Introduction
Companies within the oil and gas industry strongly emphasise the importance of their employees by focus on safety and working environment. Statistics on unexpected incidences are frequently developed, and sick leave and occupational health and safety (OHS) reports are made to show company ambitions for health and safety. Without successful health and safety, no industrial project can be considered a true success.
Heating, ventilation and air-conditioning (HVAC) systems play a key role in achieving acceptable safety and working environment conditions for liquid natural gas (LNG) vessels, offshore installations or onshore plants. When proper indoor conditions are maintained, employees are better able to concentrate and make fewer mistakes, and company economy is improved through reduced sick leave and number of accidents. Also, naturally ventilated modules can improve the working environment by using weather louvers to reduce the exposure of wind, rain and snow to maintenance personnel.
As well as fulfilling safety and working environment conditions, an HVAC system must have high operational availability, simple balance/control functionality and be cost-, space- and weight-effective.
This article highlights three aspects of HVAC design; the comparison of low-velocity versus high-velocity systems, Safety Integrity Level (SIL) and the use of weather louvers/explosion relief panels for naturally ventilated areas. It is based on more than 40 years of experience gained by AC Marine AS (previously ABB AS and Norsk Viftefabrikk AS) as total system supplier of HVAC solutions to the marine and offshore market, and now also to onshore facilities such as LNG terminals.
Low-velocity Versus High-velocity HVAC System
The selected method of providing ‘treated air’ to internal spaces of a vessel or a platform will have a significant impact on both the investment cost and operation costs. The following conclusions address these issues and highlight the key differences between the low-velocity system and the highvelocity system.
Low-velocity HVAC systems from 3m/s to 8m/s utilise large rectangular ducting that has the following disadvantages:
- requires a large amount of space for installation and is difficult to relocate for interference problem;
- all ducts penetrating A-rated decks and bulkheads must be provided with fire dampers due to the size of the duct;
- modifications of the duct system and relocation of in-line duct mounted equipment will have a big impact on other systems/equipment adjacent to the HVAC system;
- the system is significantly influenced by external wind/pressure conditions; and
- it is also common for low-velocity (also called low pressure) systems to have insufficient filtering of outside pollutants due to high pressure losses across filtering systems, resulting in high maintenance costs and degradation of components and ducts in a short period of time. High-velocity HVAC systems from 8m/s to 18m/s offer standardised, off-the-shelf components (preinsulated if required) and provide several advantages.
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