Certainly, over the last 30-40 years the world has become more concerned about the carbon footprint we all leave when we travel or as we go about our daily lives. We worry more and more about emissions and the ozone layer and the effects on the earth’s climate.
Yet, it’s only relatively recently that more focus has been put on the buildings we construct, the materials we use and the overall impact on the world’s environment. Most modern buildings last for a very long time. So, it’s not only the construction phase which needs attention, but the impact of the operating building for the duration of its lifespan.
There’s a lot of talk about striving for net zero carbon contributions in BtR development but what exactly does this entail, and just how is such a goal to be achieved?
Well, let’s have a closer look at what achieving net zero for BtR buildings means.
What is “net zero carbon contribution”?
“Net zero” means achieving a balance between the greenhouse gases put into the atmosphere and those taken out. This state is also referred to as carbon neutral. On the other hand, zero emissions and zero carbon are slightly different, as they usually mean that no emissions were produced in the first place.
In order to meet the 1.5°C global warming target in the Paris Agreement, the aim is to have global carbon emissions at net zero around mid-century, although for some of the major industrial nations such as the UK, the target date is earlier.
When considering net zero in respect of buildings and the construction industry, net zero can be thought of as in two distinct parts:
- net zero during construction means the amount of carbon emissions associated with a building’s construction stages up to practical completion must equal zero or be negative. This can be achieved by using offsets or the export of on-site renewable energy, ie by exporting surplus unused energy back to the grid;
- net zero during the operational phase of the building necessitates identifying the key processes and building elements which will support the delivery of a carbon neutral building. This may include using renewable, or low carbon heat, and designing for disassembly to reduce embodied carbon at the end of the life of the building.
A net zero carbon building is highly energy efficient and powered from on-site and/or off-site renewable energy sources, with any remaining carbon balance offset. In short, the Whole Life emissions of the building need to be considered.
Example of a new BtR project
In the UK, there are a number of new BtR projects which are adopting net zero principles in construction and for its operational or Whole Life phase.
One of the higher profile projects is Cardiff’s new Transport Interchange. This is a mixed-use scheme of 318 BtR apartments, a new central bus station, a 249-space car park and 120,000sq ft of offices is well underway. The Transport Interchange is part of the larger Central Square development scheme providing over 1 million sq ft of mixed-use property, forming a new commercial business district adjacent to Cardiff Mainline Station.
What are the processes?
Following design standards is the primary step in the design to achieve a net-zero energy building. It is important to define the sources and inputs that would be necessary to quantify the outputs and check what is required to balance the net-energy consumed.
The next step would be to simulate energy consumption using various energy modelling techniques and tools to optimise the following:
- building orientation;
- glazing areas, exposure and shading;
- heat island reduction;
- lighting systems and capacities;
- temperatures, humidity, and relative humidity levels;
- landscaping;
- natural resources;
- overall system efficiency;
All of these factors need to be considered together by employing passive heating or cooling strategies, such as solar chimney and direct heat gain through south-facing glazing and/or isolated gain or sunspace. All possible exterior wall construction that avoids thermal bridging and increasing the R-value in all roof construction needs to be considered, as well as using efficient lighting systems and so on.
Overriding principles
Going back to the example, in the Cardiff BtR project, the designers would have followed three overriding principles to achieve an effective net-zero energy building design:
Building envelope
The building should be oriented to minimise HVAC loads, and shades and overhangs used to reduce any direct sunrays. To reduce the heat gain through windows, the designer would try to avoid glazing on the east/west façade as well as increase insulation on opaque surfaces, use glazing with low solar heat gain coefficient values, use a double-skin façade, and refine the building envelope to suit locational conditions.
Daylighting sensors and occupancy sensors, plus energy-efficient office equipment for commercial buildings and energy-efficient utilities for the BtR component would also be incorporated.
A life cycle analysis would be prepared having regard to forecast occupancy levels.
Energy efficiency
The most important factor should be to select correctly sized systems for the building.
This would be achieved by following ASHRAE Standard 90.1 safety factors in the design, applying factors to reasonable baseline cases, and using modelling simulation to design and predict the optimised requirements.
Part load performance would be considered when using variable volume systems, variable capacity: speed drives, boilers, chiller and pumping systems. In addition, the designer would plan to use high-efficiency lighting and control systems such as LED lights, high-performance ballasts, dual circuited task lighting, occupancy and daylighting dimming sensors.
The commissioning phase which starts at the end of the construction phase will verify that the building’s energy-related systems are installed and calibrated. They need to be ready to perform to the owner’s project requirements, basis of design and construction documents. This phase should cover at least the HVAC systems and controls, lighting and daylighting controls, domestic hot water system and any renewable system such as wind and solar.
Building commissioning can reduce energy use, lower operating costs, reduce contractor call backs, and improve occupant productivity and yield 5–10% improvement in energy efficiency.
Renewable energy
Renewable energy measures are relatively expensive, so designers need to optimise their initial design in order to reduce such renewable energy requirements.
There are various renewable energy resources which may be considered, such as solar systems which can be used for generating electricity, storing energy, and heating water.
Wind systems provide energy at a very effective cost if the wind is continuous and steady with a speed above 10 mph (4.47 m/s), although above 25 mph (11.2 m/s) is better.
Biomass systems can provide heat by burning biomass material such as material from forests, urban tree pruning, farming wastes, wood chips, or pellets. However, the burners usually require more frequent cleaning than other heat sources.
Final thoughts
More than often the greatest changes occur once something becomes more meaningful to us.
With investment flooding into the BtR market over the last 18 or so months it is time that the BtR sector embraces its role as leaders in the UK property sector.
Instead of focussing on getting a return on investment as quickly as possible the market needs to review how it can use this mini boom to truly make a difference to what we are contributing to our cities and planet!
Subscribe
Every Friday we send an email with that weeks published posts. Subscribe to our weekly newsletter to make sure you don’t miss a thing.
