Nottingham City Council expects proposals to begin by considering

passive design and climate mitigation form concept design stage.

Site Planning

The main objective of site planning for passive solar buildings is to consider where to position different buildings and each room/function within buildings – including gardens - making the most of the existing landscape, topography and orientation to achieve the best possible outcome.

The position of buildings on the site can make a huge difference in how the spaces in between buildings feel, both in terms of solar gain and ventilation. Comfortable environments tend to be more successful because people - and other species - tend to spend more time there.

The idea in solar passive buildings is to allow as much unshaded exposure in the south aspect as possible during the winter months. However, a good design balances energy performance with other important site factors like micro climatic reasons, the direction of prevailing breezes for summer cooling, the views, the street lay out, environmental noise and so on.

Orientation

Positioning the building’s long axis facing solar south will maximize solar gain during winter months and limit western exposure in the summer. If an optimum orientation cannot be achieved, designers must explore opportunities to address solar heat gain through design. It is also very important to consider how dominant winds cross the site to take advantage of natural ventilation.

Layout

Place rooms used more frequently on the south side for optimal use of natural light during day. Planning room layouts by considering how the rooms will be used in different seasons and at different times of the day, can save energy and increase comfort. In general, living areas and other high-activity rooms should be located on the south side to benefit from the solar heat. Clustering baths, kitchens and laundry rooms near the water heater will save the heat that would be lost from longer water lines. Another general principle is that an open floor plan will allow the collected solar heat to circulate freely through natural convection.

Landscaping

Carefully planned landscaping and planting can aid in maximizing performance of Passive Solar Design and assist with imperfect situations and site problems.  Trees and other landscaping features may be effectively used to shade east and west windows from summer solar gains. When a building relies on solar gain as a form of heating, trees located on the south aspect can hinder passive solar performance unless they are very close to the house and the lower branches can be removed to allow the winter sun to penetrate under the tree canopy. A careful study of shading patterns and tree canopies will be required to understand how the design will perform in different seasons; this is no reason to avoid using trees in south aspects, as it should be possible to accommodate them in optimum locations.

Natural light

Windows are essential to achieve two fundamental aspects of passive design: sunlight/heat and ventilation; let’s consider solar light/heat gain first. The best approach is to install energy efficient windows, arranging them with consideration to minimize summer heat gain and maximize winter heat gain. It is important to note that the same large areas of glazing that let heat in during the day can also readily let heat out at night. Thus, some form of night-time protection should be incorporated to minimise any conduction and convection losses through windows. Thick drawn curtains with a pelmet that forms a good seal at the top can be used as well as brise soleil and insulated shutters. Ideally, the glazing on the building should be exposed to sunlight with no obstructions within certain angles, which are determined by local sun paths. A sun and shade analysis might be required to demonstrate how the proposals perform in different seasons.

Shading

Configure shading devices, such as eave overhangs or external shading devices to permit low winter sun into building and to keep the high summer sun out. Overhangs are one of the best (and least costly) shade design elements to include in a building. If overhangs are designed according to local sun angles, when the sun is high in the sky in the summer, should be able to shade the room completely. In the winter, when the sun is low, they should allow the full sun to enter, warming the air as well as the floor, walls and other features. Shading devices can also affect the way the air moves and the how the rooms ventilate. There are software options available to simulate the air movement for different design options, documentation like this can be good evidence to support design decisions.

Ventilation

Ventilation is essential to sustain good indoor air quality. Energy efficient, airtight buildings will need a heat/energy recovery ventilation system. Managing how air moves within a building can help control the temperature, humidity and comfort levels in different rooms. The science of natural ventilation can be complex and requires specialist software tests, however, some key principles relate to how air travels across rooms both in a three-dimensional way. Below, some diagrams show how air moves plan and cross section according to the position of windows.

Air Sealing

Supplying a continuous air-barrier surrounding the entire building envelope in contact with the insulation layer, helps minimise loss of heat in winter and heat gain in summer months. Air sealing can be tested at different stages of the construction stage, documentation like this can help achieve a higher environmental performance credential. The difficulty with air sealing is that natural ventilation is not an option and air flow, heating and cooling become more reliant on mechanically assisted systems. Although air sealing produces a more reliant result that can be easily measured in terms of temperature control, it also removes the possibility to adjust the levels of comfort by opening a window. During the Coronavirus pandemic, air some sealed environments and those relying on mechanical means of heating/cooling/ventilation (like some office buildings or cruise ships, for example) became problematic as the best way to prevent contagious environments was known to be natural ventilation. Air sealing can also work in combination with passive design solutions, for example to ensure air can only entre and exist the building through specified points which can be opened and closed as necessary to control room temperature and comfort (see Passive Solar Heating).

Insulation

Supply a continuous insulation layer, with thickness appropriate to climate, surrounding the entire conditioned space of the building, minimizing loss of heat during winter and heat gain in summer. Fabric-first approach is the best approach to design a passive house. It means building with very high quality materials, to try and reduce the heat losses from the house. This approach provides a simple solution because, by making just small changes to the products used and the construction methods, it is possible to achieve better results at little, or no extra building cost. One typical design error is to leave parts of the building without insulation, which results in thermal bridges. It is very important to eliminate “thermal bridges” (also called cold bridges) in a passive house, creating a good barrier between the inside and the outside, to avoid any heat loss and possible condensation.

Thermal Mass

If solar heat is to be used when the sun is not shining, excess heat must be stored. Materials that can absorb and store heat have high thermal mass and are an integral part of most passive solar designs. Heavy materials such as brick, concrete, tile and stone should be applied in appropriate thicknesses and in the right locations, to insulate the building envelope and to store heat, which can help balance the temperature fluctuations. Colours are also an important factor. Light coloured surfaces will reflect light within the space, distributing it over a greater number of surfaces. Dark coloured materials will absorb most of the incident energy as soon as it strikes. Highly conducting materials will quickly transfer any heat build away from the surface deeper into the material, which means less energy will re-radiation back into the space. In poorly conductive materials the surface will heat up more and will quickly re-radiate most of the heat back into the space. Different materials and material combinations transmit heat in different ways, this can be measured. Thermal transmittance, also known as U-value, is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure. The units of measurement are W/m²K. The better-insulated a structure is, the lower the U-value will be. Workmanship and installation standards can strongly affect the thermal transmittance. If insulation is fitted poorly, with gaps and cold bridges, then the thermal transmittance can be considerably higher than desired. Thermal transmittance takes heat loss due to conduction, convection and radiation into account.