Monitoring loads in HVAC systems

[Dean-KS]

I have found the Vue modules very useful for monitoring heat pump loads and cycle characteristics. That might seem obvious enough, But I want one step further. As well as having a current tap, CT, for the furnace or air handler breakers, I treated one furnace as a subpanel.

In the furnace, I mounted the antenna in a 3/4″ knockout in the cabinet. There was of course no need for the 200 amp CTs. The Vue 120vac power is spliced into the power going to the 24VAC transformer. That power is appropriately controlled by the cabinet safety switch.

Carrier variable speed, modulating gas furnace, 100,000 btu

There are 5 CTs that turned out to be beneficial:

Neutral wire for the variable speed ECM blower motor. There are many wires, but all amps must return to neutral.

Neutral wire for the induction ECM blower motor

Neutral wire for the modulating gas valve 24VAC

Power to the hot surface ignitor 120 vac

Power to to the 24 VAC transformer 120VAC

With this I can see the plotted power that the blower consumes under variable loads as well as constant fan. The constant fan is 77 watts at over 700 CFM. The hot surface ignitor shows when a gas cycle is starting up. The induction blower and gas valve are both proportional, maybe not linear, to gas flow. When the HP is running, the gas valve or induction blower activity indicates that a defrost cycle is underway. The system can use gas heat to speed up defrosting. The gas valve 24vac watts are not power, but a useful indicator. I could correct with a multiplier, but expect the numbers would be too small to plot propery.

Overall, inexpensive and effective instrumentation.

• This topic was modified 2 years, 9 months ago by Dean-KS.
• This topic was modified 2 years, 9 months ago by Dean-KS.
• This topic was modified 2 years, 9 months ago by Dean-KS.

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