• Which factors should be considered during HVAC planning? How does design process work with these factors?
There is almost a whole book on the practice of environmental design and engineering embodied in this seemingly harmless question!
The most important thing to us as designers at Atelier Ten is a building cannot be designed to be environmental without a keen understanding of the context and climate. In the 20th century, the so-called ‘international’ style of architecture become the new norm as the rapid development of mechanical building services liberated architecture from needing to be the sole controller of the environment. More advanced building services allowed architects to design buildings without a thought for their orientation to the sun and the wind or to external temperature and humidity. The volume of space, regularity and flexibility (and the expulsion of ornament) were the by-words, not comfort or efficiency and for the most part, the ‘international’ style of building did not advance either.
So, we always start with site context and external environmental conditions when looking at new projects. The other key aspects of briefing for the HVAC planning are of course function / activity and usage pattern. Although we should always strive to make the built form have some aspect of ‘long life loose fit’ (A. J. Gordon, 1972) the systems almost always need to be tailored to the building and function they are serving.
The design process for HVAC in buildings is very similar to any other design process. It requires briefing, research, conceptualisation, integration, collaboration and ultimately delivery in that sort of order. There are often / usually iterative loops along the way – one rarely lands first time on the final answer.
• Are there natural solutions applicable to HVAC like considering maximum utilization of daylight for lighting?
All design should be rooted in an understanding of the importance of natural systems. In some situations, this is taken to mean natural ventilation and natural light but where completely natural systems are not possible it also references the fact that the human body performs better when in harmonious, natural or biophilic surroundings.
So, whenever we can we design to maximise the availability of natural light to occupants, appreciating always the balance with excessive heat gain, glare and excess light at the perimeter of buildings. Where possible we always aspire to naturally ventilate buildings, in the UK this is typically in the spring and autumn (we aim to conserve in the winter and manage heat in the summer) through the planning of floor plates and locating windows appropriately. We also try and use the density and conductivity of materials to manage temperature by activating thermal mass.
All of these strategies can be seen in the design of our headquarters building for the WWF in Woking, UK – completed in 2012 the building is designed around providing exceptional daylight in the workplaces, natural fresh air and night cooling for summer comfort.
Life, air quality, oxygen, CO₂ are all in the control of the designer and these days this is one of our main areas of work with architects, clients and design teams as we move away from the ‘sealed box’ as an architectural type.
• How should ‘passive climatization’ be defined and how should this method be used and applied?
Passive climatization we define in a few ways. It is the work that the building façade / envelope does to mitigate the worst of the external climate variations through insulation and glass performance. It is also recognised as some of the internal climate control strategies that make a building comfortable. Mainly good light, natural ventilation and thermal mass.
Some purists would say that a ‘passive’ control system would have no active parts – fans or pumps for example. I would argue that a nominally ‘passive’ building can still use fans and motorised control dampers and shutters to achieve the desired effect and reduce energy demands. As an example of this, I would cite the labyrinths that we have been involved with at several locations around the world. The labyrinth at the Federation Square in Melbourne, for example, is made up of a series of concrete walls arranged as part of a low-velocity air supply system. The air is driven through the labyrinths by a fan which does use some energy, but the labyrinth replaces a much larger energy user – the chiller – and stores night-time ‘coolth’ for release next day to replace mechanical cooling. This we would still call ‘passive’ climatization.
• Which materials and methods should and how to be used for energy saving by thermal insulation of buildings? To what extent are these materials efficient?
There are so many options for insulation buildings in different situations and so it is difficult to say what is best. Where possible we try to use a material with low embodied carbon / energy to do the insulating job. Sheep’s wool, recycled newspaper, and wood-wool all have a good environmental footprint but usually require a greater thickness than insulating materials made for blown foams which have a greater thermal resistance. At the extreme end of the options are materials like nano-gels (which have been used on the International Space Station) which are super-insulating with minimal thickness.
Materials and systems resist heat transfer by a combination of conduction, convection and radiation effects and the best insulation systems use a combination of all three in order to deploy the minimum amount of material.
With many modern buildings, it is the insulating properties of the glass that comes under the most scrutiny. A window can have literally hundreds of different properties depending upon the number of panes, the extent of tint, type, and position of coatings and type of cavity fill (or vacuum). The challenge is to achieve the right balance of visible light transmission, solar heat transmission, and thermal conduction to suit the location of the building and orientation of the window.
The glazed roofs at Gardens by the Bay allowed 65% of the visible light to be transmitted but less than 35% of the solar heat gain by the use of coatings that are invisible to the human eye (in the infra-red spectrum).
• Please evaluate integration of HVAC systems to sustainable buildings and renewable energy technologies?
As we work towards ‘net zero’ buildings there is an imperative to reduce the demands on infrastructure to the absolute minimum by designing well integrated high-performance building envelopes and systems. There might include mixed-mode ventilation systems (described above), earth ducts or labyrinths, heat pumps and great daylight to minimise reliance on artificial light.
Once the loads have been reduced to a minimum, the remaining demands can be met from low carbon or renewable energy systems. For the most part, we tend to use solar hot water or solar photovoltaic systems as our main renewable system in urban areas. Wind turbines tend not to be effective due to turbulence of the air patterns.
At the Kohler Environmental Center in Connecticut, USA the building has been designed to achieve net zero in operation by a combination of very low energy environmental design and a significant PV system in the adjoining landscape.
• What is the role of building shell in natural ventilation or what should it be according to you?
For buildings to successfully naturally ventilate in all seasons it is important that the planning of the rooms and spaces will somehow relate to wind direction and for the most part, at least, be set out to encourage the cross flow of air from side-to-side. Single-sided ventilation is only really effective for a relatively shallow space and the air inside a deep space with ventilation from one side only will tend to stagnate and get hot. The depth of space that can be effectively naturally ventilated tends to be a function of height and a tall space will tolerate a much greater spacing from the inlet to the outlet then a lower one will.
Even with two-sided ventilation, there are limits on the distance between inlets and outlets, the rule of thumb being that the distance from window (vent) to window (vent) should not exceed five times the height of the space. Natural ventilation is
driven by momentum effects (known as cross ventilation) and driven by the pressure differences caused by wind on the façade and by temperature / height effects (known as stack ventilation) and driven by temperature differences. The former tends to be the dominant force, except on very still days.
There are many modern buildings that have integrated vertical stacks to encourage natural ventilation, these very much mimic vernacular building types and the idea is to increase the amount of airflow in the centre of a plan to allow windows to be further apart, by introducing a route to the outside vertically.
We have worked on many naturally ventilated buildings going back to the breeze chimneys at Wood Green Community Mental Health Centre in the early 1990s. The WWF headquarters (2012) with Hopkins Architects has many of the characteristics discussed above.
Finally, there is an increasing trend to integrate operable ventilation panels alongside windows to allow secure ventilation of rooms even when unoccupied and at night when great benefit can be derived from passive cooling in many climates.
• HVAC is one of the most important elements of comfort. Also offering aesthetical solutions is a necessity. How does functionality which provides comfort and aesthetic appearance balance?
Like almost everything else in the world of architecture and construction, there is no right or wrong answer when it comes to aesthetics. Bluntly put, an ugly space need be no less comfortable than a delightful one, though we of course always
strive for delight!
These days there is an increasing tendency to do away with ceilings and have all of the services on display. This can either look a terrible mess or be highly organised. BIM is helping all members of the design team understand clearly in three
dimensions what this is going to look like.
But there are still many situations where there is a desire to keep the HVAC services more invisible. In the Flower Dome at Gardens by the Bay in Singapore, we went to great lengths to make the services very discreet. The concrete pathways conceal many miles of piping that is used to remove the heat from incident solar radiation to reduce the apparent heat gains into space, while air is delivered from ‘drums’ built into the flower beds and linear diffusers built at low level into planter walls.
So, generally, the idea is that aesthetics should not compromise comfort through the design of HVAC system. They can coexist – beautifully.
• How are HVAC solutions different depending on the kind of project? For instance, how are these solutions varied in housing and commercial spaces?
Many of the components of an HVAC system are common to all types of building from housing to office to museum but the way in which they are deployed differs greatly from typology to typology as a function of climate, occupancy, loading, zoning and aesthetics. A treatise on the differences would not make great reading but it basically falls to the engineer to determine in each situation and climate how the context and usage will impact the selection of systems.
The basic ‘boxes’ that form the systems – boilers, heat pumps, chillers, pumps, cooling towers, air handling units and so on, will recur in most types of building in some form or matter.