What is a tall, supertall and megatall building?
Peter Simmonds said: „The definition of tall buildings states: a building with a height of 200 meters is defined as a ‘tall‘ building, a building with a height between 300-600 meters is called a ‘supertall‘ building, and a building with a height of over 600 meters is a ‘megatall‘ building.”
Peter showcased impressive buildings, starting with the three tallest ones: the Kingdom Tower in Jeddah, Saudi Arabia (1 000 m), the Burj Khalifa in Dubai, UAE (828 m) and the Ping An Finance Center in Shenzen, China (562 m). There are more than 27 buildings higher than 600 m, i.e. considered a megatall building.
The use of tall buildings has changed in the last 10 years, and a tall building has many different functions, each function being specific. The modern day description is “mixed use”: the ground level could be retail and food, the first part of the building may be commercial, such as offices and the second part may be residential. And lucrative parts at high levels could be a hotel.
Building envelopes for megatall buildings
As buildings get taller, different climatic effects vary depending on the height of a building. The façade becomes essential not only due to the size of the building but also how it responds to ambient conditions and how it contributes to the heating and cooling loads.
When designing a megatall building, Peter´s team looks at the location and position of the building, what people will see from the building and the façade response to the urban context. The usual task to solve is how much glass they can put in the façade because the building code says 40%, but architects usually want up to 80% of the glass façade. It is also essential to look at the natural daylight factors, the thermal comfort and positioning of the building´s core (where the lifts and building services are), so it does not create too much shading and block too much light. And important is to get the maximum ceiling as possible and focus on efficient HVAC systems.
Many functions of building facades vary greatly in aspects such as heat, air, moisture, light/views, noise and transparency. And façade performance is also vital for energy-efficient buildings and future net-zero buildings.
Peter has put extreme importance to climatic data. „Influence of ambient air temperature on the height of buildings, especially super tall and mega tall buildings, as ambient climatic conditions vary with altitude, and these changes in ambient conditions can seriously affect load calculations and the performance of super and mega tall buildings.”
The biggest single element that many forget when designing tall buildings is the stack effect, i.e. what is the pressure differential within a building. This element is crucial for fire safety, which influences the air movement and the spread of fire. Peter´s team published an interesting Excel tool for stack effect calculation.
Peter introduces steps on how to design and calculate models for tall buildings (all the work to be carried out within 1-6 months of designing, prior construction):
- Step 1: Provide design solutions proposed by the architect, including basic design information, glazing analysis, and calculations to ensure code compliance.
- Step 2: Calculate the external loads per floor for cooling loads verification and compliance with the relevant energy code.
- Step 3: Provide preliminary annual simulation results for building and basic systems.
- Step 4: Confirm load calculations and airflow rates for conventional building systems (VAV, etc.) and proposed systems (active beams, etc.).
- Step 5: Carry out preliminary thermal comfort studies of a typical floor to show the comfort conditions for occupants with an energy code compliant façade and the architect´s proposed façade.
- Step 6: Provide a design document that includes a schematic design basis, outlining the design intent and design criteria for HVAC systems and a narrative of the proposed designs (described in the following chapter).
Indoor air quality, thermal comfort and ventilation in megatall buildings
Peter also focused on ventilation and comfort. „Ventilation and thermal comfort with the required ventilation aspects of tall buildings, especially when exploring the possibility of natural ventilation of spaces such as residential or even offices. The thermal comfort of occupants is also import, not only because of the large number of occupants in these buildings but also for the use of assessing glazing, specific HVAC systems and the use of natural ventilation when assessing occupant comfort.”
Peter stressed the pollution of outdoor air that needs to be taken inside the building. Natural ventilation systems are sound, but sometimes the outdoor air is not as clean; therefore, therefore air filtration with a mechanical system will be necessary based on the location and conditions.
Peter´s recommendations for ventilation are:
- Provide suitable air and quantity for each room or zone.
- Continuously monitor and control the outdoor air delivery.
- Effectively distribute ventilation air to the breathing zone and to multiple spaces.
- If appropriate, use: dedicated outdoor air systems, demand-controlled ventilation or natural & mix-mode ventilation.
According to Peter, thermal comfort can be thought of as a puzzle consisting of the following pieces: dry bulb temperature, humidity content, air movement, mean radiant temperature (MRT), occupants are seated, and clothing may vary.
Peter is an expert in HVAC systems and he talked about several HVAC systems including traditional systems such as VAV, fan coils, underfloor air distribution and displacement ventilation. And he also mentioned some newer trends such as radiant systems (both ceiling panels and embedded systems), active and passive beams (VRV systems, VAV + variable speed fan coils, etc.).
Peter uses spreadsheets for calculations because of the visibility and clarity of the results. Peter said: „Many young people use the software, but they only produce results, but they don’t see behind it.”
At the preliminary stage, the load calculations need to be done with airflow rates for conventional building systems (VAV, etc.) and components such as beams, etc. Temperatures in glazed façade determine important conditions for HVAC systems. Spreadsheets with load calculation and solar transmission for façade performance need to be compared with the local building code. Peter uses a typical floor calculation for a building with multiple floors (tall building) and calculates how much energy it needs to maintain the operating of these floors in respect to the HVAC system.
All about Peter Simmonds!
Peter Simmonds holds a bachelor´s degree in mechanical engineering and in research and development from Reading Technical College, a master’s degree from HTS, Den Bosch, the Netherlands and a PhD from T.U. Delft. He has been a member of ASHRAE since 1989. Peter has travelled and worked around the world with many exciting projects in San Francisco, Hong Kong, London, New York, etc.
Peter is a recognized authority in the field of radiant heating and cooling systems, as well as thermal comfort. Peter is one of the co-authors of the ASHRAE/REHVA Passive and Active Beam Design Guide Publications and the author of the new ASHRAE Design Guide for Tall, Mega Tall and Super Tall Building Systems.
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