Refrigerator Analysis Part #2

 

While collecting data on my current refrigerator to determine if it makes sense for me to replace it, I placed a data collector inside the refrigerator to monitor how the temperature changes throughout the day and also to see when and how long the refrigerator door is open. 

The data logger was an Arduino Uno with an Adafruit Data Logging Shield, a DS18B20 temperature sensor and a photo resistor to detect when the door was open/shut.

Below is a 24 hour graph detailing the temperature swings and the frequency at which they occur.  I was quite surprised by how often the refrigerator cycles on and off.  I assume that the temperature spike at 11pm was due to the freezer going through its defrost cycle.

Also included in the graph (in red) is when the refrigerator door was opened and for how many seconds within that one minute period that the door was open.  It’s interesting to see the effect that opening the door has on the temperature.

Has anyone else ever put a temperature logger in their refrigerator?  And if so, is my temperature cycle normal?

Refrigerator Analysis

 

Our current refrigerator is a GE Profile 24.7 ft^3, model number TBX25PAB that was manufactured in March of 2001.  As part of our Half Project, I was interested is seeing how our refrigerator (which is not Energy Star rated) compared to a newer model refrigerator and to see if it made sense to upgrade.

The power consumption of the current refrigerator was measured with a Kill-A-Watt meter over the course of several weeks at 2.4 kWh/day, or 876 kWh/year.  For our area, Dominion Power charges us approximately $0.11/kWh, so our cost to run the refrigerator is $96/year which is about 3% of our yearly energy consumption.

The Energy Star website has a refrigerator/freezer calculator that you can use to calculate the operating costs of your current appliance.  I used this to compare the actual usage data that I collected with the estimated usage from Energy Star.  The chart below shows that the estimated usage is slightly higher than my actual usage, but it is within 10% which is acceptable for an estimate.

Model	Data	kWh	$/kWh	Per year cost
GE TBX25	Actual	876	0.11	$96
GE TBX25	Estimated	961	0.11	$106

 

GE makes a newer version of the Profile series which is a direct replacement for what I currently have.  It is a little pricey at $1800 but let’s look at its performance.  First of all I’ll ignore the fact that the Sears website has conflicting data with the Energy Star label over yearly kWh usage and I’ll just use the data from the Energy Star label. 

Model	Data	kWh	$/kWh	Per year cost
GE PTS25	Estimated	560	0.11	$61

Using the Energy Star estimates for both the old and new refrigerator I can expect to get the following savings.

Energy Saving/year	401 kWh
$’s Saved/year	$44.11
Initial Cost	$1800
1st year Return	< 2.5%
CO2 Reduction	441 lbs

With a payback period of ~40 years, upgrading to the newer model GE Profile just doesn’t make sense right now.  It’s time to research other models of refrigerators.

Solar Site Survey And Collector Output Comparison

 

I recently conducted a solar site survey for the area by my shop where my solar air heaters are located.  This should normally be done before you build and mount your collector, but in my case, I had never heard of a solar site survey before I built my first collector.

The purpose of the solar site survey is to determine where obstacles are that will block the sun from reaching your collector and to determine if those obstacles will interfere with your collector all year or just certain times of the year.

To do a solar site survey you will need a few simple things…

• You’ll need to know which direction solar south is
• A sun chart
• An elevation and azimuth gauge

 

Determining Which Way South Is

Solar south (or true south) differs from magnetic south depending on where on the planet you are.  For our collectors, we don’t care where magnetic north/south are, we care about how the sun tracks across the sky and where true south is in relation to the sun.

BuildItSolar has a list of several methods for determining solar south.  One that is not listed is the “I’m in the middle of nowhere but I have a stick and 2 rocks” method.  To determine true south take a mostly straight stick/rod that is about 3 feet long and stick it in the ground vertically.

Stick with first marker placed.

Where the stick’s shadow stops, place a marker such as a rock, quarter, or large washer on the ground.  Then sit back, enjoy the sun and wait… 20 to 30 minutes should be fine.  After some period of time has elapsed, place a second marker on the ground where the stick’s shadow now is.

Stick with second marker placed.

With the two markers now on the ground, draw a line between the markers.  This line will run east – west.  A line drawn perpendicular to the east/west line will give you north/south.

Direction of true south determined.

 

Tools For The Survey

As mention above, you’ll need to obtain a sun chart and an elevation/azimuth gauge.

A sun chart shows the position of the sun (elevation and azimuth) for every minute of the day.  Sun charts are available from the University of Oregon here.  You just need to enter your zip code (or your latitude/longitude), download the pdf file, and print it out. 

The elevation/azimuth gauge can be downloaded from here courtesy of BuildItSolar.  You’ll need to print out 2 copies.  One will be used to make the azimuth gauge, the other will make the elevation gauge.

Once they are printed out, make the azimuth gauge first.  To do this, attach the print out to a piece of cardboard (I used some adhesive spray), and then attach a small wooden pointer to it with a nail through the center point of the reference circle.  Then take the gauge and place it on a flat surface and align it so that it is pointing south.  When you’re done it should look something like this:

Azimuth Gauge

The elevation gauge will also need to be attached to a piece of cardboard.  Once that is done, trim the paper and cardboard along the “site line” that is marked on the paper.  Next you’ll attach a piece of string with a small weight attached to the end (like a washer) to a nail that is pushed through the center of the reference circle.  When you’re done it should look something like this:

Elevation Gauge

 

Conducting The Survey

To start the survey, make sure the south marking on the azimuth gauge is inline with solar south and then move the pointer on the azimuth gauge so that it is pointing east.  As you move the pointer from east around to the west, note the position of any obstacles such as trees, buildings, mountains, etc.  When you find an object, take the elevation gauge and site along the “site line” to the top of the object.  Note the angle that the string is at and place a pencil mark on your sun chart for the corresponding azimuth and elevation angles. After you’ve worked your way around to the west, you’ll need to draw a horizon line on your sun chart by connecting the dots.  When you’re done it will look something like this:

Site Survey Sun Chart Showing Obstructions

 

 

 

Comparing The Survey to Collector Data

From the survey sun chart you can see that I have a large obstruction due south (at the 180 degree mark) of my collector location.  I have another tree 40 degrees west of that, and by the time the sun is 60 degrees west of due south, it’s behind the tree line and done for the day as far as generating useable heat.  If we look at the line for Jan 21 and where it intersects with the horizon line, I should start getting sun on the collectors from 9am – Noon, from 1pm – 3pm, and a little between 3pm – 4pm.  When we compare this to the graph of the temperatures from the collector we see that the data matches up pretty close.  The collector starts warming up a little after 9am and runs until roughly noon.  It then comes on again about 1:30pm and stays on until 3pm. 

Temperature Graph From Solar Collector

One nice thing about the site survey is that you can look at the sun chart and determine how long certain objects will affect the collector performance.  The sun chart shows that starting in mid-Feb, the sun will clear the top of the large tree to the south of the collectors and that the collectors will get full sun from 8am - 2:30pm and from 3pm – 4pm. 

Solar Air Heater #2

I recently completed the build of a screen based solar air heater that is now attached to my shop next to the soda can based solar air heater that I built last year and detailed here.  It is based on designs from BuildItSolar and the Yahoo Simply Solar group. 

Screen and Soda Can Heaters

 

Construction

• Frame:
  • Constructed from ¾" x 4 ⅝" oak. This size was selected to match the finished depth of the can based collector that it is mounted next to.
  • Outside dimensions of the box are 96" x 49"
  • The back of the box is a piece of ¼" plywood.
  • The outside of the box was painted with exterior latex paint that matches the paint on the building.
  • There is a cap on top of the collector box that is sloped to shed water.
  • There are trim strips on the sides to close off the gaps between the box and the siding so that the local wasp population can't build nests behind the collector.
• Insulation
  • The back and sides are insulated with ½" R3 polyisocyanurate. ½" is the thickest any of the local home centers in this area carry.
• Screen:
  • Two layers of 18 x 16 x 0.011 mesh aluminum insect screen spaced 1 ¼" apart and painted black with high temp grill paint.
  • The screen is mounted on a ¾" wide by 1 ¼" deep frame that fits just inside the insulated sides of the box.
  • The wood for the screen frame was not perfectly straight and required that a horizontal spreader be placed across the screen frame at the mid-point to keep the frame from bowing in.
  • The spreader is ¾" x ¾" and will block some of the vertical flow of air that is between the 2 layers of screen. This might possibly force some of the air back through the screen. Is this good or bad? After completion I realized I could have used a much smaller spreader, maybe 3/8 dowel.
  • The screen is mounted parallel with the glazing. It is not tipped outwards from the bottom to the top as some collectors I have seen.
  • The screen frame is held up off of the back insulation with 4 small wood blocks that are sized to center the screen in the box between the back insulation and the glazing.
• Glazing
  • The glazing is 2 pieces of Suntuf from Home Depot.
  • There is a vertical support bar in the center of the box where the 2 pieces of glazing overlap. At first I tried just sealing the 2 pieces together with silicone but this failed to hold up while moving of the glazing panels prior to installing them and I realized it wouldn't hold up during expansion/contraction of the glazing panels either. The glazing is now screwed to the support bar to hold the 2 pieces together. There is a bead of silicone run between the 2 pieces to help with sealing.
  • The glazing is currently not sealed to the collector frame. It is screwed to the frame at every valley location on the wiggle strips. It is also screwed to the stiles of the collector box about every 15 inches.  This was done so that the glazing could easily be removed if I decide to add a third layer of screen.
• Fan and Ducting:
  • The air inlet and outlet ports are 4" round duct. They are centered in the box horizontally and are offset from the top and bottom by 2".
  • The fan is a 125 cfm fan. General guidelines from the Yahoo Simply Solar email group suggests 3 cfm per sqft of collector.
  • This is the same model fan used in the soda can based collector.
  • The fan is mounted at the lower duct location and pushes air through the collector instead of being mounted at the top and pulling air through the collector.
  • The temperature control is provided by a 90/110 snap switch. It is mounted to the back right next to the outlet port.

 

Thoughts After Construction

• Twin-wall polycarbonate looks much better.  However, 
  • The 2 pieces of Suntuf cost $42.
  • The closest place I can get twin-wall is 100 miles round trip and is $90 for a 4' x 12' sheet. 15 mpg in the truck and $3.15 for gas adds another $21 to the twin-wall price.
• I was surprised that with 2 layers of screen how easy it is to see the insulation on the back of the collector.  Based on Gary Reysa’s tests on BuildItSolar it appears that 2 layers of screen will absorb approximately 52% of the incoming light.  This collector has a reflective back so the screens will get a chance to absorb some light on its way back out for a total of about 80% absorption.  While the collector seems to be performing well, I’m not pleased with having possibly 20% of the light reflected back out of the collector.  I need to investigate adding a third layer of screen or painting the back of the collector black.

Crawlspace Insulation Fail

I recently did a full survey of all the insulation in my crawlspace. I've been under the house on several occasions before but I never really looked at the insulation other than to say "yep, there's some there."

I'm not really sure what inspectors look for before signing off on the different phases of construction, but I have a feeling that when it comes to insulation and crawlspaces, the inspectors just ask the contractor if they insulated the crawlspace and if the contractor says yes, then it passes inspection.

Armed with a flash light and camera I dove in to see what I would find.  Below are a few of the flaws/shortcuts that the contractor took. 


On the north side of the house, there is a just a partial floor joist bay between the band joist and the first floor joist.  Since this is an odd size the easiest thing to do is not install any insulation.

Whenever there are pipes in the way, obviously the best thing to do is to push all of the insulation to one side. 

When you encounter duct work, you must not install any insulation above it.  No one is ever gonna look up there anyway, right?  And when you do put a section of insulation in, you should grab a piece that's 16" wide even though the engineered joists are on 19.2" centers. 

When you get to the end of a roll and you're 12-14 inches short of making it to the end of the joist bay, it's probably good enough.   On the east side of the house, every single bay was short by about a foot.  Lovely...

On the left side of this picture the exterior wall makes a 45 degree turn and runs right into "it's Miller time".  The end result is a three foot gap.  Notice that the insulation isn't pushed up tight against the sub floor either.  This allows cold air to get another 6-8 feet further in before it finds an insulation hanger that is properly installed.