a guide to XA

Bio-Dynamic Lighting

Up until recent times, it was believed that light was only needed for seeing. However, in 2001, American scientist, Brainard, discovered a circadian photoreceptor in the retina of the eye, that receives a specific quality and quantity of light, which sets the biological clock.

He discovered that light not only provides us with the ability to see, but that light enters the eye via the ‘fourth pathway’, which has a vital non-visual or biological effect on the human body. His studies show that a certain quantity and quality of light stimulates the biological clock, also known as the circadian rhythm, which regulates hormone levels, particularly melatonin and cortisone in the body.

Bio-dynamic lighting is a technical method of achieving the biological effects of daylight in an artificial lighting environment. This method of lighting mimics the cycle of natural daylight, changing colour temperature and intensity throughout the day. In very simple terms, it is brighter and whiter in the morning and dimmer and warmer in the evening – but there is far more to it than simply changing the colour and intensity of the light.

Bio-dynamic or circadian lighting is most often used in a healthcare or office environment, although it has started to become popular for general residential lighting as well. Our biological clocks are genetically preset to work with the 24-hour cycle, but we need to re-synchronise daily through exposure to daylight, or to artificial light designed to replicate daylight. This synchronisation helps regulate the levels of the hormones melatonin, cortisol and serotonin, all crucial elements in keeping our biological systems in balance. If exposure to daylight is missing, sleep disorders, chronic fatigue and/or depression can follow.

Bio-dynamic lighting should be considered for any environment in which people spend a significant amount of time without getting regular and prolonged exposure to daylight. Many offices and healthcare facilities fall into this category, as well as all types of buildings in countries that experience extended periods of darkness during winter such as those in the extreme northern latitudes.

Read more about it all HERE

Understanding Sisalation

Everything has an emissivity value, your clothes, a table… for example, cast iron has an emissivity of .85 which means that 85% of heat that comes in contact with its surface will pass through/into it.

Aluminium has a natural low emissivity value of just .03… This means that aluminium will only allow 3% of radiant heat that comes in contact with its surface to pass through it, the rest will be reflected back to the source.

Most common thermal insulation materials (like Mineral Wool or Extruded Polystyrene) work by slowing conductive heat flow, but reflective insulation works a little differently as this type of insulation is designed to reduce radiant heat gain.

When the sun heats a roof, it is primarily the sun’s radiant energy that makes the roof covering hot. Much of this heat travels by conduction through the roofing materials to the inside of the roof. The hot roof material then radiates its gained heat energy (infrared energy) onto the cooler roof and dwelling spaces.

Reflective foil insulation thus reduces the radiant heat transfer from the underside of the roof to the other surfaces in the dwelling helping keep any home cooler and more comfortable. Reflective insulation and radiant barriers of course work well in warm climates like KwaZulu Natal or Mpumalanga or anywhere that has high solar irradiance levels.

Foil insulation depends (essentially) on an air gap of 20-30mm between itself and the roof, or any other insulatory or building material below it, in order for its low emissivity surface functionality to be effective otherwise the radiant heat energy will just bridge (conduct) across regardless into any nearby material and make the foil insulation redundant. A layer of dirt or dust on the top of any foil will also greatly reduce the effectiveness of reflective foil insulation (can reduce its effectiveness four-fold!) so one always needs to consider how the effectiveness of the material might deteriorate over time.

When installed correctly, reflective foil insulation may significantly reduce the amount of radiant heat transfer into the roof space, which in turn will affect the overall temperature in the living spaces below. Sisalation works better the lower the roof pitch with a roof at 45 degrees having about half the effectiveness as a roof at less than 10 degrees. The effectiveness of sisalation is not a constant and is still regarded in many countries with some skepticism.

It is important to realise that sisalation (any foil faced insulation) does not have a R-Value… the scientific effect of the low emissivity functionality is commonly however translated into a R-Value equivalent so that we can more clearly calculate the product’s contribution in our roof detailing and specifications. That (hypothetical) R-Value however assumes that the product is installed correctly and has the required minimum clear air space above and below it.

Foil insulation can be installed separately and in combination with bulk thermal insulation, or as a single combined product, such as Isover Factorylite or Factoryboard, or foil-faced Isobard, etc.

In the South African context, depending on the pitch and nature of the roof, sisalation can contribute up to about 17-30% of the required total insulatory R-Value but it is never sufficient on its own without additional insulation over ceilings or incorporated into the rafter build-up. Careful thought and competent consideration is certainly required to ensure that any proposal will in fact do what it is intended to achieve.

Understanding Emissivity

The ability of a material to radiate energy is known as emissivity. In general, highly reflective materials have a low emissivity and dull darker coloured materials have a high emissivity. Low emissivity (low-e) refers to a surface condition that emits low levels of radiant thermal infrared (heat) energy.

Surface emissivity is the amount of infrared energy emitted by a specific material and is often expressed as a ratio or percentage of “1” with the “1.0” value being a perfect “black body”. A material that emitted heat energy at half that rate, like polyester film, would have a rating of .50 or 50%.

Objects like aluminium or copper, with low surface emissivity (low-e) do not transmit/radiate heat well because most of the infrared energy is reflected instead of absorbed. Aluminium (shiny foil faced sisalation) only absorbs around 3% of the radiant energy hitting it, reflecting the other 97% away from its surface.

In the insulation industry, surface emissivity is a major factor in the effectiveness of any product, yet one often overlooked and overshadowed by thermal conductivity or “k values”. Both are important in that they address different methods of heat transfer (infrared radiation vs conduction) but in some applications, like roof insulation in warm climates, infrared radiation plays a bigger role than conduction, and low surface emissivity is key.

Low-emissivity coatings (silver or tin oxide) are also used to minimise the amount of ultraviolet and infrared light that can pass through glass without compromising the amount of visible light that is transmitted. All materials, including windows, radiate heat in the form of long-wave, infrared energy depending on the emissivity and temperature of their surfaces. Radiant energy is one of the important ways heat transfer occurs with windows. Reducing the emissivity of one or more of the window glass surfaces improves a window’s insulating properties (albeit minimally in the greater context of holistic whole-building performance).

Low emissivity products are also useful in roof insulation by minimising the amount of infrared energy that is radiated downwards into roof spaces and into the habitable spaces of dwellings. Sisalation is a product that we are familiar with in the South African context although foil-faced insulatory products are commonly used worldwide (Kingspan, Celotex, etc).

Solar Horizontal Irradiance across South Africa:

The truth about low-e glass

In colder climate locations single-glazed low-e glass can sometimes be used to reduce heat loss in winter. Normal clear glass allows most of the heat radiation coming from inside your house to pass through to the outside. By using low-E glass this radiant heat is largely reflected back into the room, thereby reducing heat loss through windows.

Low-e glazing can also reduce the amount of the sun’s heat and UV light coming in through the windows and thus reduce overheating and fading of furnishings in summer but can also reduce the amount of free passive heat your house can soak up in winter.

BRANZ research (New Zealand) shows low-e glass can reduce heat loss through single glazing by up to 25% (in a super cold winter climate zone), and this can be a useful statistic for making it seem like the product has tremendous value in a South African (or any general) context. The truth for us however, substantiated through our now four years and hundreds and hundreds of real-time local-specific building science analysis, is that on a well-designed (optimally shaded) dwelling fenestration actually plays a very small part in the holistic gain and loss of heat.

In a warm climate zone like Durban or Nelspruit the use of low-e glass might only influence the holistic performance of any moderately glazed dwelling by perhaps 3-5 % overall. So the reality, translated into real-term values, is that a client might invest a R200,000 capital cost overspend (over rather just using single-glazed clear glass) for a meagre R1,400 per annum operational cost saving on hypothetical heating and cooling. So that gives the capital investment a 143-year payback period before it is even able to pay for itself and substantiate its cost!

In a colder winter climate zone like Johannesburg, Pretoria or Cape Town the use of low-e glass might only influence the holistic performance of any moderately glazed dwelling by perhaps 5-9 % overall. So the reality is that a client might invest a R200,000 capital cost overspend (over rather just using single-glazed clear glass) for a meagre R2,500 per annum operational cost saving on hypothetical heating and cooling. So that gives the capital investment an 80-year payback period before it is even able to pay for itself and substantiate its cost!

On the downside (aside from the substantial cost) single-glazed low-e windows can also suffer from increased condensation which then largely negates the effectiveness of the low-e coating. As the coating reflects heat, the glass itself becomes colder and condensation is more likely to form on your windows. Like condensation on a bathroom mirror, the condensation means the glass surface is no longer reflective. While condensation is present, the low-e surface provides very little benefit over normal glass. Once the condensation has dried up, the performance of low-e window film is restored.

Low-e glazing falls into two broad categories: soft coat and hard coat. Both applications involve depositing a thin, transparent coating of silver or tin oxide on the glass surface to allow short-wavelength sunlight to pass through while blocking long-wavelength heat radiation. The difference between the two coatings lies in their application, which affects the glazing performance and durability.

Soft (or sputtered) coat: is the most common type of low-e glazing. In this application, the layer of silver is deposited onto the glass through a sputtering process after the glass has been manufactured. Although it provides the best U-value available, this type of coating is fairly delicate and has to be protected within an insulated (double-glazed) glass unit to prevent scratching.

Hard coat: Added during, rather than after, the manufacturing process, pyrolytic or hard-coat low-e glazing incorporates a thin layer of tin oxide into the glass while it is still hot. Applying the tin at this stage welds it to the glass, resulting in a more durable coating. Hard-coat glass can be used in single-glazed windows with better resistance to scratching but their emissivity is not as low as that of soft-coat glass. Because the glass has a higher solar heat gain coefficient (SHGC) it works well for houses that rely on passive solar heating.

Low-e windows may generally also block radio frequency signals so buildings without distributed antenna systems may then suffer degraded cell phone reception.

In summary, given the relatively low impact that fenestration has been shown to play on holistic building performance in the South African context (3-9% of holistic building performance), single-glazed clear glass is always the substantiated (cost vs return on performance) optimised building solution given the substantial capital cost saving (and paltry return on performance) that can rather be invested into items that do indeed rather provide a real bang for your clients buck (LED lights internally or a most efficient hot water heating system).

The key to great architecture remains vested in great architects designing great architecture by getting their first design principals correct… back to basics… shading is king… optimally placed shading from screens, verandas and roof overhangs to keep high altitude sun out of windows and off the thermal mass of walls in summer yet still indeed permitting solar ingress for passive warming of buildings from low altitude winter sunshine.

On my soapbox I will forever provocate that Regulations and legislation should encourage great architecture, not hinder it. Competent rational design energy modelling with a thorough location and altitude specific analysis of how any building design might perform is thus an invaluable vehicle for ensuring that optimised cost and energy efficient architecture is ensured for your clients.

Let great architecture be king…!

Why SANS 10400 XA is important

In April 2014 atmospheric carbon dioxide levels exceeded 400 parts per million for the first time in recorded history. The readings are taken hourly at Mauna Loa in Hawaii and updated daily on the NOAA website and as of 11th January 2018 are already at a value of 408.74 ppm

The “Keeling curve,” overseen by Scripps, is the longest continuous record of CO2 measurements. The measurements were started in the late 1950s by Charles David Keeling on the Mauna Loa volcano on the Big Island of Hawaii, accepted as being fairly representative of the level of CO2 around the world.

Increasing amounts of CO2 and other gases caused by the burning of the oil, gas and coal that power the planet are enhancing the natural “greenhouse effect,” causing the planet to warm to levels that climate scientists say can’t be linked to natural forces. Interestingly (worryingly) despite worldwide reductions in carbon emissions through legislation, the carbon content in earth’s air is continuing to rise!

Carbon dioxide levels were about 280 ppm before the Industrial Revolution, when humans first began releasing large amounts into the atmosphere by burning fossil fuels. When Keeling first began his measurements in the 1950’s, the amount of carbon dioxide was 316 ppm.

In direct relationship ocean acidification is also on the rise. It’s estimated that ocean acidity levels have increased by as much as 30 percent as a result of our fuel burning activities.

C02 is also produced by plants. CO2 levels peak in the northern hemisphere spring when plants come alive, then drop when the plants die in the autumn.

By us South Africans reducing the energy consumption utilised in the new properties we design we reduce the damage/ impact caused by the amount of coal that ESKOM has to burn, and the amount of carbon thus released into the atmosphere, in order to produce electricity. Of course all this could be mitigated in an instant if the Government implemented an agenda for more solar or wind farms rather than archaically burning fossil fuels to generate power!?



Sizing Heat Pumps

In order to ensure that the heat pumps you specify will perform adequately all year round it is vital that they are accurately specified in terms of their CoP Coefficient of Performance and also their kW power capability.

The performance and effectiveness of heat pumps varies considerably between the seasons and in the various climate zones around South Africa. They are ideally suited to warmer climates as their CoP is substantially higher when the inlet water temperature and ambient air temperature is higher. When the ambient air temperature and/or the inlet water temperature is low they have to work very hard in order to heat water up effectively and their CoP can in reality drop back down closer to just over 1.0 which makes them no more efficient than a traditional electrically fuelled hot water tank under these conditions.

Heat pumps should obviously always be located outdoors and NOT in enclosed spaces (i.e. garages) – they exhaust cold air as a by-product which would slowly reduce the ambient air temperature in any enclosed space and thus reduce their CoP efficiency over time.

The advice for sizing heat pumps is generally accepted as: use a 5kW heat pump on a 200 litre hot water tank, a 7.5kW heat pump on a 300 litre hot water tank and use a 9kW heat pump on a 400 litre hot water storage tank.

The type of gas that any heat pump uses is also an important consideration to review and understand. R22 gas was phased out due to the Montreal Protocol in 2010 so we shouldn’t be using or seeing that in the industry. R407C (the replacement gas for R22) and R410A are the most common gasses now used whilst R134A gas type is commonly used in commercial and high-end pumps.

R407C however doesn’t heat water very well above 45 degrees without requiring electrical resistance backup in the hot water tank and can reportedly be quite problematic with high humidity summer temperatures (especially in Durban) causing the units to trip out. The solution to this seems to be to drop the heating capacity of the heat pump to just 50 degrees C meaning the electrical element has to pick up the 10 degree C shortfall required to get the storage water to the required 60 degree C level. This means that in reality the average efficiency on a R407C gas type heat pump is heavily reduced and these ‘cheaper’ units will simply cost the client more money to run as the electrical back-up element in the hot water storage tank is still doing quite a lot of work in heating their hot water and pushing up their electricity bills.

R410A gas can heat water comfortably to around 50-55 degrees C and thus relies less on the electrical element in the hot water tank to heat the water. The ‘little bit’ extra a client thus pays for these units will result in a comparatively reduced electrical bill and the units thus pay for themselves quite quickly within a year or so dependant on use.

It is vital that an appreciation of how heat pumps perform and what factors influence their performance are considered when specifying units for your clients. Don’t be mislead with a cheapest price approach as clients will pay more for the cheaper unit in the long run with reduced efficiencies and higher electrical bills.

Heat pumps in South Africa should be SABS tested & approved (although most of them aren’t) so the actual CoP performance values of any unit should be available from the supplier – Insist that they be transparent with those reports and make them available for you to review and understand! One of the biggest challenges we currently have is that manufacturers only typically reveal their units maximum performance CoP values achieved under ideal test conditions (in a lab overseas somewhere) which bear little to no relevance to location-specific or climate-specific local performance!


The truth about glazing

In providing Rational Design energy assessment services we have modelled and assessed every classification of property type, in every climate zone in the country, and are yet to see any single building that couldn’t be shown to be fully regulatory compliant with single-glazed clear glass when alternative more cost-effective design solutions could be brought into play to ensure that the energy efficiency targets of the regulations were achieved.

When one looks at the payback period of installing any design solution it becomes impossible to substantiate the use of high-performance glazing systems when one could achieve a similar, or frequently better, level of energy efficiency through enhancing the hot water system, introducing air-conditioning to control thermal comfort, minimising electrical consumption with LED lights, etc, on any building at a fraction of the capital cost.

Competent energy modelling would look at the true energy loads incurred through the prescriptive glazing and would seek to identify alternative more cost-effective ways of substituting that energy requirement.

Energy modelling is not however just about making single-glazing magically seem possible without validation; it is about being able to competently demonstrate that the heat loads therein have been assessed and that alternative solutions can be clearly validated in trading back the resultant energy consumption caused by reducing the glazing specification.

On heavily glazed properties, particularly in KwaZulu Natal where solar heat gain is the major challenge, the energy loads incurred by the windows can be substantial and single-glazed tinted glass can frequently prove to be the ‘right’ solution when insufficient alternative energy savings measures prove to be available and the impact of solar heat gain is competently assessed. Good architectural design always wins and in any hot climate area the provision of adequate shading against peak summer solar ingress is paramount to a truly energy efficient building.

Tinted or low-e glass can frequently be shown, and validated with calculated data, to reduce internal heat loads in some buildings helping enhance thermal comfort and reducing the kW loads on HVAC equipment saving clients money in the long term. This can be true on highly-glazed residential properties and certainly on office buildings were radiant heat may be problematic for people sitting and working near to windows.

Single-glazed fenestration systems can almost always be shown to be compliant but do not assume that clear glass is always the right answer…!

In this instance below, spending R150,000 excess on high-performance glass, even though it appeared to be the better performing product, was futile given a paltry R1,112 per annum saving on theoretical heating and cooling costs…? Single-glazed clear glass was thus the optimised design solution given the acceptable compromise on cost and performance.


What ‘works’ in the Eastern Cape…?

We have extensively modelled residential properties in the Eastern Cape climate zone with interesting results – what ‘works’ in Cape Town does not necessarily work in the milder Eastern Cape climate in Port Elizabeth, Cape St Francis or Plettenberg Bay, etc.

Every property will respond differently of course dependent on orientation, internal volume, effectiveness of shading, etc, but as a general rule of thumb the following are some base-case construction technologies that produce good energy efficiency in this region:

  • Single-glazed clear glass – this actually proves most favourable as it enables low altitude winter sun to penetrate properties in a ‘cold climate’ and assist with free passive heating which proves to substantially reduce heating requirements and costs (as long as sufficient shading is in place to protect against high altitude summer sun heat gain).
  • Cavity wall construction – cavity wall construction is a requirement in this high condensation risk climate zone but sometimes adding just 25mm XPS closed-cell extruded polystyrene to the cavities substantially increases the thermal performance of properties increasing energy efficiency.
  • Energy efficient hot water – heat pumps or solar hot water with gas backup (rather than electrical backup) work well in this region. Heat pumps have a lower average CoP Coefficient of Performance in reality in a cooler climate so one needs to be very careful to ensure that these are adequately sized to suit their specific demand requirements. If not then their efficiency can easily drop and in essence be no more efficient or effective than a traditional electrical hot water tank. The reduced efficiency of heat pumps, with their lower contribution on energy efficiency, must be competently considered in any rational design assessment.
  • Perimeter foundation insulation – XPS extruded polystyrene can do wonders for keeping properties warm under-foot, enhancing levels of thermal comfort, and minimising heat loss & cold ingress. On larger properties it may be prudent to insulate the outer couple of meters to the perimeter of the dwelling underslab.
  • Roof insulation – adequate insulation of any pitched roof proves to be critical anywhere in South Africa and there is common misunderstanding about how to use/detail sisalation in pitched roofs by architects (it MUST have a clear air space below it in order for the low emissivity surface to work).
  • Adequate winter space heating – the Eastern Cape has long cold winters and hot dry summers with scorching Berg winds so adequate thought must be given to how buildings will be kept warm in winter (SANS 10400XA gives little consideration to efficient winter warming energy consumption).

The mid-year energy loads can clearly been seen on this graph below that indicates the carbon cost of heating (substantially) and cooling (hardly) a property in a predominantly cold winter location…

Rational Design for ‘F1 Large Shops’

If the glazing-to-net-floor-area percentage is less than 15% then the SANS 10400XA prescriptive deemed-to-satisfy compliance route may appear to be the most simplistic path to follow on F1 classification projects. We have modelled and assessed numerous retail stores this year and without fail it has proven that substantial long-term running cost savings can be brought to bear in every instance by rather using a rational design assessment to understand and develop designs solutions for the project.

On a new 5,000m2 SPAR project we assessed recently in Durban North, KZN, the building only had 9% glazing and yet through a rational design assessment we are able to help identify ways of giving the client an estimated R42,000 per month savings on their electricity bills over what could have been achieved through a prescriptive design solution.

An analysis of the two routes to compliance is quite frightening when the energy use is compared:

Deemed to satisfy route: 368 kWh/m2.annum energy consumption & 115.9 VA/m2 energy demand

Rational Design solution: 236.3 kWh/m2.annum energy consumption & 79.1 VA/m2 energy demand

Although the relatively energy-hungry prescriptive deemed-to-satisfy route will meet the requirements of the SANS 10400XA requirements with lowest specification in terms of hot water heating, HVAC performance and relatively inefficient lighting at 24W/m2 the energy usage and demand performance can be reduced in this instance by around 35% if the performance route is rather followed.

The SPAR building was simply specified with cavity wall construction, single-glazed clear glass throughout, reduced flat slab roof insulation, energy efficient lighting, heat recovery for hot water generation and an efficient HVAC system at little to no extra capital cost on construction.

If you are working on any F1 classification project be wary of thinking that the seemingly-simplistic prescriptive route is the right way to go when it in fact may not be serving your clients best interests in the least!