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Forum Index : Microcontroller and PC projects : How Log When Gas HWS Runs?
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| Andrew_G Guru  Joined: 18/10/2016 Location: AustraliaPosts: 842 |
Hi All, I want to log when my gas hot water service (HWS) runs (approximate time of day and duration) - to help plan my new solar/heat pump installation. It is about 10 years old with a pilot light and thermocouple. Do any of you have ideas or comments?? (I don't want to break into the gas supply side but could after the control valve - but gas flow sensors are not cheap. I have a number of DS18B20 encased in a bullet-like tip and a lead long enough to get indoors to my study. One simple solution is to locate one near (but not too near) the burner so that hot is "on", cool is "off". There will be a little lag and I'll need to locate it carefully but it should work. The MM side of it is simple. I'm just checking to see if you have better ideas.) Regards, Andrew |
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| BrianP Senior Member  Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Hi Andrew What about a VERY simple thermistor (only cost a few cents) attached to the flue? You would very quickly see when the gas was on... You could make the thermistor sensing a low impedance loop to the MM - then no need for fancy signal processing or whatever. No need for any accurate measurements, just to know when the flue temp spikes. Run the thermistor loop from the MM 3.3v supply, no need for any level translations. Hope this helps... B |
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| PicFan Senior Member Joined: 18/03/2014 Location: AustriaPosts: 133 |
Maybe a „Flammen - Sensor“, like this: LINK Wolfgang |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 842 |
Hi Brian and Wolfgang, Many thanks. My German is non-existent but Dr Google translated it for me. I like the idea of putting any "sensor" in the flue as this helps manage the temperature. I'll experiment and report back. Cheers, Andrew |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
As something related to what I -Think- is your end goal/ Question,Let me relate an experience/ Finding. After putting up a load of solar Panels, I took my electric HWS off the off peak and put it onto the normal power. I connected a Voltage monitor which switched the heater on when the line voltage hit a certain level indicating the solar was generating significantly. I did not change anything else, just went from the 11 Pm to 5 Am off peak heating to what was normally 11 AM to 3 pm depending on time of year. The wife and Daughter both completely unaware of what I did both asked me within a week separately if I had turned the hot water up to make it hotter? I had felt when showering myself the water seemed warmer and less was needed than before. We all tend to normally shower at Night. This being the case, as it is normally shortly before bed time, If the water finished heating at 5am ( the latest it could with off peak) and We showered around 10 PM which is normal and usual for us, The water could well have been sitting in the tank 18 hours loosing heat. Hard to say what the temp drop may be but digging up numbers I came up with figures of around 4Kwh for the big tank I have which would have to translate into several degrees at least. Of course through the day the water would also have been used for washing up, maybe clothes washing, A bucket full for doing the floors etc. Not hard to see the water temp could easily drop 5-10o before anyone gets in the shower. Now when I have seen the water being topped off at 5 in the afternoon in summer, that dead time could be 5 hours or less And... any water used for washing dishes or clothes or whatever would have been significantly or completely replaced and the water is at the cutoff setting rather than have been diluted with cold water. I did also see a significant reduction in over all power usage to the heater which I monitored. That could only be explained by less loss through insulation copper pie work etc. Having experienced this, off peak heating is really anything bar ideal... especially if one looks at the power generation Data for the grid, night time now is HIGHER demand than through the day. As you will have solar and be using a heat pump, it will be better to use your own power and also run the heat pump when the ambient temp is the warmest. As my house only has reverse Cycle heating, I have also found it more economical to leave the AC to bounce off the thermostat as it needs even though I turn the temp down a bit during the day then I turn it up again about 3 PM when there is still some solar but more over, a lot more heat in the air the AC can extract rather than wait and ask it to warm the place up when the air it's Pulling through is 1-2o or less as is the winter norm. If you have the ability to go between a smaller or larger solar setup, ALWAYS go for the largest you can. The power you get in winter will b3 30% if that of what you get in summer and what the advertising projections and averages will say. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Davo99 said: "Hard to say what the temp drop may be but digging up numbers I came up with figures of around 4Kwh for the big tank I have" We use 3-4 KwH daily at this time of the year just to counteract the heat loss in a 315L HWS so your calcs are spot on. Your argument about off-peak heating of water is also spot on, but we are still stuck with the system which has been the norm for nigh on 100 years. The idea of course at the time was to spread the load on the power stations more evenly over the 24hr period. Yes, go for the biggest solar installation you can, even if in summer you can't use all that you generate. Winter is a completely different ball game. And I love reverse cycle AC for heating - it's very, very efficient - except maybe at the south pole...  B |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3018 |
What is "reverse cycle AC"? Should I be thinking "Alternating Current" or "Air Conditioning" (heat pump) or something else? Edited 2019-09-17 08:35 by lizby PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5914 |
"Reverse cycle" is a heat pump that does heating and cooling. The earlier ones only did one or the other. The idea to switch between the two modes was first put into domestic products by a Tasmanian retailer. We thank him for the foresight. Jim VK7JH MMedit  MMBasic Help |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3018 |
Thanks, Jim--I had understood the concept (and the practice), but had never heard it referred to as "reverse cycle AC". And I was confused because my first thought was "Alternating Current"--some magic new to me, I hoped. PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
G'Day All. If you stick a sensor in the flue it will eventually get gunked up with all the muck going past, If the flame is visible an IR sensor may work. Many years ago I had to time flares, they produce great heat and smoke when stuck on a post so I used sound via a 20 ft length of water pipe to get away from the heat. Peter |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Another thing I worked out is that just the DIFFERENCE between the incoming water temps in summer and winter could be an extra 3-4 Kwh to bring the winter water temps up to the summer temp over the amount of water we use on average before the heating even properly begins. The winter water temps straight out the pipe I measured here were a fair bit lower than I expected with plenty of days when it was down to 8o C. In summer it can be over 30. I guess the pipes aren't too deeply buried round here. Then again, with winter temps of -3 Not uncommon and several days over 45 and a a week at a time hitting 40 in the summer, spose that's not too bad really. It's easy to see though how solar generation rates can disappear in winter. Shorter daylight hours which is what affects my setup the most being it's all well over clocked anyway and then the HWS burning an extra 3-4 Kwh just to get to what the incoming water temp would be in summer means things take a hit straight off. I thought of getting a big Gas Hws and converting that to waste oil so I could have a pre heat tank I fired up every couple of days or so to reduce the hot water load but they only seem to do up to about 175L Gas heaters which is bit of a bummer. I thought of getting a big electric just to use as storage and circulating the water through a gas heater but then it starts getting pretty ugly and I don't have the space for all that. I changed my solar setup significantly on the weekend to allow higher outputs. Of course, true to form, it's forecast to rain for the next week. I'm certainly not complaining, If it means another week of rain, I'll keep swapping things back and forth for the next 6 weeks given we are over 2 years behind average rainfall. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Edit - deleted - I hadn't read TassyJim's post Edited 2019-09-17 13:09 by BrianP |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
If your attach a thermistor or whatever sensor to the outside of the inner insulated flue pipe you should get fairly accurate readings with no worry about it becoming polluted... B |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
You win.  Peter |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
I wasn't aware it was a contest I had the distinct impression from your initial post that what you were looking for was an indication of when the gas was on. My last suggestion would give a result within a few degrees of the actual flue gas temp provided there was a layer of insulation around the flue. Let us all know how it all ends up  B |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Pretty much the same case here. Interestingly as I read this my Electricity usage was open in Excel. Average usages of off-peak controlled load for our 315l tank is:- Quarter to 16/04/19 - 6.64kWh/day Quarter to 15/07/19 - 11.61kWh/day Quarter to 16/10/19 - 13.09kWh/day (Projected) Have thought about diverting some solar, but catch is water usage at night gets heated after 11pm & morning usages reheated up to 7am. Other thought I'm toying with is using the Spare 315L tank I have as a solar heated pre-storage. Figure anything I can get out of it that's better than the 10°C mains water in the later winter months is a bonus. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
If the winter and summer temps of the incoming water are 20o C Different, on 315 L of water ( not you'd likley use the whole tank but as an example) thats 7.3 Kwh right there. Even if you are only using half a tank, 3 Kwh day over a quarter even at .11 C kwh is still $30 a quarter. And thats just to bring the water up to summer input temps before the real heating starts. Of course in summer, it's quite reasonable your water heating bill could be $10 or less. With a preheater, what I would do would be set the pre heater to maximum temp and the main heater to Minimum. This way you'll compensate some of the losses in the main heater and give the best chance of the main heater not kicking in at all. Where I am ( Sydney) I'm buying used panels depending on the size for as little as $12 ea for something like a set of 190s. 250's I will pay up to $25ea for as long as they are in sets of 5 Kw or more. Over all I work on $100 Kwh which allows a size comparison. Plenty of dreamers out there wanting stupid money for used panels because they think because they paid $10K for a system 7 years ago they are worth more than new, larger panels can be bought for now. Don't even get me started on these clowns. Firstly, they didn't pay $10K for the panels, They paid for The panels, the cabling, the inverter, the racking, installation and someone putting through all the relative paperwork. IF they are only selling panels, Then they only paid about 1/3rd the price for them anyway. Dunno how many times I have seen people trying to sell 2 KW of panels and inverter for more than a 3 Kw new system can be bought for. There are however far more reasonable people although a lot farther and fewer but if you are patient they will come along. Also if you are looking for a HWS, don't pay the also stupid asking prices many people advertise 10 YO systems for. My local scrap yard gets a Stack of heaters and often they appear the tanks are in good nick. Pretty easy to look around them and if there are no rust marks, You are in with a good chance. The thermostats and elements are all that makes them work and I take something down to my local bloke and he lets me pull all the elements and thermos I want. A lot of people change tanks to put on gas or solar , heat pumps whatever and discard perfectly good Systems. If you only get a few years and the thing cost you 10 Bux, you are well in front on power savings so take that leaky one back and get another good one, maybe even as a swap. :0) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
There is a much easier way. The plasma in a burning flame is electrically conductive. All you need is a metal electrode poking into the flame, a very high resistance pullup resistor and a cmos logic gate. Logic high, no flame, logic low flame present. You will need a good quality stainless steel electrode that won't burn away, and a ceramic insulator to support it. The spark igniter electrodes used in gas stoves are available on e-bay, and would be ideal. This is just one example: https://www.ebay.com.au/itm/Gas-Grill-Ceramic-Igniter-Electrode-Pin-Spark-Ignition-Cable-400mm-For-Heater/163650519219?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649 But to just experiment with initially, a nail or piece of steel wire will work just as well, for a short time anyway. This electronic flame sensor method is used in most types of modern automatic gas appliances these days, and is usually connected to a microcontroller that controls the spark ignition, and gas valve. Cheers, Tony. |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 842 |
Hi all, Some interesting comments - please keep them coming. Here is an update. Because I had some, and it was easy, I put a DS18B20 probe just into the HWS flue (exposed to both exhaust gases and ambient air flow). A simple MM170 circuit uses an HC-12 to show the temperature every minute on my PC (and every 15 seconds on an LCD BackPack).  In this image the HWS plot is in red, the two green tracks are external air temperature (every 10 minutes). Some observations: - there is a lot of scatter in the 1 minute readings - WHY? My other (green) temperature sensors are more sheltered and may be less effected by wind. There is no averaging employed. - my HWS is sick, it sometimes doesn't fire up despite a long shower (at about 10:00) (confirmed by the pilot being out). That little rise just after 10:00 is more to do with ambient temperature - not the HWS. When I lit it (about 11:10) the displayed temperature shot up to above 40degC (off the plot) and came back down before 12:00. - just after 12:00 there was a second shower and the HWS fired up (as it should) to just over 40 (off scale). This means it sometimes works. Its temperature tailed off after about 12:15. - I am surprised how quickly it heats the water after a shower! I can thus detect when it is on (ie when it is above say 35 and ambient isn't) vs off (ie when it is closer to ambient). I have another possible option. Before embarking on this "project" I replaced the thermocouple (which I now suspect was OK). My DMM shows a change in resistance when I heat it (but I cannot trust the reading as it sometimes shows a negative value) - can I place that nearer the gas ring and get a more direct measure. How would the circuit look? (Beginner's question I know, but, how does the HWS use a change in resistance on the thermocouple to sense heat when there is no power source to the HWS?) Cheers, Andrew |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1985 |
Unless you specifically want temperature, you only need significant change from ambient. I would go for a really easy option here of two thermistor/resistor voltage dividers and simply monitor the junctions. One outside for ambient (a foot below the flue pipe and in the shade) and one in the flue outlet gasflow at the top. Both suitable coated in a decent lacquer and train it for the voltage difference between the two. xV Below ambient you know the boiler is running, really simple solution and will naturally iron out the bumps Edited 2019-09-22 06:15 by CaptainBoing |
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