1 / 35

Passive Technologies and Other Demand-Side Measures

Passive Technologies and Other Demand-Side Measures. Overview. energy consumption in buildings passive demand reduction examples insulation thermal mass natural ventilation nat. vent alternatives demand management and “demand-shifting”. Energy Required (Revisited). space heating

olympe
Download Presentation

Passive Technologies and Other Demand-Side Measures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Passive Technologies and Other Demand-Side Measures

  2. Overview • energy consumption in buildings • passive demand reduction examples • insulation • thermal mass • natural ventilation • nat. vent alternatives • demand management and “demand-shifting”

  3. Energy Required (Revisited) • space heating • hot water • electricity • lighting • appliances • cooling • … also for space heating and hot water demand in a typical commercial building

  4. Energy Required (Revisited) • “Typical” average energy consumptions for dwellings: • Source: Domestic Energy Fact File

  5. Energy Required (Revisited) • “Typical” average energy consumptions for offices: • Source: ECGO 19

  6. 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

  7. Illustration: Domestic Sector target

  8. Illustration: Domestic Sector target

  9. Illustration: Domestic Sector target

  10. 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!

  11. 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

  12. Passive Measures

  13. Fabric 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.

  14. Fabric Improvements • Source: EC

  15. Fabric 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

  16. Fabric Improvements

  17. Thermal 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

  18. Thermal Mass daytime: Te > Tm evening: Te < Tm ventilation air exposed mass exposed mass insulation insulation

  19. Thermal Mass start of night flush heat release from mass end of night flush heat gain by mass

  20. Thermal 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

  21. Thermal 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.

  22. Thermal Mass • testing thermal mass + night flush strategy with ESP-r

  23. Natural 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)

  24. Natural 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)

  25. the reality! the drawing … Natural Ventilation

  26. Natural 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

  27. Nat. 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

  28. de –pressurised interior Nat. 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”

  29. Demand Shifting load (GW) • 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 cost £ CO2 g/kWh

  30. Demand Shifting

  31. Demand Shifting • different power generation “mixes” means different electricity carbon intensity during the day

  32. 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 CO2 g or £/kWh

  33. Demand Shifting • opportune loads are loads that can be moved in time without inconveniencing the user or causing adverse effects

  34. 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

More Related