By Kenneth Li, Hong Kong, 852-2856-8899, li.kenneth@pbworld.com

Building Energy Codes (BEC s ) have been adopted in many countries worldwide to control building design practices, promote energy efficient designs, encourage energy performance and develop energy efficiency policy. The formulation of BECs is essential because they:

• Allow energy consumers to benchmark the performance of their buildings with objective yardsticks
• Allow the regulatory bodies to calibrate regulations and to compensate market inefficiencies
• Act as the catalyst to trigger the building industry and developers to invest more in designing buildings that use less energy, which, in turn, reduce the continual demand in electricity and lessen the environmental impact of energy generation.

Figure 1: PB-BEC Compliance Mechanism

Table 1: Examples of Commercially Available Software Programmes for Building Energy Simulation

Table 2: Demonstration of Changing System Performance to Achieve an Acceptable TBE

Commercial buildings are attractive targets in formulating energy conservation measures because

• They are the major energy consumers, accounting for 34 percent of the total energy consumed (Figure 1)
• Once built they are long-lived and their lives normally extend beyond the life span of the energy infrastructure put in place to supply them.

With the prime objective of encouraging energy efficiency and better building design, The Government of the Hong Kong Special Administrative Region of the People's Republic of China has devoted effort to developing building energy codes (BECs). In 1995, Hong Kong 's first BEC was promulgated by the Buildings Department to control the use of building envelope materials through the application of overall thermal transfer value (OTTV). The OTTV is a mandatory code enacted under the Building (Energy Efficiency) Regulation, Building Ordinance.

Four other BECs on lighting, air conditioning, electrical, and lift and escalator Installations were introduced subsequently from 1998 to 2000. Implemented by the Electrical & Mechanical Services Department (EMSD), Hong Kong Special Administrative Region, PRC these four BECs are voluntary in nature. The current BECs are basically prescriptive. They set out the minimum energy performance requirements for buildings relating to power consumption, system design and energy monitoring provisions.

When a building complies with any one of the four voluntary BECs, a registration certificate is awarded to the building owner/management. Up to now, more than 119 registration certificates have been issued to more than 73 buildings. Coupled with the BECs, the Hong Kong Energy Efficiency Registration Scheme for Buildings (HKEERSB) was launched in 1998.

In recognition of the introduction of standards on total building energy approach in other energy conscientious countries, EMSD commissioned PB in 2001 to develop a Performance-Based Building Energy Code (PB-BEC) with the objective being to meet the demand of the building industry for more innovative energy-efficient building design. PB has conducted a study on the implementation of PB-BEC in Hong Kong . A Task Force consisting of 17 member organizations from professional institutions, trade organizations, academia and government bureau/departments was established to develop the PB-BEC.

Figure 1. Energy End-use Consumption in Hong Kong

Prescriptive Approach. Prescriptive requirements are straightforward and easy to follow and check. For example, the BEC for lighting stipulates the maximum allowable lighting power density (LPD), whilst the BEC for air conditioning depicts the minimum allowable chiller coefficient of performance (COP). They have their drawbacks, however, including the following:

• Their effects on building energy conservation are indirect because none of them deals with the building as a whole.
• They may have been written into the codes before current technology, products and designs that may achieve the same or even better results were in existence, making it difficult for new, innovative and possibly more cost-effective products and designs to gain wide acceptance in the marketplace.
• They are inflexible as far as innovative design is concerned.
• They make it difficult for the designer to cost-optimise building design and construction. The prescriptive criteria may “imply” a certain level of performance, but this is usually not explicitly or quantitatively stated.

Performance-Based Approach. Performance-based building codes simply state what must be achieved and are by nature very broad and versatile. The adoption of this approach opens up the possibility of new and innovative solutions to the construction process. At the same time, it provides a clear definition of the levels of health, safety, and other societal issues that a particular country has chosen to establish as a minimum standard for its own society.

To determine the format and approach of Hong Kong 's PB-BEC, we conducted a review of BECs used worldwide to serve as reference. Our findings of countries with PB-BECs were as follows:

•  U.S. and Canada . BECs of many states are based widely upon the relevant ASHRAE standard, which is currently ASHRAE 90.1. ASHRAE 90.1 stipulates a comprehensive scope of control, both prescriptive and performance-based, on the building envelope, heating, ventilation and air conditioning (HVAC), lighting and service water heating. Its energy budget method requires computer building energy simulation for the entire building. (ASHRAE 90.1 is comprehensive and served as a good reference for developing Hong Kong 's PB-BEC.)

• UK . The BEC focuses on the building envelope, hot water system and lighting.
• Australia and New Zealand . BECs focus mainly on the building envelope.
• Norway , Sweden and Netherlands . BECs focus mainly on heat loss from building envelope and boiler efficiency.

A PB-BEC is also being developed in a number of countries, as follows:

• Mainland China . The BEC is mainly prescriptive in nature; however, new codes for the southern region and commercial buildings have adopted the performance concept.
• Japan . The BEC focuses mainly on the building envelope heat loss and equipment efficiency.
• The ASEAN countries, such as Singapore , Malaysia , Thailand , Philippines and Indonesia . BECs have been developed based on the U.S. methodology, with the introduction of control over OTTV to restrict the solar gain.

Hong Kong's PB-BEC, which adopts an international approach of using total building energy budget concept, compares the energy consumption of a reference building (one complying with the existing building energy codes) with that of a design building in which the designer chose energy efficient building components and equipment options. The reference building is identical in respect of building shape, orientation, number of floors, floor area, glass area, equipment power density, occupancy, operating schedules and usage, and it is in full compliance with the prescriptive BEC requirements. Using the total building energy (TBE) approach, the PB-BEC provides an alternative channel that building designers can adapt to a variety of their proposed designs. In addition, it gives them an option to deviate from the conventional design that satisfies the prescriptive requirements.

The PB-BEC can also cover energy efficient features not included in the current BECs. Designs such as the use of natural daylight, waste heat regeneration etc. can be taken into account in the new design. In this context, the building designers will be given more freedom in adopting environmental friendly and energy efficiency facilities.

Figure 2: Simulation Output; (top) TBE Load Distribution of the Reference Building and Different Cases of the Design Building; (bottom) Profile of Monthly Energy Consumption

The principle of compliance of PB-BEC is simple and straight-forward—building designers need only to ensure that the TBE of the building being designed is not greater than the energy budget of its reference building. Whilst the design building will not be required to comply with all the prescriptive requirements of the BECs, there are certain basic requirements , as given in Annex 1, that apply to the design building as well as the reference building. These basic requirements are prerequisite to the PB-BEC, and are inherently energy effective. The fundamental principle remains that the design building must not consume more energy than does the reference building. The flow process illustrating the compliance mechanism is shown in Figure 2.

Figure 2. PB-BEC Compliance Mechanism

As the reference building basically has incorporated all energy efficient elements as stated under the prescriptive BEC requirements, it represents a model building that is energy efficient in nature. In such respect, if the building is designed in accordance with the reference building, it has complied with the PB-BEC already. In addition, apart from strictly following all requirements of the reference building, a designer will be given an opportunity to “trade-off” different aspects of a building design, provided that the energy budget will not be exceeded.

Numerical analysis is normally required to calculate the TBE, and in general, computer programmes are adopted due to the iteration processes and complexity of the calculations. These simulation programmes are similar to those used to calculate building air-conditioning cooling load, but they also take into account the lighting, general power, service hot water, renewable energy, etc. for computation of the building energy demand over a whole year. Figure 3 shows in general the simulation process and the input parameters for computing TBE.

Examples of commercially available simulation software programmes are given in Table 1. Because of the complexity of building energy simulation, not all software programmes can fully model heat transfer equations and the algorithms involved. Different software programmes are developed based on different assumptions so, as a result, the TBE values simulated from different software programmes will not be exactly consistent.

As an illustration, a 30-storey hypothetical office building covering a gross floor area of 50,000m 2 with air-cooled chillers is shown in Figure 4 . It has an OTTV of 30 W/m 2 , a window/wall ratio of 0.6, and a window shading coefficient of 0.29. The output of TBE simulation is shown in Figure 5 . The computer simulation result of its reference building indicates an energy budget of 10,650,470 kWh/year, which forms the baseline in TBE for comparison with eight cases in the building design shown in Table 1.

Figure 3. Simulation Process for Computing TBE

Figure 4 . Hypothetical Building Typical Floor Layout

Figure 5 . Simulation Output

As indicated in Table 2, the design building (Case 1) originally has a TBE of 111.49 percent when some building components and design parameters (such as higher lighting power density) have been chosen. With progressive design improvements in selecting energy-efficient air-conditioning chillers and fan-drive-motors, adding photovoltaic panels, and adopting variable air volume flow, there are accumulative energy savings and the TBE is reduced to 99.71 percent (Case 6) of the total energy budget of the reference building. Hence, the PB-BEC requirements are met. Adopting an economizer (free cooling during cool months) and using daylight control of lightings will further bring down the TBE to 98 percent (Case 8).

The PB-BEC was launched under the Hong Kong Energy Efficiency Registration Scheme for Buildings in March 2003. By following the PB-BEC, it is believed that the building designers and developers will be able to adopt a more innovative and energy efficient approach in enhancing the energy performance of buildings in the years ahead.

Building designers are given more flexibility to design a building without compromise in energy efficiency.