Fundamentals on HVAC systems and District

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 1

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i. ii. iii.

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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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

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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

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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

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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

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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:   

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. 

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    

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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2.0 

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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 ) 32

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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) 

Water supply to development

Local Authority 

Building Permit

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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

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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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