A/C replacement advice

[nicholb]

I have on order a 8.4kW solar roof with 2 Powerwalls which will hopefully be installed next spring. I also have a ~20 year old central A/C unit that is on its last leg. I'll be replacing it this coming spring. I want to make sure whatever A/C unit I install will be able to run off solar or PW in case of grid outage.

Does anyone have info on what I should look for on the new AC to make sure it is compatible with Solar/PW?

 

[wwhitney]

You want an inverter driven compressor. That means that the starting current will be no more than the operating current, which will make it much easier to run off Powerwalls.

Also, a couple things to be aware of: you want an HVAC company that will do a proper Manual J heat gain computation and not oversize your system (oversizing is rife in the HVAC industry, although an inverter driven system usually modulates quite low, which would mitigate oversizing, perhaps at the cost of some efficiency). It's also worth considering at this point whether additional insulation or air sealing is feasible and would reduce your heat gain, thereby reducing your required equipment size.

Cheers, Wayne

 

[dhquigley]

Be sure to review the a/c discussion on the following page. Very useful. What Does Powerwall Back Up | Tesla Support. I replaced my a/c right before the install, but my house is single zone with a large (5-ton) a/c. I went scroll compressor but because of the size my LRA was up over 139, so needed the third powerwall. That page walks you through everything you need though. When Tesla arrived, they simply put a sure start in the compressor and everything works fine.

 

[wjgjr]

Be sure to review the a/c discussion on the following page. Very useful. What Does Powerwall Back Up | Tesla Support. I replaced my a/c right before the install, but my house is single zone with a large (5-ton) a/c. I went scroll compressor but because of the size my LRA was up over 139, so needed the third powerwall. That page walks you through everything you need though. When Tesla arrived, they simply put a sure start in the compressor and everything works fine.

Interesting that their website suggests you need 3+ PWs for an electric dryer. Tesla never mentioned that as a concern for us, and I don't see it as being a real issue. (Like with pretty much any PW install, in an outage, we wouldn't want to run all our electrical appliances, including A/C, stove/oven, dryer, and microwave, at once, but we can certainly run any one of them with plenty of capacity to spare, even with no solar production - though it would obviously drain the batteries.)

For OP, it is a good reference for A/C info, but I would agree with the prior advice (inverter driven compressor) to look at a variable speed unit that falls into Tesla's first category of devices where you don't have to worry about the LRA number and don't need Tesla to install a soft/sure start device. We have had no issues with our sure start device so far, but if I were to buy a new A/C, I would lean towards one that doesn't need an external device which is an additional point of failure and possibly an issue with any warranty claims.

 

[BrettS]

Interesting that their website suggests you need 3+ PWs for an electric dryer. Tesla never mentioned that as a concern for us, and I don't see it as being a real issue.

Yeah, that is very odd. Especially since my range (which is listed as working with two powerwalls) is on a 40A circuit and my dryer is on a 30A circuit.

 

[holeydonut]

You want an inverter driven compressor. That means that the starting current will be no more than the operating current, which will make it much easier to run off Powerwalls.

Also, a couple things to be aware of: you want an HVAC company that will do a proper Manual J heat gain computation and not oversize your system (oversizing is rife in the HVAC industry, although an inverter driven system usually modulates quite low, which would mitigate oversizing, perhaps at the cost of some efficiency). It's also worth considering at this point whether additional insulation or air sealing is feasible and would reduce your heat gain, thereby reducing your required equipment size.

Cheers, Wayne

What you actually want someone come out and do "maths" for HVAC? My installer (yes, I'm joking) just used this template.

Personally, I think the safest approach is if a 2.5 ton unit results in your wife complaining it's too cold in the winter and too hot in the summer, then you upsize the replacement.

Joking aside, you can get a soft start (sometimes branded a Secure Start or Safe Start) installed on your AC unit to reduce the locked rotor amp current draw on "normal" copeland style compressors. This means you can use 2x Powerwalls to power an AC unit without over-loading the Powerwalls when the compressors start up. So, you don't necessarily have to get a variable speed compressor.

But DO NOT GET A LENNOX SYSTEM. If you go Lennox, they won't let you add the soft start on the non-inverter driven compressor unit without voiding the new product warranty. Plus Lennox Industries (HQ) treat their end-purchase customers like crap unless they threaten them with legal action. Dealing with Lennox is a headache I wouldn't wish on anybody.

I agree with Wayne that the absolute best outdoor air conditioner unit will be a variable speed with an inverter driven compressor. But keep in mind these are outrageously expensive compared to a single or dual stage unit. For example, the Lennox XC25 Signature with variable speed (inverter driven) compressor was quoted to me (3 ton unit) as $5k more expensive than the Signature XC21 dual stage unit.

PS, if your area isn't very humid, for your AC system I suggest you upsize your evaporator coil slightly larger than your outdoor condenser tonnage. For example, if you put in a 3.0 ton condenser unit; get a 3.5 to 4 ton evaporator coil. This larger coil results in a higher surface area to cool the air and you'll see a bit better SEER and energy efficiency. The trade-off is that the coil will be worse at removing humidity from the air, which means your home will be more humid. I'm in NorCal so that's not an issue (hence why the state is always on fire and our electricity is always being shut down). I also don't know if this evaporator step-up approach works on heat pump systems.

 

[wjgjr]

But DO NOT GET A LENNOX SYSTEM. If you go Lennox, they won't let you add the soft start on the non-inverter driven compressor unit without voiding the new product warranty. Plus Lennox Industries (HQ) treat their end-purchase customers like crap unless they threaten them with legal action. Dealing with Lennox is a headache I wouldn't wish on anybody.

As somebody who has a Lennox, I can't speak to the part about dealing with them, but I am not clear that their position on adding a soft/sure start is any different from other manufacturers (unless you find one that will install its own brand.) As a general matter, installing a soft/sure start does not void the warranty, but it does add another component to the mix that potentially complicates a warranty claim. Lennox (or another company) cannot legally void the warranty because of the existence of the soft/sure start device, but they can deny a claim if they feel the device is what caused the issue. (This is similar to fights car companies and consumers have had over "unauthorized" repairs/modifications, as an example.)

The personal gripe I have with Lennox is their smart thermostat product that I have did not support IFTTT or a SmartThings integration. Though I just looked and they have a banner announcing IFTTT support, so maybe some good news finally.

 

[holeydonut]

As somebody who has a Lennox, I can't speak to the part about dealing with them, but I am not clear that their position on adding a soft/sure start is any different from other manufacturers (unless you find one that will install its own brand.) As a general matter, installing a soft/sure start does not void the warranty, but it does add another component to the mix that potentially complicates a warranty claim. Lennox (or another company) cannot legally void the warranty because of the existence of the soft/sure start device, but they can deny a claim if they feel the device is what caused the issue. (This is similar to fights car companies and consumers have had over "unauthorized" repairs/modifications, as an example.)

The personal gripe I have with Lennox is their smart thermostat product that I have did not support IFTTT or a SmartThings integration. Though I just looked and they have a banner announcing IFTTT support, so maybe some good news finally.

I posted this in a different thread about soft starts:
Day 1 of install of 14.28kW system with 4 Powerwalls

While I agree with you that what you say is "legally" accurate - my point is that Lennox makes things a legal battle when it ought to be more straightforward than that. I dislike "legal" as a fall back argument since legal by definition is the worst/lowest standard to operate. If you want to feel good about a purchase, you must expect to operate above a low legal bar. My neighbor has Carrier units and he said Carrier gladly referred him to the parts that he'd need to add soft start benefit to his compressors.

Carrier = Good. Lennox = Sh!t

Lennox who literally lists a soft start on their own website, then proceed to tell me using this part would void my warranty. They say this because an authorized Lennox technician would need to do the installation, and a authorized tech is not allowed to install this soft start on an XC21.
Emerson 543-0120-00 Soft Start, 200/230V

If I had a soft start installed, Lennox asserted this would be proof that an unauthorized tech worked on my ACs. And their position is that work voids the entire warranty since they wouldn't know what the unauthorized tech did or didn't do. I'm sure I could go into a legal battle; but who wants or is able to afford that against a publicly traded corporation?

 

[wjgjr]

I posted this in a different thread about soft starts:
Day 1 of install of 14.28kW system with 4 Powerwalls

While I agree with you that what you say is "legally" accurate - my point is that Lennox makes things a legal battle when it ought to be more straightforward than that. I dislike "legal" as a fall back argument since legal by definition is the worst/lowest standard to operate. If you want to feel good about a purchase, you must expect to operate above a low legal bar. My neighbor has Carrier units and he said Carrier gladly referred him to the parts that he'd need to add soft start benefit to his compressors.

Carrier = Good. Lennox = Sh!t

Lennox who literally lists a soft start on their own website, then proceed to tell me using this part would void my warranty. They say this because an authorized Lennox technician would need to do the installation, and a authorized tech is not allowed to install this soft start on an XC21.
Emerson 543-0120-00 Soft Start, 200/230V

If I had a soft start installed, Lennox asserted this would be proof that an unauthorized tech worked on my ACs. And their position is that work voids the entire warranty since they wouldn't know what the unauthorized tech did or didn't do. I'm sure I could go into a legal battle; but who wants or is able to afford that against a publicly traded corporation?

I agree with what you are saying as to falling back on legalities and guess I would mostly add that I hope the story you are sharing is the exception (as it pertains to Lennox) rather than the rule. As with most support requests, it seems like the luck of the draw, and once an employee makes a decision - good or bad - it seems like it is really hard to change minds. We see this with Tesla energy from the many posts here. And if you can find an A/C company that will install everything you need without relying on third parties, that is absolutely a bonus. At the end of the day, though, whatever support/customer service tells you is not going to be binding as to what the actual warranty will or won't cover, and it is not until you actually need to make a claim that you will know how easy they are to deal with.

(And all of this is not really to defend Lennox... I can't say I'm upset with what I got for the price, but I'm not going to run arround recommending them either.)

 

[CrazyRabbit]

The car manufacturers lost this argument, it might have been because of a law.

 

[holeydonut]

I agree with what you are saying as to falling back on legalities and guess I would mostly add that I hope the story you are sharing is the exception (as it pertains to Lennox) rather than the rule. As with most support requests, it seems like the luck of the draw, and once an employee makes a decision - good or bad - it seems like it is really hard to change minds. We see this with Tesla energy from the many posts here. And if you can find an A/C company that will install everything you need without relying on third parties, that is absolutely a bonus. At the end of the day, though, whatever support/customer service tells you is not going to be binding as to what the actual warranty will or won't cover, and it is not until you actually need to make a claim that you will know how easy they are to deal with.

(And all of this is not really to defend Lennox... I can't say I'm upset with what I got for the price, but I'm not going to run arround recommending them either.)

The customer service rep said they flagged my warranty-registered units in the system; and I don't want to call their bluff.

The law that you and Crazy Rabbit are referring to is the Magnuson-Moss Warranty Act. Under this law, "routine maintenance" is allowed outside of the authorized repair network. The equipment seller must be able to demonstrate that the unauthorized work led to the damage. So yes, voiding the warranty out-right for a soft start is probably illegal. But good luck arguing this when the person you're arguing with has dozens of lawyers.

The Magnuson-Moss Warranty Act
Auto Warranties & Routine Maintenance

I'm glad your experience with Lennox was good. Personally I was disappointed with the corner cutting that Lennox was ok with. They simply don't stand behind their brand. For me my Lennox installer tried to short change me on the purchase. I tried to resolve with the installer and the assistance of HQ. But HQ just sided with the installer, and I had to threaten a law suit to sue them before they put their lawyers in touch with me and we sorted something out without the courts.

1) I ordered two "complete Lennox iComfort systems" which were supposed had their Signature multi stage furnace, dual-stage condenser, and iComfort thermostat. But they installed these as single stage since they wired the iComfort thermostats without communication mode. They also argued there was no way to use Y2 or W2 cables. When pressed, Lennox said "the staging is just a marketing gimmick, you won't notice dual stage heating or cooling". They added purchasing dual stage equipment does not imply that it will be installed as dual stage. You have to pay extra for that.

2) I asked for an upsized Lennox evaporator to get better SEER. Instead the installer put in an evaporator from Lennox's bargain bin brand "ADP" that was 0.5 ton smaller than what the matching air handler and air conditioner were rated. Their sales person pitched a "complete iComfort system" that included a depicture of a Lennox branded coil. When I asked them why they felt it was ok to substitute an ADP coil into what was pitched as a complete Lennox system, they said "all evaporator coils are the same and Lennox branding is just marketing". But, I'd have to pay extra to get a Lennox branded evaporator coil since it costs more.

3) Per the AHRI, the smaller evaporator that they used cost me 3 SEER on each system as compared to the AHRI measured SEER had they stepped up a half-ton with a Lennox branded coil as requested. Lennox initially argued that SEER was just a marketing gimmick and didn't matter to costs in the long term".

So, do yourself a favor and do not buy a Lennox. I guarantee you'll notice the savings in your pocket and you'll end up happier.

 

[MXDogCrate]

We ran into this issue just last week. Had forgotten it might be an issue and our HVAC unit which is definitely oversized for our home. It is over 20 years old, but not on its last leg.

When discussing with our PW installer, he commented we would need an HVAC unit with an LRA less than 60 amps.

Any thoughts on the difficulty backward engineering a new HVAC unit post PW and Solar Roof install?

 

[holeydonut]

We ran into this issue just last week. Had forgotten it might be an issue and our HVAC unit which is definitely oversized for our home. It is over 20 years old, but not on its last leg.

When discussing with our PW installer, he commented we would need an HVAC unit with an LRA less than 60 amps.

Any thoughts on the difficulty backward engineering a new HVAC unit post PW and Solar Roof install?

I think this depends on the way your house is wired.


I can think of a scenario where things work out:

Maybe your house is 200A or less and you have a single breaker panel with everything in it (including your current AC unit),. So with this, when you get PW and Solar, they will relocate your AC breaker to a sub-panel that is outside of the Energy Gateway. So the only loads backed up are the ones remaining on your breaker panel. They can still run CTs to your AC so your Powerwall or solar can energize your AC when the utility is active. But if your utility goes offline, then no electricity will make it to the AC since its outside the gateway.

So down the road, when you get a snazzy new outdoor condenser that is inverter driven or with a soft start, you can probably have an electrician bring that one circuit from outside the gateway and put it back on your regular breaker panel.


I can also think of a scenario where it doesn't work out:

My house is dumb and has 90A going to a panel in the house and 60A going to a sub panel outside that only has my two ACs on it. The Powerwall stuff will only backs up the main panel in the house. I'm guessing if I ever were to try and get those two ACs into the panel in the house under a new 200A single service that is backed up; I'd have a pretty expensive rewire on my hands.


Third Scenario: Pay @Vines to come over and pay him with beers and steaks after you get your new AC installed.

 

[nicholb]

Thanks all for the replies and info. Now I know what to talk to my HVAC person about when I get the new A/C unit. The plan is to get it done before the Solar Roof install but of course you never know when Tesla is going to want to schedule the installation until they do.

 

[jjrandorin]

What you actually want someone come out and do "maths" for HVAC? My installer (yes, I'm joking) just used this template.
View attachment 600100

Personally, I think the safest approach is if a 2.5 ton unit results in your wife complaining it's too cold in the winter and too hot in the summer, then you upsize the replacement.

Joking aside, you can get a soft start (sometimes branded a Secure Start or Safe Start) installed on your AC unit to reduce the locked rotor amp current draw on "normal" copeland style compressors. This means you can use 2x Powerwalls to power an AC unit without over-loading the Powerwalls when the compressors start up. So, you don't necessarily have to get a variable speed compressor.

But DO NOT GET A LENNOX SYSTEM. If you go Lennox, they won't let you add the soft start on the non-inverter driven compressor unit without voiding the new product warranty. Plus Lennox Industries (HQ) treat their end-purchase customers like crap unless they threaten them with legal action. Dealing with Lennox is a headache I wouldn't wish on anybody.

I agree with Wayne that the absolute best outdoor air conditioner unit will be a variable speed with an inverter driven compressor. But keep in mind these are outrageously expensive compared to a single or dual stage unit. For example, the Lennox XC25 Signature with variable speed (inverter driven) compressor was quoted to me (3 ton unit) as $5k more expensive than the Signature XC21 dual stage unit.

PS, if your area isn't very humid, for your AC system I suggest you upsize your evaporator coil slightly larger than your outdoor condenser tonnage. For example, if you put in a 3.0 ton condenser unit; get a 3.5 to 4 ton evaporator coil. This larger coil results in a higher surface area to cool the air and you'll see a bit better SEER and energy efficiency. The trade-off is that the coil will be worse at removing humidity from the air, which means your home will be more humid. I'm in NorCal so that's not an issue (hence why the state is always on fire and our electricity is always being shut down). I also don't know if this evaporator step-up approach works on heat pump systems.

Just as a FYI, I marked your post "funny" because of HVAC "go to the other side of the street and look through this card" part, not the rest of it, which I found very informational. The internet being what it is and all, its hard to see intent sometimes, so I wanted to be clear that I was not making fun of your post or anything.

 

[holeydonut]

Just as a FYI, I marked your post "funny" because of HVAC "go to the other side of the street and look through this card" part, not the rest of it, which I found very informational. The internet being what it is and all, its hard to see intent sometimes, so I wanted to be clear that I was not making fun of your post or anything.

Lol no worries! The things that I find offensive are PG&E and arguments that defend PG&E.

 

[wjgjr]

Thanks all for the replies and info. Now I know what to talk to my HVAC person about when I get the new A/C unit. The plan is to get it done before the Solar Roof install but of course you never know when Tesla is going to want to schedule the installation until they do.

Definitely worth trying to get the new A/C first as it will probably save you some hassle and money because then you might not need to deal with sub-panels and moving items from non-backed-up to backed-up panels if the new A/C is in before Tesla arrives to wire things.

 

[nicholb]

Definitely worth trying to get the new A/C first as it will probably save you some hassle and money because then you might not need to deal with sub-panels and moving items from non-backed-up to backed-up panels if the new A/C is in before Tesla arrives to wire things.

I intend to do the A/C after the snow melts in the spring. Tesla says they intend to start MN installs in 4-6 months but I would not expect them to be able to start in MN any earlier than April or May.

 

[Doom Man]

I think a variable-speed A/C is the way to go. (I believe "inverter-driven" is the same thing.) You want an A/C that never needs more amps than the PW's can provide. A variable-speed unit is more expensive, but they're much more efficient and are likely to be cheaper in the long run, assuming you stay in the house. It will certainly keep your house more comfortable and manage humidity better than a traditional one-speed or two-speed split system. Myself, I had to replace my A/C about 18 months before I decided to go solar, so I got a 2-speed unit -- that's a lot better than a one-speed in terms of efficiency, but not remotely as good as a variable speed.

I put a SureStart (a.k.a. "soft start" kit) on that unit because the A/C requires more startup amps than my two PW's can provide, and it works well. Some people have had trouble with those devices, but mine seems to work fine -- I wonder if others' are just hooked up wrong or improperly sized. It took my A/C guy quite a while to get the SureStart hooked up properly. Most A/C contractors will think you're talking about a "hard start" kit, which is a different thing that's commonly used with generators.

Another option would be to get a mini-split unit. I think those all function like variable speed units in terms of power draw, but I'm not certain of that. If your A/C is over 20 years old, odds are that your ducts aren't properly insulated or sealed, so you could just abandon the ducts and get a mini-split instead.

 

[h2ofun]

I replaced two multipack propane systems with Mini split heat pump.air systems. I have 9 heads in the house. Since these are 100% electric works great with my solar, and hopefully future batteries.

I love a person I just had a discussion with who said he has 53 panels and 3 PW's and is 100% off the grid. I said what is your heat? He said propane. I said well thats great, but your net energy bill is not zero, mine is with mini splits.