Ventilation and Cooling
Adequate ventilation in buildings is crucial if its occupants are to feel healthy and comfortable. Artificial cooling is implemented only where really required. Building Regulations Part F specifies requirements to ensure that smells and moisture are removed, particularly from bathrooms and from kitchens in order to prevent damp and consequent damage to the building skin.
Cooling will become an important consideration as climate change brings increased temperatures across the UK. This is currently a design priority for commercial buildings, but will become a design consideration for residential buildings as well. Hence, where cooling is required, it is best to minimise the use of the cooling technology by designing mixed-mode buildings.
"Mixed-mode" refers to an approach to servicing (cooling and ventilation in particular) that does not rely solely on mechanical systems for air distribution equipment and refrigeration equipment for cooling, but uses these in combination with natural ventilation from operable windows. (Windows can be either manually or automatically controlled).
Low Carbon Ventilation Strategies
Low carbon ventilation needs to address carbon emissions at two levels: those emissions caused by powering electric fans and those associated with ventilation heat (or cooling) losses.
Stack ventilation deals with the first of these. It uses a combination of cross ventilation, buoyancy (warm air rising) and the venturi effect (wind passing over terminals at roof level, causing suction). There are particular designs for the stack terminals at roof level, which allow ventilation of buildings with a depth of up to 15 m. Usually the need for fans is avoided altogether, through some systems are assisted by low-speed fans.
Heat recovery on the other hand saves energy by reducing heating or cooling losses, typically by about 70 per cent. It can be applied to either stack ventilation systems or fan driven systems. It uses a counter-flow heat exchanger between the incoming and outgoing air flow. The two airstreams are separated so that cross-contamination does not occur.
A guide to energy efficient ventilation can be found here
Layout & Geometry
Offices buildings
Cooling loads are created by internal heat gains (people, computers, refrigerators etc), and also by external heat gains (solar gain, ingress of warm external air, conduction through building fabric).
Masterplanning of commercial developments should pay attention to the solar path, and place major areas of glazing on the south and north facades while shading the former externally. It is easiest to cut out unwanted solar gain with external shading from the south. East and westerly facades are more difficult to manage as the sun's angle creates a complex, dynamic geometrical puzzle to solve. In addition, if primary glazing is placed to the south and north, only one façade needs to be shaded. Low sun angles from the east and west, which particularly in offices can create unwelcome glare, can also be managed in this way.
It should be noted that internal gains should also be cut out as far as possible to reduce cooling loads. This involves, for example, low energy lighting with advanced controls, low energy appliances and location of refrigeration heat outputs outside the thermal envelope.
In residential buildings layout will have a lesser impact on cooling demand than on heating demand. Nevertheless, allowing cross-ventilation by careful space-planning is something that designers should aim for.
Fabric
Cutting out unwanted heat gains from conduction is achieved by good insulation. Glazing needs to face north, or to face south and be well shaded.
Mass
The case of lightweight vs heavyweight build has been polarised by industrial association studies selling one point of view or the other. This is not helpful. Thermal mass is better known as dense materials with high heat capacity such as stone, concrete, rammed earth, bricks and even paraffin wax. Its value is in delaying, and reducing internal peak temperatures. It is also important to understand that thermal mass is only of use within the thermal envelope.
Office building
Offices generally require some cooling because of their high level of occupancy during the day and their internal heat gains resulting from IT equipment and occupants. Thermal mass within offices does provide a useful buffer to peak temperatures. For this to work, night cooling must be made possible in order to discharge the build-up of heat accumulated during the day. Designing in night time ventilation opening that do not compromise security as well as the designing in of cross-ventilation paths are therefore important considerations.
Cooling requirements in residential buildings are not significant, and in the south west are unlikely to become a major concern as the climate is for the most part coastal, not continental. Peak temperatures are therefore lower than in London and the south east.
The diurnal temperature swing in the south west of England is also very low compared with countries where thermal mass is used to very good effect, such as the Gulf States. This means that internal temperature build-ups during the day are more difficult to discharge during the night in South West England.
For this reason, thermal mass should be used only where a demonstrable benefit is clear. Moreover, the considerable carbon impact of higher thermal mass materials such as concrete must be justified.
Links to further information:
http://www.metoffice.gov.uk/climate/uk/averages/regmapavge.html
http://www.greenspec.co.uk/html/lowcarbon/lowcarbonthermalmass.html
Behaviour & Control
Occupants perceive buildings to be healthier and more comfortable if there is an element of user control.
Hence, where cooling is required, it is best to minimise the use of the cooling technology by designing mixed-mode buildings, which allow for windows to be opened. Artificial cooling should be used only where it is really required (e.g. server rooms). Occupants should also be educated with regards to set points, so that users would in the first line take other adaptive measures (eg appropriate clothing), with cooling only kicking in at extreme temperatures.
