Non-Integrated Solar Thermal Heating Systems

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Although it is usually preferable to connect your solar thermal space heating installation into a grid-tied system and have the two work together, it's not always possible. Some retrofits simply do not lend themselves to integration, so you will end up with two separate systems. They can still work together, just not to the same extent.

The most common difference between solar thermal and grid-tied heating is that the renewable option favors radiant panels, whether they're in the floor, walls or ceiling. Most grid-tied systems work with wall-mounted heating of some kind, whether traditional radiators, hot air blowers, baseboard radiators or something else. If this is the case in your home, your solar thermal system can produce the other kind of heat to that which your grid-tied system provides, without doubling up on equipment.

Although a separate radiant floor system is the most efficient method of delivering heat generated by a solar thermal installation, it is not the only method. Radiant panels, fan convectors and baseboard units are also available if you prefer.

Fan convectors are basically a liquid-to-air heat exchanger with a blower attached to help circulate the heat. They are very common in motels, where they are usually installed under the windows: those 2-feet tall, 3-feet wide, 10-inch deep things that make a constant low noise! Fan convectors are very easy to fit, they don't take up much room and they can deliver enormous amounts of heat in a very short time, so they are understandably popular. They are particularly good at providing extra heat when a radiant floor doesn't quite do enough (e.g. in a bathroom where you want the temperature a little higher than normal). The downside is that they use electrical power for the blower.

Baseboard units are like traditional radiators: those oddly heartwarming metal-finned, wall-mounted heaters with which everyone is so familiar. Although they're called "radiators", they actually work by convection. The system circulates hot fluid through the fins; the fins heat up and warm the surrounding air which rises and pulls cooler air into the radiator area. They are much more efficient heaters than a forced-air system, providing comfortable heat in even large rooms (provided the insulation is good). Cast iron models are very good at delivering a lot of heat efficiently and work well with dump systems, though such models are hard to find because they are so old-fashioned.

The good news is that the control circuit for any of the delivery methods is very simple and is exactly the same for all of them.

You will need:

  • A thermostat
  • A circulating pump
  • An aquastat (or setpoint thermostat)

The thermostat detects the temperature at the delivery mechanism. The aquastat monitors the temperature in the heat storage tank. The circulating pump switches on when the heat delivery equipment needs warming and the fluid in the tank is hot enough to provide that heat.

There's an additional advantage to a non-integrated system: the control mechanism can all be run on standard voltage supply instead of having to downrate everything as in an integrated setup. You'll need