Control gutter/roof heaters based on outside temperature

[87squirrels]

I have two long gutter/roof heaters to prevent formation of icicles along our roofline, and they 400 Watts each

 

I also have a Davis Instruments weather system, which I interface to my computer with an open-source package called wview. A feature of wview is that it can run a script on the computer when certain events occur. I have one script that runs every minute that uses the ISY's REST interface to switch the gutter heaters off when they are not needed (temp below 25 or above 35), and on when the temp is inside that window, which saves considerable power, and keeps the gutters flowing when the temp is in the critical zone.

I also use the network modules to log messages back to my computer when they are turned on and off so that I can check in to see that all is working as expected.

 

Before setting this up, I was either forgetting the plug them in, or forgetting to disconnect them; I guessing that I will save $20-30/month during Dec - Feb by virtue of not having these suckers on any more than needed.

 

I have one thing left to do, which is decide how to handle the "clear roof" scenario. I'll probably put the program triggers by the REST interface in a folder that I will disable when there is no snow on the roof, but I may handle it on the server side.

 

Edit: include actual power ratings.

[TomW]

Hi 87,

What a great application. I didn't plug my gutter heater in before some amazing ice dams formed. Next year I plan to install two additional gutter heaters.

 

Can you please share your code that you run on your computer and the ISY. Thanks.

/Tom

[stevehoyt]

It looks like this is for unix only. Is there a version or some other program to interogate the Davis weather station that will run on windows 7?

 

Thanks

Steve

[87squirrels]

@stevehoyt -- Davis does have a Windows program, but I don't know if you can access the data remotely. Since the only computer I run 24x7 is Linux, I didn't really look for alternatives.

 

@TomW -- code coming up.

 

Sorry for the delayed responses!

 

-tom

[87squirrels]

Here's the entry in wvalarm.conf:

OutsideTemp		1	-40	    60		/etc/wview/alarms/outdoorUpdate.sh

This causes the script outdoorUpdate.sh to be called once a minute whenever the temp is above -40.

 

outdoorUpdate.sh

 

#!/bin/bash

# Run as an alarm script every minute
# Notifies the home automation controller and copies a status file to the web directory

# argv[1] -- Alarm type (always 0 in this case)  from wvalarm.conf
# argv[2] -- Alarm threshold (always -40)  from wvalarm.conf
# argv[3] -- Current value (outdoor temperature)

# Status file
#               w1 [w2 w3]
#               w1 = ON|OFF -- last known status  
#               w2 = MANUAL|{null}  -- MANUAL if no automated control desired
#               w3 = ON|OFF -- manual setting 
# ISY's REST URL
ISY_REST_URL=http://isy99/rest

# Commands to send to the ISY's REST interface, based on desired state
ISYGUTTER_ON=/programs/0036/runThen
ISYGUTTER_OFF=/programs/0036/runElse

GUTTER_LO_TEMP=25
GUTTER_HI_TEMP=35

NOW=`date`
echo "$NOW: outdoorUpdate temp alarm script called with $*" >>/tmp/wvalarm.log

# Gutter heaters -- should be on from 25 - 35F
file1="/var/www/wview/outdoorGutterOn.xml"
file2="/var/www/wview/outdoorGutterStatus.txt"

# Strip decimal places so we can do integer comparisons
TEMP=${3%\.*}

if [[ $TEMP -ge $GUTTER_LO_TEMP && $TEMP -le $GUTTER_HI_TEMP ]]; then
       GUTTERMODE=ON
else
       GUTTERMODE=OFF
fi;
MANUAL=""
MANUALMODE=""

if [[ -r $file2 ]]; then
       GUTTERSTATUS=`cat $file2`
       GUTTERWORDS=(${GUTTERSTATUS})
       if [[ ${GUTTERWORDS[1]} == "MANUAL" ]]; then
               MANUAL=MANUAL
               GUTTERSTATUS=${GUTTERWORDS[0]}
               MANUALMODE=${GUTTERWORDS[2]}
               GUTTERMODE=${GUTTERWORDS[2]}            # Force to our desired mode
       fi;
else
       GUTTERSTATUS=Unknown
fi;

echo "$NOW: outdoor temp is $TEMP; gutters should be $GUTTERMODE currently $GUTTERSTATUS $MANUAL"  >>/tmp/wvalarm.log

# If the calculated mode is different than the saved mode, send an udpate to the ISY99 controller
if [[ $GUTTERMODE != $GUTTERSTATUS ]]; then
       echo "$NOW: gutter status is $GUTTERSTATUS; need to set $GUTTERMODE" >>/tmp/wvalarm.log
       ISYCMD=ISYGUTTER_$GUTTERMODE
       wget -O /tmp/isy99gutter.log --user ***** --password ***** ${ISY_REST_URL}${!ISYCMD}
       echo $GUTTERMODE $MANUAL $MANUALMODE >$file2
fi;

exit

 

The status file can also be updated by an external script to force the gutters into always-off (MANUAL OFF) or always-on (MANUAL ON) state. That script merely sets

nn MANUAL OFF

(i.e.) and waits for this script to actually update the isy.

[87squirrels]

Here's the (trivial) program.

 

If
  - No Conditions - (To add one, press 'Schedule' or 'Condition')


Then
       Set Scene 'Outdoors / Gutters' On
       Resource 'Log: Gutter On'

Else

       Set Scene 'Outdoors / Gutters' Off
       Resource 'Log: Gutter Off'


Program is triggered by script running on server's /etc/wview/alarms directory when tripped by temperature in range calling for gutter heat.

 

The network request merely creates a log file on the server, mostly for when I was first debugging the code. It's not important to the actual functionality.

 

As you can see, I could have simply set the scene on or off from the external script.

[TomW]

Hi Tom - Thanks for the code. - Tom