Powerwall and high heat!!

[BGbreeder]

@SMAlset Yes, adding garage door insulation will certainly help. Easy to do, and yes, keeps things warmer in the winter and cooler in the summer. I am curious what the temperature difference is on the two walls. Given the energy that the Powerwalls use to warm and cool themselves, I suspect moving the location was a good long term call for energy reasons, although I personally wouldn't be wild about "wum-wum" noises coming through a bedroom wall.

Yes, I agree with @wwhitney that HVACs are routinely oversized, I think for many reasons; rule of thumb, rather than Manual J sizing, profit incentives of HVAC installers who will make more on larger, more complex systems and owner complaints about how fast it cools down. (I think that we are spoiled by automotive air conditioning which are ridiculously oversized because of glass area and single pass cooling.) I think that HVAC systems have changed a lot for the better in the last twenty years, in particular ECM fan motors and variable speed controls on compressors, enabling more efficient operation, and higher comfort levels. Hmmm, probably time to upgrade mine...

All the best,

BG

 

[h2ofun]

Proper sizing procedure:

Conduct an ACCA Manual J calculation (likely using software) based on detailed information about the building's construction, number and orientation of windows, etc. to determine the cooling load at the 99.5% high outdoor temperature for the target indoor temperature (say 72F). Using that size, the system will run 100% of the time without cycling during those conditions; and 1 or 2 days a year (such as the current heat wave), the temperature will exceed the 99.5% high outdoor temperature, so it won't be able to maintain the 72F target temperature, and the indoor temperature will rise a bit higher while the system runs constantly.

Typical sizing procedure:

- Most houses in this area need about 1 ton per 750 sq ft. This house is 3000 sq ft, so let's put in a 4 ton unit. [Not an awful starting point if the rule of thumb is based on ACCA Manual J calculations, rather than historic oversizing.]

- Last time we put in a system sized by Manual J, the customer complained that when they got back from vacation and it was 85F inside, the system took six hours to cool the house down to 72F, and that was too long. So now we add another 50%.

- Bigger is always better. [Far from true.]

Cheers,
Wayne

So, what is the downside of adding that 50%?

 

[wwhitney]

So, what is the downside of adding that 50%?

The equipment cycles a lot more (particularly as most of the time the demand is quite a bit less than the design conditions). That reduces the efficiency and increases the wear on the equipment. Frequent cycling also tends to cause more variation in indoor temperature.

Oversized equipment provides more of its cooling as temperature reduction, and less as humidity removal. So if humidity removal is a concern in your climate, you end up with higher than optimal indoor humidity.

Cheers, Wayne

 

[BGbreeder]

So, what is the downside of adding that 50%?

Yes to what @wwhitney said.

Here are a few; Higher energy costs, lower comfort as blasts of cold air alternate with warm air, and often impaired/reduced humidity control.

Depending on where you live, it can be more energetically efficient of oversized the evaporator to get more efficient evaporation of the Freon (better energy transfer). The downsize is that this system won't dehumidify as well, so for high humidity areas it may be preferable from a comfort standpoint to use the smaller evaporator and get more water out of the air, resulting in improved comfort.

All the best,

BG

 

[wwhitney]

We can also add that oversized equipment is harder to backup with PWs. : - )

It's fair to say that if for the current heat wave (in most of CA) your AC system is able to maintain the design temperature fairly evenly through the house, and it is still cycling, it is oversized.

Cheers, Wayne

 

[Redhill_qik]

We have an older home automation thermostat that has settings like that, I think. Something like a deadband and some sensitivity settings. I’d be surprised if other higher end thermostats didn’t offer something similar.

Currently using an ecobee and there isn't a setting for the range. Prior simpler scheduling Honeywell also didn't have a setting for that. Hobbyist home automation systems I can understand having that as an option.

 

[SMAlset]

I can add that our 3800 sq ft two-story stucco house did come new at construction time with this scroll wheel 5-ton split system installed. When we set the thermostat to 77 upstairs for example it seems to kick on at 78. Guessing there’s a cool down to 76 until it reaches 78 again. So 2 degree swing. The 76-77 setting range seems to be the sweet spot for our house and comfort level for us. As luck would have it my husband’s upstairs office room, and our upstairs master bedroom and connected master bath all face either SE or SW so the stucco on the outside retains a lot of heat. Will be some years still before our palm tree provides shade on the SW wall.

We did have the developer add extra insulation where ever an option, including attic and between floors and above garage. But will look into adding those garage door panels now. With this trend of hotter summers, kind of makes sense. Our old original AC unit Is still working well so we’ll keep for time being but switching out to something more efficient will be our next upgrade.

Being SF bay area California our home sits on concrete slab so the downstairs stays pretty cool generally but even so with continuous days of 90-100 heat it too does get warmer after a few days so the AC will trigger more often downstairs as the space heats up.

Don’t have a temperature device but might pick up one and check out the difference between the interior garage walls. The Bdrm adjacent to our PW units isn’t slept in but we use the room and adjoining bathroom and can’t say we’ve ever been bothered by any noise from the PWs.

 

[BGbreeder]

FWIW: My meat thermometer is stunningly accurate 32.0F/208.1F(we are not at sea level, but it also can be calibrated.)

All the best,

BG

 

[t153]

Currently using an ecobee and there isn't a setting for the range. Prior simpler scheduling Honeywell also didn't have a setting for that. Hobbyist home automation systems I can understand having that as an option.

We have ecobee4 and it definitely gives you an option to control the dead band

Help Centre

support.ecobee.com

 

[Redhill_qik]

We have ecobee4 and it definitely gives you an option to control the dead band

Thanks for this. It isn't in the app and only available to change on the unit. It is a bit confusing, but I've made some adjustments and will see how it responds.

 

[t153]

Oh yea, definitely not in the app. It’s pretty advanced with how much you can control on the unit itself. I just wish we could control where it gets its weather info.

 

[Electrph]

Now you guys have me curious as to the sound of ours during these really hot days. Our PWs are in our double garage on the opposite side of the outer stucco wall which is SW facing — so that wall really heats up in afternoon with little to no shade. Our electrical panels are on that wall (main on outside, whole house loads to two panels inside garage). Our NEMA 14-50 and Tesla charger are located inside the garage near the panels.

We paid extra to run the electrical from there to across garage ceiling to the other side wall (opposite side of interior bedroom btw) so that our 3 PWs, Gateway 2 and Solar Edge inverter could be installed on that wall, thinking cooler location for the electronics. The garage doors in our complex are those rather thin I think aluminum ones, no windows in garage. Wondering if adding garage door foam panel sections to our current garage door would help keep the garage cooler during summer (and warmer during the winter). Any thoughts on that?

Yesterday it got to 102-104 during the afternoon. Had our AC (old 10Seer 5-ton Carrier unit, split for 2-story) set to 76. Fully charged early on and we turned up to 77 around 10-11pm. PWs were at 44% after midnight and with it cooling down outside we opened windows although no real wind last night. Figured with it approaching 100+ after noon today wanted to be fully charged then. Woke to it still at 44%. In case Cal ISO orders cutbacks/blackouts this afternoon-evening want to have sufficient SOC to run some AC in addition to necessary loads which would be minor.

Lots of AC use yesterday:
View attachment 683241

I added the foam panels w/ the aluminum heat barrier “bubble wrap“ under .. this is on 3 car south facing doors w/ windows in top door panels .. it lowered peak temp by about 5 degrees .. but also seem to retain heat in morning by about same anount … so peak lower / avg higher
I will be swaping out ng water heater for hybrid next time they go on sale .. hopefully that will lower avg summer garage temps .. winter temp seemed a bit higher but I did not actually measure them as it was not a major concern in my case

 

[t153]

Thanks for this. It isn't in the app and only available to change on the unit. It is a bit confusing, but I've made some adjustments and will see how it responds.

Here’s a more comprehensive guide, btw

Heat Pump & Electric Heat Strip Auxiliary | Notion

Overview

www.notion.so

 

[aesculus]

I came out of peak period and my Powerwalls were no longer charging or discharging. Temperature was 104F and the fans were almost silent now.

 

[jboy210]

On a tangential note, does anyone know how much adding a gable vent does for temps in the garage? Also, is that legal?

 

[roblab]

Venting an attic space is a good idea, and can lower your attic temp 40 - 50 degrees. You'd want a powered vent fan pushing air out of a vent that sits higher in your attic, to pull air in from lower vents. This way the high temp air gets exhausted.

A lot of home heat buildup comes from the ceiling, and the ceiling is a lot of area. Inside air conditioning has a hard time cooling it, and when it cycles off, the infrared from the ceiling heats up everything again and again. There's often quite a temperature difference between your ceiling and your floor.

 

[wwhitney]

On a tangential note, does anyone know how much adding a gable vent does for temps in the garage?

A ventilated attic needs a design with low intake vents and high exhaust vents, or possibly a powered exhaust vent with distant intake vents. So a gable vent could be part of that design, but adding one to an existing design may be a negative. You need to consider the overall air flow pattern.

Cheers, Wayne

 

[Electrph]

I came out of peak period and my Powerwalls were no longer charging or discharging. Temperature was 104F and the fans were almost silent now.

Yes forgot to mention this .. same here ..when garage temp high 90’s / at 100 fans will go silent if pw not charging or significantly discharging

 

[Electrph]

On a tangential note, does anyone know how much adding a gable vent does for temps in the garage? Also, is that legal?

Similar to what @wwhitney mentioned they sell components for garage cooling including powered thermostat controlled fan (mounts in attic above garage) you must add a min amount of intake vents in garage doors or wall … fan vents thru and out attic so cools both .. fan includes fire damper to maintain fire wall (remain code complaint) company claim 20 F degree drop so maybe 10-15 F ?
I have read there is downside to power venting out of attic vents but do not recall reason(s)

 

[BGbreeder]

Similar to what @wwhitney mentioned they sell components for garage cooling including powered thermostat controlled fan (mounts in attic above garage) you must add a min amount of intake vents in garage doors or wall … fan vents thru and out attic so cools both .. fan includes fire damper to maintain fire wall (remain code complaint) company claim 20 F degree drop so maybe 10-15 F ?
I have read there is downside to power venting out of attic vents but do not recall reason(s)

Depending on the home design, you can end up pulling air out of the house, causing warm outside air to infiltrate the house, warming it. Some soffit/eave vent designs are not designed to have large volumes of air moving through them and adding a fan will cause problems. A half a psi of pressure differential would generate 2300lbs of force on a 4x8 area.

The damper is an important fire consideration, and often overlooked.

To @jboy210 question about a garage, yes, it can really help to reduce the temperature, though I would recommend a solar water heater type controller that runs the fan based on the temperature difference that will cool the garage overnight.

All the best,

BG