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 well spent

Energy well spent

EnergyWellSpent_5aAlthough it is impossible to arrive at a single figure, one can safely say that energy is a major input cost for the fruit export industry. It is also the cornerstone of the cold chain. The combination of keeping costs down and production up is reason enough to invest energy into energy efficiency.

IN 2008, South Africans were shocked into a new appreciation of electricity. For the first time we could remember, load shedding was a part of our lives. As the national electricity utility struggled to keep the lights on, both households and industry had a taste of life without power.

Although load shedding did not cause significant fruit losses, the export industry wisely decided to heed the warning. Further motivated by substantial electricity tariff increases and global pressure to reduce the industry’s carbon footprint, an energy benchmarking project was launched under PHI-1 in 2008.

EnergyWellSpent_6aThe aim was to develop and implement a benchmarking system for energy consumption on farms and at pack houses and cold stores to improve electricity and fuel efficiency. Koos Bouwer, from KBC Industrial Engineers, was appointed to oversee and coordinate the project.

“The benchmarking results showed that it was virtually impossible to make generalisations about energy use in the industry,” says Koos. Not only did the different facilities’ energy use vary widely, they also paid vastly different tariffs – from less than R0.40 per kilowatt hour (kWh) to more than R1.40 per kWh. The best performing pack houses used around 15kWh of electricity per ton of fruit packed, while others used three times as much.

It was also clear that the different methods of cold storage had different energy implications. Storage of apples in a controlled atmosphere was extremely efficient at less than 1kWh per ton of fruit per day, whereas fruit packed in cartons on pallets used almost 8kWh of electricity per ton per day. “The important conclusion drawn from these varying results was that there were many opportunities for energy efficiency improvements,” says Koos. “If one pack house could be more efficient, there was no reason why others couldn’t.”EnergyWellSpent_1a

FROM “WHERE ARE WE” TO “WHAT CAN BE DONE”

EnergyWellSpent_3aIn 2012, the United Nations Industrial Development Organisation (UNIDO) approached the South African government to take part in its Industrial Energy Efficiency (IEE) improvement project. Funded by the Swiss Secretariat for Economic Affairs and the UK Department for International Development, the local IEE project is hosted by the South African National Cleaner Production Centre (NCPC-SA) at the CSIR. The IEE project focuses on five industry sectors, including agro-processing. Under the project’s auspices, the NCPC-SA agreed with PHI-2 to conduct fully subsidised energy audits at interested pack houses and cold stores in the fresh fruit industry. The coordination task was again entrusted to Koos. “The process we followed was more an assessment than an audit,” says Koos. “Instead of looking at how facilities adhered to standards and specifications, the consultants assessed energy use and trends.” The difference between audit and assessment is also clear from the stated purposes of the project:

  • Assist to quantify energy consumption at a facility and identify the significant energy users.
  • Identify opportunities for the reduction and more efficient use of energy in the plant as part of an energy management plan.

The energy efficiency audits initiative was rolled out in January 2012 when Koos embarked on a campaign to raise awareness in the industry. He arranged several regional workshops where NCPC-SA representatives explained the nature and process of the project and recruited participants. Companies that wanted to participate signed a memorandum of agreement with the NCPC-SA. A total of 29 pack houses and cold stores agreed to take part. The NCPC-SA assigned trained energy consultants to spend three to four days at each of the participating facilities. The audit was fully subsidised by the NCPCSA. All the participants had to contribute was their cooperation. Once the audits were completed, the energy consultants discussed their detailed reports with the owners of each individual pack house and cold store. The reports highlighted, among others, savings options, results on feasibility, quantification of behavioural changes and the expected payback periods for energy saving investments.EnergyWellSpent_2a

THE FINDINGS

The 29 participating facilities had a combined energy use of 101.1 megawatt hours (MWh) of electricity at a cost of R77 million for the year 2011. The energy audits revealed that they could save a combined 27MWh per year, putting R20.7 million back into their collective pocket. This 26.8% saving would require an investment of R26 million that will, on average, pay for itself in only 1.26 years. The potential electricity saving equals a reduction in CO2 emissions of 27 000 tons per year.  Some of the areas in which considerable efficiencies can be gained are energy efficient lighting, variable speed drives and energy management systems. The single biggest opportunity, however, is to improve the efficiency of cooling equipment.

THE WAY FORWARD

Koos points out that it is important to understand that the facilities are all unique and that the same change will have different impacts at different facilities. “It is literally impossible to generalise because one size does not fit all. The only way to improve facilities’ energy efficiency is to use individual energy audits or assessments as the starting point.” A number of the facilities who took part in the audits are doing just that. Using their site-specific recommendations, they have started to implement the suggested energy efficiency measures and are reaping the benefits. “The project seems to have acted as a catalyst,” says Koos. “It made the saving opportunities visible and facility owners are acting on it.”

© Koos Bouwer Consulting 2014

Apple packhouse

Background

The client is a large apple packhouse operation in the Western Cape where apples are stored, sorted and packed for the export market.   Due to confidentiality purposes the name of the client cannot be revealed.

The main energy source is electricity obtained from Eskom.  Apples are harvested by farmers during February to April and then stored in controlled atmosphere cold stores for up to 10 months at the packhouse facility.  Short term storage is done with regulated atmosphere cold stores and forced air cooling for packed pallets.  The cold storage and packing operations continues throughout the year.

The Issue

A previous energy audit was done at this client during 2010.  One of the recommendations was to implement an energy information model for better energy management.  This model was implemented and maintained during 2012 and 2013.  The client requested a second energy audit during 2013 to assist with the development of a detailed action plan.

Energy Audit Methodology

Information gathered in the energy model was analyzed to obtain a better view on the electricity consumption patterns in the facility.  The assessment was done for the electricity consumption period from January 2012 to December 2012.  During this period almost 7.1GWh of electricity was used at a cost of R4.59m, an average unit cost of R0.67/kWh.  The electricity balance (see below) shows that 89% of the electricity is consumed in cold storage operations.  The client agreed that this significant energy user should be the focus point of the improvement action plan.

Apple_Pie

A checklist was compiled from literature on best practices for energy efficiency in refrigeration applications.  This checklist was followed as a guideline to evaluate all the cold storage operations at this packhouse as an input towards developing the improvement action plan.

Major Findings

The major findings of this energy audit are twofold:

  1. Technical improvements can be made to improve the energy efficiency of the facility. These steps are summarized in the table below.
  2. It was clear that there was a lack of energy management skills at the packhouse. The energy information was gathered in the model, but nobody really attended to the information and acted upon it. The audit also indicated that some of the information was not correctly captured, which may lead to false conclusions.  The technical people were found to be very competent in running the cold stores, but during their busy season they do not have time for energy management activities.

Proposed Action Plan

The proposed technical action plan is summarized in the table below.  These actions would require an investment of R390 000 and will lead to an energy saving of R1.35m per year.  The projected saving of 1.84GWh per year is a saving of 26% on the electricity consumption of the packhouse facility.

apple_table

A good energy management approach is essential for sustainable energy improvement.  The packhouse has implemented sub metering and an energy information model to assist in energy management. The information should provide a baseline against which performance improvement can be measured.  The following improvements to this approach were recommended:

  • Determine the roles and responsibilities for energy management at Valley.
  • Revise the data for 2012 and establish a baseline.
  • Revise the data for 2013 and determine improvement against the baseline.
  • Set improvement targets for 2014 and beyond.
  • Continue with short interval control during 2014 based on weekly results.
  • Allocate resources for the energy management actions or subcontract.

A solar PV analysis was done for the packhouse.  A 741kWp system is recommended before excess power is fed back into the grid.  This system will cover 5200 square meters of existing roofing space. The total investment cost is R9,6m after tax rebates.  The costs of the proposed solar PV system equates to effectively paying only 34.7 cents/kWh over the next 25 years.  The projected average cost of electricity obtained from Eskom is R2.66 /kWh over the next 25 years.

Actions taken by the Packhouse:

  1. The outcome of the energy audit was received with great appreciation by the packhouse. The action items requiring capital investment were put on the budget for next year.
  2. The packhouse is also negotiating with an outside energy consultant to assist with the energy management process during next year. This will include the energy projects for improved refrigeration control.