Sunrooms By Brady Sunrooms By Brady

August 25, 2010

Solar Screens vs. Solar Glass

Filed under: Business News,Glass,Solar Glass,Solar Screens,Solarium,Sunrooms — Sunrooms by Brady @ 11:36 am

Solar screens, the best way to manage sunroom temperatures year-round.

There are many competing claims by sunroom manufacturers about glass.  Some claim to have the “best” glass in the industry, others claim that their glass blocks out most of the sun’s heat in summer; others say theirs allows most of the sun’s warmth through in the winter.  Like so many things in life, you can’t have it all.  Magic glass is a myth.  Designing glazing systems is a science that requires a clear understanding of what it will be used for, what qualities are most important and where compromises can be made.  Glass, if not modified, allows most of the visible light spectrum to pass through and has virtually no insulating value.  What this means is any light that passes through the glass will strike another surface (inside your house or sunroom) and either be reflected or absorbed.  The light that is absorbed is converted into heat energy (remember the conservation of energy law from high school physics class?).  This heat in the winter is desirable and in the summer can make the room uncomfortably hot.

Since un-modified glass has no meaningful insulating value, most manufacturers of sunrooms offer “insulating glass”.  This is an assembly of two or more plates of glass that are separated by spacers,  The void in-between the sheets of glass is filled with a dry gas, most often argon.

Engineers have developed a set of values that allow us to compare the insulating qualities of one product to another.  In this system, a single sheet of glass has a “U” value of 1.0.  When two sheets are assembled with a small gap in between (usually less than ¾”) that is filled with dry air the U value is about 0.60.  In this system, the smaller the number, the better the material’s insulating qualities.  The insulating properties of the glass assembly can be further improved by using argon gas (less conductive than air) and by using non-metal spacers.  The standard insulating glass used by Brady-Built Sunrooms has a U value of 0.24.  Brady-Built offers as an option, triple glazed insulating glass that has a U value of 0.12.  These glass options are state-of-the-art in glass manufacturing.

The insulating glass panel described above helps to improve the sunroom’s insulating properties so that on a cold cloudy day or at night, the heat loss through convection and transmission from the sunroom is reduced.  To make the glass even better at reducing heat loss from your sunroom a coating is added to the glass that helps reduce radiant heat losses.  This coating, called a low e (for emissivity) coating reflects selected wavelengths of light (usually in the red to infrared spectrum).  The insulating glass with an argon filled space helps reduce convective and conductive heat loss, the low e coating adds significantly to the glass’ insulating performance by addressing the only other means of losing heat.  Obviously the measures described don’t eliminate heat loss from the glass; they simply reduce it to the extent possible without compromising the glass’ aesthetic qualities.

What about those hot summer days when any heat gain is objectionable?  Some sunroom manufacturers imply that their glass allows the greatest warmth inside the sunroom during the winter months, while preventing significant heat gain in the summer.  This is impossible.  When heat gain is objectionable, glass is modified by adding tints to the glass itself or by coating the outside pane of glass surface with a thin metal coating to create a reflective mirror surface.  Sometimes both methods are used in the same insulating units.  Scientists have come up with a system to measure this characteristic as well.  It is called the Solar Heat Gain Coefficient (SHGC).  Like the U value system, the lower the SHGC, the less light is allowed through the glass and therefore the less heat gain in the room.  Brady-Built uses a glass assembly with an SHGC of 0.385.  Most other sunrooms manufacturers use glass with a SHGC of 0.15 (meaning much less light gets through).  What this means is in the winter months, the Brady-Built Sunroom will warm more quickly on a sunny day and will be comfortable at much lower temperatures with less dependence on auxiliary heat sources.  In the summer months, use of the removable Brady-Built externally mounted solar screens, in combination with the standard glazing will prevent 90% of the heat gain that would otherwise occur.  The solar screens act like an artificial shade tree without blocking views of the sky.  Other sunroom companies depend upon dark tint for most of their heat gain control.  The problem with this approach is you lose a significant percentage of desirable heat gain in the winter and though it reduces the solar heat gain coefficient in the summer, it does not reduce the actual heat gain as much as the lower SHGC numbers suggest.  The dark tint absorbs light, preventing it from entering the sunroom directly, but that absorbed light is converted into heat energy and the hot glass warms the air in the room.  Using externally mounted solar screens causes this waste heat to dissipate into the air outside of the sunroom.

Brady-Built Sunrooms have been designed with hot summers and cold winters in mind.  Our glass, manufactured for us by Guardian Industries, has been designed to give Brady-Built Sunroom owners the optimum comfort and energy efficiency when used with Brady-Built Solar Screens.

3 Comments »

  1. […] Subscribe to the comments for this post? […]

    Pingback by Solar Screens vs. Solar Glass « The Sunroom News — November 29, 2010 @ 5:31 pm

  2. […] assume it might get hot in your sunroom! Make sure you have a few windows that open, or invest in solar screens, which make the room about the same temperature as under a shade tree on a hot summer day. Using […]

    Pingback by How can I get the most out of my sunroom? « The Sunroom News — September 28, 2012 @ 9:41 pm

  3. This is some really great information you have provided. thank you for sharing. My company in Arizona installs residential solar screens in Phoenix

    Comment by Sunscreens of Arizona — February 2, 2017 @ 4:58 pm

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