Novel Technique Taps Cows for Thermal Power by Jesse Broehl

Novel Technique Taps Cows for Thermal Power

by Jesse Broehl, Editor, SolarAccess.com

Sure cow's manure can be tapped for power, but their milk's heat?

Image: NREL

"...warm air from the bulk tank was observed being blown into the atmosphere and he immediately thought this was a complete loss of valuable heat energy."

- Hugh McClymont, Farm Manager, Crichton Royal Farm.

Brechen Scotland - March 24, 2004 [SolarAccess.com] Sure cows' manure can be tapped for power, but their milk's heat? In the same way geoexchange systems take advantage of earth's constant temperatures, a new system deployed in Scotland taps the considerable heat from dairy cattle's milk that until now has simply gone to waste.

The East Pitforthie Farm near Brechin, Scotland is installing the groundbreaking new system on their operation after a nearby research farm's experiments and trial runs with the approach proved highly successful.

During May of 2002 the Scottish Agricultural Farm's Crichton Royal Farm was approached by a company specializing in the application of Heat Pumps. The company claimed would help reduce milk production costs for the average dairy farm.

All they needed was a testing ground to prove it.

"At a time in the dairy industry when every possible opportunity to reduce costs and increase margins has to be investigated, the Crichton Royal Farm decided to offer the facilities at the Acrehead Dairy Unit for the trial," said Hugh McClymont, Farm Manager, Crichton Royal Farm.

The system is based on the heat pump technology where the heat from the milk is channeled back into the heating water up to 55 degrees C and not lost to the atmosphere via the cooling fans of the standard installations.

The milk is kept in tubing so as not to physically mix with the water, but allow the heat transfer to occur.

McClymont said the background to this idea came about when the senior partner of the company was being shown around a modern dairy where robotic milking machines had recently been installed.

"While watching the robots in action, warm air from the bulk tank was observed being blown into the atmosphere and he immediately thought this was a complete loss of valuable heat energy," McClymont said.

After further research into this observation he realized that it was standard practice in the on-farm milk cooling operation for air fans to cool the refrigerant. In the context of dairy farming, heat pumps are also used in simple form i.e. air source, to take the heat out of the milk as it leaves the cow, that heat is transferred via the refrigerant into heated air which is usually blown into the atmosphere.

McClymont said there's nothing too mysterious about heat pumps, they're used nearly every day with most people not even realizing it. As an example, the domestic fridge and freezer in your house works via a heat pump. Air conditioning system in offices and shopping malls also use heat pumps.

The Crichton Royal Farm spends a lot of time developing and installing systems with many different applications outside farming which capture wasted energy and then uses the built in efficiency of heat pump technology to produce space heating or water cooling. The use of heat pumps ensures that this is achieved with least possible outlay and minimal costs.

In dairying, the unwanted heat in the milk is regarded as an energy resource and instead of transferring it to exhaust hot air, the heat pump system transfers this into large quantities of hot water. To effect this transformation in existing milking parlors, the only alterations are in the refrigerant and hot water pipe work, the milk lines are not altered or broken into in any way.

"Over a five month period starting in July 2002, installation and operation of the system went through the various stages of problem solving and adjustment to the point in late November 2002 when the new system actually outperformed the computer model on which it was based," McClymont said.

Milk cooling was achieved (without the use of water plate pre-cooling) from the supply temperature as it reached the tank from the cow to below 4 degrees C within the required 30 minutes.

At each milking the new system captures 33 kW of heat which would otherwise be wasted. This is then stored as hot water to a maximum of 55 degrees. This hot water then becomes the supply water for the existing hot water systems, with the electric immersers then only required to take the water from 55 degrees C to the 86 degrees required for tank and pipe cleaning.

Not unlike a geoexchange (geothermal) system that uses the earth's ambient temperatures in the ground to stabilize heating and cooling systems.

The system at the Crichton Farm supplies more hot water than required for use in the pipe cleaning cycle, so the surplus can be applied to other uses throughout farm, including domestic heating and hot water in the farmhouse. In the example used at Acrehead the reduction in electrical supply costs water heating amount to £1,760 (US$3,251) per year produced from lower running costs of the new heat pumps compared the original air compressors. An initial total annual saving of £2,030 (US$3750).

A further saving is expected in long term maintenance and eventual replacement of the systems. Water source heat pumps, used in the new system, are inherently more reliable than the original air source system during the operational life of the new system. The system works equally well when applied to the installation of a complete new parlor or the installation of new tanks and chillers.

The pay back time was reduced to one year in the Crichton farm's experience.

For the trial period, the system was connected to one of the farm's 6000 Liter DXtanks. The number of cows being milked over the trial period were 140, producing 2000 liters/day, and on every third day collection.

Acrehead proceeded with the permanent installation of the system following the trial.

The cost of the new system in the UK varies from farm to farm but as a guide, the average installed price will be around £6,000 (US$11,083) giving a payback period of less than three years for the typical unit. These price projections may be different in the United States and elsewhere.

This article was largely edited from a contribution by Hugh McClymont, Farm Manager at Chrichton Royal Farm.

We highly recommend NorthTonight's TV news coverage - rife with dairy puns - at any of the first three links below...

For Further Information:

• MILK-11_56k Quicktime

• MILK-11_56k Real Media

• MILK-11_56k Windows Media, Winamp, and others

• The Scottish Agricultural College

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