Minnesota Geothermal runs 24 hours a day

Discussion in 'Maintenance and Troubleshooting' started by DanielX, Dec 13, 2014.

  1. DanielX

    DanielX New Member

    Last week we installed a water furnace 7 series 4 ton geothermal system. We have four vertical loops each 200 feet. We replaced a propane fueled forced air furnace. The temperatures have been mild, 30° to 40°F. Since it was installed a week ago it has run continuously. It's cycles up and down through the various heat settings and fan settings, but never shuts off. If I look at the energy usage on the thermostat it shows that it is running 24 hours a day for the last week. I'm concerned that when the temperatures fall which they will easily do the system will not be able to keep up and I will be constantly running it on the auxiliary 15 kW electric heat strip. I emailed water furnace, and their response was basically told me to talk to the installer. I emailed the installer and they said that it is a variable speed fan motor heating system that is designed to run all the time. Does this sound the correct? From what information I could find online, the geothermal system is supposed to run more often, but not continuously 24 hours a day.
     
  2. birkie

    birkie Member

    The variable speed compressor on the 7 series can modulate virtually anywhere between roughly 20% and 130% of nominal capacity. The control logic in the thermostat attempts to match compressor output to the load of the house. So if the control logic is doing its thing correctly, and the load of the house is above the minimum compressor output, then it will run 24x7. This covers a very wide range of temperatures, so it is not surprising that it's running 100% of the time when temps bounce between 30 and 40. In fact, it would be more concerning if it didn't!

    So on its face, there's nothing about your observations that indicate a problem. Do you mind it running all the time from a noise or comfort perspective?
     
  3. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Is it just the fan running? Thermostat set to fan auto?

    What speed is the unit running at? If at full speed (12), then there may be concerns. If at lesser speeds, it may just be matching building losses in capacity. As it should.
     
  4. DanielX

    DanielX New Member

    The fan is on auto. Fan and pump speed vary from 1-7. 12 speeds available. I just thought it odd that it never shuts down completely.
     
  5. DanielX

    DanielX New Member

    The fan is on auto. Fan and pump speed vary from 1-7. 12 speeds available.
    i don't mind it running, just wanted to make sure it was behaving as designed and intended. Thanks for the help!
     
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    That's exactly what it's supposed to do. New modulating furnaces will do the same thing.
     
  7. SeekingAdvice

    SeekingAdvice Member

    DanielX
    My 7 series 5ton does something similar by design. The key would be check the thermostat and see which stage is it running at.
    Mine runs for 23-24hrs a day if the temp falls below 40. Around 35-40 it is stage 1/2, when if falls into the lower/mid 20s it is stage 4/5. Plus every 30 minutes it will bump up to stage 6 to get oil running through the compressor.
    Although your temperature/stage levels might differ from mine (your design minimum might be lower than mine), but as long as it is running in a lower stage at 30 to 40 it should be fine.
    If you look at the history section of the thermostat though it only says stage 1/stage 2, which it defines stage 1 as stages 1-6 and stage 2 as 7-12.
    So, look at it realtime to see what stage it is running in, and then if you look at the history, look at the daily kWH. For my 5 ton, stage 1 is ~800kW live, or 18-20kWH/day, stage 2 stays just below 24kWH/day, while stage 4 is 45-50kWH/day, and if I extrapolate stage 6, it would likely be at 55-60kWH/Day.
    I haven't seen stage 7+ yet, and again, my system is larger, so your numbers (I assume) would be a little bit lower (you have 80% of the capacity I have, so it should use less electricity).

    To go on a second rant, that has already partially be covered:
    A typical 2 stage ground source heat pump can either run at 70% or 100% of rated capacity, and at the coldest part of winter should be running at 100% 99.9% of the time (if properly sized).
    The WF 7 series has a variable speed fan, pump and compressor to run as low as 20% of rated capacity, so that your 4 ton can operate as a 0.8 Ton system. If setup properly, it would not go to Stage 2 (of 12) until the control board determines that stage 1 cannot maintain temperature, thus providing long (continuous) run times for efficiency. My 7 series is designed to be always on at a stable temperature below 42F (most of Dec, "all" of Jan/Feb and most of March).
     
    Last edited: Dec 15, 2014
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Here I go again.

    When looking at heat pumps in general one is looking at a system in motion. As conditioned space temps change so do pond, ground or outdoor air temps change. The only time operation is stable is in the test lab.

    This is sort of like the "nest" TV add where grandpa say when the internet goes to the dark side the kids will not be able to run away on spindly legs caused by, setting the "nest" with their phones. The anti-point is w need exersize.

    Now with a VRF machine we add something new. The machine is designed to never turn off. Never turning off stops the on/off issue of mechanical wear and start/stop power demands.

    SOOOOOOOOOOOOO. If sized correctly and designed correctly your machine is doing what it was told to do by it's manufacturer.

    Un-like the Cleveland Browns..

    What needs to be looked at is how much does it cost to be running when.

    Mark
     
  9. mrjazz

    mrjazz New Member

    It's pretty obvious that Water Furnace should put a notice in large letters on the 7 Series owner's manual that if you are in a cold climate, don't expect your unit to turn off until Spring arrives. Excepting an unnaturally warm day in there, I don't think these things will ever be off. I had a three ton 7 Series installed on Wednesday (replacing a Premiere 2). This unit is for my first floor which is about 1500 feet. The masterful installation was by Ryan, Inc. in Union N.J (about whom I couldn't possibly say enough nice things) and they had the unit up and running by 4 pm. The first day it ran for eight hours, from 4:00 to midnight and since the first floor space was about 48 degrees at turn on, it ran about half of the time with auxiliary heat for a total of 38.1 kw/h, to get the temperature up to 65 degrees, for a cost of about $4.95. The next day it ran for 24 hours for a total of 30.8 kw/h for a cost of about $4. The next day (Friday) it ran for 24 hours for a total of 24 kw/h for a cost of $3.12. I guess the hopelessly insecure (of whom I number myself) will just have to get used to the idea of something being able to run 24/7, just like your heart. Sunday is supposed to be a little warmer so it'll be interesting to see how much time it spends off.
     
    Last edited: Jan 17, 2015
  10. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Sorry about the Browns, they keep running all the time too.

    Your heat pump will not turn off.

    Your heat pump will not turn off, if there is a call for heat or cooling.

    To get why, one needs to know a bit about toy trains. Model toy trains run on DC motors. To make the train go faster one needs to turn up the voltage of the transformer. The train goes faster. To slow the train one turns down the transformer/voltage and the train goes slower.

    On and off is the wear point on electric motors. Once spinning they are happy at their steady state operation.

    Westinghouse and Tesla won the battle with Edison over ac/dc,(not the band or sexual preference). A/C won because of shipping costs. Now the light bulb turns on over the heads of the electrical engineers, and we take all motors back to our toy trains. We do that with ECM drive motors. They work like the toy train locomotive.

    So once the EE guys got blowers and pumps to do what they wanted when they wanted, they moved onto variable flow refrigerant systems. This is sort of newer engineering, they are not done with it yet.

    To error is human, but to really screw things you one needs a computer. That is where we are now.

    Once the toy train is going the EE guys do not want to turn it off. So they added ECM drives to refrigerate systems. NOW they control all of the electrical motors in a system. Your normal home A/C is either on or off and the EE guys adjust the comfort settings with blower speed and run time. Now we vary the amount of heat transfer taking place by controlling how much refrigerant we move, using ECM drive compressors.

    What could go wrong?
     
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I liken it to "highway" vs "city" miles. As a kid shopping for a car I always heard that comparison. It was explained to me that city miles were much worse on a car due to all the starts and stops.

    FWIW, new variable furnaces will behave the same and we dealers need to remember to have our client's expectations in the right place.
     
  12. Dan Dillner

    Dan Dillner Member

    Very interesting discussion and good explanations! (I always admired how Einstein could explain his new theory in terms average person could relate to. Unlike his fellow physicists he gained enormous notoriety & interest in his topics and caused many young people to follow and study physics.)

    How about the water source is it a variable as well in the WF 7? I know in a loop system circulating pump energy is low but in a open standing column well it is much higher.
     
  13. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Yes - WF 7 outputs a modulating signal able to control a water valve or variable speed circulating pump.
     

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