Window sensors, digital twin, improve energy systems

Materials World magazine
26 Nov 2019

Measuring shade could help reduce the energy consumption of buildings

Residential and commercial buildings in developed countries account for up to 40% of the total energy consumption, according to Renewable and Sustainable Energy Reviews. But while building automation and control (BAC) systems can collect data from physical sensors, they only react to changes in the environment.

Technology is being developed to shift such systems from reactive to proactive, which may help improve buildings’ energy efficiency and user comfort. A building’s energy performance depends on its envelope – the doors, roof and windows – of which the latter have been found to be responsible for up to 40% of wasted energy.

The energy behaviour of a building’s envelope can be studied with software and sensors working together to minimise energy losses. The Leaftech Virtual Sensors (LVS) - Shade conducts shading analysis for the building envelope and provides the results to the BAC system. The effect of this simulation is semantic, which enables communication between the server and the BAC system.

Digital infrastructure

Using computer data for digital twin purposes enables the planning of building design and monitoring results once it is built. In computing, extensible markup language (XML) is a markup language that defines a set of rules for encoding documents in a format that is human and machine-readable. The geography markup language (GML) is an XML grammar defined by the open geospatial consortium (OGC) to express geographical features. There are other languages dedicated to geographical features, but GML builds on the existing XML schema model instead of creating a new schema language.

CityGML is an open standardised data model and exchange format to store digital 3D models of cities and landscapes. The system is implemented as a GML application schema and as such, can be used with GML-compatible web services for data access, processing and cataloguing, such as web feature and  processing services, and catalogue services. The Leaftech database has been developed according to the CityGML format. A digital 3D model of the structure in Building Information Model (BIM) or CAD format is then merged with the data from the surrounding environment, captured by CityGML data. This is then enriched with data such as the weather, solar information, and digital surface models (DSM).

This open data can be used to perform the modelling and testing. For example, the city of Berlin, Germany, is providing a 3D model of the city for free public use. The model is a joint project of the Berlin Senate Department for Economics, Energy and Public Enterprises and Berlin Partner for Business and Technology. In line with the Open Data Initiative of the city of Berlin, the Senate Department for Economics, Technology and Research provides Lightweight Omega Digital Dropwindsonde building models for free download. However, these are not always complete and may require modifications.

Minimising shade influence

Shading patterns on a building can be complex in urban areas, as trees, neighbouring structures and other subjects influence outcomes. Measuring patterns can be difficult as hundreds of sensors would be needed and could lead to rebound effects. The system solves this as a set of virtual sensors are located on the building’s façade or windows in the digital model of the building. In the next step, a shading analysis is composed for each virtual sensor, and the results are communicated to the controlling logic of the shading systems through an application programming interface. In a picture of the digital model and the virtual sensors mounted on each façade, the colour of each sensor represents the cumulative hours of sunlight within a year. The darker the sensors, the less direct sunlight has reached them in the course of a year.                              

The system determines certain factors for each sensor at any time. The most crucial factors are the solar position and solar incident angles, shadiness from surrounding buildings and trees, and solar radiation – how much solar energy is reaching the sensor. This information is used before and after the construction. During the planning phase, the information produced could help inform choices about energy-effective design and placing of openings such as windows, and whether a window requires a shading system.

The company has so far focused on the after-construction phase, where the technology could be used to boost the performance of various controlling systems. By creating awareness about their unique shading characteristics, the monitoring package enables shading systems to act independently according to the shading characteristics of the related window. To be compatible with the related standards e.g. VDI-381310 and EN15232, various features were defined and developed in the system, such as the data required for slat tracking, which is a function of solar angles and building orientation.

To maximise capability and control – which is challenging using hardware sensors – more sublet control of shading systems is possible since every window receives the shading information specific to itself. One way to take advantage of the solution is through the feature Single-Shade, which ensures that windows shaded because of neighbouring trees, buildings, etc. are not structured further by the system.

Passive design

Absorbing more natural light benefits the building residents’ health and productivity. These benefits are not easy to quanify but the company has conducted a case study to at least measure the energy related benefits.

The standard office building in Germany consumes 118.4kWh only for heating purposes as well as 23.4kWh electricity for lighting purposes per annum, per square meter of gross floor area (GFA). This corresponds to annual energy costs of approximately €19.3/m2/annum (a) – assuming heating energy price of €0.11/kWh, and electricity price of €0.27/kWh. A demand-orientated sun protection control reduces the cooling and heating energy by 5% and the light energy requirement by up to 13%. Therefore, the energy requirement in a German standard office building can be reduced by sun protection solutions by up to €1.5/m2/a.

In Germany, many offices do not have air-conditioning, while they are common in other countries. Such devices have an impact on automated shading systems, especially in sunny countries and during summer months. One study found the total annual energy consumption of a residential building in Dubai, United Arab Emirates, may be reduced by up to 23.6% when passive cooling strategies such as automated shading systems are used.                                             

To show the potential of the Single-Shade, the company conducted shading analysis for the Landtag Brandenburg building in Potsdam, Germany. The building is shaded through a high-rise neighbouring building. In this study, every shading system is lowered for 520 hours per annum on average – almost 90 minutes a day – without any need for sun protection. This corresponds to calculated unused diffuse irradiation potential of 132kWh per window, per annum. In addition, user comfort is restricted.

With a controller based on the product, the shading system only shuts down when there is an actual need and there is no waste of usable diffuse radiation energy.

Assuming that 50% of the incident energy can be used directly for lighting purposes, at an electricity price of €0.27/kWh, the system could save €16-17 per window, per annum of lighting energy.

About 45% of the energy can be used as a heat source during the heating period. With a heating energy price of €0.11/kWh, using the system leads to heating cost savings of €5-6 per window, per annum. Moreover, benefiting from more natural light penetration into the room and longer availability of the outside view, the building user’s comfort improved. This makes the internal rate of return (IRR) of the LVS-Shade more than 30% for a building with only 100 shading systems. The higher the number of shading system, the higher the IRR. For example, a building with 300 shading systems will benefit from an IRR close to 100%. This means that the savings during the first year will be equal to the amount of money invested.

The software is complete and the platform is being developed to connect directly with business partners. The company is also working on the API to connect directly to BAC systems.

Commercial energy consumption in the UK

The thermal losses through windows, among other aspects of a building, are part of a wider issue about the energy consumption of buildings and their contribution to total emissions across the region.

The report Energy efficiency – building towards net zero, by Business, Energy and Industrial Strategy Committee (BEIS), published in July 2019, identified that about 19% of the UK’s total emissions came from heating buildings – including 77% from homes, 14% commercial and 10% public buildings.

For commercial buildings in particular, the report identified that better fabric, heating, ventilation and air-conditioning equipment, and energy management, would contribute savings of £6bln by 2030.

The main mechanism to drive change in efficiency improvements in the commercial sector is the Minimum Energy Efficiency Standards (MEES) for rented commercial buildings, which make up about 60% of commercial properties. But those standards look at the design of the building, not how they work.

‘We are concerned that the continued strengthening of the MEES regulations, if in isolation, will not bring about the full energy efficiency potential available for commercial buildings. Rather, it risks perpetuating a “design-for-compliance culture” where buildings are designed to meet the required compliance standard, with negligible attention paid to how the building actually performs,’ the report said.

BEIS called for the government to disclose operational energy data for the commercial sector, and to use rating tools that focus on performance outcomes from 2020. The report cited the National Australian Built Environment Rating System, which enforces operating ratings. ‘Since the scheme’s mandatory introduction in 2010–2011, the average energy intensity of Australian rated offices has improved by 28%. Such an approach could supplement minimum standards by offering a review process to ensure that the design of the building performs as planned,’ it said.

BEIS said insulating buildings is an ‘obvious and practical first step to decarbonising the economy. While the decarbonisation of buildings is contingent on energy efficiency, the heat supply of buildings must also be decarbonised.

‘These challenges are interlinked – low-carbon heat cannot be deployed cost-effectively unless buildings are properly insulated, regardless of the technology pursued, for example heat pumps, hybrid systems and hydrogen. Energy efficiency is, therefore, a core element of the heat decarbonisation pathway. Decarbonising heat at an acceptable cost relies on energy efficiency investment. The total system cost of heat decarbonisation could be £6.2bln higher per year to 2050 without energy efficiency’.

Sasan Zahirnia and Aspasia Abu-Hanna are Leaftech Gmbh co-founder and CE, and Product Development team Project Engineer.