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shack cooling cost and




 
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Patrick J. / KD5OEI
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« on: September 11, 2019, 11:05:37 AM »

I'm making decisions about saving some energy this summer and although it's late I have a questuion for any electricians familiar with motor loads. Being close to retirement I'm planning a budget. Trying to understand what it costs to turn on the 3-ton air conditioning and lights all day in the workshop.

The installation is very much standard and plain*.

The 240VAC L1 and L2 come in with the neutral, and the only thing running is the 3 ton 'central air' type HVAC unit. These currents were measures with a clamp-on ammeter.
 
L1 has 15A,
L2 has 24A,
N has 5A.

I am guessing the condensing unit is using 15A because it's all 240V.
So that leaves 9A for the air handler blower.
But what about 5A on the Neutral?
4A is missing somewhere?

I know there are phase differences with the inductive loads, PSC motors and C-start/C-run compressor. They account for some of the weirdness no doubt.

I'm trying to figure out what the actual KW is. I am charged by KWh, no charge for power factor.





* Unit is a house type central air unit.
PSC type condenser fan motor -240V
Capacitor start and run compressor as usual -240V.
PSC type furnace blower -120V.
No electroncs, all good old EMP-proof mercury thermostat and electromechanical cotactors.
3 ton condenser and matched 3 ton coil.
The air handler is a decommissioned 5-ton furnace, not a 3-ton, but the air flow through the coil is normal for 3 tons due to the series filter system in place. It really keeps the dust and odors down as well as clearing smoke. Another topic maybe. My HVAC guy measured the airflow and said it was within tolerance for 3 ton system.
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« Reply #1 on: September 11, 2019, 02:17:19 PM »

hi Patrick ... so yer gonna retire .... I have been since 2013 and except for illnesses / surgeries its been great

the imbalance of L1 / L2 currents is forcing the 5A of neutral current .... I would look at reassigning some breakers for your 120 V loads to better balance them .... most load centers alternate between L1 / L2 as you go up in panel number ...this shud improve panel efficiency

9A for yer air handler motor seems high and especially set for 120V operation ....keep checking
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« Reply #2 on: September 11, 2019, 04:02:28 PM »

One of the best things I did when I built this house was install a heat pump.  It is a 3 ton unit with a 4 ton air handler.

Our total electrical bill, for an 1800 sq. ft. house, runs less than $200 per month and I have several tube type radios.  You might want to look at changing out you system before retirement if you can afford it.  That and insulation is the way to go in the Southwest.
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« Reply #3 on: September 12, 2019, 12:10:32 AM »

I need to get at the air handler to check current at the air handler motor wiring. Right now it's behind 2 if not 3 racks. - as is the breaker box for the building's outlets, lights, and a/c. I was able to measure only at the panel at the house proper.

Taking care of it has made it last a very long time. Both units are R22 and I have plenty of it. My group was just laid off last weekend so while I could have it replaced I am going to continue to lovingly care for it in case an urgent expense is required. The workshop building has insulation inside double walls but as a commercial type metal building it's not the best. I can start drawing funds in 5 months and will have a larger decision space then. Who knows the future?

The house is 1000 sq ft not counting the garage and is full of single pane windows. It is run 68 at night and 73 in the day time and the August bill which is always highest was $317. The next one will be less. If I was not working from home it would have been much lower. Anyway we have broken out the fans and the thermostat is going to be adjusted for more economy. Running the shop for 8 hours will cost about $3-4 more, but it isn't used every day, nor for 8 full hours! I may find some of those plastic strips that hang from the ceiling to section off the part I use for workbenches and ham radio operating. No need to refrigerate the junkbox! Normally the lab a/c is set at 85-90 when not in use. On the day I am going to use it I go in the morning and turn the unit on. I have a ton of CAT5 and several coax cables between the building and the house and should find a pair so I can remotely turn the a/c on and off and select between two thermostats for occupied/unoccupied. keep it simple!
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« Reply #4 on: September 12, 2019, 09:20:09 AM »

I assume the ravenous Bunker-of-Doom is one of your heat sources ... Roll Eyes Roll Eyes Roll Eyes

maybe an appeal to your fan base would help  Cheesy
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« Reply #5 on: September 12, 2019, 02:13:47 PM »

I'd clamp all your ground wires one at a time and see if you have 4 amps returning on ground, if you can.

I say if you can because a lot of old(er) wiring used the conduit as a return.

You're missing 4 amps on your neutral.  That is not inconsequential.

You can also put a PIR or dual tech occupancy sensor in the garage with a contactor or relay switching for the dual t stats.

We have to in California to meet title 24 energy code.  It's a good idea, although it does suck the first 15 or so minutes while the cooler beings a room / building down to temp.

You can use a DC unit, feed it with a series diode and put a cap after the diode on the relay to hold it in after the occ sensor says nobody is in the room if your one of those in and out kinda guys.

Or get an occ sensor with a programmable delay.


--Shane
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« Reply #6 on: September 12, 2019, 03:48:57 PM »

the imbalance of L1 / L2 currents is forcing the 5A of neutral current .... I would look at reassigning some breakers for your 120 V loads to better balance them .... most load centers alternate between L1 / L2 as you go up in panel number ...this shud improve panel efficiency
So, is this a matter of cost efficiency (higher electric bill) or a matter of equalizing current in the breaker box for cooling, creepage, etc?
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« Reply #7 on: September 12, 2019, 04:33:30 PM »

I'd clamp all your ground wires one at a time and see if you have 4 amps returning on ground, if you can.

I say if you can because a lot of old(er) wiring used the conduit as a return.

You're missing 4 amps on your neutral.  That is not inconsequential.

You can also put a PIR or dual tech occupancy sensor in the garage with a contactor or relay switching for the dual t stats.

We have to in California to meet title 24 energy code.  It's a good idea, although it does suck the first 15 or so minutes while the cooler beings a room / building down to temp.

You can use a DC unit, feed it with a series diode and put a cap after the diode on the relay to hold it in after the occ sensor says nobody is in the room if your one of those in and out kinda guys.

Or get an occ sensor with a programmable delay.


--Shane
KD6VXI

Occupancy sensor? Seriously?
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« Reply #8 on: September 12, 2019, 08:02:07 PM »

Yes, rather than running remote A/B tstat wiring from shop to the house.

What's the problem with it?

Your in the room, you have it cooler.  You leave, a half h our later it let's the temperature rise.

We HAVE to have them jn California, along with daylight harvesting and dimming lighting depending on lumens allowed through windows.

--Shane
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« Reply #9 on: September 12, 2019, 09:44:19 PM »

I'd clamp all your ground wires one at a time and see if you have 4 amps returning on ground, if you can.

I say if you can because a lot of old(er) wiring used the conduit as a return.

You're missing 4 amps on your neutral.  That is not inconsequential.

You can also put a PIR or dual tech occupancy sensor in the garage with a contactor or relay switching for the dual t stats.

We have to in California to meet title 24 energy code.  It's a good idea, although it does suck the first 15 or so minutes while the cooler beings a room / building down to temp.

You can use a DC unit, feed it with a series diode and put a cap after the diode on the relay to hold it in after the occ sensor says nobody is in the room if your one of those in and out kinda guys.

Or get an occ sensor with a programmable delay.


--Shane
KD6VXI

Hang a piece of toilet paper down from the ceiling by a thumbtack a couple feet out from the PIR sensor so that the air from the a/c keeps it moving.
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« Reply #10 on: September 12, 2019, 09:52:59 PM »

the imbalance of L1 / L2 currents is forcing the 5A of neutral current .... I would look at reassigning some breakers for your 120 V loads to better balance them .... most load centers alternate between L1 / L2 as you go up in panel number ...this shud improve panel efficiency
So, is this a matter of cost efficiency (higher electric bill) or a matter of equalizing current in the breaker box for cooling, creepage, etc?

When I did the measurement, the only thing on out there was the air conditioning. The blower is big, a 5 ton, so it might use 9A.

At this point, just to know the KW consumed by the a/c. So it's about 4800W. Knowing how much it is per hour allows cost to be known and therefore controlled when necessary.

Now it has turned into a mystery, where I want to know where that 4A is going if for no reason than there might be a safety issue. The conduit from the house breaker box to the bunker is buried electrical PVC.
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« Reply #11 on: September 13, 2019, 11:30:37 AM »

Now it has turned into a mystery, where I want to know where that 4A is going if for no reason than there might be a safety issue. The conduit from the house breaker box to the bunker is buried electrical PVC.

The neutral current is imbalance, but it is unlikely there's anything missing...remember that power factor you said you aren't being billed for? That doesn't mean that the loads on the two legs don't have power factors, and in this case they aren't the same. Current measurements don't tell you power factor, and with motor loads, the current and voltage peaks will not be in phase, there is a power factor, and because it seems one of your loads is only on one leg (120v) the factors on the legs are different. You need a wattmeter. Measure the wattage in each leg and the neutral, then you'll know your actual load that you have to pay for. Real wattmeters are hard to come by, though.  Just like a Bird 43 RF wattmeter, not everyone has an AC power wattmeter, and they are not cheap.

Ed Walters
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« Reply #12 on: September 13, 2019, 05:19:31 PM »

I don't know much about HVAC systems but is it possible that the compressor unit fan is running at 120V on L2 and N while the compressor itself is at 240 on L1 and L2?
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« Reply #13 on: Today at 02:39:21 AM »

Could be but I think not, having seen it a year ago and had to fix it  - best I can recall..
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« Reply #14 on: Today at 10:03:17 AM »

the imbalance of L1 / L2 currents is forcing the 5A of neutral current .... I would look at reassigning some breakers for your 120 V loads to better balance them .... most load centers alternate between L1 / L2 as you go up in panel number ...this shud improve panel efficiency
So, is this a matter of cost efficiency (higher electric bill) or a matter of equalizing current in the breaker box for cooling, creepage, etc?

a good question .... sorry took this long to answer .... I don't know if the electric bill would change very much because you would need to model these imbalances and then simulate them and take data .... the effect of power factor changes would need to go into the mix as well .... it would be interesting to take a center tapped fil xfmr and simulate this situation with secondary load imbalances while measuring power consumed ....intuitively I would think not too much as long as specific ratings of the system were not exceeded .....

 
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O would some power the gift give us
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It would from many blunders free us.         Robert Burns
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