www.msc.navy.mil/N7/gtr/gtr27.doc

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1.0 ABSTRACT

This Item establishes HVAC system design and construction requirements.

2.0 REFERENCES

2.1 Society of Naval Architects and Marine Engineers (SNAME) Technical and Research Bulletin No. 4-16, Calculations for Merchant Ship Heating, Ventilation and Air Conditioning Design. 

2.2 Society of Naval Architects and Marine Engineers (SNAME) Technical and Research Bulletin No.  4-7, Thermal Insulation Report.

2.3 HVAC Systems Duct Design, Sheet Metal and Air Conditioning Contractors National Association, (SMACNA).

2.4 U.S. Public Health Service and MARAD's Joint Publication No. P 161019 "Ratproofing of Ships".

3.0 GENERAL

3.1 HVAC system design heating and cooling load calculations shall be based on meeting the temperatures, relative humidity (RH) limits, and ventilation rates in Reference 2.1.  Heat transfer coefficients shall be based on Reference 2.2.  Pressure drop calculations shall be developed using Reference 2.3 as guidance.

3.2 HVAC systems shall include but not be limited to filters, fans, fan coil assemblies, fan coil units, air filters, screens, duct work, steam preheaters, convection electric heaters, cooling coils, electric and steam reheaters, unit heaters, sound attenuation boxes, silencers, diffusers, terminals, closures, louvers, splitters, turn vanes, dampers (fire, diverting, and balancing), thermostatic controls, drains, insulation (thermal and acoustic), vapor sealing and lagging, label plates, operating instructions and all other items that are necessary for safe system operation and satisfactory performance.

3.3 HVAC system design shall minimize compartment pressure with respect to surrounding spaces and to the weather.

3.4 Odor producing spaces and spaces with toxic or explosive fumes and with Class A bulkheads shall have a slight negative pressure of 0.06 kPa (0.25 in water) achieved by duct design.  Negative pressure in spaces with B or C Class bulkheads shall be achieved by natural supply through louvered doors and/or mechanical exhaust.

3.5 System design shall eliminate condensation under design conditions for both heating and cooling seasons. 

3.6 Duct sections, cooling coils, and fan coil units shall not be installed over the following types of equipment:

Computers. Control panels. Electronic equipment. Generators. Generator terminals. Power distribution panels. Switchboards. Transformer terminals.

If no alternative to installing ducting over such equipment is possible, the ducting shall be watertight or driptight.  Ducts shall be installed to preclude duct connections over such equipment. 

3.7 Where coils are installed, drains shall be installed at both ends of the pan.  System drains shall be designed for list conditions of up to 15 degrees.

3.8 Chilled water cooling coils (Navy Standard) shall be selected for use with 7 o</sup></span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial'; font-size: 12pt;">C (45 o</sup></span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial'; font-size: 12pt;">F) chilled water at a flow rate of 14 liters (3.6 gal)/minute/ton of refrigeration.  All other cooling coils shall be sized according to the manufacturer’s requirements.

3.9 Fan rooms used as plenums for air conditioning systems shall not be subject to a positive pressure and shall be limited to no more than 0.12 kPa (0.5 in water) negative pressure. 

4.0 THERMOSTATIC CONTROLS AND THERMOMETERS

4.1 Steam preheaters shall be equipped with control valves or other mechanism to prevent the coils (heating and cooling) from freezing.

4.2 Design Requirements

4.2.1 When duct bulbs are installed downstream of the coils, they shall be located at least 2.4 meters (8 ft) from the discharge face of the controlled coil and away from splits or branches.  Duct bulbs shall be shielded from the effects of radiant heat. 

4.2.2 Thermostats shall be bulkhead mounted about 1.5 m (5 ft) above the deck to sense the return air temperature of the space or positioned so that they are not affected by localized cold or heat sources.  Thermostats shall regulate space temperature and read temperature in degrees Fahrenheit.

5.0 TRUNKS AND DUCTS

5.1 Air Velocities

5.1.1 Air velocities of HVAC systems and their components shall comply with Table 27-1. 

5.1.2 Maximum air velocity at head end of berths shall not exceed 0.1778 m/s (35 FPM); elsewhere, velocity shall not exceed 0.254 m/s (50 FPM).

5.1.3 Decibel readings shall be limited to 55 decibels for living and office spaces, and 70 decibels for passageways based on measurements taken three feet away from the terminal.

5.2 Trunk and Duct Construction

5.2.1 Trunks, ducts, covers, louvers, and other HVAC items exposed to the weather, shall be at least 3.2 mm (0.125 in) steel plate and shall be watertight.

5.2.2 Vertical trunks or ducts subject to damage shall be at least 3.2 mm (0.125 in) thick.

5.2.3 Built in trunk construction shall not be used for ducts that have a cross section of less than 0.09 sq. meter (1 sq. ft).

5.2.4 Ducts shall be airtight.  Duct seams shall be constructed by any of the following methods: 

Riveted seams sealed with hot solder or fire resistant high velocity duct sealer. Welded, hooked seams and laps. Spot welded on 25 mm (1 in) centers with external seams and joints sealed by a 25 mm (1 in) wide strip of duct sealer. 

5.2.5 Ducts shall be airtight before applying duct insulation. All other ducting shall be made of hot dipped galvanized sheet steel.  The minimum thickness of the material shall be determined by the diameter of round ducts or the greatest dimension of rectangular ducts as follows:

Vertical exposed ducts:  N</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial'; font-size: 12pt;">o. 16 USSG (1.5 mm). Horizontal or concealed vertical ducts of dimension greater than 760 mm (30 in):  No. 16 USSG (1.5 mm). Horizontal or concealed vertical ducts of dimensions 470 to 760 mm (18.5 to 30 in):  No. 18 USSG (1.2 mm). Horizontal or concealed vertical ducts of 320 to 460 mm (12.5 to 18 in):  No. 20 USSG (0.9 mm). Horizontal or concealed vertical ducts less than 320 mm (less than 12.5 in):  No. 22 USSG (0.8 mm). Horizontal or vertical ducts passing through stairtowers or passing through but not serving a space with a Class “A” bulkhead:  No. 11 USSG (3.2 mm).

5.3 Access Openings, Installation

5.3.1 Access holes with bolted plate covers shall be provided as follows:

In sizes as large as possible between 8 inches by 9 inches minimum and 24 in</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial'; font-size: 12pt;">ches by 24 inches maximum.  Where located in transitioning sections from round to rectangular, the projected opening shall be rectangular or trapezoidal. On both sides of heaters that have large dimensions of 24 inches or greater. On the entering side of h</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial'; font-size: 12pt;">eaters that have large dimensions less than 24 inches. On both sides of axial flow fans of diameter up to 24 inches (minimum opening 12 inches by 12 inches) On the inlet side of all centrifugal fans. On trunks and non-removable ducts (maximum spacing 6 fee</span><span class="Normal--Char" style=" font-family: 'Times New Roman', 'Arial'; font-size: 12pt;">t) to allow cleaning of all interior surfaces. At the impeller end of axial flow fans of diameter larger than 24 inches.

5.4 Additional Ducting Requirements

5.4.1 Ducts shall be concealed by sheathing or located in recesses.

5.4.2 Duct joints shall be installed where duct section removal is required for access to piping, cabling, and other equipment.  Duct joints may be flanged, clamp type, or sleeve type and sealed with duct sealer and tape.  Flanged connections or flanged spools shall be installed if the duct is installed in the weather or in machinery spaces.

5.4.3 Elbows in ducts and trunks shall be at least one half the standard throat radius.  When the throat radius is less than the one half standard, baffles and concentric turning vanes shall be installed to provide quiet operation.  Small radius turning vanes shall not be used in elbows unless structural considerations require using miter throat radii.  Turning vanes or grids shall be installed to achieve uniform air flow to registers, grills, and diffusers.

5.4.4 Converging transition pieces shall have a taper which does not exceed 20 degrees on a side.  Diverging transition pieces which have a taper that exceeds 10 degrees, shall have splitters fitted to reduce the expansion angle to less than 10 degrees.

6.0 TERMINALS, GRILLS, WIRE MESH SCREENS AND DAMPERS

6.1 Damper and register linkages, bearings, pins, shafts, and similar working parts shall be bronze.

6.2 Terminals and Grills

6.2.1 Diffuser terminals shall be used in air conditioned spaces.  Supply terminals in working and machinery spaces shall have integral or separate throttling dampers for manually controlling the volume of air flow.

6.2.2 Terminals shall be installed so that they properly ventilate the space served.  Diffusers shall be equipped with adjustable equalizing deflectors within the neck of the diffusers to provide uniform terminal throat velocities and internal means for adjusting the discharge. The thickness of material used for cones and orifices shall be at least No. 22 USSG (0.8 mm).  Other sheet steel parts shall be at least No. 20 USSG (0.9 mm).  Heavier gages of material shall be required when aluminum alloy is used.  The air flow rate handled by each terminal shall not exceed 14 cu meters (500 cu ft)/minute.  Air terminals shall conform to the following requirements:

a. Intakes, exhausts, and outlets shall be protected by ratproof screening unless the opening is equipped with a louver in which no slot or hole is greater than 13 mm (0.5 in).  Insect screening shall not be used in place of ratproof screening.

b. Ventilating hoods and canopies shall terminate flush with the deckhead and shall be screened.  Pipes, cables, air ducts, and similar features over tops of hoods shall be grouped so that spaces or pockets, inaccessible for inspection, are not formed.  If such spaces are formed, they shall be closed completely with sheet metal of No. 18 USSG (1.2 mm), No. 20 USSG (0.9 mm), or No. 22 USSG (0.8 mm).

c. Diffusing adjustable blast terminals shall be used in galleys, pantries, and similar ventilated and heat producing spaces with joiner ceilings.

6.2.3 If register and diffuser parts are not furnished with a prime coat of paint, they shall be hot dipped galvanized or cadmium plated to prevent corrosion before painting.  Lever operators, multilouver blades, and similar parts shall be zinc or cadmium plated.  Connecting bars, bearings, rivets, springs, washers, nuts and similar parts shall be made of bronze.  Turning surfaces shall be bronze on bronze.

6.2.4 13 mm (0.5 in) wire mesh screens or return air diffusers shall be installed on return air terminals.

6.2.5 Exhaust terminals shall be of the bellmouth or expanded cone type (rectangular or round) fitted with 13 mm (0.5 in) wire mesh screens.  Exhaust terminals shall be located close to heat or fume source.

6.3 Air Conditioning System Terminals

6.3.1 Diffuser terminals shall be installed flush with the ceiling panels in air conditioned spaces.  The air flow handled by each diffuser shall not exceed 10 cu meters (350 cu ft)/minute.  The diffuser decibel rating shall not exceed 50 on the A scale.

6.3.2 Diffuser terminals serving air conditioned spaces shall be constructed so that moisture cannot be formed on the cones. 

6.3.3 Balancing dampers, when built into diffuser terminals or installed adjacent to terminal inlets, shall be opposed acting and single group operated, equalizing the air flow over the terminal and throttling air flow.  After the system is balanced, dampers shall be tack welded to secure the dampers permanently in the balanced position.

6.3.4 Balancing dampers fitted with position type indicators shall be used in splitter ducting where required. After the system is balanced, dampers shall be tack welded to secure the dampers permanently in the balanced position.

6.4 Fire Dampers

Fire dampers shall be constructed and installed in accordance with USCG rules.  They shall have an indicator showing damper position.  They shall have a combined adjusting and locking device located for accessibility and visibility.  Damper control shall be from fully open to fully closed.

6.5 Weather Terminals

6.5.1 Weather intakes shall be the self draining air lift type to prevent water and spray from entering during washdown, rough seas, or inclement weather.

6.5.2 Weather openings shall be designed to minimize the effects of wind velocity and weather, and have watertight covers as required by ABS.

6.5.3 Covers for weather openings shall be rattleproof when secured in the open position. 

6.5.4 Terminals shall be of hot dipped galvanized, cadmium plated, or corrosion resistant material.  Nuts, washers, springs, rivets, bearings, journals, and similar parts shall be bronze or corrosion resistant material.  These fittings may be constructed of integrally colored, glass reinforced polyester resin, except for the multivane adjustable louvers.  Sheet metal parts shall be not less than No. 20 USSG (0.9 mm) material.

6.5.5 Weather intake or discharge openings which cannot be airlifted shall be furnished with gooseneck or mushroom ventilators.

7.0 RATPROOFING

7.1 HVAC system ratproofing shall be accomplished in accordance with Reference 2.4 to enable the ship to maintain its Deratization Exemption Certificate and Certificate of Sanitary Construction.

7.2 Ratproofing shall not be accomplished if ducts are within ratproof double bulkheads or deckheads or in fan rooms which have ratproof boundaries and doors marked "KEEP CLOSED." 

7.3 In cargo spaces, the ratproofing material shall be at least the next heavier even numbered gauge than the space sheathing.

7.4 Natural supply and exhaust openings shall be ratproofed.  Ratproofing shall be installed for ventilation systems which serve a single space on the end which is most effective in preventing rat harborage.  Ducts extending from the weather deck directly to the cargo holds, engine room, and boiler rooms, with no horizontal extensions, do not require ratproofing at either end. 

TABLE 27-1

AIR VELOCITIES OF SYSTEMS AND THEIR COMPONENTS

FEATURE

MAX. VELOCITIES 
m/min (ft/min)

Adjustable blast terminals, machinery spaces

1068 (3500)

Adjustable blast terminals, ventilated spaces

763 (2500)

Air filters, face velocity (Outside Air Supply Systems)

244 (800)

Air filters, face velocity (AC Systems)

213 (700) *

Cooling coils, face velocity (without moisture eliminators)

159 (520)

Cooling coils, face velocity (with moisture eliminators)

213 (700)

Diffusing terminals, throat velocity (commercial flush ceiling type) air conditioned spaces

183 (600)

Ducts and bellmouth terminals (throat velocity), mechanical ventilation or recirculation (rectangular)

915 (3000)

Ducts and bellmouth terminals (throat velocity), mechanical ventilation or recirculation (round)

1068 (3500)

Supply and exhaust grill, operating room

229 (750)

Exhaust commercial grill, other

458 (1500)

Expanding cone terminals

915 (3000)

Heating coils, face velocity

549 (1800)

Return air velocities in passages

122 (400)

Weather openings, intake face velocity

610 (2000)

Weather openings, exhaust face velocity

763 (2500)

Passageways, shower spaces, and wash rooms

122 (400)

Notes: * Do not exceed moisture eliminators design requirements

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