Friday, July 15, 2016

Roof mounted solar panels cool inside the building

I was looking up at my solar panels on a very hot sunny day recently.  I noticed that they were shading the roof and wondered if they were having a cooling effect and thus reducing the air-conditioning load in my office below.  So I set up 4 temperature sensors connected to my data logger to look at a days worth of data on a clear sunny day when the ambient temperatures peaked at around 100°F in the shade.
Click image to enlarge
As you can see, the shaded roof temperature averaged about 10°F cooler than the exposed roof.  I expected the solar panel surface temperature to be significantly hotter, but it was only about 10°F above ambient.  I'm not certain that my methodology was perfect.  All I did was tape a sensor onto the back of the solar panel and secure the others to the roof with duct tape.  The ambient temperature sensor was in the shade away from the roof.

The take away here is that solar panels do have a cooling effect when covering an asphalt roof.  This is clearly an advantage when the rooms below that roof require air conditioning in the summer.

Another way to reduce air conditioning costs is to install a solar powered ventilation fan in the attic.
I installed a SunRise Solar Attic Fan many years ago and it reduced my attic temperature by up to 60°F.  These clever designs use a 10 W solar panel directly connected to a fan.  You can add a thermostat to ensure that it is not running when the attic is cool.

So one can definitely say that solar panels are cool!

Wednesday, July 13, 2016

Treating bug itch with technology

In my previous post, I reviewed small plug-in bug zappers that work very well at eliminating those few mosquitoes that get into my home.  Nonetheless, I get bitten fairly often while outside enjoying the beautiful Maine summers.  Years ago I read about a simple no-cost treatment for the itch and swelling of bug bites - you simply run the affected area under very hot water for as long as you can stand it.  Apparently this changes the composition of the histamine chemistry in your body.  I have used this technique for years and it is extremely effective at removing the itch and swelling almost immediately.  The only problem is when I get bit on a part of my body that doesn't lend itself to being placed under a faucet.

The solution is to use a device that can concentrate localized heat right on the bite.  It turns out there are a number of products on the market that do just that.  The Therapik Mosquito Bite Reliever is a small, affordable battery-powered device that works extremely well in my experience.
Therapik Mosquito Bite Reliever
This cool (hot!) device looks like a weapon from Star Trek the TV series.  One simply holds the red circle against the bite while holding down the button.  
A bright light comes on inside that quickly heats up the affected area.  The suggested hold time is around 20 to 30 seconds or to the point where the pain becomes unpleasant.  Some people make the mistake of turning off/removing the device as soon as they feel some heat which is typically within five seconds or so.  But it is important to maintain a connection long enough that the affected area is thoroughly heated up to the point of discomfort.
applying heat for 20 seconds or so
The Therapik operates from a single 9 V battery that seems to last a long time.

I read a German clinical study of a similar (but more expensive) product in which they concluded: "Locally administered, concentrated heat, which was recognized by the patients as a very short and targeted induction of almost painful high temperature on the skin, led to a fast improvement of ... swelling, pruritus (itching), and pain ... symptoms.  Compared with alternatives of pruritus and pain treatment after insect bites/stings, (it) seems to be the fastest treatment option already available."

I could not agree more.  So yes, this product (and ones like it) are the real deal.

Eliminating mosquitozzzzz in the home

Every now and then a male mosquito will find its way through my window screens or front door and into my home.  Of course that sound is extremely annoying, but it's the females that don't make so much sound that I also worry about because of the diseases they can carry.  Over the years, I have experimented with a variety of solutions and currently use a large 40 Watt zapper (Flow Tron BK-15D) that I run on a timer at night out in the backyard.  While it is very effective at reducing the outdoor population, some do get inside.  I had been using a smaller AC powered one in my front hallway that zaps them before they can get too far.  The only drawback to that relatively large zapper was the sound it makes inside the home. While the occasional ZAP was gratifying, it could often be annoying.  Unfortunately, that unit failed recently so I started researching other options.

What I found is that there are a number of simple, small, ultra-low power devices that plug into an electric outlet and consume a minuscule amount of power while solving the problem handily.  the units that I purchased are made by Kooder, and I got them from Amazon for about $12 each.
Kooder zapper with 100% recyclable cardboard packaging
I was particularly impressed that the product is packaged in a simple recyclable cardboard box.  The only instructions are on the back and were clearly translated from another language with such amusing lines as: "LED lights glow to attract mosquitoes: stimulate airs, emit violet light to attract mosquitoes into the hood."

When plugged in, 2 small ultraviolet LEDs come on to attract bugs to the electrode grid inside where they die a quick and quiet death.  No loud zapping!  This subtle purple light can also serve as a modest nightlight.
works as a nightlight
The Manufacturer suggests you to take it apart (three screws on the back) and clean up the electrodes when they catch a lot of bugs.  Here's what it looks like inside.
Remove three screws to open it up for cleaning.
I ran some electrical tests on the device to see how much power it consumes and found that it draws 3.2 mA (3.8 W).  This means that it will only add about 27 cents to your monthly bill (assuming 10 cents/kWh).  So for the energy conscious, this is not a big concern.  

I also tested it by inserting a screwdriver (holding the insulated handle carefully) to short out the electric grid and it did produce some substantial sparks.  For this reason it would be wise to keep this away from young children.

To give the device a rigorous test, I plugged it into an outside outlet for a couple of nights and it caught quite a number of bugs.
bug catch after two nights outdoors - click image to enlarge
I have deployed these clever devices in my kitchen, living room, and bedroom and I am confident they will catch the occasional mosquito that gets into my home.  I also find them to serve as a pleasant night light. 

As someone who designs electronic products for living, I would be very proud of this design.

There are quite a variety of similar devices on the market, including a very clever version that screws into a lamp socket and incorporates an LED light.
OUTXPRO Mosquito Light Bulb Bug Zapper
I did not have a suitable location in my home for this type of lamp, but would seriously consider it for laundry/utility rooms and basements etc.  Apparently the bug zapper remains on when the LED light is off consuming around 3 W, while the LED lamp uses around 10 W.  These devices seem to get very good reviews on Amazon and there are many very good deals on them if you look carefully.

I don't think these devices should be confused with heavy-duty bug zappers.  They are really designed for the occasional incursion so should not be used in the same way as a larger zapper.  I would definitely not recommend them for outdoor spaces other than small screened in porches.

Once you do get bit, there is an amazing techno fix that cures the itch and pain almost immediately.  See my next blog post for a review of The Therapik Mosquito Bite Reliever

Saturday, July 9, 2016

Calculating energy cost of lamps and appliances

Conserving energy benefits the planet, while also conserving costs.  With this in mind it is helpful to be able to calculate how much money one saves by replacing an inefficient appliance or lamp with an energy efficient one.  For this example we will look at replacing an old 100 Watt incandescent lamp (which are being phased out around the world) with an equivalent 13Watt 800 Lumen CFL (Compact Florescent Lamp) and another equivalent brightness 10W LED lamp.

First, let's review the three salient electrical properties we are looking at here.  Volts which for the sake of this discussion is the available Voltage at a standard electrical outlet in the US which is 120 V.  Amps is the amount of current, and Watts is the product of Volts and Amps (W = V x A).

13W 800 Lumen CFL
In order to calculate cost, we first need to figure out how much power we will be billed for on a monthly basis.  Electrical power is billed by the kilowatt hour (kWh) which means 1000 W per hour.  Or another way of looking at this would be the equivalent of a 1000 W heater turned on for one hour.  The average cost per kWh in the US is approximately $.10, however that rate varies significantly from state to state and region to region.  Here in Maine we are paying approximately $.15/kWh.  It is also worth noting that the percentage of renewable energy sourced electricity varies significantly.  In New England we have the RGGI (Regional Green house Gas Initiative) that mandates a minimum amount of renewably sourced electrical power.  In Maine about 30% or our power is renewable sourced much of which comes from Canadian hydro, with the remainder sourced from biomass, wind, and solar in-state.

So let's start with an old-fashioned 100 W light bulb and assume that it is on in your living room for 6 hours a day.  To calculate how many Watt hours (Wh) are used per day we simply multiply:

100 Watts X 6 hours = 600 Wh

Which can be expressed as .6 kWh
Since we are billed by the month, we can multiply this by 30 to determine how many kilowatt hours per month we will be billed for:

.6kWh X 30days = 18kWh/month

To determine our monthly cost for this lightbulb, we simply multiply by the electric rate, so let's assume the US average of $.10:

18kWh X $.10 = $1.80/month

That doesn't look too bad does it?  But if you run the math for an energy efficient compact fluorescent lamp you get the following:

13W X 6hrs = 78Wh

.078kWh X 30 days = 2.34kWh/month

2.34kWh X $.10 = $.23/month

So by replacing that old style lamp with a compact fluorescent you would be saving $1.57 every month while also reducing fossil fuel emissions required to generate power for this electricity.  If you do the math for a 10 W LED lamp it comes out at $.18 per month with a net savings of $1.62 every month.  These lamps are so inexpensive now that you will recoup the investment within 5 months and since LED lamps last significantly longer than incandescent lamps it is a gift that keeps giving both to your wallet and to the planet.  Also, LED lamps contain no mercury.
9.99W 800 Lumen LED lamp
If like me, you have been using CFLs for years and are now in the process of upgrading to slightly more efficient LED lamps, please be sure to recycle the CFLs responsibly since they contain an average of about 4mg of mercury.  Lowe's stores have bins where you can return CFL's and also rechargeable batteries and plastic bags right next to their returns counter.
Recycling bins at Lowe's - next ro returns counter
So next time you go shopping for any electrical device from a lightbulb to an appliance.  You should start by looking at the label on the appliance you are replacing to see how much power it uses and do the math to figure out what it is costing you now and how much energy the new one will save.  If the nameplate on your appliance only shows the power in Amps, then just multiply it by 120 V to get Watts.  

Newer appliances are often more efficient.  For instance, it is generally assumed that if your refrigerator was made before 2000 that newer ones will be significantly more efficient.  So you will not only be saving money, you will also be doing the planet a favor by reducing CO2 emissions from the fossil fuels used to generate electricity.