Central AC use at night in hot / humid climates

[mesquito_creek]

He actually gave me a few commercial panels to mess with when I finished my work, and started my solar adventures!

The first hit is always free…

 

[wattmatters]

He actually gave me a few commercial panels to mess with when I finished my work, and started my solar adventures!

Gateway drug

 

[Supervstech]

I can easily show you how it can be done. The house has to be built correctly. I live in central Texas and my wife demands cold t-stat settings in the summer. My house doesn't look different but it performs differently. It is 4,000 sq ft. It is air tight to .79ACH50 Rvalues to code. Decent windows. Trees on the west side of the house. Unvented, conditioned attic. I use a 3 ton 15SEER heat pump. It runs 50% of the time on a 100 degree day. It ran for 5 hours straight from 7pm to midnight one time two years ago when the temps reached 117 degrees. My total heating and cooling cost annually is 4,000 Kwh or less than 400$ if I was paying for the electric. It is cold in my house.

I build fancy houses. The last big one I completed was 10,000 sq ft. You know the kind of thing that ends up in magazines. Nobody can look at that glass house and think it's energy efficient but here is a true story that my HVAC guy still can't believe and he watched it. I installed a 3 ton air conditioner that was made by Goodman manufacturing in 1991 in that house to temporarily cool it while we were under construction. 15 people working inside. It ran 24 hours a day for two years when it was hot or cold. In the summer it only got above 80 on that one 117 degree day. Most days it stayed below 75 degrees and it stayed dry inside. The condensate line never stopped making water in the summer so there was a good bit of latent load to contend with. The air was blown from a single 16" piece of flex from one end to the other and spilling down the stairs. If you build a house correctly with the right glazing, air distribution is far less important. This unit was originally installed in my home 30 years ago and was replaced and sat beside my shop for 13 years before being used to cool the home under construction. That house was air tight with proper overhangs. Exterior r12 insulation at the walls and slab and r25 exterior insulation at the roof. The windows were thermally broken and were glazed with 3,000 sq ft of an equivalent to cardinal 366 glass argon filled. Build it right. Build it tight.

This is being done by some of us. The knowledge is out there but it is hard to come by because most of what architects learn is taught to them by manufacturers selling a product. What you find online is dominated by manufacturers and if you go to the popular youtube channels it is again dominated by people that are being paid by manufacturers "partners" to push products. They are killing access to the real information that is available from the building science community. If you want the real stuff you have to pay a building science consultant. Unfortunately people usually are only willing to pay them after the failures as expert witnesses.

I'm Ray. Nice to meet you.

This.

 

[Zwy]

Funny? Over 100 people died.

It was wink in response to your joke about the ground temp, not meant to make the tragedy of people dying any less.

What is interesting is that with a system like this in the winter, people could have maybe saved the pipes from freezing and people from dying plus reduced the load on the grid which again, would have possibly saved lives. Usually people die in such a situation by attempting an alternative heat source that ends up killing them.

 

[feo]

Thank you all for the fantastic responses and knowledge. I'll try to summarize:

Figure out consumption to to calculate ROI. I do respect the ROI perspective, but like someone else said, after what we went through in Feb - we don't mind spending a bit to be independent. Currently I am 2k in, and willing to go to 10k if it means peace of mind.

So far the options we have
1) window AC and use in emergencies only (#4,6)
2) several mini splits (#9)
3) 48V 350AH per night (#31)
4) 100kusd setup, 15ksqf house plastered with panels + 2 ground mounts (#60)
5) toss the compressor, convert to geothermal (if you have the space and either $$$ or appetite for experimentation) (#39)

Please keep them coming, particularly if you have a setup that is able to provide full house nighttime AC from solar.

ps "conservation lasts forever, nothing to wear out" well said

 

[wattmatters]

We are a version of 2)

We simply do not use the ducted AC system during grid outages or the other (large) split system. They are specifically excluded from our essential load circuits. The power and energy demand is just far too high to be scoping a backup system for that. Doing so would mean an order of magnitude increase in $ outlay and it's just not worth it for the outages we experience.

After we complete a renovation I expect we'll have a lower power split system be able to at least keep that area of our home comfortable if needed. For now we just use fans to keep air moving during outages in hot/humid weather.

For our second dwelling where my mum lives, she can use the small split system as its power draw is <400W and so is quite manageable while on backup power.

 

[RickP]

I can easily show you how it can be done. The house has to be built correctly. I live in central Texas and my wife demands cold t-stat settings in the summer. My house doesn't look different but it performs differently. It is 4,000 sq ft. It is air tight to .79ACH50 Rvalues to code. Decent windows. Trees on the west side of the house. Unvented, conditioned attic. I use a 3 ton 15SEER heat pump. It runs 50% of the time on a 100 degree day. It ran for 5 hours straight from 7pm to midnight one time two years ago when the temps reached 117 degrees. My total heating and cooling cost annually is 4,000 Kwh or less than 400$ if I was paying for the electric. It is cold in my house.

I build fancy houses. The last big one I completed was 10,000 sq ft. You know the kind of thing that ends up in magazines. Nobody can look at that glass house and think it's energy efficient but here is a true story that my HVAC guy still can't believe and he watched it. I installed a 3 ton air conditioner that was made by Goodman manufacturing in 1991 in that house to temporarily cool it while we were under construction. 15 people working inside. It ran 24 hours a day for two years when it was hot or cold. In the summer it only got above 80 on that one 117 degree day. Most days it stayed below 75 degrees and it stayed dry inside. The condensate line never stopped making water in the summer so there was a good bit of latent load to contend with. The air was blown from a single 16" piece of flex from one end to the other and spilling down the stairs. If you build a house correctly with the right glazing, air distribution is far less important. This unit was originally installed in my home 30 years ago and was replaced and sat beside my shop for 13 years before being used to cool the home under construction. That house was air tight with proper overhangs. Exterior r12 insulation at the walls and slab and r25 exterior insulation at the roof. The windows were thermally broken and were glazed with 3,000 sq ft of an equivalent to cardinal 366 glass argon filled. Build it right. Build it tight.

This is being done by some of us. The knowledge is out there but it is hard to come by because most of what architects learn is taught to them by manufacturers selling a product. What you find online is dominated by manufacturers and if you go to the popular youtube channels it is again dominated by people that are being paid by manufacturers "partners" to push products. They are killing access to the real information that is available from the building science community. If you want the real stuff you have to pay a building science consultant. Unfortunately people usually are only willing to pay them after the failures as expert witnesses.

I'm Ray. Nice to meet you.

Hey, Ray! Nice to meet you too!

Wish I could build a house like that! Normal houses in the market just aren’t doing it. Like I said, zero in my area. When the build cost for that kind and quality of construction gets compared to traditional “good enough, and a lot cheaper” turn-key costs… well, the results speak for themselves!

I was checking into a net-zero subdivision that was being built outside of Austin a few years back, but lost track of the project and am not sure how it turned out. A community approach, but maybe a new direction worth chasing. Home efficiency was a major construction focus there so, as you say, it can be done a lot better.

Most anything can be done if you have enough money to throw at it. Doing it at a competitive price point is what it’s going to take to make it happen in normal neighborhood construction. Oddly enough, it may end up being the cost of electricity (or Ercot’s failures) that drive more business your way, and I hope it does! Still, powering a central AC unit in Texas heat and coast humidity in a traditionally constructed house, without partial-grid tie, isn’t what you're describing.

Your type of construction in a simple 2500 sq ft house would be a dream home to me. And I’m going to keep dreaming… as long as I’m still breathing, it’s possible!

 

[tim0shel]

What I do to make my houses more efficient is not more expensive. I watch the other builders. They use many of the same subs and many of the same materials but they don't use them the same way. Some of them try to use the same approaches like using unvented attics but they don't train themselves in building science and they always look for magic products that don't require understanding of the systems they are building. They want to write a check and not do the work to learn the physics of heat air and moisture. They don't learn the second law of thermodynamics and how it affects everything we do and they don't learn how those principles must guide our approaches to solving problems and creating system design. Therefore they are at the mercy of the salesmen marketing products that are often not created to solve problems but are created only to sell to an unsuspecting public. Products like zip wall, mortar mesh, tyvek, pex, durorock and many more are marketed as time savers but usually are designed to be used by people that have little training or understanding of what they are building or the principles involved in creating a successful system. There is no understanding of why a tight house is critical to managing indoor air quality or the many ways water in its four forms can move through our building assemblies. Education takes time and dedication but ignorance is too costly. We need to educate our people better. When people ask me what product to use for this or that, I give them a physics lesson. It is the only way to defeat the marketers selling products they don't even understand.

This is absolutely correct! The products themselves are only as good if used properly and installed properly and in combination of other factors. A lot of this kind of stuff I would probably look into when if I Rent my house and build a tiny home. I want to down size and live in a very efficient off grid capable tiny home. You build any of those? lol

 

[Sanwizard]

We are a version of 2)

We simply do not use the ducted AC system during grid outages or the other (large) split system. They are specifically excluded from our essential load circuits. The power and energy demand is just far too high to be scoping a backup system for that. Doing so would mean an order of magnitude increase in $ outlay and it's just not worth it for the outages we experience.

After we complete a renovation I expect we'll have a lower power split system be able to at least keep that area of our home comfortable if needed. For now we just use fans to keep air moving during outages in hot/humid weather.

For our second dwelling where my mum lives, she can use the small split system as its power draw is <400W and so is quite manageable while on backup power.

I added a whole house 20k natural gas Generac for backup. It can charge my batteries also. Less expensive than solar. My solar is to eliminate as much grid use as possible day to day.

 

[wattmatters]

I added a whole house 20k natural gas Generac for backup. It can charge my batteries also. Less expensive than solar. My solar is to eliminate as much grid use as possible day to day.

A 20kW generator for backup? Yikes. The cost differential would be the other way round where I live. No reticulated gas either. Installed cost here would be close to $US10,000. Here that would get you a 20kW solar PV system which can be used all the time and cost nothing to run.

My off-grid solar and battery backup system cost less than US$2,000. The battery alone it can cover us for 6-10 hours while the 2.8kW Yamaha generator can support the solar to keep it topped up and us going pretty much indefinitely should we need it.

I also have an 11kW grid tied system which does a great job of reducing our energy bills. Based on our actual bill reduction over last few years it'll have paid for itself in a little over 4 years.

 

[Sanwizard]

A 20kW generator for backup? Yikes. The cost differential would be the other way round where I live. No reticulated gas either. Installed cost here would be close to $US10,000. Here that would get you a 20kW solar PV system which can be used all the time and cost nothing to run.

My off-grid solar and battery backup system cost less than US$2,000. The battery alone it can cover us for 6-10 hours while the 2.8kW Yamaha generator can support the solar to keep it topped up and us going pretty much indefinitely should we need it.

I also have an 11kW grid tied system which does a great job of reducing our energy bills. Based on our actual bill reduction over last few years it'll have paid for itself in a little over 4 years.

2K for the whole system? Thats great! A single 48V bank of 280Ah cells cost more than that now.

 

[Sanwizard]

Solar power is certainly viable. I don’t want to misrepresent that point. The smart money on solar is either using it to reduce grid-supplied power, or scaling use to accommodate the limited supply of a reasonably capable off-grid solar powered storage system.

It‘s a great option, and as storage costs come down it’ll get better. Reasonable uses, those which match loads to the supply characteristics, can see the best of what solar has to offer. Solar can become a real money pit if taken beyond that. Still, I’m a big fan of solar power, and very much enjoyed my experiences with it so far.

The folks in the Internation Space Station agree.

 

[wattmatters]

2K for the whole system? Thats great! A single 48V bank of 280Ah cells cost more than that now.

Yes, my project was to build something that was useful, fun to do (kinda) but also repurpose items as much as sensible and to keep costs inside a pretty tight budget. This is where you can get creative.

Because it is for occasional outage backup and to provide some ballast so the off-grid solar PV can run the pool pump, I don't need Lithium chemistry - that would be expensive overkill. It'd be fun to build but it's just not necessary. A suitable LiFePO4 battery pack would have more than doubled the project cost, and I just wouldn't have done it.

I have a modest battery with 4 x 190Ah lightly used Enersys SLA batteries (load tested and in great condition and 50% discharge is ~4.6kWh which given critical load draw of ~600W will keep us operating for 6-8 hours not including any supplemental energy from the solar PV if the outage is daytime), 6 x 370W second hand Longi panels (2.22kW), preloved rails and clamps from someone who removed a system to upgrade, some loaned bits n pieces (fuses, battery balancer and battery monitor). The rest I bought new (e.g. the 4kW 48V all-in-one inverter, cabling and conduit, connectors, combiner box, isolation switches and sundry bits n pieces).

Only other expense was the electrician to do the wiring work at main switchboard and install a few bits n pieces on the AC output side.

 

[Sanwizard]

Yes, my project was to build something that was useful, fun to do (kinda) but also repurpose items as much as sensible and to keep costs inside a pretty tight budget. This is where you can get creative.

Because it is for occasional outage backup and to provide some ballast so the off-grid solar PV can run the pool pump, I don't need Lithium chemistry - that would be expensive overkill. It'd be fun to build but it's just not necessary. A suitable LiFePO4 battery pack would have more than doubled the project cost, and I just wouldn't have done it.

I have a modest battery with 4 x 190Ah lightly used Enersys SLA batteries (load tested and in great condition and 50% discharge is ~4.6kWh which given critical load draw of ~600W will keep us operating for 6-8 hours not including any supplemental energy from the solar PV if the outage is daytime), 6 x 370W second hand Longi panels (2.22kW), preloved rails and clamps from someone who removed a system to upgrade, some loaned bits n pieces (fuses, battery balancer and battery monitor). The rest I bought new (e.g. the 4kW 48V all-in-one inverter, cabling and conduit, connectors, combiner box, isolation switches and sundry bits n pieces).

Only other expense was the electrician to do the wiring work at main switchboard and install a few bits n pieces on the AC output side.

Ha! Great work! I tried to save by doing all the wiring myself. I'm still here, so thats a win. The DC stuff was easy. The AC side much harder and scary. I had to add a new master manual transfer switch along with all new breakers in a new load panel, and then a feed panel from the main house that feeds my barn.

 

[wattmatters]

The AC side much harder and scary.

Yep. With some minor exceptions, I leave the AC side to a qualified licensed sparky.

My guy has a whole house off-grid system himself so he was more comfortable with the concepts I was outlining when it came to changes to the bypass switch and which circuits were to be grid only and which were on the backup side. It's a bit complicated as my home has a 3-phase supply with two sub supplies to outbuildings while the backup supply is single phase. It all works though!

I have a thread about my project:

Backup down under

Greetings from down under. I live in a home near the small town of Bellingen, in northern NSW, Australia. Glorious country: That's our home at left centre, and obscured by the tree and slightly off the left of the image is a secondary dwelling where my Mum lives. 12 acres, behind our home (to...

diysolarforum.com

I just ran a little experiment to test my array output and am about to start writing about it.

I'm still here, so thats a win.

And let it be so for many years to come!

 

[Sanwizard]

Yep. With some minor exceptions, I leave the AC side to a qualified licensed sparky.

My guy has a whole house off-grid system himself so he was more comfortable with the concepts I was outlining when it came to changes to the bypass switch and which circuits were to be grid only and which were on the backup side. It's a bit complicated as my home has a 3-phase supply with two sub supplies to outbuildings while the backup supply is single phase. It all works though!

I have a thread about my project:

Backup down under

Greetings from down under. I live in a home near the small town of Bellingen, in northern NSW, Australia. Glorious country: That's our home at left centre, and obscured by the tree and slightly off the left of the image is a secondary dwelling where my Mum lives. 12 acres, behind our home (to...

diysolarforum.com

I just ran a little experiment to test my array output and am about to start writing about it.


And let it be so for many years to come!

From your lips to God's ears my friend! I will take the time to review your thread!

 

[DerpsyDoodler]

Gateway drug

Are you calling me an addict?

 

[wattmatters]

Are you calling me an addict?

Not yet....

 

[DerpsyDoodler]

Not yet....

Thank goodness. I was paranoid someone was onto me.