Water Distribution Strategy

An energy assessment was previously done for a fruit farm in the Western Cape. It was found that 78% of all the electricity consumed was for pumping irrigation water from the water sources to the orchards. This case study is about the follow-on project to optimize the cost of water distribution on the farm.

All the water used for irrigation is from rainfall. The water is collected in 8 buffer dams/reservoirs which is also topped up from 10 boreholes. A network of pumping systems distributes the water from these sources to the orchards, as shown in the diagram below.

 

The cost of water distribution was obtained from the cost of electricity, the energy intensity (kWh/m3) and the flow rate per pumping system. This cost per cubic meter from primary sources to reservoir is given in the graph below. It shows a variation between 50c/m3 and R2.00/m3, with the higher cost water sources clearly indicated.

The same analysis was done for the secondary distribution of water (from reservoir to orchard). In this case the results were normalised to take into effect the differences in pumping heights and pumping distances. The results are shown in the graph below. The variation in cost is between 20c/m3 and 80c/m3.

The final step was to link the primary and secondary chains to obtain the total cost for water distribution to the orchards. This analysis also included the volume of water pumped from each primary and secondary source. The results in the graph below show the total cost per cubic meter for the orchards serviced from the secondary sources. It is clear that there is a huge variation in water distribution cost between the different applications.

These results were then used to develop a water distribution strategy to minimize the total energy cost for water distribution on the farm. The strategy included aspects such as:

  • Using the “correct” amount of water per orchard. Too much water is a waste of energy cost and water, and too little water may reduce the production output of the orchard.
  • Give preference to the lower cost pumping systems for water distribution.
  • Improve the efficiency of higher cost pumping systems and distribution lines.
  • Utilize the lower cost storage dams/reservoirs more than others.
  • Combine electricity supply points to lower the unit cost of electricity.
  • Use solar power solutions to replace the more expensive electricity supply points.

Improved Water Management

REDUCING CARBON EMISSIONS ON FARMS WITH IMPROVED WATER MANAGEMENT

Previous CCC industry trend reports have indicated that electricity consumption for the pumping of water is the largest source of farm-level carbon emissions. Irrigation of crops is a necessity in a water-scarce country and predominantly coal based electricity is used as an energy source for pumps. Improved water management has the purpose of saving water, cost and reducing carbon emissions. The following opportunities for savings have been obtained during irrigation pumping system assessments on fruit farms.

The starting point is to determine the “correct amount of water” for each tree or hectare. Too little water may reduce the production output and fruit quality, while too much water is a waste of water and energy cost. A study of water flow rates on one farm has shown that some orchards receive only 50% of the intended water supply while other orchards have received 50% more than target. A system to monitor the soil moisture contents is a necessity for good water management on farms.

A lot of water is wasted by evaporation during the irrigation process, mainly due to wind and heat on the ground surface. Improvement in irrigation technology to reduce evaporation losses can save up to 40% of water and related pumping energy.

The irrigation pipe diameters, piping network and geographical height determines the head and flow rates that the pumps are operating on. Higher water pressures require more energy and the irrigation design should attempt to maximize flow and minimize the pressure required. Many cases were identified where the pump head could be reduced significantly with improved piping and irrigation system, while still providing the required water flow rate.

The operation (pressure and flow) of the pump is determined by the irrigation network design. The selection of the pump and the condition of the pump determine the ability to convert electrical energy into the pressure and flow. The efficiency of a sample of pumps were tested and the results show that the pumps use on average around 30% more energy than needed for the required head and flow.

Pumping of water from boreholes has also shown significant losses due to inefficient borehole pumping systems. A sample of 11 boreholes on one farm consumes an average 0.35kWh per cubic meter. The average consumption of 28 other boreholes at similar borehole depths was 0.62kWh per cubic meter. This shows that the potential energy (and carbon emission) savings in improved borehole pumping systems can be as high as 50%.

Larger farms have water distribution networks where water is pumped from rivers, boreholes and dams to other dams or orchards. Sometimes water is pumped 3 times before it reaches the orchard, while each pumping operation adds to the total energy consumed. The sizes and locations of the dams and the relevant position between the dams and the orchards all have an impact on the total energy requirements for the water distribution network. The water distribution network should be optimized by selecting the lower energy boreholes and pumps to do most of the work where possible. This is a more complex and strategic approach towards energy optimization and can also be used to determine the position and sizing of future dams in the network.

The results obtained from the case studies discussed above are not visible to most farm managers and a technical analysis of the pumping systems are required to identify saving opportunities. It is however clear that an average cumulative saving of 30% to 50% on carbon emissions is possible with improved water management techniques on farms.

Pumping System Optimization

Two Oceans Aquarium is located at the V&A Waterfront in Cape Town. The purpose of the aquarium is to display marine life to the public. It is important that the water in the tanks are clear for display purposes to enhance the experience of the visitor. Animal health is also a major concern and the condition of the water influences the animal health. Filtration systems are used to clean the water, and the circulation through the filters are enabled by pumping systems for each display tank.

The focus of the assessment was to closely examine the pump system at Two Oceans Aquarium, make a series of measurements and refer to the on-site personnel for information regarding the specifications of the system as well as the methods of control. This information gathered would then be analysed to determine the potential for optimisation as well as quantifying any financial benefits that could be achieved in terms of cost of implementation and ROI (return on investment)

The pumping system at the predator tank has three 15kW pumps running in parallel. Each pump is circulating water through two banks of filters, 7 filters on each bank. Each pump is equipped with VSD control and the contents of the 2 million litre tank is circulated through the filters every 5 hours

The purpose of the filtration system is to provide clean water which is important for animal health and visitor experience. The clarity of the water is determined by the bio load in the tank, feeding of animals, top-up seawater, the effectiveness of the filter and the flow rate of water through the filter.

A schematic diagram of the system is given below. The suction side has two lines. A strainer is installed before each pump to avoid large rocks or stones to enter the pump. A pressure gauge is available before and after the pump. The pumps are heavily throttled to avoid cavitation. Cavitation should be avoided because it causes bubble sickness at the animals. Pressure gauges are also installed before and after the filter banks. The return flow is combined into a header and filtered water return to the tank via one line.

Figure 1 Schematic diagram of predator tank system

Discussion of Pump Efficiency Results

It should be noted again that the filtration media has been changed a few months ago, from sand to the OC-1 media. The OC-1 media has less resistance to water flow through the filters. The reduction of back pressure has caused cavitation, and this is avoided by heavy throttling of the pumps. There are currently two levels of inefficiency in the pumping system:

  • At the current operating point, the pump is running at 43,7% efficiency. The 15kW pump motor is consuming 8,6kW of power while the optimum is 4,6kW for the same flow and head conditions.
  • The system requires a head of 4,2m from each pump to operate under current conditions. In order to avoid cavitation, the pump is throttled to provide a head of 10,5m. This is another inefficient condition and a waste of energy.

The energy waste is graphically shown in the graph below. Energy is represented by a Constant x Head x Flow, which can be represented by various areas on the graph. The energy use at the current condition A is shown by the outer rectangle. The middle rectangle B indicates the optimum energy use at the current condition, which is 47% less than the actual consumption. The bottom rectangle C indicates the energy that the system requires to work under current conditions. This is only 22% of the actual consumption.

Figure 2 Energy Waste

 

The alternative solution shows that a higher flow rate can be obtained with a lower pump speed combined with less throttling. The maximum flow rate at 45Hz was 116m3/hr before cavitation sets in. By reducing the pump speed to 39 Hz a flow rate of 136m3/hr could be reached before cavitation sets in.

The results show that the change in filtration media from sand filter to OC-1 filtration media had a severe impact on pumping system efficiency. The pumps and motors are oversized for the new filtration media and must be throttled to avoid cavitation. The effect is that 25,8kW is consumed by the pumps for a total flow rate of 316 m3/hr through the filters. The same flow rate can be achieved with only 5,7kW consumption if more suitable pumps are installed.
A summary of the estimated saving of 78% and recommendations are contained below:

 

Pump System Analysis

Background

KBC possesses the expertise to test and consult on pumping systems energy efficiency. The pumping systems in question are mainly used for water in agricultural applications, usually for irrigation.

With the aim of providing useful insight and statistics to potential clients, an analysis was performed on pump systems audited in the past.

Issue

Pumping systems are the most significant electricity users at the production side of an agricultural application.  Most owners are happy when they see the water flowing at the intended supply pressure.  A pumping system converts electrical energy into flow and pressure.  The efficiency of this conversion is not visible to the average operator.  The obvious consequence is a pump system not operating at its optimum, and the owner paying the price for it, literally.

The results of the analysis will serve the purpose of indicating how inefficient pump systems can be when not designed properly.

Audit Methodology

The analysis involved 140 pumps, with rated powers ranging from 7.5 kW to 95 kW. These pumps have all been audited by KBC.  The approach was to check the “vitals” of the system in relation to energy efficiency.

The analysis focused on some key characteristics which can provide the most useful insights. These attributes include:

  • Operating power of motor versus optimal motor power
  • A measure of potential savings
  • Energy used to deliver water

Major Findings

  • The optimal motor power is on average 28% below the operation motor power
  • The operation motor power is on average 15% below rated power.

This means that an average of 28% energy saving is possible if all these pumps should run at their optimum condition.

motorpowergraph

These measurements compared the actual power consumed by the pump, compared to the design power according to the pump specification.  The flow and head were measured at the pump supply point and the efficiency of the irrigation distribution system was not attended to.

A useful attribute to look at is the optimization rating of a pump. The optimization rating is a measure of how well a pump is performing relative to its optimum performance. The pump systems analyzed, were found to operate with an average optimization rating of 57.8%. This is a clear indication of the improvement potential available for the average pump system in practice.

The study revealed an average specific energy value of 0.262 kWh/m3 of water delivered. Taking into account above-mentioned savings potential, the financial benefits of installing an energy efficient pumping system is apparent.

KBC specializes in identifying and consulting on energy efficiency improvement opportunities.

Energy Assessment on fruit & vegetable farm

Fruit and Vegetable Farm

Background

The client is a large farming operation in the Eastern Cape where citrus fruit and vegetables are produced.   Due to confidentiality purposes the name of the client cannot be revealed.

Energy sources used for the farming operations include electricity for irrigation pumping systems and housing, and diesel fuel for farming equipment, such as tractors and trucks, for the transport of produce.

The Issue

The client had grown its farming operations very rapidly over the past 5 years by using a very scientific farming approach.  New farms were developed and pumping stations were built at very remote locations. The steep increases of electricity costs during recent years and the responsibility towards greenhouse gas emissions were the main reasons for the owners to request an energy audit.

Energy Audit Methodology

Electricity is supplied at 19 Eskom points.  A cost analysis was done to determine whether the most suitable tariff structures were being used.  The costs were benchmarked against a sample of similar supply points to determine cost saving opportunities.

The electricity consumption was analyzed and split into major consumption groups, as given in the graph below.   It shows that 82% of the electricity was used for irrigation pumping systems – the most significant energy user.

Farm_Pie

The electricity consumption was split between citrus and vegetables and benchmarked against other similar farming operations.  The fuel consumption was also benchmarked against other citrus producers.  The fuel storage and supply procedures were audited to assure that all fuel purchases were accounted for and that control procedures were in place.  Maintenance procedures of the equipment using fuel were also audited.

Major Findings

The energy analysis was done for the period March 2012 to February 2013.  A total of 1,173,213 kWh of electricity was used at a cost of R1,25m.  During the same period 302,118 litres of diesel was used at a cost of R2,9m.

The control procedures for fuel were found to be very good.  The benchmarking results show that the electricity use was higher than the average of the sample of farms that was used for comparison.  The rest of the findings are explained in the summary of the action plan below.

Proposed Action Plan

  • Pumps
    • Optimize on pumping curve
    • Plotting values for each block
    • Take action where necessary
  • Housing, Offices, Stores, Packhouses
    • Replace lights with efficient alternatives when due
    • Install solar water geysers
  • Fuel
    • Consider packhouse at Addo to reduce logistic distance
  • Electricity Cost
    • Reduce Peak time on Ruraflex (pumps, timer for cold store)
    • Change large points to Ruraflex
    • Investigate Landrate cost/kWh exceptions
    • Combine small Landrate points
  • Renewable Energy
    • Measure benefits of the Solar and Wind solution at SR561
    • Consider Solar PV solutions for Badlands, Loftus or Falcon Gat
  • Energy Management
    • Centralize energy management (“Energy Manager”)
    • Improve Energy Information System
      • Update monthly for early warning
      • Review annually for updated action plan
    • Sub metering
      • Isolate houses, pumps, cold store and other facilities
    • Determine Energy Performance Indicators (EnPI)
    • Measure Improvement against baseline
    • Follow principles of ISO50001

 Actions taken by the Farm:

  1. A pumping system optimization exercise was done as a follow-up audit by using a portable flow meter and comparing results on the pumping curves and the PSAT optimisation software. A sample of 18 pumping systems was evaluated out of the total of 39 pumps.  The efficiency ratings of the pumps were found to be from 39% to 78% with the average around 60%. Recommendations were made to improve the efficiency by altering the application sizes, changing pumping impellors or installing VSD’s.  The changes will increase the total efficiency rating to 80% and save R200 000 in electricity cost per year.  The investment cost is estimated to be R90 000.
  2. The client changed one electricity point to a Ruraflex tariff structure which will save 15% of electricity cost with no investment costs. Other cost saving initiatives are still being investigated.
  3. A solar PV analysis was done for the client at one of the locations. Over the next 25 years the PV solar will cost an equivalent of 42c/kWh, compared to the current Eskom fee of R1.05/kWh and still rising each year. This would, however, require a high capital investment and the client is still evaluating the funding options.
  4. An energy management information model was developed and implemented at a cost of R25 000. This model will absorb the electricity and fuel consumption and cost, the production of crops and the rainfall variables and provide reports on the energy performance of the business on a monthly basis. This information can then be used to revise the action plan, motivate improvements and monitor the future energy performance against the 2012 baseline.