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Whole-House Environmental Logging By Julian Edgar In the March 2026 issue, Julian Edgar gave some tips about wiring up a newly built home. Now we look at the electronic logging and display system he has built to oversee the thermal behaviour of his house. Image: the active/passive solar house uses largely conventional current Australian construction. Here it’s shown with AI-added landscaping – the landscaping won’t be finished for several years. But the house and rainbow are real! M any Australian houses are constructed with insufficient regard to the climate, especially in the use of low-cost passive solar design approaches such as orientation, shading and use of internal thermal mass. After over 45 years of being interested in passive solar house design, I could finally incorporate as many energy-efficient aspects as my wife and I could think of, get planning permission for, and afford! In addition to obvious aspects such as insulation in the walls and ceilings and double-glazed thermally broken windows, the house uses a thick, steel-reinforced concrete slab floor supported on deep concrete pillars into the earth. Don’t many houses have concrete slab floors? Well, in our case, that floor acts as an earth-bonded heat stabiliser, keeping the house cooler in summer (it acts as a heatsink) and warmer in winter (it acts as a heat source). In passive solar house design, this temperature-­ stabilising function is often called ‘thermal mass’. 56 Silicon Chip To enhance its winter performance, the house faces north and has extensive window area on this face. Winter sunshine falls on the slab, warming it during the daytime and so providing heat at night. To prevent warming of the slab in summer, the width of the northern eaves has been carefully calculated to block the summer sun, which is higher in the sky, from entering the house. But it gets a little more complicated than that, especially in summer. On a hot summer day, the house is closed up, with the slab keeping the interior cool as it acts as a heatsink. Inevitably, the slab temperature will rise as heat passes from the house interior into the slab, so we need a way of getting rid of that heat. This is typically done when the temperature drops at night, at which time the house windows and doors are opened for cooling breezes. But what if the night is still – there’s no wind? That happens occasionally here, about 100km north of Canberra. In that case, another aspect of the Australia's electronics magazine house comes into operation. A large (600mm diameter) roof ventilator can be powered by its brushless DC motor, drawing air out of the roof space. Connecting the house interior to this roof space are ceiling vents, opened by electric actuators. Aided by the convectional flow (hot air rises), the house and the slab are cooled by this airflow. In winter, there’s another twist. Software modelling of the house design showed that, especially during a cloudy week in winter, the slab would get too cold to adequately warm the house. To cater for that, we have a modern wood stove. In this rural area, firewood is free, and the stove has low particulate emissions and high efficiency. However, the wood stove is in the lounge room and so would heat only that room. To circulate the heat more widely, a duct connects the lounge to the other end of the house, with an automatically controlled fan moving warm air through the duct. I described that system, with its custom controller, siliconchip.com.au in the August & September 2025 issues (siliconchip.au/Series/446). Now, I am sure you’re thinking, that’s all very nice – but what does it have to do with electronic logging and display? If you think about it, the occupants must control this scheme. We need to know when to close the windows and doors, and when to open them. We need to know when to open the ceiling vents, and when conventional and wind-induced airflow through the roof ventilator is insufficient and the ventilator should be powered up. Because it is automatic, we don’t need to know when it would be beneficial to switch on the ducted heat transfer fan, but we need to adjust the controller’s temperature difference and hysteresis settings for the best results. Many of these ‘house operating’ decisions need to be made in the context of temperatures – temperatures of the different rooms, of the concrete slab, of the outside air. Other decisions need to be made in the context of the season, the predicted weather over the next few days, and what weather has occurred in the previous days. What the occupants are doing also matters, eg, cooking over a hot stove, sitting at a home office typing, or sleeping. Initially, I thought of automating all these decisions – that is, having windows and ceiling vents that opened themselves, automatically switchingon the roof ventilator, and so on. Then I realised that such a system would rapidly become complicated, expensive and hard to maintain over the life of the house. So, manual control it is – but with a lot of information at our fingertips. That’s where the logging and display system comes in. Showing 25 sensed and calculated parameters, both numerically and via trend line graphs, the system allows us to see, at a glance, what the house is doing, and what we should do (if anything). If the house needs to be opened up for summer night cooling, the time to do it is when the falling outside temperature graph line crosses the interior temperature line. If, during winter, the slab temperature is getting low, lighting the wood stove early will help ‘recharge’ it with heat. The logging and display system will also show how well the house design siliconchip.com.au House passive solar design features » R5 roof and R2.7 wall insulation; periphery of concrete slab insulated to R2.3 » Thermally broken, double-glazed windows » 150mm-thick concrete slab floor with two layers of steel mesh reinforcement, multiple deep cast-in pillars » Rectangular plan-form house with extensive northern glazing, limited eastern glazing shaded by a 5m deck overhang, very limited western glazing (a door) shaded by a porch, southern glazing limited in area and illuminated in winter by a freestanding southern reflector panel (yet to be built) » Increased interior thermal mass provided by brick feature walls and two internal 2000L steel water tanks, one at each end of the house, plus a further 375L tank in the home office » 600mm wind powered roof ventilator working in conjunction with electrically opened ceiling vents The 2000L water tank in the lounge provides thermal mass, reducing indoor temperature fluctuations. The main thermal mass is provided by the concrete floor slab, insulated around its edges. The slab was strengthened to bear the two-tonne weight of the tank. The tiling wasn’t complete at the time of this photograph – it was added using AI. actually works. How hot and cold does the interior get over a year? How long does it take for heat to migrate from the northern, sunshine-exposed side of the slab to the southern side? I have many books with descriptions of a home designed with passive-­ solar optimisation principles, but invariably when it comes time to describe how effective they are, the analysis gets quite vague! For this house, I wanted hard data. So, finally, Australia's electronics magazine what does the logging and display system comprise? Logging and display The logging and display system comprises the following: • A wall-mounted, 24-inch (61cm) LCD touchscreen panel shows realtime data, such as room temperatures • A logging system records data and displays it numerically and in trend graphs April 2026  57 Two Picolog model 1012 10-bit analog loggers are used. Each logger has 12 single-ended input channels. Off-the-shelf software allows the use of lookup tables and displayed values calculated from multiple inputs. The main display is a touchscreen PC in a wall nook located centrally in the house. The PC allows easy control over the scaling and data to be displayed. Two USB cables link the PC to the Picolog loggers in the loft directly above. There is a repeater display in the home office. This wall-mounted sensor detects radiant heat. It uses a thermistor mounted inside a metal hemisphere. 58 Silicon Chip The outside sensors for the logging and display system include wind speed and UV intensity (bottom sensors). The top sensors are for a Davis Vantage Vue weather station used for calibration and redundancy. Australia's electronics magazine • Warnings/indicators are shown when certain actions are suggested The LCD touchscreen is an HP 24-cr1000a all-in-one desktop computer. This is located in a wall recess that is easily accessible from all parts of the house. A repeating LCD screen, linked by a fibre optic HDMI cable, is mounted in my home office. Data is collected and logged by two Picolog model 1012 10-bit analog loggers. Each logger has 12 input channels and two digital outputs, giving the system 24 input channels and 4 software-­ switchable outputs. The Picolog units are in a storage loft, directly above the PC, and are connected to it by two USB cables. These cables power the Picologs, and provide data transfer to the PC. I selected Picologs because the UK-based Pico company provides free logging and display software and has good technical support. The software allows quite complex treatments of input data for calibration (eg, the use of equations or lookup tables) and has easily programmable maths functions to display calculated data. The lookup tables allow non-­linear or linear sensors to be used, and maths functions can be used for functions like averaging the readings from multiple sensors. In addition, data from each individual input can be averaged over pre-selected time periods, eg, temperature readings can be averaged over 10-minute periods. The Picologs use 0-2.5V single-­ ended sensor inputs – that is, the input signal for each channel needs to be an analog voltage in this range. A regulated 2.5V output is available for powering sensors. The amount of data logged is limited only by the storage available on the PC or, if desired, the ‘cloud’ – so in practical terms, it is unlimited. In my system, nine different environmental factors are displayed: • indoor temperatures • indoor relative humidity • indoor dew point temperature • indoor carbon dioxide (CO2) level • indoor radiant temperature • outdoor temperatures • outdoor wind speed • outdoor UV intensity • the flow volume through the roof ventilator Let’s look at each in turn. Most of the logger inputs are for temperature sensors. Temperatures are sensed: siliconchip.com.au The flow through the roof-mounted ventilator is measured by a pitot tube (circled) and differential pressure sensor. The logging software shows this flow in m3/min, calculated from the velocity and crosssectional area. Electrically opening ceiling hatches allow convectional or forced air ventilation through the house. • Within the concrete slab • 1150mm above the floor in multiple rooms • Near the peaks of the cathedral ceilings in the two main end rooms • In the two internal water storage tanks (more on these later) • Outside in the shade • In the roof space near the ventilator In total, 18 temperatures are currently sensed. Not all are displayed by trend graphs on the PC screen – sometimes, an average of multiple sensors is calculated and this average then shown on the graph. Temperature sensors A lot of thought was given to using temperature sensors that would have a very long life – this ruled out IC-based sensors, for example (they would be more susceptible to lightning damage, especially on the end of long cables). Should they fail, the in-slab sensors are not easily replaceable – although, unfortunately, that has already happened. The chosen temperature sensor is a thermistor, a device that changes resistance with temperature. I used the Ametherm ACW-016 precision thermistor exclusively; this has a 50kW resistance at 25°C and an accuracy of ±0.5°C. In use, I have found them to be more accurate than their specification suggests. This sensor is also provided with a table of resistance versus temperature readings, and this table, when converted to voltages, can be input directly into the Picolog software to give a readout in °C (the change in resistance is not linear with respect to temperature). To allow the thermistor to give a variable voltage output, a precision 50kW resistor is used to form half of a voltage divider, with the thermistor forming the other half. The ACW-016 thermistor is tiny – its body is only 1.8mm in diameter, and its connecting wires are equally small – just 0.2mm thick! This means the sensors and their wiring need to be connected so that no physical stress is placed on them. The slab sensors were soldered directly across the splayed ends of the cabling conductors, with the connections and thermistors then wrapped in electrical tape before being placed in the flexible plastic conduit (truck siliconchip.com.au Before the concrete slab was poured, plastic tubes containing thermistors and their associated cabling were put into place. One of the orange tubes can be seen here. Unfortunately, nearly every tube allowed water in, wrecking the thermistors! It happened twice – I nearly cried. Australia's electronics magazine April 2026  59 air brake hose) that was buried within the slab. As events proved, taking this approach was a mistake – more on that soon. The room thermistors were wired in the same way, with these assemblies then mounted in small, ventilated enclosures that attach to standard Clipsal Classic wall plates, which visually match the rest of the wallmounted switches. The thermistors sensing the temperature of water in the internal heat storage tanks were attached to the outside of the tanks, then insulated from the room air with polystyrene blocks shaped to match the tank corrugations. All temperature sensing connections were made with 1.5mm2 shielded instrumentation cable – physically strong, with a very low resistance. Hundreds of metres of cable were used, all installed during the house construction. The Picologs are optionally provided with plug-in PCBs that have connecting terminal blocks. However, these terminal blocks were too small to take the sensor cable conductors, and physically not strong enough to resist the pull of 12 cables on each Picolog. To cater for these aspects, the Picologs were mounted in a 19-inch rack mount case with the sensor cable terminations on heavy-duty terminal strips mounted on standoffs. The required voltage divider resistors were easily installed between the sensor inputs and another terminal strip fed from the 2.5V reference supply. Other sensors Indoor relative humidity is detected by a commercial sensor that has a linear analog output. However, after monitoring the relative humidity for a while, I found it rather useless in assessing comfort. This is because, if the temperature is low, one doesn’t even notice high relative humidity – it feels ‘muggy’ only when the temperature is also rather high. I therefore added a calculated dew point to the display. Dew point is the temperature at which condensation would occur at a given combination of relative humidity and air temperature. Because it takes into account both of these factors, it is a very good guide to human comfort. If you live in a temperate climate, dew points above about 15°C start to feel uncomfortable. As with all human 60 Silicon Chip comfort parameters, it also depends on what you’re used to. The dew point calculation can get very complex; a simplified equation is (dew point) = (air temperature) – (100% – relative humidity) ÷ 5%/°C, but note that this is more like a ruleof-thumb than a rigorous equation. For more details on this calculation, including its loss of accuracy at low relative humidities, refer to “The relationship between relative humidity and the dew point temperature in moist air: A simple conversion and applications” by Mark G. Lawrence in the Bulletin of the American Meteorological Society, February 2005 (see siliconchip.au/link/ac9l). Carbon dioxide is measured with a commercial sensor. This parameter is a good proxy for general ventilation flow – CO2 levels should be kept below about 1000ppm. The normal atmospheric CO2 level is about 400ppm. I found that a correction was needed – when calibrated with outside air, the sensor tended to read too high. This offset was added in the Picolog software. Radiant temperature is measured in one room. Much heat gain in a house is via radiation through the windows – direct radiation (sunshine) and indirect radiation (reflected light). Radiant heat is measured by sensing the temperature inside a small black metal ball or hemisphere. I used a Sontay TT-BB radiant heat sensor, with the assembly disassembled and the standard thermistor replaced with an Ametherm ACW-016 thermistor to give directly comparable readings to the other temperature sensors. The difference between radiant and normal temperatures can be very small, so an offset was added to the radiant thermistor’s output until, in conditions of no radiant heat gain or loss, it was precisely the same as air temperature measured at the same location. Outside wind speed is detected by a rotating cup anemometer that has a 0-5V output. This is reduced to 0-2.5V by a voltage divider. The anemometer output was calibrated in km/h by comparison with the output of a Davis Vantage Vue weather station anemometer mounted on the same mast. The table of wind speed versus output voltage was then fed into the Picolog software. UV intensity is detected by a Sonbest SM9568V5 sensor. Sonbest makes a variety of sunlight sensors, Australia's electronics magazine including total irradiance and light level. I decided a UV sensor was the most practically useful in terms of the likelihood of getting sunburn; I also expect this sensor’s output to roughly correspond with sunlight intensity. The sensor has a 0-5V output (converted to 0-2.5V using a voltage divider); however, the manufacturer’s data sheet doesn’t relate the output voltage to UV Index. The sensor was calibrated by comparing its output voltage to the Bureau of Meteorology’s locally published UV Index daily data. This relationship was then converted to a lookup table in the Picolog software. This conversion probably needs further work – the sensor output doesn’t seem linear with respect to published UV levels. In the meantime, I use this sensor primarily to determine whether the sun has been out. The anemometer and UV sensor are mounted on a 1.4m-tall mast above the roof at the eastern end of the house. This end of the house is highest above the ground, so it is the most exposed to the wind. The mast is mounted to the fascia; during construction of the house frame, this area was strengthened with added pieces of timber. In addition, the mast carries the sensors for the standalone Davis weather station, which shows temperature, wind speed and direction, relative humidity and rainfall. The volume of air passing through the rooftop ventilator is measured by a pitot tube working with a Dwyer Magnesense II pressure-measuring transmitter. Good-quality aluminium pitot tubes are now available quite cheaply from China; these are sold for measuring the airspeed in model aircraft. The Magnesense transmitter was bought cheaply in a job lot – an alternative would be to use the pressure-­ sensing electronic modules also sold for model aircraft use. A pitot tube measures airflow speed by comparing two pressures sensed by the pitot. One is the atmospheric pressure, sensed by several tangential ports around the periphery of the tube. The other pressure is atmospheric plus the ‘impact’ pressure, sensed at the end of the pitot that faces into the airflow direction. The greater the pressure difference between the ports, the higher the airflow speed. By measuring airflow speed and knowing the cross-sectional area of siliconchip.com.au House modelling Many people are unaware that the heating and cooling energy consumption of a house can be modelled before the house is built. Or, in the case of an existing house, before any improvements are made. The software, developed under the umbrella of the Australian Government’s NatHERS (Nationwide House Energy Rating Scheme; www.nathers.gov.au) program, provides the energy star ratings that all new houses must meet. However, rather than being used just to provide an energy rating, the software can also be used to develop a house design to give reduced energy usage. Different NatHERS software packages are available, including one that is free. I initially had my house design NatHERS-modelled by an architect, and then when I saw how fascinating the results were, I took the course myself in one of the software packages. It is not something you could easily pick up just by trial and error. The software allows house design changes to be made and then the annual energy usage modelled. For example, in your climate, what difference occurs from fitting R6 rather than R5 ceiling insulation? What about adding more windows on the south wall? Changing the northern eave width? A different house orientation? And so on. Not only will the software show the annual energy consumption for heating and cooling, it can also be configured to show the modelled interior room temperatures for every hour of every day of a typical year, in every room! This is another reason I wanted a logging system – to see how well the actual house performance matches the modelled performance. At the time of writing, the performance of the house has been close to the software predictions – if anything, it is doing better than the software predicted. Finally, the CSIRO has released predicted climate data that can be used in the software, so the house design can be modelled for future climates – a good idea since the life of a house is likely to be 50+ years. The modelled temperature of my home office (blue) and the outside temperature (red) for a year, with no heating or cooling systems operating. The modelled temperatures for each room at 3pm on July 31st in a typical year. The outside temperature is only 11°C but most rooms are around 20°C. The lower temperatures are in the rooms with exhaust fans – even when closed by dampers, lots of heat is still lost through these openings. This is with no heating or cooling systems operating. These two images were made using the software FirstRate5 (www.fr5.com.au). siliconchip.com.au Australia's electronics magazine April 2026  61 Climate 80km north of Canberra These values shown in the table below are averages – the extremes are 43°C and -8°C. Note the high diurnal (night/day) temperature range in summer, allowing a passive solar home to work very effectively in this climate. Initial results indicate the house will likely not need cooling or heating more than 90% of the time. Mar Apr May Mean max. 27.9°C 26.4°C 24°C Month Jan 20°C 15.8°C 12.3°C 11.5°C 13.3°C 16.6°C 19.9°C 22.9°C 26°C Mean min. 14°C Feb 13.7°C 11.5°C 7.9°C the ventilator’s throat, airflow volume can be calculated and displayed by the logging system. I use units of cubic metres per minute. I made a lookup table to display the data in this form, with a check of the system’s accuracy made with a handheld flow meter positioned temporarily in the throat of the ventilator. Thermistor problems Unfortunately, the in-slab thermistors gave a lot of trouble. As described, the thermistors were soldered to the cables, then wrapped in tape and slid into hard plastic hoses, with the assemblies placed before the concrete slab was cast. Well before the house construction was finished, the logging system was up 4.6°C Jun 2.6°C Jul 1.7°C Aug 2.4°C and running – and this soon showed a problem. One by one, the in-slab sensors started to give incorrect readings. The readings progressively worsened until, typically, they were showing either extremely high or low temperatures. Reluctantly, because I didn’t think they could be replaced, I pulled out each cable, complete with sensor, from its plastic tube. This invariably revealed that the sensor was wet. Either the plastic hose had been holed during the concrete pour, water had entered the ‘house’ end of the plastic hose (despite it being sealed with tape) before the roof was on, or condensation was occurring. Even a small amount of moisture was enough to cause problems. Sep 4.7°C Oct 7.2°C Nov 9.8°C Dec 12°C Furthermore, even when the thermistors were dried, they still gave incorrect readings. Clearly, new sensors needed to be installed – and they needed to be waterproofed. A new thermistor was soldered across each cable’s conductors, as had been done previously. But this time, rather than wrap the sensor in tape, I slipped a 50mm length of vinyl tubing over the sensor, with about 10mm of the tubing then pushed over the full diameter of the cable, where it was a tight fit. I then used Selleys MarineFlex sealant to fill the open end of the tubing, completely enveloping the sensor and its wiring, while adding some more of the sealant around the vinyl tubing/ cable join. Screen 1: about three weeks of temperature data in November with no heating or cooling. The outside temperature (green) varied from 2-32°C, while the indoor temperature (blue) varied from 18-24°C. The concrete slab varied in temperature by only 1.5°C (red). Four of the slab temperatures (right-hand column) show the fault discussed in the article. The gap in the recording is due to an electrical storm. 62 Silicon Chip Australia's electronics magazine siliconchip.com.au With some effort, each sensor could then be pushed into the plastic hose sufficiently far that the sensors were returned to the original positions, deep inside the concrete slab and in about the middle of the respective rooms. Incredibly, this did not fix the problem! Months later, when the house walls were complete and so access to the cables and thermistors was near-impossible, one by one, the thermistors began to give the same trouble. I can only assume that again water was the culprit – and that it could infiltrate through the cable insulation. Luckily, a single thermistor cable could still be accessed – it was behind the plasterboard wall inside a linen cupboard. I was able to cut a hole in the plasterboard and fish out the cable. I then drilled a hole in the concrete slab inside the cupboard and put in a new sensor. I covered the wiring junction with a wall blanking plate. Should further problems occur, this sensor is easily replaceable. While it is not as good as having multiple slab sensors in different parts of the house, the sensor is at least located centrally and so provides a good average slab temperature. At the time of writing, three of the eight original slab sensors remain working – but I am not hopeful that will continue! Trend graphs The most useful aspect of the logging and display system is the trend graphs. Three different vertical axes can be shown on the one screen, and typically the following approach is used: • Top axis: inside temperature, concrete slab temperature, outside temperature • Middle axis: wind speed and roof ventilator flow • Bottom axis: UV index Using the touchscreen, the number of axes shown (one, two or all three) can be changed, with the graphs automatically resizing to fill the screen. The horizontal and vertical axes of each graph are also easily rescaled by two-finger pinching and expanding on the touchscreen. This approach allows many parameters to be shown in a way that allows understanding at just a glance. It’s easy to use the touchscreen to draw horizontal lines that show the maximum and minimum of each graph. The system then calculates and displays the numerical difference. For example, seeing the range over which the slab temperature has varied in the past month is quick and easy. Screens 1-5 show some of the logged data. Conclusion Apart from those darned slab thermistors, the system has worked flawlessly. The ability of the system to work with any analog sensor with an output range of at least 0-2.5V means that sensors for most environmental parameters are readily available and can be easily connected. The touchscreen PC and Picolog software give intuitive and quick interaction – selecting data, changing scales and allowing measurements to be made. Hard-wiring of the sensors avoids the need for periodic sensor battery replacement, and is more immune to interference. The system wasn’t cheap, but my major goals of ease of use, accuracy and clarity have been achieved. Plus, my wife and I find the results fascinating – while many of the measurements are as we expected, significantly, some are not. So it’s been a great learning experience – on a scale the size of a house! SC See overleaf for Screens 3-5 Screen 2: all three axes are visible: the top graph of temperature, middle graph of outside wind speed and roof ventilator flow, and bottom graph of sunshine intensity. The abrupt dips in the sunshine graph indicate passing clouds. siliconchip.com.au Australia's electronics magazine April 2026  63 Silicon Chip PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). Screen 3: the red line shows the temperature at shoulder height, and the green line the temperature at about 5m, near the ceiling. Note how the temperature at height is greater than normal room temperature during the day, but this reverses at night due to heat loss into the roof space through the upper walls and ceiling. Screen 4: logging over two days shows how slowly the internal temperature of the concrete slab (red) varies. Here, its greatest rate of change is about 0.5°C per day. The black line is the temperature of one of the 2000L internal water tanks that provides quicker-response thermal mass. The tank changes in temperature a little more rapidly than the concrete slab and is about 1°C warmer. EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK COSTS $150 JANUARY 2020 – DECEMBER 2024 OR PAY $650 FOR THEM ALL (+ POST) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS 64 Silicon Chip Screen 5: the air temperature of different rooms in the house over two days. Even with all the internal doors open, the northern rooms, exposed to spring sunshine, are 1-3°C warmer than the southern rooms. siliconchip.com.au