P2S Magazine Issue 2 | Page 7

used for daylighting and passive heating . Vertical shading panels can be used on the east and west faces to minimize the heating load in the mornings and evenings . Deciduous trees can also be used to provide shading , as they will help block sunlight during the summer , and permit sunlight during the winter once the trees lose their leaves .
Daylighting Maximizing the use of natural light will minimize the required installed lighting power . Effective daylighting strategies can be used in conjunction with shading and glazing strategies to address tradeoffs between the heating and cooling loads . Natural light can be transmitted to the space through traditional means such as vertical windows , skylights , and clerestory windows ( windows mounted above eye level , which can also be used to release heat ), however , technological advances have resulted in the ability to transmit light to interior spaces as well . Such technologies include solar tubes ( continuous mirror-like tube which transmits light longer distances6 ) and fiber optics7 . Light interior finishes can also be used to reflect more light to the space .
Construction Assembly The construction assembly is the configuration of building components ( windows , walls , slabs , etc .) and how they fit together . An optimized envelope is sufficiently sealed to minimize heat transfer and air infiltration8 . Heat transfer via conduction can be reduced by minimizing window framing , not exposing slab edges to the ambient air , and including continuous insulation in walls to serve as a thermal break and also providing an air barrier , which reduces air infiltration . Air infiltration can be further reduced by sealing any adjoining components , especially moving components such as doors and operable windows .
Thermal Insulation In addition to the placement of insulation in the construction assembly , insulation with a high thermal resistance ( R-value ) should be selected . Continuous insulation should be considered to eliminate thermal bridging . Effective R value of total construction assembly can be significantly increased using continuous insulation9 . Buildings located in areas with wider temperature variances from comfort conditions ( 70- 75 ° F ) will realize more benefits with a higher R-value . The thermal performance of rooftops in cooling climates can be further optimized by including a coating which reflects sunlight ( known as a “ cool roof ”), or installing vegetation on the roof ( known as a “ green roof ”), which provides additional insulation , assists in rainwater control , and reduces the heat island effect1 .
Natural Ventilation and Passive Cooling Wind , natural airflow , and temperature gradients can be used to cool a space by maximizing the cross-sectional surface area that is perpendicular to the prevailing winds during the summer 10 . This use of cross-ventilation is most effective if there is a temperature differential of at least 3 ° F and an adequate wind pressure gradient1 . Stack ventilation and solar chimneys use natural convection to move warm air towards the upper elevations , which then pulls colder air at the lower levels . The movement of air will be maximized if the exhaust is sufficiently high above the inlet . One consideration that should be made in the implementation of natural ventilation is the local air quality and presence of noise .
Passive Heating and Cooling Examples of passive heating and cooling mechanisms include direct gain using thermal mass , indirect gain using Trombe walls , and isolated gain using double envelopes 11 . A thermal mass is a building feature that is large in volume and is composed of a material which can adequately absorb heat energy ( high specific heat capacity ), store heat energy ( high density ), and slowly release heat energy ( moderate thermal conductivity ) 12 . Thermal mass can be used to slow the transmission of heat such that it is not released to the space during the day when the ambient air is warmer , but rather releases it to the space at night , when the ambient air is cooler and the space must be heated . It is the most beneficial in areas which experience large temperature swings between the day and night . A Trombe wall is a dark , south-facing wall that has a thermal mass and is covered with glazing . A small airspace between the wall and glazing traps solar radiation and serves as a small greenhouse 13 . Phase change material ( PCM ) is an engineered thermal mass , which absorbs and releases thermal energy during the process of melting and freezing . When a PCM freezes , it releases a large amount of energy in the form of latent heat at a relatively constant temperature 14 . Night ventilation of thermal mass can be utilized to passive cool or heat a building if diurnal temperature at the site is around 20 ° F .
Conclusion The architectural building features described above show that the reduction of building energy use extends far beyond specifying highly efficient pumps and fans or including LEDs in the lighting design . Given the high impact of building design on the heating , cooling and lighting loads , it is imperative that all disciplines be involved in the development of early building design concepts , including the building owner , architect , engineers ( structural , mechanical , electrical , plumbing , technology ), and the future building managers and operators . This integrated approach will provide the highest likelihood of success in the execution of a ZNE building .
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