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  1. #14
    Join Date
    Dec 2006
    Location
    Dallas
    Posts
    189
    Take a look at this:

    http://www.nppd.com/My_Home/Services...calculator.asp

    Per: http://www.hvacopcost.com/

    Use 2803 Cooling hours for Houston.

    For KWH cost, make sure you divide the KWH on your electric bill with the final $. This gives you the true cost per KWH after taxes and fees, fees and fees, because that's what you really care about - Not the KWH cost on your bill.

    Your house is not exactly small. Your electric rate sounds much higher than average. Yes, your systems are oversized. I think your bill sounds about right for the info you provided (It doesn't sound like the heat strips are on because the added loss would be double). A single story 4216 sq ft house has a lot of surface area to gain heat with. Replacing two 2 year old systems with smaller systems would probably have a 20+ year return on investment.

    I would look at some fancy ductwork to twin the systems to have one system as the primary (with a higher cooling setpoint), and the 2nd system (with a lower cooling setpoint) running on a separate thermostat with large hysteresis to come on when the main system can't maintain it's set point. That's just me. I don't think many HVAC companies would be able to properly re-design and alter your ductwork for this. This wouldn't necessarily yield the greatest comfort for when 5 tons wansn't enough, but the 2nd unit would probably only cycle on and off for 3 hours during the hot season. I'm just thinking out loud.

  2. #15
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    Yee gads.

    10 tons at 13 seer draws about 9231 watts. 30 days at 12 hours a day is 360 hours. That's 3323 kwh at 17 cents for $565.

    4 tons at 14 seer, 3428 watts. 30 days, 12 hours, 360 hours. 1234 kwh for $210.

    Difficult to know the real run time on your current setup, but short cycling on and off means that moisture is not removed. A lot of the moisture on the coils is vaporized right back into the living space.

    How many kwh did you use in march or november?

    Heater strip as in aux heat for heat pump.

    For sure get another Manual J on the as-built house before selecting new equipment.

  3. #16
    Join Date
    Jul 2007
    Location
    N.C.
    Posts
    712
    It would cost but with zone control and the afore mentioned duct re-design you could make this system work. I would see how far the installer is willing to go to help you get straightened out.

  4. #17
    Join Date
    Jul 2008
    Location
    Rydal,Ga
    Posts
    84

    First of all you didn't cave !!! Your HVAC broke the law!

    Quote Originally Posted by adt2 View Post
    I am going to be brief, because I have a lot of information to pass along. Bear with me.

    4216sf 1 story home built 2 years ago (I am the builder)
    Bio-base foam insulation throughout
    Unvented, conditioned attic space (insulation on underside of roof deck)
    Vinyl low-e windows, insulated doors, etc.
    Two (2) 5-ton Amana Heat Pump units
    Programmable T-stats set on 82 during the day, 74 overnight
    Last month's bill - $688 (approx. 3900 KWH)
    Prior month's bill - $461 (approx. 3000 KWH)
    Two April Aire dehumidifiers
    High bill - generally August / September - $900 +/- $50
    No pool, no outbuildings, CF bulbs everywhere, on-demand water heaters

    Recently had an energy audit performed. Was told I had one of the tightest houses they'd ever measured in the Houston area; somewhere in the neighborhood of 14% leakage. I went through the house with them with the FLIR camera; no hotspots. Duct leakage on the order of 10% on each system, but it's leaking into conditioned attic space, so I figure that's a wash. Basically beat the pants off the local Energy-Star homes.

    Only thing we could figure is the HVAC system is WAY oversized. I had an analysis done prior to building the home, gave to the A/C contractor, they used it for toilet paper or something. I have since gone back and found that analysis and deciphered it, and it appears to show that I need 6.5 tons MAX. I purchased HVAC Calc prior to building, and spent a long time inputting all the correct information. It said I needed something like 4 tons total.

    Unfortunately, I caved to the contractor at build-time, assuming he knew more than I did (mistake, apparently). So now, I can't keep the house dry (60% RH or higher, with two dehumidifiers running full-blast), the units short-cycle all day and night, and my utility bills are freaking ridiculous. We are about to pull the trigger on two new 3-ton units (or maybe two 2.5-ton units), and my question is this:

    Where can I get some kind of idea what kind of energy savings I can expect? I mean, if two 5-ton 13-seer units are, say, $500/month, what are two 3-ton 14-seer units going to cost? Or two 3-ton 16-seer units? I've googled this, but I can't find a calculator that does what I want.
    First of all you didn't cave !!! Your HVAC broke the law!
    Our SOS License Board is full of Suspensions and Fines from situations just like yours.
    I would suggest you remind him of this before you file a complaint.
    If you had a Manual J done and he didn't.... He is in big trouble if you file a complaint.... He will loose his license..

    If you don't remind him of this, you than have caved...

    I am personally conditioning 12,200 sqft with only 5 Tons $180.00 and month And I have an all foamed home/ roof as yours and my RH avg. 45% at 76*
    Next can them dehumidifier... let your HVAC do its job..
    Good luck

  5. #18
    Join Date
    Feb 2002
    Location
    Houston Tx
    Posts
    344

    Smile

    I live 25 miles from Galveston 3500 sq ft 3 tons cooling foam attic and ICF walls. ALL electric 2 hot water heater 3 fridges, hot tub, well pump, septic, kw useage per month averages 2000 kw....... I trusted my HVAC guy that was ME

  6. #19
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    If you have any circulating pumps for your hot water - turn them off.

    The dehumidifiers should not be needed during the summer months.

    Make sure any replacement systems have variable speed blowers - and I highly recommend the Honeywell IAQ thermostats.

    How is fresh air brought into your house?

  7. #20
    Join Date
    Jul 2008
    Posts
    46
    No recirc pumps for hot water. I have to run dehumidifiers in summer or the house is like a swamp. Hoping to fix that problem with pending repairs. New units will be variable speed - already made that clear to vendor. I will investigate the t-stats you mention.

    Fresh air intake is set to operate 10 minutes per hour, I believe.

  8. #21
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,097
    10 minutes per hour, at what CFM rate?
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #22
    Join Date
    Jul 2008
    Posts
    46
    No idea. How do I find that out? Is that information on the contoller near the equipment?

  10. #23
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,097
    Only if they measured it when they installed it.

    You might be bringing in too much fresh air.

    Have the contractors check to see how much it is bring in.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  11. #24
    Join Date
    Dec 2007
    Location
    Soudern Kal-e-phone-e-ya
    Posts
    278
    Quote Originally Posted by bmathews View Post
    The funny thing is that even if you use the "rule of thumb" method of sizing. It's still 2 tons too big. What was the guy thinking?
    prolly the same thing as me when I bought a new refer...........when I got it home, it was 3 inches too deep!

  12. #25
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,097
    Quote Originally Posted by Mikeylikesit View Post
    prolly the same thing as me when I bought a new refer...........when I got it home, it was 3 inches too deep!
    LOL...

    Got you beat.

    Measured mine twice. And still bought one 2" taller then would fit. (can't read my own writing)
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  13. #26
    Join Date
    Feb 2008
    Location
    Lucas, TX
    Posts
    107
    You said you have on demand water heaters - on an electric house ?!
    Aren't those things normally done with gas ? Otherwise you need something
    like 60 amps to run those things. I don't know how long they run, but that adds up.

    Hope you get some better results with the improved company.

    Adam

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