Low Energy Building Design Strategy

Low Carbon Design Aim “minimizing the impact on the wider environment through consuming the minimum resources possible in the building’s construction and operation whilst providing a healthy comfortable building that meets the occupant’s requirements” we need a coherent design and evaluation strategy to help us achieve this!

Building & Systems Design meeting the needs of occupants (comfort, utility, etc.) whilst considering environmental impact and meeting a host of other sustainability and legal criteria means that building design is a complex process fundamentally a building a complex, integrated energy system it will not “work” unless properly designed and analysed the majority of buildings in the UK are poorly designed: poor occupant comfort, high energy consumption, reliant on systems to overcome basic design faults as a start we need to prioritise our design activities …

Design Hierarchy for Low Energy Performance Form & Fabric Efficient Systems & Operation LZC Energy Supplies Impact on final energy performance demand reduction energy supplies

Design Hierarchy for Low Energy Performance the point of the previous slide is that the 1 st priority in a low-energy building design should be: -maximise the energy efficiency of the building by designing out the need for energy consuming systems (heating, cooling, lighting, etc.) -maximise the energy efficiency of conventional energy consuming systems -supply/offset energy demands using local zero-carbon sources

New Build Design Hierarchy for Low Energy without radically reducing the demand of a building (in comparison to the present-day standards) it would be almost impossible to achieve zero carbon operation

Demand Reduction Example

Demand Reduction All buildings have up to 4 basic energy needs:

Demand Reduction before deciding on what demand reduction measures it is worth looking at the demands themselves enables reduction measures to be prioritised as new build regulations change so energy efficiency priorities will change thermal  electrical

Demand Reduction: Space Heating in northern Europe the predominant load in buildings is space heating … also the load that can be most effectively tackled there are a range of options available depending upon whether a design project is new build or retrofit however the basic aims are: –minimise heat loss rate to the environment (fabric and infiltration) –maximise useful ‘free’ heat gains

Demand Reduction: Space Heating Q f - fabric Q i - infiltration Q s - solar Q g - gains Q h - heat

Demand Reduction: Space Heating insulation (walls, windows, doors) reduction of infiltration –high quality construction, draft stripping –MVHR maximise useful solar gain –positioning of glazing (south facing)

Demand Reduction: Space Heating overall demand reduction measures are one of the most cost- effective ways to reduce carbon emissions – particularly in older buildings/retrofit projects Source: EST

Demand Reduction: Space Heating

Demand Reduction: Space Cooling in warmer weather or climates or buildings with high internal heat gains we need space cooling not heating note we may have a building that has one set of requirements in winter (minimise heating) and another in summer (minimise cooling) – continental climate this tends to be an electrical load, electricity is used for compressors and pumps in the cooling system basic aims are: –minimise heat gains from the environment (fabric, infiltration, solar) –minimise internal heat gains –make use of thermal inertia and ‘free’ cooling when available

Demand Reduction: Space Cooling Q s - solar Q g - gains Q i - infiltration Q f - fabric Q c - cooling

Demand Reduction: Space Cooling shading (prevent solar radiation getting in) reflect solar (albedo) bring in air from outside when T  <T i … otherwise prevent unwanted infiltration MVHR insulation (prevent heat gains through walls) make use of thermal mass (plus free cooling) … or more exotic strategies –ground cooling –evaporative cooling

Demand Reduction: Space Cooling 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

Demand Reduction: Space Cooling insulation exposed mass daytime: Te > Tm insulation exposed mass evening: Te < Tm ventilation air Q s - solar

Demand Reduction: Space Cooling start of night flush end of night flush heat release from mass heat gain by mass

Demand Reduction: Space Cooling 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

Demand Reduction: Space Cooling 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.

Demand Reduction: Space Cooling testing thermal mass + night flush strategy with ESP-r

Demand Reduction: Hot Water hot water use is very building dependent –very little in offices/shops –medium sized load in dwellings –big load in hotels/hospitals there are a variety of measures to reduce the associate energy load ‘good housekeeping’: –reducing hot water temperature 60 → 45 o C –Why do we need to supply hot water at 60 o C?! (scalding risk) –to eliminate legionella, just occasionally raise tank temp to 60 o C or use chemical or UV dosing

Demand Reduction: Hot Water technology “fixes”: –storage tank and pipe insulation –more efficient heating devices (heat pumps, condensing gas boilers) –aerating taps and nozzles (reduce flow of water) –time limited taps/shower valves (prevent waste) –‘grey water’ heat recovery

Demand Reduction: Electricity as with hot water there are two main strategies for the reduction in use of electricity ‘good housekeeping’: –switching appliances off when not used (better control –avoiding ‘standby’ mode –awareness of energy use ‘smart meters’

Demand Reduction: Electricity Technology “fixes”: –low-energy appliances (lighting, entertainment, heating, cooling ….) –low energy fans and pumps (motors) –daylight responsive lighting –occupancy sensors in rooms –‘active’ smart metering (demand management)

Energy Supplies there are two main needs – heat and electricity (electricity could also supply heating/cooling needs) as with demands – available resources need to be analysed before deciding on appropriate supply measures … these should be appropriate for the demand of the building!

Energy Supplies available ‘renewable’ resources are entirely location dependent

Zero Carbon Electricity photovoltaics (PV) (solar resource) biomass CHP (biomass resource) SWECS (wind resource)

Low Carbon Electricity CHP (usually gas powered) –to achieve ‘zero carbon’ operation, resulting CO 2 emissions need to be offset by a zero carbon source

Zero Carbon Heat solar thermal (solar resource) biomass boiler (biomass resource)

Low Carbon Heat CHP (gas powered) Heat pumps (electricity) … energy consumption needs to be offset by zero carbon sources

Evaluating Options... there is a wide range of options for demand reduction and energy supplies how to choose between them? this requires performance evaluation this is an integral, iterative part of the evolution of a building design this type of design model requires feedback (data) on the likely performance of a system ….

Selecting/designing a system design team design process support environment selection implications

Performance Evaluation an appropriate support environment for the building design process is building environmental simulation simulation is the mathematical modelling of a building operating in realistic dynamic conditions allows the design team to assess environmental performance (human comfort, energy consumption, emissions, etc.)

Technical Assessment simulation enables a design team to make informed choices on a likely system’s performance accounting for the complex interactions between the fabric-occupants and systems

Technical Assessment Mathematical modelPerformance assessment

Exercise – James Weir Building

develop a “strategy” that would improve the James Weir Building this is one of the main teaching buildings in the University – yet is also one of the poorest energy performers, with exceptionally high electricity and space heating demand in addition – certain areas of the building (computer labs, lecture spaces in summer) over heat!!

Exercise – James Weir Building What could we do to improve this building? think about – the characteristics of the building uses of the building constraints on improving energy performance feasible improvement measures costs of improvement measures ranking improvement measures