BCM Amp Only Meters to Estimate KW in DCO?

DCIM_Support · ‎2020-07-04

This question was originally posted on DCIM Support by Gregory Garcia on 2018-09-17

Hello - I have existing amp only BCM veris meters. I'd like to sensor map these amp sensors into DCO and have the tool estimate kW. Is there a way to do that today? Someone has suggested mapping amps into the kW slot in DCO and applying 120V multiplier. Looking at the electrical physics of this, I believe this approach could be a conservative estimate but would tend to overestimate power by 5-10% depending on the quantity of 2-pole/3-pole breakers installed. This method also neglects power factor effects. Thoughts?

DCIM_Support · ‎2020-07-04

This answer was originally posted on DCIM Support by Gert Lehmann on 2018-09-24

Accurately calculating power from current values are very difficult, because you end up with some complicated math and a few unknown variables per pole. One way of finding those variables is measuring them with a power meter, but once you have a power meter in place then it would be simpler just to measure the actual power.

So instead you end up doing some estimations, but which estimations are good enough is very individual depending on how much work you want to do in oder to get the required accuracy.

Since DCO does not know what approach satisfies your needs, it is left up to you. That is, you can map the current sensors and put in an multipier with as much accuracy as you want to, depending on the amount of work needed to calculating this multipier.

Now, you are asking about thoughts on using 120 as a factor; assuming that we are taking about rack PDUs connected to the poles and these rack PDUs are powering a number of servers all having a PF=1:

3-pole breaker will have an error in the range of 0-13% depending on the phase balancing of the connected rack PDU, if it is perfectly phase balanced or it only har 120V output then the error is 0.
2 pole breaker connected to a rack PDU without neutral (pure 208V) the error is about 13% but you can fix that in the mapping by using 104 (for each of the 2 poles) instead of 120.

You can also adjust the factor for servers not have a PF=1, but then it gets really complicated, let me give you an example: in our data-center we have rack PDU (connected phase-neutral) powering different servers where some has a PF as low as 0.7 and other has a PF of 0.95, yet the rack PDU measures an overall PF of 0.8. Calculating that based on the PF of each individual server is not going to be simple...

Hopes this helps

Best,

Gert

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DCIM_Support · ‎2020-07-04