Colorcoat® Column – perforated Transpired Solar Collectors (pTSC’s)

New renewable technologies are being developed for integration into the building envelope all of the time. The complexity of these technologies, makes the task of balancing cost against efficiency, one that is extremely difficult. Pre-finished steel perforated Transpired Solar Collectors (pTSC’s) offer a simple alternative renewable energy that can be used as a solution for new build or retro-fit.

What is a perforated Transpired Solar Collector (pTSC)?

The principle of the perforated Transpired Solar Collector is simple. Installed as an additional skin to a buildings southerly facing elevation, the system consists of a pre-finished steel sheet with thousands of tiny perforations uniformly spaced across the full face of the collector (termed SolarWall® ).

As solar radiation strikes the surface of the SolarWall® and is absorbed, solar heat conducts to the fine layer of air that lines the outer face of the panel (known as the thermal boundary layer). This heated boundary layer of air is then drawn through the perforations into an air cavity between the SolarWall and the original elevation behind. From here the fresh, heated air can then be fed directly into the building as heated ventilation air, or ducted into a heating unit to supplement the buildings heating system.

What type of cost savings can I achieve by installing a perforated Transpired Solar Collector?

Perforated Transpired Solar Collectors combine high efficiency with cost effectiveness. The savings it offers on heating bills means it can pay for itself in less than five years. Very few, if any, renewable energy solutions can get close to this short payback time. SolarWall® from CA group has a proven track record and can reduce heating bills by up to 50% and the total building CO2 emissions by up to 20%.

Does the colour of the pre-finished steel effect the efficiency of a perforated Transpired Solar Collector?

Black absorbs and white reflects light so naturally it is assumed that to collect solar radiation, the collector on the building’s external wall should be black – which may not necessarily complement the aesthetics of the building. Different colours have differing absorbtivity rates and this can impact on the efficiency of a perforated Transpired Solar Collector. It is important to ensure the most effective colour of pre-finished steel is specified whilst maintaining the aesthetic of the building. The colour range provided by Corus Colorcoat Prisma® is particularly effective for solar absorption and allows a wide range of colours to be used increasing the attractiveness of the building.

For more information regarding SolarWall®, visit the CA Group website.
For more information regarding Colorcoat Prisma®, visit colorcoat-online.com

Colorcoat® Column: Sustainable Refurbishment

There are many reasons to consider the refurbishment of an existing building. The need to refurbish will depend upon the condition of the building and its application. Quite often with industrial and warehouse premises the refurbishment is undertaken out of necessity e.g. for a leaking roof!

Refurbishment should be considered as more than extended maintenance. Instead it should be used as an opportunity to make significant changes and improvements to the building.

Refurbishment of an existing building can provide very significant improvements in thermal performance and reductions in operational CO2 emissions.

How does the embodied and operational CO2 of a refurbished building compare with a new building?

Examination of the embodied CO2 of a warehouse building shows that only 10%  is contained within the building envelope. Approximately 75% of the embodied CO2 is associated with the foundations and floor slab. Refurbishment of the building envelope, utilises the existing structure and will save ~ 90% of the embodied CO2 compared with a new build.

The refurbished building will be significantly more energy efficient and have reduced operational CO2 emissions approaching that of a new building and meeting the latest revision of the Building Regulations. The operational CO2 savings over the life of the building will be significantly greater than the additional embodied CO2 from refurbishing the building envelope. In many cases the refurbished building can have a lower overall CO2 footprint than a new building. The exact savings will be dependant on building type, size and application.

Which aspects of refurbishment will contribute most to reducing the operational CO2 emissions from the building?

Industrial buildings, constructed during the 1970s and early 80s have extremely poor thermal performance when compared with current regulatory requirements.

Typically they have minimal insulation with wall and roof U-values in the region of 2 W/m2/K. Air-tightness was not a specified requirement when these buildings were constructed and air-leakage rates in the region of 30 m3/h/m2 are typical. Current regulations require new buildings to have a minimum U-values of wall 0.35 W/m2/K and roof 0.25 W/m2/K and minimum air-tightness performance standard of 10 m3/h/m2. 

Refurbishment by either over cladding or a complete strip and re-sheet will show the greatest improvement in thermal performance and associated reduction in CO2 emissions.

Increased fabric insulation will generally show the greatest contribution as the initial U-values are so poor.Air-tightness will also show very significant benefits. For an over cladding refurbishment, a membrane must be installed underneath the additional insulation, otherwise there will be minimal improvements, as the external sheet will not provide an air-tight barrier.

With careful consideration, the operational CO2 emissions of a refurbished building can approach those of a new building and show reductions over the previous building of ~75% of the envelope related CO2 emissions.

Colorcoat® Column: Gauges

What impact does the ordered gauge have on the structural performance of profiled pre-finished steel cladding?

The structural performance of a pre-finished steel profiled sheet is dependant upon 3 factors:
1.shape/geometry of the profile
2.gauge of the steel substrate
3.mechanical properties of the steel grade used.

Gauges and tolerances

EN10143:2006 specifies the maximum and minimum actual gauge, which is permissible for a nominal ordered gauge.
For example a 1250 mm wide 0.7 mm coil must be supplied within the gauge range 0.64 mm to 0.76 mm.
It should be noted that the tolerances quoted in the current 2006 version of this document are slightly tighter than those quoted in the previous document, so the specifier should ensure that material is supplied to the correct standard.
Ordering material with a lighter nominal gauge than 0.7 mm, but within the apparent tolerance range, may result in material actually produced being less than 0.64mm. The structural performance of the profile will consequently be reduced.
All Colorcoat® pre-finished steel meets the requirements of EN10143:2006.

Mechanical properties of the steel substrate

All Colorcoat® pre-finished steel for wall and roof cladding is supplied with a specified minimum yield strength. This figure is used to calculate the structural performance of the profiled pre-finished steel sheet. In practice, the actual yield point will generally be significantly greater than the minimum value, resulting in a profiled pre-finished steel sheet with a greater resistance to stress failure.

 “How do I ensure the correct structural performance of the pre-finished steel sheeting?”

Load span tablesLoad span tables are used to calculate the maximum permissible purlin spacing at which the profiled sheeting will meet the structural requirements for the building location and application.
All Corus Colors supply chain partners have load span tables that have been calculated according to EC3 and have been independently assessed and approved by the Steel Construction Institute. (SCI Assessed)
The load/spans quoted in these tables are specific to the exact profiles and material specifications supplied by these profilers and cannot be applied to different profiles or material grades/gauges.

 

CE marking

CE-marking is a European product information label that indicates that the properties of the product have been tested according to European standards. The European Commission has determined which properties for which building products in the EU are relevant and should be tested and what external verification is appropriate.  The values of the tested properties have to be stated/printed by the producer on the product, the packaging or the accompanying coupon. Country supervisors inspect randomly if CE-marks on products are complete and correct.
All Corus Colors supply chain partners are able to supply CE marked pre-finished steel profiled sheeting, which meets the requirements of EN 14782.

Colorcoat® Column: Overpainting

With the onset of summer many building owners may decide that there is a need to refurbish their building and one method they may wish to undertake is to over-paint. Here are a few queries we often get with regards to over-painting.

 

What is the preparation required prior to over-painting ?

This will depend on the condition of the existing cladding, which there are three main types:

1. Colour change e.g. change of ownership of building and a requirement for new colour scheme.

This in many cases will mean only thoroughly washing down with a suitable detergent/water solution to remove all dirt, grease and deleterious matter and fresh water rinse. New Plastisol surfaces may need to be wiped with white spirits before washing

2. Paint weathered but still sound to substrate.

Areas of algae growth should be treated with a proprietary fungicidal solution (use as per manufacturers instructions) to sterilise surfaces. This must be done prior to washing which must be thorough to remove all dirt, chalk deposits, oil, grease, residues from sterilisation and any other deleterious matter. Fresh water rinse and allow to dry. If there are any areas that have corroded remove corrosion with abrasive tools back to bright metal and feathering to sound paint

3. The original coating is very old and delaminating.

All existing coating removed back to the metallic substrate by a suitable means. These can include Chemical Stripper – use as per manufacturers instructions Abrasive Blast Cleaning – wet or dry blast clean in accordance with equipment manufacturer’s recommendations High Pressure Water Equipment With all methods you must ensure all surfaces are thoroughly clean before application of any paint. I would point out that before commencing with removing of coating and over-painting you may which to price a re-cladding of building, which often proves to be a cheaper alternative.

How is paint applied and when?

There are paint systems available that can be spray, roller or brush applied. Application technique should ensure that an even wet film is applied to surface at a thickness as recommended by paint manufacturer. If brush applied an appropriate brush size for cladding profile should be chosen. When spraying, ensure all site restrictions are considered and areas not to be treated should be protected or adequately masked up. Application should be carried out in weather conducive to painting, obviously not in heavy rain or strong winds if spraying. Otherwise problems such as rain spotting, pinholing, blisters or blooming etc. can occur.

What paint system should I use?

There are many manufacturers systems that are compatible with our coating systems and choosing the right coating for over-painting is important. Using a high performance, water-based paint can reduce the amount of Volatile Organic Compounds (VOCs) liberated during the over-painting operation compared with conventional solvent based paint. However, water-based systems can sometimes be restricted by weather conditions i.e. rain

Colorcoat® Column: Marine Environments

Question When specifying cladding systems for the construction of a building envelope in a marine environment what material would be best? Would it be aluminium?

Answer  Firstly we should define what we class as a marine environment. Under the Corus Confidex® Guarantee (available only with Corus Colorcoat Prisma® and Colorcoat HPS200® Ultra) it is classed as a building that is within 1 km from any coast. Generally aluminium is tolerant of PH values between 4.0 and 8.5 at room temperatures forming a film of hydrated aluminium oxide on the surface. A saline environment could mean a risky environment for the use of mill finished aluminium. A marine environment can cause pitting to the aluminium surface. The severity of this pitting obviously is dependant on how aggressive the environment it is subjected to. Therefore it is often recommended that painted aluminium be specified. The most common paint employed to coat aluminium is PVDF.

We at Corus do not recommend the use of PVDF on zinc coated steel substrate in marine environments as they offer markedly inferior performance. This is due to inherent coating permeability, which can lead to under film corrosion of the zinc and causes paint blistering particularly in stressed areas such as profiled bends.

Corus recommends that in saline environments a high build protective system such that is offered by Colorcoat HPS200® Ultra. The 200 microns thickness provides a more effective barrier against the permeation by salt polluted moisture than thinner coatings such as PVDF (27 microns thick). Furthermore, the excellent damage resistance of Colorcoat HPS200® Ultra is of particular advantage where a potentially aggressive atmosphere can readily attack steel substrate exposed due to physical damage.

Usually performance figures for PVDF coated aluminium when used in marine environments are in the range of 15 years. Corus offers a Confidex® Guarantee of up to 30 years for roof and wall on Colorcoat HPS200® Ultra. Euronorm 10169-2 outlines requirements for the corrosion resistance of pre-finished steels. The most onerous category, RC5, requires products to resist blistering, coating damage and edge delamination <2mm when exposed to aggressive industrial and marine environments. The unique Galvalloy® metallic substrate from Corus and step change in paint formulation that has been developed for Colorcoat HPS200® Ultra mean that it can easily meet this very high standard.