Print this page
Email this to a friend
Discuss this article (0 Comments)
zoom
Mobile
-
General Manager
Industry: Construction
Location: Saudi Arabia -
Environmental Engineer
Industry: Construction
Location: Dubai, UAE
Performance reviews
by Afshin Afshari on Saturday, 01 December 2007
The question of energy conservation in buildings can be approached in two different but complementary ways. First and foremost, it is important to enforce mandatory compliance with stringent and up-to-date building energy efficiency standards such as the American Society of Heating, Refrigerating and Air Conditioning Engineers' (ASHRAE) Standard 90.1 or equivalent.
This compliance is at the heart of most green building initiatives such as the US Green Building Council's Leadership in Energy and Environmental Design (LEED) rating system. But it is perhaps more important to diagnose efficiency issues in existing buildings and address them via the implementation of specific energy conservation measures. This process is generally termed an energy audit.
Energy audits: the theory
Energy audits aim to analyse the energy consumption in existing buildings, taking into account the building structure, the energy consuming equipment and occupants' usage profiles. Of course, a comprehensive energy audit should also consider occupant comfort parameters such as temperature, humidity, air quality and lighting.
The basic principle behind every energy audit is simple: to compare the actual and ideal energy usage, diagnose problem areas and make a financial assessment (payback analysis) of different solutions. The source of the actual usage values can be, for instance, utility bills or by a specific measurement campaign that is set up for a certain period of typically a few weeks in order to obtain a representative consumption pattern.
Furthermore, often a theoretical model of the building is established and used as predictive tool to assess energy conservation measures. The most widespread type of audit, herein referred to as ‘standard audit', relies on theoretical values derived from simplified energy balances. The more sophisticated ‘comprehensive audit' opts for a dynamic simulation model of the building, its equipment, usage profiles and the external climate. A number of commercial building thermal modelling software tools exist and can be used for this purpose.
Simplified energy balance
The most straightforward way to calculate the theoretical average daily cooling energy consumption of a building is by the simplified formula (see the image on next page).
• U is the thermal transmittance of the external walls of the building expressed in kW/ºC;
• ΔΤ is the daily average temperature differential between the internal (conditioned) space and the external environment expressed in ºC;
• f is the daily average free cooling provided by passive cooling systems (if applicable) expressed in kWh;
• η is the net overall efficiency of the building's cooling system.
Benchmarking audits
Benchmarking is the least expensive type of energy audit. A savvy building manager with access to minimal building information such as floor area, hours of occupancy and one year's worth of utility bills, can probably do it without external help.
The procedure involves calculating a set of average representative energy consumption ratios, which can then be used to characterise the building in comparison to a large database of carefully selected and categorised existing cases. Examples of so-called ‘representative ratios' include: average energy consumption per occupant and average electricity consumption per area of occupied space.
In order to constitute a valid reference benchmark the database of existing cases must include a large number of different buildings. The database is typically subdivided into classes'. A class is characterised by a set of parameters such as the building's purpose, age and size. These characteristic parameters are homogeneous within a class.
Each class is characterised by a set of average representative ratios. When a new building is evaluated against the benchmark, it is first categorised in the appropriate class then its representative ratios are compared to those other buildings in the class to which it belongs.
The extraction of the relevant data for the purpose of a benchmarking audit is usually straightforward and does not require anything beyond examination of readily available utility bills and, perhaps, a brief interview with the building manager. Based on the benchmarking results, the audit report may then suggest a more detailed study if a significant bias is observed between the building and its class.
Benchmarking is the least expensive type of energy audit. A savvy building manager with access to minimal building information such as floor area, hours of occupancy and one year's worth of utility bills, can probably do it without external help.
The procedure involves calculating a set of average representative energy consumption ratios, which can then be used to characterise the building in comparison to a large database of carefully selected and categorised existing cases. Examples of so-called ‘representative ratios' include: average energy consumption per occupant and average electricity consumption per area of occupied space.
In order to constitute a valid reference benchmark the database of existing cases must include a large number of different buildings. The database is typically subdivided into classes'. A class is characterised by a set of parameters such as the building's purpose, age and size. These characteristic parameters are homogeneous within a class.
Each class is characterised by a set of average representative ratios. When a new building is evaluated against the benchmark, it is first categorised in the appropriate class then its representative ratios are compared to those other buildings in the class to which it belongs.
The extraction of the relevant data for the purpose of a benchmarking audit is usually straightforward and does not require anything beyond examination of readily available utility bills and, perhaps, a brief interview with the building manager. Based on the benchmarking results, the audit report may then suggest a more detailed study if a significant bias is observed between the building and its class.
TOP IN MIDDLE EAST CONSTRUCTION & INDUSTRY
TOP MIDDLE EAST BUSINESS STORIES
ALSO IN MIDDLE EAST CONSTRUCTION & INDUSTRY
LATEST MIDDLE EAST BUSINESS FEATURES
USER COMMENTS (0 COMMENTS)
CLICK HERE TO POST A COMMENT
From 
RELATED STORIES
American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE)
| 10 stories- ASHRAE Qatar Chapter chartered
2 May '08 | News - Audit for energy efficiency
19 Jan '08 | Comment
International Energy Group
| 5 stories- 70% energy savings possible with green buildings
3 May '08 | News - Audit for energy efficiency
19 Jan '08 | Comment
