Solar hot water (SHW) systems use the “greenhouse effect” to heat
water or air in a thermal collector, in conjunction with a suitably
sized storage tank or ducting system to supply hot water and heat
for use in homes and businesses. SHW for domestic hot water works as
a pre-heat system that operates in series with your existing heating source
by preheating the incoming cold domestic water, with the existing hot
water heater as a backup.
The same solar heated water can be used to provide space heating.
There are also thermal collector/fan systems that heat the air directly and
are very efficient room heaters. If the sun is shining, your home or business
is heated with clean, inexpensive solar energy. If the sun is not shining,
then additional heating is provided by your backup system.
Over the year a SHW Combi-system can provide as much as 60%-
65% of all water heating needs and 20-50% of your space heating needs,
even in cold climates. During the summer months, the system operates at
its maximum, with little extra heating from conventional sources
required. Excess heat must be used (pool, hot tub, commercial process)
or dissipated. Given that about 60-80% of the average family’s energy use
comes from the cost of heating the home and heating water, the savings
garnered from an SHW Combi-system and the increase in home resale
value will usually pay the cost of installation within 7-10 years. This is
accomplished by reducing your energy bill and your reliance on imported
fossil fuels. Over the 30+ years of the system’s life expectancy, your
SHW Combi-system should leave a lot more money in your pocket than
would be true otherwise.
There are two main types of solar space heating systems: active and
passive. Passive systems (e.g. sunroom) absorb thermal energy from the
sun through appropriately sized and specified windows and store this
the energy in structures of high thermal mass (wood, tile or masonry floors
and walls) which can then be released into the room space during the
night hours, maintaining a more stable temperature environment. Active
systems absorb heat through collectors and store the thermal energy in
tanks or radiant Mooring and panel systems. As shown in the diagram
below, active solar hot water systems are made up of collectors, storage
tanks, and the solar loop (piping, controls, heat exchangers, circulators,
gauges, valves, etc.) and heat distribution systems (e.g. radiant Noor heating).
Thermal collectors, either Nat plate evacuated tube, or forced air,
absorb the thermal energy in sunlight. The collectors should be generally
south-facing (+/- 30 degrees), at a 45-degree angle to the horizon, and
un-shaded from 9am-3pm. Less than optimal orientation can be compensated for with additional collectors. In a hydronic system, a pump
circulates a glycol-water mixture transferring heat energy from the collectors through a heat exchanger to a solar storage tank. Solar storage tanks can range in size from 60-120 gallons for domestic use and from 160-
2,500 gallons for commercial use. In a forced-air system, air is heated in
collectors and circulated with low power fans.
Article by Don Wemple