Sunday, July 21, 2013

Marine HVAC system and notes....

On board every rig or vessel, there is an accomodation module or living quarter which houses the crew of about 200 men or more
working day and night offshore and in this quarter area, there is a set of offshore heating, ventilation and air conditioning, and refrigeration systems providing 24 hours non-stop either cooling ( in summer) or heating ( in winter ) for the comfort of the crew members.

Therefore there is need of professional  marine services and construction personnel to tackle these challenging projects to meet the rig specific requirements, and engineer a set of proper equipment selections.


HVAC/R systems engineering

Involves in design, fabrication , supply and installation of all kinds of HVAC systems. Based on  rig supplied general lay-outs (A-CAD) all required calculations and drawings for design and fabrication, including:

•Detailed calculations for heating, cooling, air-volumes, and humidification
•Air pressure and noise levels evaluation and treatment, carbon dioxide calculations
•P&ID, airflow and electrical diagrams
•Data sheets, material lists, instruction manuals, MRBs and supply chain information
•Commissioning plans and project supervision

Air conditioning systems -

•Water and air-cooled DX / condensing units

•Water and air-cooled chill water units
•Package air-handling and fan coil units
•Package self-contained units
•Cabins units, terminals, diffusers and accessories
•Cold room and freezer evaporators, room controllers and timer panels
•Control systems for platform integration, F&G interface, local AHUs
•Refrigeration valves, separators, condensers, and accessories
•Fire and hydrocarbon rated dampers, blast dampers, local control stations

The system package also involves supplying air conditioning systems specifically designed for the marine and offshore industries with custom-designed marine and explosion-proof chilled water systems (marine chillers) as well as marine condensing units for clients, and these air conditioning systems on board the rig or vessel could either include:
•Direct expansion (DX) cooling systems with environmentally friendly refrigerants such as R134a, R404a, R407c; sea water or fresh water cooled or air cooled

•Chilled water central cooling systems for complete accommodations Integrated or local heating systems
•Electric duct heaters
•Cabin units with integrated re-heaters
•Hot water heating coils (duct or AHU mounted) complete with two-way or three-way control valves
•Steam heating coils complete with two-way or three-way control valves and traps
•Thermal oil heating coils (duct or AHU mounted) complete with two-way or three-way control valves
•Electric unit blast heaters (safe and hazardous areas)
•Thermal oil unit blast heaters (safe and hazardous areas)

A well-designed air distribution system shall result in an efficient air conditioning system. A low-velocity duct system is practical in facilities where space is of secondary importance and a high-velocity duct system is often most practical in a facility where space is at a premium. In this instance, spiral high press duct is used.

1. Due to space constraints and considering the air flow requirements in offshore service, the designer may have to go for high pressure ducting. The pressure drop in supply air ducting will be in the range of 1000 to 1500 Pa and that in return air ducting will be in the range of 500 to 1000 Pa.

2. Ducts that may carry contaminated air or run through areas that may become contaminated shall be gas tight. Duct systems shall be designed within prescribed limits of available space, friction loss, noise level, heat loss or gain, and pressure containment.

3. Circular ducting (machine fabricated by using GS strip bands of 100 or 150 mm width) is recommended, as the helically wound longitudinal joints provide adequate mechanical strength.

4. Ductwork connections to the outside atmosphere and through fire barriers would need to be provided with fire / gas dampers rated to that of the fire barrier penetrated.

5. Ducts shall be constructed in accordance with applicable Sheet Metal and Air Conditioning Contractors National Association (SMACNA) standards.

6. Special attention shall be paid to ductwork connections to fan inlets and outlets in order to maximize the fan performance. See AMCA publication 201.

7. Flexible ducting shall be kept to a minimum and be used only for vibration damping or thermal expansion purposes.

8. Return air shall be ducted to get a proper air balance. Some contractors may use return air plenums above a false ceiling, which results in unbalanced operations within a short period of commissioning, as the space above the false ceiling is being used for other services too.  

HVAC control system :-

The HVAC system shall as a minimum have the following control provisions:

1. Auto/manual operation selecting facilities
2. Start/stop of fans
3. Fan and damper status/alarm
4. Alarm for loss of pressurization/flow
5. Auto/stand-by selecting facilities for fans
6. Temperature status/alarm for temperature sensitive areas
7. The system logic shall be equipped with manual reset
8. Controlled shutdown
9. Emergency shutdown and facilities for safe re-start after an incident

SYSTEM LAYOUT

Careful consideration should be given to the location and layout of HVAC systems and associated plant and components to enable adequate routine inspection testing and preventative and breakdown maintenance to be carried out without prejudicing safety of the installation.

1. Suitable access platforms and routes for entry and removal of expendable components or failed equipment should be provided.

2. Access doors into plant and ductwork would need to be of sufficient size to enable servicing to be adequately carried out.

3. HVAC systems should be laid out with safety aspects in mind. They should be kept clear of areas prone to damage from normal operations. Where practicable, hydrocarbon fuel lines and main power and signal cables would need to be kept clear of HVAC systems


Hull Ventilation systems -

Involves dedicated ventilation systems as well as component equipment such as fans, louvers, and moisture eliminators with filter coalescers in stainless or galvanised, and such Hull ventilation system could be in these machinery spaces :

•Engine room ventilation
•Mud pit ventilation (explosion-proof fans)
•Shale shaker room ventilation (explosion-proof fans)
•Machinery space areas
•Hazardous-area ventilation
•Hazardous-area cooling


Ventilation DESIGN CONCEPTS :-


Area classification enables all parts of the rig installation to be identified as one of the following:

1. Zone 0 (Hazardous Areas), in which an explosive gas / air mixture is continuously present or present for long periods.
2. Zone 1, in which an explosive gas / air mixture is likely to occur in normal operation.


3. Zone 2, in which an explosive gas / air mixture is not likely to occur in normal operation, and if it occurs it will exist only for a short time.

4. Non-hazardous areas - manned and un-manned areas in which an explosive gas / air mixture will not occur in normal operation.

The design of a confined ventilation system shall ensure the desired airflow characteristics when personnel access doors or hatches are open. When necessary, air locks or enclosed trap shall be used to minimize the impact of this on the ventilation system and to prevent the spread of airborne contamination within the facility. The ventilation system design shall provide the required confinement capability under all credible circumstances including a single-point failure in the system.

  Maintenance of a pressure differential between hazardous and non-hazardous areas (generally in the range of 30 to 70 Pa) is essential to prevent ingress of toxic or hazardous gases like H2S or CO or CO2. Hazardous areas (zone 0 and zone 1) shall be at negative pressure whereas the non-hazardous zones shall be at positive pressure. Positive pressurization is achieved by dumping more outside air flow than it is exhausted from the spaces. Requirements include:


1. Living accommodation should preferably be located in a non-hazardous area and shall be at a positive pressure with respect to outside ambient. Usually the passage or corridor is positive against the outside environment to prevent any ingress of gas into the living module.

2. Mechanically ventilated enclosed escape ways shall have overpressure against neighboring areas.

3. All process areas such as mud storage, mixing, chemical storage rooms, shale shakers and pump rooms should be at negative pressure with respect to adjacent lower classification zones. Arrangements shall be made to enclose the various mud handling processes within hoods, booths or enclosures so as to trap fumes, dust and gas at source and exhaust to a safe point of discharge to the outside atmosphere.


4. All areas housing hazardous equipment such as battery rooms shall be maintained at negative pressure.     


















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