Module 2: Farm Practices to Improve Energy Efficiency

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2 Module 2: Farm Practices to Improve Energy Efficiency 2.2 Dairy Energy Efficiency Author: Scott Sanford, Sr. Outreach Specialist, University of Wisconsin Peer Reviewers: Joe Horner, Extension Economist, University of Missouri Brian Holmes, Agricultural Engineer Specialist, University of Wisconsin Extension This guide is also available as an online learning module at: unit-2-2-dairy-farms/ Additional modules on Energy independence, Bioenergy Generation, and Environmental Sustainability are available online at: This material is based upon work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

3 Table of Contents Learning Objectives Introduction Vacuum Pumps Milk Cooling... 4 Scroll compressors... 4 Well-water precoolers... 4 Refrigeration heat recovery... 4 Variable speed milk pumping Water Heating Long Day Lighting... 6 Conclusion... 6 Further Information and References... 6 Dairy Energy Efficiency 1

4 Learning Objectives 1. Understand how energy is used for milk harvesting and dairy cattle housing. 2. Learn what technologies can be used to reduce energy use for milk harvesting and dairy cattle housing. 3. Learn what management changes can reduce energy consumption / Introduction There are many possibilities for saving energy on dairy farms. In general, dairy farms use between 800 and 1200 kilowatt-hours (kwh) of electricity per cow every year but in one study the range was from kwh/ cow/year. The surprising thing is that both of these were in freestall operations. Data from the Center for Dairy Profitability [1] indicates utility costs on the average dairy farm account for less than 2 percent of milk production costs on all sizes of farms although, as one might suspect, the utility costs per cow decreased as farm size increased. The utility cost per cow generally range from $45 to $95per cow but range widely depending on the type of housing and herd size. A recent study indicated that 59 percent of the energy use was for milk harvesting (vacuum pumping, milk cooling and water heating), another 35 percent was used for lighting and ventilation and the remaining 6 percent was for feeding, manure handling and other miscellaneous uses. At 27 percent, water heating uses the most energy but the energy source varies by farm; electricity, heating oil, L.P gas and natural gas. The other energy uses in the pie chart are all electricity. Milk cooling used the most electricity at 19 percent, with lighting coming in second: 18 percent follow by ventilation at 17 percent and vacuum pumps used 13 percent. A New York State study [2] suggests an energy efficient farm is one that uses 750 kwh/cow/year or less. Table 1 lists the potential energy savings for different uses of energy on a dairy. The good news is technologies are available that can save energy on most dairy farm operations without sacrifices. Figure 1: Energy distribution on New York State Dairy Farm. Graph compiled by Scott Sanford with data from Dairy Farm Energy Audit Summary (2) Dairy Energy Efficiency 2

5 Energy Use Energy Saving Technology Potential Energy Savings Vacuum Pump Variable Seed Drive 50 to 65% Cooling Precooler (Heat Exchange) 60% Cooling Scroll Compressor 15-20% Cooling Water Heater Variable Speed Milk Pump (Added to existing Precooler) High Efficiency Condensing water heater Up to 30% 25-45% Water Heater Refrigeration Heat Recovery 50% Exhaust Fans More Efficient 20% Stirring Fans HVLS Fans 60% Lighting More Efficient Fixtures 30-75% Table 1. Potential energy savings for different uses of energy on a dairy. Source: Scott Sanford / Vacuum Pumps The installation of a variable speed drive (VSD) vacuum pump, sometimes called a variable frequency drive, usually saves between 50 and 65 percent in electricity costs with the same or better vacuum regulation. The VSD can be adapted to blower or, in some cases, rotary vane vacuum pumps. They work by changing the speed of the vacuum pump according to readings from a pressure sensor mounted on the vacuum line near the receiver jar. The VSD is basically a dedicated computer capable of many adjustments, so it may be possible to improve vacuum regulation over the typical pneumatic vacuum regulator that only has a vacuum level adjustment. Adding a VSD to a vacuum pump is usually economical for a dairy that milks a total of 6 to 8 hours or more per day. Typically a VSD is not an economical option for small dairies with short milking time and thus shorter vacuum pump run times. Dairy farms with either single or three phase electric power can use variable speed drives. Converting a vacuum pump to variable speed entails installing a Variable Frequency Controller, changing the pump motor to a 3 phase motor and installing a pressure transducer near the receiver jar. The existing pneumatic vacuum regulator is removed or set about 1 inch of mercury higher than the set point vacuum level to act as an emergency vacuum regulator. If a farm was using two vacuum pumps, often one can be shut off and maintained for a backup. For smaller dairies, there are some other ways to cut energy costs. First check to make sure your current vacuum pump is not grossly oversized. A long held belief has been that more vacuum pump capacity was better. Research has since shown that a vacuum pump sized at 3 cubic feet per minute (cfm) per milking unit with a 35 cfm base capacity for up to 32 milking units is usually adequate even accounting for a milking unit falloff. Your local dairy equipment dealer can aid you in determining if your vacuum pump is sized correctly. Vacuum pump capacity is approximately 10 cfm per horsepower is a rough rule of thumb. If your current vacuum pump has larger capacity than needed, it may be possible to change belts and pulleys to slow the pump down or you may be able to trade it in for a smaller pump head. Keeping drive belts in good condition and tight reduces belt slippage and thus electricity usage. Illustration 1: Variable speed vacuum pump system. Source: Scott Sanford Dairy Energy Efficiency 3

6 2.2.3 / Milk Cooling There are three technologies that cut electrical energy use when cooling milk: scroll-type refrigeration compressors, well-water cooled precoolers (heat exchangers) and refrigeration heat recovery units. Scroll compressors are newer units and are 15 to 20 percent more efficient, have fewer moving parts, and are only slightly more expensive than traditional reciprocation compressors. Scroll compressors have been used in dairy refrigeration systems since the mid- 1990s with good results. If you are purchasing a new bulk tank, you can specify the compressor be a scroll type. If your existing reciprocating compressor fails replacing it with a scroll compressor adds about $ more than the cost of a new reciprocating compressor. The extra cost is for re-wiring and new mounting holes. This is a modest cost for the improvement in efficiency [1]. Well-water precoolers are heat exchangers that use well water to cool the milk before it reaches the bulk tank. If sized properly and have an ample water supply, they can reduce milk cooling costs by up to 60 percent. This is assuming 55 F well water to reduce the milk temperature to within 3 or 4 F of the well water temperature. Undersized water lines and water system capacity are the two largest reasons that precoolers do not perform up to their potential. It requires 1 to 3 gallons of water to cool 1 gallon of milk depending in the design of the heat exchanger (2 gallons water per gallon milk common). The precooler water should be re-used for watering cows or general clean-up. The water can be stored on a plastic holding tank until needed. If a refrigeration heat recovery (RHR) unit (see below) is being used, an energy audit should be done to assure adding a precooler will not increase energy requirements, because precoolers and refrigeration heat recovery units are competing technologies. If the milk is cooled with a precooler, then there is less heat available to pre-heat water in the RHR unit. If an electric water heater is being used, it is usually more cost-effective to maximize water heating with an RHR unit rather than to precool milk to save energy [2]. A refrigeration heat recovery (RHR) unit is typically a water tank with a heat exchanger jacket around it through which the refrigerant from the milk cooling system flows before it goes to the air heat exchanger (condenser). Some of the heat from the refrigerant is transferred through the jacket and tank wall into the water stored in the RHR tank. An added benefit is a small increase in the efficiency of the refrigeration system due to a larger heat transfer area [1]. Variable Speed Milk Pumping Variable speed drives (VSDs) can be used on milk pumps to control the flow of milk through a precooler or heat exchanger to increase its cooling efficiency. A constant speed milk pump can move milk at a rate of 30 gallons per minute (gpm) or more. To get maximum milk cooling, the water to milk flow rate ratio should be a minimum of 1:1, so a minimum of 30 gpm of water is needed. However, many precoolers require a water to milk ratio of 2:1 for maximum heat exchange rate thus 60 gpm of water is needed for a system with a constant speed pump. Most farms do not have this size of water system capacity. A VSD on the milk pump can lower the average milk flow through the precoolerwhich reduces the water demand (gpm) needed to achieve maximum efficiency from the precooler [3]. Illustration 2: Well water Precooler (heat exchanger). Source: Scott Sanford Dairy Energy Efficiency 4

7 2.2.4 / Water Heating The cost of water heating in dairy operations can be reduced in many ways: A refrigeration heat recovery (RHR) unit captures heat collected by the refrigeration system to pre-heat well water before it enters the water heater. This can provide up to 50 percent of the energy required for water heating. It is usually economical to install an RHR unit when and electric water heater is used. These units are available from all major brands of dairy equipment manufacturers. Water conservation is a low-cost way to reduce water heating expenses. For example, sometimes more water then necessary is used to wash milking systems. Having your dairy equipment dealer fine-tune your pipeline washing system can help reduce the amount of water needed to wash the milking system [1]. 24 percent daily standby heat loss. A typical gas or oil water heater can have a standby loss of 2.5 percent per hour, which equates to a daily loss of 60 percent. When shopping for a new water heater, the more insulation the better. The overall efficiency or energy factor of a water heater can range from 50 percent to 88 percent. [2] Illustration3: Refrigeration heat recovery unit next to a water heater. source: Scott Sanford Using water directly from the refrigeration heat recovery unit in situations when warm water will do and the precise temperature is not critical is another way to reduce water heating costs. This avoids heating the water up only to dilute it with cold water. Do your homework when choosing a new water heater. Their thermal efficiency, i.e. the percent of energy transferred to the water, varies greatly. Electric water heaters have a thermal efficiency of nearly 100 percent. Gas and oil water heaters have a thermal efficiency of about 80 percent unless they are of the condensing type, which have thermal efficiencies in the 95 percent range. Water heaters also differ widely in standby loss, which is an indication of how well insulated the tank is. Standby loss is the heat lost over time when the water sits unused in the tank. Electric water heaters are typically the best insulated, with standby losses of about 1 percent per hour and some as low as 0.5 percent per hour This would mean 12 to Heat loss through pipe walls can be substantial depending on the length of run. Covering the pipes with foam pipe insulation will reduce heat loss and result in higher water temperatures at outlets. In new construction insulating all pipes both in walls and exposed pipes is highly recommend. Solar water Heating generally on dairy farms there is ample waste heat from the refrigeration system to replace at least 50% of the water heating needs using a refrigeration heat recovery unit. Solar water heating systems are efficiency at heating water from well water temperature up to about 120 F but then the efficiency decreases rapidly. The payback on solar water systems is typically longer than other energy efficiency options that a dairy could invest in so they are seldom the best investment for a dairy but often a good investment for a residential home. Dairy Energy Efficiency 5

8 2.2.5 / Long Day Lighting Research has shown that when cows are exposed to 16- to 18-hour days, they will produce 4 to 5 pounds more milk per day. Long days can be simulated by exposing the cows to artificial or a combination of natural and artificial light. In a tiestall barn this can be accomplished by installing a row of T8 fluorescent fixtures over the feed alley. In a freestall barn, metal halide high pressure sodium, induction or fluorescent (T5 or T8) lamps can be used unless the ceiling height is less than 10 feet, then T8 or T5 fluorescent fixtures are recommended. Using long-day lighting doesn t reduce energy input, but the increase in milk production reduces the cost of milk per unit of energy used. For more information, refer to the links in the References section / Conclusions Although electricity is not a major part of milk production costs, there are multiple technologies that can reduce utility bills significantly and give a very favorable return on investment for most dairy farms. A variable speed vacuum pump can reduce energy use by 50 to 60 percent, a well-water cooled precooler can reduce cooling requirements by two-thirds, a refrigeration heat recovery unit can typically reduce water heating costs by 50 percent and lighting energy consumption can often be reduced by 50 to 75 percent. Some energy conserving techniques preclude that energy being available for other downstream energy recapture. Enlist the aid of an energy auditor to help decide the best combinations of technologies for you. Farms with under 100 cows may have fewer options than larger farms, but all can reduce energy usage. References and Further Information Unit J. Vanderlin Milk Production Costs in 2003 on Selected Wisconsin Dairy farms, University of Wisconsin, Center for Dairy Profitability. Available at: verified 9/4/12 2. D. Ludington, E.L. Johnson Dairy Farm Energy Audit Summary, New York State Energy Research and Development Authority. Available at: database=web verified 9/4/12 Unit S.A. Sanford Energy Conservation in Agriculture: Vacuum Systems, A3784-5, University of Wisconsin Extension. G.A.Mein et. al Sizing Vacuum Pumps for Milking, National Mastitis Council Annual Meeting Proceedings. D.J. Reinemann, Mein, G.A Sizing Vacuum Pumps for Cleaning Milking Systems, National Mastitis Council Annual Meeting Proceedings. Dairy Energy Efficiency 6

9 Unit S.A. Sanford Energy Conservation in Agriculture: Refrigeration Systems, A , University of Wisconsin Extension. 2. S.A. Sanford Energy Conservation in Agriculture: Well Water Precoolers, A , University of Wisconsin Extension. 3. S.A. Sanford Energy Conservation in Agriculture: Variable Speed Milk Pumps, A , University of Wisconsin Extension. Unit D.J. Reinemann Dairy Operators Guide to milking Machine Cleaning and Sanitation, UW Milking Research and Instruction Lab, University of Wisconsin. Available at: verified 9/4/12 2. Ratings for water heaters are available at the Air-Conditioning, Heating and Refrigeration Institute (AHRI) website ( ) Scroll down under Residential or Commercial until you find water heaters, click and proceed with search. S.A. Sanford Energy Conservation in Agriculture: Water Heating on Dairy Farms, A , University of Wisconsin Extension. Unit G. Josefsson, Miquelon, M., Chapman, L Long-Day lighting in dairy barns, Tip sheet: Healthy Farmers, Healthy Profits, University of Wisconsin. Available at: verified 9/4/12 G. Dahl Photoperiodic Manipulation of Lactation in Dairy Cattle, Summary of research work, University of Illinois at Urbana-Champaign. Available at: verified 9/4/12 S.A. Sanford Long Day Lighting Decision Tool, University of Wisconsin. Available at: verified 9/4/12 Refer to the Animal Housing Unit in 2.5 for information on ventilation and lighting. Sanford, S Farm Practices to Improve Energy Efficiency: Dairy Energy Efficiency. Module 2.2 in S. Lezberg, S. Sanford, and M. Jungwirth (eds). On-farm Energy Conservation and Efficiency. On-line Curriculum. Bioenergy Training Center. Learning for life Dairy Energy Efficiency 7