Three Office Buildings Using Passive Heating and Cooling Design
Passive heating and cooling refers to techniques to manage the internal temperature and air quality of a building without using power. Here are three examples of new buildings where such techniques have been employed.
Modelling of the effects of heat gains throughout the year is first undertaken. For example, the solar gain experienced by the building is a function of the total daily irradiation on the building surface, the glazing area, the angle of incidence at which the sun hits the window, the transmittance value (g) of the glazing, and the area of floor or wall reached by the sunlight, as well as its airtightness , U-value and thermal mass.
The stack effect is a function of the pressure difference between the air outside and inside the building caused by their difference in temperature. The stack effect can in theory be utilized to cool a building without the need for artificial ventilation systems. In practice, with existing buildings, it is difficult. The relative size of the openings at the top and ground floor is important.
If the local prevailing wind is constant, the best result is obtained by having a small inlet and a large outlet. If the wind is not constant, a large inlet is preferable because it lets in a greater volume of air.
Ground level vented wall and/or window openings must be equipped with weather, burglar and insect-protection and use automatically-controlled flaps. If daytime solar gains are reduced to a minimum and the building is otherwise airtight, night ventilation can perform well. The building must have good passive stack ventilation design.
1. The Energon passive office building in Ulm, Germany
Air intakes for ventilation and cooling outside the Energon passive office building in Ulm, Germany. Source: International Energy Agency (IEA)
This is a triangular, compact building with five storeys, and has a physically curved facade enclosing a glass-covered atrium at the centre. This provides ventilation, and daylight. The building is a reinforced concrete skeleton construction with facades made of prefabricated wooden elements of largely equal dimensions.
Insulation is 20cm-thick under the foundation slab, 35cm in the facade, up to 50cm in the roof. The windows are thermally insulated triple glazing. Heat pumps and thermal stores help to moderate the temperature.
2. Office building at the Building Research Establishment, England.
Solar chimneys on an office building at the Building Research Establishment, England. Source: BRE
'Solar chimneys' are automatically opened when required to release unwanted hot air. Their height and metal composition allows them to be heated by the sun, which heats the air internally. This rises through the chimney, drawing up air from within the building.
3. The Solar XXI building in Lisbon, Portugal
The Solar XXI building in Lisbon, Portugal Source: International Energy Agency (IEA).
This building is a combined office and laboratory at the National Energy and Geology Laboratory (LNEG). This 1500m2 (16,146ft2) multipurpose building in Lisbon, Portugal, is naturally ventilated and functions as a near zero energy building. Its cost is said to be little more than a conventional building of the same size.
The office space is on the south side of the building to take advantage of daylighting and solar heating. Spaces with intermittent use, such as laboratories and meeting rooms, are on the other side of the building. Office spaces are in use from 9am to 6pm weekdays, and the ventilation pattern was arranged to suit this.
Plan and sectional view of the Solar XXI building in Lisbon, Portugal, showing distribution of the buried air pre-cooling system. Source: International Energy Agency (IEA)
The heat output of the PV modules is ingeniously used to supplement ventilation. There is an air gap behind each panel with openings to indoor and outdoor air at both high and low level, where heat from the rear of the panel causes a convective flow.
Seasonal performance. Cross (blue arrows) and vertical (red arrows) ventilation systems acting together with the buried pipes system (blue arrows on the right). Source: International Energy Agency (IEA)
In winter, the upper opening takes air indoors, either from outside or from the room, through the lower opening to be heated. In summer, the upper opening lets the warmed air outdoors. The lower opening can either be open to the room to provide ventilation or to outside to provide cooling for the PV panels only.
The building has high thermal capacity and external installation on the walls and roof. The south facade supports 100m2 of solar PV modules and the majority of the glazing. Additional space heating is provided by 16m2 (172ft2) of roof-mounted solar thermal that also supply hot water, which can be supplemented by a gas boiler.
The 18 kilowatt-peak (kWp; the rated power output under standard test conditions) grid-connected PV arrays supply electricity; further panels are located in a car park, where they also provide shade.
The entire system satisfies heating requirements of 6.6kWh/m2 and cooling requirements of 25kWh/m2. Annual electricity use for the building is about 17kWh/m2, of which 12kWh/m2 is from the PV arrays, leaving 30 per cent to be drawn from the national grid.
Natural lighting is encouraged. In the centre of the building a skylight provides light for corridors and north-facing rooms on all three storeys. The installed artificial lighting load is 8W/m2. There is no need for an active (powered) cooling system. Venetian blinds are outside the glazing to limit direct solar gain. Natural ventilation is promoted through the use of openings in the facade and between internal spaces, together with clerestory windows at roof level, which help create a cross wind and stack effect.
Assisted ventilation is provided by convection from to the PV module heat losses. To supplement this in the cooling season, incoming air can be pre-cooled by being drawn by small fans through an array of underground pipes as shown in Figures 2.40–2.43. The openings are adjustable, and air is allowed to rise through the central light well.
The vents are manually operable, and staff needed to be educated in their use. In other buildings, such vents can operate automatically, governed by sensors. The building's occupants have been surveyed and expressed 70–95 per cent satisfaction with aspects of the air quality and temperature.
These buildings show that with a little thought, buildings can drastically reduce their heating and cooling costs and increase the comfort of occupants.
David Thorpe is the author of
- Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity
- Energy Management in Buildings: The Earthscan Expert Guide
- The 'One Planet' Life: A Blueprint for Low Impact Development
His Passive Solar Architecture Pocket Reference Book will be out later this year from Routledge.