Enertech Geo-therm w/ HBX CPU-0500 not entering stage2

Discussion in 'Maintenance and Troubleshooting' started by TimF, Jan 23, 2013.

  1. TimF

    TimF Member

    Now that weather has finally dropped well below 25F for the past several days, I've noticed my 2-stage Enertech GeoTherm (GT058A11AAACSS) HP doesn't seem to ever be going into Stage 2...at least I'm not seeing anything other than '1' directly under "Heat" on my HBX CPU-0500 controller console. I placed my hand on my first floor air handler strip heater box and it is not warm to the touch... it seems to be the same temp as the rest of the air handler sheet metal in the area of the heat strip box (which is basement temperature about 50F). My first floor Honeywell VisionPro IAQ thermostat is set to AUTO, HEAT and 65F and I haven't seen anything in it's Operating Manual for specifying anything regarding stage 2 or time delays.

    I've checked the programming of the CPU-0500 and have verified the following settings as described on pp 16-18 of the documentation:

    System Temperature 1 = 110.00

    Design Room Temperature = 70F

    Design Outdoor Temperature = OFF

    Heating Differential = 10.0

    Warm Weather Shutdown = 60.0 (I've configured this to handle the temp swings between night and day during the border months)

    Use Backup Temperature = OFF (If set to OFF, the backup (stage 2) will come on only based on time delay")

    Heating or Cooling Priority = ON (Heating Priority)

    Minimum Lag Time
    = 3.0 (Choose the minimum lag time between heat pumps in a multi-heat pump application)

    Stage Selection = 2 (2 stages of heat pumps without rotation. Use the 2 stting when a backup is being used. This way the backup will not rotate into the number 1 position)

    Based on the above, it would seem Stage 2 should be entered via a time delay, however, the definition of Minimum Lag Time seems to apply to a multi-heat pump environ. In any case, the HP has been running almost consistently with overnight and early morning temps in the -1F to +7F.

    I'm looking for:
    1) confirmation on if my CPU-0500 is set correctly
    2) if so, should the CPU-0500 be providing the time delay (either via the Minimum Lag Time setting or by other default and if not, what is the source of the time delay)
    3) beyond the CPU - 0500 console, is there anything else I can check that would verify if my HP is in fact going into stage 2.


    Thanks in advance.
    Timf
     
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    If you have a two stage heat pump with aux heat, you really have three stages. Does your tstat have a three stage setting?
     
  3. TimF

    TimF Member

    Palace,
    Thanks for your reply. I have the ability to set the thermostat to one of the following: HEAT, COOL or AUX HEAT. My understanding is regarding this thermsotat is that when in HEAT mode,if the set temperature is 2 degrees or more higher than the room temp, the thermostat will tell the auxillary heaters to turn on. Other than that, I don't see any user settings related to anything other than date, time, on/off cycle programming and filter reminders...at least nothing that would appear to be related to aux heat or stage settings.
    Timf
     
  4. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Can you change this to 3 ? You will have to go into the installers menu or advanced settings
     
  5. TimF

    TimF Member

    Palace,
    In the programming (Set) mode, for Stage Selection, the CPU-0500 only allows 3 options (which are consistent with the following from the CPU-0500 Installation Manual) :
    1 = Single stage heat pump.
    2 RT = 2 stages of heat pumps with rotation.
    2 = 2 stages of heat pumps without rotation.
    Use the 2 setting when a backup is being used. This way the backup will not rotate into the number 1 position.

    Thanks again,
    Timf
     
  6. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    I guess I am confused, why do you have both the HBX CPU-0500 controller console and the Honeywell VisionPro IAQ thermostat.

    From reading the manuals, I don't see where either of these will turn on 2nd stage on your heat pump.

    You need a tsat that will handle 3Heat/2Cool like this one
     
  7. TimF

    TimF Member

    Palace,
    My apologies for the late reply. I was a bit confused by your reply above as I recall the HP did go into stage 2 once upon a time...ie shortly after the install in 10/2011. While contemplating your reply, I remembered that there is Honeywell control box into which the thermostats are wired. I searched and found the documentation associated with the Honeywell control box and found that the Installation Guide offered far more programming options than those offered in the Honeywell thermostat Operating Manual. Long story short, the Installation Guide describes the following:

    Setup Function_________________ Settings & options (factory default in bold)
    0176 Heat or Heat Pump Aux stages 1 1 stage of heat [Other options: 0, 2 or 3 stages, or E]

    I selected setting '2', pressed Done and headed downstairs to the HP and the CPU-0500. Much to my surprise, the HP was running and the CPU-0500 console had both '1' and '2' showing under "Heat". I'm not sure yet when it is entering stage 2 but at least it is getting there. This is the first time today I have seen the HP raise the water temp in the buffer tank with either thermostat calling for heat never mind both thermostats simultaneously calling for heat. I'm not sure how the thermostat control unit lost it's programming but it surely must have. Since we have another day of +10F to -4F weather ahead of us, it will be interesting to see how the HP reacts in terms of recovery time.

    Thanks much for the help...I'll post more actual run time info tomorrow! :)

    TimF
     
  8. TimF

    TimF Member

    Palace,
    I'm still very confused. For the most part, when I looked at the HP yesterday it is in stage2, however, today when I've looked, the HP has only been in stage 1. The temps today are not much different than the past 3 days...maybe a degree or two warmer but still the temps continue to be in the -1F to +10F range both days. About all I can say at this time is I know the HP can go into stage 2 (confirmed both by the CPU-0500 and a deeper sound the HP makes)... I just don't know the logic for when it does or does not go into stage 2. I know the thermstat wires go to the air handlers, circulators and the outdoor thermometers but I don't see the thermostats or the thermostat controller being connected to the CPU-0500. The CPU-0500 only has two thermstat-like wires...one goes to the buffer tank and the other goes to an outdoor temperature sensor. My conclusion is the CPU-0500 controls the HP based on buffer tank and outdoor temps and the thermostats control the air handlers and circulators based on indoor and outdoor temps.

    Thanks again,
    Timf
     
  9. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    There has to be control wires to the heat pump. Where do they come from?
     
  10. TimF

    TimF Member

    Palace,
    Other than the two wires I mentioned above that go from the CPU-0500 to the buffer tank and outdoor thermostat, there is one thermostat wire that goes from the CPU-00500 into the HP and attaches to the top four positions on a terminal strip block...from top to bottom (if I recall correctly) they are labeled R, Y1, Y2 and O. Y1 & Y2 I recognize as being lights on the printed circuit board that represent stage1 & stage2 respectively.

    Timf
     
  11. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    so it is up to your CPU-00500 to control staging on the heat pump. I don't see from the manual how the CPU would do that. I would try asking the HBX people how to set it up to see if it is even possible.
     
  12. TimF

    TimF Member

    Palace,
    I found some time to search the web and found a few drawings that represented a geothermal environment with a 2 stage HP. Although there are some differences between the drawings and my environment, what I found was enough to confirm that 2-stage heat pumps are supported by the CPU-0500. I went to the HBX website and after finding nothing new under CPU-0500 or geothermal, I stumbled into the Technical Bulletin section and found a document entitled "CPU-0500 Staging Theory" at this link: http://www.hbxcontrols.com/Resources/technical/CPU-0500_Staging_Theory.pdf

    This document describes how the 2nd stage is activated and deactivated....basically it's based how well the HP is keeping up with demand (buffer tank temp) and whether the "staging timer has elapsed". I'm left now with determining if the staging timer is fixed or variable and if variable, then I'm assuming the staging timer equates to the "Minimum Lag Time" value. I suspect the latter but it'll have to wait for the right conditions for me to play with the Minimum lag time value because now the outdoor temps are in the normal mid-20F range for this time of year.

    Thanks again for your help,
    TimF
     
  13. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I heard you say air handler. Is this a water 2 water system? If so is the heat pump feeding into the buffering tank? Is the buffering tank just for DHW?

    Mark
     
  14. TimF

    TimF Member

    Mark,
    Water 2 water? No...water to air
    HP feeding buffer tank? yes
    Buffer tank just for DHW? No...buffer tank is solely for supplying air handlers, whereas, the DSH has a separate pre-heat tank.

    Allow me to give you what I hope is a fairly complete description of my geo environment. I have a closed loop made up of 5 each X 600' slinkies in 3'W X 110'L X 5-6' D trenches with a 2 pump QT Flow Center moving 15 gallons/minute. The GeoComfort 5 ton HP is controlled by the HBX CPU-0500 (which is not controlled by either Honeywell thermostat) and has it's own circulating pump which transfers the heated/cooled solution to a 50 gallon Bradford White buffer tank. There is one Honeywell thermostat and one circulating pump per air handler each with strip heaters. I elected to go go with two airhandlers for 4 reasons:
    1) I really didn't have a convenient/suitable space to run a large duct to the attic to heat/cool the second floor
    2) I wanted a bit of redundancy in the event I lost the HP or one of the air handlers during the winter months and needed to rely on strip heater(s) until repairs could be effected.
    3) We wanted to be able to keep the bedrooms (second floor) cooler in both summer and winter.
    4) I wanted some reserve air handling capacity in order to eventually heat a yet to be constructed mud/pantry room.

    In terms of DHW, the desuperheater has it's own pre-heat tank which I valved to either be in series with, in parallel with or completely isolated from a separate 80 gallon solar hot water tank. Currently I'm using my old oil boiler powered 30 gallon indirect water tank (not using the internal coil) as the pre-heat tank, however, it is evident that once the sun gets a bit higher in the sky and the solar hot water tank can resume supplying the whole DWH load, I'll need to upgrade the 30 gallon pre-heat tank to a 50-80 gallon tank.

    I hope this helps...please let me know if I may have left anything pertinent out or need to clarify.

    Thanks,
    Timf
     
  15. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Tim:

    That helps a lot. I did not wee the solar, sorry.

    I will read the entire post again then tell you my thoughts.

    BBL

    Mark
     
  16. TimF

    TimF Member

    Mark,
    I don't think I'd mentioned the solar in my previous updates so I don't think you missed it! Based on Palace's comments and some rationalizing of my own, I've come to the conclusion that my setup may not be mainstream. Since I hadn't given a complete description of my environment, I figured I'd better do that in hopes of avoiding confusion.

    Thanks again for your interest,
    Tim
     
  17. zacmobile

    zacmobile Guest

    TimF: by the sounds of it you do have a water to water HEAT PUMP even though ultimately the heat is distributed via air. I know quite a bit about the HBX controls, I use them quite often and yes the minimum lag time is the delay time between stages, you should be able to select anywhere from 0-30 min. Shorten it and 2nd stage will come on quicker. As you mentioned, The honeywell thermostat would have no bearing on weather or not the heat pump goes into 2nd stage, it's all the CPU0500. (unless someone wired things up funky)
     
    Last edited by a moderator: Jan 29, 2013
  18. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    I have been hoping that some who knew the CPU0500 would chime in here. Thanks zac.
     
  19. TimF

    TimF Member

    Zac,
    Thanks for the education of water2water and the confirmation regarding the CPU-0500 Minimum Lag Time = stage timer. The only thing that appears somewhat funky (to me at least!) with the CPU-0500 is that the HD (pin1) and CD (pin 3) are both jumpered to pin2. I'm assuming it is setup this way so that the HP cycles independently of thermostat demand... ie it prevents the case where the buffer tank is left depleted from one run and stays depleted until a thermostat starts calling for heat/cool again.

    Initially at least I didn't see the HP ever go into stage 2, I have to assume in those cases the HP was able to keep the buffer tank temp above the lower 25% threshold after the Minimum Lag Time expired. In any case, when the outdoor temp was 15F or lower, the HP was running non-stop in stage 1 at times for well over 30 minutes. I'm assuming stage 1 is more energy efficient than stage 2, however, I'm not sure at what point there is a resonable trade off regarding stage 1 run time vs allowing stage 2 to kick in. If you have any thoughts regarding potentially changing the Minium Lag Time, I'd appreciate hearing them.

    For me the best news is that my system did keep the house at the prescribed temps during prolonged 0F - 15F temps without having the HP lockout or the air handlers using the heater strips. Even if things like the Minimum Lag Time are not set optimally, knowing that I have some reserve in my back pocket if need be is very reassuring....this was indeed an acid test!

    Palace,
    Thanks again for your help..you got me looking into the physical setup further than I had been previously. Now, if I can just understand (and remember) everything I've learned in the process!

    TimF
     
  20. zacmobile

    zacmobile Guest

    It sounds like your system is set up to have a constant heating & cooling demand, which I personally like for heating but not necessarily for cooling. The reason I like it for heating is that if you have the heating curve set accurately the heat pump will be able to fairly closely track the heat demands of the house based on the outdoor temperature. So basically it just needs to know what it's doing outside & it can merrily chug along without being given many different calls for heat at different times from any zones present in the house potentially leading to short cycling issues. (if you are using the outdoor reset function of the CPU-0500, I'm assuming you are.) However, the cooling function is a static set point and what you can run into, in the shoulder seasons especially, is the heat pump flip flopping from heating to cooling. Say it's a warm day & the outdoor temperature goes up above the cold weather shut down point and the CPU-0500 initiates the cooling whether or not it is being needed by the air handlers, then as the sun drops it becomes a bit cool over night and heating is called which most likely will be needed, so you get this daily combat between a warm & chilled buffer tank. Most of the time it does not add up to much as you are just ferrying heat to & from the ground loop but it does take some power to do it. My preferred method is to install a simple switch (any old light switch will do) in the CD circuit interrupting the call for cooling unless YOU feel it's really needed. Another way to do it would be to have the CD circuit go through a relay that is being switched when a thermostat is calling for AC, this works OK but there can be a significant lag in a buffer tank scenario (certain thermostats have a delay that you can set for it to wait a while before turning on the fan) and it might get a little complicated wiring up 4 different air zones to accomplish this.
     

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