Passive Technologies and Other Demand-Side Measures.
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Transcript of Passive Technologies and Other Demand-Side Measures.
![Page 1: Passive Technologies and Other Demand-Side Measures.](https://reader035.fdocuments.net/reader035/viewer/2022062407/56649d9e5503460f94a8925f/html5/thumbnails/1.jpg)
Passive Technologies and Other Passive Technologies and Other Demand-Side MeasuresDemand-Side Measures
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Overview
• energy consumption in buildings• passive demand reduction examples
– insulation– thermal mass – natural ventilation– nat. vent alternatives
• demand management and “demand-shifting”
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• space heating• hot water• electricity
– lighting
– appliances
– cooling
– … also for space heating and hot water
Energy Required (Revisited)
demand in a typical commercial building
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• “Typical” average energy consumptions for dwellings:
Energy Required (Revisited)
• Source: Domestic Energy Fact File
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• “Typical” average energy consumptions for offices:
Energy Required (Revisited)
• Source: ECGO 19
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Illustration: Domestic Sector
• Using a simple housing stock model the C emissions for the domestic sector are calculated for the current electricity supply mix and post 2020 mix (0% nuclear, 40% RE, 60% fossil fuel) for the following scenarios:
– continuing current trends (increasing heat and electricity demand)– 30% reduction in heat demand– 30% reduction in heat and electricity demand
• The desired reduction for carbon from the domestic sector is also shown
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Illustration: Domestic SectorCarbon Emissions MtC
0
0.5
1
1.5
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2.5
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3.5
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Mil
lio
n T
on
nes
Car
bo
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domestic emissionsonly
emissions includingelectrical relatedemissions
current 2020
supply: 0% nuclear40% RE60% fossil
demand:static
target
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Carbon Emissions MtC
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0.5
1
1.5
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2.5
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3.5
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4.5
Mil
lio
n T
on
nes
Car
bo
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domestic emissionsonly
emissions includingelectrical relatedemissions
current 2020
supply: 0% nuclear40% RE60% fossil
demand:heat demand reduced by 30%
Illustration: Domestic Sector
target
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Carbon Emissions MtC
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Mil
lio
n T
on
nes
Car
bo
n
domestic emissionsonly
emissions includingelectrical relatedemissions
current 2020
supply: 0% nuclear40% RE60% fossil
demand:heat and electrical demand reduced by 30%
Illustration: Domestic Sector
target
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Example: Domestic Sector
• Only through reducing domestic heat and power demand do we achieve any carbon savings
• Even with 40% renewables but with increasing demand carbon emissions are still greater in 2020!
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Energy Required Revisited
• fortunately given the poor energy performance of most buildings in the UK the scope for energy savings is huge
• in this lecture we will cover passive (design-driven) energy saving measures
• … and aspects of load management
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Passive Measures
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Fabric ImprovementsFabric Improvements
• improving the building fabric reduces the thermal exchanges to/from the environment e.g.:
– heat loss from inside to outside
– heat gain from outside to inside
• this can be achieved in a number of ways
– adding/improving wall insulation
– replacing old glazing systems (also reduced unwanted infiltration)
• improving air tightness (+ MV with heat exchange)
• potential for 80%* reductions in heating-related energy loads
* Olivier D, 2001, Building in Ignorance: Demolishing Complacency - Improving the Energy Performance of 21st Century Homes, report published by the Association for the Conservation of Energy.
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Fabric Improvements
• Source: EC
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Fabric ImprovementsFabric Improvements
• however there are potential pitfalls:
– increased risk of overheating (high internal loads)
– reduced air quality (reduced infiltration)
• overall fabric improvements are one of the most cost-effective ways to reduce energy consumption and carbon emissions – particularly in older buildings/retrofit projects
• Source: EST
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Fabric ImprovementsFabric Improvements
1
10
100
1000
Insulation PV
Savings ratio £/tonne (over 30-year life)
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Thermal MassThermal Mass
• the use of exposed thermal mass is typically employed in buildings (or spaces) likely to experience overheating:
– sunspaces
– areas of high occupancy
– areas with high equipment loads
• thermal mass acts like a sponge – absorbing surplus heat during the day and releasing the heat during the evening
• however to work effectively the release of heat in the evenings needs to be encouraged through flushing of the air inside the building
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Thermal MassThermal Mass
insulation
exposed mass
daytime: Te > Tm
insulation
exposed mass
evening: Te < Tm
ventilation air
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Thermal MassThermal Mass
Thermal Mass Temps.
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hours
Tem
per
atu
re (
C)
Ambient
Air Temp
Mass Temp
start of night flushend of night flushheat release from mass
heat gain by mass
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Thermal MassThermal Mass
• useful in preventing overheating however:
– slow response to plant input
– more difficult to accurately control internal conditions (plant pre-heat required)
– risk of under-heating on colder mornings
– surface condensation risk
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Thermal MassThermal Mass
• thermally massive buildings are highly dynamic thermal systems
• typically rely on thermal modelling to gauge the effects on performance
• … particularly when also dealing with night flush, etc.
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Thermal MassThermal Mass
• testing thermal mass + night flush strategy with ESP-r
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Natural VentilationNatural Ventilation
• ventilation type in most smaller UK buildings
• driven by wind pressure and density variations
– single sided ventilation (density driven)
– stack ventilation (density driven)
– cross flow ventilation (wind driven)
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Natural VentilationNatural Ventilation
• driving force will usually be a combination of wind + density (buoyancy) forces
• influenced by:
– wind direction
– wind speed
– ventilation opening location
– interior/exterior temp. difference
– internal gains
– building geometry
• results in highly variable flow (magnitude and direction)
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Natural VentilationNatural Ventilation
the drawing …
the reality!
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Natural VentilationNatural Ventilation
• given the range of driving forces and general complexity of natural ventilation (strongly coupled with temperatures) computer modelling is often used to assess natural ventilation schemes
• gives an indication of the variability of flow and the influence on internal temperatures, comfort and air quality
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Nat. Vent AlternativesNat. Vent Alternatives
• if more control is required over the air flow in a building an alternative is to employ mechanical ventilation with heat recovery (MVHR)
• the warm exhaust air is passed through a heat exchanger to pre-heat incoming ventilation air, reducing the overall building heating load
• air flow rate is controlled by a fan – more controllable than nat. ventilation but fan consumes electricity
• In both nat. vent. and MVHR building must be tightly sealed to minimise unwanted infiltration
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Nat. Vent AlternativesNat. Vent Alternatives
• another alternative to natural ventilation is so-called “dynamic insulation”
• ventilation is drawn through porous insulation in the external wall cavity
• recovers heat that would otherwise be conducted through the wall to the environment
• interior of the building must be slightly de-pressurised in relation to the outside
• can significantly reduce the “U-value of the wall”
de –pressurised interior
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Demand Shifting• demand shifting is not the same as
demand reduction – bit both have a role to play in the low-energy buildings of the future
• both can be considered as elements of “demand management”
• with demand shifting we move appropriate loads in time for an environmental and/or an economic benefit
• this is related to time-varying cost and carbon content of electricity
• shifting can also be used to maximise the benefit of local low carbon technologies
load (GW)
cost £
CO2
g/kWh
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Demand Shifting
Electricity Buy/Sell Price 10/09/08
0
20
40
60
80
100
120
0 12 24 36 48
1/2 hr period
£/M
Wh
System Sell Price
System Buy Price
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Demand Shifting• different power
generation “mixes” means different electricity carbon intensity during the day
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Demand Shifting• with demand shifting we make use of “opportune” loads to move peak
demand out of peak cost or peak CO2 intensity periods
• note this does not reduce demand – only changes the demand profile
CO
2 g
or £
/kW
h
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Demand Shifting• opportune loads are loads that can be moved in time without
inconveniencing the user or causing adverse effects
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Demand Shifting• finally we can also use demand shifting to better match local loads to local
energy supplies
• e.g. with a PV system moving loads to the middle of the day when generation is at a maximum
• this can also be done dynamically – with loads operating when power is available - dynamic supply-demand matching
• this can also be done statically at the beginning of the design process, reducing and levelling loads as far as possible and then selecting appropriate renewable sources
• tools such as Merit (UK) and Homer (US) have emerged to assist in this process
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