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Handy Hints: The best ways to cut your dairy farm energy bills

Insights

Louise Hartley talks to energy specialist, Tom Kennard for some practical tips on how to keep your energy bills down.

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According to Farm Energy Centre, typical dairy farms consume 33 per cent of electricity costs through milk cooling, while a further 33 per cent applies to water heating.

 

 Tom Kennard, director at Granted Consultancy, says by considering some small, easily adopted changes on farm you can save money and ensure a more sustainable future for your business.

1. Milk cooling

As the milk cooling process is responsible for about 33 per cent of the energy consumed on dairy farms, it is one of the most important areas to target.

 

Mr Kennard says: “The first thing to consider is the efficiency of the plate cooler and what reduction in milk temperature it is achieving.

 

“The minimum should be 10degC, with very efficient pre-cooling systems achieving a reduction of 20degC.

 

“If the plate cooler is working efficiently, milk exiting the system should be within two to four degrees of the temperature of the water entering.”

 

The efficiency of a plate cooler can be significantly enhanced through a variable speed milk pump, as opposed to a single speed milk pump, says Mr Kennard.

 

“A variable speed milk pump will ensure a consistent flow of milk through the plate cooler, while a single speed milk pump only transfers milk when a set level is reached,” he says.

 

“With a single speed milk pump, water is often flowing through the plate cooler when no milk is passing through.

 

“When the pump kicks in, the volume of milk passing through the cooler exceeds the ideal 2:1 ratio between water and milk flow.

 

“There is little difference between the energy use of a variable and single speed pump. It is a question of whether the capital investment

is worthwhile and is solely linked to the improvement in milk cooling which can be achieved.”

 

Cooling provided by water source  kWh (per 100 litres) Pence (per 100 litres) Annual  cost (£)
No pre-cooling 1.4 13.44 1,343
10degC 0.95 8.68 867
15degC 0.73 6.8 679
20degC 0.5 4.67 467

 

 

 

2. Vacuum pumps

It is important to make sure both the size of the vacuum pump and the location of the regulator within the system is correct, says Mr Kennard.

 

“Generally, if your current pump is in good operational order, it is not economical to change to a more energy efficient model,” he says.

 

“Conventional vacuum pumps operate at a constant speed and use a vacuum regulator to admit air into the system to maintain a constant level of vacuum. Fixed speed vacuum pumps operate at the speed necessary to deliver the theoretical maximum level of vacuum demand. This is often in excess of what is required for the normal operating of the parlour.

 

“The extra vacuum capacity is built in to cover events like multiple cluster kick offs.

 

“As a result, the vacuum pump is operating at a much higher speed than is needed for the normal milking routine, wasting electricity.

 

“To avoid this waste of energy, you can purchase a new variable speed vacuum pump or retrofit a variable speed drive (VSD) to your vacuum system.

 

“Unless your fixed speed vacuum pump is nearing the end of its life, it is unlikely to be economic to purchase a brand new variable speed pump.

 

“Trials have indicated a variable speed vacuum can reduce electricity consumption by anywhere between 30 and 70 per cent, with an average of between 40 and 50 per cent.”

 

3. Water heating

Hot water should be one of the main areas to target when looking at energy efficiency, says Mr Kennard.

 

“The size of your main water heater should correspond to the number of milking points in the parlour and be sized accordingly,” he says.

 

“If your tank is too large you may be heating large quantities of hot water unnecessarily. If your tank is too small, additional heating on expensive peak rate electricity might be required to top up the system (see table).”

 

Mr Kennard also says the level and type of insulation on your tank has a dramatic effect on efficiency (see table).

 

“Modern water heaters will have high levels on insulation built into their design. If you have older water heaters, discuss the insulations levels with an electrician and see if they can be improved.”

 

He says it is important to check timers on tanks are working and set to the correct times. These should be adjusted for summer and mean time.

 

“During the milk cooling process, heat is expelled from the condenser of the bulk tank refrigeration system. This heat is transferred into the surrounding air and is, in effect, wasted.

 

The refrigerant leaving a milk cooling compressor can be 70 to 80degC, so it makes sense to try to use this heat for water heating purposes.

 

Mr Kennard says: “A heat recovery unit captures some of the ‘waste heat’ and through a heat exchanger can warm cold water. It can take water temperatures to 45 to 60degC. At these temperatures, water heating savings of up to 50 per cent are possible.”

Water tank insulation

Level of insulation Annual cost to heat 210 litres of water
None £1,419
25mm Glassfibre £155
25mm Polyurethane £91
50mm Polyurethane £55

Thermostat settings

Area Temp (degC)
Main wash-down 85-90
Bulk tank washer 85
Udder wash 35

Hot water quantities for dairy plants

Milking points Tank capacity (litres) 
0-2 65
3-6 110
7-8 160
9-12 225
13-16 295
17-20 360
21-25 450
26-30 545
31-38 680

 

4. Lighting

Lighting is likely to be responsible for about 5 to 15 per cent of the electricity used and is an area which can provide the quickest payback period.

 

Mr Kennard says: “There are a range of different lighting types available, with LED and low pressure sodium lights typically considered the most effective at producing light from power input, and tungsten bulbs the least.”

 

Lighting on farms is frequently left on for longer than necessary and often does not have any automatic control devices.

 

There are various fittings available for lighting control. Mr Kennard says: “Occupancy sensors can detect if someone is entering building/room. These can also be set to automatically switch off again if no movement is detected after a certain period.

 

“Dusk/dawn sensors can be fitted to trigger switching lights on and off as light levels change.”

 

Timers can also be used to control when lights switch on and off.

 

5. Water efficiency and rainwater harvesting

5. Water efficiency and rainwater harvesting

One of the biggest challenges facing agriculture in the future will be the availability of water.

 

“Water on farms will either come from an on-site supply (borehole or spring) or from the mains,” says Mr Kennard.

 

“Typical costs per cubic metre are £1.40 to £2 plus a standing charge for mains, and 15 to 30 pence for borehole or abstraction.”

 

One method of water conservation to consider is rainwater harvesting, he says.

 

“Buildings under construction present the ideal opportunity to install a rainwater harvesting system, but it can also be added to existing structures.

 

“There are systems available to suit all needs and budgets. A simple system might be created by diverting roof gutters into a storage tank and a more complex system could involve pumped storage, filters and UV treatment for use on ready-to-eat crops.

 

“A simple calculation can be used to determine how much rainwater you can harvest. You will initially need to measure the roof area in square metres and your average rainfall in millimetres. Multiply the roof and rainfall readings by a coefficient, as not all the rainfall on a roof will drain away (0.8 for pitched roofs and 0.5 for flat roofs). Finally, add a filter coefficient if filters are used in the downpipes to remove contaminants (a filter coefficient of 0.9 will suffice).

Example calculation for rainwater harvesting 

Roof area 1,500sq.m
Average annual rainfall 819mm
Rainfall coefficient 0.8
Filter coefficient 0.9
Annual collection volume 1,500x819x0.8x0.9 = 884cu.m
Annual cost saving  @£1.50/cu.m = £1,326

 

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