Bulletin No.

111 06/02

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Guidelines for:

Ammonia Machinery

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Room Ventilation

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International Institute of
Ammonia Refrigeration
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NOTICE

The information contained in these guidelines has been obtained from sources believed to be reliable. However, it
should not be assumed that all acceptable methods or procedures are contained in this document, or that additional

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measures may not be required under certain circumstances or conditions. The International Institute of Ammonia
Refrigeration makes no warranty or representation, and assumes no liability or responsibility, in connection with any
information contained in this document.

The Institute recommends use of and reference to this document by private industry, government agencies, and
others. Compliance with this publication is intended to be voluntary and not mandatory. The Institute does not
“approve” or “endorse” any products, services or methods. This document should not be used or referenced in any

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way which would imply such approval or endorsement.

Note that the various building codes and regulations referenced in this document may be amended from time to time
and it should not be assumed that the versions referenced herein are the most current versions of such codes and
regulations. Please consult the appropriate regulatory authorities for the most up to date versions.

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© Copyright 2002. International Institute of Ammonia Refrigeration. All Rights Reserved.

 Bulletin No. 111 06/02

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Table of Contents

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1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Rationale for Mechanical Ventilation . . . . . . . . . . . 1
1.2 Codes & Standards . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Flammability Issues. . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 Leak Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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1.4.1 Vapor Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4.2 Liquid Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

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3 VENTILATION DESIGN CONSIDERATIONS . . . . . . . . . 5
3.1 Base Case – Applicable Code . . . . . . . . . . . . . . . 6
3.2 Determine Code-Compliant
Ventilation Rates . . . . . . . . . . . . . . . . . . . . . . . . . . 6

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3.2.1 Emergency Ventilation Rate . . . . . . . . . . . . . . . . 6
3.2.2 Non-Emergency Intermittent Ventilation Rate. . . 8
3.2.3 Non-Emergency Continuous Ventilation Rate . . 9
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3.3 Ventilation Fan Selection & Layout . . . . . . . . . . . 10
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3.3.1 Fan Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.2 Intake Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.3 Intake and Exhaust Locations . . . . . . . . . . . . . 11
3.4 Ammonia Detectors. . . . . . . . . . . . . . . . . . . . . . . 11
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3.4.1 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4.2 Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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3.5.1 Machinery Room Ventilation . . . . . . . . . . . . . . . 12

3.5.2 Emergency Shutdown. . . . . . . . . . . . . . . . . . . . 12
3.5.3 Alarms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.5.4 Codes & Standards . . . . . . . . . . . . . . . . . . . . . 13
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4 OPERATION & MAINTENANCE . . . . . . . . . . . . . . . . . . 14

4.1 Ventilation Fans and Air Intakes . . . . . . . . . . . . . 14
4.2 Machinery Room Pressure Relationships . . . . . . 15
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4.3 Ammonia Detectors. . . . . . . . . . . . . . . . . . . . . . . 15

4.4 Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5 VENTILATION DESIGN EXAMPLE. . . . . . . . . . . . . . . . 16
5.1 Machinery Room Specifications . . . . . . . . . . . . . 16
5.2 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . 16
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6 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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APPENDIX A: MACHINERY ROOM

HEAT LOAD CALCULATIONS . . . . . . . . . . . . . . . . . . . 23
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1 INTRODUCTION

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This bulletin provides guidelines for the design and operation of mechanical ventilation
systems for ammonia machinery rooms. The bulletin includes: a discussion of the role
of mechanical ventilation in controlling ammonia concentrations during leaks; a review
of relevant national and international codes; ventilation design considerations; and a
discussion of recommended ventilation system operation & maintenance practices.

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1.1 Rationale for Mechanical Ventilation
Ventilation for ammonia machinery rooms serves multiple purposes:
1. To purge ammonia vapor from the machinery room in emergency situations

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to help prevent the concentration of ammonia from reaching the lower
flammability limit; thereby, minimizing the possibility of a deflagration
occurring in the machinery room.
2. To prevent excessive temperature rise (or limit temperature) in the machinery

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room during normal operation due to equipment-generated heat.
3. To provide fresh air for machinery room occupants.
4. To maintain the machinery room under negative pressure.
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5. To enhance ammonia detector responsiveness.
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The function of machinery room ventilation can be categorized into either emergency
or non-emergency ventilation. The first item above falls into the category of “emergency
ventilation” and the remaining four items fall into the category of “non-emergency”
ventilation. All are important for safe ammonia machinery room operation.
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1.2 Codes & Standards

Several national and international codes and standards specify requirements for
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machinery room ventilation systems, ventilation rates, and associated controls. The
following list encompasses the codes and standards most widely used in establishing
minimum requirements for machinery room mechanical ventilation systems.
• ANSI/IIAR 2 – 1999: Equipment, Design, and Installation of Ammonia
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Mechanical Refrigerating Systems (IIAR 2)

• ANSI/ASHRAE 15 – 2001: Safety Standard for Refrigeration Systems
(ASHRAE-15)
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• ISO 5149 – 1993: Mechanical Refrigerating Systems Used for Cooling

and Heating-Safety Requirement (ISO-5149)
• ICBO – 1997: Uniform Mechanical Code (UMC)
• BOCA – 1993: The National Mechanical Code (NMC)
• ICC – 2000: International Mechanical Code (IMC)
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• SBCCI – 1997: Standard Mechanical Code (SMC)

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Table 1 summarizes the emergency and non-emergency ventilation rate requirements
from each of the above-mentioned codes and standards.

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Table 1: Summary of ventilation rate requirements

Emergency Ventilation Non-Emergency Ventilation

Source Rate Minimum Rate Minimum
100 G a, cfm ∆T c < 18°F 0.5 cfm/ft2

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b
ANSI/IIAR 2 – 1999 12 ACH
70 GSI a [l/s] ∆T c < 10°C 2.54 l/s per m2
0.5 cfm/ft2 f
100 G a, cfm ∆T c < 18°F or
20 cfm per person f

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ANSI/ASHRAE 15 – 2001 N/Ah
70 GSI a [l/s] ∆T c < 10°C 2.54 l/s per m2 f
or
9.44 l/s per person f

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g 17.36G 2 / 3 a,d cfm
ISO: 5149 – 1993 No distinction
2/3
13.88GSI a,d [l/s] N/Ah

ICBO: Uniform Mechanical 100 G a, cfm h T e < 104°F 0.5 cfm/ft2

N/A
Code – 1997
70 GSI a [l/s]
f T e < 40°C 2.54 l/s per m2
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ICC: International Mechanical c 0.5 cfm/ft2 f
Code – 2000
a
100 G , cfm ∆T < 18°F or
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& N/A 20 cfm per person f
SBCCI: Standard Mechanical
2.54 l/s per m2 f
Code – 1997 a
70 GSI [l/s] ∆T < 10°C
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9.44 l/s per person f

BOCA: National Mechanical
No distinction 6 ACH
Code – 1993
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a where G is the mass of refrigerant in lb and GSI is the mass of refrigerant in kg

b air changes per hour (ACH) with the corresponding ventilation rate given by Q=V*0.2 (cfm);
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QSI=VSI/0.3 [l/s]
c temperature difference between machinery room and ambient
d requires the continuous operation of the ventilation system at prescribed rate but need not
exceed 15 ACH
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e temperature in the machinery room

f operated when occupied to supply at least 0.5 cfm/ft2 [2.54 l/s per m2] or 20 cfm per person
[9.44 l/s per person]
g ISO 5149 is an international standard
h a separate “minimum” emergency ventilation rate is not prescribed
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Many of the codes and standards are neither consistent nor uniform in their approach
to rate specification for machinery room ventilation. As a result, it is not possible to
conclusively identify one particular code as the “most restrictive” or “least restrictive.”

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Section 3.2.1 of this bulletin provides further discussion and comparisons among
emergency ventilation rate requirements based on the above-referenced codes.
It is essential that designers carefully consider the machinery room ventilation
requirements based on pertinent local codes in force for the machinery room being
designed. Designers may wish to compare the ventilation rate requirements based on

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their local code with the rate requirements derived from other codes and standards.
In cases where the local code is the least restrictive, designers have the flexibility to
increase ventilation rates to comply with more restrictive codes.
Apart from the codes and standards referenced in Table 1, this bulletin provides

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recommendations for both emergency and non-emergency ammonia machinery
room ventilation rates. Section 3.2.1 provides recommendations for machinery room
emergency ventilation rates and Sections 3.2.2 – 3.2.3 outline recommendations
for machinery room non-emergency ventilation rates.

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1.3 Flammability Issues
Anhydrous ammonia is flammable in a relatively narrow range. A substance (or
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mixture) is considered to be flammable if it propagates a flame. The most frequently
reported range of flammability for ammonia in air is 16%1 – 25%2 (by volume). A
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number of factors influence the flammability of an ammonia-air mixture including
pressure, temperature, mixture turbulence intensity, ignition source strength, and the
presence of water vapor or other constituents such as oil. For additional information
on ammonia flammability, see Fenton, et al. (1995) and Khan, et al. (1995).
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An important characteristic of flammable mixtures is the flame speed. The flame speed
of a combustible mixture may be subsonic or supersonic. The propagation of a flame
front at subsonic speeds will result in a deflagration. A characteristic of a deflagration is
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that the overpressure created by the event is relatively low (i.e. the ratio of final to initial
pressure is only slightly greater than one). Although the overpressure generated by a
deflagration is low, deflagrations can damage building structures and equipment. In
contrast, a detonation occurs when the flame speed propagation is supersonic.
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Detonations can lead to considerable overpressures (i.e. pressure ratios on the order
of 40 are possible from detonation events, Fenton, et al. 1995). The overpressures
generated by detonations can have devastating impacts on building structures and
equipment. Deflagration events exhibit a significantly lower energy level (i.e. they are
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not prone to result in overpressure situations) upon ignition of the flammable mixture.
Ignition of ammonia-air mixtures do not result in supersonic flame speeds that lead to
detonation events.
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1 16% is commonly referred to as the lower flammability limit or LFL.

2 25% is commonly referred to as the upper flammability limit or UFL.
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1.4 Leak Scenarios
In an uncontrolled release of ammonia during an emergency situation, the
concentration of ammonia in a machinery room is highly dynamic. The machinery room

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ammonia concentration at any instant in time will depend on the rate of ammonia vapor
production and the rate of ammonia dilution with fresh outside air. Under emergency
conditions, the goal of a mechanical ventilation system is to dilute ammonia vapor in
the machinery room sufficiently to prevent the concentration from reaching the
lower flammability limit (LFL).

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Under a leak scenario, ammonia vapor can be generated by three distinct sources.
The first source is a leak originating from a vapor source. In this case, the rate of vapor
production is equal to the vapor leak rate. The second source of vapor generation is by
evaporation of liquid ammonia outside of the system. Three modes of heat transfer

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combine to influence the rate of ammonia evaporation — conduction, convection, and
radiation. Liquid ammonia that contacts any surface warmer than -28°F [-33°C]3 will
result in evaporation by a combination of conduction and convection heat transfer.
Convection of heat from the machinery room air itself will also contribute to ammonia

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evaporation. Finally, radiation of heat from surfaces in the machinery room warmer
than -28°F [-33°C]3 will contribute to the evaporation of liquid ammonia. The third
source of vapor generation is from flash gas. Flash gas will be generated whenever
a leak originates from a liquid refrigerant source at pressures higher than atmospheric
and temperatures warmer than -28°F [-33°C]3.
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1.4.1 Vapor Leaks
Any part of a system that operates above atmospheric pressure is at risk for
leaking refrigerant to ambient. Vapor leaks can occur in high-side components
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(piping, valves, compressors, flanges, etc.) and low-side components operating

above atmospheric pressure.
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1.4.2 Liquid Leaks

When liquid ammonia leaks from a system, vapor will be generated by evaporation
and/or flash gas. Because ammonia has a high latent heat of vaporization, the rate
of ammonia vapor produced by evaporation from a heat source is relatively small
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(~0.5 cfm per 1,000 Btu/hr [0.81 l/s per kWT] of heat transferred to the liquid).
In a liquid leak scenario, the rate of ammonia vapor production by evaporation is
high initially due to the high heat transfer rate between the cold liquid and warmer
surfaces it thermally contacts. As the surrounding surfaces give up their heat to the
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liquid, the rate of vapor production by evaporation progressively decreases.

In contrast to ammonia vapor generation by evaporation, the rate of vapor
production from flash gas can be substantial when a leak originates from a high
pressure liquid source. If liquid at a pressure above atmospheric and a temperature
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3 The boiling point for anhydrous ammonia at sea level pressure is -28°F [-33°C]. For elevations
other than sea level, the corresponding boiling point will differ.
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warmer than the saturation temperature corresponding to the local atmospheric
pressure leaks, flash gas will form downstream of the leak. The proportion of source
liquid that flashes to vapor is dependent on the pressure and temperature of the

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source liquid. Figure 1 shows the rate of flash gas produced from a 1 lb/min
[0.45 kg/min] leak of high pressure liquid over a range of upstream liquid pressures
with varying degrees of liquid subcooling.

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Flash Gas Production (ft3/min)

Atmospheric Pressure Limit

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Source Liquid Pressure (psia)

Figure 1: Flash gas vapor generation rate for a 1 lb/min [0.45 kg/min] leak rate
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2 SCOPE

The scope of this bulletin is to provide guidelines for the design and operation of
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mechanical ventilation systems serving ammonia machinery rooms. It is not intended

for any other purpose or application of ammonia.

3 VENTILATION DESIGN CONSIDERATIONS

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For a machinery room to be considered a “Non-Hazardous (unclassified) Location,”

as defined by ASHRAE-15, it requires emergency ventilation. In situations where a
mechanical ventilation system is not provided in accordance with ASHRAE-15, the
machinery room would be considered a Class I, Division 2 location. In this case, all
electrical equipment in the room would be designed to conform to the requirements
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for a Class I, Division 2, Group D location, per the governing edition of the National
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Electric Code.

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3.1 Base Case — Applicable Code
The first step in the process of designing a machinery room ventilation system is to
determine the code(s) that are applicable for the facility in question. One should keep

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in mind that codes represent minimum requirements. It is acceptable to design a
system with ventilation rates that exceed the minimum requirements established by
the prevailing code.
In addition to designing the machinery room ventilation system to be code-compliant,
it is advisable to consult with the insurance underwriter for the facility to determine

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if they have requirements that may be more stringent or extend beyond the applicable
code. For example, an underwriter may have specific requirements involving
damage-limiting construction. For additional guidance on damage-limiting construction,
see IIAR Bulletin 112.

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3.2 Determine Code-Compliant Ventilation Rates
Machinery room ventilation rates can be separated into two categories: emergency
and non-emergency. Emergency ventilation is required to purge ammonia vapor

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from the machinery room in the event of a leak in an effort to prevent the machinery
room concentration of ammonia from reaching the lower flammability limit. The
“non-emergency” ventilation category can be further sub-divided into “intermittent”
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and “continuous” modes. Non-emergency machinery room ventilation is required
for several purposes. Table 2 summarizes the function of emergency and
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non-emergency ventilation modes.

Table 2: Summary of machinery room ventilation modes and their function

Ventilation Mode Function

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Emergency Purge ammonia vapor from machinery room during leaks

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Non-emergency intermittent Limit machinery room air temperature or air temperature rise
Non-emergency continuous Ventilation air for occupants
Maintain machinery room under negative pressure
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Enhance machinery room leak sensor responsiveness

Satisfy NEC requirements for non-hazardous location
Each of the above ventilation modes are discussed in more detail in the following sections.
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3.2.1 Emergency Ventilation Rate

The lower flammability limit for ammonia/air mixtures is approximately 16% by
volume (160,000 ppm). The National Fire Protection Association (NFPA 30 —
Flammable and Combustible Liquids) defines “adequate ventilation” as that which
is required to maintain concentrations below 25% of the lower flammability limit
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(i.e. 4% or 40,000 ppm by volume for anhydrous ammonia). A goal of the ventilation
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system design and operation under emergency conditions is to purge ammonia
vapors in an attempt to maintain ammonia concentrations below 4% by volume in the
event of a refrigerant leak.

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A simple rule is to recognize that at least 24 volumes of fresh outside air need to
be mixed with each volume of ammonia vapor released into the machinery room
to keep the machinery room concentration of ammonia vapor below 4 percent.
In other words, the amount of air-ammonia mixture that needs to be exhausted
from a machinery room is 25 times the ammonia vapor generation rate

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(24 volumes of fresh air plus 1 volume of ammonia vapor).
The emergency ventilation rate will depend on the specific code in force. IIAR 2
bases the minimum emergency ventilation rate requirement on (a) the quantity
of refrigerant in the largest system or (b) 12 air changes per hour, whichever

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is larger:

a.) Q = 100 ⋅ G (cfm)

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[Q SI = 70 ⋅ GSI ] [l/s]

where, f
Q is the ventilation rate (cfm),
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QSI is the ventilation rate in SI units [l/s],
G is the mass of refrigerant (lb) in the largest system, any part of which is
located in the machinery room, and
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GSI is the refrigerant mass in SI units [kg];

or
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V
b.) Q= (cfm)
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Q = VSI 
[l/s]
 0.3 
SI
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where,
Q is the ventilation rate (cfm),
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QSI is the ventilation rate in SI units [l/s],

V is the room volume (ft3), and
VSI is the room volume in SI units [m3].
ASHRAE-15 and the UMC require the same emergency ventilation rate as IIAR 2
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with the exception that neither ASHRAE-15 nor the UMC specify a minimum
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emergency ventilation rate.

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ISO 5149 bases the emergency ventilation rate on the mass of refrigerant in the
largest system; however, the formula (see Table 1) differs from that provided in
IIAR 2, ASHRAE-15, and UMC. When the refrigerant inventory is less than 36,532

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lb [16,572 kg], the ISO 5149 emergency ventilation rate will be less than the
emergency ventilation rate prescribed by IIAR 2, ASHRAE-15, and the UMC. At
this refrigerant inventory, the emergency ventilation rate is 19,114 cfm [9,021 l/s].
For systems with refrigerant quantities in excess of 36,532 lb [16,572 kg], the ISO
5149 emergency rate will be larger than IIAR 2 and ASHRAE-15. Figure 2 shows
the emergency ventilation rate relationship between these codes.

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Emergency Ventilation Rate (cfm)

ISO 5149

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IIAR 2, ASHRAE-15, UMC

19,114 cfm

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36,532 lb
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System Refrigerant Mass (lb)

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Figure 2: Emergency ventilation rate comparison

Once the code-prescribed emergency ventilation rate is established, the resulting
emergency ventilation rate on a per unit machinery room area (cfm per ft2 or
l/s per m2) basis should be calculated. It is recommended that the emergency
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machinery room ventilation rate should be at least 10 cfm/ft2 [50.8 l/s per m2]
with a minimum rate of 20,000 cfm [9,439 l/s]. In some cases, designing and
installing a ventilation system to achieve the 10 cfm per ft2 [50.8 l/s per m2] –
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20,000 cfm [9,439 l/s] minimum ventilation rate is not practical. In such cases, the
designer should consider applying the IIAR 2 emergency ventilation rate alternative
of 12 ACH.

3.2.2 Non-Emergency Intermittent Ventilation Rate

Most codes have established a non-emergency ventilation rate requirement to
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either limit the machinery room temperature rise or the absolute machinery room
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temperature. This bulletin categorizes such requirements as “non-emergency

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intermittent ventilation rates” since operation of the ventilation system in this mode
is relatively infrequent and only on an as-needed basis.
Non-emergency intermittent ventilation rates are based on a machinery room heat

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load calculation. The load calculation needs to consider all sources of heat in a
machinery room including:
• electric motors (specifically, heat produced due to the motor inefficiency)
• engine drives (heat loss from engine jackets and manifolds)

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• transmission heat gains (envelope heat gains)
Appendix A provides additional information on heat load calculations for
machinery rooms.

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Once an estimate of the total machinery room heat load is obtained, the required
ventilation rate can be determined by the following:
qtotal
Qnon − emergency = (cfm)
(
1.08 ⋅ Tsupply − TER )

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 qtotal , SI 
Qnon − emergency, SI =  [l/s]
 ( )
1.21 ⋅ Tsupply − TER 
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where,
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Qnon-emergency is the peak intermittent ventilation rate (ft3/min) [m3/s] required
to limit the machinery room temperature rise,
qtotal is the total machinery room heat load (Btu/hr) [Wt ],
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Tsupply is the temperature of air being supplied to the machinery room

(usually the outdoor air dry bulb temperature) (°F) [°C], and
TER is the design machinery room temperature (°F) [°C].
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In the case of both IIAR 2 and ASHRAE-15, the quantity (Tsupply – TER ) is equal to
18°F [10°C] since the continuous ventilation is designed to maintain a maximum
temperature rise above ambient.
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In some cases, the required non-emergency intermittent ventilation rate to limit

machinery room temperature rise may exceed the emergency ventilation rate. In
such situations, the fans selected for the machinery room ventilation system must
be sized at the larger rate. In cases where the emergency ventilation rate exceeds
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the non-emergency intermittent rate, the emergency ventilation rate operating mode
can be used to achieve the non-emergency intermittent machinery room ventilation
rate requirement to limit temperature rise. The most convenient approach for
implementing the non-emergency intermittent ventilation rate control is by the use
of a thermostat which cycles to the higher ventilation rate mode intermittently to
maintain the machinery room temperature in the acceptable range.
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3.2.3 Non-Emergency Continuous Ventilation Rate
Several codes have also established “minimum” non-emergency ventilation
rates. This bulletin categorizes such requirements as “non-emergency

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continuous ventilation rates” since the operation of the ventilation system in this
mode is non-stop. Table 2 summarizes the multiple functions that continuous
machinery room ventilation serves.
A minimum non-emergency continuous ventilation rate of 1 – 2 cfm per ft2
[5 – 10 l/s per m2] is recommended to facilitate circulation of outside air through

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the machinery room and to continually maintain the machinery room under
negative pressure. This ventilation rate should be maintained continuously while
equipment in the machinery room is operational.

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In some applications, continuously ventilating a machinery room at 1 – 2 cfm/ft2
[5 – 10 l/s per m2] may be impractical due to a number of factors that include:
significant auxiliary make-up air heating load during wintertime, machinery
room equipment idle (seasonal operations), and the absence of personnel in
the machinery room. Under such conditions, the non-emergency continuous

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ventilation may be cycled off if the following provisions are satisfied:
1. Controls cycle on the non-emergency continuous ventilation when the
machinery room concentration of ammonia reaches 50 ppm.
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2. Provisions are in place to energize the ventilation systems to provide
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non-emergency continuous ventilation rate whenever the machinery room is
occupied. This function can be accomplished by the use of a switch outside
the machinery room or through other means such as occupancy sensors.

3.3 Ventilation Fan Selection & Layout

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There are a number of considerations that arise in selecting fans and intake/exhaust
layouts to ensure good ventilation system performance during both non-emergency
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and emergency modes of operation. The first step in the process is to select fan(s) that
can provide the required ventilation air flow in accordance with the rates determined
for emergency, non-emergency intermittent, and non-emergency continuous operation.
The second step is to select intake type and the third step is to determine suitable
intake and exhaust locations.
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3.3.1 Fan Type

Consider specifying upblast, high velocity discharge non-sparking fans since they
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tend to be effective at dispersing ammonia exhaust vapors more effectively. This

type of fan employs very high discharge velocities and utilizes an entrainment
nozzle which facilitates dispersion of ammonia into the atmosphere.
A number of options are available to obtain the reduced airflow rates required
for continuous ventilation including: partial operation of a multiple fan system,
multi-speed fans, or variable frequency drive fans.
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Electrical power for machinery room fans should originate from a source outside
the machinery room to ensure uninterrupted power during a machinery room
emergency electrical shutdown as discussed in section 3.5.2.

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3.3.2 Intake Type
Do not use intake louvers with manual dampers. Consider using dampers of a
fail-open power-closed type. In sizing intake louvers, select louvers of sufficient
area to minimize the air pressure drop through the damper. If filters are used,

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select a low pressure drop type. In the design, specify filter pressure drop limits
to guide maintenance practices.
Based on the selected louver type and design face velocity, estimate the pressure
drop across the intake louvers. If filters are used, estimate the pressure drop

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across a dirty filter. The fan selection should be sized to deliver the required
emergency volume flow rate of air with all sources of external pressure drop
(intake louver, dirty filters, etc.) present.

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3.3.3 Intake and Exhaust Locations
It is essential to provide adequate openings for inlet air to replace that being
exhausted. The following are recommendations related to intake and exhaust
locations:
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1. Openings for inlet air should be positioned to avoid intake of discharged air,
i.e. short circuiting.
2. The intake (or supply) air and exhaust air ducts (if any) to/from the machinery
room should not serve any other area of the facility.
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3. Provide makeup-air intakes to replace the exhaust air to the machinery room
directly from outside the building.
4. Machinery room discharge air should be directed upward to provide good
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atmospheric dispersion. Designers should consider the natural air flow around
the building, prevailing wind, and any surrounding structures.
5. The location of intake and exhausts in the machinery room should be
arranged to provide good scavenging of ventilation air through the room. This
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can typically be accomplished by evenly spacing intake louvers low on side

walls coupled with ceiling-mounted exhaust fans set back from the intakes.
Intake/exhaust arrangements that contribute to short circuiting intake air
directly to exhaust need to be avoided. Short circuiting can also occur when
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exhausts are located close to large doors.

3.4 Ammonia Detectors

Ammonia detectors are recommended in machinery rooms for personnel and property
protection. By continuously sensing the presence of ammonia in the machinery room,
alarms or control actions are initiated based on sensed concentrations in accordance
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with limits described in Section 3.5. The selection, location, and on-going proper
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operation of ammonia detectors are an integral part of machinery room safety.

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3.4.1 Selection
Often, two separate ammonia detectors are required for emergency ventilation
control and for machinery room electrical shutdown. A low concentration range

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detector (e.g. 0 – 250 ppm) can provide suitable resolution and accuracy for
initiating emergency ventilation operation. A second high concentration range
detector (e.g. 0 – 20,000 ppm) serves as an input to initiate machinery room
electrical shutdown. The control setpoints for each concentration range detector
will differ. For example, the ventilation control sensor is set to initiate the

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emergency ventilation mode at a concentration of 150 ppm. The machinery
room electrical shutdown control sensor will disconnect electrical power to the
machinery room at a pre-determined concentration, e.g. 15,000 ppm.

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3.4.2 Location
Strictly speaking, ammonia vapor is colorless and lighter than air. However during
a larger release to the atmosphere, anhydrous ammonia can combine with water
vapor in the air and form a visible “white cloud.” In this case, the visible white

er
cloud will tend to be heavier than air and will “ride close to the ground” in a
quiescent environment. For this reason, the refrigerant concentration in each
machinery room should be monitored at two or more points within the room.
At a minimum, at least one detector should be located low in the machinery room
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to detect any vapor that would tend to ride close to the ground. Typically, this
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detector(s) will have a low range (0 – 250 ppm) for use in controlling the operation
of emergency ventilation and alarms. The other detector(s) should be positioned
high in the machinery room in a location where the continuous circulation of
ventilation air through the machinery room will be drawn over the sensor. This
detector will have a higher concentration range (e.g. 0 – 20,000 ppm) to control
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electrical shutdown. The detector(s) should be readily accessible for servicing by

maintenance personnel. Additional detectors can be installed for redundancy.
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3.5 Controls
The ammonia detectors provide information that is critical for initiating emergency
control responses. Based on signals from the ammonia detectors, controls need to
initiate the appropriate machinery room ventilation mode, machinery room electrical
to

shutdown, and supervisory alarms.

3.5.1 Machinery Room Ventilation

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Controls are required to ensure proper ventilation system operation in both

non-emergency and emergency modes. The machinery room ventilation system
should be actuated automatically by vapor detector(s) and also operable manually.
Automatic operation should be based on continuous monitoring of ammonia
concentration in the machinery room.
The typical recommended actuation level for emergency ventilation is 150 ppm
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(50% of the IDLH4); however, lower activation levels should be used if required by
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4 The IDLH (immediately dangerous to life and health) for anhydrous ammonia is 300 ppm.

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the jurisdictional authority. A manual on/auto emergency ventilation control switch
should be located outside of each machinery room exit door. The return from the
emergency to non-emergency (continuous or intermittent) ventilation mode should

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require operator intervention through a manual reset.

3.5.2 Emergency Shutdown

Machinery rooms should be designed with emergency electrical power shutdown
capability. The electrical power shutdown should disconnect power from the entire

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machinery room with the exception of ventilation exhaust fans (with non-sparking
type motors) and any equipment that is Class I, Division 2, Group D compliant.
The recommended machinery room concentration to initiate machinery room
electrical shutdown is 15,000 ppm. Lower threshold concentrations to initiate

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electrical shutdown can also be considered. The electrical shutdown concentration
should not exceed 25% of the LFL (i.e. 40,000 ppm).
Manual break glass switches for emergency electrical power shutdown for the
machinery room should be located outside each machinery room exit. Initiation

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of an electrical power shutdown should activate emergency ventilation fans
independent of input from ammonia detectors. Any electrical power shutdown
should require manual reset.

3.5.3 Alarms
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Ammonia detectors are needed for both alarm and control functions. Alarms
should annunciate visual and audible alarms inside the machinery room and
outside each entrance to the machinery room. Separate alarms should be provided
for emergency ventilation and emergency shutdown. Any alarm reset should be
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manual and be located inside the machinery room. If a detector senses a

refrigerant concentration exceeding its preset limit, the device should initiate a
supervised alarm so that emergency action can be taken.
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In addition to initiating a supervised alarm whenever an emergency ventilation

operating mode is actuated, an alarm should also be triggered whenever the
ventilation system operating under non-emergency continuous mode fails so that
corrective action can be taken. Suitable devices to detect continuous ventilation
to

air flow are pressure differential monitors, ultrasonic monitors, or sail switches.
Consideration should also be given to monitoring the operability of the non-
emergency intermittent ventilation mode. Including an alarm on high machinery
room air temperature is one approach to warn operators of inadequate (or
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non-operational) non-emergency intermittent ventilation.

3.5.4 Codes & Standards

A number of codes and standards have established specific prescriptive
requirements for refrigerant detection and control action based on the level of
refrigerant concentration in the machinery room. Table 3 summarizes the refrigerant
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detection and control requirements from widely used codes that govern ammonia
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machinery room ventilation.

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Table 3: Machinery room concentration threshold for control responses

Ammonia Concentration

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Electrical Emergency Non-Emergency
Source Shutdown Ventilation Ventilation Alarm
IIAR 2 – 1999 — 1,000 ppm 400 ppm (max) 1,000 ppm
ASHRAE-15 – 2001 None 1,000 ppma continuous 1,000 ppma

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ISO 5149 — 40,000 ppm(max)e — 40,000 ppme
UMC – 1997 40,000 ppmb 150 ppmc 50 ppmd 50 ppmf
IMC – 2000 1,000 ppma continuous 1,000 ppma

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SMC – 1997 — 40,000 ppm (max) — 40,000 ppm
NMC – 1993 references ASHRAE-15

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a an ammonia machinery room is not required to be Class I, Division 2 in accordance with the
NEC, if the machinery room ventilation system runs continuous and failure of the mechanical
ventilation system activates an alarm or the machinery room is equipped with a refrigerant
detector set to alarm at 1,000 ppm.
b

c
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code requires electrical shutdown at 25% of LFL (40,000 ppm for ammonia)
code requires the lesser of 25% of LFL (40,000 ppm) or 50% of IDLH (150 ppm)
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d intermittent fan control required to keep concentration below 50% of PEL
e code requires activation of emergency ventilation at concentration no higher than 25% of LFL
(40,000 ppm) and alarm at 25% of LFL
f code requires activation of alarms at the lesser of: 25% of LFL (or 40,000 ppm), 50% of IDLH
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(or 150 ppm), or PEL (50 ppm)

4 OPERATION & MAINTENANCE

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Having an on-going preventive maintenance program helps assure that the

non-emergency ventilation system operating modes are operable at all times and
the emergency ventilation will reliably function when the need arises. Procedures and
time schedules should be established for testing of the mechanical ventilation system,
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the ammonia detectors, and the control system (including alarms).

4.1 Ventilation Fans and Air Intakes

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Preventive maintenance on ventilation fans, bearings, fan belts, dampers, and filters
should be performed in accordance with the manufacturer’s recommendations. In the
absence of a specific schedule of maintenance, it is recommended that the following
system checks be performed on a quarterly basis:
a. Stop the non-emergency continuous ventilation fan(s) using the appropriate
electrical disconnect(s). Confirm that the alarm for non-emergency continuous
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ventilation functions properly.

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b. Using ampules or cylinders of pre-mixed anhydrous ammonia test gases,
expose each of the ammonia detectors in the machinery room to ammonia
concentrations above the alarm level. Confirm that individual detector(s),

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control circuitry, ventilation fans, dampers, and alarms function properly.
c. Visually inspect and clean, as-needed, intake and exhaust louvers, debris
screens, and filters (if equipped).
d. Check the machinery room pressure relationships in both the non-emergency
and emergency modes of ventilation system operation using the method(s)

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described in Section 4.2.

4.2 Machinery Room Pressure Relationships

A properly operating machinery room ventilation system will establish a zone of

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negative pressure, with respect to surrounding zones of the plant and outdoors, during
both non-emergency and emergency modes of operation. The benefit of this negative
pressure relationship is that ammonia vapor will not infiltrate into other areas of the
facility in the event of a leak within the machinery room. The pressure relationship

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between the machinery room and adjacent zones of the facility should be verified
quarterly with all machinery room doors in their normally closed position.
A negative pressure relationship can be established either qualitatively or quantitatively.
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Qualitative methods rely on the use of chemical smoke (such as titanium tetrachloride)
or other sensitive materials (such as tissue paper) to observe the direction of airflow. If
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the machinery room is under negative pressure, the direction of airflow will be into the
machinery room.
Quantitative methods rely on the use of manometers (either an inclined or digital
micromanometer). The differential pressure between the machinery room and its
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surroundings is measured by sensing the pressure inside the machinery room and
outside the machinery room. The UMC requires that 0.05 inch of water [12.4 Pa]
differential be maintained between inside and outside the machinery room.
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4.3 Ammonia Detectors

Maintenance of ammonia detectors is an important part of the overall viability of the
machinery room ventilation system operation. All ammonia detectors should be tested
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and calibrated in accordance with the detector manufacturer’s guidelines at intervals

prescribed by the detector manufacturer.
If the detector manufacturer does not provide guidance on testing and calibration
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intervals, each should be tested and calibrated (if needed) on a quarterly basis. The
maintenance of ammonia detectors should be conducted in conjunction with the
maintenance of controls as discussed below in Section 4.4.

4.4 Controls
Controls maintenance involves testing and ensuring the proper operation of alarms,
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emergency ventilation, machinery room power shutdown, and controlled responses

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that may be specific to a plant. Each plant should establish the appropriate procedures

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and intervals to test and maintain emergency controls. At a minimum, the function of all
controls related to the machinery room ventilation, associated alarms, and electrical
shutdown should be tested and verified annually. Function tests should include

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operational verification of all on/auto manual switches and break-glass switches.
For control responses that would result in a disruption of plant operation (such as
machinery room electrical shutdown), the use of a “calibration mode” or “test mode” in the
control system should be sought and utilized. In a “calibration mode” or “test mode”, the
control system intercepts the triggered response, thereby preventing the unwanted

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actuation, e.g. electrical power shutdown. After conducting tests, it is important to re-arm
the control system circuitry. The re-arm procedure can be accomplished either manually
(by applying documented procedures) or through software (e.g. a time-out routine).

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5 VENTILATION DESIGN EXAMPLE

To illustrate the application of these guidelines, an example of a typical ventilation

design problem will be used to compare the various minimum code requirements with

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the recommended design scheme of this bulletin.

5.1 Machinery Room Specifications

Assume that a new ammonia refrigeration machinery room is to be constructed.
Design specifications are as follows:
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• Room is 40 ft [12.2 m] by 60 ft [18.3 m] by 20 ft [6.1 m] high at ground level
• Room is designed to house four 200 HP [150 kW] compressors
• Motors, other than compressors, total 100 HP [75 kW]
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• Non-motor heat gain is 20,000 Btu/hr [5.86 kWT]

• System charge of ammonia is 15,000 lb [6,804 kg]
• Summer design temperature is 95°F [35°C]
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• Winter design temperature is 20°F [-6.7°C]

• IIAR 2 requirements apply
Refer to the following pages for an example of the Minimum Ventilation Worksheet and
to

a Ventilation System Illustration.

5.2 Design Procedure

The ventilation system design is made following the recommended ventilation design
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considerations as presented in Section 3. Details on the calculated ventilation rates are

presented in the ventilation worksheet following this section.
a. First, emergency and non-emergency ventilation rates are established for the
machinery room. The emergency machinery room ventilation rate should be
based on the quantity of refrigerant in the largest system with a minimum
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emergency ventilation rate of at least 10 cfm/ft2 [50.8 l/s per m^2] with a
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minimum of 20,000 cfm [9,439 l/s]. If that is not practical, a ventilation system

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that yields at least 12 air changes per hour should be considered. The
emergency ventilation rate based on the quantity of refrigerant in the largest
system is:

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Q = 100 ⋅ G = 100 ⋅ 15000 = 12, 247 cfm

[Q SI = 70 ⋅ GSI = 70 ⋅ 6804 = 5, 774 l/s ]

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The emergency ventilation rate based on the recommended minimum
emergency ventilation rate is 10 cfm/ft2 [50.8 l/s] would be:

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Q′ = A ⋅ 10 cfm / ft 2 = 40 ft × 60 ft ⋅ 10 cfm / ft 2 = 24, 000 cfm

 
QSI′ = A ⋅ 50.8 l/s = 12. 2 m × 18.3 m ⋅ 50.8 l/s = 11, 342 l/s
 

f er
For this machinery room, the emergency ventilation at a rate of 10 cfm/ft2
[50.8 l/s per m^2] is greater than the recommended minimum of 20,000 cfm
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[9,439 l/s]. By comparison, the ventilation rate required to achieve 12 air changes
per hour is:

V 40 ft × 60 ft × 20 ft
Q= = = 9, 600 cfm
5 5
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 VSI 12.2 m × 18.3 m × 6.1 m 

QSI = 0.3 = = 4, 530 l /s
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 0.3 

The siting and layout of this machinery room can accommodate an emergency
ventilation rate based on 10 cfm/ft2 [50 l/s per m^2]; consequently, we proceed with
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a design emergency ventilation rate of 24,000 cfm [11,342 l/s].

The non-emergency intermittent ventilation rate is based on limiting the maximum air
temperature rise in the machinery room to no more than 18°F [10°C].
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249, 050 Btu/hr

Qnon − emergency = = 12, 811 cfm
1.08 ⋅ (18ºF)

 73, 156 kWT 

Qnon − emergency , SI = = 6, 046 l /s
1.21 ⋅ (10ºC )
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 
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Based on the machinery room heat load, an non-emergency intermittent
ventilation rate of 12,811 cfm [6,046 l/s] is needed.
IIAR 2 recommends that a minimum ventilation rate of 0.5 cfm per ft2 [2.54 l/s

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per m^2] of machinery room be applied. For the 2,400 ft2 [223 m2] machinery
room in this case, a continuous non-emergency ventilation rate of 1,200 cfm
[566 l/s] is required. Section 3.2.3 above recommends a minimum continuous
ventilation rate of between 1 – 2 cfm per ft2 [5-10 l/s per m2] of machinery
room. Based on a minimum continuous ventilation rate of 1.5 cfm per ft2, the

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minimum continuous ventilation rate would be 3,600 cfm [1,700 l/s].
b. The heating required to warm 3,600 cfm [1,700 l/s] of non-emergency
intermittent ventilation air from 20°F [-6.7°C] to 60°F [15.6°C] is 155,520
Btu/hr

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[45.6 kWT]. A load calculation estimates wall and roof heat losses at
90,000 Btu/hr [26.4 kWT]. The total machinery room heating requirement is
245,520 Btu/hr [72 kWT]. Two unit heaters, each rated at 200,000 Btu/hr
[58.6 kWT], are selected.

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c. Two exhaust fans are selected for ventilating the machinery room. The first fan
is sized for 7,000 cfm [3,312 l/s] and the second for 17,000 cfm [8,030 l/s] for
a total of 24,000 cfm [11,327 l/s] at 1/4" w.g. [62.3 Pa] static pressure. The
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smaller fan is selected with an 1800/900 rpm drive motor for two-speed
operation. Based on 600 ft/min [3 m/s] velocity through the free area of the
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intake louvers, four louver sections are selected with 10 ft2 [0.9 m2] of free
area each. They are equipped with fail-open motorized dampers which are
interlocked to the exhaust fans. Other fan combinations may be used if the
use of two-speed motors, maximum starter size, etc. dictate.
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d. Equipment is located per the “Ventilation System Illustration” shown in Figure 3.

Note that the intake louvers and exhaust fans are located to minimize short
circuiting of air. Also note the location of the emergency ventilation switch just
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outside of the exit door. An additional emergency ventilation switch is located

outside the machinery room door inside the facility.
e. The two-speed fan operates continuously on low speed, unless temperature
controls or the ammonia detector call for high speed operation, at which time the
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second fan also starts. Note that temperature controls and the ammonia detector
are located in reasonable proximity to this exhaust fan to get more representative
indication of temperature and ammonia concentration in the room.
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Figure 3: Ventilation System Illustration

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Ammonia Machinery Room Ventilation Worksheet

MACHINERY ROOM INFORMATION

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Physical Dimensions Length = 60 ft 18.288 m
Width = 40 ft 12.192 m
Height = 20 ft 6.096 m
Volume = 48,000 ft3 1,359 m3

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System Charge = 15,000 lb 6,803 kg
Design Heat Loan = 249,050 Btu/hr 73 kW
Design Outside Air Dry Bulb: Toa,db 95°F 35°C

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Design Ventilation Supply Temp.: Tsa,db 95°F 35°C

VENTILATION RATE REQUIREMENTS

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ANSI/IIAR 2 – 1999
Continuous Ventilation Requirement
CFM Continuous = 12,811 cfm 6,046 l/s
Minimum CFM Continuous =
f 1,200 cfm 566 l/s
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Emergency Ventilation Requirement (larger of)
Based on Refrigerant Quantity = 12,247 cfm 5,774 l/s
OR
Based on Air Change Rates = 9,600 cfm 4,530 l/s
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ANSI/ASHRAE 15 – 2001, IMC – 2000 & SMC – 1997

Continuous Ventilation Requirement
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CFM Continuous = 12,811 cfm 6,046 l/s

Emergency Ventilation Requirement
Based on Refrigerant Quantity = 12,247 cfm 5,774 l/s
to

ISO 5149
Ventilation Requirement
CFM = 10,571 cfm 4,983 l/s
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UMC – 1997
Continuous Ventilation Requirement
CFM Continuous = 25,622 cfm 12,091 l/s
OR
Minimum CFM Continuous = 1,200 cfm 566 l/s
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Emergency Ventilation Requirement

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Based on Refrigerant Quantity = 12,247 cfm 5,774 l/s

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Ammonia Machinery Room Ventilation Worksheet

MACHINERY ROOM INFORMATION

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Physical Dimensions Length = __________ ft _____________ m
Width = __________ ft _____________ m
Height = __________ ft _____________ m
Volume = ft3 m3

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System Charge = lb kg
Design Heat Loan = Btu/hr kW
Design Outside Air Dry Bulb: Toa,db __________ °F_____________ °C

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Design Ventilation Supply Temp.: Tsa,db __________ °F_____________ °C

VENTILATION RATE REQUIREMENTS

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ANSI/IIAR 2 – 1999
Continuous Ventilation Requirement
CFM Continuous = cfm l/s
f
Minimum CFM Continuous = cfm l/s
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Emergency Ventilation Requirement (larger of)
Based on Refrigerant Quantity = cfm l/s
OR
Based on Air Change Rates = cfm l/s
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ANSI/ASHRAE 15 – 2001, IMC – 2000 & SMC – 1997

Continuous Ventilation Requirement
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CFM Continuous = cfm l/s

Emergency Ventilation Requirement
Based on Refrigerant Quantity = cfm l/s
to

ISO 5149
Ventilation Requirement
CFM = cfm l/s
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UMC – 1997
Continuous Ventilation Requirement
CFM Continuous = cfm l/s
OR
Minimum CFM Continuous = cfm l/s
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Emergency Ventilation Requirement

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Based on Refrigerant Quantity = cfm l/s

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6 REFERENCES

ANSI/ASHRAE-15, Safety Standard for Refrigeration Systems, American Society of

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Heating Refrigerating and Air-Conditioning Engineers, Atlanta, GA, (2001).
ANSI/IIAR 2, American National Standard for Equipment, Design, and Installation of
Ammonia Mechanical Refrigerating Systems, International Institute of Ammonia
Refrigeration, Arlington, VA, (1999).
Fenton, D. L., Khan, A. S., Kelley, R. D., Chapman, K. S., “Combustion Characteristics

ce
Review of Ammonia-Air Mixtures”, ASHRAE Transactions, American Society of
Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta, GA, Vol.101, Part 2,
Paper number 3922, pp. 476-485, (1995).

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IIAR Bulletin 112, Guidelines for: Ammonia Machinery Room Design, International
Institute of Ammonia Refrigeration, Arlington, VA, (1998).
ISO 5149, Mechanical refrigerating systems used for cooling and heating – Safety
requirements, International Organization for Standardization, Geneva, Switzerland,

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(1993).
International Mechanical Code, International Code Council, Falls Church, VA (2000).
Khan, A. S., Kelley, R. D., Chapman, K. S., Fenton, D. L., “Flammability Limits of
f
Ammonia-Air Mixtures”, ASHRAE Transactions, American Society of Heating,
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Refrigerating, and Air-Conditioning Engineers, Atlanta, GA, Vol.101, Part 2, Paper
number 3920 (RP-682), pp. 454-462, (1995).
National Mechanical Code, Building Officials and Code Administrators International,
Country Club Hills, IL, (1993).
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Standard Mechanical Code, Southern Building Code Congress International, Inc.,

Birmingham, AL, (1997).
Uniform Mechanical Code, International Conference of Building Officials, Whittier,
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CA, (1997).
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INFORMATIVE APPENDIX A

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MACHINERY ROOM HEAT LOAD CALCULATIONS

The first step in determining a ventilation rate based either on a temperature limit or
temperature rise is to estimate the total machinery room heat load. The primary source of
heat in a machinery room is attributable to motor loads. For electric motor prime movers,
the rate of heat production is a function of the motor power and the motor efficiency:

ce
qmotor = 2545 ⋅ HPmotor ⋅ (1 − ηmotor ) (Btu/hr)

[q motor ]
= kWe ⋅ (1 − ηmotor ) [kWT]

en
where,
qmotor is the motor’s heat production rate (Btu/hr) [kWT],

er
2545 is simply a conversion from HP to Btu/hr,
HPmotor is the rated motor horse power,
kWe is the motor power expressed in [kW (electric)], and
f
ηmotor is the motor efficiency expressed as a decimal fraction.
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If the efficiency values of the electric motors in the machinery room vary significantly,
the motor heat loads to the machinery room should be estimated separately for the
motors. If the majority of the electric motors in the machinery room have efficiencies in
a narrow range, the total heat load can be estimated based on the sum of the total
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motor power with an average motor efficiency.

For internal combustion engine prime movers, the majority of the engine’s waste heat will
be rejected through the engine’s liquid coolant system; however, a portion of the engine’s
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waste heat will be lost to the machinery room environment. The proportion of heat loss
from the internal combustion engine to the machinery room will vary depending on the
configuration of engine’s subsystems such as exhaust manifolding, oil sump, etc. and the
exposure of these subsystems to the surrounding environment. As a guide, one could
to

expect that between 5-15% of the energy input to the engine will be lost as heat to the
surrounding machinery room environment. Individual engine manufacturers can be
contacted for more detailed heat loss information on their specific products.
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The heat load on the engine room due to transmission from the outdoor environment should
also be estimated. For those portions of the machinery room that are exposed to the outdoor
environment, the heat load due to transmission can be estimated by the following:
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qtransmission = UA(Toutside − TER )

where,

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qtransmission is the machinery room heat load due to transmission through the
envelope (Btu/hr) [kWT],
U is the overall heat transfer coefficient for the envelope component such
as a wall or roof (Btu/hr-ft2-°F) [kWT/m2-°C],

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A is the envelope component area (ft2) [m2],
Toutside is the outside air temperature including the effects of solar
radiation incident on the envelope surface (°F) [°C], and

en
TER is the design machinery room temperature (°F) [°C].
The outside air temperature used in estimating the transmission gain to the machinery
room needs to be adjusted for solar radiation effects. Chapter 12 of the ASHRAE
Refrigeration Handbook provides information on allowances for solar effects. Table 4

er
can be used as a guide for increasing the design outside air temperature to account
for solar effects.

Table 4: Temperature allowances for solar effects

f
(ASHRAE Refrigeration Handbook, 1998)
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Typical Surface Surface Orientation
Types East South West Horizontal
Dark Colored Surfaces
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• Slate roofing 8 °F 5 °F 8 °F 20 °F
• Tar roofing [4.4 °C] [2.8 °C] [4.4 °C] [11.1 °C]
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• Black paint

Medium colored Surfaces

• Unpainted wood
to

• Brick 6 °F 4 °F 6 °F 15 °F
• Red Tile [3.3 °C] [2.2 °C] [3.3 °C] [8.3 °C]
• Dark Cement
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• Red, gray, or green paint

Light colored surfaces

• White stone 4 °F 2 °F 4 °F 9 °F
• Light colored cement [2.2 °C] [1.1 °C] [2.2 °C] [5 °C]
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• White paint
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The ASHRAE Handbook of Fundamentals (Chapter 27) provides design outside air dry
bulb temperatures for 1,459 locations around the world. For purposes of determining
heat gain by transmission through machinery room walls, the 0.4% design conditions

on
should be used.

The total heat load on the machinery room is the sum of the internal equipment loads
and the gains through the envelope, or

qtotal = qmotor + qtransmission

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Once an estimate of the total heat load is obtained, the required ventilation rate can be
determined by the following:

en
qtotal (cfm)
Qcontinuous =
(
1.08 ⋅ Tsupply − TER )

er
 qtotal , SI 
Qcontinuous, SI =  [m3/s]

f(
1.21 ⋅ Tsupply − TER ) 

where,
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Qcontinuous is the ventilation rate required on a continuous basis
(ft3/min) [m3/s],
qtotal is the machinery room heat load (Btu/hr) [kWT],
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Tsupply is the temperature of air being supplied to the engine room

(usually the outdoor air dry bulb temperature) in °F [°C], and
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TER is the design machinery room temperature (°F) [°C].

In the case of both IIAR 2 and ASHRAE-15, the quantity (Tsupply – TER) is equal to 18°F
[10 °C] since the continuous ventilation is designed to limit the temperature rise.
In the case of the UMC, the machinery room temperature is limited to 104°F [40°C]. In
to

this case, the values of Tsupply and TER need to be quantified separately. The design value
of TER is 104°F [40°C]. In most cases, the value of Tsupply will be the design outdoor air dry
bulb temperature for the location of interest. In some cases, the design outdoor air dry
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bulb temperature will approach the specified machinery room temperature limit and the
required ventilation rate will not be reasonable. In this case, the machinery room supply
air temperature may be reduced (by applying technologies such as evaporative cooling,
mechanical cooling, etc.) to allow reasonable values of continuous ventilation rates to
be established.
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International Institute of Ammonia Refrigeration

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1110 North Glebe Road, Suite 250

Arlington, VA 22201
Phone: (703) 312-4200 Fax: (703) 312-0065
Website: www.iiar.org