Author Topic: Heating System Monitoring  (Read 296 times)

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Offline vtwin@cox.net

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Heating System Monitoring
« on: September 02, 2019, 09:46:58 am »
I'm looking to build a system which will monitor the heating system this winter in a building I own. 3 units with 3 zones each and one common zone.

The heating system currently uses two Taco ZVC406 zone valve controllers to monitor 10 thermostats and control 10 zones via three wire zone valves (see: http://www.taco-hvac.com/uploads/FileLibrary/102-397.pdf)

By monitoring the presence of 24vac I can log the following events:

t-stat call for heat start/end (presence or disappearance of 24vac on R or W on the thermostat connections - need to check w/ my multimeter to see which line carries 24v from the transformers in the ZVC to the t-stat and which is the return line)

zone-valve open/close (presence of 24vac on zone valve controller line 1/2)

zone-valve opened / zone call for heat (presence of 24vac on line 3)

ZVC request for heat from boiler (presence of 24vac on isolated end switch)


The pumps and what not are controlled by the boiler controller, so at the moment I'm not worried about that.

With 10 zones, I see 30 monitoring points (3 for each zone) plus the ZVC's call for heat from the boiler, for a total of 31 monitoring points.

This guy (https://www.instructables.com/id/Log-and-Graph-24V-Thermostat-Events-Optocoupler-Ra/) built a circuit to monitor a single tstat. While I could duplicate this 31-fold to monitor each of the data points, I'm wondering if someone may have a better idea.

Once I have a method of monitoring the presence of voltage on each of the data points, I can use a Raspberry PI with a I2C Hat and an ADC to do the actual data collection and feed the information into a database.
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Offline vtwin@cox.net

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Re: Heating System Monitoring
« Reply #1 on: September 18, 2019, 03:21:57 pm »
bump. anyone?
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Offline Renate

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Re: Heating System Monitoring
« Reply #2 on: September 18, 2019, 04:43:12 pm »
Do you really need 3 signals per zone?

Yes, the valve power and valve sense will show a lag of a minute or so for these heated wax valves.

Why not do it the simple way? Pick off the signal from the 10 LEDs for the valves.
You could optoisolate there or run everything into a uP and isolate the output of that instead.
 
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Online jmelson

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Re: Heating System Monitoring
« Reply #3 on: September 18, 2019, 07:11:08 pm »
I have a system like this, but single family house, so 3 zones, one pump and boiler.  I built up a little perf board with 4 channels of bridge rectifier, capacitor, resistor and opto-isolator, and it feeds into a data acquisition setup I built.  I think you could probably get some Opto-22 interface boards, and they should have input modules that will take 24 V AC and convert to 5 V DC output.  Then, you need some sort of input scanner module to get this into a computer.

Jon
 
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Offline floobydust

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Re: Heating System Monitoring
« Reply #4 on: September 18, 2019, 08:20:26 pm »
For the 24VAC digital inputs, opto-couplers are the least hassle.
You'll have to decide early if you want to provision for outputs (remote) controls, say for set-back if a unit is unoccupied, or pump control. There is a danger if winter goes below freezing and your outputs go wonky.

It might be better to locally monitor say 8-10 inputs and go wireless to bring that back to a concentrator (RPi). Like using ESP32's and Wi-Fi. I would bring back air temperature.

There was a fad for having remote energy usage billed to apartment renters, by logging the zone valve on-time. I think it was the UK where they ruled this is not legal, it's not an accurate indication of dollars of energy use. But you could see the tenant that leaves their windows open in winter, thinking heating is free.

Monitoring the boiler has a big payoff, you can see when a burner is taking many retries to light or is short-cycling, or malfunctioning limit switch etc. to predict upcoming failure. You would look at demand and burner valve 24VAC signals. A few temperature inputs from i.e DS18B20 to monitor water and outdoor temperature. Send out a text message if the system is in trouble.

HVAC service bozo's are overpaid and the system pays for itself, if it saves a few callouts.
 
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Offline vtwin@cox.net

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Re: Heating System Monitoring
« Reply #5 on: September 18, 2019, 10:54:59 pm »
For the 24VAC digital inputs, opto-couplers are the least hassle.
You'll have to decide early if you want to provision for outputs (remote) controls, say for set-back if a unit is unoccupied, or pump control. There is a danger if winter goes below freezing and your outputs go wonky.
[...]
air temperature

Yea, remote control isn't an issue. The thermostats are programmable, so if a unit became vacant I reprogram them to keep the temperature at a minimum. This is principally for data collection, to see which zones are calling for heat (how often), and how long they are pumping heat through the zone (by monitoring the zone valve status.) I can get air temp from the thermostats (they communicate to a web service and I sniff the packets and extract the data I need now. I know how much heat each unit takes, but I'd like to get a better idea of the utilization per zone. By tracking events off the ZVC, and correlating it to the data I obtain from the thermostats, I can get a better handle on which zones may have heating issues I need to have addressed (e.g. poor insulation, etc.)
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Offline floobydust

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Re: Heating System Monitoring
« Reply #6 on: September 19, 2019, 12:33:05 am »
A luxury AC/DC opto-coupler with logic, like HCPL3700 is nice- but expensive $4.50 each.

You can use a low cost opto-coupler MOCD217 for $1 with MB4S bridge rectifier $0.36x2, getting two channels for 1/5 cost but higher parts count. Your software would have to debounce the pulsating 100/120Hz signal the opto outputs unless you want to add capacitors and do it in hardware. You can also get rid of the pullup resistors by turning on internal pullups in the MCU digital input.
Terminal blocks can also be expensive as part of the BOM cost. High quality Phoenix Contact Combicon MKDS are around $1 per pin.
 
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Offline soldar

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Re: Heating System Monitoring
« Reply #7 on: September 19, 2019, 02:48:40 pm »
In my boat I have a bilge pump that automatically pumps out any water that gets into the bilges. This is convenient but can hide serious leaks as the water is automatically pumped out... until the battery runs out and the boat floods.  So when I go to check the boat, every week or every few weeks, I want to know how long the pump has run in the interval. I am not concerned with specific volumes of water, power, etc. Only what amount of time the pump has been on. There are many sophisticated ways of doing this but I used a really simple one. I got one of those really cheap mechanical alarm clocks. They advance when power is on and they stop when power is off but they maintain the position, they don't lose it like LCD clocks. So wiring the clock in parallel with the pump will totalize the running time.  As the clock works at 1.5 V and the pump at 12 V I just fitted a simple voltage divider.  Simple solution for a dollar or two. Every time I checked I would reset the clock back to 12:00.

The pump would normally only run a few minutes total per week. Obviously this solution does not work if the total time "on" between checks is greater than 12 hrs because 1 hr and 13 hrs show the same reading.

Maybe someone can find the idea useful.
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