Best way to find AC power usage and battery draw?

[tacomaguy20]

So I'm designing my solar system and I have a 4 ton Carrier Split Heat Pump AC unit that was installed in 2005 and I can't figure out how much power it draws because all of the labeling has faded on the condenser. I reached out to Carrier and am waiting to see if they contact me with the details, I've searched the internet and come up empty. I'm trying to determine how much power it draws so I can determine what I need for batteries. Ideally, I'd like enough power to run the AC unit for at least 6 hours a day. Any easy way to determine this? Someone suggested that I purchase the emporia vue for the electrical panel. I do have a smart meter and my power company does tell me the usage per hour or I can read the difference in values on the meter I'm pretty sure. What would you suggest? I understand there is a large power draw immediately when turned on so I'm not sure that's something the smart meter would tell me. Suggestions?

 

[sunshine_eggo]

So I'm designing my solar system and I have a 4 ton Carrier Split Heat Pump AC unit that was installed in 2005 and I can't figure out how much power it draws because all of the labeling has faded on the condenser. I reached out to Carrier and am waiting to see if they contact me with the details, I've searched the internet and come up empty. I'm trying to determine how much power it draws so I can determine what I need for batteries. Ideally, I'd like enough power to run the AC unit for at least 6 hours a day. Any easy way to determine this? Someone suggested that I purchase the emporia vue for the electrical panel. I do have a smart meter and my power company does tell me the usage per hour or I can read the difference in values on the meter I'm pretty sure. What would you suggest? I understand there is a large power draw immediately when turned on so I'm not sure that's something the smart meter would tell me. Suggestions?

Get an AC clamp ammeter with an INRUSH function. Put it around either L1 or L2 to the A/C unit.

The INRUSH will capture the surge.

Normal mode will give you the run current.

Given the brutal surge of compressors, you'll likely need to install a micro-air soft starter, or you'll need a massive inverter to start it.

In the complete absence of spec or measured values, assuming a 12 SEER unit given the install date:

48,000BTU/hr / 12 SEER = 4000W run power with a 5X surge or 20,000W.

 

[Skypower]

Replace the run capacitor while you’re at it. They are cheap and it’s about time. The micro-air soft start has a built in anti short cycle that prevents the condenser from restarting too soon. Nest thermostats are too short so this is a good feature if you have one. Do install a “delay on make” timer and set it to 6 to 10 seconds. That will allow the blower to start first then the condenser. Spooling up that blower separately will reduce the whole house inrush by as much as 15 amps. It all adds up.

 

[tacomaguy20]

Thanks for your help. I went and looked at the label again and I was barely able to make out the model number which lead me to the manual. I found what I need I think. It's 48,000 BTUs and it's between 12 and 13 seer... not sure which indoor section I have in the attic which is why I'm not entirely sure but here are some of the other specs I found. It looks like in the summer (when it gets 115), it may draw as much as 5700 watts. Am I reading this right? Does any of this tell me what the surge numbers would be? Also, I just replaced the run capacitor on the recommendation of my AC guy the last time he was out a couple months ago.

 

[sunshine_eggo]

Yep. The LRA is your max potential surge... about 6X the run - 31kW.

 

[tacomaguy20]

That surge seems pretty high. So if I take your advice and install a soft starter, what kind of reduction would that bring me down to would you imagine? I was considering one of the All in one hybrid systems, like Sol-ark or EG4's new one, but looking up the specs, it looks like that's outside of the limits of the inverter capacity? Am I reading those spec sheets right? My system would be grid tied so does that matter in terms of surge?

 

[robby]

Practical Preppers has one that claims to reduce it by 75%.
In his videos he states that it works very well and he demonstrates the difference in start current before and after.
Soft start 6Hp

 

[tacomaguy20]

Hey guys, question for you about this. My power company uses demand charges for solar customers and they have a pilot program for non solar customers. I'm not on that plan yet but they've been tracking my demand in case I want to switch to that plan. The highest Kw draw in a half hour period is what I would be charged for the month. When I asked them what my highest draw was, they told me it was 10kw. It was likely a day when I ran my stove, AC, and washer/dryer at the same time I guess. All other months it was lower, some as low as 2.5Kw. But what I don't understand is if the surge of my AC unit is 31kw, why wouldn't that be my highest demand charge? Do you think they don't factor in surge charges?

 

[sunshine_eggo]

Are you sure it's not the highest 30 minute period for the year? I swear that was the case at one point. That's why my 70% system only reduced my bill by 30% because the demand charge was so high. I have a 5 ton unit, and our average is about 75kWh. Peak summer has been as high as 120kWh/day.

Anyway, surges aren't factored in because they are very brief. Wires, fuses and breakers don't factor surge in either because they are such a short duration. They become an issue when you have to supply the surge with an inverter.

To answer your earlier question, if grid tied, then surge isn't a concern, but if you had an off-grid inverter powering your house with the grid on the input as backup power, then the surge would be a factor.

 

[tacomaguy20]

Are you sure it's not the highest 30 minute period for the year? I swear that was the case at one point. That's why my 70% system only reduced my bill by 30% because the demand charge was so high. I have a 5 ton unit, and our average is about 75kWh. Peak summer has been as high as 120kWh/day.

Anyway, surges aren't factored in because they are very brief. Wires, fuses and breakers don't factor surge in either because they are such a short duration. They become an issue when you have to supply the surge with an inverter.

To answer your earlier question, if grid tied, then surge isn't a concern, but if you had an off-grid inverter powering your house with the grid on the input as backup power, then the surge would be a factor.

Okay, thanks for the surge information. I'm not sure if they've changed the plans recently but there are two demand plans. On one it's the highest kw usage in a 30 minute period of peak demand over the course of the month. The other one is an average of your daily on-peak maximum demand for the billing month. Nowhere does it say yearly and I've spoken to them at least 3 times to confirm. They also have the time of use plan with no demand charges but it's higher cost both off peak and on peak and you're limited to 2.81 cents export. The demand plans are 1:1 export but the demand fees will get you during on peak hours. That's why I'm trying to figure out a system where I only use power off peak and use my own batteries/solar generation on peak. I'm, testing right now to see if cooling my house early in the morning will keep it cool enough from 2pm to 8pm that I can leave my AC off during peak hours. I left my ac off between 2pm and 8pm yesterday and only used 3.2kwh over the course of 6 hours. My highest demand being .8kwh over the course of an hour, I imagine in 1/2 hour increments, that demand will be less. Summer and peak summer months are the most important because the demand charges are so high and winter demand is almost negligible. So I've decided I'm switching over to the pilot program for demand charges (I want to test it out) and I don't even have solar yet, but if I can leave my AC off from 2pm to 8pm, I estimate that I'll save about a 1000 dollars a year without solar. With solar, I'm sure that I would save quite a bit more, maybe eliminate my bill entirely (with enough panels of course). You should look the plans up again and see if they work for you now.

 

[Todd Brittingham]

Hi, I have a similar question. I have a 3-ton AC unit on my home and I am installing two EG4 6500EX-48's in split phase. I found on my AC unit the attached label. Reading this, the LRA is 100, which would equate to 24kW surge potential? Looking at the specs on the inverter it shows 13kW surge protection for up to 5s per inverter...this should give me 26kW of surge capability??? So I should be good, but that's a bit close, so to me it would make sense to just install the soft-start box and sleep well at night.

If anyone could help confirm all this, that would be great!

 

[RCinFLA]

LRA is spec'd at minimum AC voltage. It is done this way for wiring/branch breaker sizing. Usually, startup surge current is a bit greater than spec plate LRA. It also depends on wiring voltage drop to compressor. More wiring voltage drop reduces surge current but lengthens the startup time.

If you want to reduce compressor startup surge current you need a start capacitor boost/soft starter like a MicroAir Easystart. They will achieve a 65% to 70% reduction in startup surge current.

During the startup surge, the compressor motor is a highly inductive load. This is a double whammy for high frequency inverters due to the large amount of inductive reactance load. Power factor during startup surge is about 0.3 to 0.5.

Most HF inverters are limited to a load power factor of about 0.8. Their HV DC regulation can go unstable below this power factor at close to their rated current.

 

[Shimmy]

Hey guys, question for you about this. My power company uses demand charges for solar customers and they have a pilot program for non solar customers. I'm not on that plan yet but they've been tracking my demand in case I want to switch to that plan. The highest Kw draw in a half hour period is what I would be charged for the month. When I asked them what my highest draw was, they told me it was 10kw. It was likely a day when I ran my stove, AC, and washer/dryer at the same time I guess. All other months it was lower, some as low as 2.5Kw. But what I don't understand is if the surge of my AC unit is 31kw, why wouldn't that be my highest demand charge? Do you think they don't factor in surge charges?

I would recommend an IoTaWatt or similar for permanent metering if you are considering a demand-based rate plan. It might also be time to consider replacing your A/C or thinking about how you use it. A mini-split or two and a down-sized central unit is going to be more solar-friendly.

 

[dcg9381]

It's probably not the <1 second surge that they are going to measure.. It's likely highest draw for <seconds - 1 minute> or so. emporia vue is what I use.

 

[phx]

Reading this thread, I believe the topic starter is in Phoenix, and the utility company is SRP. The prices and demand-related problems are very familiar with the E27 SRP Solar plan. So, welcome to the club.

Here is my own thread, discussing a very similar problem with a detailed analysis:

Mitigation of demand from utility with solar

Hi. I'm from Phoenix, AZ with 12.96kW grid-tied system up and running. It has 5 strings of panels and two SMA grid-tied inverters working in parallel. They are AC coupled before solar meter. It's a standard design recommended by SRP (utility company) published on their Web-site I'm on "Customer...

diysolarforum.com

Hope it can help.

I have a 16kW Solar on my roof (grid-tied, no batteries), and my 5 Ton A/C is responsible for 2/3 of all my demand fees during peak times. However, my demand is capped at 5.5 kW just by manipulating the A/C compressor with a DIY "Smart Demand" solution, described here:

TOU Calculations in Phoenix

Would these panels be ok for roof mount?

diysolarforum.com

It was a lot of discussions, suggesting to switch the house loads from the grid to batteries+inverter during peak times in order to completely eliminate demand charges. However, that solution would be very expensive, as I need at least 20 kWh of energy stored in the battery to cover 5-8pm consumption (please see the screenshots below) and a very large (32 kW) battery inverter capable of giving 130 Amps LRA to my A/C unit.

The "Easy Start Soft Starter" device, suggested here, looks very promising if it can bring my LRA below 80 Amps. In such a case a 10 kW inverter (20 kW peak) for ~$400 could meet the needs of the A/C.

So, instead of the entire house, I'm thinking of hooking up just the A/C unit via a relay (transfer switch) allowing it to be switched between the grid (off-peak or on-peak with enough solar power) AND inverter (no solar energy or its production is insufficient).

I believe that could bring my demand level from 5.5 kW down to under 3 kW around the year, which is pretty cheap with the SRP E27 price plan.

The A/C unit running almost 24/7 during July-August takes 5-6 kW/hr. So, in order to offset 3 hours of its usage to "Off-peak" hours, I need a 15 kW battery and a 10 kW (20 kW peak) 240V inverter.

Does this look feasible? Any pros and cons?

 

[Skypower]

I have to supplement from from the grid this time of year because I don’t have room for adding more panels economically. I only charge during off peak hours. The tiny amount shown during peak is the power that the system needs to operate, not actual demand. Most of the time when the air conditioning is running it’s on battery and solar. Lifepo4 is efficient round trip so not much is wasted and the capacity used is so small the that is not degrading to the battery. Calendar aging will be the issue well before cycle count so why not use it. Not going to pay any more than I need to. As you can see it saves a boat load. I could probably save a lot more money if I turn up the thermostat from 73 but I just don’t want to deal with the flack and complaints.

 

[schmism]

The A/C unit running almost 24/7 during July-August takes 5-6 kW/hr. So, in order to offset 3 hours of its usage to "Off-peak" hours, I need a 15 kW battery and a 10 kW (20 kW peak) 240V inverter.

Does this look feasible? Any pros and cons?

Solark 15K inverter and 3x eg4 batts should cover it.

only $12,000 with no PV!

or $250/mo peak charges for 4 months a year ... 12 years of peak charges!