Propeller Design Challenge! Wireless HVAC Datalogger
WBA Consulting
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Propeller Design Challenge!
I was approached by a friend that owns a Heating and Air business with a request for one of his commercial clients. I have come up with a few ideas, but have pros and cons for each, so I thought I would toss this out for those on the forum to see what other solutions people might have.
An owner of a 2 suite commercial building needs to know the usage of the HVAC furnaces for each suite because they draw natural gas from the same meter. The owner is looking for an inexpensive solution that would allow him to drive to the building at anytime to get the percentage of usage between the units to adjust billing accordingly.
Here is the criteria for the project:
I was approached by a friend that owns a Heating and Air business with a request for one of his commercial clients. I have come up with a few ideas, but have pros and cons for each, so I thought I would toss this out for those on the forum to see what other solutions people might have.
An owner of a 2 suite commercial building needs to know the usage of the HVAC furnaces for each suite because they draw natural gas from the same meter. The owner is looking for an inexpensive solution that would allow him to drive to the building at anytime to get the percentage of usage between the units to adjust billing accordingly.
Here is the criteria for the project:
- Each suite has its own tenant and although they each have internet, they cannot be used for data transfer.
- This "meter reading" needs to occur without entering either suite nor having to get on the roof where the units are located.
- The HVAC units sit right next to each other on the roof approximately 40-60 feet from walkup/driveup access.
- AC power is available for any added devices.
- Access to the 24 VAC signal lines from the thermostats to each of the furnaces is available for sensing when they turn on and off.
- Total cost of system should be less than $300
- Parts to build the system should be available from standard suppliers and readily available.
- Reading can be done with a smartphone or a second propeller based device as a "remote"
Comments
Many types of rooftop units have two stage (high and low) burners. And the btu per hour rating of each unit would be needed for somewhat accurate totalizing.
Focusing on 'wireless' as meaning no-wires more than RF-Link, and using a smartphone, a somewhat left field solution would be a small LCD Graphic display Module (eg 128 x 64) that could display QR or Micro-QR codes (and some text to one side)
Capture the image on the smartphone, and you are done.
No log-in's, or any special equipment needed in the car, but you do need to mount the LCD for drive-by easy access.
An alternative would be to mount the QS and display in a key lock box and run cat cable to the roof (in conduit of course) for monitoring. Since the longest months have only 474 hours a 4 digit display is more than enough to display the unit number and a 3 digit on time hours reading. Use the 24VAC from the monitoring wires or a separate connection to trickle charge the backup battery and power the prop.
Xbees were my first thoughts as well. The cons to this method is the overall cost since you need two setups (propeller, xbee, enclosure, etc) which nearly doubles the cost. However, itdoes make it easy to make the setup since XBees are a cakewalk with the Propeller.
Intersting point about security codes. Even though I doubt any problems in that manner would arise, I wouldn't want an easy path for any curiosities.
Also good point about the two stage units. I will ask him what type they are. I do know that the units are identical and were installed at the same time last year.
I have been looking into the Spinneret paired with a single point AP like the TL-WR702N. Depending on the difficulty of setting up the Spinneret and the AP, this might be a good solution. The cost for all of the parts for that method is about $140 plus enclosure. I don't know yet if I need an outdoor enclosure or if the setup can be housed inside one of the HVAC units.
No worries about the weights and measures concern as this isn't being used to "charge for metered usage" but rather to determine if either tenant should get a discount on the "utility cost" porting of their rent.
Actually, that's a pretty clever idea. The catch is that we can't add an LCD to an easily seen location without running conduit from the roof down, which is one of the things the owner wants to avoid. One of the ideas we came up with when first brainstorming was a large 4 digit seven segment display that could be read with binoculars.
Going to chew on the QR Code idea a bit more though.......
Yes, I was thinking of a consistent gap between outputs to keep the setup simpler and keep it to one way communication.
I would love to use a mobile hotspot as that would make it a slam dunk, however, that puts the cost right out of range due to monthly fees. Verizon has a basic hotspot for free, but the monthly plans start at $30, plus you have a $20 line charge each month. So that puts the hotpsot at $50 per month.
You can install any number of free bluetooth serial terminal programs onto an ipad or android.
A prop with a bluetooth module, and you were not specific of the 24v signal that comes out of the units. Does this go high when the unit is ON? Well, then a simple 24v optoisolator pushing a transistor to the prop, prop counts timings, then stores all data and eeprom in case of power outages.
Crystal mode could even be internal, precise timings not needed.
Find a few cheap 120v to 5v power supplies?
Or you could go solar, those outdoor lights that have solar panels built into them are great housings and have the solar panel plus battery.
(LED outdoor strings with solar panel, usually push 3v, and have battery.) and are usually less than 20$
Make prop go to sleep. Most bluetooth modules have wakeup line.
The two bluetooth devices can be seen from the ipad, so the user would need to switch the pairing, however, most bluetooth modules allow pairing to themselves, so one unit would be master bluetooth that the user pairs to the handheld, and the slave unit would only attempt connect to the master periodically to transmit its data.
Then its simply a matter of transmitting serial "interface" (debug style) over bluetooth.
Parallax Quickstart Board
Parallax Wiznet 5200 for Quickstart Board
Parallax Quickstart Proto Board
Parts for Optoisolator circuit (to interface the 24vac output signal from HVAC controller)
5 volt, 1A, Power Supply
TP-Link WR702N Wireless Router (setup as an Access Point and connected to the WizNet)
I have tested the setup (minus the HVAC interface and logging code) using a Belkin AP and it works great. The end user will only need to connect to the AP with his phone (or any WiFi device) and type in the static IP of the WizNet to access a propeller served web page that displays the current monthly usage as well as links to web pages of previous months usage. I may use Phil's strip chart bitmap code if I can wrap my head around it.
I am submitting my quote an scope of work so that I have reason to get this project to the next step. With this setup, I should be able to pocket $100 for my "trouble". However, I think it will go towards another WizNet board for my home network because this has been a lot of fun. ;-)