Importance of optimizing window design for energy efficiency

Research shows that windows contribute approximately 38% of heating energy use and 29% of cooling energy use (Brownlee & Wright, 2015). Hence, window design optimization and material selection for thermal performance is important for occupants in achieving low energy consumption and increasing the overall performance of the building. To achieve energy efficiency in windows, manufactures have come up with ranking mechanism that label window products on the basis of their energy efficiency through the Energy Rating System (ERS).

Energy rating system is an assessment method of comparing the energy performance of windows. Its main purpose is to rank windows according to their energy performance in order to enable customers to relate with the windows using particular numbers that is relative to their energy efficiency. The energy rating formula is derived from the balance between heat loss through conduction and air infiltration or leakage and heat gain via the window.  It is recommended to label each window with a separate energy rating (ER) for cooling and heating conditions since heat gain and heat loss parameters have opposite effects on cooling and heating energy. A number of countries have different variation of energy ratings on windows due to different climatic condition throughout the year. An international standard method was established by ISO to determine a similar method for calculating the energy rating (ER) for windows in ISO 18292 (Sorgato, et al., 2016). Over the years, some challenges experienced in energy performance of fenestrations have raised concern in the industry that could compromise the validity of the energy ratings as a method of ranking the energy performance of windows in a predominantly hot climate. This issues mainly deal with selection of a reference building, impact of thermal comfort and the advancement in glazing technology.

Therefore, this paper will assess window materials of a builder in relation to their suitability and energy ratings by comparing the builder’s choice of selection of the window materials and comparing them with the energy rating report. The essay will go ahead to give their material properties considering the thermal and durability property of each material. I will then conclude by giving an alternative for window frame material will improve the energy performance of the building.

On technical grounds, it was reported that the window energy rating scheme was established in the year 1995 in cooperation with the University of New South Wales. The scheme founders were Dr Peter Lyons and PC Thomas (Sorgato, et al., 2016). This enabled windows to be labelled and rated for energy impact on the overall performance of the house in any climate of Australia. Therefore, window makers must comply with the energy rating standards as stipulated by the Australian Fenestration Rating Council in order to participate in Windows Energy Rating System (WERS)  

Overview of the Energy Rating System (ERS)

The builder’s choice of material was very simple. He opted to go with aluminum frames with 3mm single glazing layer of glass material labelled window 1. Aluminum is a strong but inexpensive material for home building given the advantage of its durability and the fact that it can be painted (Kibert, 2016). Aluminum may not be the choice in regard to heat transfer mechanisms since it is a good conductor of heat which translates to more heat gains and heat loss through conduction process. The single pane glass has a low rating in terms of energy efficiency since it provides only a thin barrier to heat transfer from daylight hence exhibiting very little insulating value due to a high U- factor. This will definitely add up the hefty costs of heating and air-conditioning. According to the star ratings table for generic windows created for the Window Energy Rating Scheme (WERS) of Australia, it shows that window number 1, which is 3mm single glazing clear glass with aluminum frame has zero cooling star and 1-star for heating performance. Therefore, this means that when Post Occupancy Evaluation and thermal comfort of the house is carried out, it will exhibit poor performance in terms of energy performance level of the building. 

Windows are defined by sticker ratings that gives them their performance scores to determine the best choice for building a home, if sustainability and thermal comfort is key to the design implementation.

Some of the factors that define the energy performance of windows include U-factor, solar heat gain coefficient (SHGC), visibility transmittance (VT), and Air leakage (AL).

The builders choice of single glazing with aluminum frame window had a label rating of 1.29 U-factor which is higher than the energy performance label of National Fenestration Rating Council ( NFRC) which gives a U–factor ratings of between 0.20 -1.20 (Sorgato, et al., 2016). This description states the lower the U-value, the better the insulating value of the window in resistance to heat transfer.

In terms of the heat gain which is referred to as Solar Heat Gain Coefficient (SHGC), the builders window choice indicated window performance rating of 0.73 which is within the required range of 0 and 1 with the best performance being labelled as 0.32 according to the National Fenestration Rating Council (NFRC) (Sorgato, et al., 2016).This is because, the lower the SHGC, the less solar heat is transmitted into the building or the house.

Criteria used to rank the energy performance of windows

Visible transmittance of the window glass was labelled 0.69 which is an optical property required to be within 0 and 1 (Sorgato, et al., 2016). It indicates that the higher the visibility transmittance, the more light rays are transmitted through the window hence the window property meets the energy requirement standards.

The air leakage of the window is measured in cubic feet per minute. The window was labelled 0.21cfm/sq ft which is a good rating since this property states that the lower the number/ air leakage, the better the seal hence less air will be allowed to pass through the cracks (Kotireddy, et al., 2018). 

All windows are required to meet certain requirements before being released to the builder for purposes of construction. This include being rated water tightness, airtightness, resistance to forced entry, wind load strength, insect screen strength, and ease of operation.

Short and long-term degradation is considered in relation to building life span

Since the building is considered to have a life span of 80 years, the use of aluminum window frame is the best choice since it is durable and able to withstand external forces considering it is a strong material. However, when it comes to energy efficiency, it will mean high costs of bills throughout the life span due to its heating ability and can also nullify the efficiency of glass materials installed.

Use double glazed pane since it has a dramatic increase in the energy efficiency of the window. The two panes can be filled with air between them which acts as insulating property (Kibert, 2016). Therefore, it means the thicker the air space, the more its insulation property.

Fiberglass can also be used as frame option replacing aluminum. It is also a strong and durable material that is resilient to weather with little maintenance and insulation property which will help to reduce the U- factor of the window hence reducing heat gains and heat loss transfers (Kwok & Grondzik, 2018). Moreover, it is aesthetically pleasing both on the inside and outside. Its only disadvantage is that it is expensive. 

Site safety is a major priority when avoiding work place injury cases. When simple precautionary measures and simple procedures are followed, accidents can be avoided or prevented during the building stage. It is therefore the responsibilities of both the employer and employee to work together to comply with the safety guideline stipulated in order to remain safe at any construction site. Construction site safety can be enforced if proper storage and transportation of material procedures; materials testing procedures and safety procedures on-site are followed.

Review of the builders choice of material

With regard to construction, different types of materials have different storage requirements depending on whether they are durable, toxic or non-durable. It is important for the site space to be carefully planned to avoid unnecessary congestion. Construction materials should be stored in a secure area away from site operations. The area of storage should be near the area the material is used to minimize costs and time used to transport them (Li and Yi 2015, p.34). Additionally, construction materials should be stored in a safe area for protection against vandalism and theft. When storing construction materials, items should be stacked properly to prevent accidental fall. The types of materials being stored also need to be taken into account so that specific precautions are taken when handling them. Toxic materials also need to be separated from others during storage to avoid reaction. During transportation of materials, the items should be properly stacked on trucks to prevent fall off that may cause injuries. Secondly, paths should be cleared of obstruction and other tripping hazards.

Apart from storing and safe transport of materials procedures, on-site materials testing procedures should also be kept into consideration. Firstly, materials to be tested should be sampled from the rest and transported to a designated area where they will be tested. Secondly, appropriate equipment for the test should be used to conduct the test. After conducting the test, the materials used should be disposed safely or kept in a safe place for reference. During construction, it is also important to observe safety procedure when handling items. When people observe safety procedures during construction, accidents are minimized greatly. Safety at the construction site can only be achieved when employees are given proper training (Dong et al.2012, p. 312).  Training is a fundamental part that ensures workplace safety. Training reminds workers on construction site safety procedures which further minimize fatalities. Secondly, workers should be supplied with personal protective equipment and clothing. The personal protective equipment prevents them from injuries. It is also vital for workers to ensure proper material storage and handling onsite. This can minimize breakage and further prevent potential accidents. The top management, workers and supervisors should work hand in hand to promote and enforce good practice to ensure that everyone is safe.

Notably, a Material Safety Data Sheet (MSDS) is a crucial document in a construction site. MSDS document entails information on potential hazards and further prescribes how people can work with the chemical product safely (Li & Yi, 2015). The document contains information on storage, use and handling of material in case of an emergency. During construction, MSDS can be useful when dealing with bricks and cement (Li & Yi, 2015). The MSDS gives a guideline on how to package, deliver, handle and store bricks and cement to avoid breakage. Bricks are needed to be stored on a flat surface and avoid direct contact with the surface. This will facilitate proper handling when needed.  

References

Brownlee, A.E. and Wright, J.A., 2015. Constrained, mixed-integer and multi-objective optimization of building designs by NSGA-II with fitness approximation. Applied Soft Computing, 33, pp.114-126.

Dong, Xiuwen S.,Wang, Xuanwen and Daw, C., 2012. Fatal falls among older construction worker.  Human Factors. 54 (3): 303–315. 

Kibert, C.J., 2016. Sustainable construction: green building design and delivery. John Wiley & Sons.

Kotireddy, R., Hoes, P.J. and Hensen, J.L., 2018. Integrating robustness indicators into multi-objective optimization to find robust optimal low-energy building designs. Journal of Building Performance Simulation, pp.1-20.

Kwok, A.G. and Grondzik, W., 2018. The green studio handbook: Environmental strategies for schematic design. Routledge.

Li, R.and Yi M., 2015. Rita Yi Man Li, Construction Safety and Waste Management, Springer 2015. Risk Engineering. doi:10.1007/978-3-319-12430-8. ISBN 978-3-319-12429-2.

Sorgato, M.J., Melo, A.P. and Lamberts, R., 2016. The effect of window opening ventilation control on residential building energy consumption. Energy and Buildings, 133, pp.1-13