Heat Rejection and heat Retention

July 5, 2009

Guys A question for you, yes I know with the films we install we have a good level of heat rejection, thats the main purpose of them, and I understand that there will be a element of heat retention in cold weather just because a film is applied to the glass but thats not the main function of them. What are the figures of heat retention? The reason I ask is a guy has been telling me they have been quoted with a film that provides 70 heat rejection (can see that) but also gives a 30% heat retention in the winter months? Unless im wrong that seems a very big claim for heat retention? Any thoughts?

July 5, 2009

I've heard of 15%MAX

July 5, 2009

I've heard of 15%MAX

I must say a claim of a very good heat rejection and a 30% heat loss reduction in the winter seems way too high, although iam NOT an expert on this, its just the guy I was talking to was from the local council and was meeting a rep who claimed these figures, I tinted his car and was chating too him about this, seems too good to be true to me?

July 5, 2009

typically, most silver or reflective have a bad emissivity rating. unless you use a low-e type film where the metal layer is hard-coated(facing in the room). look at the emissivity of the film you are using, the lower the number the better(low e). just google LOW-E.

Customtinting · July 6, 2009

LLumar quotes that depending on the film, you can receive 10 to 15% heat loss rejection in winter. ( have alocal fool who tells customers 50%, total bull). Any who might claim 30%, tell them to produce private lab testing to back up the claim.

callwild · July 6, 2009

Low-Emittance (Low-E) is a term used for a surface that radiates, or emits, low levels of radiant energy. Emittance refers to the ability of a materials surface to emit radiant energy. All materials absorb, reflect and emit radiant energy. Emissivity is the value given to materials based on the ratio of heat emitted compared to a blackbody, on a scale of 0 to 1. A blackbody would have an emissivity of 1 and a perfect reflector would have a value of 0. Reflectivity is inversely related to emissivity and when added together their total should equal 1. Therefore, if asphalt has an emissivity value of 0.90 its reflectance value would be 0.10. This means that it absorbs and emits 90% of radiant energy and reflects only 10%. Conversely, a low-e material such as aluminum foil has an emissivity value of 0.03 and a reflectance value of 0.97, meaning it reflects 97% of radiant energy and emits only 3%.

Most window films have a Emissivity value(E) between .70 and .89 meaning they reflect 11% to 30% and emit 89 to 70%.

Low E film has an Emissivity of .33 meaning it reflects 67% and emits 33%.

Glass alone has an E value of .95. Therefore reflecting 5% and emitting 95%

So as I understand it: Putting a standard Silver film could improve the emissivity by 6% to 25%

and putting a Low E film could improve it by as much as 62%.

I think it is these figures which make people think the film improves Heat loss.

BUT

Confusing this reduction in radiant heat through the glass with overall heat loss reduction is however quite wrong and the as the overall heat loss which will also involve the heat conducted through the glass by touch and that lost by drafts would also have to be taken into account.

Not sure where one could get figures of heat loss reduction as it would depend on thickness of glass and if double pane.

But it easy to see why high figures are quoted by those making wrong assumptions about the figures supplied.

July 6, 2009

If you check out Low E films on Google im amazed at the number of companies that state the films will retain 30-40% of heat in the winter? Its all a bit of a minefield as I can see were up against facts and figures bounded about but dont seem to be true?