Replaced old HVAC w/ WaterFurnace but our electrical use has shot up . . .

Discussion in 'Maintenance and Troubleshooting' started by nigelsthubbins, Sep 18, 2010.

  1. nigelsthubbins

    nigelsthubbins New Member

    In April 2010 had a Waterfurnace Envision 4 ton geothermal heat pump (including a water desuperheater) installed in our roughly 3,000 square foot house in the mid-Atlantic region. I am concerned because our electrical usage has increased pretty dramatically -- a table summarizing our usage over the past 6 years is below, showing an average increase of 24% for the months May through August -- and I have not been able to determine a good explanation. For the record, we are a very energy conscious family of four. The cooling temperature on our main level does not go below 76 degrees, and we are very good about not running the system when people are out of the house.

    (Back in May I posted "Geothermal heat pump, hot water heaters & high electric bill" Thanks for all of the thoughtful discussion there. It remains unclear whether and to what extent our water heater and/or desuperheater factors into this problem, though our WaterFurnace technician noted a problem with the desuperheater in mid-June, and indeed the degree of our increased electrical usage seems to have lessened since then.)

    I have been very surprised not to see a substantial electric usage decease -- even in view of the record hot summer -- having replaced a relatively inefficient 16 year old Carrier central air unit with this very expensive top-of-the-line geothermal heat-pump. Through this post I am hoping for two things: (1) ideas about how to determine whether the geothermal system I have installed is the energy culprit (including whether it is a defective unit or has installation issues) and (2) specifically, what the best way to measure energy usage is for the geothermal unit.

    ENERGY USE TABLE (I apologize that I don't seem to be able to get this to format correctly, but it is viewable correctly as an attachment)

    Date 2010kwh 2009 2008 2007 2006 2005 Ave 05-09 % increase

    May 944 503 518 646 461 690 564 40
    June 1166 701 584 860 784 860 758 35
    July 1210 664 816 924 1300 1340 1009 17
    Aug 1287 787 1072 1044 1492 1370 1153 10

    I should point out, because the geothermal installation was part of a larger renovation, we do not have a direct "apples to apples" comparison. The differences include:

    *Adding on roughly 450 square feet, but it was all in the basement (we virtually never have the A/C on down there)
    *Increasing the energy efficiency of our 1920s house, including replacing all of the original windows with high quality energy efficient windows, blowing in insulation, installing insulated siding, replacing the roof with a lighter colored, high quality roof, performing an infra-red analysis to close off all gaps around windows.
    *We replaced our gas water heater with an electric one (resulting in gas savings of approximately $25 - $30 per month).
    *We installed a wine cooler and hooked-up the (previously dormant) ice-maker in our refrigerator, and are now using our washing machine routinely (we line dry roughly 80% of our wash).

    Our WaterFurnace installer has not revealed his thoughts about what could be the cause of our increased energy use, and we are growing desperate for advice that will enable us to low our bills. As (hopefully) you can see from the chart, our electrical usage trend is getting better, but the bottom-line is that we are using more electricity than before installing the WaterFurnace, rather than substantially less.

    Any thoughts you can supply would be really appreciated!



    Attached Files:

  2. zach

    zach Member Forum Leader


    How big is your electric hot water tank and what is the temp of your hot water at the tap?

    I am a homeowner as well and began taking daily meter reads to watch consumption. It would be interesting to know your consumption on days with A/C v. days without A/C. My install was completed June 29 and we had record heat here this summer.

    If it were me, I 'd be looking at the hot water tank. Are you running a buffer and finish tank or just one tank?

    I am running a 3T Hydron Module combination unit. so I am heating all of our hot water and sending it to an unpowered 80 gal tank (electric back-up with breaker off). Family of 5 in upstate NY.

    With no A/C, our daily usage is about 26 Kwh. On a hot day with A/C, the usage goes up to about 40Kwh. There were a few days in early and mid-august we hit 50Kwh per day.........very hot and humid.

    And, get some other opinions, but in the hot weather you may be better in running the system even when no one is home as, otherwise, you are trying to play catch-up with the sytem entering second stage for sure.

    How many ton was the old Carrier?

    Last edited: Sep 18, 2010
  3. nigelsthubbins

    nigelsthubbins New Member


    Thanks for your reply. I need to educated myself more about how the system works, but the the best of my knowledge we are running just one tank of a standard size (80 gallons?). We seem to have about normal hot water usage (3 or 4 showers per day and run our washing machine on cold or warm). With the desuperheater apparently functioning properly, I would think the hot water energy add on should be minimal. The water temperature is set just hot enough that it is uncomfortable (but not scalding) to stand under the shower turned up to the hottest temperature. When it has been hot weather, we have certainly run the system to make it comfortable, but don't ever really "crank it."

  4. zach

    zach Member Forum Leader


    A typical "standard size" hot water tank is 40 gallons. You need to educate yourself on the tank size. 3-4 showers at the same time of day is going to burn thru 40 gallons and I doubt the DSH is going to make that up w/o the water tank element running a bit. Again, if it were me, I'd be looking at hot water as your energy culprit.

    The pro's will chime in but I am not sure you are not getting your best desuperheater "bang for the buck" running a one tank set-up.

    Start taking daily meter reads.
  5. geome

    geome Member Forum Leader

    Nigel, have you compared the cooling degree days for 2010 to prior years? This past cooling season has been brutal. Also, maybe you can calculate kW equivalent of the previous $25-30 gas usage for the old hot water heater so you can better compare apples to apples.
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Question is broad and the water muddy. You are going to have to isolate new power users and compare their contribution to the bill.
    Depending on the price/kwh a geo system may not save you a ton over a 16 seer AC.
    good luck,

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