The Facts about sun tunnels
The things you need to know before buying a solar tube
The chances are that you’ve only just discovered sun tunnels but have no idea how to work from all the things that you read what is fact and what is total nonsense?
At this point I need to state my interest. My name is Chris and I am the UK importer for Solarspot tubular daylight systems. Solarspot was founded in Italy by Dr Gennaro Bracale, scientist and practitioner in daylight technologies and most likely the world’s leading exponent in tubular daylight guidance systems. It’s through this expertise that Solarspot systems are able to deliver up to 70% more daylight than the nearest competitor (based on size for size comparisons).
So whilst there is an element of self-interest here, I’m frankly fed up with reading the vast amounts of ignorant, ill-informed and blatant lies about sun tunnels published online. We simply want to inform potential solar tube customers like yourself of all the facts, and dispel the myths, so that choose the best option for your home.
Dispelling the myths about solar tubes – make sure you read this before buying anything.
So what is a sun tunnel, sun pipe, solar tube? The system, whatever you want to call it, works on a very simple basis; a hole in your roof covered in plastic or glass, with a reflective tube through the loft, down to a diffuser in the ceiling. This means that you can bring daylight into rooms that have no windows, or windows that don’t provide enough light to illuminate the room enough.
Within the category there are a couple of basic variants; systems with domes or systems with flat roof panels, and tubes that are either flexible or rigid. This all sounds fairly straightforward so you could be forgiven for thinking that the levels of daylight that you could expect would be similar.
Flexible or rigid sun tunnels, does it make a difference?
Fact number one is that the performance of these systems – performance being the ability of these units to bring daylight into your home – varies massively with the systems like the Velux flexible system delivering only around 5% of the amount of daylight that the best rigid system will do.
So when you read something online saying that there’s very little difference between flexible and rigid sun tunnels then you know the author hasn’t got a clue what they are taking about, as on the Fix My Roof website. He says that ‘flexible sun tunnels can give very good results’ but when you consider that you could get around 20-30 times the daylight from the best rigid system he’s clearly got very low expectations, or he wants to sell you a flexible sun tunnel.
So are all rigid solar tube systems good?
It’s fair to say that the worst rigid system is better than the best flexible tube. However, there’s still a massive difference between the rigid units with the best residential system delivering around 70% more light than the next-best and, depending on the location on the roof, it could be 4 or 5 times brighter than some other systems.
What if the sun tunnel needs a bend or to go around a corner?
Ironically, one of the big selling points of flexible systems is that the tubes can easily be ducted in any direction. What you won’t be told is that if you introduce a bend into a flexible tube you can virtually say ‘goodbye’ to any daylight from the diffuser.
With rigid tubes it is possible to introduce multiple bends and still get excellent levels of daylight from the system. The amount of daylight that is delivered will depend on two factors; the width if the tube and the reflectivity of the tube material.
There’s not a lot that you can do about the width of the tube as this will be most likely be dictated by the structure of your house. What you can do is make sure that you use a system with the most reflective material.
Rigid tubes tend to come in two reflective values; 99.7% and 98%. Whilst this may sound like it doesn’t make a lot of difference, in a 90 degree bend the more reflective material will only lose around 6% of the light, the slightly less reflective material loses around 25% – a massive difference.
Domes or flat roof panels, does it make a difference to the amount of daylight?
A very popular myth is that a dome will give you more daylight than a flat panel. This is not the case, well not with any significance anyway. What does make a difference is daylight capture lenses. If the dome has ‘Fresnel’ lenses moulded into the dome it can act to refract the morning or evening light into the tube – this is the case with the Solatube system. But what Solatube are not going to tell you is that these same lenses actually block around 50% of the daylight during the main part of the day.
At Solarspot we have similar Fresnel lenses technology that maximise low level light but the top of the dome is clear so that overhead light has an unimpeded entry into the tube opening. This is one reason why the Solarspot is so much brighter than its nearest rival.
Do I need to install my sun tunnel on a south-facing roof?
I’m not sure whether this is another example of extreme ignorance from sun tunnel suppliers or a case of ‘getting their excuses in early’ but it’s certainly another popular myth. I read, with significant annoyance, on the Sterling Build ‘Things you need to about sun tunnels’ that ‘positioning is key…’.
This is a totally ignorant remark from a supplier of second-rate systems. The truth is that a quality system, with light-capture lenses, will deliver the light on all roofs regardless of aspect. A Solarspot system with RIR light capture lenses will redirect daylight casting across a north-facing roof back down into the tube. Now you can have direct light sunlight in all of your north-facing rooms – all day long.
So what should I look for in a sun tunnel?
In a word, EFFICIENCY. The only problem with this is that most solar tube suppliers would tear their own fingernails out before they would disclose this information. And he’s why; if you had the efficiency figure for all of the systems available you would be able to see at a glance just how one system would compare to another.
For example, who would buy a Velux flexible unit if they knew that it was only 3.8% efficient when compared to the most efficient system, in the same size category, is 63% efficient. This means that you would need around 16 of the flexible units to give you the same amount of light as the more efficient unit.
Polycarbonate, acrylic or glass domes?
Domes or covers of sun tunnels are made of either Polycarbonate, acrylic or glass. Each material offers different characteristics so how do you decide what is best for you? Polycarbonate is the strongest of the three materials and is virtually indestructible but on the downside it has the worst light transmittance of the three and will go cloudy and yellow when exposed to UV. This makes it a really bad choice to put on top of a solar tube.
Acrylic is not as strong as polycarbonate but it’s still around 10 times stronger than glass and full tested to withstand the conditions that it will encounter on your roof. Acrylic also has the advantage of having the best light transmittance of the three as well as having excellent resistance to UV, lasting around 10 times longer than polycarbonate.
Glass also has excellent light transmittance but it’s nowhere near as strong as the other two. This means that the glass dome has to be much thicker, around four times thicker, than the either acrylic or polycarbonate dome which dramatically reduces its light transmittance.
To put this into context; an acrylic dome will have an efficiency factor of around 92%, a polycarbonate dome around 85% (although this goes down around 3% per year when exposed to UV) whilst the glass dome, due to the thickness, is around 65%.
Clearly, pardon the pun, acrylic is the best choice for any dome or covering of a sun tunnel.
Polycarbonate, very strong but has the worst light transmittance and goes yellow and cloud under UV light.
Acrylic, also strong, has the best light transmittance of the three and stays clear for many years
Glass has good light transmittance but due to its fragility needs to be very thick so absorbs too much light before it gets into the tube.
So which sun tunnel system is the best for your home?
Under normal circumstances this would be a multi-facetted answer depending on what you looking for in a product. What makes this product category unique is that these systems can only be judged on a single criterion, the amount of daylight it delivers. And as the Solarspot delivers around 70% more light than its nearest competitor, and up to 30 times more light than a cheap flexible system, it’s a clear winner as the best Solarspot for your home.