Tuesday, July 02, 2019

improving cell data with a refrigerator

I have been experimenting with my cell phone as the hot spot for my home internet. The pic is my Rogers cell based internet after placing my phone in the best location which I discovered here yesterday, on a box on top of my fridge.

Rogers is offering an unlimited data plan which was a $5/mo upgrade so I took it. I intend to drop my land line based internet to save by having cell only.

My current ADSL (phone line based) internet is the least expensive plan from the only landline provider in my area, Eastlink. I enjoy slow but solid internet, 5 Mbps download, 1 Mbps upload, unlimited for $75/mo. Rogers will now cost me $80/month for their cheapest wireless unlimited plan. (see their website and the pic above)

Before yesterday, my Rogers cell data and reception were not good inside the house. And highly variable, from un-usable to outstanding. Today, reception has not changed except that I found the best location from which to access my available signal. I am pleased with what I found but there are a couple of caveats (read on).

Where I live has two negatives for cell data. My house is low in elevation relative to the two area cell towers so much of the cell signal is blocked by surrounding hills. Second, my house is covered with a metal mesh based cement that effectively shields electromagnetic radiation, like cell signals. Two negatives.

I looked at 4G cell repeaters/boosters. Hundreds of dollars and not all work with Rogers. I haven't tried one yet.

I learned about cellular booster reflectors from old satellite dishes.

Instead, I loaded an app to measure cell signal strength. I am using Network Cell Info Lite. This one is for Android.

The gauge display shows main and next best cell signal strength in dBm. The gauge updates every second or so.

Most people don't think much about where they put down their phone. Or maybe your carry yours? Our phones are marvelous little radios which are sensitive to orientation and surroundings! Especially when we need them to work their best.

I have been exploring my house for my BEST signal. Signal inside my house varies over a huge range from -100dBm to -125dBm. The dBm scale is logarithmic. Lower numbers in this case are hugely better.

I can see that I am using band 12. This changes sometimes to band 4. Both of these are 800-900 Mhz. In rural areas like mine, lower frequencies like these will travel further and have adequate data rates to impress me when working well!

I don't get to pick a tower or frequency. Those are selected auto-magically between my phone and my provider.

I can see LTE on the display. This might mean 4G but it's complicated in Canada.

Yesterday I drove to the two towers that serve my area. look up your local cell towers, operators and frequencies Each is about 6 km distant, one is to the north and one is south. Using my app phone signal strength meter I measured the signal about 1 km from the towers at about -60dBm! But nobody lives there, well not many anyway...

By clicking once on a tower in the map, I learn that at the northern tower, Rogers uses 700MHz, 850 MHz and 1900MHz, Bell uses 700 and 850. At the southern tower, Rogers uses only 700 and 850. Bell is not on the southern tower. More specific information on all of the cell transceivers at a tower comes up in a table if you double click on that tower.

Back at my house, quite by accident, I found TWO spots where the signal is best. Both are on top of large grounded metal objects: my refrigerator and my clothes dryer. The metal case of both appliances is attached through their electrical cords to earth ground.

With my phone flat directly on top center of either the fridge or the dryer, my signal strength is the best inside my house. The fridge is slightly better at -97dBm.

When I check download data rate using speedtest.net from either of those spots, it is noticeably higher (twice as high!) than most anywhere else in the house!

But Upload data rate is much worse when the phone is placed directly on top of these large metal objects! It slows to less than 1 Mbps. But - if I lift the phone up about 5 inches high and place it on an empty cardboard box (about 1/4 wavelength, my phone is using 850MHz) the download data is still good and the upload data improves enormously!

Is it possible that the appliances are making a ground plane for the phone, helping with receive and transmit?

I tried different height boxes (two, three, five and eight) and the five inch seemed to be best.

I tried changing the phone's orientation, on either side, on the ends, rotating it slowly in different planes while holding it approximately 5 inches above the fridge and trying to watch the display. But placed down flat on the phone's back on the 5 inch box seemed the best (lowest) dBm reading. Minor changes if rotated slightly and slowly on the box.

I tried putting the phone over a large un-grounded metal plate on the kitchen table, with and without the 5" cardboard spacer box. The metal plate made no difference.

I rarely use my phone for voice so parking it on top of a box on the fridge is no problem for me. I can hear it ring anywhere in the house.

When I go out, the phone comes with me so the home network stops. I don't have any "smart home" devices that need always internet so this is not a problem.

If there were two phones in the house, one could set up sharing of two cell links with two hot spots (with bridging?) to further improve data rate?

If you try this, please let me know.

This experience has caused me to clean the top of the fridge. It was pretty dirty up there but cleaning had no effect on the signal strength.

Thanks for your interest.

George Plhak
Lions Head, Ontario, Canada

Update Jul 22 2019 Eastlink has been OFF since I wrote this and I have been accessing the web with Rogers cell only. I frankly haven't noticed the change, except for generally better responsiveness (plus!) and having to retrieve my cell phone off the fridge when I go out and then putting it back (negative). The actual internet data service is far superior to what I was getting with Eastlink (5mbs down 1 mps up) as this speedtest just now shows. I was worried about the throttling back "feature" but that does not seem to have happened yet. I get my latest full Rogers bill with usage and dollars on the new plan tomorrow.

Monday, June 24, 2019

hot wire foam cutter

I built a simple hot wire foam cutter to make parts for a couple of projects.

I wanted to slit a full sheet of 1.5 inch insulating foam into strips for a mooney wall. Another project, a water heater insulator, required large foam discs.

What started as quick and dirty ended up a very useful tool.

Using scrap wood, I began by adding a slot and a "fence" to a partial sheet of particleboard to make the table. The board was what I had, about 3 foot by six foot supported on two saw horses. I added a strip of wood lengthwise opposite the fence to support the front edge. The table is hung on the wall when not in use. [click any pic to enlarge]

Using particle board was problematic. When fed across the table, large pieces of foam would catch on the tiny sharp fibers sticking out of the particleboard. I later sanded and painted the top surface with several coats of latex paint which helped. It would have been better to use a smoother surfaced board.

The cutter arm is U shaped to support the cutter wire and slides in a groove under the table to adjust. It is then fixed in place for the cut.

I thought to make a variation with the hot wire slide-able to make cross cuts but haven't done that yet.

The slotted hole in the table is for the hot wire. I didn't want to cut through the fence on the back of the table. There is a minimum width that the wire can be set to, about 6 inches and a maximum of about 18 inches. The width of the slots for the mooney wall are 14.5 inches so this is a good amount of adjustment. Varying the dimensions could give other capacities.

The hot wire on the bench with power supply testing cutting action!

It turns out that the wire does not need to be red hot as shown, but just slightly less, sort of a dull red. I have an adjustable DC supply giving the wire about 4 amps at 8 volts. The voltage and current will depend on the wire type, gauge, length and the desired temperature so the adjustable lab supply is a good fit for a hot wire cutter. Normally the supply sits under the table and is connected to the two ends of the hot wire with test leads.

The wire I am using is heater wire (nichrome), typically used in toaster ovens. The first samples of wire I used were harvested from an old appliance. Later I found that I could easily buy small amounts of nichrome wire on Ebay from China so ordered 0.3, 0.4 and 0.5 mm coils.

I found that 0.4mm nichrome gave good cutting life and resistance to breaking. Getting the right temperature and the feed rate requires a bit of experimentation.

Nichrome wire expands when heated, as much as 5%, so there is a spring in the mount to put the wire under tension. When at the operating temperature, there should still be a bit of tension from the spring to get a straight cut.

The wire is simply looped through the eye bolt and wound around itself a few turns. The nuts on the eye bolts are adjusted to put the wire under tension. Normally I form, adjust and test the wire on the bench out in the open, then remove it from the arm, mount the arm on the table and then remount the wire through the slot in the table. It's easier.

Shows the smooth cut on blue type styrofoam. The edge obtained is very smooth.

Cutting foam discs with a pin through the center into the table as a pivot.

Using a thin template to guide the wire to produce a cutout in one of the discs.

Again using a template to make cutouts in one of the discs which has been already cut in half with the wire.

One of the many eight foot by 14.5 inch slabs for the mooney wall that was cut with the wire cutter.

Thanks for your interest.

George Plhak
Lions Head, Ontario, Canada

Detail under the table showing the mount for the arm made from scrap wood. The arm (with the wire removed) is inserted in a slot from the back and fixed in place with the screws that protrude to the right. Crude but adequate.

Thursday, June 20, 2019

water heater update

INDEX to the series

This graph [click to enlarge] shows the big reduction in standby energy use between my old (blue) and new (red) water heaters at different basement temperatures. The new uses much less electricity, about 25% less. Same capacity, same size heat elements. 25 year age difference.

What's changed?

The new heater has better insulation, a DIY insulated mounting base and is time of use controlled so it does not use peak priced electricity.

I will show the key physical differences between the new and old. The old was produced in 1994.

My old water heater had been quietly making hot water in the basement here for 25 years. It was not leaking and did not require replacement. It had no maintenance during the last five years with me. It worked well but could have been more efficient.

I pay tribute to this fine Canadian product by Giant Factories Inc. It owed me nothing.

To become more efficient, I purchased a competitor's product from GSW (division of A.O.Smith). Although Fergus is on the nameplate, the GSW factory in Fergus hasn't made anything in years.

I might have made a better comparison by getting a replacement Giant. Local stock product was competitive in price.

In any case, I will compare old product to new product. Both are standard electric domestic hot water heaters, now called "Automatic Storage Water Heater". Both are the same size (give or take a cm or so, I lost my actual measurements). About C$350 cost now. The technology of even the most simple commodity hot water heater has improved dramatically. Much of the improvement is federally mandated to improve efficiency. My old and new have the same capacity and the same elements but are 25 years apart in manufacture.

In other words, GSW's Fergus product of 1994 is probably much like the Giant of 1994.

So if you haven't thought about improving your trusty old hot water heater, you might save significant electricity if you do. Here is what I found:

The top of the old with the cover removed. I can see the steel tank where there is no insulation.

I am holding the anode which does not help efficiency but adds life expectancy. This anode rod (aluminum or magnesium usually about the size of my little finger) is completely corroded. An anode rod is replaceable but who ever does that?

The anode protects the inside of the steel tank by being sacrificially dissolved itself as a dissimilar metal, like a zinc anode on the hull of a sailboat. When it is gone, the tank starts to corrode so this one is well past its best before date. 25 years old! Probably never been changed.

Note the iron pipe fittings out the top for inlet, outlet and pressure relief. Copper lines were attached to these fittings with no thermal break (insulated coupling).

These UN-INSULATED metal pipes had been heat radiators into my cold basement. The pipe from the hot water outlet (the one on the left with the pressure relief valve) was always HOT to the touch. Lost heat.

Note also that the insulation inside is a glass fiber wrap with lots of empty space/air! Particularly over the very top center. Perhaps I pulled some of it off with the top? It could not have been this bad could it?

I didn't determine how the steel tank was supported inside the steel can but there must be some metal support structure from the tank to the outside which would probably cause some heat loss.

The new heater has about 2.5in / 6-7cm of foamed in place insulation at the top near the center. I am measuring to the steel tank through the anode access.

In fact I had to dig out some insulation to get access. I wanted to look at the installed anode. The top of the anode rod bolt will be my measuring point for water tank temperature once I insert a sensor and cover/insulate the opening I have made in the insulation.

The anode access has a cute cover plug but once removed, you need to dig out the foam down to the hex head on the anode bolt.

Note the insulated fittings for hot and cold on the top of the tank. The pipes that lead to these fittings are no longer warm to the touch.

Likely the foamed in place insulation completely supports the tank mechanically (unlike glass fiber) so no need for a bridge structure hence lower heat loss.

The fitting to the drain valve at the bottom of the tank was an iron pipe to a metal valve. Both good conductors of heat to the basement.

The old tank used to sit right on the cold concrete basement floor.

"Verified for Energy Performance" in 1994!

The drain is now a recessed plastic valve, a much better insulator.

I've raised the tank off the floor on an insulated base, making it easier to do the annual residue draining and reducing the heat lost to the cold concrete floor.

The wooden base (about 8 inches high) is topped with a 1.5 inch foam disk.

The diameter of the base is larger than the water heater by about the thickness of a batt of rock wool insulation. It could have been a square platform to be simpler to make.

I will wrap the entire new water heater with an insulating blanket after installing seismic straps. Not required by the code here but a good idea anyway for a 100 year event. Earthquakes do occur in Canada.

Time of use inhibit I wrote about here.

I plan to install direct energy metering for the water heater as it is one of my top energy consumers. NRCan on water heaters. Note that there are no storage tank electric water heaters that are Energy Star rated. I think mine will qualify when finished!

Thank you for your interest,

George Plhak
Lions Head, Ontario, Canada.

INDEX to the series

Nameplate for the old Giant.

The date code means the tenth month of 1994.

Nameplate for the new GSW lists Fergus, ON CANADA for address of manufacture?

Monday, June 03, 2019

reader project 6

Project description from Matt Janssen:
[click any pic to enlarge]


Here is a 3/16" laser-cut steel-framed parabolic trough array based on your design.

There are a lot of things I really like about your design and there is no way I could have learned so much about parabolic trough technology that would have not taken more time and more money than building your design and experimenting with it. I believe your geometry with the fixed absorber tube is key for small trough construction. I have fought rotary joints on steam projects before and they are just too finicky and expensive.

One improvement I made after my first trough using your CAD files is to add a countersunk angle iron under the sheet at the longitudinal rim edge of the trough which assists with clamping the edge and avoiding corrugation caused by bending stress around fasteners.

We re-drew the ribs and added this countersunk notch as well as an offset for the reflector sheet thickness. The troughs have 68" T316 24 gauge Super 8 SS sheets which have about a 63% reflectivity. I am using one of the bottom holes for a 1/4" through stay rod. The troughs are powdercoated.

I started out with (9) 3/8" black pipe return bend elements slid in the borosilicate vacuum tubes running forced-flow in series and at no flow could make 200F. The geometric concentration ratio of this setup is about 22. While the array could make significant hot water with flow, I did not test it further as the max temperature was too low. I then installed 1/4" sch 40 pipe bare absorber tubes and reconfigured the pipes to parallel flow. In 40F with high insolation I could make 265F steam with no flow. This is about the limit of concentration ratio that a thin sheet reflector compressed to a rib frame will support - about 35.

I think even more performance could be achieved with these troughs by using silvered mirror film and encasing the tubes in glass. I have decided to start over and this array is now available.

I have about $15K in parts in it and a reasonable offer with timely removal takes it. There is one spare trough like these, my first trough, an aluminum trough, the other absorber elements, a bunch of borosilicate tubes, and a welding fixture.

The array was stored inside all winter and was just hauled-out 05/30/2019.


Matt Janssen mjanssen@monida.us
Sandpoint, ID

If you like, you can email Matt directly.

Thank you for your interest

George Plhak
Lions Head, Ontario, Canada

reader projects
reader project 0
reader project 1
reader project 2
reader project 3
reader project 4
reader project 5
reader project 6 this article

Wednesday, May 29, 2019

rain barrels 2

Barrel equalization with a siphon bridge and flood control continued

rain barrels part 1

Lessons learned: This is a former rain barrel setup where I had re-used three food grade barrels on a raised platform behind a pool shed/pump house. The location was ideal, steps away from a large (5m x 10m) vegetable garden. The edge of my solar pool heater array can be seen at left back.

Using only rain water my three barrels were adequate to spot-water my garden over several hot summers without diverting the pool waste water. I used a watering can, not a hose. Better exercise and water control.

The two downspouts delivered all the rain water from the shed roof into the outer barrels.

I considered diverting some of the waste water from cleaning the pool sand filter (the single white pipe lower right) into the barrels. The high flow rate of the waste water made it difficult. I had once measured the flow rate as 37 gallons per minute. There was no "low" setting for the pump and 50000 gallons of water available in the pool. Better to just let it blast out into the seasonal stream. The wastewater pipe extended about 5 meters from the shed toward the stream.

So diversion of the pool waste water was not really required. But some of the details of that system could have been improved.

Covers on the barrels prevented insects from entering and laying eggs (like mosquitoes). Some designs have a screen at the top of the barrel. Any debris from the roof would have to be cleared regularly from this screen. That sounded like a bad idea.

Here, rainfall via the downspouts dropped straight into the barrels through tight seals in the covers, keeping insects out. But was not a good idea for a couple of reasons.

Any debris from the roof went directly into the barrels. By the end of the season, there was a thick bed in the bottom of the outer barrels, enough to clog the equalizer hoses.

There was no provision for overflow. During torrential rain a small lake would form at the back of the pool shed from the water that overflowed the barrels. Next to the house this might cause water to enter the basement or saturate the foundation. But behind the pool shed this wasn't a serious problem.

The single tap was on the center barrel. I had used a fancy and expensive bulkhead valve from Lee Valley Tools, so there was only one tap from which to draw water from three barrels.

I needed a way for the water to flow between the barrels, as new water was added to the outside or as I took water from the center tap. You can see my solution in this picture [click any pic to enlarge]. I used Carlon electrical fittings and short lengths of garden hose to connect the three barrels at about the same level as the tap. The tap height establishes the lowest level that the water can be in the barrels so the equalizing hose should be at the same level so all three tanks drain equally.

If the equalizer hoses or the tap are up on the barrel somewhere, not at the bottom, you won't be making full use of your barrel capacity.

A barrel should be raised off the ground, at least as high as the top of your watering can, or higher.

Back to here and now: I have re-arranged my two 55 gal re-cycled food grade barrels to be at one end of the roof rather than one at each end. I want to do some work on the other end of the wall so that barrel had to be moved. I have adjusted the trough on the roof edge to slope downward to this corner rather than down from the center so all the water now flows to this corner.

I have a single diverter (at the green arrow - the Canadian made "Catch-A-Raindrop" described in part 1) in the downspout to the ground and a single fill pipe to the left barrel. The downspout sends overflow into a drainage ditch to get the water further from the foundation. The diverter will not send water into the barrel when it is full. Leaves and debris from the roof continue to the ditch. It works great!

But it only feeds one barrel while maintaining auto shutoff to prevent overflow.

I needed a way to equalize the level in two barrels. I could have used the same arrangement as I did above but instead I decided to try a siphon bridge.

My siphon bridge is a length of hose which reaches the bottoms of both barrels. Primed with water (no air inside) the siphon bridge will allow water to flow from the barrel with higher water level into the barrel less full. I am using PEX.

Here I am demonstrating to myself that the concept does indeed work. The right barrel had been about a foot lower in level. After about 1/2 hour, the two barrels equalized.

The siphon bridge was attractive because I didn't have to put any new holes in the barrels. I had already emptied, cleaned and refilled them. To accommodate the siphon bridge needed two pipe sized holes drilled in the barrel lids.

The final configuration with both barrels full and ready. The blue arrow shows the siphon bridge in place. The yellow arrows show the tips of the water level gauges.

Note that insects have no way to enter the water. The tops of the barrels are essentially sealed although some air can enter as water leaves the barrels.

I suppose the siphon bridge could be used to connect three or more barrels.

Although simple, the siphon bridge needs to be primed. This means sucking the air out. I used my mouth on one end, holding the other end deep in one barrel. I held it low to the ground to ensure that water was flowing at a good clip and then closed the end with my thumb and stuck it underwater in the other barrel.

It was necessary to have the PEX already inserted through the covers so they could be screwed down once the siphon was primed.

The siphon bridge has the disadvantage that it needs priming and it might again if it looses prime. The horizontal tube at the bottom approach does not require priming but it is more complex and needs more holes in the barrels.

rain barrels part 1

Interesting video of siphon bridge used between two raft beds.

Thanks for your interest.

George Plhak
Lions Head, Ontario, Canada

As before, not wanting to pick on Home Hardware. This is a current example of a popular rain barrel product with an insect screen at the top. Roof debris would clog this filter unless cleaned regularly. No overflow consideration. With tap at the bottom of the barrel you'd get more water out if the barrel was raised off the ground, at least as high as the watering can filler. Not sure how you would cascade two or more of these if you wanted more capacity.

Monday, May 27, 2019


a short photo essay

A small footbridge I built 2005-07 across a "seasonal stream" at my last home. Tiny fish would swim up the stream in the spring. By late summer no water.
[click any pic to enlarge]

I had intended the bridge to support a lawn tractor so I overbuilt. But I never drove the tractor over it. Used it only as a footbridge. But it was strong enough.

The foundation started as two piles of random rock. Still wet and mucky underfoot in late August.

Hand mixed cement foundations. Rain overnight. The tarps were over the forms. The half round ends are cut from Sonotube joined to plywood and backed with 2x4's. The 2x4s across the top hold the steel brackets in the correct places.

The foundations held a temporary bridge the first winter.

Frame detail. The bridge is four feet wide - bigger than it looks.

Finished footbridge.

You may like another bridge project.

Thanks for your interest.

George Plhak
Lions Head, Ontario, Canada

Saturday, April 27, 2019

CO2 meter

We hear so much about CO2 these days.

I want to measure indoor or outdoor CO2 concentration at a reasonable cost (~$100).

These are first reactions to HT2000, a portable recording CO2 meter which also measures temperature, humidity and dew point.

My HT2000 came from bangood.com product ID: 1258981 "USB Carbon Dioxide CO2 Data Air Temperature Logger Humidity Meter Monitor LCD" US$99 and arrived promptly in a little over a week. I noticed shipping was from a depot in Mississauga.

I think what I have is an unbranded generic version since I see others like it when I search "CO2 meter". Mine is one of the cheaper ones.

The case is bigger than I thought it was going to be, about 5.5"/14cm long and about 1-1/2"/4cm thick. Case is not sealed or waterproof. It can't be, air has to move through it. You wouldn't carry it in a pocket easily, nor would it work very well in your pocket.

HT2000 needs to be out in the open on a table, desk or dashboard, for example. I've concluded that HT2000 is sufficiently sensitive to CO2 that if I hold it at arms length in an enclosed space, my own body expelled CO2 will affect the measurement.
My CO2 aura in effect.

My HT2000 arrived in a clam shell carrying case with manual, software CD, USB cable and charger (mini-USB, not micro). Under a cover on the back holds 4x AA conventional batteries. I found run time of about a day on the internal batteries since HT2000 is hungry. Draws about 1.1 watts from AC when plugged in.

I tried to measure actual battery pack current after getting inside the unit. The current drain is very peaky rising to almost 2A at 6 volts then dropping then rising. It was impossible to get a stable reading from my digital amp meter. I will try again later with an RMS reading milliamp meter. HT2000 seems pretty demanding on batteries. There is a hole in the side of the case for what might fit an optional DC input but there is only USB power or internal batteries on mine. When I plug in USB power it switches from battery but there is no indication on the display.

[click any pic to enlarge]

The manual I received is in English. A challenge to read but all the right information is there. I found another version of the manual online by searching "HT2000 manual". Between the two and fiddling with the unit, I was able to figure it out.

On power up, the unit performs a short self test and the display shows all digits and characters, some of which seem to be for other versions of the instrument since I never see them lit during use except at self test?

After self test, the unit counts down seconds from 30 to zero to "preheat" the sensor as explained in the short manual.

When I first started the unit at my desk, the CO2 numbers were over 1500ppm and I was a bit concerned that the instrument was faulty. I had been looking at it closely before starting it up for the first time. When I put it at arm's length and left it alone for a while, the number dropped to a level more like the first picture 600-800 ppm so it was quickly apparent that it was responding to me!

There are alarms for CO2 and the other measurements that can be set in the software. The default alarm for CO2 is 2000ppm. I can reach that level easily by just blowing at the instrument from a foot away! The alarm is a loud constant tone that continues until the level drops or the unit is switched off! I am glad that it didn't alarm the first time! It was close.

Yesterday was a beautiful Spring day so I spent the afternoon cleaning up winter debris in the back yard.

Outside, HT2000 gave readings from 350 to 400 ppm, about what it should be. I was burning wood scraps in a fire about 5 meters away from where this picture was taken so there may have been some effect from the fire? It seemed to me that when I got close enough to the unit to read the display, CO2 started to rise but I can't be sure of that! There was gusty wind.

The reading update frequency is changable in the software. I currently have it set for 1 second update. This is a different setting from the recording frequency which I have set for 1 minute.

The software has two main sections. The Communications section lets you connect, setup and read the instrument via USB. I am in the Data section in this picture showing the results of my first overnight test recording of CO2 concentration and temperature in my bedroom last night.

The data is scroll-able on the left side and graph-able on the right. The settings for the graph can be changed.

I found the Data view a bit restricted so tried the data export to a spreadsheet and graphed the results from there. I gave the Temp its own axis so it wasn't constrained down at the bottom of the plot.

The measurements are every minute, there are 890 measurements. #1 is 15:48 when I installed it upstairs, pushed the record button and left the room. There is no one else upstairs. You can see the CO2 and the temperature settling over the next 100 or so measurements. About #100 the CO2 goes up slightly but the temp keeps dropping slowly. I think the furnace may have started and stirred the air in the house? The windows are all closed. It is still heating season here.

About #342 (21:30) I enter the room to sleep. I don't close the door. A bit later, the furnace shuts down to overnight temperature. Temperature starts a slow decline and that's MY CO2 increase in the room! I think I can see that the variability (the envelope?) of the CO2 data also gets larger.

Around #784 (5:00 morning) the furnace starts to warm the house. Temp abruptly starts to rise and CO2 falls abruptly as my CO2 is spread around the house.

Around #852 (6:00) I rise and move around the room before exiting. I leave HT2000 in the room for another hour before taking it downstairs and downloading the data.

A look inside the unit shows the IRM300SS sensor from SemeaTech. [the gold thing at the top]

There are two versions of this sensor. This one is accurate to 5000ppm but has a 5 year life. The "non-SS" version measures to 2000ppm but has a 10 year life expectancy. These are nondispersive infrared sensors (NDIR), specifically for CO2. A "simple spectro graphic sensor" using IR light which is tuned to a specific gas.

There is one peculiarity regarding the batteries. When the batteries are low, the unit will start displaying 0 ppm. Before that occurs however, the display will start flashing what looks like "Bar" every few seconds. Really means "Bat" which was confusing the first time and alerted me to the short battery life.

To prevent problems with recordings, rely on the batteries only to move the unit when it is not recording. Or you can take measurements without recording when you have fresh batteries. Plug the unit into USB power for recordings.

Once you push the Record button you MIGHT see the REC record indicator flash ONCE briefly. It's on the left side middle of the display. From then unit is recording and you will see REC flash BRIEFLY every time it makes data. If you have recording set to once per second, you will see REC flash every second. If you have the duration set longer, you may not see it flashing easily.

One more thing: CO2 must propagate into the sensor and this takes time. There is no fan. You can speed reaction by moving the unit around in the air causing airflow through the case. There are slots in the top back and sides for airflow but it's passive. Nevertheless, unit does respond to changes in seconds. It just may take minutes to reach some equilibrium.

I purchased HT2000 because it looked potentially useful. I am not sure yet what specific uses it will find with me. It is always good to be able to measure. Do you need one? I have no idea but perhaps you now know more to help you decide. If you do find cool uses, let me know.

Thank you for your interest.

George Plhak
Lions Head, Ontario, Canada

You may also like my radon test

As is my custom, this is not a paid review nor do I receive or solicit any product in return for writing. I am not selling these products. Just ideas. I don't get a commission. I don't show ads. I don't have a fundraising or patreon page.
I write in the hope that this is interesting or useful to you.
If you would like to show support for my independent work,
please consider commenting or buying one of my books? Thank you. George

update June 24 2019 CO2 in my home varies over a wide range. This is a low I saw June 10. I haven't noticed a pattern.