12 August 2016
n WITH TIM BROWN
• Solar Heating System Controls
• Inertial Navigation System Basics
Solar Heating System Controls
QI want to build a home heating system that uses olar energy to provide the heat. What types of electronic controls will I need? Tom Jenson
Gila Bend, AZ
AIn Figure 1, I show a solar powered residential heating system schematic; in Figure 2, I have included a cutaway drawing of a flat plate solar energy collector for reference. The active solar
heating system uses a pump to push water or a water/
ethylene glycol (antifreeze) through a series of tubes in
the collector. Inside the collector, the water is heated and
returned to a storage tank (think battery) until it is used for
the heating system.
Water from the storage tank is recirculated back to the
collector to improve the system’s thermal efficiency and
prevent wasting water by using it in only one pass through
the system. The storage tank’s cold water line is used to
keep the tank full in case of evaporation or small leaks
in the system which could result in lost water. The pump
could be damaged if the storage tank were to run dry, so
its level is maintained to protect the pump and insure that
hot water is available when needed.
The storage tank may include an electrical heating
element like that used in an electrical water heater to
provide auxiliary heat when there is not enough sunshine
for a couple of days to provide what’s needed. The hot
water out of the storage tank will be pumped through a
heating element(s) in the home (hydronic piping in the
floor or air duct heat exchanger) using a separate pump
and piping loop before being returned to the storage tank
(not shown in the drawing).
In locations where the outside temperature can
drop below freezing, the closed loop system with freeze
protection is used. In the closed loop system, the water/
glycol mixture can be used in the outdoor loop only so
that water from the storage tank can be used for human
consumption (ethylene glycol is sweet, so children
and animals will readily drink it and be poisoned). The
expansion tank is needed to hold the extra volume of water
in the closed outside loop which accounts for the increase
in water volume as the water heats. Plus, as the expansion
tank fills, the air in it compresses and removes any pressure
pulses generated by the pump (think filter capacitor).
Passive solar heating systems with fluid stored at a
height above the system provide pressure to push the fluid
through the system, and gravity-assisted flow (cooler water
sinks and warmer water rises) to replace the pump in the
outside loop. This reduces electrical costs and complexity,
but requires a good structure to hold the stored fluid above
the system and requires low pressure loss designs in the
piping to function properly.
Designing the solar heating system is well beyond
the focus of this column, but here are some design
Collector Design Factors
• Fluid channels should have high thermal conductivity
to allow maximum flow of heat into the water.
Q & A
In this column, Tim answers questions about
all aspects of electronics, including computer
hardware, software, circuits, electronic theory,
troubleshooting, and anything else of interest
to the hobbyist. Feel free to participate with
your questions, comments, or suggestions.
Send all questions and comments to: Q&A@
n FIGURE 1. Open Loop Active Solar Energy Residential
Heating System. n FIGURE 2. Solar Energy Collector.