There is an upper limit on how much Pex tubing you can use in a radiant heating installation. If the circuit is too long, the solar fluid will cool off before it reaches the end and you will get uneven heating. For standard-sized Pex tubes (half-inch or 5/8-inch internal diameter), the circuit length should not exceed 300 feet – which is conveniently the size of the coil supplied by many manufacturers.
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Before you begin laying Pex tubes into your heating area, you must prepare the ground. The area should be flat and level, with the insulation in place and a vapor barrier under the insulation. If you are going to enclose the Pex tubes in a slab, you can cover the insulation with reinforcing wire or rebar.
Radiant floor installations rarely need more than seasonal adjustment. Typically, they are set up at the time of installation and just need to be switched on or off depending on the time of year.
At installation, the ball valve on the heat exchanger bypass stays about 1/3 closed at all times, forcing some of the hot solar fluid through the heat exchanger, but allowing most of it to go to the radiant floor heating (or shunt loop in the off-season).
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.