Need advice for new setup

I’m new to the forum and just found out about iotawatt by searching for energy meters.

I’m looking to monitor usage (and therefore costs) for HVAC in a commercial building in the US.

One of our electrical panels is dedicated to HVAC, and has about 10 circuits ranging in amps from 50 - 150 (different sizes of HVAC units) - running on I believe 208v - not standard 220v.

I’d like to be able to monitor and store the data gathered by something like an iotawatt - maybe combined with a Raspberry PI and Grafana (which I am familiar).

recommendations for purchase (bundle, etc…) ?


Hello @ismgr,

I’d have to know more to give specific purchase recommendations, but in general:

That you have 208V indicates that your service is three-phase, which is usually a given anyway in commercial buildings.

There are two methods of measuring three phase with IoTaWatt Direct-Reference - using three voltage reference transformers, and Derived-Reference - using just one transformer. Both produce good results. You can use either with a standard IoTaWatt V5.

Given 10 HVAC units ranging from 50-150 Amps, what is the capacity of the Mains, and do the they use multiple cables for each leg (3 or 6 incoming service cables).

If the HVAC units do not use a neutral wire (no white conductor), then you can monitor each HVAC load with one CT. There are 100A and 200A models available.

At first glance it looks like you could do it all with one IoTaWatt, 1-3 reference transformers, a USB power supply, 3 mains CTs (probably 400A) and up to 12 individual circuit (HVAC unit) CTs of 100 or 200 Amps.

The IoTaWatt will save all of the data in fine detail, and you can plot it out from any local browser. You can also upload to an influxDB database with Grafana or Telegraff.

This should cost between $350-$400. If you need 400A mains CTs, there may be a lead time of a few weeks. I have a few right now, but doing a large 277V/480V industrial install and don’t know yet if I will need them all.

Hi-Res pictures of the load center with the circuits to be monitored labelled or otherwise identified would help to fine tune this. You would be well advised to have an electrician install the unit and the CTs.

That’s a bit different than originally described. Each unit is three-phase, as opposed to two-phase 208V. There are two ways to approach this:

If you want to just get a rough idea (say +/- 5% or so), then you can just measure a single phase and scale it up by three. That would require one IoTaWatt with one VT and up to 14 200A CTs.

If you want more accuracy, you would have three plugs installed near the IoTaWatt to accomodate three VTs. These three VTs can supply any number of IoTaWatt. You would then install three 200A CTs on each breaker (AC unit) and connect up to 12 (four AC units) per IoTaWatt. You would need to upload to influxDB or Emoncms to get a combined view of all of the units.

One IoTaWatt with 12 200A CTs would cost about $363. So for the first option, that’s about what it would cost.

To do 9-12 units would require 3 such units at a cost of about $1,089. That would include three VTs which can be shared across the three units for direct-reference three-phase.

These are some big units. The circuit breakers alone list for close to $900. By the power implied, running these units must be expensive. Makes a lot of sense to measure it and see where the power is going. The solutions may not be in HVAC equipment, but things like ventilation air volume, building insulation, and solar gain.

Out of curiosity, can you say which state this is located in?

I originally described it as I understood it - sorry for confusion.

to answer your ‘curiosity’: This is a daily newspaper in central texas. The building was built in 1987. The HVAC’s on average are 20 ton units. We use an electricity broker, so our rates are pretty good (today around $0.05/kwh) Most of our usage is in the printing press and packaging equipment.

For the simple option, you mentioned 1 IoTaWatt and 12 CTs at around $363. Besides this, what else would I need to connect it & start recording data ? (maybe a Pi & electrician to hook in the CTs ?)


Not a problem. That’s why I asked for pictures.

Short answer is nothing. Your electrician will probably want to put it into an enclosure, and it must be a plastic enclosure because of the WiFi. This works well for one IoTaWatt. For multiple you would need what is referred to as a “Media Cabinet” usually used to run phone, CATV and network.

The IoTaWatt is fully capable of recording all of the data for ten years or more. You can access it from a browser connected to the local LAN. Use a Pi or other server if you want to upload top influx and use fancier graphics. All that can be done after the fact as well because IoTaWatt can upload history.

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