Prince Edward Island Excessive kWh/day

Discussion in 'Maintenance and Troubleshooting' started by lieut_data, Dec 7, 2020.

  1. lieut_data

    lieut_data New Member

    I'm very new to the geothermal scene, having just recently purchased a home on the island with such a system, distributing via in-floor heating to the ~1800 square foot, slab foundation house. As a family of six (doing lots of laundry), we're accustomed to 1000-1200 kWh/month over the past few years.

    Having been heating with oil and a small pellet stove, the idea of saving money with the geothermal system excited us! Unfortunately, this past electricity bill for October/November billed us for just over 3000 kWh. We're on track for 3500-4000 kWh this month, and it hasn't even consistently gotten below freezing! (We lowered the thermostats for a day to confirm the daily kWh dropped accordingly, even though the system was still contributing to the hot water heater.)

    Given the daily kWh usage, I have a feeling that something isn't working correctly with the system, and I'm trying to engage with the original installers -- put in about 10 years ago -- to try to figure things out. But I get the impression that I'll make the most progress if I try to take ownership of the problem for myself. A lot of this new vocabulary, so if I make a mistake, please help correct me!

    Note that when we first powered on the system, the overflow valve on one of the buffer tanks was leaking a small, but consistent amount of water. I put a bucket under it, and it eventually stopped leaking when the system got up to pressure.

    The unit in question is a Geosmart Premium E. I believe I have an open loop setup, with two wells connected to the system (one used for drinking water). The five distribution zones are controlled by single wire thermostats. I've taken a stab at diagramming the pipes as best as I can understand it, but am not sure where to go from here. See attached image -- feel free to challenge anything! I'd be happy to share pictures of the actual setup as well, but the room is definitely chaotic -- it used to use an electric heating system that's still there, but closed off.

    A few open questions that I'd love to understand better:
    * It's not clear why I have /two/ buffer tanks.
    * It's not clear why both desuperheaters are connected to the same buffer tank, one at the top and one at the bottom.
    * There's a closed valve that appears to connect the cold water distribution with the hot water distribution. (It's a tiny valve, like the kind on in-floor inputs.) I have no idea why it's there.
    * I was surprised to realize that I'm circulating "new" water under the floors all the time, or at least as I consume hot water, instead of the in-floor heating piping being closed.

    How can I best equip myself when the installers come and try to figure out what I think is excessive kWh usage? Much obliged for any help!


    Attached Files:

  2. gsmith22

    gsmith22 Active Member Forum Leader

    most geo units have electric resistance heat included. Depending on system design, this may have been done to cover the few coldest days of the year (possibly because the loop field, equipment sizing, or some combination of both would have gotten prohibitively expensive otherwise) or is simply present to be a backup source of heat in an emergency should there be a unit failure. I would start there and see if you a) have electric resistance heat and b) has it been running. Elec resistance heat uses a lot of electricity so its the common starting point to see if that is the culprit. If the answer to both of those questions is yes, then you need to figure out why its running so much - whether its a problem with the system or its by design. Its early in the season so a design reason seems unlikely to me.
  3. SShaw

    SShaw Active Member Forum Leader

    It all looks pretty standard.

    One buffer tank is for the domestic hot water. This tank holds pre-heated water going into the water heater.
    The second, larger, buffer tank holds the heated water for the in-floor radiant heating system.

    You have one desuperheater. It has a loop with the output going into the buffer tank and an input coming back from the buffer tank. Water comes in from the buffer tank, heats up inside the heat pump, and is returned back to the buffer tank. That's how the buffer tank gets hot.

    This looks like a connection to the domestic water supply to allow for topping-off and pressurizing the closed loop system used for the in-floor heating.

    Your diagram shows the in-floor loop as a closed system, as it should be. Why do you think you are consuming hot water.
  4. lieut_data

    lieut_data New Member

    Thank you both for your replies!

    Working backwards: you’re right, I was mistaken about in-floor loop being open. And the loop for the desuperheater makes a ton of sense!

    The ability to top off and pressurize the system hadn’t occurred to me! If I look at the pressure gauge coming out of the buffer tank and into the radiant system, it reads about 5psi. Could this be a problem?

    On the electric resistance heat, the exterior label on the geothermal system has a section to be filled out as such but is left blank. I admit I’m not sure how to check further to determine if there is still one inside and if it’s running, but I’ll try to get that answered when the installer has a chance to come out.

    Lastly, I’ve been up since about 4:30am my time hearing the system run and wondering what’s going on. I came out here and watched the temperature reading on the unit hit 110, begin to shut off, and then over the course of just 10 minutes, drop to 101 and start all over again for about 15 minutes. Any thoughts on what might trigger such a dramatic loss of temperature?
  5. SShaw

    SShaw Active Member Forum Leader

    Perhaps you have air trapped in the lines, which would require purging each of the in-floor loops. Probably best to have the installer come out and make some measurements on the load and source sides to determine where the problem is.
  6. ChrisJ

    ChrisJ Active Member Forum Leader

    There must have been a call for in-floor heat. Cement slabs quickly suck heat out of water. I would check to see if there is an electric element in the load side buffer tank connected to electric

    In the diagram it looks like the 184L tank is the finish tank for domestic hot water(DHW). Is that an electric tank? The heating elements are running a lot with lots of laundry/hot water use.

    It also looks like this is an open loop on the source side, which means the well pump runs whenever the heat pump is running.
  7. gsmith22

    gsmith22 Active Member Forum Leader

    google "electric resistance heating element in furnace" to see what these look like. Essentially they look like a bunch of slinkys stretched (usually) across the output end of the heat pump duct work.

    But ignore what I wrote - just looking back at your original post, you state in floor heating and your diagram shows a water based system so with a water-to-water heat pump you won't have slinky style electric resistance heat because you won't have ductwork. Electric use is therefore coming from the heat pumps, all of the pumps used to distribute the water around the house, your open loop well pump, or as ChrisJ pointed out maybe from electric hot water heating tanks. Its probably some combo of all of these things. Maybe the best way to get a sense of where the electric is going is to get a clamp meter and systematically hook it to one lead on the electric feeds to all of these elements to see what type of current they are all pulling. Amps x voltage = watts and with some estimates of runtime for each of these items you will be able to back into how much electric they should be using on a monthly basis to confirm your bill. THey actually make tracking systems like this with small clamp meters on the feeds in the electric panel so you can track usage over time.
  8. lieut_data

    lieut_data New Member

    Thanks for all the replies! The installer kindly came by and addressed a remarkable number of things:
    * Broken pressure reducing valve
    * Punctured water bladder tank
    * Defective capacitor in the geothermal unit itself

    He also had some history on the original install, and it turns out that the pumps to actually move the water throughout the system were controlled by the /old/ electric heating system which I had left off altogether. He was surprised we had managed to heat anything over the past few weeks!

    The house warmed up wonderfully (beyond what we had experienced previously) after these repairs were done. Electricity usage still seemed high, but I discovered the garage heating engaged and quickly disabled that. I'll give it a few more days to see where it goes from here.

    I am worried about remaining air in the line, as I saw the pressure drop to 0 again tonight. I brought it back up by forcing open the pressure reducing valve (which I thought was supposed to engage automatically, but maybe it needs further turning). I may consider draining the lines to force all the air out if this doesn't resolve itself over the next few weeks.

    Appreciate the help, and I'll keep you updated :)

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