Benefits of various types of shading and night cooling by vent windows

A publication produced by Somfy and Delft University of Technology investigates the benefits of shading systems that combine control of solar shading, vent windows and HVAC systems. It concluded that advanced window systems are cost effective and can reduce Co2 emissions of buildings, but this is dependent on the involvement of manufactures of window system at an early stage in the design process.

Key Findings

  • In general it can be concluded from the data that a well-controlled shading systems have large impact on cooling capacities of HVAC systems
  • …well controlled shading systems have (a) large impact on cooling capacities of HVAC systems.
  • The reduction of Co2 emission of 28% in office buildings can roughly be estimated at 3% for the whole country

Further Detail

Included within the paper is a simulation study using Enerk Software that investigates the energy, Co2 and cost saving benefits that advanced facade systems can provide. Simulations are compared that include no shading at all, use of indoor and external Venetian blinds. Six methods of implementation of control strategies were analysed. These included:

  1. Double glazing with indoor Venetian blinds always down which requires artificial light to be turned on when indoor lux levels drop below 500 lux.
  2. Double glazing without any type of shading used.
  3. Outside Venetian blinds where blinds are always down and positioned at a 45-degree angle.
  4. The same as 3 but where blinds are only utilised when solar radiation levels outside are higher than 250W/m2.
  5. Outside Venetian blinds are controlled by internal lux level with a set point of 500 lux. Additionally, automated artificial lighting is used to maintain steady lighting levels inside.
  6. The same strategy as 5 but where motorised ventilation of window openings is utilised for night cooling. Opening windows outside office hours until an internal temperature of 21°C is achieved as long as external temperatures are above 15°C.

All simulations included the use of the same HVAC system and double glazing in the window system.

The results revealed that Co2 emissions can be reduced by 18% when external Venetian blinds are used in conjunction with technology that allows blind movements to be controlled by internal lux levels and when working in a system with automated artificial lighting (option 4). A 28% reduction was also achieved when motorised ventilation for night cooling was included (option 5). Energy requirements were reduced by 29% when motorised ventilation for night cooling was included.

The paper also concluded that extra costs for the advanced solar protection, even when combined with vent window systems, delivers profit right away. However, if this is implemented at the end of the design phase long pay back periods will be incurred. The paper echoes that this information needs to be passed onto architects, real estate developers and building owners in order to incorporate window system manufactures at an early stage to avoid over-sized HVAC systems being implemented which cannot be reduced easily later in the design phase.

To read more on this report, click here.

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