energy savings in utility systems - university college cork · potential solutions to said faults....

ENERGY SAVINGS IN UTILITY SYSTEMS

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Energy savings in utility systems

2016


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Table of Contents Executive summary ................................................................................................................................. 3

Compressed Air Systems ......................................................................................................................... 4

Running costs and energy losses ........................................................................................................ 5

Compressed Air Leakage ..................................................................................................................... 6

Low Dew point .................................................................................................................................... 6

Refrigeration Systems ............................................................................................................................. 8

Running costs and Energy losses ........................................................................................................ 8

Poor Control ........................................................................................................................................ 9

Refrigerant Leakage .......................................................................................................................... 10

HVAC (Heating, ventilation and Air conditioning) ................................................................................ 12

Running costs and Energy losses ...................................................................................................... 12

Poor Maintenance regimes ............................................................................................................... 14

Poor Control ...................................................................................................................................... 14


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Executive summary

This purpose of this white paper is to summarise where energy savings can be made in the utility

systems employed in the industrial sector and to describe some of the faults that cause these

inefficiencies.

This white paper aims to answer the following questions:

What are the main energy performance issues and inefficiencies in industrial utility systems?

What are the costs relating to these issues?

How can these issues or faults in system performance be identified?

Is it cost effective to remedy them?

How long (if possible to calculate) will it take for these changes take to return on the

investment it takes to remedy them?

This paper introduces industrial utilities and highlights two of the most common faults or bad

practises for HVAC (Heating, ventilation and air conditioning), Air-compression and Refrigeration

systems. It then goes on to explain how to determine if energy savings are possible and to describe

potential solutions to said faults.

This paper demonstrates that small but targeted changes to HVAC, air-compression and refrigeration

utilities can result in major energy and cost savings with the more serious issues delivering a payback

on investment of less than one year


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Compressed Air Systems Compressed air generation systems (Figure 1) form an integral part of any factory where

pneumatically actuation takes place, with upwards of 10% of a pharmaceutical plants electricity

being used on air compression. Use of compressed air varies with the type of factory however some

common examples would be; air brakes, air jet, air motor, valve actuation, boiler tube cleaning,

cleaning, buffing and work positioning. With such a large percentage of all electricity in a plant being

used for air compression, implementing some simple changes could result in large reductions in

running costs.

Figure 1. General Arrangement of an industrial Air Compressor System


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Running costs and energy losses As detailed in Figure 2, the majority of cost associated with air compression is electrical. Though end

use is key, the most cost effective place to identify energy savings on air compression systems would

be with the general running and efficiency of the air compressor itself.

Figure 2. Running costs over a 5-year period

Figure 3 details the losses associated with compressed air generation. These would typically be

motor losses, compression and idle losses, cooling and drying losses, pressure losses in filters, dryer

and pipework and leakage and expansion losses. However, for the purpose of this paper, high

leakage rates, which are a major component of idling losses, and low dew point temperatures are

discussed as these are two of the most prevalent issues in industrial compressed air systems.

Figure 3. Energy losses in compression

Electrical, 71%

Servicing, 15%

Purchase cost, 14%

Running costs of an air compressor over a 5 year period


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Compressed Air Leakage Many factories can operate compressed air systems with leakage rates of approximately 20 – 30.

Leakage is commonly found at, but not limited to, joints, drains, valves, flexible hose pipes, filter and

lubricator units, pressure regulators, condenser traps and thread sealants. A 2007 report published

by the Sustainable Energy Ireland (SEI) found that a 4mm hole in a system, operating at 8 Bar, or

800000 PA (pascal) could result in losses of over €2000 per annum. Adjusting for inflation and energy

price increases, this would equal almost €3000. On a factory wide scale this can result in large losses

in energy and an inefficient compressed air system. It is therefore essential to monitor the leakage

rate from industrial compressed air systems to ensure the generation system is not operating at

unnecessary high levels servicing high leakage rates. Figure 4 details losses due to air leakage for a

variety of hole sizes and typical plant compressed air operating pressures.

Figure 4. Costs of leaks in compressed air system for a range of pressures

Low Dew point In an air compressor air can become saturated due to isentropic compression and expansion. This

moisture in the air can become problematic to end users who require a certain dryness of air. Driers,

which are usually mounted in the compression air generation station, are employed to remove this

moisture from the air. A dew point is defined as the atmospheric temperature (varying according to

pressure and humidity) below which water droplets begin to condense and dew can form. Choosing

a dew point which is suitable for a factory/ plant is very important. Choosing a dew point which is

too low will result in over drying the air and hence will result in unnecessarily high energy costs to

operate the system. Choosing a dew point which is too high may result in poor air quality for the end

users.

Table 1 can be utilised to determine a suitable dew point for a specific plant. It is therefore critical to

monitor the dew point set points in use in industrial compressed air installations to ensure they are


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as economically advantageous as possible while not impacting on end use requirements. Too often

multiple systems on the same industrial site will operate with differing dew point settings with no

quality requirement to do so. Therefore, it is essential to monitor the dew point on each system in

isolation and in parallel for maximum energy performance.

Table 1: ISO 8573.1 Quality classes of compressed air


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Refrigeration Systems Refrigeration systems (Figure 5) are core to the operation of any factory which requires cooling of a

process medium or has extensive HVAC equipment and a significant cooling load. Some examples of

where refrigeration may be required in industry are; chilled water, data storage cold rooms, product

storage, air conditioning and mixed use heat exchangers. Refrigeration is expensive and savings of 25

– 30% are easily attainable in most plants by implementing more efficient control and maintenance

practices. These savings can be achieved with little initial cost and can pay off within two years.

Ensuring that a refrigeration system is more efficient ensures better reliability, which in turn results

in fewer breakdowns and less maintenance costs and down-time losses.

Figure 5. A common industrial refrigeration system

Running costs and Energy losses Table 2 shows some examples of typical refrigeration system energy usage in a number of sectors.

As seen in the table, refrigeration costs vary considerably depending on sector. Costs may also be

greatly influenced by ambient temperature. Refrigeration generally amounts to 20 – 70% of overall

energy costs in most facilities requiring cooling. Therefore, if refrigeration efficiency is increased, this

will amount to large energy savings overall.

Energy losses in a refrigeration system are typically as a result of one or more of the following issues;

blocked condensers, Recycling of warm air, oil level too high or too low, inadequate maintenance,

leakage, poor control, distribution head too low, poor choice of refrigerant and obstacles in air flow.


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Table 2: Refrigeration energy usage by sector

Poor Control Often in industrial utility systems, control set points are not optimal for the service that they need to

deliver. While these set points may be safe they do not ensure maximum efficiency. Customizing

these set points to a particular plant can have a large effect on the efficiency of the system.

Commonly plants use traditional control methods resulting in systems potentially running when not

required or sub optimally when they are. Plants with multiple condensers or cooling towers, still

relying on traditional pressure switches would see a large rise in efficiency due to installation of

control microprocessors. Poor sequencing control of processors will cause several processors to

operate at part load simultaneously.

A condenser receives hot refrigerant gas from a compressor and condenses it into a liquid. At lower

temperatures the pressure produced by the compressor may be lower, this reduces the amount of

work required by the compressor. Installing floating pressure head control allows the compressor to

float between high and low pressures according to ambient conditions. This will allow the

compressor to operate most efficiently and cost-effectively. It is therefore essential to monitor the

evaporator and condenser temperature values in comparison to the outside temperature and

humidly levels to ensure optimum energy performance of equipment.

Figure 6 details is a schematic of a typical industrial control system.


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Figure 6. Control schematic

Refrigerant Leakage Refrigerant leakage is a major issue in industry for a number of reasons. Leaking refrigerant greatly

lowers the efficiency of the refrigeration process, increasing operation costs and energy usage.

Refrigerants such as R171, R404A, are also very expensive to replace, often upwards of €45 a kg.

Some of the chemicals contained in a refrigerant can be hazardous and therefore would pose a

considerable risk to staff and end users of the system. Due to the hazardous nature of refrigeration

chemicals, they pose a large risk to the environment, it is illegal to knowingly allow them to leak,

therefore it is a crucial responsibility of a company to ensure that these leaks are repaired.

If leaks are not repaired they will greatly affect the efficiency and day to day running of the plant,

driving up energy usage and costs, as illustrated in Figure 7 below. The effects of leakage will grow in

severity over time as materials and equipment degrade. It is therefore essential to monitor

refrigerant charge levels to ensure optimum refrigeration system operation in terms of energy

performance


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Figure 7. Breakdown of costs associated with neglect of leaks


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HVAC (Heating, ventilation and Air conditioning) HVAC systems (Figure 8) are made up of air handling units services by chilled water and hot water

systems in order to maintain thermal and air quality conditions within an industrial environment.

This system can include ducts, vents, water-coolers, air-coolers, heat exchangers, heat pumps,

boilers and fans each with a packaged AHU or as separate components of a larger system. These

systems maintain conditions in general work areas and also in more extreme environments such as

clean rooms with the latter being especially energy intensive.

Figure 8. A typical AHU

Running costs and Energy losses According to a study conducted by the SEAI in 2007, HVAC can account for up to 80% of a sites total

energy usage. In a study of 14 major manufacturers, it was found that HVAC accounted for 356 of

1000 GWh of total electrical energy and 322 of a total of 726 GWh thermal energy as detailed in

Figure 9.


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Figure 9. HVAC % Energy usage

Possible sources of energy loss/ fault in a HVAC system may be; poor control, design issues, poor

maintenance or calibration, an excessive number of air changes, wasted heat, poor insulation, a

passive control valve, stuck damper, poor control logic, supply set points conflicting with room set

points, poor management and erroneously selected set points.

In a 2007 report, SEI identified 137 opportunities for energy savings in HVAC, having carried out a

case study on a number of factories. Figure 10 identifies the opportunity frequency distribution of

potential energy savings as observed by SEI.

This report will focus on the two largest opportunities, poor maintenance regimes and inefficient

control.

Figure 10. Categories of opportunities, based on frequency of occurrence


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Poor Maintenance regimes Effective HVAC maintenance is key to its efficient operation. Poor maintenance in a system, can

result in large losses in energy. A lack of emphasis on utility systems maintenance with specific

attention to HVAC systems can lead to the number of AHUs in a plant outnumbering those

maintaining them by a factor of 20 to 1. Deficiencies in system operation can hence go undetected

and unrepaired for long periods of time. Maintenance in HVAC systems is generally only carried out

following complaints of end users or from breached limit alarms. Preventative measures are not in

place and parts are not replaced before they fail. For example, filters may be changed on a time

basis, rather than when the maximum differential pressure is exceeded. Policies such as this can

result in parts remaining in place long after fail, seriously effecting the efficiency of the system.

AHUs (Air handling units) are self-correcting and therefore will consistently supply air at the required

standard. Should a fault such as a passing heating coil occur in the AHU, it will over-compensate with

an overly open cooling coil. Therefore, faults that go undetected and unrepaired can have a knock

on effect, over-working other components and causing further failures. It is therefore essential to

monitor key operational parameters within an AHU and HVAC system in general, to ensure it is

operating as efficiently as possible.

Often faults in HVAC systems require down-time for repair, which may affect the overall plant.

Therefore, components should be tested to ensure they will perform until the next annual or

quarterly shut-down. It is therefore essential that HVAC systems are properly maintained, with

proper maintenance policies in place, to prevent energy wastage, failures and to ensure maximum

efficiency.

Poor Control Similar to refrigeration systems, HVAC control set points often are not optimised according to

specific service requirements. This may result in a system operating above the required standard, at

a cost to the factory. Customizing these set points increases efficiency and limits energy losses. It is

common for a plant to rely on the traditional control systems installed with the machines, replacing

entire systems after a period of time. However, minor alterations undertaken to modernise these

control systems can dramatically increase the efficiency of a machine or system, allowing it to

function at a higher standard for longer. This will result in energy savings, while also prolonging the

life of the machine, limiting replacement costs.

Hunting which occurs in most plants, as a direct consequence of poor control, results in the over-

working of HVAC systems, prematurely degrading components and wasting energy. Typically plants

do not have an enthalpy control for its mixing box which would enable free heating and cooling.

Variable load fans running at flat rate, not adjusting output according to demand with use of a VSD

(variable speed drive), run at a constant cost. These systems which are not reconfigured at times of

low occupancy or demand, when temperature, heating and airflow need not run at a continuous

standard, are expensive. Similarly, HVAC systems which use radiators and split air-conditioning units

often run simultaneously, without control in place to prevent this from occurring. Introducing

control measures can result in large energy savings.

Where possible, systems should be automated to optimise control and not left to run in manual sub

optimal operation to overcome some short term issue. For example, often in plants, exhaust fans

have no temperature control, which could automate control of the fan, limiting energy use and

extending life-time of the fan.


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References

Air compression

A guide to ISO 8573.1 – High quality compressed air from generation to application-Domnick Hunter.

Compressed air technical guide – SEI

GPG216-Energy saving in the filtration and drying of compressed air

Refrigeration

Running refrigeration plant efficiently- a cost saving guide for owners (Guide 279)

Good Practice Guide 280 Energy efficient refrigeration technology – the fundamentals

Good Practice Guide 283 Designing energy efficient refrigeration plant

HVAC

SEI, special working group- HVAC spin 1- 2007

HVAC optimisation in pharmaceutical facilities- Biopharma

energy savings in utility systems - university college cork · potential solutions to said faults....

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