Zoning for efficiency (Questions)

[nmp0]

So I was reading this (http://hvac-talk.com/vbb/showthread.php?t=498022) thread:

and read this by CynicX:


Keep in mind, zoning, and multiple staging is for comfort. Not efficiency.

Longer run times of 2 stage equipment will make for better dehumidification in the summer and more even temps through out the home summer and winter.

Zoning is for room to room or level to level comfort. Leaving a zone off between uninsulated rooms wont save you money.

I have a slightly different scenario then the OP in that thread and I don't have any reason (or knowledge) to suggest CynicX is wrong, I would just like to see mathematical proof. I am replacing the existing unit and going for the highest efficiency I can get with a reasonable ROI.

Please see house layout here: http://img51.imageshack.us/img51/105/layouthvac.jpg

Assumptions:
- Red and Blue do not represent heating and cooling - just the colors I picked for the zones.
- House is located in St. Lucie County, Florida. Hot humid summers, warm fall and spring and cool winters. Assume no A/C or Heating necessary Dec-Feb, A/C only rest of year.
- A/C system is the same for zoned and unzoned. 2 stage compressor (or 2 compressor model) and var speed fan high efficiency, new install. A/C system is located in SE corner of garage.
- Ducting is the same with the exception of extra needed for zoning, new install.
- Unzoned has one return on wall opposite A/C system down low. Zoned has same return plus return in red zone (if I'm correct that it is necessary).
- The wall between the two zones is well insulated. Insulated door between two zones.
- Attic is well insulated with even insulation, same ceiling height (~8') throughout.

Scenario 1 (Zoned):
- Red Zone is set at 74* from 9pm - 6am, 80* from 6am - 9pm every day with slight variation on weekend.
- Blue Zone is set at 80* from 10pm - 5am, 74* from 5am - 6am, 80* from 6am to 4pm, 74* from 4pm to 10pm on weekdays. Weekends run 74* from
5am to 10pm or later.

Scenario 2 (Unzoned):
- 74* all weekend except when house empty, then up to 80* but scheduled to cool before return. 80* from 6am to 4pm and 74* from 4pm to 6am on weekdays.

Questions:
1) With these variables, would a zoned system save money (electricity bill) versus a non-zoned system?
2) If yes, is it possible to calculate (or estimate) what the savings would be on an annual basis to determine ROI of installing a zoned system?

If you managed to get all the way to the bottom, thanks! :anyone:

[im4snow2000]

What are you electricity rates, and what SEER equipment do you plan to install? Where's your ductwork, in the attic?

Assuming this is one story home, how is the attic insulation? Does the attic have sufficient ventilation?

I'd be suprised if a decent zoning system will justify itself with ROI.

[nmp0]

What are you electricity rates,
and what SEER equipment do you plan to install?
Where's your ductwork, in the attic?
Assuming this is one story home, how is the attic insulation?
Does the attic have sufficient ventilation?


Current elec rate is 12.5c/kwh and it will probably increase to 15c/kwh or higher within 5-10 years.

Minimum 16seer (tax credit eligible) but with a zoned system and staged compressor it would be higher seer. I'm looking at Trane XL16i, XL19i, XL20i or an Infinity series. Exact system depends on price, rebates, tax credits, warranty, etc. I'll pay now for extra efficiency that has a 4 year ROI or less.

Ductwork is in attic. Small attic, hip roof that is going to be redone in asphalt shingles (likely one of the few energy star models with cooling granules).

One story house, attic is getting new blown in cellulose insulation after the HVAC install and any necessary attic wiring is run.

Attic has soffits around perimeter and a ridge vent. What is how sufficient defined? The difference between attic temp and outside temp, the difference between attic temp and conditioned temp?

------------------------------

The goal is highest energy efficiency that makes sense financially. "Going green" and saving energy is great but if it doesn't save me money after a couple years than I am likely to wait for the technology to come down in price. Solar water is an example - I have the perfect location but right now the ROI is a bit too long for me and the tax credit runs till 2016 so I'm going to wait till the prices come down or there are better incentives to install one.

I called the elec company and they told me the houses averages $200/mo which was quite shocking for the size of the house and the fact that it had a retired couple in it. Obviously upgrading the A/C, replacing ducts, adding attic insulation will have a HUGE impact on the cooling costs. There are a couple of "whole house" energy credits being proposed (one by the state of FL and one federal) that could credit up to $3000 and $1500 ($3000 - $1500 federal tax credit if you take it) for reducing the whole house energy usage by 20% (discussed goal) with extra credits for going higher. If these credits materialize and if zoning in this case would save money then I want to consider all my options.

[badtlc]

Zoning probably doesn't change performance efficiency mathematically. What it will do is change economic operating costs. Zoning is going to provide "more" climate control in areas that currently are not getting enough heating/cooling. This in turn adds load to the system and therefore will cost more money because you are heating and cooling more load.

The actual operation energy efficiency could go up due to a higher load and systems tend to be more efficient as they reach 100% capacity. That still won't prevent the operating costs from going up.

[btuhack]

The fractions of dollars saved on your monthly bill will never recapture your installation cost or the ongoing repairs associated with zoning. Raise/lower your cooling/heating setpoints for savings. Sounds like you have addressed every other opportunity aside from glass, which can have huge implications on cooling loads and load diversity.

[nmp0]

The fractions of dollars saved on your monthly bill will never recapture your installation cost or the ongoing repairs associated with zoning. Raise/lower your cooling/heating setpoints for savings.

That is what I am thinking. New equipment plus insulation will cut my cooling portion of my energy bill to a point that additional savings will never repay the cost of zoning.


Sounds like you have addressed every other opportunity aside from glass, which can have huge implications on cooling loads and load diversity.

The windows are old, single pane windows - perhaps even the originals from 1970. Replacing them is on the list but not this year. The west side only has a garage window and a slider that is nearly 100% shaded under the porch. The south windows are all under the porch which is 11' off the house and the west side windows are bedroom windows that will have curtains or shades 99% of the time. When I replace them hopefully it will be with hurricane glass.

[nmp0]

One last question for now -

Currently the A/C is located in the unconditioned garage which of course gets quite hot during the peak of summer and warm most of the year. Do you think moving the A/C to the small closet by the entrance to the bedrooms would make enough difference on electrical use to justify the expense of moving it (assuming it would fit)?

- The house is getting new ducts and line sets so I wouldn't think location would impact cost too much on those.
- Electrical would have to be provided but there is currently a short (40? gallon) water heater there now which I want to relocate to the garage so perhaps it already has the correct wire size run for the air handler.
- A new return would have to be put in and the old one patched.
- A condensate pump would have to be used instead of gravity feed in the garage.
- Noise next to the spare bedroom is a consideration but I'm not sure if that bedroom will be used at night (roommate short term) or just as an office/hobby room by me.

Thoughts?

[im4snow2000]

Current elec rate is 12.5c/kwh and it will probably increase to 15c/kwh or higher within 5-10 years.

Minimum 16seer (tax credit eligible) but with a zoned system and staged compressor it would be higher seer. I'm looking at Trane XL16i, XL19i, XL20i or an Infinity series. Exact system depends on price, rebates, tax credits, warranty, etc. I'll pay now for extra efficiency that has a 4 year ROI or less.

Ductwork is in attic. Small attic, hip roof that is going to be redone in asphalt shingles (likely one of the few energy star models with cooling granules).

One story house, attic is getting new blown in cellulose insulation after the HVAC install and any necessary attic wiring is run.

Attic has soffits around perimeter and a ridge vent. What is how sufficient defined? The difference between attic temp and outside temp, the difference between attic temp and conditioned temp?

------------------------------

The goal is highest energy efficiency that makes sense financially. "Going green" and saving energy is great but if it doesn't save me money after a couple years than I am likely to wait for the technology to come down in price. Solar water is an example - I have the perfect location but right now the ROI is a bit too long for me and the tax credit runs till 2016 so I'm going to wait till the prices come down or there are better incentives to install one.

I called the elec company and they told me the houses averages $200/mo which was quite shocking for the size of the house and the fact that it had a retired couple in it. Obviously upgrading the A/C, replacing ducts, adding attic insulation will have a HUGE impact on the cooling costs. There are a couple of "whole house" energy credits being proposed (one by the state of FL and one federal) that could credit up to $3000 and $1500 ($3000 - $1500 federal tax credit if you take it) for reducing the whole house energy usage by 20% (discussed goal) with extra credits for going higher. If these credits materialize and if zoning in this case would save money then I want to consider all my options.

Factoring in upfront investment and operating costs.....and with somewhat limited info......your best bet is probably a 16 SEER operation (could be a model 15 outdoor coupled with variable speed indoor....to achieve operating efficiency of 16 SEER).....no zoning, add solar attic fan(s) assuming your soffit vent is not block, air seal the attic, and add sufficient insulation to attic.

If the current A/C is ~15-20 years old, and avg monthly elec bill is $200, a new 16 SEER coupled with the above measures will probably suffice. Going with maximum SEER and/or zoning, you'll spend A LOT more $$ for a very small savings......relative to what I noted above.....in my opinion.

As you step from the 15/16 SEER range, into 17/20+, the upfront costs accelerate quite a bit....which is how I came to my position noted above.

[nmp0]

As you step from the 15/16 SEER range, into 17/20+, the upfront costs accelerate quite a bit....which is how I came to my position noted above.

I helped my mother pick a system for her house that was installed March 2009. The Carrier comfort 16seer was actually the same price as quote on a Carrier 14seer from another company that insisted 16seer was not cost effective. We also looked at higher seer in Carrier and Trane but even with additional rebates from the power company and a Trane rebate it didn't make sense. She also replaced her OLD leaky ducts (confirmed by power company test and given the max rebate to replace/repair) and added R-30 blown in Fiberglass insulation to the attic. Her electrical bill dropped $480 from March 2009 to March 2010.

Some of the rebates and tax incentives have changed now so I'm trying to figure out the best system I can get for the money before I start getting quotes.

Thanks for everyones replies.

[Todd S 2]

I already had hi-efficiency equipment in my home before I installed zoning.
I left the blower running 24/7 to try and help the uneven comfort issues and also to improve the IAQ.
After I added zoning (3 zones) the comfort level terrific.
I also experienced a 10%-15% utility savings because we are only heating/cooling the areas as we occupy them.
I hope this helps.

[nmp0]

I already had hi-efficiency equipment in my home before I installed zoning.
I left the blower running 24/7 to try and help the uneven comfort issues and also to improve the IAQ.
After I added zoning (3 zones) the comfort level terrific.
I also experienced a 10%-15% utility savings because we are only heating/cooling the areas as we occupy them.
I hope this helps.

That does confirm what I thought about utility savings when I started the thread. I'm also convinced now that there is no ROI potential and I don't think there will be comfort issues unzoned in my house, I'm guessing yours is a bit larger than mine.

Thanks.

[Todd S 2]

That does confirm what I thought about utility savings when I started the thread. I'm also convinced now that there is no ROI potential and I don't think there will be comfort issues unzoned in my house, I'm guessing yours is a bit larger than mine.

Thanks.

My home is a 2-story, built in 1946 (no sidewall insulation), poor windows (wife won't let me get new ones) with 2 new room additions over crawl spaces (no choice). The home is 2,250 sq. ft. I'm live in the mid-west, cold, long winters and hot, humid summers (usually).
I pay $150.00/ month in (all) utilities.

[tedkidd]

I already had hi-efficiency equipment in my home before I installed zoning.
I left the blower running 24/7 to try and help the uneven comfort issues and also to improve the IAQ.
After I added zoning (3 zones) the comfort level terrific.
I also experienced a 10%-15% utility savings because we are only heating/cooling the areas as we occupy them.
I hope this helps.

If you have difficulty with even temperatures zoning is likely to be a huge comfort improvement with some energy savings as well. You can also get smaller equipment because you have better control, does that make sense?

As far as return on incremental cost I don't think Zoning is going to give stock market returns via energy savings (although one client with zoning is reporting a 36% energy savings (http://tedkidd.blogspot.com/)),

Also, if the zoning is not communicating it may shorten equipment life through increased cycling.

The big return on zoning is comfort and control, energy savings is the frosting.