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Fundamentals of HVAC systems and District Cooling

Fundamentals of HVAC systems and District Cooling. Objectives:

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Fundamentals of HVAC systems and District Cooling

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  1. 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

  2. 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

  3. 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

  4. Typical Metabolic Rates of Human Beings

  5. Air Velocity and Comfort

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Fundamentals on Conduction

  11. Heat Gain Through Conduction

  12. 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

  13. 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

  14. Impact of Solar Radiation on a Building

  15. 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 )

  16. Analytical Study of Heat Gains - A Typical House in Sri Lanka with Brick Walls and 30% Glass and Asbestos Roof with Wooden Ceiling

  17. 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.

  18. 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:

  19. 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

  20. 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

  21. 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

  22. Wind Tower – Technique

  23. 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.

  24. Air Conditioning Systems Air – Water systems: • Fan coil systems • Induction unit systems • Chilled beam and displacement ventilation systems.

  25. Typical Air Conditioning Equipment Range

  26. Typical Air Conditioning Equipment Range

  27. 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).

  28. 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

  29. 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.

  30. 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

  31. 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.

  32. 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 )

  33. 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

  34. 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

  35. 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 %

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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

  42. 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)

  43. Typical Connection Diagram

  44. Metering Systems Communication Architecture

  45. Typical District Cooling Plant Building

  46. Cooling Tower Cooling Tower Fan & Motor

  47. Typical Thermal Storage Tank Thermal Storage Tank

  48. Air Cooled Chiller Water Cooled Chiller Module

  49. Fan Coil Unit AHU Unit

  50. Motor Control Center 11kV Switchgear

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