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General: Flow sensor for DHW

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  1.  
    • CommentAuthorborpin
    • CommentTimeJun 13th 2022
     
    I am after a flow sensor for my DHW. They seem remarkably difficult to find.

    I have found the Sika VTL20 which looks ideal, but cannot find any suppliers.

    Does anyone have any suggestions?
  2.  
    You could try asking sika for a UK supplier (Sika - German company Email: info@sika.net )

    Otherwise are you trying to measure DHW usage? I needed to do this and put in a standard water meter for hot water, easily available here at about 13 GBP.
    https://www.ventil.hu/vizora-1-2-b-meters-melegvizre-110mm.8038.phtml
    Down side you can't have remote reading.
  3.  
    https://uk.rs-online.com/web/c/automation-control-gear/sensors/flow-sensors/

    Any of these? Are you looking for a particular feature which is providing hard to find?
    • CommentAuthorrevor
    • CommentTimeJun 13th 2022
     
    Are you looking for a flow sensor to switch on a pump. e.g sensing that water is going into a heat exchanger so you can switch on the HE hot water side? or is it metering you are looking for?
    • CommentAuthorborpin
    • CommentTimeJun 14th 2022 edited
     
    I am after a flow sensor to detect when the DHW is flowing. I'll then use a combination of flow/time to determine if it is likely to be a shower, and then check and see if there is sufficient hot water. If not, I'll kick the boiler off earlier than the temperature settings (I have several sensors on the tank) would otherwise do so to avoid a dip in water temperature.

    Interface providing a pulse output should be enough to hook it up to an ESP.

    The VTL20 looks ideal (22mm fittings), but as I say, I cannot find a supplier for that or a suitable alternative. I have tried Sika, but didn't get a response.
    • CommentAuthorrevor
    • CommentTimeJun 14th 2022
     
    This is what is fitted to my thermal store to sense water flow that will then turn on a pump to push the tanks HW through the heat exchanger.

    https://www.supplieddirect.co.uk/collections/gledhill-boilermate/products/gledhill-boilermate-flow-sensor-xb095

    Don't know if something like this would do but might be worth following the trail to see if it may lead you to similar sensors that may suit you.
  7.  
    I'd suggest to select a sensor by its flow measurement range and resolution/accuracy, rather than by the size of the end fittings, as you can use reducers to adapt the size, and the gubbins inside the sensors will be similar for any given measurement range. The RS components I linked above cover several ranges of flow (small range one for a shower, bigger one for a bath) but sure that others are available, maybe sold as spares for boilers or washing machines?

    It's also a good principle to measure whatever parameter interests you, as directly as you can, rather than inferring it. If you need to know that the shower is flowing, then put a small flow sensor in the pipe supplying to the shower, rather than a big one in the pipe supplying to the whole house. If you need to know when the hot cylinder is being depleted, then use your thermocouples at different heights up the cylinder, or strap on a few more.

    Look at the rate-of-change-of-temperature if you want to forecast when you are about to run out of hot water, rather than waiting until the stat has already reached its 'cold' setting, but filter any rate-of-change calcs as they are prone to noise.
    • CommentAuthorborpin
    • CommentTimeJun 14th 2022
     
    Posted By: WillInAberdeenI'd suggest to select a sensor by its flow measurement range and resolution/accuracy, rather than by the size of the end fittings
    I appreciate your input, but I only need a general idea not precise measurements and I am more concerned over pressure loss. So reducing to 15mm for instance is not an option.

    There are 4 showers in the house - I'm not intending to fit 4 sensors.

    Posted By: WillInAberdeenIf you need to know when the hot cylinder is being depleted, then use your thermocouples at different heights up the cylinder, or strap on a few more.
    Currently 8 sensor on the tank (in pre-fitted pockets recording every 10s) and this doesn't tell me quickly enough. There is also a lag between the boiler starting and having an effect on the tank, that lag is what I am trying to reduce. I could kick in at a higher temperature, but I maintain the tank at a lower temperature during the day. I also want to stop the boiler if the shower stops so it doesn't overshoot.

    BTW, I *hate* cool showers - really hot is the only way to go - YMMV.

    The key metric I need is the time the DHW is running for. Anything over 90s is going to be a shower.

    Posted By: WillInAberdeenLook at the rate-of-change-of-temperature
    Tried that - really doesn't help as the rate of change is about the same for a sink, but happens over a shorter period, but the ROC tends to overshoot. It also depends on how recently the boiler fired (as the water from the boiler is hotter so kicks the tank quicker on start.

    There are lots of variables, I have tried various mechanisms for detecting a shower using data manipulation, none work reliably.

    So I'd like a flow sensor :bigsmile:.

    Enclosed is a sample of data I have, including when the boiler is on.
      Screenshot 2022-06-14 113038.png
    •  
      CommentAuthordjh
    • CommentTimeJun 14th 2022
     
    To know whether a shower was being taken in our house it would be sufficient to measure the temperature of the hot pipe leading to the shower. I expect it's the same in most plumbing.
    • CommentAuthorcjard
    • CommentTimeJun 15th 2022
     
    @PeterInHungary

    > Down side you can't have remote reading.

    Raspberry pi with camera looking at it, possibly with tesseract/opencv OCR?

    Cheap ip camera looking at it?
    • CommentAuthorcjard
    • CommentTimeJun 15th 2022 edited
     
    @borpin

    >i am after a flow sensor for my DHW. They seem remarkably difficult to find.

    22mm:

    https://www.amazon.co.uk/Kyrio-Sensor-Switch-Flowmeter-Liquid/dp/B082HQ3WL5/ref=asc_df_B082HQ3WL5/

    Or if you're finding 15mm common, maybe let go of the 22mm requirement - if you're bothered that 15mm will restrict your flow too much, put a 15mm sensor in and bypass it with 15mm too; it matters not that half your water flows through the sensor and half doesn't because all your determinations are relative (but if you're bothered to track all water, put two sensors in, one on each 15mm split). Or, at a fiver for a sensor like a seeed yf-b1 fit one to every shower..

    https://www.digikey.co.uk/en/products/filter/flow-sensors/520?s=N4IgjCBcoLQdIDGUBmBDANgZwKYBoQB7KAbXAFYBOAdhAF0BfJoA

    22mm to two 15mm tee:

    https://www.toolstation.com/solder-ring-reducing-tee/p52307
  12.  
    Borpin it sounds like you just want an on/off paddle flow switch, presumably there is one shower you use most often, or they are cheap if you want to sense all 4 of them?

    Any turbine sensor will use up pressure from the flow because it has to squeeze the flow into a jet to spin the turbine. If it's a 22mm pipe it has to squeeze the water more to achieve the jet, or else be insensitive to lower flow rates. If pessure is tight, could you mount the sensor in the cold feed to the cylinder, upstream of any pressure regulating valve set (if fitted?)


    Thanks for sharing the data! There is something interesting with the primary circuit from the boiler to the cylinder, the temperature of "tank to boiler" kicks up immediately after the boiler switches off, could it be siphoning backwards?

    Measuring pipe temperature to infer that the shower is running, seems attractive but it could be difficult to detect when the shower is switched off again, because the pipe stays warm for quite a while afterwards - green line on right of the chart above. Likewise difficult to tell if it is switched back on by the next user 10mins later.

    Good links thanks cjard!
    • CommentAuthorMike1
    • CommentTimeJun 15th 2022
     
    How about building a few piezo-Arduino sensors based on this:
    https://www.instructables.com/Low-Cost-Water-Flow-Sensor-and-Ambient-Display/
    • CommentAuthorcjard
    • CommentTimeJun 16th 2022
     
    (I did also have an alternative wondering whether you could just put an infrared sensor on the shower area angled so out can't see people standing in the other places; it's rare for someone to stand in a shower cubicle and not be showering.. it only provides on/off but that might be all that is required. Or what about an open/close sensor on the shower door?)
    • CommentAuthorborpin
    • CommentTimeJun 16th 2022 edited
     
    Posted By: WillInAberdeenAny turbine sensor will use up pressure from the flow because it has to squeeze the flow into a jet to spin the turbine. If
    yes. I had the impression the Sika one was a hall effect, rather than a turbine. As I say, it is the fact it is flowing that is important not the rate or volume measurement.

    Posted By: WillInAberdeenThanks for sharing the data! There is something interesting with the primary circuit from the boiler to the cylinder, the temperature of "tank to boiler" kicks up immediately after the boiler switches off, could it be siphoning backwards?
    No, there is a load valve close to the boiler so the water in the pipes to/from the boiler circulate and heat before being dumped back into the tank (else you get a cold 'slug' dumped into the tank). The water to the boiler is also blended so the minimum temp to the boiler is 40°C to help the boiler reach a better delta quicker. There is a little bit of the effect of the heat in the tank transferring via the pipework to the sensors (they are close to the tank). I think the effect when the boiler switches off, is heat transfer from the tank along the pipework as the cooler flow stops and the water stratification settles.

    Posted By: WillInAberdeenMeasuring pipe temperature to infer that the shower is running, seems attractive but it could be difficult to detect when the shower is switched off again,
    Yes, precisely my issue.
  16.  
    Thanks for sharing, this is interesting stuff!

    A hall effect sensor is a variety of turbine sensor, the sensor uses the magnetic hall effect to count the rotations of the turbine.
    https://how2electronics.com/arduino-water-flow-sensor-measure-flow-rate-volume/#YFS201_Hall_Effect_Water_Flow_Sensor
    • CommentAuthorborpin
    • CommentTimeJun 16th 2022
     
    Posted By: cjardI did also have an alternative wondering whether you could just put an infrared sensor on the shower area angled so out can't see people standing in the other places; it's rare for someone to stand in a shower cubicle and not be showering.. it only provides on/off but that might be all that is required. Or what about an open/close sensor on the shower door?
    The main shower doesn't have a door (I'd totally recommend that - one this less to break - and there isn't really anywhere for a movement sensor that would make sense.
    • CommentAuthorborpin
    • CommentTimeJun 16th 2022
     
    Posted By: WillInAberdeenA hall effect sensor is a variety of turbine sensor, the sensor uses the magnetic hall effect to count the rotations of the turbine.
    I looked at exactly that one but I felt the construction simply not robust enough to put on effectively incoming mains pressure water!

    The driven blade doesn't need to be in the flow really, just enough to detect flow.

    I think I am out of luck :cry:
    • CommentAuthorborpin
    • CommentTimeJun 16th 2022
     
    Posted By: WillInAberdeenThanks for sharing, this is interesting stuff!
    The cold water slug issue became apparent, when I started measuring the tank temps and this effect made a noticeable difference to the hot water available at that point.

    At the time the boiler was controlled by a simple stat on the tank.

    It is now controlled by a relay mimicing the thermostat input and readings from the top 3 sensors. The relay is in parallel so if the Home Automation fails, the thermostat will kick in eventually. Controlling it this way means I let the tank get cooler in the day than for my 'shower period'. That period can be manually triggered if someone wants a shower out of peak time.

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