Energy Audit

An energy audit is an examination of an energy system to ensure that energy is being used efficiently. In many ways, this is similar to financial accounting. The building manager examines the energy account of an energy system, checks the way energy is used in its various components, checks for areas of inefficiency or where less energy can be used, and identifies the means for improvement. Energy audit is an effective energy management tool. By identifying and implementing improvement as identified in an energy audit, not only can you achieve savings on energy bills, but also the equipment will be able to attain a longer life under efficient operation. All these mean actual dollar savings. Energy audit has to be conducted by a competent person having adequate technical knowledge on building services installations. The auditor will come up with a report with recommended plans on the Energy Management Opportunities (EMO) for energy saving. The report will provide easy reference to the management for understanding the energy consumption scenario and considering the energy saving plans.

In energy audit, the means to achieve energy efficiency and conservation is technically more appropriate to be called Energy Management Opportunity (EMO). According to the cost and the complexity of implementation, EMOs are classified as follows:

Category of EMO Capital cost
Cat I

Involves practically no cost investment. Normally involving general house keeping measures e.g. turning off A/C or lights when not in use, revising A/C temperature set-points, etc.

Cat II

Involves low cost investment, e.g. installing timers to turn off equipment, replacing T8 fluorescent tubes with T5 fluorescent tubes, etc.

Cat III

Involves relatively high capital cost investment, e.g. adding variable speed drives, installing power factor correction equipment, replacing chillers, etc.

After an energy audit, a number of EMOs can be identified. Some EMOs may involve changes which you can implement immediately with little or no cost. Others may require a larger investment in capital. Calculations should be performed to substantiate the improvement works by quantifying energy savings Significant amount of energy saving can be achieved if appropriate EMOs are applied.

Some of the typical findings in an audit, the corresponding EMOs and energy savings percentage are shown in the following tables.

Audit findings

Corresponding EMOs

Approximate energy savings*

HVAC installation – EMO Cat. I

1. A/C remaining “ON” outside office hours

The last man out or install a timer to turn off A/C

Unnecessary consumption during off hours

2. Too cold in summer, e.g. measured room temperature 21oC

Set thermostat to desired room temperature, say 24oC; or repair/replace the thermostat if it is not functional

10 to 30%

3. Door or window left open when AC is “ON”

Close door or window

5 to 20%

4. Excessive air pressure drop across air filter of AHU

Clean air filter

5 to 20% fan power

5. Chiller set to provide 6oC chilled water outside summer

Re-set operating temperature to 8oC

3 to 6% chiller power

HVAC installation – EMO Cat. II

6. No blinds or blinds not closed for window with strong sunshine

Install or close blinds

5 to 30% cooling energy to offset solar heat gain through window

7. Access door for cooling AHU or ductwork has air leakage (say 3%)

Identify and rectify the leaking gasket/sealant of the access door/ductwork

3% fan power

8. Excessive water leaving chilled water pump glands

Check & improve shaft seal

A flow of 1 L/min excessive flow means 1000kWh per year

9. Overcooled spots due to improper air balancing

Balance the air supply system, add dampers as appropriate

15 to 25%

10 .Overcooled spots due to improper water balancing

Balance the water supply system, add valves if practicable

15 to 25%

HVAC installation – EMO Cat. III

11. Window exposed to strong sunlight

Apply “ anti-ultraviolet film

>20%

12. Boiler with 25% excess air (combustion)

Adjust excess air to 10%

1.5%

13. Air flow of VAV AHU controlled by inlet guide vanes

Add VVVF

10 to 30% fan power

14. Secondary chilled water pump driven by constant speed motor

Add VVVF inverter type variable speed drive (with controlling sensor at strategic point downstream and at setting such that adequate pressure at low load condition can be provided to far away cooling coils)

10 to 30% pump power

Lighting installation – EMO Cat. I

15 .Lighting level in corridor area at 500 lux, which is on high side, however capital cost not available for retrofit

Disconnect power supply to some lightings and lower illumination to suitable level, say 100 lux.

15 to 30% for corridor lightings

16. Lightings along window areas turned “ON” at day time, providing a lux level well over 700 lux

Maintain the lighting level at 500 lux by:

Turning off corresponding perimeter lightings;

or if both interior lightings and perimeter lightings share the same control switch re-wire to facilitate 2 independent control switches for each of the 2 zones;

or replace the ballasts of lightings (only if lighting can suit) at perimeter with dimmable electronic type and control by photo sensor.

20 to 30% for lightings at perimeter

Lighting installation – EMO Cat. I

17. T12/T10 fluorescent tube used in lightings (e.g. exit sign)

Replace with T8 fluorescent tube (not feasible for quick start type)

10%

18. T8 fluorescent lighting (fixture & tube) used

Replace with T5 fluorescent lighting

30-40%

19. Manual control for lighting ON/OFF

Add occupancy sensor control

>20%

20. Electromagnetic ballast used in lightings with T8 fluorescent tube

Replace with electronic ballast

20 to 40%

21. Incandescent lamp being used

Change to compact fluorescent lamps

80%, plus if space is AC the cooling energy to offset the higher heat dissipation from incandescent lamp

Electrical installation – EMO Cat. III

22. Over sizing of motor by 30%

Replace with smaller motor of proper rating

Add VVVF

5%

 

50%

23. Overall power factor of 0.8

Improve to min. 0.85

Minimize I 2 R losses through distribution network

24. 30% total harmonics distortion (THD)

Add harmonics filter to reduce to the extent of THDI subject to the circuit current, I at rated load condition

Minimize I 2 R losses through distribution network

* The figures are for reference only. Actual energy savings will depend on different conditions and applications.

Further sources of information:

1. EMSD website, Energy Management - Guidelines on Energy Audit:
This web page has hyperlinks which may transfer you to third-party website. http://www.emsd.gov.hk/emsd/e_download/pee/ guidelines_on_energy_audit_2004.pdf
 
2. EMSD website, Energyland - Energy Audit:
This web page has hyperlinks which may transfer you to third-party website.http://www.energyland.emsd.gov.hk/en/audit/ index.html
 
3. Environmental Protection Agency (EPA) - Energy Star Program - Guidelines for Energy Management:
This web page has hyperlinks which may transfer you to third-party website. http://www.energystar.gov/index.cfm?c= guidelines.guidelines_index
 
4. The University of Michigan, Plant Operations Division - Energy Management:
This web page has hyperlinks which may transfer you to third-party website. http://www.energymanagement.umich.edu/ utilities/energy_management/ EnergyGeneralTips.html
   
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