MECH3005 Building Services http://www.hku.hk/bse/mech3005/ Electrical Supply Load Assessment and Regulations Dr. Sam C M Hui Department of Mechanical Engineering The University of Hong Kong E-mail: cmhui@hku.hk hk Sep 2010
Basic Terms Active power (useful or real power) Time average of instantaneous power when the average is taken over a complete cycle of an A/C waveform, expressed in Watt (W) For single phase, P = V I cos ø For balanced three-phase, P = 3 V ph-ph I cos ø Apparent power For single phase, AP = V I For three phase, AP = 3 V ph-ph I
Basic Terms Connected load Sum of all the loads connected to the electrical system, usually expressed in watts Demand factor = Maximum demand / Connection load Load factor: ratio of the average demand to the maximum demand over a defined interval In commercial buildings, between the hours 9:00 to 18:00 the load factor is usually close to unity
Typical load profile for an office building Max. Average Min.
Basic Terms Power factor The ratio of the apparent power in a circuit (V.A) to the useful power (W) if the voltage and current are sinusoidal Power factor = kw/ kv.a
Load Evaluation Tenant supply energy consumed by each tenant; monitored by separate energy meter Landlord dsupply: Non-essential supply: plumbing and drainage, passenger lifts, air-conditioning plant, public lighting g Essential supply: fire protection/detection system, fireman s lifts, essential lighting, PABX system, building management system, important computer room
Load Evaluation Objectives Ensure loading demands are estimated accurately What happens if they are under-estimated? What happens if they are over-estimated? Important factors Load research data (from power company) Design margin Checking & monitoring at each design stage Obtain info from the client (e.g. by questionnaire)
Load Evaluation Preliminary stage Estimate total loading so as to: Plan the transformer (Tx) & main switch room Apply to power company for supply Based on rough info or past experience Important t to know the loads of other BSE systems Detail design stage Update the estimate w/ more accurate info Detail design e.g. protective device & circuiting
Load Evaluation Load evaluation by power company Architect/Engineer/Developer submit application For typical categories, planning engineer of power company assesses the load estimation using the database Load Assessment Programme (LAST) Compare the declared load with assessed load If declared load > assessed load, justification is needed After finalising the total load, determine the nos. of transformer and transformer bays
Assessment Guidelines General Usable floor area (UFA) Follow Building (Planning) Regulations Development information Floor area usage, public services, any special loads Standard load estimation sheet (see handouts) Public services Assessed independently Public lighting, lift, water pump, fire services, lobby air g g,, p p,, y conditioning
Minimum design load capacities for lighting gand small power requirement for various types of building Building type Minimum load capacity (W/m 2 ) Office 60 School 30 Residential building 30 Hospital 25 Hotel 25 Church 15
Assessment Guidelines After diversity maximum demand (ADMD) Load densities derived by dividing the aggregate load by the corresponding UFA or flat nos. Cover most typical cases; for special situation, designer/planning engineer may exercise his own discretion to adjust the load estimates ADMD is for planning supply Tx capacity, it may not be suitable for designing customer raising mains and lateral mains
Assessment Guidelines Load assessment data (see handouts) Residential development Commercial development Industrial development Municipal development Mixed development diversity factor (MDDF) Central air conditioning load Other special loads Reference (from CLP Power) Code of Practice 215: Load Assessment Procedure
ADMD figures for Residential Development kva A/Flat 60.0 50.0 40.0 30.0 20.0 ADMD for UFA < 50m2 ADMD for UFA 50-80 m2 ADMD for UFA > 80m2 10.0 00 0.0 1 6 11 16 21 26 31 36 41 46 51 No. of Flats What is the effect of load diversity on the kva/flat data? (Source: CLP s COP 215 Load Assessment Procedure)
Assessment Guidelines Load assessment forms For central air conditioning load For general development Example of electrical load estimation Estimation of total electrical loading Estimation of essential loads Electrical supply arrangement
Assessment Guidelines Electrical load within most commercial buildings can be arranged into the following broad categories: Lighting Small power and special user equipment HVAC equipment Lifts and escalators
Legal Framework Typical legal system in Hong Kong (statutory) Ordinance (Laws of Hong Kong) Regulations Code of Practice Supporting documents (non-statutory) Technical Guidelines Technical Notes or Technical Memoranda Circular letters Reference standards (usually from other countries) Rules (from utilities companies)
Legal Framework Electricity Ordinance & subsidiary regulations Electricity Ordinance (Cap. 406) * Electricity (Exemption) Regulations Electricity (Registration) Regulations Electricity Supply Regulations Most important Electricity (Wiring) Regulations Electricity Supply (Special Areas) Regulations Electrical l Products (Safety) Regulation Electricity Supply Lines (Protection) Regulation (* can be read from the website www.justice.gov.hk)
Legal Framework Relevant codes and guides to statutory regulations Code of Practice for the Electricity (Wring) Regulations Code of Practice for Minimum Fire Services Installations and Equipments Non-statutory regulations/standards d IEE Regulations for Electrical Installation, 15th edition and/or 16th edition * Supply Rules (from power companies) British Standards Specifications & Codes of Practice or other equivalent e national a standards ds and publications (* IEE = Institution of Electrical Engineers, now IET)
Legal Framework Electrical Contractors and Workers Registered Electrical Contractors (REC) Registered Electrical Workers (REW) Grade A Electrical Work ( 400 A) Grade B Electrical Work ( 2500 A) Grade C Electrical Work (any capacity) Grade H Electrical Work (high voltage) Grade R Electrical Work (special, e.g. neon sign) NS: neon light; WH = water heaters; AC = air-conditioners In 2006, about 8,500 REC and 68,000 REW
Legal Framework Registered Electrical Workers (REW) Permitted work: code 0 = any categories 1 = only issue design certificate 2 = only perform installation & repair works 3 = only perform repair works Example: B0 means REW grade B ( 2500 A) who can design, install and repair electrical works
Legal Framework Certification (new work, alteration or addition) Completion of an installation Certification on the design Certification on the installation Work completion certificates Form WR1 a complete installation Form WR1(A) Part of an installation (e.g. for a repair) Periodic test certificates Form WR2 a complete installation Form WR2(A) Part of an installation (e.g. for a repair)
(Available from www.emsd.gov.hk)