
(125 Pa) shall be manufactured in accordance with
d. BACK-DRAFT DAMPERS
Back draft dampers shall be installed to close under
the action of gravitational force when there is no air
flow, and open when there is a drop in pressure
across the damper in the direction of desired air flow.
Multi-bladed back-draft dampers shall have suitable
seals on the blade edges, and appropriate seals
along the sides. Light-weight rubberized fabric dampers of the type shown in Figure 13-3 shall be tilted
sufficiently to ensure closure when there is no airflow.
Single blade dampers shall have seals along the seat
and the pivot shall be off-center and horizontal to
ensure closure when there is no airflow.
Figure 13-3 RUBBERIZED FABRIC
Figure 13-2 MULTI-BLADE VOLUME DAMPERS
DUCT DESIGN TABLES AND CHARTS
This chapter of the "HVAC Systems-Duct Design"
manual combines all of the recognized basic duct
system design tables and charts into an easy-to-use,
single source. Prior to the first edition of this manual,
duct system designers had to search for fitting loss
coefficient tables and duct pressure loss charts
through many fluid flow handbooks, manufacturers'
literature, and other sources.
New in this revised edition, are many duct fitting loss
coefficient tables and a new duct friction loss chart
developed as a result of research data funded by
SMACNA in an extensive research program at the
ETL Testing Laboratories, Inc. in Cortland, New York
and by ASHRAE research, partially funded by
Chapter 5-"Duct Design Fundamentals", Chapter
7-"Duct Sizing Procedures (U.S. Units)", and
Chapter 8- "Duct Sizing Procedures (Metric Units)"
show how to use the various duct design tables and
charts. The step-by-step examples use the prescribed procedures for designing basic duct systems.
Some of the tables come from unconfirmed sources.
A world-wide literature search on fitting loss coeffi-
cients was conducted by I.E. Idel'chik in Russia and
the resultant compilation was published in 1960 and
updated in 1975. Although some of these loss coefficient tables (recently corrected with newer data)
conflict with existing tables used in segments of the
industry, the consensus of members of the SMACNA
and ASHRAE Duct Design Committees is that the
data is reasonable to use for the design of HVAC duct
systems. Therefore these tables, which are contained
in this chapter and in the ASHRAE 1989 "Fundamentals" Handbook, should continue to be used until current and future research programs can validate the
figures or establish new verified data. Some of the
most recent duct fitting loss coefficient data from limited SMACNA research also may be found in Chapter
5, Section H-"SMACNA Duct Research."
The duct fitting loss coefficients used to calculate the resistance to flow are in terms of total
pressure. When static regain occurs, it need not
be addressed separately because it is included
in the fitting loss coefficient and therefore in the
calculation. When these values are added to the
calculated friction loss of the straight duct sections, the total system resistance (pressure
drop) will be in terms of Total Pressure.
W. David Bevirt, P.E.
Numbers in parentheses, when found at the end of a table or figure title, indicate the number of the reference
source in the front of the manual. Where no reference number is indicated, the data was developed or obtained
from SMACNA research.
TABLE OF CONTENTS
ADuct Friction Loss-Tables and
Duct Friction Loss Chart (U.S. Units)
Duct Friction Loss Chart (Metric Units)
Duct Material Roughness Factors
Duct Friction Loss Correction Factors
Circular Equivalents of Rectangular Ducts (U.S. Units)
Circular Equivalents of Rectangular Ducts (Metric Units)
Spiral Flat-Oval Duct Equivalents (U.S. Units)
Spiral Flat-Oval Duct Equivalents (Metric Units)
Velocities/Velocity Pressures (U.S. Units)
DUCT DESIGN TABLES AND CHARTS
Figure 14-4 Correction Factor for Unextended Flexible Duct
Table 14-7 Velocities/Velocity Pressures (Metric Units)
Table 14-8 Angular Conversion
Loss Coefficients for Straight-Through Flow
Figure 14-5 Air Density Friction Loss Correction Factors
FITTING LOSS COEFFICIENT TABLES
Loss Coefficients, Elbows
Elbow, Smooth Radius (Die Stamped), Round
Elbow, Round, 3 to 5 pc-90°
Elbow, Round, Mitered
Elbow, Rectangular, Mitered
Elbow, Rectangular, Mitered with Converging or Diverging Flow
Elbow, Rectangular, Smooth Radius without Vanes
Elbow, Rectangular, Smooth Radius with Splitter Vanes
Elbow, Rectangular, Mitered with Turning Vanes
Elbows, 90°, Rectangular, Z-Shaped
Elbows, 90°, Rectangular in Different Planes
Elbows, 30°, Round, Offset
Elbows, 90°, Rectangular Wye or Tee Shape
Loss Coefficients, Transitions (Diverging Flow)
Transition, Round, Conical
Transition, Rectangular, Pyramidal
Transition, Round to Rectangular
Transition, Rectangular to Round
Transition, Rectangular, Sides Straight
Transition, Symmetric at Fan with Duct Sides Straight
Transition, Asymmetric at Fan with Duct Sides Straight, Top Level
Transition, Asymmetric at Fan with Duct Sides Straight, Top 10° Down
Transition, Asymmetric at Fan with Duct Sides Straight, Top 10° Up
Transition, Pyramidal at Fan with Duct
Loss Coefficients, Transitions (Converging Flow)
Contraction, Round and Rectangular, Gradual to Abrupt
Contraction, Conical, Round and Rectangular
Contraction, Rectangular Slot to Round
Loss Coefficients, Converging Junctions (Tees, Wyes)
Converging Wye, Round
Converging Tee, 90°, Round
Converging Tee, Round Branch to Rectangular Main
Converging Tee, Rectangular, Main and Branch
Converging Wye, Conical, Round
Converging Tee, 45° Entry, Branch to Rectangular Main
Symmetrical Wye, Dovetail, Rectangular
Converging Wye, Rectangular
Wye, Rectangular and Round
Loss Coefficients, Diverging Junctions (Tees, Wyes)
Tee or Wye, 30° to 90°, Round
90° Conical Tee, Round
45° Conical Wye, Round
90° Tee, Round, Rolled 45° with 45° Elbow, Branch 90° to Main