This project is a
monitor for my gas
water heater. It
consists of a phototransistor aimed at the burner through a small
I have a new 'Flame Lock' style burner, access to the combustion
is very limited, and I was unsure if enough light would hit the
phototransistor. This project was started and completed in
weekend (hardware and most of the software).
Schematic of the monitor. R1 is adjusted to produce a full
swing with the gain and incident light of the
The OUT terminal is connected to the Power
, which was already hosting the water
. I do not have a part number for the
as it was from my spare
The water heater monitor before the wiring was dressed with ty-wraps.
The phototransistor is held by a stiff 16 gauge copper wire (red) so
that it can be freely positioned in front of the window.
The black film container holds the R1 resistor and
has enough room to allow reconfiguration of
Close-up of the phototransistor. It is held in a two pin socket that is
soldered to the
wiring and then wrapped with heat shrink. The red copper wire
around the heat shrink to hold the assembly. The glass lens
does not touch the little glass window of the combustion chamber.
View along the phototransistor aimed at the
burner. The sensor is aimed at the
brightest part of the flame. By manually dialing the
on the water heater, I could fine tune the value of R1 to optimize the
Cost analysis of a shower
The home control system allows me to plot any of 24 parameters that are
monitored by the system. The chart below shows only the water
and the gas water heater run time. The latter
of this project.
Chart with only the water
gas water heater run time plotted. The
chart has been zoomed into the region of when the shower took
place. The user is able to
position a cursor to read the data value at any time and point in the
chart. The axis for the water heater run
time is on the left (cumulative minutes - red trace),
and the axis for water usage is on the right (gallons - yellow trace).
A cost analysis of this shower is as follows:
|Length of shower
|Amount of water used
|Run time of water
|Gas consumption rate
|Amount of gas used
|Cost of water and
|Cost of natural gas
|Cost of water
|Cost of gas consumed
The gas usage rate of
the gas water
heater was determined by using the dials on my gas meter and a
stopwatch. The 'half cubic foot per rev' dial makes one full
revolution per minute when the gas water heater is running.
Future uses of this system
- A monitor for a setback
temperature down during vacations or
overnight periods. The actuator for this may, for example, be
RC servo. Proper safety measures would need to be in place to
prevent the accidental setting of a very hot temperature.
- The monitoring of the
of the home if I should
install a radiant heat
- After some usage, I may
software monitor to alert me if
the water heater burner runs beyond a time threshold.
- October 10, 2004 - Sensor installed, power node updated,
initial changes made to home control software.
- October 11, 2004 - Graphing support added to water heater
- October 12, 2004 - Cost analysis of shower.
- January 15, 2005 - A 15 day absence provided information on
efficacy of the insulation of the water heater. During that
period, the water heater did not run a single time! Presuming
that it was about to cycle the burner upon our return, we can calculate
the upper bound of the heat wasted per day through the insulation of
the tank. Since the water heater runs for about 11 minutes at
minimum (due to its hysteresis), the maximum average run time (due to
energy lost) is 11/15 minute per day. Using the data in the
above, a calculation shows that it costs less than 0.5 cents per day to
maintain the water hot in the water heater. I found this very
amount very amazing.
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