How to build it clean and green

2019-12-02T13:13:58+00:00November 28th, 2019|Features|

By Eamonn Ryan

Unfortunately, when it comes to building affordable housing developments so as to be ‘affordable’, many developers continue to build as cheaply as possible rather than employ the number of energy savings practices that drive down the future running costs of the homes for those that can least afford it. Energy bills have increased in the region of 300% over the last fifteen years.

Barry Bredenkamp, general manager for Energy Efficiency at The South African National Energy Development Institute (SANEDI). Image credit: Eamonn Ryan

Barry Bredenkamp, general manager for Energy Efficiency at The South African National Energy Development Institute (SANEDI). Image credit: Eamonn Ryan

“But we are seeing a change,” says Barry Bredenkamp, general manager for Energy Efficiency at The South African National Energy Development Institute (SANEDI), “Home buyers are starting to insist upon it because energy and water costs are becoming unaffordable for the average person.” People are increasingly looking not just at the capital cost of a home, but its running costs, and are demanding a house which has the cheapest possible costs. “Energy saving construction techniques are invaluable, as building an energy-efficient home will not only cut costs in the end, but is environmentally responsible and aesthetically pleasing.”

For the past nine years, developers have had to comply with SANS standard 10400-XA. So, from the moment of building the foundation, the developers should simply adhere to South African national standards. In order for any building to receive a certificate of occupancy, every involved professional from the architect to the builder needs to have complied.

These are not necessarily high-tech solutions but include choice of building materials. It can, for instance, mean the use of high-quality roofing insulation such as polystyrene ceiling boards which might need to be 100mm thick (though by Rational Design it could be as low as 30mm, or roll-on glass wool insulation or blankets. In addition, all hot water pipework is required to be insulated to a minimum of class R1 (‘R’ stands for thermal resistance. The R value depends on the type of material, its density and thickness). In a ceiling, if you have the insulation resting on the ceiling boards, there is a cold void created at night in the roof space. In all areas, particularly in winter, where thin copper piping has been installed without insulation, there will be significant heat losses, and as a result it takes some time to get hot water if some time has elapsed since the previous hot water usage. If insulation is applied to the piping there is almost no noticeable drop in temperature, thereby saving electricity.” He says this can be done not only in new developments, but can be retrofitted to existing homes.

Image credit: SP Energy

Image credit: SP Energy

How to reduce energy consumption on an estate

In this respect, says Bredenkamp, we are seeing a focus among affordable housing developments on a ‘thermal passive’ design which builds in insulation and orientation – in South Africa that would mean being north-facing to maximise light and heat in winter, something which was not a concern for such developments as recently as ten years ago, he explains. “Architects are designing and building according to window building specifications which prescribes how much window area there must be in relation to the total square footprint (or net floor area) meterage. This is to allow more natural light and reduced heat losses and reduces the need for energy-using mechanical lighting and heating.

“In summer, we advise people to practise the low-cost option of keeping the curtains closed from midday to limit the need for artificial cooling.”

While many savings on estates are based on economies of scale due to the number of units, Bredenkamp makes the point that many technologies relating to energy saving have fallen in price to such a degree in recent years – and the cost of energy in turn increased to such a degree – that they are affordable for smaller developments, and even individual homes on a ‘retrofit’ basis. “The pay-back period on such technologies as LED lights is one to three years and they have lifespans of five to ten years. For instance, even a few years ago the payback period for solar heating was over 20 years, and today it is five to seven years and continues to fall on virtually a monthly basis.

“When it comes to building an energy efficient house, the first consideration is the best way to achieve cooling and heating, without ‘money’ evaporating into the air,” says Bredenkamp. He lists the most economical savings as the orientation of the home and insulation at the time of construction, followed by use of LED lighting. If retrofitting a home, he suggests residents at least insulate the ceiling and the first two meters out of the geyser and last two metres into the geyser, convert their geysers to solar water heating and install a geyser blanket.

Solar heating vs heat pumps

Heating water typically amounts to 30-40% of the electricity bill. The time to do these interventions is at the beginning of the design work, so that the best use of energy saving technology is built into the cost of the house.

Many developers have preferences for heat pumps over solar or vice versa, and Bredenkamp is a proponent of solar heating, though he says there’s a place for both technologies. He explains that many of the boasts of heat pumps to save 60% to 80% of the heating bill is achieved under laboratory conditions, ‘all things being perfect’, when the reality is that the coefficient of performance is entirely dependent on the ambient temperature out in the real world. From his experience the actual savings are in the order of 40% to 50%. “The higher the temperature in the area, the better heat pumps work. In contrast, the solar resources of this country are of such an order that solar heating can be installed anywhere and use no electricity.

Another consultant suggests the main reason there are a lot of negative reports on solar water heaters to the effect that they are saving only 20-30% of electrical usage is because the resistance heating back-up is uncontrolled, and because hot water storage volumes are insufficient in relation to daily usage. A Geyserwise timer and heating controller is essential. Hot water storage volumes need to be at a minimum equal to the daily household usage. The amendment of SANS10252 Table 5 to provide storage volumes for solar water heaters has been stalled in the SABS for near on four years. Why?

“The solar thermal (ST) systems provide hot water and the solar photovoltaic (PV) systems generate electricity for the household. Both systems are coming down in costs and payback period (on average, five to seven years), so homeowners should include these systems into the financing at construction stage, rather than as an add-on.

“From an environmentally conscious point of view it’s the way the world is going because it reduces carbon emissions completely, whereas heat pumps reduce it by about half.” The downside of solar heating, also mentioned in The Parks project in this issue [page 22], is that the panels are exposed on the roof and consequently open to vandalism in estates.”

“Otherwise, if you have a SANS-compliant quality product you won’t have to worry about it for at least ten years, and in addition all go through stringent hail-resistant testing. Developers must ensure they buy only from reputable importers, as unapproved versions are pouring across the borders,” says Bredenkamp.

“In comparison to other regions of the world, the use of solar thermal energy is still very low in South Africa, even though solar radiation is one of the highest worldwide.”

“ST systems are well-known in the South African low cost housing market. The majority of the installed systems are thermosyphon systems, relatively small in scale and not needing electricity for a pump or an electronic control, so they can be used without access to the electricity grid.

“PV solar panels absorb and convert sunlight into electricity, a solar inverter changes the electric current from DC to AC, connecting to the house’s wiring. A battery storage system allows for days without sunshine, though this is an expensive option that should be included in the original finance deal.

“The installation of solar systems in the construction of housing developments is certainly a step in the right direction in the fight to conserve natural resources, save money on utilities and combat the negative effects of climate change. The prices of these technologies have reduced significantly over the past three to five years and the technology has come a long way in terms of quality and are designed to last anything from 10 to 20 years,” says Bredenkamp.

Cool surfaces

Cools Surfaces roof coatings, formulated for South African conditions, can reduce internal temperatures by as much as 2°C to 4°C, as SANEDI has proven in large-scale informal housing settlements. “Cool Surfaces refers to all materials and technologies, such as white roofs, light-coloured pavements and specialised cool coatings used in the construction of the building envelope to improve thermal comfort through surfaces that reflect much of the solar energy and release much of the stored heat energy.”

Cool Surfaces are light coloured polymer-based paints or coatings with infra-red light reflecting pigments. They can be used to passively cool buildings, and the energy absorbed is lower than dark coloured materials.

“Reflective roof surfaces not only have an impact on individual buildings but deploying them across a whole community can have a net effect on reducing overall local ambient temperatures in a localised area (the so-called heat island effect). Furthermore, the deployment of reflective materials creates sustainable job and skills opportunities for low skilled workers in both rural and urban contexts.”

Cape Town takes the lead

The City of Cape Town has launched a booklet about resource efficiency to inform residents and developers about the sustainable use of water and energy in our homes and new developments. The booklet also advises on how to consider our natural environment as we are building a resilient Cape Town that can withstand the impact of climate change. It can be downloaded here or from http://bit.do/ResourceEfficiencyCriteriaDevelopmentGuideline.

According to the booklet. “Recent technological advancements in building materials and construction techniques make the process of building an energy-efficient home less challenging. Most energy-efficient homes have several things in common: a tightly sealed thermal envelope; controlled ventilation; high-efficiency heating systems; energy-efficient doors, windows, appliances, and home electronics; and high indoor environmental quality.

“The City’s Energy2040 goals include a 37% reduction in carbon emissions, with 21% coming from energy efficiency. The built environment (commercial and residential) is a large energy user and accounts for approximately 33% of energy consumption and 58% of carbon emissions in Cape Town. Reducing demand and improving efficiency measures through building design principles and practices is of utmost importance.

“The transport sector consumes 64% of energy and accounts for 34% of carbon emissions in Cape Town and provides an immediate opportunity to significantly reduce the City’s emissions. To become a lower carbon, more resource efficient, resilient and equitable city, Cape Town must be remodelled with increased densification and mixed-use in areas of economic activity, with modal shifts to public transport and smarter mobility such as electric vehicles and more efficient private transport through, for example, higher passenger occupancy and flexible working arrangements and increased efficiency in water, energy and waste management, in the use of construction materials and the increased use of renewable energy sources.”

The future

Bredenkamp expects the use of solar heating to become much more ubiquitous in South Africa over the next five to ten years, as renewable energy comes with government support as seen in the recent energy plan which anticipates a big shift from coal to renewables such as solar, though more prominently wind. “From an electricity tariff point of view people will be encouraged to move to solar heating,” he says.

A study published in the Journal of Real Estate Research notes that business owners are showing increasing interest in sustainability and that when browsing for office space, prospective tenants often prioritise buildings with eco-friendly features, high energy efficiency and similar attributes. The study concludes that this is more than a passing trend and constitutes a significant pattern that property investors need to consider. The same will most likely apply to housing.

“Retail malls or commercial properties with lots of under-used roof space are ideal for solar power generation,” says Lance Green of SolarSaver. “Solar installations make particular sense for retailers as they require energy consistently during the day, seven days a week, with demand usually peaking at midday. This mirrors daylight hours when the supplementary energy produced by grid-tied solar installations is available.”

As a result, Green says that SolarSaver has seen strong for solar from the retail property sector. As an example, SolarSaver installed a 250kWp system at Lifestyle Mall in Rustenburg in mid-2018. Since then the system has produced 387 840kWh of electricity, supplementing roughly 20% of the mall’s power needs. SolarSaver has completed similar installations in Cape Town, Johannesburg, Durban and Windhoek.