SOLAR HOT WATER SYSTEMS - PART I

Heating with energy from the sun is not new.

With Energy prices continually rising, global warming, peak oil, and other issues facing us today, solar energy systems make more sense than ever before. Parts I and II will focus on solar hot water systems. Parts III and IV will cover Solar Electric (Photovoltaics). Some technologies are more appropriate for our Northwest environment than other, and we'll help you learn the basics.

SOLAR THERMAL: Capturing HEAT energy from the sun to use either directly or indirectly.

Capturing heat from the sun is easy, efficient, and the most cost effective 'solar power' you can use for your home. You may have noticed that your car heats up inside while its in a parking lot even on an overcast day. When the sun is shining brightly, temperatures inside a car can become extreme, demonstrating clearly how effectively solar thermal energy is captured. Now imagine telling a bunch of engineers and inventors to take that same heat-capturing principle and develop systems specifically designed to capture and retain heat. The results are excellent!

Note on Solar AIR heating: Unfortunately, capturing solar thermal energy and using it to directly heat a home in the winter just isn't very practical for us here in the Puget Sound Area. Too many cloudy days, not enough energy in the few hours of sunlight we do capture, and moving heated air is not a very efficient method of transferring heat. So, we'll skip solar thermal AIR heating in this report.

The most practical use of solar thermal energy is to heat water, either directly or indirectly. The simplest solar hot water heaters must be those black plastic bags you can buy at camping stores. Fill it with water, hang it out in the sun, and voila, you can have a hot shower. Not great for a home, but nice while camping. (This is direct heating.)

You'll probably hear or come across a lot of terms describing solar hot water heaters: Open system, closed loop, active vs. passive, unglazed, glazed, and evacuated tube collectors, and so on. We'll take a look at a few of these terms and try to make them easy to understand.

Types and Categories of Systems

• OPEN LOOP (or Direct System)
  In an Open Loop System, potable (drinking) water flows through the collector system. Any Pump must be stainless steel or bronze. NOT RECOMMENDED due to possible water stagnation, freezing, Legionnaire’s disease, etc.
  
  
  
  An Open Loop system using a Batch type collector.
  
• CLOSED LOOP (or Indirect System)
  A heat transfer fluid (HTF) flows through the collectors. A Heat Exchanger is used to transfer the heat from the fluid to the water. A lower cost iron pump can often be used IF the HTF is something other than water. Highly recommended.

COLLECTORS - Different collectors for different uses!

• UNGLAZED
  No transparent protective 'sheet' covers the collectors. Used for Pool Heating. Low cost, light weight, lower temperatures, least expensive. Not suitable for cold, windy locations as heat loss can be great. Not suitable for Domestic Hot water use.
  
  Solar panels are mounted on the south facing roof.
  
  
  Note the pool's cover which is essential to retain heat over night!
  
• GLAZED
  A transparent protective sheet of glass or other material is used to help trap heat in the collector. ("Flat Plate" Collectors) Higher temperatures, heavier, more expensive, not as efficient in winter due to heatloss from large front plate of glass. Can be used to heat domestic hot water (DHW), year-round pools, etc.
  
  
  
• EVACUATED TUBE
  Heat collection and retention is highest in a vacuum.(Think Thermos Bottle). Highest temperatures, low heat loss, more fragile, works well even in sub-freezing temperatures, high winds, more expensive than other 2 types. Used for Domestic Hot Water, pools, spas, radiant heating. Installing tubes and heat pipe into manifold of evacuated tube system.
  
  

END OF PART I
Part II will explore systems, performance, and costs