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Gifford Studios
Published in George Baird, Sustainable Buildings in Practice, 2010
An air-to-water heat pump (38.5kW heating; 51.0kW cooling) located in a compound near the south-west corner of the building serves the studio spaces via pipework in the raised floor system – this has a dual function, acting as an underfloor heating/cooling system, and tempering the air supply to the spaces (see later). A gas-fired 120kW condensing boiler system, located in the lower ground floor, is used to heat conventional radiators in the non-studio spaces as well as serving the domestic hot water system. This allows for the different load patterns and requirements of the two types of spaces. A mixed-mode ventilation strategy is used comprising very low energy mechanical ventilation system and occupant-controlled supplementary natural ventilation. The mechanical system uses low pressure fans mounted in the floor cavity and pulling outside air in through the cedar cladding [Figure 8.10]. The floor voids act as supply air plenums and the fresh air is distributed into the space through floor mounted swirl diffusers [Figure 8.9]. [The 100 per cent fresh] supply air is unfiltered but tempered in the floor void … Occupants are able to open toplights in the ground floor windows and a proportion of the rooflights [Figure 8.7], providing the facility for free additional cooling through natural ventilation in intermediate seasons.(Pettifer, 2004)
Mechanical and Mixed-Mode Ventilation in City Centre Buildings
Published in Dejan Mumovic, Mat Santamouris, A Handbook of Sustainable Building Design and Engineering, 2018
Jarek Kurnitski, Olli Seppänen
Mixed-mode ventilation combines mechanical ventilation with the use of natural driving forces. When stack effect or wind pressure differences are available fans are no longer operated. Mixed-mode systems are either low pressure fan assisted mechanical systems or two mode ventilation systems operating mechanical ventilation or natural ventilation depending on conditions.
Case Studies
Published in Antony Wood, Ruba Salib, Natural Ventilation in High-Rise Office Buildings, 2012
A “zoned” mixed-mode ventilation strategy (where occupied office spaces are air-conditioned and public/circulation zones are naturally ventilated) could be very suitable for tall buildings in places that experience hot and humid climates. Occupants tend to have less temperature demands in a circulation space as opposed to a working space.
Performance analysis of transparent BIPV/T double skin façades integrated with the decision-making algorithm for mixed-mode building ventilation
Published in Architectural Engineering and Design Management, 2023
Prapavee Karunyasopon, Dong Yoon Park, Duc Minh Le, Seongju Chang
Mixed-mode ventilation or hybrid ventilation in buildings utilizes a combination of natural ventilation and a mechanical system (HVAC). In automatic control systems, sensors, and window actuators, along with control algorithms, respond to outdoor and indoor space conditions in real-time. Natural ventilation provides passive cooling or passive heating by introducing fresh air to the cavity or an indoor space. However, there are weather constraints and environmental conditions that must be factored in when applying natural ventilation mode (Chen et al., 2018). Mechanical systems can be shifted to operate when natural ventilation mode is not sufficient or suitable. With its reduction of mechanical fan use, mixed-mode ventilation can create sustainable buildings, diminish energy demand, and save energy costs, while maintaining thermal comfort for occupants (Berkeley, 2018). Even though natural ventilation is a preferable operation mode, not all periods and climates are advantageous for this ventilation strategy. Therefore, the optimum control achieved by the mixed-mode ventilation strategy is needed to maintain an adequate level of indoor air quality and avoid building tendencies to overheat (CIBSE, 2005).
Regulating window operations using HVAC terminal devices’ control sequences: a simulation-based investigation
Published in Journal of Building Performance Simulation, 2022
Weihao Liu, H. Burak Gunay, Mohamed M. Ouf
People spend over 90% of their time in buildings, and a large fraction of energy consumption in buildings is dedicated to maintaining their thermal comfort and indoor air quality (Wang et al. 2018). It is reported that nearly 60% of the total energy consumption of buildings in Canada can be attributed to space heating and cooling (Natural Resources Canada, [Online]). Mixed-mode ventilation is a design feature introduced to reduce energy consumption without compromising indoor air quality (Brager and Baker 2009). It is a system that can manually or automatically shift between mechanical and natural ventilation (Wouters et al. 1999). It can also operate in different modes, such as concurrent and change-over modes, to satisfy various demands from certain zones in a building (Brager, Borgeson, and Lee 2017). The concurrent mode refers to the ventilation mode in which mechanical and natural ventilation are provided in the same space simultaneously. In contrast, the change-over mode allows the systems to alternate completely between mechanical ventilation and natural ventilation for a thermal zone or even for the entire building (Salcido, Abdul, and Issa 2016). Extensive research has shown that mixed-mode ventilation buildings have considerable energy-saving advantages over mechanical ventilation buildings (Salcido, Abdul, and Issa 2016; Wang and Greenberg 2015; Brager 2006) while receiving higher satisfaction rates from occupants regarding thermal comfort and indoor air quality (Rowe 2003; Ackerly, Baker, and Brager 2011). As a result, mixed-mode ventilation has gained popularity over the past decade.
Modeling window and thermostat use behavior to inform sequences of operation in mixed-mode ventilation buildings
Published in Science and Technology for the Built Environment, 2021
Weihao Liu, H. Burak Gunay, Mohamed M. Ouf
Prior to the 1950s, only 2% of North American buildings were equipped with mechanical ventilation (Biddle 2008). Natural ventilation was the primary approach for cooling and maintaining indoor air quality. With the widespread use of mechanical ventilation in commercial buildings in North America, thermal comfort was improved compared to naturally ventilated buildings (Drake et al. 2010). However, mechanically ventilated buildings had much higher energy consumption, largely due to over-ventilation in low occupancy sections of a building. Further, indoor air quality issues (e.g. “sick building syndrome” in the 1970s) began arising more frequently, particularly where occupants formed large and dense clusters within parts of buildings (Brager, Borgeson, and Lee 2007). Consequently, local building codes and guidelines have been constantly updated to ensure acceptable indoor air quality. Aiming to achieve the higher goal of balancing indoor comfort and energy consumptions, mixed-mode ventilation has gained much popularity in the past years. Mixed-mode ventilation, also known as a hybrid ventilation system, combines mechanical and natural ventilation (Brager, Ring, and Powell 2000). It was described by Wouters et al. (2000) as a system that can manually or automatically shift between mechanical and natural ventilation to reduce energy consumption and improve comfort. It was found that 17% to 47% of heating, ventilation, and air-conditioning (HVAC) related energy savings can be achieved through mixed-mode ventilation (Wang and Greenberg 2015). In terms of indoor thermal comfort and air quality, mixed-mode ventilation buildings also tend to receive higher occupant satisfaction compared to mechanically ventilated buildings (Brager and Baker 2009; Rowe 2003; Ackerly, Baker, and Brager 2011).