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 1
Transcript
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 JayasuriyaMSc. (Eng.), C Eng., MCIBSE, MIET, MASHRAETechnical DirectorEmirates District Cooling L.L.C
2
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:
i. Evaporationii. Radiationiii. Convection
Thermal Comfort
3
The environmental factors that influence the modes of heat transfer and hence, thermal comfort are:
i. Dry bulb temperatureii. Relative humidityiii. Air movement rateiv. Mean radiant temperature
Two other ‘personal’ factors are also influential, namely:
v. Activity levelvi. Clothing
Factors affecting Thermal Comfort
4
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
Typical Metabolic Rates of Human Beings
5
Air Velocity (m/s)
0.1 0.2 0.25 0.3 0.35
Dry bulb Temp. °C
25 26.8 26.9 27.1 27.2
Air Velocity and Comfort
6
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.
Design Criteria - (summer indoor conditions)
7
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.
Load Assessment
8
i. Solar gain through glazing ii. Transmission gains arising because of temperature differences
between the room and the outdoor air temperature.iii. Transmission gains due to outside surface temperature rise with
the impact of solar radiation.iv. Infiltration of warm humid airv. Room occupantsvi. Electric lightingvii. Electrical equipment such as computing equipment and
photocopied.
Sensible and Latent Heat Gains
9
ConductionHeat Transfer by molecular motion in a material in direct contact
Convection Contact Between fluid in motion and a solid
RadiationNo 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
Heat Transfer Mechanisms Fundamentals
10
Fundamentals on Conduction
11
Heat Gain Through Conduction
12
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 airQv = q m Cp (t ao - t ai ) WattsVolume 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 ------------- 2Where N = number of air changes , V = Room Volume in m3
Heat Gain due to Ventilation
13
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
Solar Radiation
14
Impact of Solar Radiation on a Building
15
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 )
Impact of Solar Radiation on a Building
16
Analytical Study of Heat Gains - A Typical House in Sri Lanka with Brick Walls and 30% Glass and Asbestos Roof with Wooden Ceiling
Conductive(55 W/ SQ.Mt.)
43%
Convective( 40 W/SQ.Mt.)
34%
Radiation (20 W/SQ.Mt.)
18%
Occupancy + Electrical
(5W/SQ.Mt )5%
HEAT LOAD IN A BUILDING (Total Load 120 W/SQ.Mt. )
17
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.
Annual Building Cooling Energy Assesment
18
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:
Degree days or degree hours of cooling needs per annum
Year: 2010 Month January February March April May June July August September October November December Annual Total
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 Systems
24
Air – Water systems:
Fan coil systems Induction unit systems Chilled beam and displacement ventilation systems.
Air Conditioning Systems
25
Typical Air Conditioning Equipment Range
26
Typical Air Conditioning Equipment Range
27
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).
Principles of District Cooling
28
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
WHY DISTRICT COOLING?
29
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 efficientlyIt maximizes efficiency and minimizes wastage.
ADVANTAGES OF DISTRICT COOLING SYSTEM PLANT TO THE CLIENT, DEVELOPER & CUSTOMERS
30
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 STUDY
31
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 STUDY
32
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 STUDY
33
Business Plan- Business Growth- Market analysis- Sensitivity analysis- Critical issues & strategic analysis
- Risk analysis, risk management, and risk mitigation
- Major challenges
FEASIBILITY STUDY
34
Economics: comparison with alternative
Capital costs (Capex)
Impact on cost Redundancy
Thermal Storage
Capital Cost per ton
Distribution System
Connection
Overall
Energy Usage
Water Consumption
Overall
Diversity Factor
Opex costs Maintenance
35
Economic characteristics of district cooling
Capex
Opex
Capital Intensive
Attractive to
Strong Predictable Cash Flows
Typical Returns
Attractive to
Project IRR
Equity IRR
10 – 15 %
15 – 20 %
Lenders
Investors
Debt
Equity
36
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 Study
37
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
Feasibility Study
38
A. Mechanical
1. Centrifugal Chillers2. Condenser water Pumps3. Chilled Water Primary Pumps4. Chilled Water Secondary Pumps5. Cooling Towers6. Make up water pumps for Cooling Towers7. Chemical Dosing system for Cooling Towers8. Chemical Dosing system for chilled water network9. R.O Plant for blow down water re-claim10. Water Storage Tank for Cooling Towers / Fire Pumps11. Blow Down Storage Tank12. Thermal Storage Tanks
District Cooling Plant Equipment
39
B. Electrical
1. 11 kV Switchgear (3.3 kV if applicable)2. 11kV Capacitor banks3. 11 kV / 400 Ton Transformers (11 kV / 3.3 kV Transformers if
applicable)4. H.V Cables and containment systems5. UPS / Battery Charger for 11 kV vacuum circuit breakers6. L.V Switchgear7. Motor control centres8. L.V capacitor banks
District Cooling Plant Equipment
40
C. Control Systems
1. Building Management System (BMS) or CMS (Plant Control Management System).
2. PLC System for data control3. System Data server4. Operator work stations5. Energy work station
District Cooling Plant Equipment
41
Types of BTU Meters:A. Electromechanical metersB. Magnetic metersC. Ultrasonic meters
Communication modes for data collection:1. Data bus cables2. Fiber Optic Cable3. Radio Receiver / GSM
Billing and Metering System
42
System Components:A. Electromechanical Metersi. Concentrator (Collect readings from meters)ii. Data converter portiii. M-Busiv. Fiber Optic Cablev. GSM unitvi. Server (collects readings from GSM)B. Wireless Metersvii. Concentratorviii. Radio receiver (collect data from a group of building)ix. GSMx. Serverxi. Work Stationxii. ERP System for billing (Enterprise resource planning system)
