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Heat PumpsHeat pumps
HVAC Inverter DrivesHVAC inverter drives
Invertor Drives Controls Motors Inverter drives
Controls motors Controls motors 
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Optimising air quality and saving costs in ships

The indoor air quality is critical in ships – especially vessels carrying passengers. The air cannot be too humid, too dry, too cold or too hot. Pressure must be higher in some rooms, yet doors must open easily. It takes experts to arrange all this in a cost effective way.

Pumps, chillers, and humidification comprise 40% of the energy used for the air handling. Further expenses may derive from environmental regulations. Proper solutions reduce energy expenses from 10 to 25 %.

Energy savings are mainly achieved through electronic motor control. Traditional air handling solutions have AC motors connected to the main power supply – with speed fixed to the frequency and voltage of the AC supply. These are designed for maximum capacity with valves and dampers to regulate flow.

Since energy consumption is proportional to flow cubed, it is extremely important that fans and pumps run as slowly as possible while maintaining indoor air quality.

In 1968, Danfoss became the first company in the world to mass produce electronic variable frequency motor controls, making it possible to disconnect the motor speed from the mains frequency and vary the speed of the motor. Later technology made it possible to regulate the torque as well.

All the tricks

In pump and fan applications some form of flow control is used. This may be just a flow setting device (e.g. throttling valve or damper) to set the flow rates to system design point during commissioning and balancing of the system. However, all HVAC systems are designed for worst case conditions. They must be able to provide the necessary cooling load for the hottest, most humid days of the year. The majority of time, there is an excess capacity.

In efficient ships some form of active flow control is used (e.g. inlet guide vanes or variable speed drives in VAV systems) to match the capacity of the system to the actual requirements of the ship. Matching the capacity to the requirements increases the comfort of the ships occupants and saves energy.

Condenser water, primary and secondary chilled water pumps in HVAC systems are centrifugal type pumps. Examples of the types of fans used in AHUs (Air Handling Units), frequency converters (FCUs) and Cooling Towers include forward or backward curved centrifugal fans, plug fans, vane axial fans or variable pitch vane axial fans.

Requirements to the drives
Variable speed drives used in HVAC applications ideally have the following features:
• Quiet motor operation – this is particularly important when the motor is driving an AHU (Air Handling Unit) fan. The noise will travel down the ductwork, a possible source of annoyance to the ship occupants.
• Reliable flying start – although a fan (e.g. cooling tower fan) may be off, it is very likely to be spinning due to natural air convection. If a variable speed drive does not incorporate a “flying start” function, which detects the fan spinning in either direction, when it is given a start command, it will likely cause a shock mechanical load on the fan and its mechanical coupling. This increases wear and tear and results in a major current pull by the motor, which will either cause the variable speed drive to trip or incur damage. HVAC dedicated variable speed drives incorporating a flying start function should be able to “catch” a spinning fan at any speed in either direction and smoothly control it when starting.
• Automatic Energy Optimisation – some HVAC dedicated variable speed drives have this function. With this function they are able to typically provide an additional 5 to10% energy savings compared to variable speed drives without this function. They automatically optimise the magnetisation of the motor when the motor is operating at part load.
• Built in hand-off-auto pushbuttons. This feature removes the need for the switches to be fitted to the switchboard/control panel.
• Display of motor current, kWHr, pressure and/or temperature (as relevant) in engineering units.
• Fan belt breakage detection – this should be built into the variable speed drive so it removes the need for a differential pressure switch installed across a fan to detect air flow in an AHU.

Variable Air Volume systems
Variable Air Volume (VAV) systems are the most energy efficient method of maintaining a ship’s environmental conditions. In a VAV system the temperature of the supply air is kept constant by modulating the cooling coil chilled water valves and the volume of air to each zone is varied by the VAV boxes modulating based on the temperature of the zone.

Some form of flow control (e.g. inlet guide vanes or variable speed drive) is used for the supply fan to maintain the required static pressure in the supply duct as the VAV boxes modulate open and closed.

Depending on the complexity of the design there may be temperature sensors in the supply air duct, mixed air and rooms to control or monitor the temperatures, and the digital controller maintains a constant supply air temperature by controlling ventilation and cooling loops (and heating if relevant), in sequence. Relative humidity control may also be provided by a duct humidifier.

Using a variable speed drive for variable air volume applications a pressure sensor, measuring the supply air static duct pressure, typically two-thirds of the way along the duct, is connected directly to the variable speed drive. Using its PID controller the variable speed drive operates in closed-loop control to maintain the static pressure at the required set point. As the VAV boxes close the increase in static pressure is detected by the sensor and the variable speed drive reacts to reduce the speed/flow of the supply fan to maintain the pressure at set point.

Smart solutions

In the life-saving override mode, the VLT® HVAC Drive FC 102 can be set to over rule all its self and motor protecting features in order to secure operation for as long as physically possible; far longer than during normal operation.

The feature is standard when intended for use in functions where continued operation is vital in emergency situations, such as a fire.

This is often the case in HVAC applications, where air supply is vital for rescue personnel as well as for people inside a burning ship.
When set the drive will ignore warnings and alarms and may run to destruction. The fire mode is clearly indicated in the VLT® HVAC Drive FC 102 display to prevent any confusion.

Case Study

The World – a floating, silent village…

The luxurious ship of flats, called The World, left the shipbuilding yard Fosen Mek. Verksteder in Norway March 2002, and have since then offered unsurpassed luxury for its inhabitants. 40 – 50 air conditioning systems – the most silent in the world provide The World with a pleasant atmosphere – controlled by VLT® drives - when the ship cruses the Bahamas as well as the shores of Iceland.

The World is a floating luxury village where people can take up permanent residence in one of the 110 luxury flats, each between 103 and 300 square meters. The price is between 2.5 and 8 million U.S. dollars.
The World’s maiden trip started on May 2nd, 2002.
Travellers have the opportunity to visit Danish castles, learn how to dance salsa at the Mexican Riviera, visit vineyards in France and Italy, and celebrate New Year’s Eve in Hawaii. Each year, the luxury ship will be in port for about 250 days in consideration of major cultural and sports events around the world.

976 people to play and work
The World is about 200 meters long and has 12 decks with enough room for 976 people to play and work. Of nearly 1,000 people aboard, about 320 work on The World, doing everything from steering to cleaning the ship.

Modern cruise liners are frequently described as floating hotels and as such they require all the facilities and services of a major hotel. However, their HVAC requirements exceed those of a land based hotel as the environmental conditions change rapidly day to day and day to night as they cruise the oceans. In addition, the passengers are paying handsomely for and demand a high level of comfort.

For this reason, Novenco AS, Bergen, Norway, selected Danfoss VLT® drives for the air handling systems for The World, a 40,000 tonne cruise liner of the highest luxury that is also the only permanent residential community at sea, combining all the desirable features of a private yacht, seaside villa and exclusive country club. With suites from $2mill to over $6mill the residents expect the ultimate in comfort at all times.

The air handing units and chiller pumps are equipped with a total of over 80 Danfoss VLT® HVAC drives of ratings 10 – 30 kW, maintaining a stable environment through the 12 decks over the 200 m length of the ship, regardless of whether the vessel is cruising in the tropics or the arctic. The control system was engineered and designed by Novenco HI-Press in Denmark, and all air outlets were special designed to be as invisible as possible. No ventilating noise could be accepted. Critical to securing the contract was the DNV marine approvals, which was fulfilled by Danfoss. This, in addition to technical support and good relationship to the customer, put our four competitors behind.

Since this contract was won in 2000, Danfoss has secured a substantial number of marine contracts throughout the Scandinavian shipbuilding industry. In addition to HVAC applications, and as a consequence of their being able to meet marine standards and to supply 690 V drives, systems have been supplied for engine room fans, pump applications as sea water pumps, product and cargo pumps, for vessels as offshore supply and anchor handling, ferries, live fish carriers, fishing vessels and oil tankers.


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Arundel Jones Associates Ltd Registered in England and Wales No. 07334149
Hill Farm, Linton Hill, Maidstone, Kent ME 17 4AL
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News Categories : Heat pumps
HVAC inverter drives
Invertor drives
Controls motors 
Variable speed drives 
Cooling towers