Geo energy usage for new construction

Discussion in 'Maintenance and Troubleshooting' started by thomasjeremyl, Jul 5, 2012.

  1. thomasjeremyl

    thomasjeremyl New Member

    Hello all,

    First time to post here. Great forum. My apologies for long post but wanted to include pertinent and useful info. Hopefully someone can shed some light on our situation. We just finished our new home in central Arkansas and moved in about 6 weeks ago. Just in time for the hottest June on record here. Dry and hot. About 8 degrees hotter on average than previous years. I expected my electrical usage to be high but not what we are experiencing right now. Since moving in we are averaging 3.25 kW per hour. Actually, that really doesn't vary hour to hour. 3.25 kw/hr at 2pm and 3.25 kw/hr at 2am. That is one thing that has me puzzled. The other is that we built a fairly tight, well insulated house and are still using that much energy.

    Had a blower test done that revealed a 170 cfm loss in the air ducts which appears to be good. (Energy star requires less than 204 cfm for this size house.)
    Also revealed a ENIR of 0.17 which is less than the Energy Star requirement of 0.35. So it is pretty dang tight.

    3400 sqft including 600 sqft bonus room upstairs.
    We have PU SIP exterior walls providing an R26 and very little thermal bridging. Used the cam-lock SIPS so no 2X4 splines.
    Open cell spray foam layer over all ducts (in attic) to minimize air loss.
    2 - 3 inches of open cell foam on attic floor to "air seal" the house with another 12" of loose blown cellulose to get the R value up.
    The bonus room has a full 3.5" of open cell foam on walls.
    Windows are double pane Integrity by Marvin.

    Also all energy star appliances. So I don't think we are using a lot of energy other than the heat pump to cool the house:
    4 ton WaterFurnace Envision (in a cooled utility room)
    Five 125' extended slinky loops. Depth is 4 feet. About 6 to 10 feet apart. I know lots of people go 5' here but installer showed me the numbers and 4 feet looked good. He doesn't like those 5' trenches so much anymore. He is reputable installer. Early adopter of geo years ago.
    4 zones: living area, master area, kids bedrooms, upstairs.

    Installer did a manual J which said use a 4 ton unit. All other quotes suggested larger units, "sizing up a bit". For some reason other installers also wanted to use only one or two returns for the whole house. This installer went with 4 returns.

    I wasn't anticipating using this much energy to cool the house. The installer is coming back out on Saturday to look everything over. Am I off on this? 3.25kW/hr for this type of geo unit and house? Please any help at all is appreciated. My reputation is at stake here! Wife keeps asking why we spent all the extra money on the geo and insulation just to get a huge bill.
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Start by answering as many questions you can in the troubleshooting checklist in this section
  3. thomasjeremyl

    thomasjeremyl New Member

    I have tried to provide answers to all of the checklist items in the troubleshooting list. I have the WaterFurnace Energy Analysis Ground Source System Performance Report from my installer. There is a lot more info on there so I can provide more if needed.

    1) Location: Little Rock, AR
    2) Heat loss calculation- 55810 btu/hr and heat gain calculation- 34868 btu/hr
    3) Waterfurnace Envision 049 Dual Capacity Oversized ECM
    4) Five 125' extended slinky loops, avg depth 4 feet, report says a total of 900' for trench (maybe that includes header?)
    5) Averaging 78/Kwh of electricity per day
    6) EAT- 78 deg and LAT 68 deg
    7) EWT 90 deg and LWT- 94 deg
    8) Percent of load to be covered by geo and balance point- not sure about this??
    9) Installers assessment of your systems operation-says it is running fine, compressor is drawing about 5.5 amps and blower about 1 amp
    10) Projected operating costs, actual operating cost and previous heating and cooling costs: From WaterFurnace Energy Analysis Report from Installer-
    Projected Cooling Costs- Load: 55.4 million btu, WF Unit: 3653 kwh, Average EER: 15.2, Cost of Operation: $402

  4. thomasjeremyl

    thomasjeremyl New Member

    More info

    Sorry for multiple posts but here is some more info:

    Correction: seven 125' loops in sandy soil.

    Log of EWT/LWT and EAT/LAT:
    7/7/12 at 5pm with 97* outside air: EWT- 90* LWT- 94* EAT- 78* LAT- 60*
    7/8/12 at 10am with 85* outside air: EWT- 88* LWT- 92*
    7/8/12 at 6pm with 87* outside air: EWT- 88* LWT- 93* EAT- 76* LAT-44*

    Not sure why I saw the big change in air temp drop.

    The loop temps seem a little high but we have had record highs recently. Until this weekend (we finally got some rain!) 10 out the last 14 days we were over 100.

    Also the kW usage is averaging 3kWh for the whole house not just geo. Last bill we were at 78kw per day for the whole house.
  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Per the load calc you are somewhat oversized for cooling but that is no big problem since your system is two stage.

    I would want to know why the system needed the oversized ECM blower...that suggests undersized ductwork, and an oversized blower is a bandaid rather than a real solution. That said, if the technician's reading can be trusted, 1 amp blower current suggests the blower is just loafing along, and that is a good sign.

    Compressor amperage of 5.5 almost certainly represents low stage operation. I'm a bit skeptical that an 049 compressor in low stage would draw so little current while working with 90+ degree waterside. My own 038 (next size down) draws about that in low stage and I have 71*F entering water.

    Air temps suggest a problem. System should be able to cool air moving through it by 15-20 degrees. A 10 degree delta is not enough to deliver full cooling capacity or proper dehumidification.

    If 5.5 compressor amps and 1.0 blower amps are accurate, system is probably drawing about 1.75 kw while operating. If it is only cooling air by 10*F, then it may be operating nearly continuously to maintain setpoint

    Under the described conditions I would expect the system to kick into high stage much of the day. Compressor and blower amps would both rise substantially, perhaps to 9 and 2 respectively, for a total of 2.75 kw or higher.

    I suspect a refrigerant charge, ducting, or controls setup problem, but that is based on scanty information...this one will almost certainly require boots on the ground to solve.
  6. thomasjeremyl

    thomasjeremyl New Member


    "A 10 degree delta is not enough to deliver full cooling capacity or proper dehumidification."
    That should have been 60*F for the LAT, not 68. Typo. My apologies. That gives us a delta T of 18*F.

    We are a bit oversized. Much less than the other quotes I received (5 or 6 tons instead of 4) but still oversized. Installer said he does upsize a bit too when homeowners are talking spray foam and lots of insulation early in the building process. He said most don't follow through. We did.

    "Under the described conditions I would expect the system to kick into high stage much of the day."
    Funny thing is we hardly ever kick into high stage. I think the answer may lie in your post on the thread "Is a buffer tank always better than a single tank?" where you explained how a DSH without the buffer tank can actually raise energy use. Thanks for the info. That may be what is going on here. Not sure yet. Going to turn off the DSH and see.

    Is it safe to just turn off the DSH once it has been primed and running? Can I just flip the switch on the unit and shut the valves going to and from the hot water tank?

    I think I read a post by Dewayne or you on another forum that said it may not be that simple.

    "I'm a bit skeptical that an 049 compressor in low stage would draw so little current while working with 90+ degree waterside."
    I should have clarified the difference in dates on the high loop temps and the amp measurement by installer. High loop temp was recorded just after massive heat wave. It has since rained :D and cooled down significantly. Installer checked amps on the cooler day with the loop temps in the 80s. Still higher than your 71* though. May get my own meter.

    I do wish he would have gone with the smaller blower or larger ducts. He said the ducts are sized appropriately. The main runs are big but I think the branches may be too small. Two of our four zones are a little small and we can hear the air through the registers in them. It was really bad. He adjusted the dampers a bit and that helped some. It's not so loud it is waking the kids up anymore but not the quiet flow like I expected.
  7. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Duct shortcomings can be quantified by TESP (Total External Static Pressure) measurements. Ask that such be done and the results. Units are hundredths of inches water column (inWC). Values much above 0.75 are suspect.

    Ahh...a four zone of my specialties! 4 zone duct systems are hard to get right with two stage heat pumps. The big limitation is that two stage units drop only a third of their capacity in low stage. In cooling mode a 4 ton system in a southern humid climate should flow 1300-1500 CFM in high stage and 900-1000 CFM on low stage; a bit more yet in heating mode

    I'm likewise guilty of waking / scaring small children whose bedrooms occupy a small zone off a 4 zone two stage system. If just one small zone calls and the system tries (know that air handlers with ECM blowers try VERY hard) to force 900+ CFM into a zone that needs / can accept far less than that, it will sound like the system is trying to blow the registers off the walls.

    The industry-standard answer is to add a bypass duct that short circuits a bunch of air from the supply right back into the return. I don't like those and refuse to install them. They are prone to icing the evaporator / sweating the air handler in cooling mode and stressing the compressor with excess refrigerant pressure and current in heating mode.

    A better solution is to "crack" (prevent from fully closing) one or more dampers into larger zone(s). That gives some of the excess air flow a place to go where it will pick up some load before returning to the system. Generally the extra air doesn't pose noticeable comfort problems in the target zones. Cracked zones will sometimes experience temperatures a degree or so off setpoint, but I educate my clients that is sometimes a normal condition for a 3-4 zone system.
  8. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Other than the 4 ft slinkies in sandy loam, nothing sounds alarming. Your loop is definately not performing well (yet). Your loop temp is too high for this time of the year. But keep in mind that the loop is fresh, and is not compacted very well around the pipe yet.
    Plus you never took heat out during a winter, so you started warm into the summer.
    Given the whole house usage, the loop temps indicating a continous running in at least 1st stage for quite a while, and also indicate a high a/c load ( probably higher than the 35 kbtu in the manual J heatgain cals), I would say it does not look bad given the current load, and the fact the loop is fresh. Novertheless, I think you would have benefitted from a deeper loop. Sitback, relax, and see how next year is, with the soil compacted better and more heat taken out of the ground during the winter.
  9. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Are you able to soak the ground above the loop to speed the compaction process?
  10. thomasjeremyl

    thomasjeremyl New Member

    The loops have actually been in place for almost a year. We had the loops put in when the unit was installed last summer during framing. I was doing a lot of the work on the house so it took a while to get it done. So they should be pretty well compacted with the wet winter we had here.

    However, they only partially filled the trenches to allow for really good compaction over the winter. About 3/4 the way full on the loops and only about 1/2 on the header line (pretty long too-- a good 60 or so feet). On July 5th I had all the trenches filled up the rest of the way. I didn't realize it might make that big of a difference. Loop fields seem to be pretty sensitive! With temps over 100 for 10 days straight and no rain the ground may have been really warm. With no grass and only 2 to 3 feet of dirt above the loops may have been just really warm.

    The last few days the loop temps have been running a little lower. EWT of 84*F and LWT of 88*F yesterday and today. of Air temps are back to normal with most days in the mid to high 80s for highs.

    I hope the high loop temps is a combination of the trenches not being filled completely, extremely high temps, and little heat deposited in the winter. Hopefully we didn't spend a tremendous amount of money on this system just to lose efficiency because of a foot of dirt. The installer said over and over, 4 feet vs 5 feet really wouldn't make that big of a difference. I hope he turns out to be right.

    I would like to shut the DSH off just to see if it could be running the energy use up as described by engineer in another thread. If it is already hooked up and working can I just turn the switch to "off" on the unit and close the valves to and from the hot water heater? Is it that simple?

    thanks for all your help on this. i really appreciate this forum.
  11. Altnrgy

    Altnrgy Member

    I'm not alarmed at all by 78 kWH's total per day for a 3600ft2 house. That's ~2400 kWh/month. We're all electric at our 2400ft2 house in southern Missouri and used just under 60 per day on during the last month.

    If you're not sub-metering your GEO then you can't blame it yet. Are you all electric? Family of 1 or 15? How many fridges? Deep freezers? Well Pump or Rural water? Swimming Pool? Hot Tub? There's a lot of things beside the GEO that can use a lot of energy.

    How many satellite receivers do you have? We have 4 and each one uses just over 30 watts 24/7 which adds up to around 90kWh's per month if I don't stay on top of turning them off at the power strip which is hard to do since these new ones take at least 3 minutes to boot back up after being powered off.

    FWIW, I have two 300' vertical loops for my 3 Ton ClimateMaster system. During this last month my EWT starts out around 73 in the morning and normally ends the day just under 80.
  12. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Refresh my memory...dedicated preheat tank or not?

    Before I cut off the DSH, I'd try cutting power to the water may find DSH provides almost all your water heating during steadily warm-to-hot weather.

    DSH normally removes heat, helping the loop in summer, so I'd be reluctant to dump it unless it is proven to be exracting heat from main water heater

    If you do have a single tank DSH setup, reduce the bottom element setpoint to as low as family can stand...90-100
  13. a0128958

    a0128958 Member

    I would be alarmed. I have a 3400 sf home in the hot Dallas climate, built in early 90s with average construction, and right now, with temperature highs each day right around 100°F, my day to day kWh run rate, just for HVAC, is 35 kWh. Eight tons of WaterFurnace Envision GHP capacity, all running in 1st stage only, with entering water temps at the moment at 81°. See 3rd and 9th charts at Web Energy Logger: .

    Best regards,

    Last edited: Jul 23, 2012
  14. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    I would be alarmed

    Apples to oranges comparison. They are talking full house and you are talking hvac comparison. At least as I understand it.

    Nice setup though.
  15. Altnrgy

    Altnrgy Member

    The way I read the original post was it 78 kWh per day for the total house. If I'm reading your WEB data correctly it looks like you're at 85 kWh/day for the last 30 days. Nice set up by the way!

    This supports the point I was trying to make which was there's likely nothing wrong with the OP's geothermal. I'm really not trying offend anyone by pointing point out that it's very easy to spend a lot of time fixing things that aren't broken.

    I'm an industrial energy manager and am frequently called in to troubleshoot non existent energy problems. I can recognize this quickly now because I've been guilty of it.

    At my house we're right at 30 kWH per day for my 3 ton ClimateMaster Tranquility with the average daily high of 100+ and we keep our house a very comfortable 72f 24/7.

    All the best!

Share This Page