I am working on a solution to add a fairly low cost emoncms monitoring solution for new heat pump installations (mostly vaillant). Most customers don’t want to pay for the proper full Level3 monitoring, which I understand. It just has to work from their perspective.
My current solution is a standard 3B+ with emonSD image and ebusd. This works, and the power and flowmeter are fairly accurate, but the temperature sensors are not.
To make it better I would like to add 2 external temperature sensors for flow and return. I have no idea what I need from hardware perspective to add 2 sensors to a 3B+.
Ideally I would add the sensors to M10x1 test points in the flow and return ball valves. Does anyone know any accurate sensors that can be used in M10x1 pockets?
If you use the DS18B20 One-wire sensor, the answer to
is, in the emonPi2, temperature measurement is handled by the RPi, so the software will be part of the emonSD image. The One-wire ‘Temperature’ input on the emonPi2 goes straight to PB4 on the RPi, with a 4.7 kΩ pull-up to 3.3 V, so all you need is a suitable connector and pick up GND, +3.3V and PB4.
I can’t help with mounting the DS18B20 sensors, other than the usual comments like silicone grease or heat sink paste to assure a good thermal contact. You should calibrate the pair of sensors together before installation to determine the difference between their readings, it’s the difference that’s most important.
Thanks for the info Robert. I did not realise these temperature probes were digital and you can have more than one of those on the same wire. Nice.
Mounting will be another thing entirely, as I would really want them immersed in the heating circuit like the real heat meters. However, finding DS18B20 sensors with M10x1 is not so straightforward it seems. I noticed the shop has M10 probe seats but in another thread is mentioned those are for heatmeter sensors and not the DS18B20 ones?
I could go for the external mounting, but then I wonder if that will end up in any way more accurate than the vaillant ones…
We know the DS18B20 is 6 mm diameter. No size is given for the sensor the M10 Temperature Probe Seat is designed for. ½" BSP is 21 mm clearance. It might actually be 10 mm, but it’s not clear. We’ll wait for a definite statement.
The M10 seat does not fit our DS18B20 stock. The seat is for 5mm. The profile of the ‘ridges’ where the temperature sensor would sit are also different.
The temperature sensors on the heat meters are a factory calibrated pair.
The description for the M10 seat in the shop now mentions it being a ‘backnut’ - I’m not sure about that. The thread is on the outside - I think it is more of an adaptor.
It looks as if the recommendation then will be to attach the DS18B20s to the outside of a copper pipe, with heat sink compound to improve thermal contact, bound with copper tape or wire and well insulated. And as I wrote earlier, calibrate the pair first so that you at least know the difference between the two over a range of temperatures, and which way it is - because it’s the temperature difference that’s critical to the calculations.
Yes thanks for the effort Gwil. Outside of the pipe is always an option, but I feel like it will never be correct.
In the current setup with the internal vaillant sensors I “calibrated” the sensors by looking at both during a time the pump is on and the compressor is off. I have a heatmeter in my “test” installation, so I know which of the two is most wrong. I add 0.22 degrees to that one to be the same as the other one. When the compressor is off and the pump is on both give the exact same value in emoncms. However, when the compressor is on and temps rise they both start deviating from the actual value. The flow ends up more than 0.5 degrees off of the actual value resulting in a big COP difference.
Not that I would install the ebusd solution for actual COP values> It is more to verify everything works as expected, but still. If I would install the extra sensors, I believe they will need to be in the flow to be worth the extra effort.
There are some M10x1 or G1/2 DS18B20s to be found online, but most are expensive and/or come from china.