2xPowerwall whole house backup - HVAC sure start problem

[af88]

Reality bites, this is why relying on specs and speculation doesn't mean anything. Having gone through this process I have a little more know how. I've spend a lot of time on the phone with Tesla engineering and installers engineering sorting out all the issues and options. Frankly it does not surprise me anything I hear when it comes to HVAC and PW. Your hope is that this advertised Tesla energy cap increase will solve your problem. As you can see right now it does not.

The reason it starts is b/c the solar is offsetting what the PW can't support with its ~58-9A cap that is why. It is also why I made the statement I made earlier about having solar in the loop or not to avoid causing confusion. The PV output and day and conditions all make a difference, if your reliance is on solar than you have not designed the system properly as it should work without it if that was your requirement.

In regards to the wiring the HVAC has a longer pull up than PW so it will trip the breaker. Can't compare apples to oranges

---------------- I'm going to repeat this again for others:

Bottom line, if you have an AC requirement, and are being told by the installer it works fine with just 2 PW, you are rolling the dice, be prepared to purchase a 3rd PW.

Lastly you should do your own math and due diligence, the PW is rated at 30A each but realistically it only provides about 28.5-29.5A for inrush startup, assuming you have absolutely no other load (lights, fridge, etc..) which is unrealistic, keep these factors in mind when calculating startup amperage needed without AC before making assumptions how well the soft starter will work and aggregate amperage and what 2 PW will support.

 

[RKCRLR]

Reality bites, this is why relying on specs and speculation doesn't mean anything. Having gone through this process I have a little more know how. I've spend a lot of time on the phone with Tesla engineering and installers engineering sorting out all the issues and options. Frankly it does not surprise me anything I hear when it comes to HVAC and PW. Your hope is that this advertised Tesla energy cap increase will solve your problem. As you can see right now it does not.

I'm not sure what you mean about the increased LRA rating not working but my Powerwalls are too old for the firmware upgrade (or so I've been told). Tesla proposed using the load shedding terminals using the terminals on the Gateway to keep my compressor from running during an outage. This would prevent me from operating my AC in limp mode like I can now during an outage. However, they wanted to splice into wire between the thermostat and the outside unit. But my thermostat wire doesn't go to the outside unit. It is a Carrier proprietary communicating thermostat that uses data A and data B signals to communicate with the inside unit and then the inside unit uses data signals to communicate with the outside unit. I wanted them to explain exactly how they were going to incorporate load shedding but they pretty much wanted to come out and wing it. After my experience with the last technician leaving with the AC not working, telling me something must be wrong with my AC unit and to call a HVAC repair place, and me having to rewire the system myself per the schematic to get it working again; I'm not going to let them come out without a plan.

What frustrates me is my system has a utility curtailment feature that allows for load shedding. I could then manually control whether or not the compressor runs and at what stage from the wall unit. Tesla would just have to connect to the Gateway load shedding terminals to the utility curtailment terminals of my system. But tesla refuses to incorporate that into a plan.

In regards to the wiring the HVAC has a longer pull up than PW so it will trip the breaker. Can't compare apples to oranges

I disagree that this is apples and oranges. Just like it is acceptable for my HVAC unit to draw more than the 50 amp breaker limit during compressor startup, it would be acceptable to have a Powerwall provide more than 30 amps through a 30 amp breaker during a transient situation. We just don't know how much more and for how long.

 

[af88]

Wong again, the data is known and easy to measure if you have the proper instrumentation which I have tested and passed the data along to Tesla Engineering and others. I also spend quite a bit time talking to Daniel and Hyperenginering and the developers at Micro about improvement their product to work more seamlessly with Tesla PW.

Again I tried to help you and all you want to do is argue. Your problem is actually relatively easy to fix to with your HVAC issue and not as complicated as you think. You made assumptions about my system and falsely claim 2 PW can work when you have no data to back it up. Lets not mention the code mess that can occur if Tesla pushes a FW update to increases energy cap without installers being made aware like most as is now including Tesla who continue to install using legacy wiring specs.

What frustrates me is people like you who read a spec and spread false information. I'm done trying to help you and I will not be responding to your nonsense any more.


For Others who are considering a PW and HVAC: I'm going to repeat this again from someone who has a lot of experiencing and real world data.

Bottom line, if you have an AC requirement, and are being told by the installer it works fine with just 2 PW, you are rolling the dice, be prepared to purchase a 3rd PW.

Lastly you should do your own math and due diligence, the PW is rated at 30A each but realistically it only provides about 28.5-29.5A for inrush startup, assuming you have absolutely no other load (lights, fridge, etc..) which is unrealistic, keep these factors in mind when calculating startup amperage needed without AC before making assumptions how well the soft starter will work and aggregate amperage and what 2 PW will support.

 

[RobertLParker]

MicroAir EasyStart, works well, actually much better than surestart unit but also costs more.

I'm going to repeat this again for others:

Bottom line, if you have an AC requirement, and are being told by the installer it works fine with just 2 PW, you are rolling the dice, be prepared to purchase a 3rd PW.
Lastly you should do your own math and due diligence, the PW is rated at 30A each but realistically it only provides about 28.5-29.5A for inrush startup, assuming you have absolutely no other load (lights, fridge, etc..) which is unrealistic, keep these factors in mind when calculating startup amperage needed without AC before making assumptions how well the soft starter will work and aggregate amperage and what 2 PW will support.

Hi af88,

I had my surestart stop functioning last summer on a very hot day and bypassed it to the ac working perfectly. Tesla was extremely unhelpful and hyperengineering had me rewire it to a 4 wire setup and it worked better but still the compressor would occasionally not fire. This summer on the first hot day I had to bypass it again. So now I’m in the sticky situation of having no soft start on my ac with my 2x powerwall setup.

My lra is only 78 on my 3 ton ac. I’m thinking about taking a shot on the micro air easy start device. Have you found it to be still more reliable than the sure start? My other option is to move the ac back to the main panel and off the powerwall. I did also see in the powerwall installation manual that a 24v load shed device can be hooked up directly to the gateway. Maybe that would be a better solution than moving the breaker back. Thanks for any feedback.

 

[nwdiver]

Hi af88,

I had my surestart stop functioning last summer on a very hot day and bypassed it to the ac working perfectly. Tesla was extremely unhelpful and hyperengineering had me rewire it to a 4 wire setup and it worked better but still the compressor would occasionally not fire. This summer on the first hot day I had to bypass it again. So now I’m in the sticky situation of having no soft start on my ac with my 2x powerwall setup.

My lra is only 78 on my 3 ton ac. I’m thinking about taking a shot on the micro air easy start device. Have you found it to be still more reliable than the sure start? My other option is to move the ac back to the main panel and off the powerwall. I did also see in the powerwall installation manual that a 24v load shed device can be hooked up directly to the gateway. Maybe that would be a better solution than moving the breaker back. Thanks for any feedback.

Depending on how old your AC is it may be worth investing in the new unit. A truly variable speed compressor (not just staged) completely eliminates any starting issues.

 

[RobertLParker]

Depending on how old your AC is it may be worth investing in the new unit. A truly variable speed compressor (not just staged) completely eliminates any starting issues.

It’s only 6 years old, builder model carrier on a new build house.

 

[af88]

Don't bother your compressor is fine. I bought a 3rd PW and I'm also on easy start with no issues.

 

[cali8484]

Has anyone done or know of a cost/benefit analysis of adding a 3rd PW with conventional central A/C vs converting to variable speed compressor A/C or heat pump?

 

[dcoakley]

I’m also looking at adding a 3rd power wall and my lowest bid so far is 18.5k, highest is 22k. One company is adamant I need two gateways and have not even looked at my system.

Regarding soft starts all 3 hvacs have them and so far all start when I go off the grid. Note I only start and stop one at a time. I’ve learned just from reading threads and blogs soft starts are far from reliable and power walls have their limits.

 

[sunwarriors]

Depending on how old your AC is it may be worth investing in the new unit. A truly variable speed compressor (not just staged) completely eliminates any starting issues.

Can you/anyone share a link to a truly variable speed compressor AC? We will probably have to replace out AC in a bit/soon and might as well start the research. Thank you.

 

[RKCRLR]

Can you/anyone share a link to a truly variable speed compressor AC? We will probably have to replace out AC in a bit/soon and might as well start the research. Thank you.

This one is truly variable speed:

Infinity® 26 A/C With Greenspeed® Intelligence | 24VNA6

24VNA6

www.carrier.com

However, they are top of the line and expensive.

I just installed the heat pump version of this one:

Infinity® 19VS Central A/C Unit | Carrier Residential

The Infinity 19VS central air conditioner unit (24VNA9) offers 5 stage, variable-speed compression which provides quieter operation, optimal dehumidification and efficiency.

www.carrier.com

It only has 5 set stages but is an inverter type. The compressors are the same in both units but the controls only allow for 5 steps instead of many very fine steps. I believe the start current draw is about the same for both of them.

I'm not enamored with Carrier. They are more expensive because of their name and they use their proprietary communications protocol so you either have to get another Carrier product if something goes bad or replace the whole system. And there are fewer Carrier dealers around than other dealers (there was only one that would service my system).

The Bryant unit system is less money and is the exact same as the Carrier unit with different badges:

two stage air conditioners - air conditioners | Bryant

Learn more about the 189BNV two-stage central air conditioning unit from Bryant.

www.bryant.com

The other brands have similar units. If you are concerned about current draw during starting the important thing is that they are an inverter type compressor.

 

[holeydonut]

I agree with @RKCRLR … I didn’t know enough about hvac and screwed myself with 2x two stage Lennox systems. I couldn’t afford a full electric overhaul, but I could have had Bryant variable speed for the same money as my less efficient Lennox spec.

 

[daniel]

Has anyone done or know of a cost/benefit analysis of adding a 3rd PW with conventional central A/C vs converting to variable speed compressor A/C or heat pump?

I considered getting a third Powerwall, but it just didn't seem worth it to me. A/C here is a convenience and a comfort but not a life-or-death necessity.

However, now that my old A/C died and I didn't want to be entirely without it, I'm having a true soft-start A/C system installed. This is costing me a lot more than a third Powerwall would have cost, but the differential between the cost of this new unit and a straight replacement of the old unit is far less than another Powerwall would have cost.

 

[nwdiver]

If you are concerned about current draw during starting the important thing is that they are an inverter type compressor.

Yep. I run my house off-grid a lot. I'm always amazed at how I can notice my fridge cycling but not my HVAC. Really kinda want an inverter driving fridge now too...

 

[holeydonut]

Yep. I run my house off-grid a lot. I'm always amazed at how I can notice my fridge cycling but not my HVAC. Really kinda want an inverter driving fridge now too...

Is there a list of inverter home fridges?

I don’t think Miele, Thermador, or True make inverter compressor units?

 

[sunwarriors]

This one is truly variable speed:

Infinity® 26 A/C With Greenspeed® Intelligence | 24VNA6

24VNA6

www.carrier.com

However, they are top of the line and expensive.

I just installed the heat pump version of this one:

Infinity® 19VS Central A/C Unit | Carrier Residential

The Infinity 19VS central air conditioner unit (24VNA9) offers 5 stage, variable-speed compression which provides quieter operation, optimal dehumidification and efficiency.

www.carrier.com

It only has 5 set stages but is an inverter type. The compressors are the same in both units but the controls only allow for 5 steps instead of many very fine steps. I believe the start current draw is about the same for both of them.

I'm not enamored with Carrier. They are more expensive because of their name and they use their proprietary communications protocol so you either have to get another Carrier product if something goes bad or replace the whole system. And there are fewer Carrier dealers around than other dealers (there was only one that would service my system).

The Bryant unit system is less money and is the exact same as the Carrier unit with different badges:

two stage air conditioners - air conditioners | Bryant

Learn more about the 189BNV two-stage central air conditioning unit from Bryant.

www.bryant.com

The other brands have similar units. If you are concerned about current draw during starting the important thing is that they are an inverter type compressor.

Many thanks for this...Is this the same as that carrier one, but the Bryant version? Our current AC is single stage only and I assume, probably has less than 5 years on it. Would be nice with lower power draw since I notice the A/C drains our batteries real quick right now when we have no sun out.

EVOLUTION™ EXTREME 26 VARIABLE-SPEED AIR CONDITIONER, 186CNV

186CNV

186CNV

www.bryant.com

 

[wwu123]

Is there a list of inverter home fridges?

I don’t think Miele, Thermador, or True make inverter compressor units?

Pretty sure my Liebherr fridge is a dual variable-speed (aka inverter) compressor unit, based on the twin humps I see in my baseload at night. Also there are similar OEM models from other brands that are made in the same factory, and like with the same guts, though not all advertise inverter or variable speed - Thermador Freedom, Miele, Bosch, Dacor, Fisher & Paykel. Doesn't mean every fridge in these brands' line-ups are inverter units though. Jenn-Air is also said to have used inverter compressors for a long time.

US Appliance seems to have a search category for inverter refrigerators, which gives a partial (likely incomplete) list. On the non-built-in end of the price range, it seems there are a number of LG models that have inverter compressors:
Inverter Refrigerator at US Appliance

 

[RKCRLR]

Many thanks for this...Is this the same as that carrier one, but the Bryant version? Our current AC is single stage only and I assume, probably has less than 5 years on it. Would be nice with lower power draw since I notice the A/C drains our batteries real quick right now when we have no sun out.

EVOLUTION™ EXTREME 26 VARIABLE-SPEED AIR CONDITIONER, 186CNV

186CNV

186CNV

www.bryant.com

I think they are the same. Definitely compare the price difference between the ones they call "truly" variable and the 5 speed units. My understanding is the compressors are the same (Toshiba?) and the difference is in the complexity of the electronics that control the compressor. The 5 speed units have a good reliability history so far.

Also look into American Standard (same as Trane) variable speed units.

 

[holeydonut]

Has anyone done or know of a cost/benefit analysis of adding a 3rd PW with conventional central A/C vs converting to variable speed compressor A/C or heat pump?

Specific to AC... here's an example of a 3 ton Lennox Signature system (3 ton Lennox evaporator, generic coil, and Lennox air handler).

With an XC21 (dual stage condensing unit), the AHRI measures 18 SEER.
With an XC25 (variable speed condensing unit), the AHRI measures 22 SEER.

Assuming a run time of 2,000 hours of cooling per year, this calculator estimates per year savings of 727 kWh. So you can take that times whatever you think your electricity costs to get at today's annual savings.

Going from NG furnace heating to wintertime heat pump heating is a tougher conversion. I don't know a good way to estimate that. But with NG costs going through the roof the heat pump + solar seems like a good idea if your family and budget are ok with it.

For Reference, here are the AHRI certificates for the above SEER...

Lennox XC21-036 is a 3 ton unit. SL280*V36 is a 3 ton air handler. ADP 18/36 is a 3 ton coil. 18 SEER

Lennox XC25-036 is a 3 ton unit. SL280*V36 is a 3 ton air handler. ADP 18/36 is a 3 ton coil. 22 SEER

 

[RKCRLR]

Specific to AC... here's an example of a 3 ton Lennox Signature system (3 ton Lennox evaporator, generic coil, and Lennox air handler).

With an XC21 (dual stage condensing unit), the AHRI measures 18 SEER.
With an XC25 (variable speed condensing unit), the AHRI measures 22 SEER.

Assuming a run time of 2,000 hours of cooling per year, this calculator estimates per year savings of 727 kWh. So you can take that times whatever you think your electricity costs to get at today's annual savings.

Going from NG furnace heating to wintertime heat pump heating is a tougher conversion. I don't know a good way to estimate that. But with NG costs going through the roof the heat pump + solar seems like a good idea if your family and budget are ok with it.

For Reference, here are the AHRI certificates for the above SEER...

Lennox XC21-036 is a 3 ton unit. SL280*V36 is a 3 ton air handler. ADP 18/36 is a 3 ton coil. 18 SEER
View attachment 823663

Lennox XC25-036 is a 3 ton unit. SL280*V36 is a 3 ton air handler. ADP 18/36 is a 3 ton coil. 22 SEER
View attachment 823664

That was one of the things that frustrated the HVAC sales guys. They were always trying to up-sale me to split mini systems touting that I'd save money.
I'm a a net producer so every kW that I'd save by getting a more efficient system only saves me ~$0.04. I told them that and asked them to run the numbers for me. They never did.