Building Services Engineering Flashcards
Indoor Comfort Dependencies
Thermal - Thermal Environment
Acoustic - Sound Level
Visual - Luminance / glare / daylight
Indoor Air Quality - Indoor Pollution / Air Quality
Thermal Comfort Definition
That condition of mind which expresses satisfaction with the Thermal Environment
Issues caused by over/underheating
37 Overheating 34 Undercooling Heat stroke Heat Exhaustion Frostbite Hypothermia
Fangers 7 Point Thermal Scale
3 - Hot 2 - Warm 1 - Slightly Warm 0 - Neutral -1 - Slightly Cold -2 - Cool -3 - Cold
Fangers Considerations
Environmental - Air temp, Mean radiant temp, Air velocity, Relative humidity
Personal - Metabolic rate, Clothing insulation
Mean Radiant Temperature
Average effect of temp from surrounding surfaces
Operative Temperature
Meausred by combining air temperature, mean radiant temperature and air speed
Three modes of Adaption
Behavioural Adjustment Adaption - Adaptive actions when uncomfortable
Physiological adaption - Heritage / acclimatising
Psychological adaption - alter perception expectation
Adaptive Thermal Comfort Model
Linking people comfort temperature indoors with temperature outdoors in naturally ventilated buildings
Radiant Asymmetry
Ration heat gain/loss from different sides of the body
Solid / Liquid / Gaseous Pollution
Solid - Dusts / fumes / smokes
Liquid - Mists / fogs / smokes by tars in cigarette smoke
Gaseous - SO2 / CO
Indoor Pollutant Sources
Paints / Adhesives / Smoking / Moulds
Co2 respiration / skin particles / Odours
Filters
Efficiency 20-90%
Type depend on application
Check / clean / replace periodically
Illuminance
Total luminous flux incident on a surface per unit area (Lux)
Measure for brightness
Daylight
Combination of all direct and indirect sunlight during the daytime
Sick Building Syndrome
A range of symptoms attributed to spending time in a certain building
SDS Factors
Poor maintenance / management
Lack of control over environment
Poor design
Poor indoor air quality
Types of Ventilation
Natural - Least improving Comfort Ventilation
Mechanical Ventilation
Comfort Cooling
Air Conditioning
Close Control Air Conditioning - Most cost
Wind Driven
Wind entering through windows on all floors
Buoyancy / Stack Driven
Enters and heat gains from the inside makes it rise through the building
Low pressure sucks in air
Scoop Ventilation
Using the direction of the wind to channel through stack to other parts
Ducted Ventilation
Wind directed by ducts to other parts of the building rising / falling
Disadvantages of Natural Ventilation
Air Pollution Noise Overheating Poor Security Lack of control
Advantages of Ventilation
Cheap, Simple and Renewable
No / Little maintenance
Occupant controlled
Occupant Behaviour Definition
If a change occurs such as to produce discomfort, people react in ways that tend to restore their comfort
Adaptive Behaviour Examples
Fans
Shading devices
Clothing
Activity levels
Retrofit Measures
Improve air tightness
Upgrade external wall insulation
Upgrade roof insulation
Increasing window layers
Heat Losses / Gain
Ventilation
Infiltration
Conduction through building fabric
Solar / People / Equipment / 3 abve
What makes up a conventional heating system
Fuel Heat Source Heat transfer medium water/air etc + pipework Power Heat Emitters Control devices
Pump in Series vs Parallel
Series - Same flow rate
Parallel - Same pressure
Expansion tank configuration
Open Tank - Open to atmosphere
Closed Tank - Captured air
Diaphragm Tank - Membrane inserted between air / water
Single Pipe System
Two / Dual Pipe
One pipe to everything
Hot Feed + Cold Return
Heat Emitters
Radiators Convectors Underfloor Heating Radiant Heating Air Handling Units
Radiator Pro’s / Con’s
Temp Control / low maintenance
Slow thermal response / Impact floor layout
Natural Convector
Room air pulled in
Finned heating tube
Warm air out
Air Handling Unit
Air Noise attenuator Frost coil Filters Cooling coil Re-heat coil Fan Humidifier Noise attenuator Duct
Fan Coil Unit
Air Filter Cooling Coil Heating Coil Fan Conditioned air
Metals with low resistance
Copper Aluminium Platinum Gold Silver
Electric Current Effects
Heating - Heat
Magnetic - Magnetic field
Chemical - Electrolysis
Ohm’s Law
V=IR
Volts
Amps
Ohm’s
Energy Equations
Energy = Power x Time
Inductance vs Capacitance
Inductance - induction of voltages in conductors self induced by the magnetic fields of currents
Capacitance - Electrostatic storage of charge induced by voltages between conductors
Inductance Examples
Motors
Heating Coils
Lighting chokes
CHP
Combined Heat and Power
Heat engine to generate electricity and useful heat
Transformer Equation
Vprimary / Vsecondary
Isecondary / Iprimary
Used to change voltage and current
Medium Voltage Switchgear
Switch / protect cables against faults
MV distribution network or intake
Air / vacuum circuit breakers
Low Voltage Switchgear
Large intake can be split to serve smaller loads
Protective devices to protect cables and equipment
Moulded case circuit breakers
Busbars
High Power Loads
Use less space than multiple power cables
Distribution Boards
Receive feed from main switchboard
Feed out to smaller local circuits such as lighting and small power
Water Treatment Process
Coagulants added, Heavy particles stick
Heavy particles drop, removed, fertiliser
Filtered through fine materials
Disinfectants added
pH maintained by adding Alkaline substances
Alternative Supplies of Water
Wells / boreholes
Springs / streams
Reclaimed water (rainwater)
Bottled water
Grey Water
Relatively clean water from baths, sinks and washing machines etc
Toilet / Garden Use / Cleaning
Incoming water supply
Incoming water supply from utility mains
Isolation value
Water meter
Water Heater Types
Direct Gas fired Water Heater
Electric Water Heater
Solar Water Heating
Mechanical Ventilation Definition
Movement of air through a building using fan power, filtration and heating of the air
Why Ventilate
Provide fresh air ventilation
Fume control
Cool the building
Effective Ventilation
Provide Oxygen Reduce Co2 build up Control body odour Minimise effect of some smoking Minimise effect of heavy smoking
Domestic Ventilation System
Internal Grille Fan Module Fan Spacer Sealing Plate External Grille
3 Types of Mechanical Ventilation
Filtration Only
Filtration + Heating
Filtration + Heating + Cooling
Duct Sizing
Static Regain
Equal Pressure Drop
Velocity Method
Static Regain
Long lengths of high velocity
Duct gets bigger to maintain velocity after branches to increase static pressure
Equal Pressure Drop
Duct size reduces through system
3 Fan Types
Backward Curved Fan - Lower Volume Higher Pressure (high efficiency)
Forward Curved Fan - High volume system (low noise lower efficiency)
Axial Fan - High Volume Low Pressure system (Higher noise)
Duct Work Shape
Circular - Most efficient / cheap
Rectangular - Greatest flexibility in aspect ratio
Flat Oval - Most expensive
Duct Materials
Hot Dip Galvanised Steel Plastic Stainless Steel Aluminium Pre-Costed Steel
Thermal Comfort Factors
Temperature Humidity Air Velocity Clothing Direct radiation
Air Conditioning Components
Filters
Heating Coil
Cooling Coil
Humidifier / De-humidifier
Psychometric Chart
Psychrometric processes of air
dry bulb temp / wet bulb temp / humidifier / enthalpy / air density
Displacement Flow
Piston Flow - Air moved slowly, prevents pollutants being mixed
Displacement Ventilation - Air introduced low level, convection currents to high, extract high
Mixed Flow
Mixes pollutants with room air
Suitable with mobile pollution source
Uniform temp distribution
Diffuser Terminology
Throw - Distance to which jet has slowed to terminal velocity
Buoyancy Effect - Jet drop / rise
Surface Effects - Air discharged clings to ceiling Coanda Effect
Building Fabric Serves to…
Protect building from weather Provide Privacy Provide Security Regulate indoor environment Transmission of Noise
Window Properties
Reflectance - Ratio of luminous flux reflected to flux incident
Transmittance - Ratio of luminous flux transmitted to flux incident
Absorbstance - Ratio of luminous flux absorbed to flux incident
Thermal Mass
High Heat capacity
High Density
Double Skin Facade
Warm - Warm air rises and draws cooler from bottom
Winter - Draws in cold air and heats it
Double Skin Facade Adv/Dis
Acoustic Insulation / Thermal insulation / Reduce wind effect
Reduces space / Weight increase / Cost
Low-E (emissivity) Windows
Minimise the amount of UV and IR that can pass without compromising the visibility
Switchgear
Combination of disconnect switches, fuses and circuit breakers to protect and isolate electrical equipment
RMU
Cheaper than panel boards
Outdoor use
Bottom entry
LV / MV Switchrooms
Easy maintenance
Ventilation to dissipate heat
Allow space for extension
Building Service Principle
Decrease energy demand
Maintain a constant load
Improve efficiency of energy required
Ways of Affecting Form
Physical - Space planning / concealing services
Visual - Exposing services
Performance - env perf / reduce need for systems / equip
Physical space for services
Space for equipment plant room and risers
Vertical distribution
Horizontal distribution
Air plant on roof energy plant basement
Space for Equipment
All air system 3-5%
Eletrical, boilers, chillers, water 1-2% floor area
Total area 5-11%
Orientation and Massing
Position building to capture sun for heating
Reduce east and west exposure because of low sun angles
External Shading
Protect solar gain
Reduce glare
Reduces radiant temperature of glass
Controlled to allow daylight
Refrigerant
Phase change from gas to liquid to gas
Refrigeration Cycle Components
Compressor - Compresses refrigerant incr temp / pressure
Condensor - Release heat to ambient environment
Expansion Valve - Expand refrigerant to decrease pressure and temperature
Evaporator - Absorb heat from the indoor environment
Factors considered for refrigerant
Low specific volume
High latent heat
High thermal conductivity
Low viscosity
4 Refrigerant Groups
Inorganic
Organic
Zeotropes
Azeotropes
Environmental factors affecting building shape
Sun External temperature range Wind Rain Noise
System Approaches Priority Rank
Natural Ventilation
Mechanical Ventilation
Mechanical Cooling or Air Conditioning
Mechanical Ventilation Pros / Cons
Easily controlled
Greater flexibility in floor plan design
Energy Required / service costs
Mechanical Cooling Pros / Cons
Flexibility in building layout
Can offset heat gains from equipment / people etc
Control over internal environment Temp/Humidity/Air flow/Noise
Energy / service costs
Effect on building Form
Energy Use
Effect on floor Plan
Natural / Mechanical / Mech Cooling
Sig / Less Sig / Least Sig
Low / Medium / High
High / Minimum / Minimum
FCU’s
Fan Coil Unit
Air cooled in the space by fan coil in ceiling
Air recirculated and mixed
Define Voltage
Voltage is a measure of a systems ability to do work moving charge (-ve electrons) around an electrical circuit. (A house has 230V in outlets).
Resistance Depends Upon
The material type
Cross-sectional area
Length
Temperature
Most effective way of converting thermal energy into heat Electricity
Turbine Driven Alternator that turns coils producing alternating current. Direct current are batteries created through a chemical reaction
Drax Power Station
Generators fitted with FGD (Flue Gas Desulphurisation)
Removes 90% of the sulphur dioxide from emissions
Direct injection allow biomass injected directly into boiler.
IEE Wiring Regulations (BS7671)
Tells you how to size cables
Current carrying capacity
Fault conditions
Voltage drops
Transformers
Used to charge voltage and therefore current
Transmit at high voltage to avoid heat loss
Air Conditioner How it works
Liquid is sent through coils and evaporates
This makes the coils very cold
Air is passed over these coils to cool your house
Gas goes through a compressor to a turn back to liquid
Why use ductwork
Delivery to and from spaces
Required air volume known
Central plant to rooms
Reduces leakage and space requirement
Factors influencing duct design
Duct Size
Effect of velocity
Setting Duct Size
Small is cheaper
Friction in duct work increases power
Power = Pressure x Flow Rate
Duct Extractions
Kitchen / Dust / Chemical
Static Regain Adv/Dis
A size for all ductwork
Self balancing system
Energy Efficient
Not applicable to extract systems
EPD Adv/Dis
Quick and easy
Gives reductions at branches
Commercial building with complex routes
Use more energy than static regain
Velocity Adv/Dis
Avoids noise issue
Simple Sizing approach
Widely used
MRT Equation
A1 T1 + A2 T2 + A3 T3 / A1 +A2 + A3
Heating Correction Factor Equation
Flow Temp + Return Temp / 2 - indoor temp
Power Equation
P=IV
Fan Power Equation
Pressure x flow rate
Enthalpy Equation
Internal energy of system + (pressure x volume of system)
Duct Size Equation
Volume flow rate = velocity x cross sectional area
Heating Equation
Fabric + Ventilation + Infiltration - solar - internal
Losses 3 Gain 2
