Soak up the sunshine
This is an excerpt from an article in Sanctuary magazine issue 5.
If you want to keep your home warm during winter the first step is to consider good passive solar design and high levels of insulation. If extra heating is required for comfort, solar hydronic heating is often a good option. Solar hydronic heating warms your home by taking advantage of an environmentally friendly energy source—the sun. Hydronic heating systems are typically gas-fired and have been used in Europe for almost a century. Solar hydronic heating systems that use evacuated tube solar collectors as the primary method of heating the water needed for the hydronic circuit are now available on the market.
How does it work?
Solar collectors capture energy from the sun and heat the water in a storage tank to the required temperature via a coil in the top of the tank. If the solar system does not heat the water in the pipes sufficiently, a backup boiler comes on and boosts the temperature. A pump circulates the hot water through pipes around the hydronic circuit, and the heat is transferred into the room through wall mounted panel radiators or through piping laid in a concrete slab floor during house construction. A separate heat exchange coil in the tank can provide domestic hot water for household use.
The backup burner can be run off natural gas, solid fuel or LPG. If you live in an urban area the most economical and environmentally friendly fuel for the backup is natural gas. Solid fuel can be labour intensive and LPG can be up to two and a half times more expensive than natural gas and will significantly increase the running costs of the system.
The components that make up a solar hydronic system are:
- an evacuated tube solar collector to capture energy from the sun
- tanks to store the hot water that is heated during the day
- backup burner which can heat water to a thermostatically-controlled temperature
- a pump to circulate water through the hydronic circuit
- piping that carries the water from the boiler to the panel radiators or to the in-slab pipes and back again for reheating.
A crucial component of the system is the mixing valves, which regulate the water temperature. The evacuated tubes are capable of producing high temperatures, so for safety and reliability reasons it is essential that these temperatures are controlled.
Getting the heat out
Panel radiators are most commonly made of pressed steel and can be installed in existing homes or during the building process. Each panel can be controlled independently, which gives you the benefit of being able to shut off heating in rooms that are not being used.
In-slab piping or ‘foil coils’—made from polyethylene—are generally installed during the building process, but a concrete slab can sometimes be introduced to an existing home during renovations. When considering in-slab piping for your home talk to a concreter who is familiar with your area to ensure that your slab is not likely to shift or crack. The piping can tolerate some kinks and movement, but in-slab piping will not be suitable for all land areas. The piping is usually laid out in a minimum of three zones, which gives you the benefit of controlling heating to only the rooms which are being used. Once heated, the concrete slab floor converts into a radiant heat bank that releases heat evenly throughout an area.
In-slab floors can be tiled or the slab can be finished as a polished concrete floor. Carpet is generally unsuitable, due to the carpet underlay acting as an insulator and preventing the heat being released, but floor rugs can be an option. Timber floors can be laid over in-slab piping. However, the thickness of the wood can impact on heat transference and may also affect the warranty on the timber as the wood may shrink and buckle if it is not already kiln dried.
