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fundamentals of hvac systems and district cooling

Fundamentals of HVAC systems and District Cooling

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

thermal comfort
Thermal Comfort
  • 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
factors affecting thermal comfort
Factors affecting Thermal Comfort
  • 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:

  • Activity level
  • Clothing
design criteria summer indoor conditions
Design Criteria - (summer indoor conditions)
  • 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.
load assessment
Load Assessment
  • 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.
sensible and latent heat gains
Sensible and Latent Heat Gains
  • 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.
heat transfer mechanisms fundamentals
Heat Transfer Mechanisms Fundamentals
  • 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 m20K/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

heat gain due to ventilation
Heat Gain due to Ventilation

Ventilation Heat Gain Calculation

Heat gain due to ventilation (Qv ) = q m (h ao - h ai) Watts

q m = mass flow rate ( kg/sec.)

h ao = Enthalpy of outdoor air

h ai = Enthalpy of indoor air

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

solar radiation
Solar Radiation
  • 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.

  • 9% - ultra violet region
  • 91% - 380 to 780 visible and infrared region
  • Solar constant : 1416 watt/m2 maximum
  • What reaches the earth is 1025 watt/m2 at no clouds
  • Direct solar radiation - 945 watt/m2
  • Heat enters a building through direct and scattered radiation

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

impact of solar radiation on a building15
Impact of Solar Radiation on a Building
  • 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 )
slide16
Analytical Study of Heat Gains - A Typical House in Sri Lanka with Brick Walls and 30% Glass and Asbestos Roof with Wooden Ceiling
annual building cooling energy assesment
Annual Building Cooling Energy Assesment
  • 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:

    • 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.
    • 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.
degree days or degree hours of cooling needs per annum
Degree days or degree hours of cooling needs per annum
  • 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:

ventilation in buildings
Ventilation in Buildings

The need for ventilation :

  • 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
natural ventilation
Natural Ventilation
  • Natural Ventilation is the air flow through a building resulting from the provision of specified routes such as:
        • Operable windows
        • Doors
        • Shafts
        • Ducts
        • Towers
natural ventilation strategies
Natural Ventilation Strategies
  • 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
air conditioning systems
Air Conditioning Systems

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.
air conditioning systems24
Air Conditioning Systems

Air – Water systems:

  • Fan coil systems
  • Induction unit systems
  • Chilled beam and displacement ventilation systems.
principles of district cooling
Principles of District Cooling
  • 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).
why district cooling
WHY DISTRICT COOLING?
  • 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
advantages of district cooling system plant to the client developer customers
ADVANTAGES OF DISTRICT COOLING SYSTEM PLANT TO THE CLIENT, DEVELOPER & CUSTOMERS

Other advantages are as follows:-

  • Environment-friendly

The plant design and equipment selection utilize an innovative technology with minimal impact on the environment.

  • Lower carbon foot print
  • Promotes healthier living

The system helps to create a working environment that is safer and healthier for people.

  • Uses energy more efficiently

It maximizes efficiency and minimizes wastage.

feasibility study
FEASIBILITY STUDY

1.0 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

feasibility study31
FEASIBILITY STUDY
  • 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.

feasibility study32
FEASIBILITY STUDY

2.0 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 )

feasibility study33
FEASIBILITY STUDY
  • 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

economics comparison with alternative
Economics: comparison with alternative

Impact on cost

Capital costs (Capex)

  • Redundancy
  • Diversity Factor
  • Thermal Storage
  • Capital Cost per ton
  • Distribution System
  • Connection

Overall

Opex costs

  • Energy Usage
  • Water Consumption
  • Maintenance

Overall

economic characteristics of district cooling
Economic characteristics of district cooling

Capex

Equity

Capital Intensive

Opex

Debt

Strong Predictable Cash Flows

Investors

Attractive to

Lenders

Attractive to

Typical Returns

Project IRR

10 – 15 %

Equity IRR

15 – 20 %

feasibility study36
Feasibility Study

Time Assessment

  • 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)

  • Water supply to development

Local Authority

  • Building Permit
feasibility study37
Feasibility Study

Risk Assessment

  • Lower than projected load
  • Lower energy sales / revenue generation
  • Reduced building occupancies
  • Timely permits from Utility companies for Power and Water
  • Weather variations
district cooling plant equipment
District Cooling Plant Equipment

A. Mechanical

  • 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
district cooling plant equipment39
District Cooling Plant Equipment

B. Electrical

  • 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
district cooling plant equipment40
District Cooling Plant Equipment

C. Control Systems

  • Building Management System (BMS) or CMS (Plant Control Management System).
  • PLC System for data control
  • System Data server
  • Operator work stations
  • Energy work station
billing and metering system
Billing and Metering System

Types of BTU Meters:

  • Electromechanical meters
  • Magnetic meters
  • Ultrasonic meters

Communication modes for data collection:

  • Data bus cables
  • Fiber Optic Cable
  • Radio Receiver / GSM
btu metering system
BTU Metering System

System Components:

A. Electromechanical Meters

  • Concentrator (Collect readings from meters)
  • Data converter port
  • M-Bus
  • Fiber Optic Cable
  • GSM unit
  • Server (collects readings from GSM)

B. Wireless Meters

  • Concentrator
  • Radio receiver (collect data from a group of building)
  • GSM
  • Server
  • Work Station
  • ERP System for billing (Enterprise resource planning system)
slide46
Cooling Tower

Cooling Tower Fan & Motor

slide47
Typical Thermal Storage Tank

Thermal Storage Tank

slide48
Air Cooled Chiller

Water Cooled Chiller Module

slide50
Motor Control Center

11kV Switchgear

c control systems
C. CONTROL SYSTEMS

Control System

SCADA System Projector Screen