Solar-heated water with radiant floor heat

By Ole Sorensen on 03/16/2006

Imagine your solar hot water system heating your kitchen, laundry and bath water as well as heating your home. You’d have the comfort of rolling out of bed to the touch of a warm floor on cold winter mornings, and basking in the heat of yesterday’s sunshine as you shower. You’d also have peace of mind knowing that while your radiant floor heating system provides you with health and comfort, it is also a contribution to a healthier planet.

Hydronic radiant floor heat is a wonderful way to heat your home because it is energy efficient, quiet, very comfortable, invisible in the living space, and safe for allergy sensitive people, as it keeps out the drafts that bring in dust. Radiant floor systems allow even heating throughout, not just in localized spots as with forced air. The room heats from the floor up, warming the feet and body first.  The components such as tanks, pumps, boilers and controls are long-lasting and the tubing products have warranties of 25 years or more.

Radiant floor heating systems are available using air, electric or water.  The focus here is on hydronic (water) radiant floor systems, which are the most efficient and have been used extensively in Europe for decades. Today, 50 percent of new heating installations are radiant floor heat. Here’s how it works: Heated water from a boiler is pumped through pex (a type of strong non-toxic plastic) tubing laid in a pattern underneath the floor. The tubing can also be embedded in a concrete foundation slab, a lightweight concrete slab on top of a subfloor, or over a previously poured slab. A wide variety of floor coverings can be used such as tile, wood, concrete or laminates.

A hydronic radiant floor heating system can be powered by fossil fuels, but it is highly efficient because it is considered a low-temperature heating system.  A typical solar-heated water system starts with a solar collector that absorbs the sun’s radiation and converts it into energy that is used to heat water.  The stored heated water is then applied to supplement the heating of household water and the water used in the radiant floor system.

Recent developments in solar technology provide even greater energy efficiency. The basic flat plate collector is the more commonly used type of solar collector, but a new technology called solar evacuated tubes with heat pipes offers an improved performance of 200-400 percent. The basic flat plate collector is a flat box containing absorber plates-that’s where the sun’s radiation is absorbed-with water filled pipes running through them. This type of collector tends to lose heat through the glass. The solar evacuated tubes, on the other hand, also use an absorber plate, but instead of water running through there is a special vacuum-sealed tube.  The vacuum eliminates heat loss.  The solar evacuated tubes are arranged in a row that is connected to a copper bar (manifold) by a heat pipe. The pipe heats the water running through the manifold, and the water is circulated to the storage tank.

Solar evacuated tubes are available in arrays of 30 or more and perform well in both direct and indirect sunlight, making them useful in areas with cold, cloudy winters while achieving both higher temperatures and higher efficiencies than flat-plate collectors.

The tubes can be adjusted to face the optimum orientation for maximum solar radiation absorption.  Because each solar tube is an independent collector with its own heat transfer mechanism, each one can be individually oriented to optimize the heat gain.  And because the tubes are lightweight and never hot to the touch, installations and maintenance are simple.  The direct flow concept permits installation horizontally, vertically or at any required angle, allowing for architectural and aesthetic freedom. So if you can’t put it on your roof you can put it on an outside wall.

When considering renewable energy, heating your home with solar heated water and hydronic radiant floor heat is the one of the most financially feasible options.  With system lifetimes well above 30 years and payback times as short as 7 years for domestic hot water systems, and 12 years for home heating systems, solar energy is a healthy solution that will bear fruit for many years to come.  The combined North Carolina and Federal Tax Credits for renewable energy installations as of 2006 will amount to as much as 55 percent of the project cost. We strongly suggest researching the specific rules that apply to various tax credits (www.ncsc.ncsu.edu is a good place to start).

When you decide to reduce the use of fossil fuels by installing a solar hot water (SHW) system to heat your domestic hot water, consider your contribution a worthy one.  There are more than 300,000 SHW system units (not including swimming pools) installed across the United States, and installations are continuing to increase.  In fact, a June 2004 report describes the installation of a Thermomax SHW system consisting of 360 evacuated tube heat-pipe solar collectors at the top of the hot water circulation loop in the Social Security Administration’s Mid-Atlantic Center in Philadelphia.  And between 1996 and 2004, the consumer base of the Hawaiian Electric Company installed more than 25,000 SHW systems. In doing so, they effectively reduced utilities demands by a total of 12.7 megawatts: enough to power approximately 18,000 typical US homes.

According to the US Department of Energy, heating domestic water today accounts for up to 14 percent of the average household’s energy use and nearly 4 percent of the total US energy consumption (1.7 quadrillion kilowatt hours from 2004), which on average created 1.18 trillion tons of carbon dioxide.  Considering our need for independence from fossil fuels and the staggering amount of pollution they produce, an investment in solar certainly brings with it the heartfelt comfort of knowing we are giving ourselves and our children a healthier future, and bringing a much-needed balance back to our ecosystem.

[Ole Sorensen is the owner of Solar Dynamics in Asheville, NC. You may contact him by calling (828) 665-8507, or e-mailing ole@solardynamics.org.]