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Solar liquid collectors are most appropriate for central heating. They are the same as
those used in solar domestic water heating systems. Flat-plate collectors are the most
common, but evacuated tube and concentrating collectors are also available.
In the collector, a heat transfer or "working" fluid such as water, antifreeze (usually
non-toxic propylene glycol), or other type of liquid absorbs the solar heat. At the
appropriate time, a controller operates a circulating pump to move the fluid through
the collector.
The liquid flows rapidly through the collectors, so its temperature only increases 10°
–20°F (5.6°–11°C ) as it moves through the collector. The liquid flows to either a
storage tank or a heat exchanger for immediate use. Other system components
include piping, pumps, valves, an expansion tank, a heat exchanger, a storage tank,
and controls.
There are different ways to distribute the solar heat: with a radiant floor, with hot
water baseboards or radiators, or with a central forced-air system.
Radiant floor heat
In a radiant floor system, a solar-heated liquid circulates through pipes embedded in a
thin concrete slab floor, which then radiates heat to the room. Radiant floor heating is
ideal for liquid solar systems because it performs well at relatively low temperatures.
A carefully designed system may not need a separate heat storage tank, though most
systems do for temperature control. A conventional boiler or even a standard domestic
water heater can supply backup heat. The slab is typically covered with tile.
Radiant slab systems take longer to heat the home from a "cold start" than other
types of heat distribution systems. Once they are operating, however, they provide a
consistent level of heat. Carpeting and rugs will reduce the system's effectiveness.
See the radiant heating section for more information.
Hot water baseboards and radiators
Hot-water baseboards and radiators require water between 160° and 180°F (71° and
82°C) to effectively heat a room. Generally, flat-plate liquid collectors heat the transfer
and distribution fluids to between 90° and 120°F (32° and 49°C).
Therefore, using baseboards or radiators with a solar heating system requires that
either the surface area of the baseboard or radiators is larger, that the solar heated
liquid is heated more with the backup system, or that a medium temperature solar
collector (such as an evacuated tube collector) be used.
Central forced air system
It is possible to incorporate a liquid system into a forced-air heating system through
the use of a water to air heat exchanger.
those used in solar domestic water heating systems. Flat-plate collectors are the most
common, but evacuated tube and concentrating collectors are also available.
In the collector, a heat transfer or "working" fluid such as water, antifreeze (usually
non-toxic propylene glycol), or other type of liquid absorbs the solar heat. At the
appropriate time, a controller operates a circulating pump to move the fluid through
the collector.
The liquid flows rapidly through the collectors, so its temperature only increases 10°
–20°F (5.6°–11°C ) as it moves through the collector. The liquid flows to either a
storage tank or a heat exchanger for immediate use. Other system components
include piping, pumps, valves, an expansion tank, a heat exchanger, a storage tank,
and controls.
There are different ways to distribute the solar heat: with a radiant floor, with hot
water baseboards or radiators, or with a central forced-air system.
Radiant floor heat
In a radiant floor system, a solar-heated liquid circulates through pipes embedded in a
thin concrete slab floor, which then radiates heat to the room. Radiant floor heating is
ideal for liquid solar systems because it performs well at relatively low temperatures.
A carefully designed system may not need a separate heat storage tank, though most
systems do for temperature control. A conventional boiler or even a standard domestic
water heater can supply backup heat. The slab is typically covered with tile.
Radiant slab systems take longer to heat the home from a "cold start" than other
types of heat distribution systems. Once they are operating, however, they provide a
consistent level of heat. Carpeting and rugs will reduce the system's effectiveness.
See the radiant heating section for more information.
Hot water baseboards and radiators
Hot-water baseboards and radiators require water between 160° and 180°F (71° and
82°C) to effectively heat a room. Generally, flat-plate liquid collectors heat the transfer
and distribution fluids to between 90° and 120°F (32° and 49°C).
Therefore, using baseboards or radiators with a solar heating system requires that
either the surface area of the baseboard or radiators is larger, that the solar heated
liquid is heated more with the backup system, or that a medium temperature solar
collector (such as an evacuated tube collector) be used.
Central forced air system
It is possible to incorporate a liquid system into a forced-air heating system through
the use of a water to air heat exchanger.
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Alternative-Heating-Info.com
The hot water from the solar panels enters the heat exchanger through the intake
port then circulates through copper tubing located directly behind the rows of exterior
heating fins.
After circulating through the heat exchanger, the water returns to the solar panels for
reheating.
When the thermostat calls for heat, a fan blows air through the heat exchanger and
up into the house through existing duct work.
Additional heat is supplied as necessary by the furnace. The coil must be large enough
to transfer sufficient heat to the air at the lowest operating temperature of the
collector.
Storing Heat in Liquid Systems
Most storage tanks require 1–2 gallons (3.8–7.6 Liters) of water for each square foot
(0.093 square meter) of collector area. Tanks are pressurized or unpressurized, and
the type used depends on the overall system design.
Before choosing a storage tank, you should consider several factors, including cost,
size, durability, where to place it (in the basement or outside), and how to install it.
The simplest storage system option is to use standard domestic water heaters. They
are designed to meet building codes for pressure vessel requirements, are lined to
inhibit corrosion, and designed so it is easy to attach pipes and fittings.
port then circulates through copper tubing located directly behind the rows of exterior
heating fins.
After circulating through the heat exchanger, the water returns to the solar panels for
reheating.
When the thermostat calls for heat, a fan blows air through the heat exchanger and
up into the house through existing duct work.
Additional heat is supplied as necessary by the furnace. The coil must be large enough
to transfer sufficient heat to the air at the lowest operating temperature of the
collector.
Storing Heat in Liquid Systems
Most storage tanks require 1–2 gallons (3.8–7.6 Liters) of water for each square foot
(0.093 square meter) of collector area. Tanks are pressurized or unpressurized, and
the type used depends on the overall system design.
Before choosing a storage tank, you should consider several factors, including cost,
size, durability, where to place it (in the basement or outside), and how to install it.
The simplest storage system option is to use standard domestic water heaters. They
are designed to meet building codes for pressure vessel requirements, are lined to
inhibit corrosion, and designed so it is easy to attach pipes and fittings.
Air returning from the living space is heated as it passes
over the solar heated liquid in the heat exchanger.
The basic design is to place a liquid-to-air heat
exchanger, or heating coil, in the air return duct
(plenum) that sits on top the furnace.
over the solar heated liquid in the heat exchanger.
The basic design is to place a liquid-to-air heat
exchanger, or heating coil, in the air return duct
(plenum) that sits on top the furnace.
Water to air heat exchanger
Liquid-Based (Radiant) Active Solar Heating