One of the most cost-effective alternatives to both liquid-based and high-mass space heating systems is an air-based installation. This is because the equipment used is relatively cheap and simple, and the transfer medium has no special requirements. Air-based systems cannot be used to heat a domestic water supply, but work well for space heating.
Pressurized systems for space heating are very similar to drainback installations, though they have additional considerations because the solar loop is always full. Unlike a drainback system, they can't just be switched off. This puts the system at risk of overheating during the hot months when it is not in use (assuming it is not drained).
Air-based space heating systems work very well in areas with high load requirements and, although they cannot be used to heat a domestic water supply, can generate as much heat as a liquid-based system. They are also very cost-efficient because the equipment is simpler and cheaper. Air-based systems come in two main types.
In general, solar thermal space heating installations that include storage use either water or sand as the heat storage medium. They use one big tank or a series of smaller ones plumbed together to provide the same volume of storage. If the system uses a single tank, it's generally unsealed: the tank can be opened without affecting the system, unlike pressurized tanks for domestic hot water applications. Both drainback and pressurized solar thermal systems can use storage tanks for space heating purposes.
Unlike liquid-based solar thermal systems, air-based installations do not suffer when they are allowed to remain idle. This advantage works to your benefit when setting up control systems, as you only need to figure out how to switch the system on when it's needed and off when it isn't.
If you're installing a solar thermal space heating system and including a storage tank, you need to bear several important factors in mind, beyond the basics of materials and the practicalities of installation.
The best storage tanks are those with no joints or seams to provide weak points for leaks. Of course, since the water has to get in and out somehow, a totally seamless tank is impossible. In practical terms, your tank will need:
Before you choose a solar thermal system for your home, it's important to go through the steps of energy conservation. We've said it before and we'll say it again: improving your home's energy efficiency is less expensive and more effective than any new renewable energy installation in the short term.
A multi-tank installation usually costs a lot more than a single-tank design and requires a lot more equipment and piping. The advantage is that the layout is a lot more flexible and retrofitting can be much simpler with several small tanks, rather than trying to get one monster tank through doorways.
The ideal location for a solar thermal collector array is one in which the sun's radiation falls full and unobstructed on the collector surface between the hours of 9:00 a.m. and 3:00 p.m., with the collector facing the noon sun directly. However, the perfect location isn't always available, so here are some pointers to help you decide whether a site is acceptable or not.
Pressurized solar thermal installations for space heating follow the same solar loop layout as similar systems for hot water. They can use single or multiple liquid tanks or they can use sand as a storage medium.
