I am happy to announce the ground temperature sensors are in place. There have been couple changes to the above plan.

First, there are now 11 sensors. The deepest one is at 11 feet. Each sensor is one foot lower than the previous sensor (1 foot to 11 feet in depth).

I placed 3/4 inch PVC in the ground for each sensor to the appropriate depth. This was to act as a sleeve to lower the sensor in the ground. I did this so that if a sensor needed to be replaced, I can replace an individual sensor without disrupting the others.

Each sensor was placed in a 3 inch piece of copper pipe with a cap at the end. Around each sensor, the tube was filled with fiberglass resin.

I used direct bury wire to each sensor individually. The wire was then sent through piece of 4:1 dual wall shrink tube and a 1/2 inch CPVC pipe. The CPVC pipe then connected to the junction box.

The junction box is a watertight fiberglass enclosure. The junction box is at a depth of about 12 inches below the surface. In the junction box, each ground sensor wire pair was soldered to a twisted pair which then goes back to the WEL unit. The solder connections were sealed with double wall shrink tube, liquid electrical tape or a combination.

For now, the ground temperature sensor readings can be viewed at the (real time data page)

Parts list for the final assembly of Ground Sensors:

• 11 – Length of 3/4 inch PVC pipe cut to 1 foot 6 inches short of desired depth.
• 11 – 3 inch pieces of 1/2 inch copper tubing.
• 11 – 1/2 copper pipe caps.
• Fiberglass Resin and Hardener.
• 1 – Watertight Fiberglass enclosure.
• 11 – 1 inch to 3/4 inch CPVC threaded reducers.
• 11 – 3/4 inch to 1/2 inch reducers.
• 11 – 1/2 inch CPVC pipe cut to 1 foot 3 inches short of respective lengths.
• 11 – 1/2 inch 90 degree elbows.
• 1 Roll of direct bury twisted pair cable (4 pair per wire).
• 4:1 Double Wall Shrink Tube (to secure 1/2 inch Copper pipe to 1/2 inch CPVC).
• 3:1 Double Wall Shrink Tube (for solder connections).
• 11 – DS18S20 Temperature Sensors (from (http://www.ourcoolhouse.com)

This was a fun project. And as usual, I found better ways of doing things after the fact, so I am thinking of a second generation ground sensor system.

Well, I am running into issues with deploying the ground sensors. Five of the 10 sensors which were originally assembled had to be replaced. Once replaced, these sensors seemed to operate well with all the existing sensors.

The next step was to place the sensors in a length of copper tube surrounded with bentonite (grout). This was not an easy task. Finding the right consistency of water and grout was a trick. Then during the drying process, the grout was compacted. I found that this is a difficult process to make sure that there are not air pockets left in the tubes.

Now the problem I am running into is the rest of the monitoring system. It seems that there is an issue which periodically causes the temperature sensors to register false readings, extremely high or no reading at all.

I checked the humidity in the crawl space which was very high. I started a dehumidifier to bring down the humidity level. The level is now about 50% and the occurrence of temperature spikes has been reduced. I have set the dehumidifier to 45% to see if this will eliminate the temperature spikes completely.

At first I thought it might have been caused by a bad temperature sensor again from the ground sensor group. All those sensors were already removed from the system.

I was hoping to get these sensors in before the start of winter (2006), but this may not happen this year.

Summer 2006

Well, this has been accomplished. I tested it yesterday. Now during the heating season, if my geothermal HVAC system calls for auxiliary heat or if the emergency heat is required, electric resistance heat run time will be tracked.

What will be displayed on the Live Data page are two variables at the Air Handler display. These two variables are daily run time and total monthly run time.

Now we can see during the course of the winter how much the system actually goes into auxiliary heat. This will also give us an idea of how much this is costing and a ball park as to how much power is being consumed. We will also be able to tie it in with the outdoor temperature, loop temperature, etc.

Ok, now I am looking forward to winter!

The 10 temperature sensor assemblies have been completed.

A twisted
pair wire has been soldered to each DS18S20 temperature sensor. Each pin and solder connection on the temperature sensor has been covered with shrink tube.

Each temperature sensor was then covered with 3:1 dual wall shrink tube. Each end was sealed to prevent moisture from contacting the temperature sensor.

The temperature sensor assemblies have been added to the 1-wire system. The temperature values can be seen on the live data monitoring page.

Once the grout material has been received, each sensor assembly will be placed in the copper tube and the copper tube assembly created.

At that time, all 10 copper tube assemblies will be bound together and placed in a sealed plastic bag and the temperature sensors calibrated. After calibration, the copper tube assemblies will be removed from the 1-wire system and the ground monitoring assembly put together.

The hole will then be bored in the ground and the ground monitor assembly placed and then connected to the system.

I have been thinking of creating another temperature sensor assembly and placing it in water to test to temperature sensor assembly should it come in contact with water.

Let’s monitor the temperature of the ground!

Well, I have been busy with my next project for my Geothermal HVAC monitoring system.

What else could I do with the system?

I am going to put temperature sensors in the ground! I plan on placing a temperature sensor from 1 ft below the surface to 10 ft below the surface.

I now have the temperature sensors, twisted pair wire, shrink tube, copper tube, CPVC pipe and connectors. I am going to start by wiring the sensors, placing them in the copper tubes and then placing them on the monitoring system to calibrate them. I will be adding to this post with materials, lists, plans, status, and other details.

Here’s the project:

I thought it would be neat to monitor the ground temperature at 1 foot intervals. There is no real value to this project accept monitoring the ground.

I have been curious that Geothermal Installers and other professionals claim that the loops can be as shallow as 5 - 8 feet.

Now, in my area the frost line is considered to be 42 inches. In the winter, when temperatures are below zero I would think that if it is near freezing at 42 inches, another 42 inches down it would be cold.

We shall soon see. Here is what I plan on doing.

• Part List:

  10 DS18S20 1-wire temperature sensors will be placed at 1 foot intervals starting at a depth of 1 foot.

  10 pieces of 1/2 inch copper tubing, each 3 inches long.
  10 pieces of 1/2 inch CPVC pipe, each 9 inches long.
  19 1/2 inch cpvc pipe union connectors.

• Twisted pair wire is soldered to pins 1 and 2 of the temperature sensors. Shrink tube covers the solder connections and pins to insulate them from each other.
• Each sensor assembly is covered with 3:1 dual wall shrink tube. This is done to protect the sensor from moisture.
• Each copper tube assembly will contain a temperature sensor assembly. A small piece of tubing will be placed in each copper tube assembly to run the 1-wire twisted pair through the entire monitor assembly. The bottom copper assembly will have a copper cap soldered to it. Each copper tube assembly will be filled with grout material used to seal vertical geothermal well shafts. This is done to improve the thermal conductivity of the copper tube assembly.
• In between the copper tube temperature assemblies will be a 9 inch piece of 1/2 inch diameter CPVC piping. The CPVC piping will be attached to the copper assemblies with union connectors. Each copper assembly’s temperature sensor wires will be connected to the twisted pair wire running the length of the entire monitor assembly. This connection will be soldered and then covered with 3:1 dual wall shrink tube to prevent moisture from entering the connection. Each one of the CPVC pipes will then be filled with low expansion foam. This is being done to help keep the temperature sensor assemblies isolated from the others.
• To prevent the 1-wire twisted pair from being accidentally cut, the wire will be placed in CPVC tubing at a depth of about 1 foot below the grass as it goes to the house to be attached to the WEL monitoring system.
• Creating the hole to place the ground monitoring assembly in place appears to be a challenge. At this point, I believe I will use a process which I learned as my ground loop was installed.
• I will use 3/4 inch diameter CPVC piping about 3 - 3 foot lengths. I will dig a hole about two feet deep and then using the 3/4 inch diameter CPVC piping and a high pressure nozzle on a garden hose literally pushing the 3/4 inch pipe in the ground.
• Each one of the 3 foot pieces will be connected using union connectors. When the entire length of 3/4 inch CPVC is in the ground, then the entire length will be pulled out. The ground monitoring assembly will then be placed in resulting hole.