I am just setting up my IoTaWatt for the first time and have started getting some data, and it seems a little weird to me, so I thought I would ask the experts.
Background: US 2-Phase power, 4 Temperature Zones in our house (I am only monitoring half right now. Gas Furnaces, and the thermostats are powered by the furnace. All zones are set specifically to “Heat”.
Looking at the usage, the 2 heaters are using power as I would expect. Our bedroom A/C is using 0 as I would expect, but the Main Floor A/C is using ~46 W consistently. (always between 42-48). Is it normal that an A/C unit would be pulling that much power all of the time, even when “off”?
I would expect there to be some draw to power the controls, but 50 Watts is not reasonable for that. Is this the compressor/condenser unit with the evaporator in the heating system plenum or is it a standalone system like a mini-split or multi-split? What is the make and model of the AC unit?
My furnace uses 7-8W doing nothing. I think this is somewhat excessive, but it wasn’t designed for low power usage. Almost 50W is a lot. It seems like there is probably a fan that is running constantly. I have small fans that use that amount of power when they are on. Do you have it in fan mode?
I am not very well versed in HVAC, so I’m going to be honest that I don’t know what most of these terms mean .
I believe it is a compressor/condenser unit and the AC unit is CPLJ30-1A, or at least that is one of the 4 on the house. It is currently cold, wet, and dark here. The furnace is what powers the thermostat. Hubby says he isn’t certain but he also thinks it is a compressor/condenser in a system.
@frogmore The fan is not on as far as I can tell from inside the house, the air stopped blowing during this time (It is possible that the device is on outside I suppose, again, cold, wet and dark )
When I turn on the fan via the thermostat, the furnace measurement spikes but the A/C remains at the constant 50W
When I look up that unit it’s a heat-pump, so it it’s designed to be capable of operating in cold weather. There is a crankcase heater feature that prevents compressor damage when operating in low-temperatures. That may be what is consuming the 50W since its
If you intend to only use the unit for A/C, then you may be able to turn off the breaker, but you should get a HVAC opinion on that. If you do turn off the breaker, the HVAC consultant should advise you how long before using you should turn the breaker on to heat the crankcase up to safe temp. I don’t know your climate, but there is probably a relatively low temperature where the heatpump is more economical than gas, and hopefully a way to program your system to crossover.
NC, so winters rarely get below about 20 degrees F, usually it’s above freezing. Google tells me the average high for (Jan/Feb/March) is around 50, average low is around 30. Thermostat is a Nest, as far as I can tell there is no way to specify where the heat is coming from unfortunately.
You said you have 4 temperature zones in your house. Do you have 4 Nests or something else?
If you had a competent installer install everything, they would have made sure everything was hooked up correctly. But, even competent people can make mistakes. I have heard of systems when the furnace and heat pump were fighting each other. I don’t believe you have that.
The question is, how is your system set up to work. If the main AC (which is really a heat pump) is really only used for AC, is most likely does not need a pan heater (since it will never be used in below freezing weather). At 50W usage, you are looking at $50/year (if it is on all the time, depending on your electric rate). Since the heater is probably only on when it is really cold, the actual amount is probably much less. You can verify this by looking at you IotaWatt readings when it warms up some. This should also show if the heat pump is being used at all. If it really is just for AC, you can turn it off at the breaker during the winter. You will just need to remember to turn it back on in the summer.
It is also possible you have a more complex system. Since you have 4 zones, I say your system qualifies as, at least, unusual, if not complex. In a moderate climate, using the heat pump can be cost effective to provide heat. It depends on the cost of gas vs electric where you are. Typically, gas is cheaper (by quite a bit) per BTU than electricity is. The heat pump can still win, since it is generally more than 100% efficient. It can do this because it doesn’t generate heat, it just moves it from outside to inside. You generally need a very competent HVAC professional to set up a system like this. If you don’t already have one you trust, it might be worth finding one. Once you find one, they can advise you on what to do better than we can from such a distance. I say it is the pan heater and you probably don’t need it (and fixing this will quickly more than recover what you spent on the IotaWatt).
Yes, we have 4 nests. The nests were installed by me, so not a professional. We bought this house 2 years ago, the system they had on it was not great and I couldn’t get to it remotely. It is a pretty large house, each floor has its own system (Basement, Main floor, Second floor) and the master bedroom suite (bed/bath/office) has its own.
The system is definitely overkill, it was built in 2004 and we are finding lots of things that are either weird (wires coming out of drywall and being plugged in), poor decisions, or just completely over designed, it’s a weird combo!
Gas is definitely cheaper than electric where we are. Electricity is some ridiculous co-op system and pricey, hence the IoTaWatt to see why we have such high electrical usage!
Sure, kWh for kWh gas is less expensive, but a heat pump multiplies the kWh that you put in. The units you have claim to produce about three times energy input when the outdoor temperature is 47 degrees. It’s called the coefficient of performance, or COP. So at 47 degrees electricity would need to cost three times as much per kWH as gas to make gas the preferred fuel for your heating. That COP goes down as the outdoor temp goes down, but there is a “crossover” temp where it begins to be more economical to use the heat-pump to collect heat from outdoors and “pump” it into the house.
Now is the time to bring out the thermal imager. 50W is quite a bit, it should be easily visible. Of course, most people don’t have a thermal imager. So, since it is an AC and it is cold outside, it is probably safe to just turn off the breaker to the AC compressor in the winter. That should eliminate the 50W. If all your Nests stop working, then you know that they are part of what is using that 50W.
Darn, I left mine in my other jacket… I already know cutting that breaker doesn’t stop the nest (tried it when we were attempting to label all the breakers).
I guess I’m just worried if it is pulling a constant 50W I’d like to know why so when I do turn A/C back on for summer I’m not having that draw for no reason on top of what it draws to cool.
Looks like it is normal for older AC systems. I don’t know about newer ones. Also looks like it is okay to turn off the breaker, just remember to turn the breaker on at least 24 hours before you need cooling in the spring or summer.
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