Saving Money With Pre-Cooling

[IndyMike]

I'm sure you are correct. I think digging more into these rates will be my next task.
 
 
Wow those are some good observations.  So the next question would be how do I use that information? While certainly South/East walls take exposure earlier, its rooms with walls with Western exposure that get the hottest by 7pm.  Maybe its wall sun exposure AND outdoor temps that combine.  South/East rooms maintain their cooling the best.
 
My goal is to save money with a minimum of discomfort, of course.  ^_^  As I said, I think I next need to REALLY dig into these different rate plans.  I think its very interesting how the utility just throws out all these rates, then basically says, "go pick one" when basically few if any customers have REALLY figured out how to best profit from these rates. They should provide a "roadmap" of how to best use each rate, but they don't.  They will tell you what you'd pay under each rate but only for a full year and after-the-fact. 

 
ano,
 
My focus on the East exposure was due to the fact that you appear to have a lot of rooms on that side.  Very interesting that your Southern exposure is the cooler.  Do you have fewer windows or a trellis/other shading on this side? 
 
Your Western exposure will take roughly the same amount of Radiant heating as the Eastern.  Since this is at the end of the day, when your temps are peaking, it makes sense that this is a hot area.
 
Wall reflectivity (stucco?) and window SHGC can make a huge difference in internal temperatures.  The best windows that I've seen (Low E) offer a SHGC of 0.25.  For your area these windows will transmit 352 watts/sq ft/day on your east and west exposures.  Even with Low E windows, you need external shade or blinds/UV screen to cut back the Solar. 
 
My home is older with 0.51 SHGC windows.  I like these a lot for my area.  I have over 300 sq feet of glass facing South.  In the summer, trees shade the house and I use built-in blinds (between the glass).  I've gotten by with a 3.5 ton single stage A/C unit in a 4500 sq. ft home.  In the winter, the same windows allow Solar energy into the home for heating (leaves are gone from the trees).  This same home would do very poorly in your area due to the lack of shade, poor reflectivity of the Brick, and the same .51 SHGC windows.
 
If you're interested in the window calculations, you can download a spreadsheet from here (Solar Heat Gain Calculator): http://cchrc.org/calculators
 
As a side note, I was working on Solar radiation calculations for the Phoenix area for a co-worker who is trying to decide whether to install a PV system.  Really not trying to stalk you...
 
IM
 
Edit: Your Southern temps were bugging me so I had to run the numbers.  Bottom line - I'm a dope.  This time of year the sun is at it's highest.  In your latitude you are taking far more radiation on the East/West than on the North/South.  The following is the output from the SHGC calculator for your various exposures.  The calculations are for 0.25 SHGC Low E windows.  Btu's are per Sq foot of glass area.
 

 

[IndyMike]

Mike,
 
That is a great article.  Tell me, where did you get these graphs?  Are these your own measurements at your house?  If so, what did you use to make the measurements?  I see that dip in the red line, I assume clouds?
 
 
I did some much less complete stuff measuring the temp of the exterior surface of my house and measuring the interior temp of those same spots.  It was a testament to how well foam insulation works.  For example, at 5pm last summer the spot surface temp of my roof was 145 degrees and the surface temp of the insulation on that same spot underneath was 88.  That is a huge delta.  This particular patch of roof was East facing, high pitch no less, but the sun was high enough that it still was hitting it, albeit at a rather sharp angle.  West facing roof just can't be gotten to without serious effort and risk (and extreme discomfort from ridiculous temps).  My attic stays in the 80's even when it is 105 and sunny outside.  The attic has no vents, just the cooling that occurs by virtue of the fact that there is no insulation between it and the conditioned house underneath.
 
Regarding the window gain.  Of course this depends on what type of glass and frames you have.  The various low-e glass and glass with various types of reflective materials applied to the interior and exterior have a huge impact.  The window companies design different windows for different latitudes, specifically blocking or allowing IR in vs out and high angle vs low angle passage of IR.  I have also had some more vulnerable windows tinted such that IR is not passed through (at the expense of visible lights as well).  But it does have a fairly obvious reduction in the temp of objects the light strikes inside the house.  Just as an interesting note, I can't get grass to grow under my windows.  At first I didn't get it, thought the irrigation was missing.  Then I figured out it was the IR reflection off the glass when the sun was higher in the sky.  The visible light really did not reflect much, you couldn't see that it was brighter in those areas.  But if you laid on the dead grass and looked up into the windows, you could see the reflection of the sun in the glass.  As you moved around, you could see that dead grass corresponded very well to the areas that received reflection.

Hi Lou,
 
The graphs are actual data from a Weatherundergound site in the Phoenix area.  Not many of the Weatherunderground sites provide solar radiation.  You have to search a bit to find one.  In your area there appear to be a number of sites http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KTXAUSTI90
 
Keep in mind that the Rs is measured for Horizonal surfaces.  For vertical surfaces the PVWatts calculator is extremely handy: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
The calculator is designed for computing Photo Voltaic module output, but you can also use it to determine the amount of solar radiation that is incident on a surface.  The calculator uses historical data for Rs and can output to a CSV (text) file.  A caution here again - the calculator does not take reflected or diffuse radiation into account.  In other words, it should under-predict the Solar radiation on the surface.
 
I have spray foam in 6" stud walls as well - love them.  Not only does the foam have a much higher R factor, it provides wonderful sound deadening, and rack bracing in a stud wall.  This is my first home with spray foam.  If I had any idea how well it performed when I built, I would have had then floor joists foamed as well for strength and sound.
 
IM

 

[apostolakisl]

IM,
 
Are you using closed cell foam?  I'm using open cell, and it doesn't provide squat for structure.
 
I only have standard 2x4 walls with open cell.  But it works quite well.  In August we are using about 3,000kwh/mo on 6000sf with the temp at 74 24/7, except the bedroom which goes to 70 at night.
 
The only time we get harder hit is actually the odd COLD month.  No gas service here and if it gets too cold the heat pump stops being efficient and it goes to heat strips which can start the meter flying (even at that though we only go up to about 3500kwh).  But it almost never gets cold here.  Last winter we never went to heat strips at all.  Most of our bills were around 1800kwh last winter.
 
I put the stuff in my office too (foam).  I did also replace the HVAC equipment and put in all LED lights when I did the remodel (if you ever need office ceiling LED's, I highly recommend the Cree).  The previous owners of my building were paying over $700/mo on average.  I have yet to have a bill over $300 and have no been moved in 8 months.  This is on 4000 sf of medical office that is regularly in use including a bunch of high juice/high heat lasers.

 

[IndyMike]

Lou,
 
That's a roger on the closed cell foam.  I have a county road ~150' from the Master bedroom.  At night I can here truck traffic, but it's not through the walls.  The sound comes through the 30" of attic insulation.  I was wishing that I had foamed the ceiling, but thinking about it now - probably can't do that.  Closed cell foam is also a moisture barrier and you can't use that on a ceiling below the attic.  Can you do this with open cell foam?
 
Like ano, I've had to adapt to a house that is extremely tight.  I had to add inlet air vents for makeup air for the water heater, bath fans, etc.  House is 2x the size of my previous ranch and uses less electric/gas.  If the house were smaller, I'd think about retiring here.  Just a bit too much for 2 people.  Right now I'm thinking about a nice pole barn with a detached house.  My better half refers to the current location as a nice garage with an attached house - my builder showed extremely bad form when he informed her that my garage footprint exceeded that of the house. 
 
We're at the opposite ends of the spectrum on the heating/cooling issue.  I spend roughly $350/year on cooling using a barebones SEER 10 single stage unit.  Every year I run the numbers on the newer 2 stage high efficiency units - can't make it work.  Heating is the opposite - I have a 93% efficient zoned system.  The house is so blasted tight that I have to bring in cold air to reduce the humidity (typically 50% in winter) when it gets below zero.  It kills me to have put in the effort to insulate and seal the house, only to bring in 0 degree air to control humidity.  It also kills me that I have a really nice Airprilaire humidifier that has never been powered up.  Live and learn.
 
IM

 

[ano]

We're at the opposite ends of the spectrum on the heating/cooling issue.  I spend roughly $350/year on cooling using a barebones SEER 10 single stage unit.  Every year I run the numbers on the newer 2 stage high efficiency units - can't make it work.  Heating is the opposite - I have a 93% efficient zoned system.  The house is so blasted tight that I have to bring in cold air to reduce the humidity (typically 50% in winter) when it gets below zero.  It kills me to have put in the effort to insulate and seal the house, only to bring in 0 degree air to control humidity.  It also kills me that I have a really nice Airprilaire humidifier that has never been powered up.  Live and learn.

30" of insulation? Hmmm.
 
Yeah, I got the 80% gas furnace here. The 90% efficiency model was like $200 more, but the sales guy said I'd never get my money back from it.  My heating is maybe $200/year.  My AC bill is really not bad either. With my old 10 seer systems last year, my worst month was $350 for 3000 sq. house, but it wasn't very comfortable.
 
One of my new systems has 3 zones. Greatest invention in the world. But the company that installed it had no idea how. Initially they just added dampers, but no clue that the ducts had to match the thermostat locations. Then I had way too much air through too few vents on one zone. I had to add a vent, and I replaced all my diffusers with commercial ones. Works MUCH better. Then I had to do some automation tricks to keep zones in sync.
 
I also added an outside air intake to each system controlled by my automation system. What I learned from that is to watch out for allergies, but with 12x12 1500 Filtrete filters (good luck finding those) I think I got a good handle on the allergy problem (with some reduction in air flow.) Even when its over 100 during the day, I usually get in a few hours under 75 at night. 
 
It is amazing how relatively simple things like zoning and air intakes really help, but good luck finding a company that knows anything about them. 

 

[tmbrown97]

I guess we're the odd ones - we suffer through all kinds of misery to keep that electric bill down, including allergy suffering and extreme temperature swings - but that's because at 2200kwh we're looking at a bill of ~$800
 

You know there is a great solution to this problem. . . . move :mellow:   Where I live we complain about .12/kwh.  We also have no income tax.  Property taxes are high, but I bet you have those too.  Highest bill I ever had was just over $400 and that was actually a bizarre cold spell where it got down to 16 at night for quite a while.  I have all electric and at those temps the heat pump has to switch to regular heat strips which is not efficient.  This last winter we barely topped $200.  And that is for more than 6000sf.  August bills usually get up close to $400, but that is with highs of 105 and lows of 82. . . so no rest for the AC.  The Phoenix guys at least get the cool nights.  I am sure that has a lot to do with the longer warmups during the day, especially with a brick or stone house with a lot of external thermal mass.

We have been talking about it often; we're talking about 5 years from now being able to move and are looking at where to go right now.
 
I have a family of friends that just left CA for Texas specifically because of cost of living - a retired gentlemen and he convinced his kids and their families to all sell their houses and move together... this is such an expensive place to live here.  Although, I'm not sure I could survive any place that still has dry counties!  Then again, maybe it'd be good for me...
 

Hmm, I know we're in the same general area, but that's not my weather underground station is it?  KCAELDOR9
 
I do the same thing with the whole house fan but let the house get a bit warmer during the day since we're not normally around.  I'll let it go up to 78 and unless it's close to 100, the AC doesn't come on until 5pm or so when it's dropped down to 76 for our return.  Once it's in the high 90's and above, it gets harder to cool the house down at night and the AC will be on in the early afternoon.
 

No - based on that code you're close to where I work - I'm 30 miles or so northwest.

 

[apostolakisl]

IM,
 
 

Lou,
 
Closed cell foam is also a moisture barrier and you can't use that on a ceiling below the attic.  Can you do this with open cell foam?
 

 
 
 
Yes, open cell breathes much like fiberglass, but unlike fiberglass, it blocks air infiltration.  Most people put it on the bottom of the roof deck, that gets the attic into the insulated envelope of the house and removes all your troubles of ceiling penetrations between house and attic.  It also makes your attic into a reasonably conditioned space and thus much more usable.  All of the mechanicals for the house are in the attic freeing up space in the house.  It also means that your attic doesn't stay 150 degrees all night long.  Basically you have removed that thermal mass of the attic as a reservoir for daytime heat, cooking the house well after things have cooled off outside.  I do believe that closed cell is sprayed on the under side of roof decks when requested, this is based on seeing it done on This Old House.  No one here offers closed cell foam so I didn't bother getting into too many details on my research.
 
I am a bit surprised that you can't put closed cell on the ceiling between the house and attic.  I am not sure why you would have more trouble with condensation there then on the vertical surfaces.  This assumes an attic that is well ventilated.  I also assume the concern is with condensation on the attic side of the foam?  My experience with foam is that it insulates so well, that even if it were really humid on one side or the other, the temp at the surface would be so close to the air temp that no condensation would form anyway.

 

[ano]

I don't think the rates have changed very much for this plan. You may have been looking at the rates for another similar plan. I believe it is hour on the hour then take the total # of kW you use within that hour (same as avg kWH) and take the maximum such value for the billing period.

I asked the utility (APS) how they calculate the peak demand charge.  They say it is "the highest continual 60-minute period during on-peak time."  I read this to be that it is NOT an hour-on-the-hour, but a moving average.  You could also read this another way, that it is only a peak that is sustained for more than an hour, so if a peak only lasted 55 minutes, it wouldn't count. I'll ask them for clarification.

 

[IndyMike]

30" of insulation? Hmmm.
 
Yeah, I got the 80% gas furnace here. The 90% efficiency model was like $200 more, but the sales guy said I'd never get my money back from it.  My heating is maybe $200/year.  My AC bill is really not bad either. With my old 10 seer systems last year, my worst month was $350 for 3000 sq. house, but it wasn't very comfortable.
 
One of my new systems has 3 zones. Greatest invention in the world. But the company that installed it had no idea how. Initially they just added dampers, but no clue that the ducts had to match the thermostat locations. Then I had way too much air through too few vents on one zone. I had to add a vent, and I replaced all my diffusers with commercial ones. Works MUCH better. Then I had to do some automation tricks to keep zones in sync.
 
I also added an outside air intake to each system controlled by my automation system. What I learned from that is to watch out for allergies, but with 12x12 1500 Filtrete filters (good luck finding those) I think I got a good handle on the allergy problem (with some reduction in air flow.) Even when its over 100 during the day, I usually get in a few hours under 75 at night. 
 
It is amazing how relatively simple things like zoning and air intakes really help, but good luck finding a company that knows anything about them. 

ano,
 
Hmmm indeed - this is what happens when I try to post well past my bedtime.  I have 15" of blown in cellulose.  somewhere in the range of R-50 to 60 depending on whose numbers you use.
 
I'm surprised that zoning hasn't caught on more.  It's very common in the commercial world.  Just hasn't carried over well to residential. 
 
Interesting that you installed the Filtrete filters on your air intakes.  I had to do this a couple years back when my better half began experiencing allergies.  I tried the 800 MPR rated filters first since they were rated for Pollen - these didn't cut it.  I then swung to the opposite extreme with the 1900 MPR filters.  These work well for her.  My local Menards carries them in stock for ~$20 - not sure if Menards is in your area,
 
IM

 

[apostolakisl]

I asked the utility (APS) how they calculate the peak demand charge.  They say it is "the highest continual 60-minute period during on-peak time."  I read this to be that it is NOT an hour-on-the-hour, but a moving average.  You could also read this another way, that it is only a peak that is sustained for more than an hour, so if a peak only lasted 55 minutes, it wouldn't count. I'll ask them for clarification.

 
I agree, that sounds like it needs more clarification.  As it is written, if you shut your entire house down for 1 minute every 59 minutes, you would have 0 as a peak.  I bet it is more of a running average of the previous 60 minutes where the peak of that graph is your demand rate.  More like "the highest continual 60 minute average during on peak time" If that were the case, you would not need to stagger your different AC units provided you made sure the sum of the previous hour of the 2 combined units never exceeded 60 minutes on.  Of course that math is easier said than done, unless you just do 30 on 30 off for each unit.
 
Anyway, I would get it in writing whatever it is and see if you can't measure it yourself just to make sure they aren't making stuff up on your bill.

 

[ano]

Interesting that you installed the Filtrete filters on your air intakes.  I had to do this a couple years back when my better half began experiencing allergies.  I tried the 800 MPR rated filters first since they were rated for Pollen - these didn't cut it.  I then swung to the opposite extreme with the 1900 MPR filters.  These work well for her.  My local Menards carries them in stock for ~$20 - not sure if Menards is in your area,

Yeah tried the 800 first. Didn't work.  I tried the 1500 because the flow resistance is a bit less than the 1900.  The 1500 does work pretty well.

 

[ano]

Anyway, I would get it in writing whatever it is and see if you can't measure it yourself just to make sure they aren't making stuff up on your bill.

These rates are such a joke anyway.  These are the charges I have to pay every month:
Basic Service Charge, Delivery Service Charge, Environmental Benefits Surcharge, Federal Environmental Improvement Surcharge, Competition Rules Compliance Charge, System Benefits Charge, Power Supply Adjustment, Metering, Meter Reading, Billing, Generation of Electricity, Transmission and Ancillary Services, Transmission Cost Adjustment, Franchise Fee, Regulatory Assessment, and of course State Sales Tax, County Sales Tax, and City Sales Tax.  The sad part is, the charges for actual electricity are only about 25% of the total.  I pay something like $3 just for them to read my meter, but the reading is automated, so where is this $3 going? 
 
But its really easy to cut your bill in half. Get together with your neighbor. Have them on the standard rate which at most is $0.17 KWH.  You stay on the peak rate that charges big bucks for peak electricity, but only $0.044 off-peak.  During off-peak time, you sell your neighbor electricity for $0.044.  This is a whole lot less than they normally pay.  During peaks, you buy electricity from your neighbor at $0.17 KWH, much cheaper than the $.40 you would pay on peak.  You both win.

 

[apostolakisl]

But its really easy to cut your bill in half. Get together with your neighbor. Have them on the standard rate which at most is $0.17 KWH.  You stay on the peak rate that charges big bucks for peak electricity, but only $0.044 off-peak.  During off-peak time, you sell your neighbor electricity for $0.044.  This is a whole lot less than they normally pay.  During peaks, you buy electricity from your neighbor at $0.17 KWH, much cheaper than the $.40 you would pay on peak.  You both win.

 
In theory, but you best make sure you trust your neighbor and that he isn't the kind to rat you out as some kind of plea for some other trouble he might be in.  Also consider the costs of running the power cables, switching equipment, and sub meters.  You would probably put in a couple days work and 1 or 2 grand worth of stuff.

 

[az1324]

I asked the utility (APS) how they calculate the peak demand charge.  They say it is "the highest continual 60-minute period during on-peak time."  I read this to be that it is NOT an hour-on-the-hour, but a moving average.  You could also read this another way, that it is only a peak that is sustained for more than an hour, so if a peak only lasted 55 minutes, it wouldn't count. I'll ask them for clarification.

Yes there is some question as to whether the demand interval is fixed block or rolling, but the historical data available from the website lists it by the hour though I have not compared to the bill. I believe the meter has the capability of doing rolling interval calculations though. Either way, it is the amount of energy used in one hour so spacing things out is good. However rolling intervals would make it even harder to keep the demand low.

@Lou - it is the time that is continual not the energy usage. Energy usage is the sum total during the continual 60 min period.

I'm sure they have algorithms in place to detect things such as one house that uses all its power during the day next to a house that uses all its power at night.

 

[tmbrown97]

What about a big bank of batteries? Charge them during off-peak, then cutover to them during peak.  Toss some solar on the roof to help slow drainage and reduce the number of batteries required.