Solar Thermal Information

combination with a mixing device to regulate the temperature

of the supply air stream. Such regulation prevents very hot

water in the solar storage tank from creating a burst of very

warm air to the heated space.

The size of the plenum coil should allow relatively low water

temperatures in the solar storage tank to meet the heating load.

Coils with multiple tubing rows and large aluminum fins improve

heat transfer at low water temperatures, and as such are preferred.

Coil manufacturers can size coils for the required rates of heat

transfer at specified entering water and air temperatures.

This type of system may not always create supply air

temperatures as high as those created by a furnace, especially

if the water temperature supplied to the coil is regulated by

outdoor reset control. The registers and diffusers used for

such a system should be carefully sized and placed to avoid

creating drafts within the heated space. Ideally, supply air

from the diffusers should be mixed with room air above the

occupied zone. Vertical air velocities into the occupied zones

should be minimized to avoid drafts.

Fin-tube baseboards, although commonly used in conventional

hydronic systems, generally do not provide good performance

duct coil

(in plenum)

blower

ﬁlter

furnace

return air

to/from

solar storage

tank

supply air

burners off

when heated

water is supplied

from solar 

subsystem

mixing valve

check valve

supply air temperature sensor

figure 3-10

figure 3-11