High Tech Windows Help Your AC

Home Inspector with About the House - Home Inspections

I found this great artcile about the relationship between window and air conditioning that I wanted to share. Here is an excerpt:

Windows Pave Way For HVAC Innovation
High-performance glazings plus radiant heating and cooling can be a cost-effective combination

By Geoff McDonell

A high-performance glass unit offers superior thermal resistance (R or U value) and infinite variations in low-e coatings, tints and ultraviolet light control, along with solar energy control. High-performance glazing can reduce energy use, benefit lighting design and improve comfort. What's more, high-performance glazing can help reduce the size of the HVAC system.

So why aren't high-performance glazings more widely used? The main barrier is the long payback for the premium cost of the glazing. And that issue arises because virtually all HVAC systems in North America are conventional all-air heating and cooling systems, which must do two things: control space temperatures and ventilate space.

With an all-air system, high-performance glazing often shows a long payback period. The reason is that, no matter how well the glass performs, there is an infrastructure cost for all-air systems; they require a certain amount of equipment, building volume and servicing, no matter how efficient they are. Likewise, costs for energy use, maintenance and operations level out at a nearly base-cost level. After all, even on the most efficient all-air systems, filters need to be changed, fans and bearings need to be maintained, and controls on each terminal device need to be maintained.

For the last 20 years, European HVAC engineers and building designers have been using building mass with radiant cooling and heating and a high-performance building envelope to produce superior indoor comfort with very low energy use and minimal operating costs. The key is to decouple the cooling and heating functions from the ventilation function by using a hydronic-based radiant cooling and heating system.

The advantage of that approach is that, for heating and cooling, it takes a lot less energy, space and equipment to transport water around the building than it does air. What's more, with radiant heating and cooling, the air handling system simply has to provide 100 percent outdoor air for ventilation at a rate of 20 to 50 cfm/person or so at a relatively constant temperature to ensure good indoor air quality. Indoor pollutants are 100-percent exhausted using a general exhaust system serving point-source exhaust terminals at washrooms, photocopiers, and similar areas. An air-to-air heat exchanger may provide virtually energy-neutral ventilation in many climate zones.

The use of the high-performance glass allows enough daylight in to help reduce lighting loads and to eliminate the common interior and exterior thermal zones. And perimeter areas will not experience the transient heating and cooling loads associated with conventional glass units.


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