Shading & HVAC

The need to heat, cool and ventilate a building is affected by a whole range of factors and solar control management is often not one of them

Blinds and shutters can help to reduce heat loss in the winter and heat gain in the summer so reducing heating and cooling requirements.

HVAC is a key building service considered at an early stage of building design due to the pipe and ductwork that will be needed and the space needed for the plant.

Solar shading is typically not considered as part of the building services package and as such its benefits are rarely optimised.

Cooling

Solar shading can help to reduce heat gain in the summer so reducing the need for air conditioning and if considered at the outset of a project could reduce the size of the air conditioning plant required with the capital, running and maintenance savings that will bring.

The Federation of European Heating, Ventilation and Air-conditioning Associations (REHVA) which represents over 100,000 engineers across Europe in their guidebook Solar Shading – How to integrate solar shading in sustainable buildings elegantly highlight that the benefits of this approach:

“Solar radiation is an important issue in all building projects as it has significant impact on the internal environment and affects the design of HVAC systems. Selection of solar shading should always be one of the first steps in the design of HVAC systems, as the demand for power and the energy consumption are greatly influenced by solar shading. Shading makes it possible to prevent extra solar heat from entering the building and to avoid the need for additional cooling to remove this heat, which costs precious energy. In winter time, however, the free heat from the sun is very welcome to reduce the building’s heating cost.”

This REHVA Guidebook includes a detailed cost benefit analysis of solar shading in relation to HVAC systems across three climate zones; Stockholm, Amsterdam and Madrid. In each instance the payback of solar shading was less than one year. Solar shading is thus an investment not a cost.

A two-year government-commissioned study by BRE on electricity use in air conditioning systems in UK office and retail buildings published in August 2016 highlights that current energy demand for air conditioning is rising rapidly and stands at 29 TWh which represents about 10% of all electricity use and costs around £4bn per year. Or to put that in perspective about 4 times the size of the total window covering industry in the UK.

Air conditioning can use a huge amount of energy. In fact, air conditioning can increase a building’s energy consumption and associated carbon emissions by up to 100% (Carbon Trust).

Heating

The UK is typically a heating nation and correctly specified and operated solar shading can help to prevent heat loss in the winter and at colder times of the day. This is particularly true of night time heat preservation with highly glazed office buildings.

The best U-value of glazing with a low-e coating is around 1.0 W/m2K – in comparison the walls are likely to be around 0.3 W/m2K so the transparent parts of the building need insulating too. Solar shading can help and you can see more here.

Ventilation

Ventilation is a key element in maintaining good indoor air quality and a key way of removing waste heat.

nZeb building designs such as Passivhaus have high levels of airtightness to ensure heat retention on the winter. This can also lead to heat retention in the summer and as such cause overheating and poor indoor air quality unless ventilation is effective at all times of the year.

This is a complex area of building physics as acknowledged in the Building Bulletin 101 Ventilation of School Buildings which is the subject of a public consultation.

Shading & HVAC
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