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Biggest bang for the $ - reduce electical/cooling demand

Posted by wizard19 (My Page) on
Wed, Feb 29, 12 at 11:46

We are considering several options for trying to reduce our electrical bill. Living in central Texas, the focus is on cooling costs in the summer. I realize there are several variables so looking at general thoughts on the options below. Last year was a scorcher, temperature wise, and we had our daughter's family living with us which added to the electrical/cooling demand. We are probably looking at staying in the house about 7 years.

Two story home, 3700 sq ft built in 1992. Original A/C's (Trane Seer 9) are 3 ton (downstairs) and 4 ton (upstairs). I am assuming they are now probably operating less efficiently given their age. The upstairs unit evaporator coils have been replaced twice (HSA home warranty covers the cost) and usually end up with 3 calls/summer for freon leaks. Current initial quotes are around $11,500 to replace both units or about $6,500 to replace just the upstairs unit (runs much more than the lower unit.

Need several windows replaced (fogging/moisture due to leaky seals) in front entry way (open two story foyer) facing South and gets lots of afternoon sun. The two main ones are a 4' x 6' and a 3' x 6' above entry door. Considering good low-E windows. Current quote is about $4,000 and includes several other smaller windows.

Additional insulation in attic. R-36 (blown cellulose) when built. About $1,300 to go to R-49.

Considering radiant barrier (foil attached to ceiling of attic, not spray) in attic. About $2,000.

Add solar film to inside of windows. About $1,500.

Solar screens on windows are original and need replacing. less than $1,000.

One local company states a "good efficient home" should result in highest electrical bill about .07 * sq ft or $259 for our house. Our Jan-Mar and Oct-Dec electric averages about $215 and Apr-Oct average $421 with the max $520.

We can't do it all at once so we are looking at either replacing the upstairs a/c or doing some of the other items this year.

Any thoughts are appreciated.


Follow-Up Postings:

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RE: Biggest bang for the $ - reduce electical/cooling demand

9 seer isn't very efficient. A new 15 seer unit would help alot. If you already have r-36 in the attic boosting to r-49 might not help too much but it wouldn't hurt.

With all the sunshine you get I wouldn't be surprised if a solar film might be helpful. Do you have lots of windows? Facing south?

If your units are from 1992 its probably time to stop investing money in them and replace them both. Make sure new units are highest efficiency single stage. The new systems should having matching most efficient air-handlers if possible.

You might want to consider upgrading to heatpump's if it doesn't cost to much extra (which it shouldn't).


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RE: Biggest bang for the $ - reduce electical/cooling demand

Is your domestic hot water provided by electric hot water heater?

If so, consider a Heat Pump hot water heater such as the GE sold by Lowes. Pricey up front cost, but a huge electic usage savings. Additionally, you may have tax credits and other forms of rebates available. I am seeing $600 Annual savings in electrical usage with my 50 Gal GE Heat Pump hot water heater.


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RE: Biggest bang for the $ - reduce electical/cooling demand

I suggest that you hire a local, certified energy rater to evaluate your house and help you formulate a plan that will take you to where you want to be working over a year or three. Someone local will know what is appropriate for your area. It is hard to make recommendations without looking at your house. I think it would be well worth the investment in their fee. You might start at RESNET. Call more than one and interview them. Tell them that you want are going to choose someone based on calls. You might ask them what they think works best in your area in general terms.

They will know of incentive programs to help with the costs. Their job is to identify the low-hanging fruit for you.


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RE: Biggest bang for the $ - reduce electical/cooling demand

Saltidawg is on target. Heat pump water heaters are usually a good idea in hot, humid areas if you are heating water with gas with the HWH inside the house.


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RE: Biggest bang for the $ - reduce electical/cooling demand

Heat pump hot water heaters are noisy. It should be noted in a local study, hot water cost $350 a year - using electric resistance. I suspect TX ground water is even a bit warmer than ours so the cost should be less. So while some might save $600 a year, most would save a lot less - maybe $200. Still not bad. Low flow shower heads and HE washers payoff pretty well.

Radiant barrier depends greatly on where your ducts are. If they aren't in the attic, you would be crazy to spend that kind of money. Even with ductwork in the attic, it is still a really tough sell. It would not save $100 a year.

Ditto the attic insulation.

Solar film when you have solar screens seems like a waste. Now upgrading your solar screens seems like a better idea but obviously we don't know what your baseline is.

I would upgrade your upper unit and then see if you can get some of that air downstairs. Impossible to know if this is feasible given your setup.

$215 is a pretty steep baseline. Do you have led or CFL lights. I recently discovered some really good $20 800 lumen LED bulbs at Lowe's. These work in most applications and are great if you don't like CFL's. I even like them in recessed cans.

If your ductwork is in your attic, you probably need to seal it better. That is cheap and DIY.


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RE: Biggest bang for the $ - reduce electical/cooling demand

david carey,

"It should be noted in a local study, hot water cost $350 a year - using electric resistance."

I don't know what "local study" means, but go to the Lowes web site and look at electric heaters and pick a few at random and look at their Product Information: Energy Guide and you'll see typical usage for a 50 gal electric tank is on the order of $400-$550 - and that is for electricity costing like .107$/ Kwh. Electricity in my neck of the woods is nearly twice that.

I don't believe that "most" would save "less."


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RE: Biggest bang for the $ - reduce electical/cooling demand

Energy guides are based on relatively old data and are probably worst case scenario. Our local utility did a study (with me in it) and that was the result. It is further south than some parts of the US which makes a difference and the kwh rate was $.10. The local study was 2010-2011 so it represented more up to date data. That energy guide probably uses data from many years ago before water saving appliances.

But you have a good point that some people pay a lot more for electricity. But average is still 11.5 cents.

Someone with electric hot water in New York with a hot water heater in a colder area (like attic or garage or even basement) will pay a lot more than someone in Texas (OP).

Even the Energy guide doesn't suggest people would save $600 a year vs conventional - but if your electric rate is very high it certainly could. But "most" would save "less".


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RE: Biggest bang for the $ - reduce electical/cooling demand

Thanks for everyone's input so far. I know its hard to know exactly what the best options are with limited background info.

We replaced our water heater (gas) last year.

Our ducts are in the attic. One potential issue with the ducts I see is there are no return vents in the rooms. A common design around here is to have a central return vent in the hallway on each floor. So if you close the door to the room it will tend to be a little warmer (or cooler in the winter).

I like the RESNET recommendation and will pursue that.


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RE: Biggest bang for the $ - reduce electical/cooling demand

good.
make sure the rater you hire is experienced in
existing homes.

best of luck.


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RE: Biggest bang for the $ - reduce electical/cooling demand

"We replaced our water heater (gas) last year."

Not a likely candidate for a Heat Pump hot water heater.

How much does your electricity cost per Kwh?


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RE: Biggest bang for the $ - reduce electical/cooling demand

Electrical rates are tiered and seasonal:

.0355 first 500 kwh
.06 >500 kwh (winter)
or
.078 >500 kwh (summer)


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RE: Biggest bang for the $ - reduce electical/cooling demand

If you haven't replaced all possible light bulbs to compact fluorescent then you should. These save alot of energy. You should also upgrade your upstars unit for sure. If you can get a better price by replacing both units at the same time replace your downstairs unit also. It is 20 years old and only 9 sseer after all. To improve your efficiency drastically you should get the highest effieciency single stages.


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RE: Biggest bang for the $ - reduce electical/cooling demand

If I read you correctly, you have rejected spray foam on the underside of the roof deck and sealing the attic in favor of radiant barrier. The radiant barriers have problems. If it is humid where you live, sealing an attic that contains ducts can be a very good thing.


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RE: Biggest bang for the $ - reduce electical/cooling demand

Wiz, ditto on the advice to make sure those ducts in the attic are sealed up absolutely as tight as you can get. Don't use "duck" tape, either. Use something built for the purpose, or apply duct mastic.

On the doors to bedrooms, either undercut them more or add registers to let the air out. When the door retards air flow significantly, the ductwork and everything downstream to the blockage is pressurized, forcing conditioned air out through myriad cracks and holes in the building shell. At the same time, the spaces "open" to the return ducts become depressurized, and unconditioned outside air is sucked in through the myriad other cracks and holes in the shell.

Besides alleviating the return air paths from the bedrooms, it follows from the paragraph above that a great DIY project is going over as much as the external shell (attic floor, walls, sill, etc.) as you can get to and seal up all the cracks and wiring/plumbing holes you can find with can foam or acoustic (nonhardening) sealant. Tightening the home against outside air leakage can go a long way in many homes toward keeping the conditioned air in and unconditioned air out. Don't worry about "too tight." Most existing homes leak far too much, and even with whatever tightening you reasonably can do the house still will leak air sufficiently.


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RE: Biggest bang for the $ - reduce electical/cooling demand

3 cents/kwh in Texas? I thought it was more like 14 cents since deregulation took effect. Here we pay two values, one for the electricity and one for the transport. You might want to check to see if your bill is split in such a way.

Going from a 9 SEER to a 15 SEER should get you something like a 25% reduction in electricity for the AC.


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RE: Biggest bang for the $ - reduce electical/cooling demand

weedmeister - 3 cents for the first 500 kwh, then 7 cents for the rest. You are correct, though, there is a 3 cent transport charge so we are at 14 cents.

ionized - The "spray" I referred to was the spray version of radiant barrier (vs. the foil) I did not consider foam spray as my initial investigation was that it was a source of "fumes" and haven't seen many companies offer that option of insulation.

neo - Not sure going away from the incandescent bulbs is really that cost effective (at least my understanding):

20 lights at 60 watts = 120 watts
5 hr/day * 21 days = 105 hours
120 watts * 105 hours = 12,600/1,000 = 12.6 kwh for a month

However, I am interested in more info about the one stage vs two stage discussion on your a/c efficiency point.


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RE: Biggest bang for the $ - reduce electical/cooling demand

Sealing the attic and spray foaming the roof deck will eliminate the need to seal the ducts and track down all the leaks between the house and attic space. There are lots of the latter. The original construction might not have been sealed well. Have any old can lights in the ceiling? They are terrible leaks. Every time someone installs a new circuit, telephone or coax cable, they drill a hole.. You don't have to worry so much about your barrier at the roof line because no one is going to drill a hole in that. A radiant barrier will help cool until it gets dirty, but foam will seal out humidity as well.

If you have a gas furnace up there, you will need to install an interlocked combustion air source, but that is not a big deal.


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RE: Biggest bang for the $ - reduce electical/cooling demand

20 lights at 60 watts is 1200 watts so you just found close to $20 a month in savings and that assumes only 21 days a month?

So you might be close to $300 a year switching bulbs. Not too shabby. Far more than a radiant barrier or upgrading insulation. All for $400 with LED or as little as $50 for CFL. That math assumes 30 days in a month, 14 cents a kwh, add in reduced cooling load and assuming 80% savings for CFL/LEDs. In a cooling environment, it is a reasonable assumption that every watt changed from incandescent to CFL is saved at 100% (is is closer to 80% but you get an extra 1/3 or so in reduced cooling load).

I think you will find it easier to save some of your $215 month base electricity than your cooling. I just assumed you didn't have NG. If you are spending $215 excluding HVAC and hot water that is a lot. Bulbs are first. Then look at electronics particularly computers left on all the time. Do you have a pool? Look at your pumps. Plasma screens are energy hogs and LED can pay for themselves in a few years if on a lot. Old PCs, Old refrigerators. These are cheaper than a new a/c unit.


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RE: Biggest bang for the $ - reduce electical/cooling demand

I'd put that radiant barrier & insulation upgrade
towards creating an unvented attic.
open cell foam on the roofline to meet code
for your area.
with foam, the minimum insulation value works
because of the other things that foam provides.
an unvented foam sealed attic puts ductwork
in a semi conditioned attic. that alone makes
a big difference in our climate.

by moving the air and thermal barrier to the
roofline, the house to attic leaks are less of
an issue.

30% duct leakage is the average for existing homes.
so I'd still seal ductwork, plenum connections,
and supply boxes. also sealing return air is a priority.

foam insulated attics provide about a 20-25% savings

windows on the other hand, provide about half of that.
14% is the number I come up in my area.

having an energy rating is a blue print for efficiency.
do what you can now, then as you can afford, do more.

more efficient hvac equipment will also offer a
savings depending upon how high SEER you
choose.

best of luck.

best of luck.


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RE: Biggest bang for the $ - reduce electical/cooling demand

ERLA - so if foam insulated attics provide 20% savings (and I don't disagree with that) how does one justify the cost?

OP has $1200 of AC per year so you are talking $240 a year savings. I suspect the foam would cost $5000. While that isn't terrible, I think there are much lower hanging fruit. He could save more that that with a new a/c unit although at slightly higher cost.

And couldn't you get a good chunk of that 20% by sealing every penetration and mastic sealing the ducts for a few hundred dollars?


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RE: Biggest bang for the $ - reduce electical/cooling demand

Could be $3000 for foam. It is kind of hard to tell from here.


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RE: Biggest bang for the $ - reduce electical/cooling demand

I just know that is was closer to $10k for me on a slightly bigger house but I do have a complicated and high pitched roof line.

Even at $3k - it isn't exactly a great bang for the buck. PV panels run about that payback depending on incentives. I think my latest quote is $9k for $600 a year savings. On a newer home I spend about $500 a year on AC despite ducts in the attic so obviously foam didn't seem worth it for me.


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RE: Biggest bang for the $ - reduce electical/cooling demand

even mastic sealing ducts they are still located in
the hot attic.
R-38 insulation on attic floor isn't doing
anything to keep air cool in R-8 ducts surrounded by attic
temps.
R-8 isn't anything when it is surrounded by
130 degree attic air. (this is why second floor's that
share attic walls are difficult to heat and cool)

rather than crawling around moving insulation in the
attic to seal leakage between living & attic
then caulking from inside the house to create an
air barrier at the attic floor, foaming the roofline
saves time. labor and materials vs one step install.

also having blower door tested before work and after
work is complete..it takes a LOT of effort to create
the air barrier at the ceiling.

I find the payback is 8-10 years, but the comfort
is amazing when the foam is installed well.
of course I test the foam once it is installed as
well. and I mark areas that leak for foam company
to come back and fix.

its taken me a long time to recommend foam.
I never recommend foam in walls, but in attics
and under floors of homes on piers..is a good
upgrade/investment.
over the years I've run the numbers on all kinds
of scenerios...
traditonal vented attics.
radiant barrier with foam on attic floor
has a good performance...but you still have ducts
in unconditioned space. getting the ducts into
conditioned space is the best 'bang for the $'.

in hot humid climates this is the install that
works for us...unless moving ducts inside the
conditioned space is an option.
in design stages people don't do that, to expect
some one to retrofit ..not happening often.

foam prices are all over the road in different parts
of the country. closed cell is more expensive than
open cell. open cell is what we use for attics
and is around $1.40 sq ft.


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RE: Biggest bang for the $ - reduce electical/cooling demand

If you get a really high-eff 2 stage a/c-heatpump. You could likely run in the lower stage alot. This would dehumidify better and you might be comfy at a couple degrees warmer. Those 2 stage a/c's are especially good when you live in a hot and humid climate. A 17-18 seer would probably run more money also though. Going from 9-seer to 15 seer would probably save significantly. I think a 18 seer uses half the electricity of a 9 seer. So 15 seer might use 2/3's the energy. That is very significant.


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RE: Biggest bang for the $ - reduce electical/cooling demand

david_cary - LOL at my light bulb calcuation with 21 days in a month! I was in "work day" mode. Obviously as you mentioned its more realistic to be using 30 days a month.


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RE: Biggest bang for the $ - reduce electical/cooling demand

neohioheatpump, I find that 15-17 SEER is the best
for this climate.
cost effective and good dehumidification.
as most systems are oversized, when you get to 4 ton
you can do variable speed.
these unit runs low speed
90% of the time, providing more dehumidification
and higher efficiency.

the few days when you have 30 people over it ramps
to higher speed. satisfying homeowner in cooling
and hvac company cause you don't call them.

its very difficult to get hvac companies to downsize.
variable speed units are the hvac industries
answer to the problem.

I do have clients who opt for higher than the 15-17
seer units. usually the trane 20i units.
personally I don't advise it, but ultimately it
is homeowner's decision.


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RE: Biggest bang for the $ - reduce electical/cooling demand

I had a 13 seer 3.5ton no name builders grade unmatched system with a piston orifice that was installed in my home. I had a horrible duct system that had more leaks than swiss cheese and the returns were horribly done. I fixed the returns and sealed them along with the rest of the duct system and installed a visionpro stat with outdoor temp sensing. This made a huge comfort difference and probably my best bang for the buck. I also added more attic insulation and insulated and sealed recessed lights and other leaky places.

I later had an opportunity to upgrade and went with a 3ton 15.5 seer matched system with a txv and visionpro iaq but did have some miscommunication and didn't end up with the variable speed blower. I also downsized from 20kw of staged strips to 15kw staged. The txv helps cut the humidity in cooling mode which allows a person to raise the temp on the stat and still be comfortable.

I have to say duct sizing and sealing and other sealing and insulating was the best bang for the buck by far.

The smart stat and staging the strips on the old system made a huge difference in winter.

The txv and better efficiency numbers helps even more on cooling. A variable speed blower would be just all the better.

The old system if it got cold enough to call for strips to help the heat pump would draw @100 amps on strips and the indoor blower and the heat pump pulled @25 amps which is 30kw which would rack up a tremendous bill in a hurry.

I agree with energy rater... The 15-17 seer is really hard to beat. Moving up past 14 gives options like the txv and demand defrost which are essential to pull the efficiency numbers needed to get the ratings


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RE: Biggest bang for the $ - reduce electical/cooling demand

weedmeister - 3 cents for the first 500 kwh, then 7 cents for the rest. You are correct, though, there is a 3 cent transport charge so we are at 14 cents.

ionized - The "spray" I referred to was the spray version of radiant barrier (vs. the foil) I did not consider foam spray as my initial investigation was that it was a source of "fumes" and haven't seen many companies offer that option of insulation.

neo - Not sure going away from the incandescent bulbs is really that cost effective (at least my understanding):

20 lights at 60 watts = 120 watts
5 hr/day * 21 days = 105 hours
120 watts * 105 hours = 12,600/1,000 = 12.6 kwh for a month

However, I am interested in more info about the one stage vs two stage discussion on your a/c efficiency point.


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RE: Biggest bang for the $ - reduce electical/cooling demand

"20 lights at 60 watts = 120 watts
5 hr/day * 21 days = 105 hours
120 watts * 105 hours = 12,600/1,000 = 12.6 kwh for a month "

Check your math in line 1.

You use lights at your home for 21 days and not during the other 9 days each month?


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RE: Biggest bang for the $ - reduce electical/cooling demand

Agree about changing out lightbulbs

You will realize both energy savings operationally, and by throwing off less heat, lower the AC cooling load.


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RE: Biggest bang for the $ - reduce electical/cooling demand

If your house has a "smartmeter" look into time of use billing. Some utilities structure the rates so you pay different prices depending on time of day. This doesn't cost anything to switch over on our utility, YMMV.


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