Hi Walter,

Thanks for that information.  I did find it interesting, and will keep it in mind if I decide to add to my current setup.  I put some comments inline with your text below. 
I have added to the data analysis since the last email I sent on this subject.  I've got a scatter plot of daily boiler run-time vs. average outdoor temperature, and a daily bar graph showing hourly boiler run-time.  Based on the daily bar graphs I could see that the boiler runs a lot when the first floor heat is turned up in the morning, so I've raised the nighttime setback temperature a couple degrees.  It seems like the difference is made up in keeping the temperature 2 degrees higher at night, but then it gets up to temperature a little faster in the morning, with no extra net run-time.  The scatter plot shows a pretty clear (and obviously expected) trend of lower temps and longer boiler run-time.  It also shows about a 30-50% savings on days when we use the woodstove.


(more comments inline below)

On 2/18/07, Walter Sams <walter@samsco.biz> wrote:
Ben, et al

I am not much of a perl programmer, but I do have quite a number of years in
the HVAC industry and have a couple of suggestions for MH users who have hot
water boilers for heat.  This would be my answer to the " and what to do with
the data" part of your email.

While, ingenious, the monitoring of the led light really doesn't tell us that
the boiler is on, the boiler control could be malfunctioning and the burner
not actually be lit.   I would lean toward the ct device  (MS_TC)  which is a
current sensing device that will produce a signal when there is current
present in any wire that it is clamped around.  Mh will then see that the
boiler is on and engage the rest of your code.  Just be sure that the ct
device has the right range for the current you are sensing.   I would also
want it installed on the power wire going to the gas valve, again not on the
boiler control. Most gas valves are controlled with either 24 VAC or 110 VAC
so they would not pose any problem, but some are controlled with millivolts
and monitoring the gas valve current may pose a problem.

I've got an oil fired boiler, and the LED only comes on when the burner is on (and not when the blower turns on a few seconds before the burner fires up).  The LED isn't one in a separate control box -- it's right on the burner/blower unit.  I guess there must be a valve for the oil (and a pump), but I think it's integral to the burner unit and I don't want to go digging into that.  I'm content with the reliability and ease of using the LED, since for now I'm just gathering data, and not actually controlling the boiler.

The other thing I would look into since you have a sensor both on the
discharge pipe and I believe you indicated an outdoor temperature sensor
(both of which are important)  is outdoor temperature reset of the boiler.

Simply stated, you want the boiler set-point to drop as outdoor temperature
goes up.

I like this idea, but I have a tankless hot water coil, which won't work very well at lower boiler temperatures.  My hot water is practically free in the winter, but the price I pay is not being able to turn down the boiler temperature in the summer. 
I actually have a 40 gallon electric water heater that's currently unused (the tankless replaced it when the new boiler was installed on previous homeowners' dime per pre-sale arrangement).  I've thought about piping that to the tankless coil with a circulator so the sensor that formerly controlled the heating elements would instead control the circulator.  I think that should enable me to turn down the boiler temp, or even use an outdoor temperature reset, and also eliminate the problem where the tankless coil can't keep up if one person is showering and then someone else decides to start washing dishes.

You could do this with an x10 thermostat wired into the boiler, but I believe
that it would be simpler and much less expensive to use a relay with a 110 v
coil and an x10 wall receptacle  or an x10 appliance module and a relay with
a 110 v coil.  you would break the power wire going to the gas valve through
the relay.   the existing boiler thermostat would be set to 180 deg  ( the
thermostats in the living space are not involved here as they should be
connected to zone valves and only control water flow to zones)

now you are all set to write your code and let MH actually control the set
point temperature of the boiler

What we use is a proportional relationship that sets 35 degrees as the low end
of the scale, 65 degrees as the upper end   135 degrees is the lower end of
the boiler setpoint range and 180 is the upper end.
at thirty- five degrees the relay will stay on until the water temp is 180
(the existing tstat will act as a safety to make sure the boiler doesn't run
past 180 degs)  at 65 degrees you want the discharge water temperature to be
135 degrees.  ( you could do this with calculus but why bother)

your code will follow this logic
$x10boiler = x10 device
$OAT   -outdoor temperature as measured by sensor
$value  -algorithem to determine setpoint based on oat
$setpoint -a generic item
$DWT -discharge water temperature  a generic item
if ($OAT= 55) { set $setpoint = $value:}
if $DWT < $setpoint {set x10boiler ON;}
if $DWT > $setpoint {set x10boiler OFF;}

I havent tried to code this in perl for use in MH, but we do have it written
in basic running commercial enterprises

Since I use heatpumps at home, I am not pushed to work wonders with
boilers.  :)

I hope you find this at least interesting if not helpful

Walter Sams

PS:  I didnt see a reply to button on the mail list but a read only note, if
anyone knows how I can change that I would be most appreciative.