Fundamentals on HVAC systems and District

Report
Objectives:
The attendees may be able to gain a better understanding of fundamental of human
thermal comfort, Thermal heat gains in buildings, Climate and design conditions, Heat
gains from solar and other sources, ventilation principles, fan coil units, Air handlers,
BMS, Refrigeration Plants and applications, benefits of District cooling and DCS system
details.
Speaker:
Fabian Jayasuriya
MSc. (Eng.), C Eng., MCIBSE, MIET, MASHRAE
Technical Director
Emirates District Cooling L.L.C
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The body core temperature associated with a healthy human body is
37°C (98.6 °F) and in order to remain comfortable the body attempts
to maintain thermal equilibrium with the surroundings.
Thermal balance between the body and it’s surroundings occurs by
means of:
Evaporation
Radiation
Convection
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iv.
The environmental factors that influence the modes of heat transfer
and hence, thermal comfort are:
Dry bulb temperature
Relative humidity
Air movement rate
Mean radiant temperature
Two other ‘personal’ factors are also influential, namely:
i.
ii.
Activity level
Clothing
3
Degree of
Activity
Total Rate of
Heat Emission
for Adult Male
(Watt)
Average Value
of Male &
Female (Watt)
Sensible (Watt)
Latent (Watt)
Seated
115
95
65
30
Walking
160
130
75
55
Dancing
265
230
90
160
Sedentary Work
160
130
75
55
4
Air Velocity
(m/s)
0.1
0.2
0.25
0.3
0.35
Dry bulb
Temp. °C
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26.8
26.9
27.1
27.2
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It is essential that the buildings be adjusted to serve people. It
should not be the people who are required to be adopt to the
buildings.
Summer design temperature of 22°C - 24°C is a suitable choice for
long term sedentary occupancy in the U.A.E with humidity allowed
to swing between 50% -60% having air movement of 0.1 m/sec.
Benchmark optimum energy usage in summer satisfying thermal
comfort criteria with room temperature of 24°C at 55% humidity.
Higher energy penalty in lowering of room temperature from the
benchmark level. Example, room temperature thermostat set at
23°C will increase 9% more energy consumption. At 22°C, 18%
energy penalty.
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Load assessment is carried out as part of the design and selection of
comfort air conditioning systems and equipment. It is directly
related to the assessment of sensible and latent heat gains and
losses that occur within the condition space.
When sensible heat gains occur within a space their effect is to
increase room air temperature.
Whereas latent gains increase the moisture content of room air.
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i.
ii.
iii.
iv.
v.
vi.
vii.
Solar gain through glazing
Transmission gains arising because of temperature differences
between the room and the outdoor air temperature.
Transmission gains due to outside surface temperature rise with
the impact of solar radiation.
Infiltration of warm humid air
Room occupants
Electric lighting
Electrical equipment such as computing equipment and
photocopied.
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Conduction
Heat Transfer by molecular motion in a material in direct contact
Convection
Contact Between fluid in motion and a solid
Radiation
No contact required. Heat transfer by electromagnetic waves
Units & Measurements
Thermal conductivity (k or λ) = W/m/0K
Thermal Resistance (R) = d/ k in m2 0K/W ( d = Thickness )
Heat Transfer coefficient or Thermal Transmittance (U )
U = 1/R Watts / m2/ 0K
Steady state Heat Transfer Equation (One dimensional Heat flow ) Q =U A
∆T Watts
A = Area in m2 , ∆T = Temperature difference in 0K
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Ventilation Heat Gain Calculation
Heat gain due to ventilation (Qv ) = q
q m = mass flow rate ( kg/sec.)
h ao = Enthalpy of outdoor air
h ai = Enthalpy of indoor air
m
(h
ao
- h ai) Watts
Simplified equation without considering moisture in air
Qv = q m Cp (t ao - t ai ) Watts
Volume flow rate in Litres /Sec. ( q v )
Qv = 1.2 q v (t ao - t ai ) ------------1
Simplified Heat flow equation with number of air changes
Qv = NV/3 Watts
------------2
Where N = number of air changes , V = Room Volume in m3
12

The Sun radiates energy as a black body having a surface
temperature of 6000 0 C over a spectrum of wave length 300 – 470
nm in ultra violet region.
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9%
- ultra violet region
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91% - 380 to 780 visible and infrared region
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Solar constant : 1416 watt/m2
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What reaches the earth is 1025 watt/m2 at no clouds

Direct solar radiation - 945 watt/m2
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Heat enters a building through direct and scattered radiation
maximum
Boltzman Equation for radiant heat:
Q = σ A T4 watts
Where σ = 5.663 x 10 - 8 J//m2s K4
A = area in m2 ,T = temperature in 0K
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The impact of solar radiation varies upon the building location and
orientation
Building walls:
Colour of the surface
Surface roughness
Building material
Sunlit area
Building Roof
Slope of the roof
Roof material
Colour of the roof
Surface reflectance
Building Windows :
Sunlit area
Glass type , thickness and colour
Reflectance factor
Shading coefficient ( a property of glass )
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Radiation
(20 W/SQ.Mt.)
18%
Occupancy +
Electrical
(5W/SQ.Mt )
5%
Conductive
(55 W/ SQ.Mt.)
43%
Convective
( 40 W/SQ.Mt.)
34%
HEAT LOAD IN A BUILDING
(Total Load 120 W/SQ.Mt. )
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Degree hours or Degree days concept provides a measure to assess
cooling energy demand hours based on the temperature difference
between inside and outside of a building as related to period of time
under consideration.
Example:
i.
At external outdoor temperature 28°C and indoor temperature
setting at 24°C in a particular hour cooling demand is considered
as 4 degree hours.
ii. As the outdoor temperature changes hourly, If the total degree
hours within a 24 hours period is added up to a value of 60
degree hours, then the average cooling demand is considered as
2.5 degree days.
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As base temperature of 24°C calculated degree hours for the year 2010 &
2009 in Dubai is indicated below.
It was reported that the year 2010 matches for world hottest year (see Gulf
News article on 21st January 2011). The attached degree hour calculation
sheet indicate the influence of temperature variation for space cooling.
Based on calculations summary of degree hours for each month is as follows:
Year: 2010
Month
Total Degree
hours
January
February
March
April
May
June
July
August
September
October
November
December
Annual Total
110
680.0
1687.6
3659.1
6339.9
8422.9
9934.5
9615.9
7446.8
5437.9
2171.8
469.5
55975.9
Year: 2009
Month
Total Degree
hours
January
February
March
April
May
June
July
August
September
October
November
December
Annual Total
27.3
696.2
1433.3
2979.2
6735.5
7544.3
8283.4
8873.8
6936.9
4871.6
2065.2
265.6
50712.3
The number of Degree hours excess in year 2010 compared with 2009 is 5,263.6
Percentage increase: 10.4%
Summer months (April - November increase) 9.8%
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The need for ventilation :
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Fresh air required for breathing
(0.2 litres/sec.) directly proportional to metabolic rate
Dilution of the orders present to a socially acceptable level (7.5
litres/sec. )
Minimize the rise in air temperature in the presence of excessive
sensible heat gains
Dealing with high humidity or condensation
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Natural Ventilation is the air flow through a building resulting from
the provision of specified routes such as:
•
•
•
•
•
Operable windows
Doors
Shafts
Ducts
Towers
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Avoid noise and traffic fumes from busy roads
Consider Security
Consider Insects
Draw cooler air from a shaded side of a building to maximise the
cooling
Cross ventilation
Buoyancy driven ventilation
Atrium ventilation
Chimney ventilation
Wind tower ventilation
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Air conditioning systems can be simply classified as follows:
 Unitary system
 All air systems
 Air water systems
Unitary systems
 Self contained room air conditioners
 Split systems
 Water loop air conditioning heat pumps
All Air systems
 Constant volume single ducted systems
 Dual duct system (for heating & cooling)
 Multizone system
 Variable air volume system.
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Air – Water systems:
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Fan coil systems
Induction unit systems
Chilled beam and displacement ventilation systems.
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District Cooling is a system in which chilled water is distributed in
pipes from a central cooling plant to buildings for space cooling and
process cooling.
It contain three major elements: the cooling source, distribution
system and customer installations.
Cooling sources: Vapor, compression chillers, absorption chillers.
Distribution system:
Chilled water pumps and buried piping
network
Customer installation: Tie-in connection Energy Transfer Station
(ETS) ie. Heat Exchanger connected with secondary pumps for
distribution of chilled water to fan coil units & AHU’s.
Conventional chilled water supply temperature: Between 4°C - 5°C
(in the U.A.E).
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Reduction of electricity peak demand
Reduce over all power generation and infrastructure electricity
distribution cost including operational cost over years.
Cost savings on develop electricity infrastructure.
Designed to meet the needs of customers
Lower tariffs
Lower capital investment to client, developer
No operation & maintenance cost to client, developer and
customers
Overall aesthetic appearance
Space saving to client, develop
Reliable supply
Provision of various useful energy i.e cooling
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Other advantages are as follows: Environment-friendly
The plant design and equipment selection utilize an innovative
technology with minimal impact on the environment.
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Lower carbon foot print
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Promotes healthier living
The system helps to create a working environment that is safer and
healthier for people.
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Uses energy more efficiently
It maximizes efficiency and minimizes wastage.
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1.0
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TECHNICAL:
Understanding the technology and different approaches
DC with all electric chillers or mixed
DC with chilled water TES or DC with Ice TES
Heat rejection based on
- Fresh water
- Sea water
- polished Treated Sewage Effluent (TSE)
- Desalinated water
- Direct TES water with chemical treatment
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Understanding the Project:
- Plot areas
- Land use & building classification
- Population & growth
- Development phasing
- Building codes & permits
- Environmental regulations
- Cooling demand estimates – sq. mts per ton
- Utility plots & areas
- Piping network corridors
- Access to nearest Power, Water & Sewage source
- Geological site investigations & site instructions
- Other utilities inter-phasing etc.
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FINANCIAL
Understanding the different Business Models
- Design, Bid, Build
- Joint venture / SPV (special purpose vehicle )
- Build Own Operate (BOT)
- Build Own Operate Transfer (BOOT)
- Engineer, Procure, Construct (EPC)
-O&M
Project costs & Financial analysis including budgeting:
- CAPEX costs
- OPEX costs
- Tariff structures
- Revenues streams, cash flows & expenditures
- Profit & loss
- ROI (rate of investment return )
- IRR ( internal rate of return )
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Business Plan
- Business Growth
- Market analysis
- Sensitivity analysis
- Critical issues & strategic analysis
- Strengths, weakness, opportunities, threats (SWOT)
- Risk analysis, risk management, and risk mitigation
- Major challenges
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Impact on cost
 Redundancy
 Diversity Factor
Capital costs
(Capex)
 Thermal Storage
 Capital Cost per ton
 Distribution System
 Connection
Overall
 Energy Usage
Opex costs
 Water Consumption
 Maintenance
Overall
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Capex
Opex
Strong Predictable
Cash Flows
Typical Returns
Capital
Intensive
Attractive to
Attractive to
Equity
Debt
Investors
Lenders
Project IRR
10 – 15 %
Equity IRR
15 – 20 %
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Time Assessment
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Availability of Bulk Electrical Power Supply to the development and
the time constrains to build H.V Power substations / Local Authority
Power Supply.
Infrastructure piping network construction.
TES (Treated effluent sewage)
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Water supply to development
Local Authority
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Building Permit
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Risk Assessment
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Lower than projected load
Lower energy sales / revenue generation
Reduced building occupancies
Timely permits from Utility companies for Power and Water
Weather variations
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A. Mechanical
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Centrifugal Chillers
Condenser water Pumps
Chilled Water Primary Pumps
Chilled Water Secondary Pumps
Cooling Towers
Make up water pumps for Cooling Towers
Chemical Dosing system for Cooling Towers
Chemical Dosing system for chilled water network
R.O Plant for blow down water re-claim
Water Storage Tank for Cooling Towers / Fire Pumps
Blow Down Storage Tank
Thermal Storage Tanks
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B. Electrical
1.
2.
3.
4.
5.
6.
7.
8.
11 kV Switchgear (3.3 kV if applicable)
11kV Capacitor banks
11 kV / 400 Ton Transformers (11 kV / 3.3 kV Transformers if
applicable)
H.V Cables and containment systems
UPS / Battery Charger for 11 kV vacuum circuit breakers
L.V Switchgear
Motor control centres
L.V capacitor banks
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C. Control Systems
1.
2.
3.
4.
5.
Building Management System (BMS) or CMS (Plant Control
Management System).
PLC System for data control
System Data server
Operator work stations
Energy work station
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Types of BTU Meters:
A. Electromechanical meters
B. Magnetic meters
C. Ultrasonic meters
Communication modes for data collection:
1. Data bus cables
2. Fiber Optic Cable
3. Radio Receiver / GSM
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System Components:
A. Electromechanical Meters
i.
Concentrator (Collect readings from meters)
ii.
Data converter port
iii. M-Bus
iv. Fiber Optic Cable
v.
GSM unit
vi. Server (collects readings from GSM)
B. Wireless Meters
i.
Concentrator
ii.
Radio receiver (collect data from a group of building)
iii. GSM
iv. Server
v.
Work Station
vi. ERP System for billing (Enterprise resource planning system)
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Typical District Cooling Plant Building
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Cooling Tower
Cooling Tower Fan & Motor
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Typical Thermal Storage Tank
Thermal Storage Tank
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Air Cooled Chiller
Water Cooled Chiller Module
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Fan Coil Unit
AHU Unit
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Motor Control Center
11kV Switchgear
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Control System
SCADA System Projector Screen
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