MECH3005 – Building
g 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:
E
mail: cmhui@hku.hk
cmhui@hku hk
Sep 2010
Basic Terms
• Active power (useful or real power)
• Time average of instantaneous power when the
average is
i taken
k over a complete
l cycle
l off an A/C
waveform, expressed in Watt (W)
• For single phase, P = V I cos ø
• For balanced three-phase,
three phase P = √3 Vph-ph I cos ø
• Apparent
pp
power
p
• For single phase, AP = V I
• For three
h phase,
h
AP = √3
√ Vph-ph I
Basic Terms
• Connected load
• Sum of all the loads connected to the electrical
system, usually
ll expressedd in
i 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
h useful
f l power (W) if the
h voltage
l
andd current
are sinusoidal
• Power factor = kW/ kV.A
Load Evaluation
• Tenant supply
pp y – energy
gy consumed by
y each
tenant; monitored by separate energy meter
• Landlord
L dl d supply:
l
• Non-essential supply:
pp y pplumbing
g and drainage,
g
passenger lifts, air-conditioning plant, public
g
g
lighting
• Essential supply: fire protection/detection system,
fireman’ss lifts, essential lighting, PABX system,
fireman
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
I
t t to
t know
k
the
th loads
l d off other
th BSE systems
t
• Detail design
g stage
g
• 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
p y assesses the load estimation usingg the
company
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
p
information
• Floor area usage, public services, any special loads
• Standard load estimation sheet (see handouts)
• Public services
• Assessed independently
• Public lighting,
g
g, lift,, water pump,
p p, fire services,, lobbyy air
conditioning
Minimum design
g load capacities
p
for lighting
g
g and small p
power
requirement for various types of building
Building type
Office
Minimum load capacity
(W/m2)
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
l d by
load
b the
h corresponding
di UFA or fl
flat nos.
yp
cases;; for special
p
situation,,
• Cover most typical
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
60.0
ADMD for UFA < 50m2
50.0
ADMD for UFA 50-80 m2
ADMD for UFA > 80m2
kVA
A/Flat
40.0
30.0
20.0
10.0
00
0.0
1
6
11
16
21
26
31
36
41
46
No. of Flats
What is the effect of load diversity on the kVA/flat data?
(Source: CLP’s COP 215 Load Assessment Procedure)
51
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
b d categories:
broad
i
•
•
•
•
Lighting
Small power and special user equipment
HVAC equipment
Lifts and escalators
Legal Framework
• Typical
yp
legal
g system
y
in Hong
g Kong
g (statutory)
(
y)
• 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
El t i l Products
Electrical
P d t (Safety)
(S f t ) Regulation
R l ti
Electricity Supply Lines (Protection) Regulation
(* can be read from the website www.justice.gov.hk)
Legal Framework
• Relevant codes and g
guides to statutoryy regulations
g
• Code of Practice for the Electricity (Wring) Regulations
• Code of Practice for Minimum Fire Services Installations
and Equipments
• Non-statutory
N
regulations/standards
l i /
d d
• IEE Regulations for Electrical Installation, 15th edition
and/or 16th edition *
• Supply
pp y Rules ((from ppower companies)
p
)
• British Standards Specifications & Codes of Practice or
other
ot
e equ
equivalent
va e t national
at o a sta
standards
da ds aand
d pub
publications
cat o s
(* 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
W k completion
l i certificates
ifi
• 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
(e g for a repair)
• Form WR2(A) – Part of an installation (e.g.
(Available from www.emsd.gov.hk)