Thermal Continued from page 34
drop. Also, the power consumption of the pumps can be substantially less than those of a drainback solar sys- tem since the pump is only overcom- ing pipe losses and not vertical lift. This can be especially important in commercial applications where pan- els may sit a significant height above the storage tanks.
ALL THE PERFORMANCE half the energy
T1
manufacturers have begun to produce glycol mixes that are able to handle temperatures up to 350°F. The addi- tives and inhibitors in these products help extend the life span of the anti- freeze, but most of the time the addi- tion causes the fluid to no longer meet the FDA’s generally regarded as safe (GRAS) guidelines. While still
Freeze Protected Area Free ze Protecte d Are
zea Cold Wat er I WIn Wtater In WO
IndicaIndicator and Flow Meter
Fluid Level Flow Meter
Fluid evel r and Wl Water Fil at er Filll Level eve
Preheated Water Out
Preheate d at er Out
Drainb a ck T
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The new Halsey Taylor® HVRGRN water cooler series spurred the creation of a new GreenSpec listed product sub-category, bringing sharper focus to the value of clean, safe, efficient delivery of drinking water.
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T2
Drainback Tank
An example of a drainback system utilizing a hot water storage tank with an inter- nal coil heat exchanger. When the system is not operating, fluid sits inside the freeze protected area. Certain valves and small components are not shown.
The biggest issue seen in anti- Assembled in the USA
Circle 22 on Reader Reply Form on page 57 Page 36/Plumbing Engineer
freeze based systems is the degrada- tion of system fluid over time. During periods of non-use, or in sys- tems with undersized storage, it is possible for some collectors to sit hot on the roof and reach temperatures over 250°F. This causes some types of glycol to break down resulting in degraded freeze protection capabili- ties and raised pH levels. This can harm other system components and create the formation of “sludge” which can cause further issues in the system. In order to combat this issue many
non-toxic, certain codes require that a double wall heat exchanger be used, adding cost and potential- ly lowering the systems efficiency. Other non-propylene glycol based fluids are becoming available that can withstand high temperatures (over 450°F) but issues such as high viscosity at lower tempera- tures can cause pumping issues. Systems that do not regularly
experience stagnation are in less danger of fluid degradation and may require minimal maintenance. If a system is designed properly with
Continued on page 56 April 2011
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