where we are located, SRI is not a common terminology and we are currently in the process of specifying an SRI compliant roof coating for a roof which is currently undergoing repainting/repair.
the product we are looking at gives us the following data:
heat reflectance: >99%
emittance: 0.88
if i assume that heat reflectance equates to solar reflectance, we can achieve an SRI of over 126. Are my assumptions correct? or is heat reflectance not the same as solar reflectance?
all the other information contained in the data spec for this particular product indicate that this is a cool roof product - but since it is not a US product, the terminology is a bit confusing to us.
many thanks!
Jacob Arlein
Director of Energy ServicesEnvironmental Building Strategies
64 thumbs up
August 31, 2010 - 11:54 am
Jutta,
I am not exactly sure what you mean by heat reflectance, do you mean thermal reflectance? Either way, heat reflectance is not the same as solar reflectance or albedo. Albedo is the ratio of total-reflected to incident electromagnetic radiation from the sun. This is a measure over all wavelengths of light.
It is likely that this product is still a cool roof product with such a high thermal emmitance level, but you will have to determine the solar reflectance of the material to be able to accurately calculate SRI.
Jutta Berns
onwer and principalecocentric (pty) ltd.
130 thumbs up
August 31, 2010 - 12:27 pm
many thanks for the response and i understand the point you make.
unfortunately the data sheet simply states "heat reflectance" and "emittance" - as above - and also has a value for thermal conductivity (0.09 W/m°K).
are there any other resources we could consult to help us calculate the SRI correctly with the information that we have available?
indeed all products that we have been able to source so far (we are located in South Africa) only provide, if at all, values for heat reflectance and emittance.
we are being pushed to make a decision on the coating and really do not want to lose the point on documentation, if it seems that we may be quite close!
many thanks!
Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11477 thumbs up
August 31, 2010 - 12:45 pm
Can you ask the manufacturer to clarify, or offer better data?This may simply be a language issue, where what they are calling "heat reflectance" is in fact "solar reflectance."
Jutta Berns
onwer and principalecocentric (pty) ltd.
130 thumbs up
September 1, 2010 - 10:08 am
Many thanks! have done so and it was indeed simply a language issue and the test reports have now confirmed the values. Such is the excitement of working on projects outside the US!