March 15, 2007
Summer in Tashkent runs 45 outside and 38 inside with the air conditioning at full output, because the heat is not coming through the wall; it is coming through the glass as radiation. Solar heat gain, cavity convection, external shading, dust and thermal expansion — and why thicker glass is usually the wrong answer.
Uzbek summer air reaches 42 to 48 degrees, and indoors often feels worse. Not because it is hotter, but because there is no breeze, humidity is low, and the glazing keeps pumping radiant heat inward. A person can survive 45 degrees of dry heat by sweating; 38 degrees in still air is where heat stroke happens.
Heat enters a room three ways: conduction through the wall, air leakage, and solar radiation through glass. The first two are minor in a hot dry climate, where walls are insulated and buildings are tight. The third dominates. A west-facing ordinary double-glazed unit delivers 500 to 700 W/m2 of heat into the room every hour in the afternoon, an order of magnitude above conduction through an entire wall. In hot climates the governing figure is therefore not the U-value but the solar heat gain coefficient.
The phrase double glazed aluminum windows supplier invites the assumption that two panes are enough. The cavity does raise thermal resistance to conduction, but it is nearly helpless against solar radiation. Visible and near-infrared light pass straight through, land on the floor and the furniture, and become heat. Blocking radiation is a job for the coating, not the cavity.
Solar heat gain coefficient, or g-value in Europe, is the first number in a hot climate. Ordinary double glazing sits between 0.6 and 0.7; adding a solar-control low-e layer brings it to 0.3 or 0.4; double-silver and triple-silver systems go below 0.25. Every 0.1 removed keeps 400 to 600 watts out of a twenty-square-metre room at noon, which is a small air conditioner. A quotation that lists a U-value and no solar heat gain coefficient is an incomplete quotation for this climate.
Physically, the best place to stop the sun is outside the glass, where a shade can reject over ninety percent of the radiation. A coating can only absorb or reflect part of it, and the rest still becomes heat. Southern Europe and the Middle East build external roller shutters, external louvres and fixed overhangs for exactly this reason.
Central Asian dust discounts the approach. Spring brings frequent dust storms; sand packs the roller guides until they seize, louvre pivots wear out, and maintenance costs more than the electricity saved. The practical answer is a combination: solar-control low-e glass as the maintenance-free base layer, fixed overhangs or deep reveals on west facades where nothing moves, and adjustable external shading reserved for villas and commercial work. This has to be decided on the drawing; afterwards it means demolishing a wall.
Slim frame aluminum windows are fashionable and they do admit more light. In a hot climate they carry two extra problems: profile wall thickness against structural strength, and differential expansion between glass and aluminium.
The narrower the frame, the greater the deflection under the same wind load, and the less evenly the glass edge is supported. Daily swings above twenty degrees combine with a threefold difference in expansion coefficient, glass near 9 and aluminium at 23.6 times ten to the minus six per kelvin, so an over-constrained frame concentrates stress at the glass corners. Slim frames are buildable, but they need thicker profile walls, wider setting blocks and softer sealant. A slim frame quoted at half the price has usually economised on exactly those three.
Dust is not dirt; it is abrasive. Quartz grains approach hardness seven and will grind grooves into gasket surfaces, removing their rebound until the gap widens, more sand enters, and the process feeds itself. Three gates have to work together.
Material first: EPDM outlasts PVC by a factor of three or more at seventy degrees of surface temperature. Second, pile weatherstrip on sliding units should be silicone-treated, since ordinary pile mats down within six months. Third, drainage and equal-pressure chambers, because dust travels back through drain slots and needs a wind baffle. All three are testable on a sample: blow compressed air at the joints for five minutes and look for dust on the inside face.
Aluminium expands at 23.6 times ten to the minus six per kelvin. An eight-metre-wide window moving through a fifty-degree daily swing changes length by about 9.4 millimetres. That is small, but if both ends are rigidly fixed, the movement becomes internal stress and shows up as cracked welds, glazing beads popping out, or a distorted frame.
The correct detail is fixed at one end and sliding at the other: anchor bolts at the fixed end, slotted holes at the sliding end, so the profile can move along its length. Installation drawings rarely show this and rely on crew experience, and crew quality across Central Asia varies widely. A buyer should either write the fixing detail into the contract or require the factory to supply an installation manual with node drawings.
Behind the search for aluminum windows price per square meter China sits a common comparison trap. One factory quotes per square metre with glass included, another without; one includes hardware, another prices profiles only; one includes wooden crating, another charges for a timber frame separately. Three quotations spread forty percent are usually not a price difference but a scope difference.
Comparability requires splitting the quote into five parts: profile by series and wall thickness, glass by build and coating, hardware by brand and set count, fabrication and assembly, and packing with freight. Then require the same five parts back from every quotation. As a buyer dealing with an aluminum windows China supplier, or sourcing aluminum windows from China for the first time, ask one more question: is the glass sourced locally or bought in? Glass is 35 to 45 percent of unit cost, so its origin moves both price and lead time. On commercial work the effect is sharper, because high performance windows for commercial projects usually specify the glass build in the tender, leaving only profile and hardware as variables.
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