Dashboard source...finally

After a long time not having the time to take care of this, and knowing that a lot of you are out there eagerly awaiting it, I finally decided to publish it.

Then the problems started: my outdated OS doesn't interface well with github, which in turn doesn't allow for easy upload of binaries via the web interface.

So after a log of fiddling around, I managed to make a tar.gz file, with, I hope, all the necessary files to get an idea of how it works. here is the link to google docs, where I hosted it:

Dashboard: click here to download

There are a series of PHP files in there ending in "_service.php". These are the files called by the HTML5 page to update the data. They now have fixed data, and you'll have to adapt them to your own infrastructure. Also, I didn't include these service files for every functionality in the dashboard, leaving that as an exercise to you.
Also there are a few places where you'll have to insert the links to your own google agenda(s).

This is how it should look like if you dump it into a folder and access it via a suitable webserver.

Anyway, I think you probably can deal with it, and want to have it more for the design aspect then the actual infrastructure. Either way, enjoy it and have fun with it!

Having seen the recent developments in web technology with respect to sockets and stuff, I think I'll soon take my time to make this more real-time!

Let me know if it works, and if you use it, and also what you make with it!

Fan controller

As mentioned in the previous post, I am busy with changing a radiator here in the house, and, as part of my investigations into heat distribution efficiency and space efficiency, I decided to try a radiator built in the ceiling with forced air circulation.

This will be placed in the bedroom, in the ceiling, so out of sight, apart from the ventilation grills, in the attic.

The radiator receives the heat from the standard hot water circulation system, and uses a ventilator fan to take the heat to the room.

This particular unit has a 24V DC motor, whose speed is controlled by a 0V to 10V signal, so, like I mentioned before, I built an amplifier which takes a 0 to 3.3V filtered PWM JeeNode output and multiplies it by 3, giving me a nice 0-9.9V. Here is the schematic, made using Fritzing:

It works, a basic test with a very slow sweeping output turns the motor on slowly, ramping it up to maximum speed, and back again to off.
The controller in the JeeNode will read the input and output temperatures using a pair of good old DS18B20's, and controlling the speed accordingly. I am still developing the algorithm for that (will certainly pass by some sort of PID controller).
I don't really plan on using the JeeNode radio for the control part, but will certainly be feeding back statistics later on!
The regulation of the water will be by means of the FHT8V which has now been serving in the room for the last 5 years or so!

This weekend I'll disconnect the current radiator, which takes a huge amount of space in front of the windows, and start the process of assembling the new one. We'll move to a spare room for thermal confort!!

Dashboard once again

It's been more than a year since I last published about the dashboard. And that it because not much happened in that front.

Meanwhile, a friend gave me a tablet, cheap chinese thing, which I planned to use to display the dashboard in a visible place in the house.
The thing could even display the HTML5 and handle the AJAX calls and all, but it was unstable, sleep mode would spend the battery almost as fast as normal mode, slow to boot, bad touchscreen (resistive), and so on, and so on, so I quit on it, and consequently on the progress on the dashboard, as the experience while using it is, in my opinion, of great importance!

A few months later, my wife offered me an iPad, the new retina display model! so that rekindled my interest in the dashboard. I came back to iWeb, expanded the design a bit, and have spend a couple of evenings implementing the functionality...this is the result:

And for the explanation:

electricity and gas consumption: the pointers move, as the data is updated, and shake slightly when stable, to indicate that the thing is alive. The numbers are updated twice a minute.

House control: this interfaces mainly with the FHZ1000 part of the automation. It reads set, measure and desired temperatures, displays the measured, and makes the box green if the room is set for comfort temperature (even if it has not yet been reached) and blue for low temperature. The boxes turn orange is there is no reply.
The buttons for the awnings are toggle buttons: click to extend them and click to retract them, since the system has no idea of what their status is (they can be operated locally). They briefly blink through orange to give feedback that something happened!
climate limited: is a button to limit the maximum temperature to which any room can be set
holiday mode: should set all rooms to a low temperature and out of the standard program. this is the only button not yet functional (and therefore transparent).

Door events: list of the last 4 events on the RFID door.

System messages: reports errors on the system, like now, the weather station has stopped transmitting.

Agendas: list a few items (enough to fill the respective boxes) taken from google calendar. I have a google calendar for the house, where I put the garbage schedule, and other maintenance activities that need to take place.

Outside temperature: like the name says, displays the data from the weather station. Now it displays nothing, since the station stopped working - see system messages :)

And that is it! data is updated on timers, and the agendas on loading of the page.

There has been talk in the tubes about some mechanisms to update data in real-time. That should be the next development, but that might take another few years :) This is nice enough to show to my friends :)

AH! last but not the least, I found out that one can include some lines in an HTML page to make it a iPad app, so, by adding:

    <meta name="apple-mobile-web-app-capable" content="yes" />
    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />

I can save the page onto the iPad desktop (is it what it is called?) and run it as any other app, without the safari address bar. Only the top bar with the clock and stuff is still visible, but that is even a plus, as it gives you a clock and iPad info!

I'll try to post a screenshot from the iPad soon!

Small update!

It has been a while since I posted something here...the truth is, not much has happened in the electronics front.

The JeeTherm has been working flawlessly since I installed it, on the 15th of January, so that it over 2 months ago. During those 2 months, we had some serious cold coming this way, I measured -15C on my weather station! That is the lowest ever recorded here.

One interesting thing about this whole story of the efficiency of an HR boiler, is that, due to some graphics I found I limited the temperature setpoint of the boiler to 55 degrees, as this is the limit above which the efficiency decreases rapidly, thinking that, if it gets really cold, I could raise this limit, as it is all software anyway, and there was no need to recompile anything (on the JeeTherm the limit is 80C, on my PID controller implemented in PHP, the limit is 55C).

As the cold came and settled in, I noticed that the boiler, and the whole heating system was still able to warm up the house, and keep it warm, even in the coldest days! so I ended up never having to raise it! I was glad, I had days where the boiler worked nonstop, but down to a simmer. My energy saving correlation calculation also indicated that the gas spent was way below expectations, although the curve fitting was not done with any data in that kind of cold range.

What bothers me the most, is that I could never really find any good info about this efficiency story. In many forums you can find people saying that an HR boiler needs a 20C difference between feed and return to operate at optimal performance, but all the graphics I find of performance, none indicates such a difference, the efficiency being a simple function of the return temperature. Furthermore, if that is the case, then the boiler should be set to start modulating to try and achieve such a difference, but the behaviour I see with my boiler is that it modulates to have a 7C or 8C difference between feed and return. sometimes even 5C. I start to think that all that matters is the return temperature...and that one, I have it limited to 55C now!

Now I'm in the mood

For doing calculations, as I have to ascertain whether all the effort was worth it or not.
So, I have this curve fitting against which I can compare my gas consumption based on the average outside temperature for the month. But his is done for a month, and I wanted to see if I could go to a lower level, so I found in the KNMI website a service from which you can download all kinds of meteo data for a time period.
I downloaded the average month temperatures for "De Bilt" as that is where I have been basing my calculations all these years, although not the closest station, and plotted it against the daily gas consumption. I couldn't go away without putting it here, so here goes, for the month of November:

Considerations on the boiler system

The behaviour I mentioned at the end of the last post, does make sense.
That is, for the boiler to overshoot by a few degrees, once it has reached the set temperature, and by those means bringing the return temperature to the set point is the only way of avoiding it to cycle more.
Once the boiler stops burning, the temperature of the outgoing water drops almost immediately to the return temperature, so to avoid it turning on again, the return should be close to the set temperature, and that is what the boiler is doing, thereby keeping the water in the whole system at the set temperature, and not at the return temperature that happen to be there when the set temperature was first reached... (I hope someone can make sense of all this rambling...)

The system , with the DIY OpenTherm master, has now been running for a few days, with no problems, and quite an accurate temperature in the rooms. The PID controller just needs some small adjustments in order to converge a bit quicker, and converge always (I sometimes have 0.2 degrees below the set point, which is no big deal anyway...)

I found a few graphics depicting the boiler efficiency as a function of the return temperature. Here are a few, all in Fahrenheit (didn't find any in C):

http://www.mnshi.umn.edu/kb/scale/boilers.html

http://blog.triangletube.com/blog/hydronic-heating-solutions/outdoor-reset-maximizes-spring-energy-savings

http://www.navitron.org.uk/forum/index.php?topic=9066.0

The last is not the efficiency, but the relation of water temperature to outside temperature that I am using. I use a curve near the "1" curve.

On the way to a finished project

An enclosure is also important! and now that the OpenTherm interface is working, all the software is written, and I just put it to work less than an hour ago (lets see how that goes...), I also went searching for a box.

I went to my trusted shop, probably one of the last in Holland to sell components offline, it is the last one for at least 40Km around...probably more...and found some boxes from Hammond Manufacturing.

These are great, as they have card guides and can fit a Jeenode precisely!! here are some photos:

1591MSBK

1591LSBK

The low one, one has to cut the flange of the lid to be able to close it (and maybe grind a bit of the sides of the JeeNode), the higher one, which I will be using just fits it all with no problems!!

Here is also a graphic of the gas usage with the first hour with the OpenTherm:

before I always about 4 blocks of burning, as a saw tooth -  burning level increasing slowly, from 0.01 to 0.05m3 per minute in 4 to 5 minutes...maybe I'll try to get one of those images for comparison.


And a bit of the radio transactions already digested:

seq: sequence
set: set temperature received from server
out: temperature of the water leavng the boiler
ret: temperature of the water returning to the boiler
status: status of the boiler

seq       set   out   ret  status
3483    38    42    37    10    @    Sat Nov 26 16:04:19 2011
3523    38    42    38    10    @    Sat Nov 26 16:04:59 2011
3563    38    43    38    2    @    Sat Nov 26 16:05:40 2011
3603    38    39    38    0    @    Sat Nov 26 16:06:20 2011
3643    38    38    38    0    @    Sat Nov 26 16:07:00 2011
3683    38    38    38    0    @    Sat Nov 26 16:07:40 2011
3723    38    38    37    0    @    Sat Nov 26 16:08:20 2011

apparently, the boiler allows an overshoot, or tries to control the water such that the return temperature is controlled...still need to investigate this further...

Opentherm JeeNode shield PCB

Progress has been slow, but steady, in the opentherm front!

As I mentioned before, JCS is helping me out with the PCB part, and he has produced a nice PCB in the form of a shield for a JeeNode, which should be able to connect to the boiler! I leave to him to explain how he does his magic...

I have drilled the holes today, big victory for me, and now I just have to populate the board, cut it to the proper size, and develop the software.

I also still need to properly dimension the resistor at the detector optocoupler before I solder the whole thing on the PCB.

In the picture some resistors are still missing, but I just wanted to make this public! The designs and software will come soon!

i just realised that I should have included a couple of LEDs on the board to display status, but it can still be added in a later revision :)

OpenTherm Circuit diagram

Here is a nice circuit diagram, made by JCS (from Coffee, Bits and Bikes), who is helping me with it.

The value of R2, which is indicated as 470 Ohm, is not yet final, as I still have to do some tests. The problem is the CTR of the optocoupler, which can be quite high, and so I will have to define the resistor such as to cause the transition in the proper place.
Next posts will be the code! so stay tuned!

More OpenTherm

Back from holidays! and with good news - I managed to communicate with the boiler using OpenTherm!

If you remember, the last time I managed to communicate, however, the boiler was not doing what I was telling it to do, namely, to heat up the central heating water to 35 degrees, instead, it was displaying an error state, and not a very informative one, in the small display.

Here is a picture showing the oscilloscope trace, where both the master to slave and slave to master burst messages are visible.

Since I had not implemented a decoder for OpenTherm, to analyse the reply from the boiler, I could not know what the boiler was complaining about. So I came up with a solution: I installed the OpenTherm arduino decoder found in the palebluedot site, and commented my emitter directly to the arduino with the decoder. As expected, the message was going with an data error. After finding a couple of bugs in my manchester encoder, I managed to get a correct message across.

Time to send the message to the boiler.

Another trip to the attic, and the boiler received the message, but didn't start heating up, but also no longer went into the error state. A careful read of the protocol, and I realised that I was disabling the CH when sending the message with ID=0. At the end of page 24, one can read that the "CHenable bit has priority over the Control Setpoint". So, another change to the message, another trip to the attic, and success!! The boiler started up, heating up the central heating water to the set temperature of 35 degrees!!

Next step is to implement the decoder in the same JeeNode, and the make a little PCB shield. After that, it is a matter of software, both in the JeeNode and in the server, to implement the communication layers, and of course, the much awaited and though of PID controller!

Thermal camera

This past week I got a hold of a nice infrared camera! or thermal camera or however those things are called...

Due to unforeseen circumstances, however, I didn't have as much time to play with it, as I had foreseen, but nevertheless, I managed to take a few snapshots.
The weather has also been pretty warm (as warm as it get in Holland...) and so it was difficult to get the ideal conditions to identify heat leaks.

One of the main purposes that I was interested in it, is that we are about to change the windows, which are now steel frames - ideal cold bridges - to some high-tech aluminium profile with high performance double glass. So I wanted to snap some shots of the current windows before the new ones come in so that I can compare. I will anyway compare in the energy spending next winter. By the way, the next post will probably be the energy assessment for the past winter.

I'll get the camera again once the windows are in! and the cold sets in!

So, there is not much to say about these, but the images are nice! Here are some samples, outside the temperature was about 6C and inside 15C:

Fig. 1: The iron/steel frames, almost as cold as the outside

Fig. 2: The house outside. Upstairs we already have the nice aluminium windows, with the super glass

Fig. 3: The electricity meter - gets pretty warm in there. It would be interesting to compare it to an old fashioned one.

Fig. 4: The CNY70 doing the gas metering

Fig. 5: Heating pipes when starting to warm up, the inflow is pretty warm , as the return is still cold. That is the best case.

Fig. 6: Old cast iron radiator warming up.

Fig. 7: GU10 spots - This one is a kind of CFL

Fig. 8: GU10 spots - this one is a standard halogen.

Fig. 9: GU10 spots - this one is a 3.5W LED

Fig. 10: Just a funny picture of a plug with a switch that I use in the computer to have it completely off when not in use.

Weather station

The Weather Station is finally complete! That is at least the beta stage!
(the beginning of the development was a long time ago)
Here is a picture of it standing outside:


It has been there for a few weeks now, since the 13th of December, enduring the snow and ice that this winter has brought us, sending a packet every 10 minutes.

The station is based on a JeeNode, with a LDR to sense the daylight, an SHT11 to sense temperature and humidity, and a home made anemometer to sense the wind speed. Here are some photos:

Complete setup, fits nicely inside an electrical box fit for the outside.

Details of the main box. The JeeNode is visible on the left. I had to take about half a millimeter from it in order to fit inside the box. I painted pin 1 of each port with tippex and put a dot in each of the ports to know which one is which as I kept having to refer to the datasheet. The whole thing is powered by 3 AA Alkaline batteries. The wholes that lead to a sensor are covered with corks to prevent water from coming into the brain of the station..

Detail of the light sensor: an LDR. The window I made by warming up a package of hard(ish) plastic and pushing it into the whole using a small spoon. All the electronics for each of the sensors are near the sensor itself, and only 3 cables leave the sensors: Vcc, Gnd and signal (except for the SHT11).

Detail of the SHT11. This one is floating, protected inside a little cheese box, painted white using tippex (I was too lazy to use proper paint...and it was cold outside to use it anyway...and the tippex was right in front of me...and I don't use tippex for anything...)

Detail of the anemometer. I used the center of a CD spindle, attached 3 half's of ping-pong balls, and improvised a bearing from a VHS recorder roller. It fitted nicely in some electrical tube. The sensor is a optical emitter/receiver in the same package. It has not been calibrated, as I only need an indication of the amount of wind, in order to automatically lift the sun screens.

The nice thing is that I initially built the sensors to work with 5V, as I always used arduinos, then the JeeNode uses 3.3V, so I thought I had to adapt some things...not for the light sensor, as it is a basic divider, but for the optocoupler. But I tried it, and it worked fine even at 3.3V!

I spent a lot of time fighting with low power modes of the JeeNode, and finally got it to some sort of power down...which I believe will allow it to work for a few months from the batteries...lets see...I will try to make a post about that soon, as it is also of interest for the JeeLabs community.

So far it has sent 3271 packets. Here are the latest ones:

3267 1 0 0.5 87.4 @ Tue Jan 5 21:26:58 2010
3268 1 0 0.5 87.2 @ Tue Jan 5 21:37:17 2010
3269 1 0 0.5 87.3 @ Tue Jan 5 21:47:37 2010
3270 1 0 0.4 87.6 @ Tue Jan 5 21:57:57 2010
3271 1 0 0.3 87.6 @ Tue Jan 5 22:08:17 2010

The sequence of numbers corresponds to: sequence number, light level, wind level, temperature in Celcius and relative humidity in %.

I have now to put the JeeLink receiver in the server to be able to put all data into a database and use it for something useful!

(2 posts in a day! great! it must be the cold outside...)

Heating system rundown

Recently I met one of the persons behind the Wattcher, a nice little device to measure the electricity consumption of the house and show it in an accessible way to the users. Furthermore, it is a design piece as it was designed by the famous dutch designer Marcel Wanders.
Talking about the wattcher and my own power ball, I mentioned by automated heating system, and he was interest in it, so I wrote an extensive email about it, which I think should come here to the blog as well. So here it is, slighly adapted for the bolg:


Here is a quick breakdown of how my system works.
First, in Holland, the central heating works by having a thermostat in the living room which commands the boiler to burn gas when heat is needed. The remaining rooms then keep a temperature which is relative to the temperature in the living room, since the radiators in those other rooms will be more or less opened depending on the wishes of the inhabitants.
Some places have thermostatic valves, in which you can set the desired temperature and it will open and close the radiators according to the need of heat. However, for this last setting to function it is necessary that the living room thermostat turn on the boiler time enough for the heat to get there, and at the necessary moments.

This situation always annoyed me, since to get some decent temperature in the sleeping room in the morning, the living room would have to be heated up in order for heat to circulate in the system and heat up the sleeping room. The same for e.g. the bathroom.

So, I thought of a system where each room would have its own thermostat, able to request heat from the boiler (turn it on) and ways of opening and closing the radiator valves.

These systems are not new, and they exist for office buildings, high end residential buildings, and in other countries where the standard central heating system works according to different principles. Companies like Honeywell also have similar packages, but they are very expensive.


So, I found these room thermostats and radio controlled valve actuators, in elv.de

http://www.elv.de/FHT-80b-Set-2-Raumregler-FHT-80b,-1-Stellantrieb,-Batterien,-Adapterset/x.aspx/cid_74/detail_10/detail2_10647/flv_1

These are room thermostats, and function just like a thermostatic valve (like mentioned above), but one that you can program the day/night cycle. Furthermore, these thermostats can communicate with another device from ELV:

http://www.elv.de/FHZ-1000-PC-Software-zur-Ansteuerung-der-FS20-,-HMS-100-Komponenten-der-FHT-80b/x.aspx/cid_74/detail_10/detail2_9859/flv_1

which is a device to connect to a computer and that receives state data from the thermostats.

So, I got all these together, and built a computer system which receives desired and current temperature data from the thermostats and decides if the boiler needs to be on or not. If the boiler needs to be on (somewhere there is need for heat in the system) the system turns on a relay switch (also a wireless switch from ELV) that turns the boiler on.

I hope I didn't make it very confusing.

Meanwhile, ELV developed a device that does essentially the same:

http://www.elv.de/Wauml;rmebedarfsrelais-FHT-8W/x.aspx/cid_74/detail_10/detail2_22834

JeeNodes

I just bought a couple of JeeNodes from JeeLab, the Lab behind bringing affordable wireless technology to the arduino! It is not mainstream yet, in fact I think only a couple have been built and sold, but I think it is great simple technology!



So I got my kits, 2 boards, with all the necessary components, and assembled it. The Atmega168 that comes in it already has the arduino boot code burnt in it, along with a demo of the RFM12 radios for test purposes.

To interface with the little JeeNodes a FTDI interface cable (?) is necessary, but since I didn't have one, I remembered that the Arduino can function as a serial data relay when the Atmega is not there, so I connected the jeenode to the Arduino. Only 4 cables: GND, Power, RX and TX. I guess you could only connect the reset, but I couldn't figure that out, so I left it out.


My plan is then to burn the images using the arduino and then transfer the Atmega to the JeeNode board.

Plugged it in, only one, and I could communicate with it. Checked both, and both work!! great little boards, kits and service from JeeLab!

now I still have to solder the antennas (forgot those) and the headers (was too much in a rush to get it running) and then start playing with these little devices.

I am even happier since I think one can connect 8 inputs to it. I thought it was only four. So I can make my little remote weather station, with wind speed sensor, light sensor, temperature, humidity (maybe these can even get in through the TWI) and if I am lucky wind direction sensor.

More on the consumption

The progress on the light to indicate energy consumption is going steady, but the camera ran out of juice, so I can't put a picture online. Maybe tomorrow.
So I decided to report to you about the consumption curves.
In the picture you can see a plot of the gas consumption versus the average monthly temperature for the last 3 years - 2006, 2007 and 2008. The "trendlline" is a excel computed trendline, and its equation for 2006 is my basis for the energy saving calculations.
In 2006 I did' have in place any energy saving measures for the heating, and a sinple manual thermostat, so I consider that to be the baseline against which all gains are to be measured.
I think the line approaches quite well the measured results. It is a second order polynomial equation.
Also in the graphic is the date for 2007, when my automated zone controlled system was already in place.it;s line is quite deviated from the line of 2006, so I can safely assume that there have been some considerable savings, and that my calculations might be close to the real thing.
As for the data points referring to 2008, these come quite close to the predication from the trendline for 2007, apart from the 2 slightly removed dots at the right. These correspond to February, when we spent a week off and therefore saved quite a bit on the heating bill, and December, when most of the roof insulation was already in place! Which makes me very hopeful that the insulation really is doing its job and saving quite some gas and CO2 from going up into the atmosphere!
Byt the way, for January, which just finished, I got a saving of 40% with respect to the 2006 equation, whereas in January 2008 and 2007 the saving in January was only about 12%.
I am hopeful to see what the coming months bring, with the added sun exposure hours (they do make a difference)!
I'll keep posting about it!

3 years of gas consumption logging

For the last 3 years, since we have been in our current house, I have been taking very regular readings of the gas and electricity meter, usually daily, sometimes, skipping a day or 2. Recently, I have automated that process with the help of an Arduino and some additional electronics. That has removed the burden of collecting the data, and allows to see the evolution of the consumption to the minute! (note to self, explain the circuit to collect gas data!)
But all this accumulated data also has a good purpose, besides making nice graphics. It allows me to evaluate the measures I put in place to reduce the overall energy consumption.
In the first year, we only had an old Honeywell thermostat, manually operated. That was replaced in the second year by a fully automated system (see post regarding the uptime of the server). In the 3rd year nothing changed, but now that the 4th year is about to start, I am about to finish the roof insulation. All the accumulated data allows me to compare the increase in performance.
So here is a graphic of the monthly gas consumption for the last 3 years, along with the average temperature for that month as reported by the KNMI (dutch meteorologic institute) for Holland.

It is funny to see the relation to the temperature. In fact, from the data of the first year, I have managed to calculate a second order curve which relates temperature to gas consumption, so for a given monthly average, I can calculate how much the consumption would be. It is using this curve that I calculate my savings. I'll elaborate more on that soon.

Worth noticing is also the fact that December 2008 was much colder than December 2007, yet the gas consumption remained similar. I attribute that to the roof insulation, which I did mostly during November (not yet 100% finished).

Results! and progress in the logging!

So finally I managed to write about the results of my logging experiment!

I didn't get to collect much data before a considerable portion of the attic was insulated, but nevertheless I guess it is enough to get a rough idea that the stuff is at least doing something to prevent heat from escaping - at least it prevents drafts in the attic, which I guess is half way to improvement!

So here is a rundown of the results:

before the insulation: average of 4.8 degrees C difference between inside and outside
more than half installed: average of 6.5 degrees C difference between inside and outside
almost all of it installed: average of 8 degrees C difference between inside and outside

The split in the graphic corresponds to the moment when more than half the stuff was installed, so before the split is before the insulation, after the split is more than half installed. One can see that the graphic for the inside temperature in the second part is smoother than in the first part, even as outside temperatures drop further down!

These results have to take into account that the house below the attic is warmed up regularly (although to a low setting of 18 degrees C), but nevertheless, for the same outside temperature before and after I do see that the inside temperature is higher now. Also the variance of the inside temperature is much lower than the variance of the outside temperature, which was not the case before the insulation was applied.

Overall, I think it was worth the money and work invested.

Furthermore, and as an additional proof of the worthiness of the investment, I verified that I spent an amount of gas in December 2008 identical to December of 2007, while the average month temperature was 1.4 degrees Celsius lower, and I spent the whole month of December 2008 at home, whereas in 2007 we took 4 days of holiday.
My estimate is that the extra insulation gives me an extra 10% savings in gas consumption compared to the situation without.
Next Spring - Insulate the floor of the ground floor of the house!

On another subject, I was finding it strange that the temperature logger was not going below 0 degrees, so I decided to investigate. I placed the sensor in the freezer, and it did go to -16 before I took it out. I then figured that due to rounding, the temperature would need to be below -1.45 before the sensor and the arduino code would register a negative temperature of -1. All this due to the quantification in the A/D converter and integer logic.
SO I have decided to adapt the code to include a true low pass software filter (and an efficient one also, from the computational point of view) and work with one decimal place, so I managed to get better results! Send me a note if you are interested in the arduino code to do it.
It also includes 2 keys - Select and Reset - which allow you to navigate in a small menu showing the maximum and minimum temperatures, reset the max min log, and see how full the inside EPROM is.

I also included a low pass hardware filter - RC - but somehow it prevented the sensor from registering values below 0, so I took it off for the outside sensor. Still must investigate what went wrong!

There are some more news, but I'll keep that for the next post!