D H Drives Ltd

Energy Savings For Pumps and Fans

Huge amounts of energy can be saved in the HVAC industry through the use of
variable speed drives. A mere 20% drop in speed of centrifugal pumps and
fans can save as much as 50% in energy. Yet, many buildings still use
traditional mechanical devices to control system flow and therefore have
considerable potential for saving energy. Here, Mike Carman, UK sales
manager for HVAC products at ABB, explains how the technology works and how
it can be implemented.

Many heating, cooling and ventilation distribution systems operate at a
constant flow rate, even though peak demand may only be required for a few
hours. The conventional response to meeting the changing demand for heating
and cooling within a building is to restrict flow to individual rooms, while
maintaining peak flow in the central HVAC system. However, through the use
of this approach, considerable energy is used and equipment lifetime is
shortened.

A much better approach is to use a variable speed drive on HVAC pumps and
fans to vary air or water flow to meet more precisely changing load demands.

Savings in running costs

Pumps and fans offer the best energy savings potential of any equipment in
the building services industry. A fan running at 80% speed only uses 50% of
the energy, compared to one running at full speed. Yet far too many pumps
and fans run continuously at full speed, with the output regulated by
inefficient throttling devices such as vanes or valves. A mere 20% reduction
in fan speed can reduce energy consumption by up to 50%. Applied to a 75 kW
motor in continuous duty, this means nearly Ł15,000 per year in saved energy
- on one single application.

It is estimated that Ł1,000 million is spent each year on running electrical
motors in commercial applications, excluding industry, in the UK. As much as
20% of this could be wasted through the use of inefficient throttling
mechanisms.

Energy saving opportunities with variable speed drives

Variable speed drives are designed for optimum energy efficiency. Without a
variable speed drive, the a.c. motor runs at full speed all the time.
Variable speed drives enable the speed of pump and fan motors to be
infinitely variable Drives operate by switching the fixed mains supply
voltage to a variable voltage and frequency f in response to an electrical
control signal. When coupled to a fan or pump motor, the change in frequency
will result in a corresponding change in motor speed.

Variable speed drives are most commonly used on supply and extract fans for
variable air volume systems, circulating pumps in hydronic systems and water
booster-pumps in high-rise buildings.

In most cases, the motors are controlled to maintain a constant pressure
within air ducts or water pipes. A pressure sensor in the pipe or duct
measures the system pressure and as this changes sends a signal to the
building automation system, which in turn sends a speed demand signal to the
drive. Thus, as valves and dampers close, the pressure rises in the ducts or
pipes, this in turn reduces the speed of the fan or motor.

Retrofitting

There are enormous opportunities for retrofitting drives in variable flow
applications across the HVAC industry. It has been calculated that only one
in four motors used in HVAC applications are controlled by an AC drive. This
means that there are many pumps and fans that could benefit from being
controlled by a variable speed drive.Although the initial capital investment
is often higher, the amount of energy saved by substituting inefficient
control methods such as vanes and valves can result in large energy savings
and short payback periods. Additional benefits include higher comfort levels
for staff because of better temperature and ventilation control, along with
lower noise levels and reduced maintenance costs.

As an example, retrofitting boiler forced draft fans with variable speed
drives could provide two distinct benefits:

Firstly, the use of a variable speed drive would provide a significant
reduction in fan output, particularly when the fan is operated at partial
loads to accommodate boiler turn down.

Secondly, boiler fans with variable speed drives and sophisticated
microprocessor based control systems can deliver simpler control strategies
and improved performance.

Estimating running costs

Pumps and fans are the best applications for variable speed drive retrofits.
The best way of determining the cost effectiveness of a potential variable
speed drive retrofit is to look at the power needed at each operating
condition firstly with and then without a variable speed drive.

Proposed energy savings can then be calculated by taking the reduction in
power at each condition and estimating the savings based on the actual or
expected operating time of that condition.

Examples of applications for variable speed control are those which: -

oHave a single large pump or fan rather than a series of staged pumps or
fans that come on sequentially as the process needs increase

oHave variable flow, where throttling (by valves or dampers) provides the
variation and where the majority of the operation is below the design flow.

oWhere the operating hours are more than 8 hours per day

Energy audit

In order for a company to reduce energy costs, it needs to evaluate how it
uses energy and in what way it can make its operations more efficient.
Before you can make the savings you want, you need to establish just what
your current energy usage actually is. This is usually done in the form of
an energy audit.

An energy audit is a systematic examination of key pump and fan applications
that include the monitoring of energy consumed both before and after the
change to variable speed drives.

It defines where energy can be saved and quantifies how much energy can be
saved with the installation of variable speed drives. These figures are then
translated into a possible monthly saving, the amount of money that will be
saved, in energy bills alone, if the equipment is installed.

Replacing existing drives improves efficiency

Existing drives should also be considered for replacement, even if they have
not actually failed. An old drive could be costing money unnecessarily,
compared to more modern and efficient products.

Today's drives are at least 3% more efficient than their predecessors. For
example, a new 75 kW AC drive from ABB's new range would consume 6,704,082
kWh of energy, at a cost of Ł301,684, over a 10 year period. A 75 kW drive
from the older SAMI STAR range would consume 6,915,789 kWh, at a cost of
Ł311,211, over the same period. This is a saving of almost Ł1,000 per year.

Replacing old drives brings several benefits to the HVAC user:
oIncreased energy efficiency
oReduced running costs
oFrees up floor space

Variable speed drives not only decrease energy use as well as lessen the
burden on the environment, they also qualify for the Government's Enhanced
Capital Allowance scheme. This grants 100% capital write-off in the first
year.

It is not unusual for user to dismiss the promise of 50% energy saving on a
20% speed reduction as the exaggerated claims of a manufacturer. However the
savings can be verified and the best way to start is with an energy survey.
This will enable you to see the potential savings in black and white,
enabling you to make the decisions that bring your company improved
profitability.

Distillery cooling pump - AC drive with flux optimisation

A Scottish distillery uses Ac drive with flux optimisation for two 30 kW centrifugal cooling pumps. Flux optimisation feature offers energy savings higher than other AC drives. Drive losses can be reduced by 30% when the pump is less than 30% loaded. Comparison against throttling gives:
Energy save about 131,400 kWh/year
Reduction in CO2 emissions 65,700 kg/year
Other benefits:
Reduced maintenance cost
Accurate flow control
Reduced reactive power

Appliances plant water pump - AC drive instead of throttling

A UK domestic appliances manufacturer invested in AC drives at its factory. Borehole water is pumped directly into the mains by a 30 kW motor. The drive installed on this motor resulted in a 30% saving and the drive installed on the raw water pump produced savings of 88%.
Energy save total 191,000 kWh/year
Reduction in CO2 emissions 95'500 kg/year
Other benefits:
Payback period of 14 months
Reduced stress to the supply
Reduced reactive power

Bank's computer centre cooling pumps - AC drives instead of throttling

A British bank has invested in variable speed control. Four frequency converters were installed in the cooling system of the bank's computer centre to control the speed of four pumps (total power 240 kW). The pumps were previously running at constant speed.
Energy save about 1,000,000 kWh/year
Reduction in CO2 emissions 500,000 kg/year
Other benefits:
Improved cooling control
Payback in less than a year
Reduced reactive power

Boiler feed pump - AC Drive instead of fluid coupling

An European power plant was comparing Fluid coupling with AC drive for their feed pump (1450 kW) control. The comparison show that within the speed range needed the AC drive consumed about 150 kW less than the Fluid drive.
Energy save about 1,200,000 kWh/year
Reduction in CO2 emissions 600,000 kg/year
Other benefits:
Reduced reactive power
Reduced stress to the supply
Reduced need of maintenance

Chemical industry acid pump - AC drive instead of throttling

A Finnish chemical industry replaced their existing constant speed acid pump control with an AC drive (37 kW). The process is running about 8000 hours a year and the average flow less than 50% of the pump rated flow. The results were:
Energy save about 120,000 kWh/year
Reduction in CO2 emissions 60,000 kg/year
Other benefits:
Reliable control for a demanding material
Reduced maintenance cost
Payback period about 1.3 years

Clean water pump - AC drive instead of on-off

A German city waterworks improved their clean water pumping station control by installing an AC drive (185 kW). Estimated energy saving was about 50% with other benefits.
Energy save about 740,000 kWh/year
Reduction in CO2 emissions 370,000 kg/year
Other benefits:
Constant water pressure
Reduced pressure shocks
Reduced maintenance cost

Dairy boiler feed water pump - AC drive instead of throttling

A US producer of dairy products improved their total heating and cooling processes by using so called pinch technology. There were several changes in the system including a new AC drive to a 7.5 kW boiler feedwater pump.
Energy save about 55,400 kWh/year
Reduction in CO2 emissions 27,700 kg/year
Other benefits:
Reduced maintenance cost
Payback period 3.6 years
Reduced reactive power

District heating emissions reduced by upgrading

The German town upgrading project included not only the pumps control, but also flue gas cleaning and change from brown coal to coal. All this reduced the burning process emissions of dust, CO2, CO, SO2 and NOx.
Heating energy save 38,000,000 kWh/year
Reduction in CO2 emissions 19,000,000 kg/year
Other benefits:
Reduced maintenance cost
Reduced noise
Reduced reactive power

District heating pump - AC drive instead of throttling

A small town in Germany had throttling and on-off control for their seven district heating pump stations. In September 1992 AC drives were installed to control the pumps. During 1993, the first full year with the AC drives the energy consumption was reduced by about 60 per cent. Energy save about 330,000 kWh/year
Reduction in CO2 emissions 165,000 kg/year
Other benefits:
Reduced maintenance cost
Reduced noise
Reduced reactive power

Fabric dyening pump - AC drive instead of throttling

An Australian Dyening company retrofitted their dye circulation pump with an AC drive (30 kW). The energy consumption was monitored before and after the drive installation. The average power was reduced from 14.1 to 2.1 kW. With 6000 operating hours per year the results are:
Total energy savings 72,000 kWh/year
Reduction in CO2 emissions 36,000 kg/year
Other benefits:
Payback period was 32 months
Mass throughput increased 9.7%
Fabric length throughput increased 10.3%

HVAC Chiller water pump - AC drive instead of throttling

In the chiller water distribution system of a big hotel, a conventional throttling control was replaced by 34 pcs 100 kW AC drives. The system is running 4000 hours a year.
Energy save about 4,000,000 kWh/year
Reduction in CO2 emissions 2,000,000 kg/year
Other benefits:
Reduced reactive power
Better flow control
Less supply problems and mechanical wear

Irrigation pumps - AC drive instead of on-off control

A farmer irrigates his fields during periods of dry weather to ensure normal growth. As the irrigators are driven by water flow, a constant pressure is essential for even water distribution over the fields. To keep up the constant pressure a 75 kW AC drive was installed instead of on-off control.
Energy save about 60,000 kWh/year
Reduction in CO2 emissions 30,000 kg/year
Other benefits:
Reduced maintenance cost
Water pressure peaks eliminated
Farm's profitability increased

Metal industry scrubber pump - AC drive instead of throttling

A Norwegian aluminium producer compared their scrubber circulation pumps (8 units 100 kW each) existing throttling control against variable speed control.
Energy save about 2,240,800 kWh/year
Reduction in CO2 emissions 1,120,400 kg/year
Other benefits:
Payoff period 0.5 years
Improved controllability
Reduced reactive power

Mine submersible pump - AC drive instead of throttling

A Finnish chrome mine compared control methods for a submersible pump 37 kW. Power saving with an AC drive was 16 kW in average. Pump is running about 8000 h/year.
Energy save about 128,000 kWh/year
Reduction in CO2 emissions 64,000 kg/year
Other benefits:
Better flow control
Reduced reactive power
Reduced maintenance cost

Oil terminal pumps - AC drives instead of throttling

An oil terminal in United Arab Emirates was looking for new solutions to control the oil pumping between tanks, from tank to ship an from ship to tank. This was a green field project with 20 centrifugal pumps (350 kW each) and a Multidrive with 2 supply units was chosen.
Energy save about 580,000 kWh/year
Reduction in CO2 emissions 290,000 kg/year
Other benefits:
Ultimate flexibility in choosing pumps
Less moving parts and less maintenance
Simple and effective solution - user friendly

Pulp mill pumps - AC drive instead of throttling

A Swedish pulp mill discovered that at 850 kWh per pulp ton, its energy consumption was far too high. Variable speed control of pumps, changing too large pump motors with more suitable and making changes in pipe layouts were the actions causing a reduction to 635 kWh per pulp ton. With variable speed AC drives:
Energy save about 134,400,000 kWh/year
Reduction in CO2 emissions 67,200,000 kg/year
Other benefits:
Improved pulp process control
Less maintenance by soft starting
Return on hardware investment about 12 months.

Pulp pumping - AC drive instead of smaller impeller

Quite often are industrial pumping systems oversized for the real average need. If the maximum capacity is never needed, there is an opportunity to reduce the pump impeller size. This case was with an original pump impeller of 410 mm.
Energy save about 461,000 kWh/year
Reduction in CO2 emissions 230,500 kg/year Other benefits:
Improved pulp process control
Less maintenance by soft starting
Reduced reactive power Pump speed control instead of recirculation

Centrifugal pumps can be controlled by methods similar to those for controlling fans. In practice, the most common method is throttling by means of a control valve. Recirculation is also used, but it is most inefficient in energy point of view. Using AC drive instead in case of 30 kW motor running 5000 hours/year:
Total energy savings 100,500 kWh/year
Reduction in CO2 emissions 50,250 kg/year
Other benefits:
Soft starting less maintenance
Short payback period
Better flow control

Pump speed control instead of throttling

Centrifugal pumps can be controlled by methods similar to those for controlling fans. In practice, the most common method is throttling by means of a control valve. Throttling causes quite a lot of losses both in the pump and in the valve itself. Using AC drive instead in case of 30 kW motor running 5000 hours/year:
Total energy savings 58,500 kWh/year
Reduction in CO2 emissions 29,250 kg/year
Other benefits:
Soft starting less maintenance
Short payback period
Better flow control

Pump flow control - PFC instead of fixed speed

An European water utility compared the energy consumption a fresh water pump with existing On-off control against proposed variable speed AC drive with PFC (one pump with variable and 3 pumps with fixed speed. 55 kW each). With 7000 h/year were results:
Energy save about 195,000 kWh/year
Reduction in CO2 emissions 97,500 kg/year
Other benefits:
Payback period only 3 months
Better water pressure control
Less reactive power

PumpSave for pump energy calculations

PumpSave is a Visual Basic Application for MS Excel to estimate the energy savings available when using an adjustable frequency drive compared to other pump control systems. Calculations are based on typical pump operating characteristics. Results should be used only for estimating purposes. The outputs of the calculations are:
Total energy savings kWh/year
Total energy cost savings Currency unit/year
Direct payback period
Other benefits:
Quick way to make alternative calculations
Simple drive selection is included
Available on the web

River water axial pump control - AC drive instead of throttling

In a river-water pumping station, an axial pump with a rated output of 1500 kW is used. Considering the energy efficiency for partial load the axial pump at constant speed and with throttling as flow-rate control is extremely inefficient. In contrast to this, the pump output can be matched to the output of the installation with low losses if electronic speed control is used.
Total energy savings 2,386,000 kWh/year
Reduction in CO2 emissions 1,193,000 kg/year
Other benefits:
Soft starting less maintenance
Payback period one year
Energy saving 32 per cent

Ship sea water pump - AC drive instead of throttling

The sea water of a freight ship was dimensioned according to the engine cooling demand in tropical waters of 30 degrees C. Most of the time it is sailing in waters which are much cooler, the average only 15 degrees C. With variable speed AC drives the 45 kW pump motor power goes down to 5 kW. With 5000 hours running time:
Energy save about 200,000 kWh/year
Reduction in CO2 emissions 100,000 kg/year Other benefits:
Less corrosion
Less mechanical stress
Less reactive power

Sewage pump - AC drive instead of throttling

For an outdoor pumping station, the following data are available: Maximum flow of waste water is 750 m3/h and the average flow is 400 m3/h.The pump is operated for 8,000 hours per year. Motor output is 70 kW. Average power input with three control methods were compared: Throttling: 44.4 kW, On-off Control: 32.4 kW and AC drive: 23.0 kW. AC drive compared to throttling gives:
Energy save about 172,000 kWh/year
Reduction in CO2 emissions 86,000 kg/year
Other benefits:
Payback period only 6 months
Accurate control of treatment process
Less reactive power required

Wastewater pumping - AC drive instead of on-off control

The efficiency of a Scottish wastewater pumping station has more than doubled since two AC drives were installed. This arrangement replaces simple on/off control of the motors, with the level monitored with a mechanical float.
Energy save about 130,000 kWh/year
Reduction in CO2 emissions 65,000 kg/year
Other benefits:
Pumping index up from 14 m3/kWh to 30 m3/kWh
Maintenance cost reduced
Risk of overflowing is minimised

Water booster pump - AC drive instead of throttling

A UK water utility designed a booster pump station to maintain a minimum suction head and to output a maximum of 17 million litres per day. Two variable speed pumps (total 680 kW) were needed instead of four fixed speed pumps. Energy saving are approximately 34%.
Energy save about 990,000 kWh/year
Reduction in CO2 emissions 495,000 kg/year Other benefits:
Lower construction cost
Better water pressure control
Less reactive power