Pennsylvania Low Delta T & Short Runtimes

Discussion in 'Maintenance and Troubleshooting' started by csementuh, Jan 20, 2017.

  1. csementuh

    csementuh Member


    Near Pittsburgh, PA. I have a 3.6 ton Carrier GTX setup with two zones of forced air in a 2600 ft^2 two store house. Unit is controlled by a Honeywell HZ432 panel and two Honeywell zone motor gizmos. New construction, finished July 2016. Now that we've been in the house for 6+ months and I finally have some temp data (thanks to a Raspberry Pi & Domoticz setup) I am seeing some things I think may be concerning...

    My Delta T of EWT-LWT is very lowww. I only have about 12 hours of 'good' data, but I'm seeing maybe 2* at most and lots of negatives? Perhaps the negatives are because the system is off? Right now outside temps are cold, 35-50*, and my EWT is quite chilly!


    - I will change my filters tonight, just in case. Some basement drywall finishing may have clogged them quickly.
    - My Grundfos pump is set to a medium flow, do you think my flow is too high and hence heat isn't transferring well?

    Another oddity I have found is that the system wants to kick on and off more than I expected. I envisioned a long time run, low and slow with a geo system, however there are times where the system will kick on for 5-10 minutes to satisfy a zone, then kick off for 5-10 minutes and then back on for another short cycle. Is that normal? Doesn't sound super efficient..

    -I had the well people out once to verify the loop and they indicated that they re-purged the close loop and it seemed fine.

    On a positive note, I do think my desuperheater is working well, as the in and out temps going into my buffer tank are in the 110-120 region, which seems great! Also, after a shower, the system seems to recover the heat pretty fast, despite dropping to 50* water during the shower. The delta T of the DSH system is also quite low, just a couple degrees, but it seems to be doing something overall, as I can't image the 110* water comes from thin air, (unless my finish tank is somehow sending it backwards?). If you notice the two big dips down to cold, that was two morning showers at 7:05AM and 730AM that brought in a flood of cold water. It does look like the temp recovered pretty decently!


    Any thoughts on how my system is running, and other things to test or monitor? Thanks!
    Last edited: Jan 20, 2017
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You are likely a victim of sensor calibration, or a lack of such.

    You EWT is around 40F , not chilly but warm. Your system likely only runs in 1st stage, thus a lower delta T.
    If your sensors are correct, you might over pump your system a bit. what is your model number? of your heat pump and your circulation pumps? How many loop field circulation pumps do you have?

    Your system seems to be running fine, let it run and enjoy geo.
  3. csementuh

    csementuh Member

    Hello and thanks for the reply! Yes, the house is comfy, so I don't think there is a major issue, but perhaps only a small problem or performance issue.

    The sensors are the stainless steel tube 1-wire sensors from SheepWalk Electronics UK. Totally could be a calibration issue where one is off a little, but those sensors generally have a good track record of providing good data.. I slit the heavy insulation on the lines and push a sensor down inside along the pipe then tightly wrapped back up. Now one thing, I did have to go about a foot into the lines where they're inside the cabinet, because as soon as they enter the cabinet they go through the coil and make a sharp bend to the rear. I installed the sensors there toward the rear in about the same place on both lines in/out. The DSH readings are right where the water enters and exits the cabinet inside, and the sensors are covered in metal tape and some foam.

    Yes, EWT is around the outside temp or a little warmer so I guess OK. I don't have a basis for comparison with anyone local, except for a guy at work who told me his is 60*, but I doubt he has ever measured properly in winter.

    Dumb question is, why am I seeing negative delta? Shouldn't the water leaving always be colder when in heating mode? What would cause the system to put heat back into the water?

    Should I kick the heat up and force a 2nd or 3rd stage heat to see if I can get a bigger delta T? I'm certainly not stressing over it, but I was thinking I should see more then .5-1.5 degree difference? Some people state they have 5-10* easy. I guess cooling in the hot sun may be better!

    I was thinking perhaps the water flow is a little high. Can I safely troubleshoot by lower the pump flow setting to low? Is it more efficient to have more delta (more heat transfer) vs the higher flow? I'm just looking for efficiency here.

    Heat pump is a Carrier unit, model # GT036VTLCDET1XX1

    gt = top tier
    036 = tonnage
    v = vertical cabinet
    t = discharge top vertical
    l = air return left
    c = copper source heat exchanger
    d = desuperheater
    e = fan motor ecm
    t = tin plated
    1 = voltage 208v/230v
    xx = nothing
    1 = domestic package

    The borefields are 3x vertical wells, 185' deep, spaced about 15' apart and filled with Bentonite clay. Just dug in May 2016.

    Not 100% on the pump, but there is only one I believe and it is a Grudfos setup with two in-outs and the one pump body installed. On top of the pump body is a little switch for low-med-high. I can get a model number when I get home.

    Here's a pic:
  4. Andrew Kulin

    Andrew Kulin Member

    With respect to your temperature data it is very odd that you have some very noticeable spikes in LWT where the LWT greatly exceeds the EWT, which shouldn't be the case in heating mode. I also notice that as the time approaches 3 PM, your EWT also shows a noticeable rising trend. Is your thermostat/system set up such that it can automatically switch between heating and cooling mode depending on the temperatures inside the house? Perhaps that may explain why LWT sometimes exceeds EWT and seemingly at random. You may also be able to correlate these oddities with what you are aware of going on at the house. Maybe your new home has a big panoramic set of windows facing southwest, it's a sunny day and the thermostat is in that area and temperatures rise above your set-point and so the system runs in cooling mode.

    I just purchased a WEL kit to do my own temperature monitoring and installed it last weekend up at the cottage and I was in contact with Phil (the guy who makes and sells these devices) discussing installation strategies. With my EWT/LWT he told me not to install them inside the furnace because he felt that heat off the compressor unit could affect the sensor readings and he recommended that I install them along the plastic hose between the flow center and the P/T ports. He also told me to wrap the wire around the hose a few turns so that it wold be at same temperature as the probe because he found that could also affect the accuracy of the temperature (heat coming in off the wire). So I installed as he suggested, including applying a thermal paste to one side of the probes (I had thermal paste that is used for computer heat sinks lying around (used between the CPU & its Cooling heat sink) which Phil said was fine, then wrapped it tightly with metal tape, and topped that off with a hose clamp which I tightened snugly, but not tight enough to bend, squish or otherwise damage the temperature probe). This is illustrated in the attached photo. I then replaced the foam insulation around the entire assembly and used electrical zip ties to hold the insulation in place tightly.

    The other thing he told me to do was to then calibrate the sensors by measuring the temperatures at the P/T ports, comparing to the readings off the sensors and applying an adjustment (+ or - value) to the raw data so that temperature on the sensor matches the temperature on the thermometer (digital probe, using same thermometer to measure at each P/T port.

    I agree with Doc that calibration of the temperature probes is likely one cause but would add that the EWT/LWT sensors may not be making good contact with your piping/hoses based on how you described their installation on those lines. You implied that the readings from your DSH seemed to be what you expected and I see from your post that you installed the sensors on those pipes more in line with how Phil told me to install mine.

    Attached Files:

  5. Stickman

    Stickman Active Member Forum Leader

    Your negative delta T is possibly when the system is off and the LWT sensor warms up to ambient. The graph below is from the last 24 hours of my system. Each spike in LWT is when it cycled off.
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Your system seems to be running fine, appears to be well designed. The raw data you display appears to be prone to sensor readings influenced by factors which you misinterpret. For example, some residual coldness in the heat exchanger can cause EWT and LWT go in different directions, so can the influence of ambient heat, different conductivity of the material used, among other factors.

    Do not fall for the illusion of precision. The monitoring is great, learn from it how your system behaves, but you are also the one who needs to learn to interpret the data correctly without jumping to the conclusion too quickly.

    The holy grail of understanding the monitoring and to learn from it is not to answer the questions, but to question the answers!
  7. mrrxtech

    mrrxtech Member

    Consider turning off the desuperheater pump during the heating season if the back up electrical heat comes on. It would be wiser to heat the hot water tank with heating elements than to heat the house with heating elements, since the hot water tank will use less power to keep the water warm.

    3.6 Tons in a 2600 sq ft home will prove to be too small when the cold weather stays with us for a few weeks below zero. I have 4 Tons in a 2300 sq ft home and wish I had a 5 Tons or one of those Inverter powered variable speed compressor Geothermal Units that can produce 1 Ton over the rated capacity. A 4 Ton Variable Speed Compressor can produce 5 Tons when needed.

    I would have put the temperature sensors outside of the Unit, since the fan motor produces heat that can warm up the internals of the Geothermal Unit causing your water temperature spikes. Take the cover off of the fan compartment after the Unit has been shut down for 5 minutes and you'll see why your LWT is spiking high. If you want to know the inlet & outlet temperature, why not measure at the inlet and outlet immediately outside the unit. The area where the heatpump is housed probably will stay at basement temperature during the winter, which will still cause a warmup when the loop temperature is in the 20s, which it will be before the winter is over.

    My Trane owners manual directs me to pull the fuse for the Desuperheater pump when in the Heating mode. Apparently no other company sees this as an issue, trying to heat the hot water tank while the Unit is working hard just to maintain set point temperature in the house.
  8. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Superheat is best used in domestic water vs. heating a mechanical room at best.
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Wouldn't it be wiser to make your hot water with the efficiency of the geo system throughout the heating season, rather than worry about the electrical heat coming on during occasional cold weather periods? That way you use the capacity of the geo heat pump much better for the whole winter.
    The unit is 3 tons, not 3.6 tons, and might be very adequate sized for a new built 2600 sqf house Pittsburgh, as indicated by the short run times during weather in the low 30s during Jan 20th in Pittsburgh. Title of the Thread? "Short Runtimes"! Nor do you have any clue how the loop will perform. If the loop is around low 40s right now, it is very well sized and will not drop much below 35F by the end of the heating season.

    Indeed no other company sees this as an issue, not even Trane, because it is no issue. Making your hot water full time via electric resistance heat will use up much more energy than you gain by increasing the heatpump capacity by 10% (witch is about the DSH capacity you propose to eliminate) during cold spans requiring supplement heat.
    You continue your pattern: Not understanding how geo systems work, and giving bad and unrelated advise to people coming here for help, misleading them.
    Last edited: Jan 23, 2017
  10. ChrisJ

    ChrisJ Active Member Forum Leader


    "My Trane owners manual directs me to pull the fuse for the Desuperheater pump when in the Heating mode. Apparently no other company sees this as an issue, trying to heat the hot water tank while the Unit is working hard just to maintain set point temperature in the house."

    Please post the manual that states that.
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Yet another example of Wrecks diverting the scarce and valuable support resources of this site's members to debunking his nonsense.
  12. csementuh

    csementuh Member

    Thanks for the responses gentleman!

    Yes, I'm thinking that negative delta T is just the unit's off time. Actually coming today in the mail I have an energy monitor that I can hopefully monitor and graph along side the temps. That should show me when the unit is on and it should coincide with the temp differences. I will certainly think about remounting the probes in a different location as well.

    I bought 4 ZWave energy monitors so I'm hoping to break them down and monitor the whole house, the geo unit's 3 breakers, my heat pump water heater circuit and then finally my server rack. That way I can get a pretty specific breakdown of what is sucking up all the juice! I'm especially interested in seeing what the geo costs per month vs a natural gas bill, also what the 'base house' energy usage is minus the geo and HW generation. All LED lighting and nominal other stuff and I think it will be low. Right now I'm seeing $160-$225 a month electric bills at around $0.12 a KWH so I'd like to see where it's going. :)

    I do really hope my heat pump is sized correctly! This house is only six months old and I paid around $36K for the complete geo setup (Damn builders! ;-) Includes 2 zones of ductwork in new construction, and my DSH work for the second HPWH tank. The builder was clueless but picked a HVAC contractor who said they had the geo experience. I was told that Carrier is sent a copy of the house plans and they do a manual J assessment on the house, but I never saw this. The house is insulated pretty well, and I actually insulated all of the interior walls for sound reduction as well (but I do have a big open foyer which kinda negates most of that). So all in all I'm hoping this system is appropriate for the house and will give us many, many years of worry free operation.

    Here's a quick question: To what temperature should I be 'happy' that my geo works without engaging the supplementary electric heat strips? Just looking for a quick metric here so I can monitor it all. I guess the target may be 'all temps' but I know that isn't practical when we sometimes get -10 or worse temps in the winter and 100+ in the summer. The short run times had me convinced the system is actually 'too big' but IDK I'm just a learning novice here.

    I was in the bottom cabinet and I saw a lot of condensation pooling on the part I believe is called a 'filter-drier'. Is that normal for 1/2 cup of water to be laying in the lower cabinet there (and not in the top where there's a condensate drain)? I'm thinking and hoping this is just because I had the door off and the air condensed there, but there is a stain like it has happened before.

    Thanks as always!

Share This Page