Practical Ventilation Measures for Livestock Vessels

Summary

The following “dot points” summarise and form an index to the concepts explained in the report. While this report is a summary of practical measures noted during work for the Livestock Vessel Ventilation Report, the “dot points” below are still further distilled. As a result, caution is urged in interpreting this summary without also referring to the explanations available.

2. Practical Measures for New and Existing Ships

2.1 Ventilation Intakes

‘Mushro​om cap’ intakes decrease flow, or cost power, or do both together. ƒ A little bit of inlet flaring helps a lot.

2.2 Ducts Bends and Elbows

Avoid sharp duct elbows where possible.

A little bit of corner smoothing helps a lot.

2.3 Duct Discharges

Supply air outlets should be smooth, with no extraneous grilles or baffles.

2.4 Flow Balancing (Supply vs Exhaust)

For closed holds, reversing exhaust fans to supply is likely to be counter-productive.

2.5 Flow Balancing (local outlets)

Restrictions applied to balance the supply outlet flows should be the minimum practical.

2.6 Jetting of Air

Supply air should be delivered in jets over the backs of animals in each pen.

2.7 Avoiding Dead Spots

To avoid dead spots, air should be actively supplied (in jets) to all areas (preferably each pen).

Local fans may also ensure the necessary air exchange through mixing if jetting is not possible.

2.8 Measuring Air Properties

Shippers should ensure that the crew members are fully informed on the correct use of instruments to measure air properties.

2.9 Pen Air Turnover

Pen Air Turnover (PAT) is the preferred measure of ventilation rate. It is the ventilation flowrate divided by the pen area.

2.10 Wet Bulb Temperature

Wet bulb temperature is the appropriate measure of the thermal environment for cattle on ships.

Relative humidity is not useful except in calculating wet bulb temperature.

2.11 CO2 As An Indicator

CO2 level gives a direct measure of the ventilation effectiveness at any location. ƒ CO2 is also useful for identifying recirculation of exhaust air.

2.12 Cattle Wetting

Wetting livestock so that water runs off the skin will remove body heat and give some respite.

2.13 Course Alteration

In a following breeze, altering course by say 10 to 30 degrees can significantly improve open deck conditions with minimal increase in sailing time.

Turning circles gives only temporary relief and is not worth doing.

2.14 Hot Bulkheads

Hot surfaces (bulkheads, cover decks or tanks) can add significantly to the stress of nearby livestock.

Animals should be shielded from hot surfaces by insulation or “double skinning” on the surfaces.

3. Practical Measures for New or Re-fitted Ships

3.1 Avoiding Recirculation

Recirculation of exhaust air can be a serious problem.

Recirculation has been observed to result in effective ventilation rates being halved.

Exhaust should be directed forcefully away from the ship.

Intake air should not be sourced alongside open decks or near exhausts.

3.2 Air Supply and Exhaust Locations

It is beneficial to provide many supply air outlets closely spaced around the hold.

Preferably each pen should have two or more supply jets directed at it.

Exhaust may be collected at fewer, more central locations without detriment.

3.3 Cost Functions

Much can be learnt about the economic trade-offs in ventilation design by a mathematical approach relating cost to the various parameters.

3.4 Noise

Noise can be an issue for port neighbours, crew quarters and personnel working below decks.

The first effort in minimising noise should be to minimise the total fan power.

Industrial ‘splitter’ attenuators could control the noise but may be excessively bulk and clumsy to fit on board.

Cylindrical ‘jet fan’ style attenuators appear to be a practical approach, offering a noise reduction of 8 to 12dB.

3.5 An Ideal Ship?

The “ideal” ship will be different for each shipping business. The following “dot points” represent only one such solution.

Subject still to the findings of the sheep ventilation project, forced ventilation with high sided ships is preferred to open decks.

Below the weather (sea tight) deck, supply and exhaust ventilation would be balanced.

​Upper decks would be exhaust only, with intake through the (non-sea tight) sides.

Supply air would be through multiple nozzles with exhaust in large, more central risers.

4. Air Flow Facts

4.1 Composition of the Atmosphere

Dry air is almost four-fifths nitrogen and around one-fifth oxygen, with only around 1% made up of other gases.

The most humid air carries only around 4% water vapour.

4.2 What is a Gas?

Air is a chaotic mixture of widely spaces molecules.

Although gas molecules can be ‘squeezed’ closer together to increase density, air can be treated as an incompressible but light liquid when calculating ship ventilation flows.

4.3 Air Flow Friction

Ship ventilation flows are fully turbulent.

Duct pressure drop is proportional to the square on the duct velocity.

4.4 Fan Power

Fan power is proportional to the cube of the duct velocity.

Small changes to the duct size will have much larger effects on fan power.

4.5 Humidity, Density, Pressure Change and Flow Resistance

As in Section 4.2, changes in humidity, density and temperature of the air are small enough that they need not be considered in design of mechanical ventilation for livestock vessels.

4.6 Fans and Rain

There should be no harm to the fans by eliminating intake caps and allowing rain to enter intakes freely.