Marine energy efficiency: prioritising the energy audit

The principle of energy efficiency has been around for a long time and is widely deployed – basic energy efficiency awareness can achieve savings of up to 40%. However, the marine industry often lags behind in this field. Shipowners face difficulties such as frequent crew changes and lack of technical expertise, making it more difficult to become energy efficient.

When considering energy and operating expense (OPEX) costs, energy savings are often twice as effective on a ship as the same type of facility on land. This statement is worth great consideration, particularly in light of current fuel cost increases. On the other hand, shipowners are obliged to reduce vessel emissions and reducing energy consumption will both reduce emissions and be more cost effective. A well-implemented marine energy efficiency plan will pay for itself within one or two years. A range of studies have shown that improving energy efficiency is the most profitable action a shipowner can make.

Energy efficient methods of operation are already recognised as beneficial and are standardised in ISO:50001 (Energy Management). This standard inspires International Maritime Organization (IMO) recommendations such as the Ship Energy Efficiency Management Plan (SEEMP). However, SEEMP needs better integration. There are too many generic plans onboard that do not reflect ship specific conditions. On many occasions follow-ups are not completed, and the plan objectives are not met.

When we go back and consider the ISO and IMO SEEMP standards, it becomes clear that an energy audit is the first step in implementing a credible energy efficiency programme and the second step is the follow-up. The marine energy audit is considered mandatory and is well described in ISO;50002, which indicates the rules and principles governing the auditor and the process. These include but are not limited to: appropriate auditor training and certification, thoroughly calibrated instruments and equipment, as well as correct application of standard procedures. These methods have proven successful in many industrial fields and a ship is no different.

However, a land-specialised energy auditor is not always qualified to understand all the technicalities of ship operation. Each ship category (passenger ship, ferry, oil tanker, bulk carrier, self-unloading vessel, etc.) has its own particularities and specific energy optimisation options. There are even differences between ships in the same category (sister ships). It is very rare that two sister ships behave in exactly the same way with regard to fuel consumption; a marine energy auditor can explain why and present recommendations and potential solutions. Unless the auditor comes from the marine business, these particularities are not easy to learn and understand.

Trade activity also influences the methods that are used in terms of implementation towards being more energy efficient. A ship spending half a year at anchor or berthed cannot be analysed in the same way as a ship sailing at sea at full power most of the year. For example, in Canada in the St-Lawrence River, the Great Lakes and the Seaway a vessel must go through several locks and manoeuvring areas. Under these conditions, ship performance cannot be evaluated with standard performance indicators – such as the IMO’s Energy Efficiency Operational Indicator (EEOI) – without taking this specificity into consideration. A ship that is in the locks 10% of the time will have higher figures compared to one sailing along the coast without necessarily being less efficient.

The marine energy audit

GHGES Marine Solutions specialise in ship energy audits. We have performed marine energy audits on more than 35 ships of various types and our methods are proven and recognised. In Canada, the Quebec Government has implemented funding programs for shipowners to reduce their ships’ greenhouse gas (GHG) emissions. As with any other government funding programme it is contingent on a thorough checking of audit results. The projected goals are verified by external auditors in compliance with ISO:14064-2 and ISO:14064-3 standards at the end of the first year of implementation. Not meeting the GHG emission reduction goals can result in a funding cut. GHGES has developed great expertise in the marine field, ensuring the accuracy of its figures and predictions and we have adapted our method to the ISO:50001 for the marine business.

On average, our intervention reduces marine energy consumption by anywhere between 3-20% (the more fuel a ship uses, the bigger the potential enhancement of the fuel economy). Shipowners often start with one ship and then, having noticed the savings made, end up doing their whole fleet.

We always use the services of two experts – a senior marine engineer and a technician, usually an electrician. Most of our marine engineers are certified energy managers and certified measurement and verification professionals. We also comply with the international standard EVO (Efficiency Valuation Organization).

The team members usually stay on board for two to three weeks and bring with them several thousand euros’ worth of equipment. The audit includes observation of at least one load, one unload and one sea trip.

A full report on the ship’s energy status is then produced, giving details about potential cost-effective upgrade projects, GHG reductions and onboard processes and methods which are impacting the ship’s energy efficiency. All applicable data is quantitatively measured. A financial evaluation based on return on investment (ROI) and net present value is also detailed. We rarely present projects with a ROI over two years.

Because a ship is new it does not mean that it is operating at the highest energy performance level. Obviously, it all depends on the way the vessel is managed and its trade activity. Sadly, we have noticed that frequently, unless special attention is given to the design of the ship by an energy efficiency specialist, flaws still occur, especially when designers continue to follow old methods and conservative concepts. Classification societies, naval architects and maintenance superintendents are not specialised in marine energy efficiency, they concentrate on their own field of expertise and do their best for the energy consumption. But today this is not enough.

Where are the savings?

Tests at sea

As stated previously, each ship has its own particularities that impact optimisation opportunities. Investing in marine energy efficiency has the advantage of being profitable in a relatively short time, especially considering higher energy costs at sea than on land. Reducing GHG emissions also increases shipowner benefits.

During each audit we draw propulsion curves (they are often different from the original sea trials). The curves detail ship fuel consumption versus its speed and engine power. We calculate a mathematical model that then allows the shipowner to accurately determine the so-called economic speed. This value must consider fuel price, OPEX, marketing specificity and the speed vs fuel consumption equation. We calculate the economical speed according to those parameters. If you input a new fuel cost or OPEX then the economic speed will change accordingly.

Where is electric power consumed?

Normally a commercial vessel should not use more than 200-250 kW of electricity at sea. The exhaust gas boiler should also be more than enough for the ship’s heat needs when sailing, and not only at the maximum continuous rating (MCR).

During our intervention, we draw a full picture of electrical loads on the ship in order to reduce marine energy consumption. The first step consists of eliminating any electric heaters, domestic water heaters, engine block heaters, cabin heaters, etc. Replacing such devices for steam or thermal oil heating reduces GHG emissions and associated costs by 50% in port and 100% at sea.

For example, 50 kW electric, at $0.15 (~€0.13) kWh on average equals $65,700 (~€58,000) per year and 322 tonnes of CO2 equivalent emissions. The savings are substantial.

Pumping systems, mostly in cooling systems, are the second thing to be optimised. A ship is designed to support much greater needs than required for normal operation. We automate these pumps for a better match with real ship needs according to our own logic control, considering sea water temperature, heat exchanger capacity and heat load. Manual operation of variable frequency drive (when installed) does not provide optimum savings. Operators like to be within a comfort zone that does not always match the ideal settings.

Next, compressed air systems are analysed. Production of one kilowatt of compressed air requires nine kilowatts of power, so air should be used with extreme care. Any air leak is identified with our high quality ultrasonic detectors and characterised by air flow and monetary value. The compressor performance index is expressed in m3/kWh. A ship commonly uses 1,000 m3 of air per day while consumption over 1,200 m3/day is not normal. Installing and/or using a screw type compressor should be prohibited for service air on a ship. Very often screw type compressors are modulated by choking the inlet. During this unloading process, the compressor uses 30% of its power without producing any compressed air which highly decreases the system performance. Also, a vessel should never use starting air to supply service air as by doing so it doubles the compressed air cost and puts unnecessary running hours on expensive starting air compressor maintenance. How much does this cost you a year? You will be surprised. The marine energy auditor will tell you so you can make the most cost effective decision.

Ventilation and heating systems (HVAC) can also be upgraded with well-known American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) marine energy conservation methods. These systems are frequently oversized to face extreme situations. Modulating inlet and outlet air supply with real load and air quality sensors to avoid expelling air that has been heated or cooled at great expense can be profitable. Better HVAC systems can decrease energy use by 20–30%. Accurate measurements are necessary to determine if investing in updating these systems is appropriate. The energy auditor will make these calculations for you.

Modulating engine room ventilation according to needs often allows us to reduce fan use by 50%, i.e. 25-40 kW less use at sea. We also know that engine room relative pressure control does not provide the best control solution for engine room fans. Other control methods – like our feed forward logic – usually allow a positive ROI in two years or less while reducing emissions.

On a ferry do you need all the lights illuminated on the car decks while sailing? Is the ventilation on these decks always on while in transit? Why not modulate ventilation according to the air quality? How much money is involved? How much green-house gas is produced by these behaviours? The energy auditor will tell you.

Economically, what is the best way to pump ballast on board a vessel, what is the cost difference and GHG emissions variance between various procedures?

As these examples indicate, individual ships have their own particularities and project/operation methods. Each ship must undergo an appropriate expert evaluation to determine which actions to take in order to realise potential savings and GHG reduction.

Heating and heat recovery

Heat recovery is the cornerstone of marine energy saving as its thermal efficiency depends mostly on its recovery capacity. The thermal efficiency of a diesel engine is at best 50%, so half of the fuel energy is wasted in the environment as heat. This huge amount of power must be recovered and if a vessel requires external heat sources for heating there is a serious design problem.

More and more ships use thermal oil as a heat carrier. Thermal oil use can be necessary on specific vessels such as asphalt carriers, but what about other vessels? Thermal oil has some assets, including no water quality issue, no steam traps and no pressure vessel to maintain. However, steam also has its advantages, such as thermodynamic and thermal performance and the fact that it is a non-toxic heat carrier.

A steam boiler needs three things to work properly: good water quality, constant heat load and cleanliness. Use of impure water, packed with oxygen, and use of an on/off type burner will eventually lead to malfunctions. These were some of the factors that originally gave steam a bad reputation over the years, mainly on diesel vessels. But these basic principles are well known and widely implemented on thousands of steam plants worldwide to make them run economically and without technical issues for years. In some cases class approval is required before we do a system modification. We will handle the discussions and provide the acceptance if needed

Steam has many benefits in the regard that it moves by itself. This means that it is not necessary to run a 20 or 30 kW pump 24 hours a day (~$33,000), only to circulate the thermal oil. Thermal oil-specific heat is only 2.6 kJ/kg−1 K −1 versus 4.18 kJ/kg−1 K −1 for water. That means one and a half times more oil than water is needed in a low temperature network to transfer the same amount of heat. Larger pipes are also necessary to reduce pressure losses due to oil viscosity. Steam also allows a benefit from the change of state from steam to condensation, i.e. about 2,500 kJ/kg of latent heat. This is close to 1,000 times more than thermal oil.

Water boils at 100°C at atmospheric pressure and at 159°C at five bar. Whatever the temperature and pressure conditions are, latent heat always produces close to 2,500 kJ/kg. However, oil often needs around 170-185°C to transfer energy. A higher operating temperature also implies more losses in the pipe and higher exhaust gas temperature from the diesel engine. On most vessels using thermal oil, the heat exchangers are sized for 180°C and it is impossible to run at a lower temperature. However, maybe it is worthwhile to replace some heat exchangers with bigger ones in order to be able to reduce the thermal oil temperature and reduce burner operation. The auditor will calculate the ROI for you and find the bottleneck that needs attention.

A boiler can support heat for much longer than a thermal oil network, should a burner failure happen. There is enormous potential energy stored in a boiler. Modern diesel engines are more efficient than older ones and have better thermal performance, exhaust gas temperature is lower and cooling water temperature is often higher than in older engines. Low exhaust gas temperature requires an oversized exhaust gas boiler to recover heat, especially if thermal oil is used. Oversized thermal oil recovery systems can become so expensive that some shipowners decide to reduce boiler size in order to meet their ship construction budget. Often choice is made to size the heat recovery unit according to MCR. This is a big mistake and such a decision can lead to a thermal oil system unable to recover enough heat to supply the vessel in slow steaming or manoeuvring situations.

The construction cost is then passed to OPEX in fuel, the chances are that the extra thermal oil boiler cost will be paid many times over during the life of the vessel and produce tonnes of GHG. However, with steam the pressure can be lowered and still provide the necessary heat, due to the latent heat.

Most of the time, high temperatures are not necessary for ship operation. Most heat-consuming processes, such as cabin heating, bunker tanks heating, domestic hot water, lube oil purifiers, etc., operate at low temperature (<100°C). Only the main engine fuel and some heavy fuel oil purifiers need higher temperatures. We can easily supply a jacket water heat recovery system and boost the remaining heat with alternative marine energy sources for high temperature clients.

We have applied this principle on four ships sailing in Canada; they use heavy fuel without a heat recovery boiler. A hot water network is interconnected with generators and both main engines. This system heats purifiers, cabins, domestic hot water and keeps the diesel engines warm when not in use. Even fuel tanks are heated with this system. This was a retrofit that cost the shipowner $250,000 and brought more than $175,000 per year in savings and an 8% emission decrease.

Let’s go for innovation and efficiency

A good marine energy efficiency auditor will present innovative, cost-efficient and eco-friendly solutions, specifically tailored for the ship. There are numerous technical solutions, but changing mindsets and approaches is always the biggest challenge.

At least three steps are necessary to implement a functional and effective marine energy efficiency program:

  1. Do an energy audit of your vessel. This will lead to listing the most effective methods of improvement and create the base line or what we call the reference scenario.
  2. Implement the specific project and procedures, turning them into SEEMP.
  3. Implement the follow-up period, including data logging and validating that goals are met as well as remedying any issues that may have arisen.

We consider remote supervision to be the best solution for the follow-up period. This is why we developed the MET© (Marine Energy Tracker). This low-cost system only collects information related to the follow-up period. The shipowner can view the result directly on the internet with trends, reports, emails etc. Our innovative, patented model-building method does not require any fuel meter. After an audit we can sell or rent the MET to the shipowner on an annual basis and installation costs are either included in the rental service or paid directly. The MET will calculate the savings and CO2 equivalent reduction almost in real time, thereby quantifying your investment.

The systems and techniques are now accessible and standardised to enable the implementation of a quality energy efficiency and emission reduction program for each ship, following ISO:50001 and SEEMP.

As stated in IMO SEEMP guidelines section 3.3; “it is important to determine and understand the ship’s current status of energy usage.” This is the basic first step. However, experience shows that marine energy audits conducted by qualified professionals are the only ones to result in real energy performance increases. Their expertise is essential to selecting the most cost effective means of attaining significant savings and environmental benefits.

Business with specialised companies such as GHGES Marine Solutions offers the shipowner the opportunity to get an accurate picture of existing ship operations; and to avoid expensive mistakes when designing new vessels.

Gaetan Simard

GHGES Marine Solutions

+1 418 907 8826

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