Some aspects of a zero carbon building in the northern hemisphere, temperate zone.
Passive solar architectural principles have come of age. They have given rise to thousands of buildings of all sizes and purposes around the world, in all climate types, to demonstrate how buildings don't need to consume fossil fuel energy to support their occupants. They can even generate more power, or absorb more carbon, than they use. Below is a ten-step guide to how to go about designing and building one.
But first, the benefits of passive solar architecture:
- Saves energy and running costs from the start;
- Comfort in all seasons and climates;
- Safe investment and resilience into the future;
- Added value every year through decreased operation costs;
- Longer useful life with high quality standard;
- Contributes to climate change protection.
Sustainable solar building is also known as passive house (Passivhaus in German), although this is also a strict standard.
There are currently 30,000 Passivhaus structures built around the world. The principle is that the architecture is designed to provide comfort for the occupants with minimum need for additional energy. This is achieved using design tools to establish the needs and requirements of all functions in the building and their inter-relationships. Energy savings are maximised by placing spaces in the most advantageous position for daylighting, thermal control, and solar integration.
This process may also reveal opportunities for multiple functions to share space and reduce the footprint of the building.
General principles of a passive solar buildingBuildings should be at least zero carbon on balance, when totalling the impacts of materials, construction, use and demolition. Features of this are to:
- minimise the use of fossil fuel energy during the supply chain and process of construction;
- encourage the use of materials which store atmospheric carbon in the fabric of the building;
- encourage the generation and even export of renewable energy by the building;
- construct and manage it in such a way that it minimises the emission of greenhouse gases during its lifetime and eventual demolition.
Such a building could, over its lifetime, become zero carbon, or even negative carbon by generating enough power to more than make up for the fossil fuels it has used. To achieve this, the following features are needed:
- favouring the use of ‘natural’ and cellulose-based materials (timber products, and other products made from plant-originating materials);
- making the structure very airtight;
- making the structure breathable;
- making it durable, resilient, low-maintenance, fire- and weather-resistant;
- incorporating a large amount of insulation;
- taking advantage of free, renewable energy.
10 steps to a zero energy buildingSo here, now is a summary of 10 steps in the design and build strategy of a zero-energy passive solar building, averaged for any climate zone in the world.
1. Site selection
- Secure optimum location, as free as possible from non-useful shading relative to the seasons and time of day.
- Research the available solar resource and wind factors for the site using local and freely available data.
- Orient optimally.
Example of a sun chart to view the azimuth angle through a year at a building location.
2. Concept development
- Minimize shade in winter, minimizing parapets, projections, non-transparent balcony enclosures, divider walls etc.
- Choose a compact building structure with low skin to volume ratio. Use opportunities to combine buildings.
- Use a simple shell form, without unnecessary recesses.
- Survey and model the expected internal and external heat gains and cooling requirements, and other building energy loads.
- The following energy performance targets and air changes per hour define the Passivhaus standard and must be met in order for certification to be achieved:
- Specific heating demand ≤ 15 kWh/m2/yr
- Specific cooling demand ≤ 15 kWh/m2/yr
- Specific heating load ≤ 10 W/m2
- Specific primary energy demand ≤ 120 kWh/m2/yr
- Air changes per hour ≤ 0.6 @ n50.
- Optimize glazing, shading and aspect/form according to latitude and climate zone, to maximize the use of daylighting, balancing against the appropriate heat gains.
- Concentrate the utility installation zones, e.g. bathrooms, above or adjacent to the kitchen, in coolest areas in summer (temperate zones) or hottest (hot zones).
- Model and decide on the ventilation scheme making best use of the stack effect and Bernoulli principle. Is additional mechanical ventilation (with heat recovery) needed?
- Thermally separate basement from ground floor (including cellar staircase), make airtight and thermal bridge free.
- Derive an initial energy use estimate.
- Evaluate the potential for renewable energy technologies: solar thermal, PV, wind, heat pumps, etc.
- Consider use of underfloor heating to save energy (water or electric).
- Check the possibility of government subsidies.
- Commence consultations with the building authority.
- Contract agreement with architects, including a precise description of services to be rendered.
3. Construction plan and building permit planning
- Select the building style – thermally massive or light. Sketch out a design concept, floor plan, energy concept for ventilation, cooling, heating and hot water.
- Floor plan: short pipe runs for hot/cold water and sewage.
- Consider the space required for utilities (cooling/heating, ventilation etc.).
- Short ventilation ducts: cold air ducts outside, warm ducts inside the insulated building envelope.
- Further calculate and minimize the energy demand, e.g. with the Passive House Planning Package (PHPP) available from the Passivhaus Institut, Darmstadt. Climate data sets are available for most areas in the world which plug into this.
- Plan the insulating thickness of the building envelope and avoid thermal bridges.
- Calculate cost estimate.
- Negotiate the building project (pre-construction meetings).
4. Final planning of the building structure (detailed design drawings)
- Insulation of the building envelope: the absolute U-values will vary according to context (location, form etc), but in general aim for:
- walls, floors and roofs ≤ 0.15 W/m²K;
- complete window installation ≤ 0.85 W/m²K.
- Design thermal bridge free and airtight connection details.
- Specify windows that comply with passive house standard: optimize type of glazing, thermally insulated frames, glass area, coating, shading.
- 5. Final planning of ventilation (detailed system drawings)
- General rule: hire a specialist.
- Ventilation ducts: short and sound-absorbing. Air flow velocities below 3 m/s.
- Include measuring and adjusting devices.
- Take sound insulation and fire protection measures into account.
- Air pathways: avoid air current short-circuiting.
- Consider the air throws of the air vents.
- Provide for overflow openings.
- If MHVR/cooling is used, install in the temperature-controlled area of the building shell.
- Additional insulation of central and back-up unit may be necessary. Soundproof the devices. Thermal energy recovery rate should be > 80 %.
- Airtight construction to be checked at every stage.
- The ventilation system should be user-adjustable.
- Optional: ground or water-source heat pump (air or water as medium) and/or air pre-cooling/heating pipes; may be reversible for summer cooling and winter heating.
6. Final planning of the remaining utilities (detailed plumbing and electrical drawings)
- Plumbing: Install short and well-insulated pipes for hot water in the building envelope. For cold water install short pipes insulated against condensation water. Use no greater bore than needed to conserve water and heat.
- Use water-saving fittings.
- Sub-roof vents for line breathing (vent pipes).
- Plumbing and electrical installations: avoid penetration of the airtight building envelope – if not feasible, install adequate insulation.
- Use the most energy-saving appliances/equipment.
- Situate switches for ring mains alongside light switches to enable easy switching off of phantom loads when leaving rooms/building.
- Plan installation of (perhaps wireless) building energy monitoring system.
7. Call for tenders and awarding of contracts
- Plan for quality assurance measures in the contracts.
- Set up a construction schedule.
8. Assurance of quality by the construction supervision
- Thermal bridge free construction: schedule on-site quality control inspections. Take photographs.
- Check of airtightness: all pipes and ducts must be properly sealed, plastered or taped. Electrical cables penetrating the building envelope must be sealed also between cable and conduit. Flush mounting of sockets in plaster and mortar. Take photographs.
- Check of thermal insulation for ventilation ducts and hot water pipes.
- Seal window connections with long-lasting adhesive tapes or plaster rail. Apply interior plaster from the rough floor up to the rough ceiling.
- n50 airtightness test: Have a blower door test done during the construction, when the airtight envelope is complete but still accessible, i.e., before finishing the interior work, but after completion of the electricians' work (in concert with the other trades), incl. detection of all leaks.
- Ventilation system: ensure easy accessibility for filter changes. Adjust the air flows in normal operation mode by measuring and balancing the supply and exhaust air volumes. Balance the supply and exhaust air distribution. Measure the system's electrical power consumption.
- Quality control check of all cooling, heating, plumbing and electrical systems.
9. Final inspection and auditing.
10. Conduct post-occupancy monitoring...to determine if building performs as expected.
David Thorpe is the author of