Pennsylvania Higher than expected electric use

Discussion in 'Maintenance and Troubleshooting' started by AndrewL, Jan 22, 2015.

  1. AndrewL

    AndrewL Member

    I'm trying to put together a summary of the issues with my system by identifying the problem and fix required. Please edit/add to as you see fit. My understanding of some of these issues might be limited.

    Tubing not sized properly for flow to / from storage tank. Each HP should push 18 GPM. Four of these would be 72 GPM. The tubing installed is 1-1/4 and steps up to 2” after the third pump connects. 2” copper will accommodate only 40 GPM. This plumbing needs to be increased in size to accommodate the flow from the HPs.

    Storage tank undersized. Rule of thumb is 10 G storage for each Ton of capacity; therefore this system should have 200 Gal. Only 80 was supplied. As mentioned above, the tubing size is also an issue as the 80 GAL tank has only 2” copper inlets. Additional storage capacity is required.

    Controls for staging heat pumps are inadequate. The system as designed and implemented is very wasteful. The 406 is aware of only two heat pumps and the remaining two are slaved to the primary two by a simple timer. Contrary to the proposal that states, “For maximum efficiency, the system also monitors the energy demands and activates each the ground source heat pump individually and only as necessary.” the control system activates the secondary pumps very frequently when not necessary resulting in short cycling. HP2 DELAY was set to AUTO. Changing it to 20 min seems to have reduced short cycling to some degree. A more sophisticated control system is required.

    Controls don’t adjust humidity target based on outdoor temperature - The Tekmar controls do not adjust the target RH value based on the outside temperature. The system was setup with a target value of 40% and I was given no instructions on requirements to change this as outdoor temperature changes. In addition, the system in the attic will require a trip up to the attic to modify this setting. The controls must be modified to use the outdoor reset to properly adjust the target RH level.

    Tank Design Temperature of 112 too high. The tank target frequently reached 120F which is a high temperature and leads to very inefficient COP; lowering the Design Temp to 100F is a 12% increase in COP. Consider lowering temperature even more to increase COP. Take into account heating requirements of Air Handlers and radiant under tile / carpet.

    Verify tank target actually being adjusted by the 406 as outdoor reset.

    Bleeders not on ground loops. Air separators should be installed on all ground loops. Install air separation units.

    Poor utilization of ground loops. Most times only 2 or 3 HPs are running. All ground loops should be connected via a manifold so that all can be utilized no matter how many heat pumps are operating. Connect all ground loops and install a single circulation pump.

    HP DIFF too small. The HP DIFF temperature was set to 4F, making the system over responsive. It has been changed to 8F. Consider changing this value based on system performance.

    Delta-T not proper. (I don't have a good enough understanding of precisely what this is...)

    Zone-side plumbing arrangement doesn’t provide for adequate hydraulic separation. For more efficient operation, closely spaced Ts and a circulator should be used to provide adequate flow and prevent cross talk among zones. Install equipment as necessary.

    21 pumps is overkill for system and wasteful. The entire system could be run using only 3 circulators, saving lots of energy each year. Remove existing pumps and replace with 3 high efficiency pumps and zone valves. When implementing these changes, tubing sizes and zone side plumbing to be addressed.

    High-pitched sound coming from 2nd Floor air handler. Determine root cause and fix.
     
    Last edited: Feb 4, 2015
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    "Tubing not sized properly for flow to / from storage tank. Each HP should push 18 GPM. Four of these would be 72 GPM. The tubing installed is 1-1/4 and steps up to 2” after the third pump connects. 2” copper will accommodate only 40 GPM. This plumbing needs to be increased in size to accommodate the flow from the HPs. "
    There is no reason a 5 ton it cannot live with 10 gpm on the load side, plus usually not all HPs are running at the same time.


    "Storage tank undersized. Rule of thumb is 10 G storage for each Ton of capacity; therefore this system should have 200 Gal. Only 80 was supplied. As mentioned above, the tubing size is also an issue as the 80 GAL tank has only 2” copper inlets. Additional storage capacity is required."
    I disagree. Although you see that rule of thumb in some installation manuals, read up about the purpose of the buffer tank.


    Controls for staging heat pumps are inadequate. The system as designed and implemented is very wasteful. The 406 is aware of only two heat pumps and the remaining two are slaved to the primary two by a simple timer. Contrary to the proposal that states, “For maximum efficiency, the system also monitors the energy demands and activates each the ground source heat pump individually and only as necessary.” the control system activates the secondary pumps very frequently when not necessary resulting in short cycling. HP2 DELAY was set to AUTO. Changing it to 20 min seems to have reduced short cycling to some degree. A more sophisticated control system is required.
    Yes, you essentially just have 2 stages


    Controls don’t adjust humidity target based on outdoor temperature - The Tekmar controls do not adjust the target RH value based on the outside temperature. The system was setup with a target value of 40% and I was given no instructions on requirements to change this as outdoor temperature changes. In addition, the system in the attic will require a trip up to the attic to modify this setting. The controls must be modified to use the outdoor reset to properly adjust the target RH level.

    Tank Design Temperature of 112 too high. The tank target frequently reached 120F which is a high temperature and leads to very inefficient COP; lowering the Design Temp to 100F is a 12% increase in COP. Consider lowering temperature even more to increase COP. Take into account heating requirements of Air Handlers and radiant under tile / carpet.
    No, it might be OK on the coldest days. You need to find out what is the coldest you can go. Depends on the efficiency of your distribution system.


    Verify tank target actually being adjusted by the 406 as outdoor reset.
    Yes


    Bleeders not on ground loops. Air separators should be installed on all ground loops. Install air separation units.
    Or switch over to non-pressurized flow center. See pumps


    Poor utilization of ground loops. Most times only 2 or 3 HPs are running. All ground loops should be connected via a manifold so that all can be utilized no matter how many heat pumps are operating. Connect all ground loops and install a single circulation pump.
    Yes, see flow center and pumps


    HP DIFF too small. The HP DIFF temperature was set to 4F, making the system over responsive. It has been changed to 8F. Consider changing this value based on system performance.

    Delta-T not proper. (I don't have a good enough understanding of precisely what this is...)
    Difference between incoming and outgoing water. Looked OK to me.

    Zone-side plumbing arrangement doesn’t provide for adequate hydraulic separation. For more efficient operation, closely spaced Ts and a circulator should be used to provide adequate flow and prevent cross talk among zones. Install equipment as necessary.
    Disagree. You don't want more pumps, you want less. All you need is some zone valves.


    21 pumps is overkill for system and wasteful. The entire system could be run using only 3 circulators, saving lots of energy each year. Remove existing pumps and replace with 3 high efficiency pumps and zone valves. When implementing these changes, tubing sizes and zone side plumbing to be addressed.
    Yes.
    High-pitched sound coming from 2nd Floor air handler. Determine root cause and fix.
     
  3. AndrewL

    AndrewL Member

    Thank you. So the significant factors are all of the circulators, the HP staging control, and loop field configuration.

    The loop circulation pumps' electric comes from the HPs, so their draw is baked into the power usage of the HPs--8 for the loops and 4 for the storage tank.

    I'd like to get a handle on bang for the buck to implement these changes. Below you can see some daily and monthly power consumption and cost figures. Can you point me to costs for these circulators and flow centers? If i'm essentially replacing pumps with valves, i would think the plumbing costs wouldn't be too bad b/c most of the existing plumbing would remain.

    How do I get a sense of the "efficiency of the distribution system?"

    I put together some power usage for the various components of my system. Data was taken over an 8-day period and averaged. I'm using an electric rate of 0.11 $ / kWH for the $ values. How can I determine BTUs used to do a comparison to the costs of other types of heat? I'd love to know if I should feel good or bad about the cost of running this system.

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  4. heatoldhome

    heatoldhome Geo Student Forum Leader

    I will throw my 0.02 in here. I am a Electrician and still learning Geo so keep that in mind.

    I would start with what we think is the most consumption. The 21 pumps on the load side.
    What I think you could do it figure out your total flow requirements and ft hd in the system, then pick probably a big Wilo stratos or what ever brand ECU variable speed pump your system needs. Then take the full wattage of that Ecm pump and divide that buy the wattage of all 21 circulators. This should give you a multiplier.

    Now if you have known usage from just the circulators multiply that by your multiplier and that should theoretically be close to what usage you would use with a Ecm pump.


    Example 21 pumps at say 250 watts each (yours will vary) = 5250 watts total
    ECM pump full load watts(guess)=400 watts
    400/5250=0.0761

    Say you track your circulators and they cost you on average $7 per day in electricity, in this example the Ecm pump would cost $0.53 per day on average.
    7x0.0761=0.53

    Not sure if this helps but if you plug your numbers in it should give you a estimated savings.
     
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    • Zone-side plumbing arrangement doesn’t provide for adequate hydraulic separation. For more efficient operation, closely spaced Ts and a circulator should be used to provide adequate flow and prevent cross talk among zones. Install equipment as necessary. Disagree. You don't want more pumps, you want less. All you need is some zone valves.

    I know doc dismisses this, but I'll defend it. Unless he sees a different way with the existing setup to not have the fan coils dictate an overall high temp.

    You can use less pumps with all the options available - combining the high temp fan coils on one multi-speed pump for example. I should have been more explicit in that regard. Zone valves won't prevent pump interference.

    • "Storage tank undersized. Rule of thumb is 10 G storage for each Ton of capacity; therefore this system should have 200 Gal. Only 80 was supplied. As mentioned above, the tubing size is also an issue as the 80 GAL tank has only 2” copper inlets. Additional storage capacity is required."
      I disagree. Although you see that rule of thumb in some installation manuals, read up about the purpose of the buffer tank.

    Well, with a larger buffer tank (and a proper deadband), I'd argue you don't need all the system staging. But, this is not a better way. Just different.

    Keep in mind, we don't often get to "rebuild" a system. As I step out the door, I end up having to work with what is pre-existing fairly often. And sometimes the $'s don't make sense to go after some things. Though, if I get called to replace a zone circulator and find the makeup water plumbing is inadequate or their is no air removal, I have to tell the client we have to increase the work we have to do.
     
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    You GO Chris.

    I have used Wilo ECM drive pumps since they got here, and Caleffi low CV zone valves since they got here.

    There are some days when primary/secondary, injection piping works better for a given comfort level. The pumps are cheaper and given a choice I make them all the same size. Then toss an extra pump on a shelf in the mechanical room, new in the box.

    Mark
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Chris,
    I guess with modern constant pressure pumps I don't see the need for individual pumps on each zone (which is part of the culprit here), I also do not see the need for primary/secondary piping. Simply have a variable speed pump there with some zone valves, the buffer tank is your hydraulic separator. May be that is partially why I do not see the need for a larger buffer tank either.
    I welcome to discuss your rationale.
    I mentioned before that I like the idea of having 2 separate load circuits, one for higher load temps like the fan coils or carpeted areas, fed by a couple heat pumps, depending on the exact load requirements, and a couple heat pumps serving a low temperature distribution circuit. That way you save energy because of a lower supply temp to part of your house. Yes, a separate load circuit would require a separate buffer tank.

    Sure, you want to salvage the heat pumps, maybe a couple circulators, the buffer tank, but the rest you should simply cut out and repipe.
     
  8. dgbair

    dgbair Just a hobby Forum Leader

    Andrew, not sure if you got all your questions answered or not... There are many options here and it will come down to the person who is doing the work to choose the 'best' option. The guys here can point you in a direction but the exact route you want to take is hard to say. Is your original installer back in the picture at this point?

    Focusing on the loop side... IF I understood your loop field (and that is a big IF), a new non-pressurized system like doc was talking about goes for $5k on the web. (ie flow center GV20) MAX power consumption is 620W vs your current 8 pump setup of (230W)*(8)=1840W. Given your load data, I would think it would be reasonable to downsize to the GV15... 450W max.
     
  9. AndrewL

    AndrewL Member

    dgbair,

    Original installer is not back; and I'm not optimistic about that avenue. If I installed a second tank and had one or two HPs dedicated to it, this would then limit the stages that are available for cooling in the summer--unless the piping was flexible enough to allow them to work both separately and in tandem. From a gut level, I would assume 3 HPs on the high temp / cooling and one on the lower temp radiant.

    To install that flow center, would I just connect the loops in a manifold type arrangement? 4 loops > manifold > flow center > manifold > zone valves > HPs > manifold > 4 loops?

    Is there a way that I can back into BTUs from the HP usage to see what the heating costs would be using other fuels or is the fact that the distribution is less than ideal impacting the efficiency of the system?

    Doc, do you make house calls in Eastern PA? While I have the know-how and skills to do all of the plumbing and most of the controls, I'd rather not take this on myself in the middle of winter. There are also a few other tweaks to make--like ensuring a constant floor temperature in the bathroom (rather than relying on the wall thermostat sensing air) and I have separate electric radiant system for heating my kitchen counter tops that I'd like to add as an additional zone on this system, to utilize the Geo. Any salvage value for all of the pumps that I have? They've been in use only a few months--since November/December.

    I'm still not sure how to control the 4 HPs better. One thought it to buy a programmable PLC and write an algorithm myself. It would seem that the target temperature, actual temperature and outside temperature should all be inputs to this.

    Thanks

    Andrew
     
  10. dgbair

    dgbair Just a hobby Forum Leader

    Let's look at the loop side:

    Head pressure per circuit (@15GPM/circuit):
    ~20' for the unit
    ~10' for the 400' of 1.5" pipe
    ~17' for the (400' of 3/4" pipe (x4))
    ~47' of head pressure total​

    Looking at the Wili-Stratos data - GV15z2 should do the job ... (assuming there isn't a ton of fittings)
    GV20 looks like it can only handle ~32' of head at 60GPM
    This is where a pro should chime in. ;-) They usually know if/where they can take a short cut.

    -- yes, and trying to keep your pipe elbows to a minimum. I would also step up/down your manifold as you bring-in/take-out branch circuits. (I just realized I never install a half decent drawing program on my computer since the re-build... guess I'll need to do that.)
     
    Last edited: Feb 8, 2015
  11. AndrewL

    AndrewL Member

    At present, each loop has 5 90 deg elbows, and not the sweeping kind, in the house. One loop has 6. That is on both supply and return, so total elbow count is 5 x 2 x 3 + 6 x 2 x 1 = 42. I'm not sure I can determine what is outside the house, but I would err on the side of caution.
     
  12. heatoldhome

    heatoldhome Geo Student Forum Leader

    You could find your current ft of head or pressure drop on each loop by measuring the pressure drop at the units Petes ports then compare that to your circulators pump curve.

    The pressure drop should give you a gpm figure for that loop. Then go to the pump curve and see how much total ft hd you have. (This will include the gshp exchanger)
     
  13. dgbair

    dgbair Just a hobby Forum Leader

    And you will need to pay close attention to this.... if you can't re-coup money on the old pumps, it will be real tough to justify new ones...
     
  14. AndrewL

    AndrewL Member

    Any recommendation for a pressure probe?
     
  15. dgbair

    dgbair Just a hobby Forum Leader

  16. dgbair

    dgbair Just a hobby Forum Leader

    Running some of your number again and something doesn't seem to add up.
    Edit: Darn, I knew something didn't add up... and it was me, I had a zero where it didn't belong.

    If I break your load into 3 - 5 ton HP, I get a annual heating cost of $1507. So that would be $4521 total.
    Add on top of the circulators for 3 units (245W)(6)=2070W
    The run time I get for heating is 2544 hours.
    (2.07kW)(2544h)(.11)=$580 for annual heating cost

    So a total bill of $5100 (I'm not using your exact model number)
    But looking at your chart (ignoring HP#2) at a 30 day projection you have: $224+299+182 = $705 for the month......
     
    Last edited: Feb 9, 2015
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    How are you getting an annual heating cost of $420 with 3x5 = 15 ton heat pumps running?
     
  18. dgbair

    dgbair Just a hobby Forum Leader

    Doc, I didn't realize that the append posted. :-( I was just running some quick numbers and I knew I made a mistake somewhere when entering in the data... I was just typing up the numbers in my browser as I went along and unfortunately it got posted.

    The updated numbers are surely better but I really never intended to post it at all.
     
  19. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I just do this for a hobby. Doc thinks I make all this stuff up because he will not try to communicate. His loss.

    dbgair:

    I love what you post. Keep up the good work.

    Mark
     
  20. AndrewL

    AndrewL Member

    We need to include #2 as it was supplying heat over this period (and not just short cycling).

    Including #2, I'm at $756/30 days. Total run time across all HPs averaged 46.9 hrs / day. Cost per day, at $0.11 $/kWh is 756/30=$25.2. So the cost is $25.2 / 46.9 running hours = $0.54 $/HP-hour.

    2,544 / 24 = 106 days of constant running. If we assume 3 HPs running for 2,544 hours, that would be 2,544*0.54*3 =$4,121 to supply heat for the year. The power for the loop circulators is included in my numbers. The control system and 9 zone circulators are $2.11/day, but they should not be included in this.

    These numbers are in the ball park of yours, and my numbers are based on an average outside temp of 21.6F

    So, does this seem reasonable? Can we determine BTUs to compare these numbers to other energy forms?
     

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