Massachusetts Ranco setpoints for buffer tank

Discussion in 'Maintenance and Troubleshooting' started by rscott, Dec 10, 2014.

  1. rscott

    rscott New Member


    I have been doing a lot of work trying to find out why my water-to-water geothermal system (using 2 air handlers) is not performing as well as it should (using 2-3x as much electricity as expected). I am now looking at the settings on the Ranco ETC (which appears to control the temperature of the buffer tank). Information on appropriate settings are very sparse.

    The Ranco (for heating) is set to:

    Stage 1 setpoint: 105 degrees F, 5 degree differential (100 degree activation)
    Stage 2 setpoint: 103 degrees F, 3 degree differential (100 degree activation)

    Over the course of about 30 minutes, I checked the Ranco while the main geothermal unit was on, and the temperature shown was always 96-98 degrees. And it showed both Stage 1 and Stage 2 as being on whenever I checked. Air coming out of the air handler at the time was about 101 degrees.

    Each time the thermostats called for heat, the geothermal unit came on (and I believe stayed on until the thermostats stopped calling for heat).

    Does this seem normal? The two examples I could find (both from manuals for other geothermal units) show having the Stage 2 activate at a temperature 5 degrees lower than the where Stage 1 activates. My settings have both activate at the same temperature.
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Hello and welcome.

    The control is doing what it has been told to do.

    What is the highest temp for the units? Delivery temp. Look at the tables and find out how hot you can go without lowering efficiency.

    What is your delivery system? HV or standard velocity?

    I would split the stage 1 and 2 by ten degrees for a start, but I think in water. OK. Start with five degrees.

    What provides aux heat? Turn it off.

  3. rscott

    rscott New Member

    Hi Mark,

    Thank you for your response. The table I find shows performance, but you need to know the source GPM, and ELT, which I do not know.

    I believe the air handler is standard velocity (it's the same ductwork normally seen with other forced air systems).

    One of the air handlers has electric as auxiliary, but has a switch, which I normally keep off.
  4. rscott

    rscott New Member

    I'm starting to think that investing in a monitoring solution would worthwhile.

    I am confused with the Ranco, however, as when the thermostats call for heat and the Ranco turns on, it is usually around 94 degrees, and will heat up to about 99 degrees, and then seems to shut off the geothermal unit at that point (with the air handler still running). From the settings, I would assume that it would leave the geothermal unit on until 103 or 105 degrees. Is the Ranco not behaving properly, or am I misunderstanding how it works?
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    There are likely a few things up, but one simple thing. Confirm the temps are reading correctly. How are you verifying the temp readings?
  6. rscott

    rscott New Member

    I am going by the readings on the Ranco (except for the air temperature mentioned in the first post; I'm using an IR thermometer for those).
  7. rscott

    rscott New Member

    I think this is why some people love geothermal, and some people hate it -- quite a few people have serious problems with geothermal (such as using 2x as much electricity as quoted, undersized systems, etc.), and consumers are given a "black box" that has some very simple troubleshooting tool -- yet inaccessible to the consumer. In my case, I am looking at spending $800 to have someone come and analyze the system (which has no guarantee of success).

    I imagine all geothermal installations must have settings on a Ranco or similar device (otherwise, the heat pump would run forever), yet the details on what the settings *should* be are nearly impossible to find. There really needs to be a "Geothermal 101" book out there for consumers, not just describing what geothermal is, but covering what you might need to know after you buy the system.

    I am fortunate that my system provides the heat we need, but all the hype out there about long-term cost savings is really inappropriate if a reasonably high percentage of customers have problems that outweigh the savings. Geothermal today seems to be very similar to autos of yesteryear, where "lemons" were very common. And until people put up a big fuss, it's going to continue.
  8. ChrisJ

    ChrisJ Active Member Forum Leader

    We hear from "quite a few people with serious problems" because the hundreds of thousands of others are not searching the web for solutions because theirs are working fine.

    Also many ways to skin a cat (sorry I know that sounds bad) Installers have different ways of doing things to get similar results.

    I have a hybrid unit which heats water like your water to water, but also heats air. Doesn't have a Ranco it has internal controls. My buffer tank and controller work independent of the thermostat, as if your ranco was always on and all it cares about is keeping that tank up to temp.

    I have a sensor on the buffer tank, slipped under the insulation making good contact with metal, as your Ranco must have a sensor somewhere.

    Now I have read where the sensor was attached to a pipe going to or from the tank so it wasn't real accurate to what the tank temp was.

    My settings are done a little different: 101*F target temp, 3.5 deg drop and 1st stage kicks in, another 4 deg and 2nd stage kicks in.

    I learned so much reading on this forum.

    Geothermal unit are usually not lemons, it's they way they are installed and controlled that makes them look inefficient.

  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    If you have a water-water system with air handlers being fed by 115-125F water without an outdoor reset, then your system is inherently less efficiency due to high load supply temperatures. Check your supply temperatures going to the air handlers, I don't buy the 100F supply temperature to the air handlers. There might have been reasons for that design, sometimes with retrofits you have to play with the cards you got. How many pumps do you have, and what is the model number? Do you have a piping diagram?
  10. rscott

    rscott New Member

    The 100F is what the Ranco shows (I'm trying to see if I can get the the leaving load temperature). That's what confuses me; logically, if it is set to 105F -5 and 103F -3, it should keep running until it hits 103F or 105F (but it seems to shut off at 100F). And the actual temperature makes no sense to me; why does it typically show 94F-99F if the temperature is being read from the buffer tank (which can heat the air to 100+F, and seems to have an entering load temperature of over 100F)?

    It sounds like you may have hit the nail on the head there with the 115-125F water temps the air handlers must be receiving. There is one heat pump (GeoComfort GWT060), 2 Grundfos UP26-116F circulation pumps for the loop, and 2 Grudfos UPS 15-58 FRC circulation pumps for the water going from the buffer tank to the air handlers.

    I don't have a piping diagram, but am pretty familiar with the pipes and where they go.
  11. ChrisJ

    ChrisJ Active Member Forum Leader

    What about a pump from the heat pump to the buffer tank?
  12. rscott

    rscott New Member

    Hi Chris,

    There is a Grundfos UP26-116F circulation pump connected to the pipe taking the water from the buffer tank to the heat pump.
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Argh.....I hate to be the messenger of bad news, but whenever I see or hear about one or multiple 26-116 on the system, that indicates that the person who designed it has no clue about efficiency. The 26-116 uses 400 watts each, compared to 230 watts each for the 26-99 pump, but delivers only 10% more head, which you unlikely will need in your application. So you have 2 on the source side, at least one on the load side, plus at least 2 Grundfos UPS 15-58 FRC which use about 90 watts in stage 3.
    1400 watts pumping, when 700 or less could do it. Any more pumps in the system?
    This coupled with the design for a high load temperature is explaining the inefficiency of the system.
  14. rscott

    rscott New Member

    Aha, thank you -- that is very concrete data. It's just those 5 pumps (3 of the 26-116, 2 of the 15-58), but that 700W or so whenever the system is running will really add up.
  15. FryDaddy

    FryDaddy New Member

    Just an FYI. I have a new system and started to use an IR thermometer like "rscott" to get a feel on how the system was working. I found that my IR thermometer was very erratic. After some research I found the emissivity setting on the IR thermometer helped but I also found a tip in a blog that said to use a flat black paint on areas you want to measure temperature to stabilize readings and not have to mess with the emissivity settings. This has worked great for me and I get very consistent readings where before they were all over the place. Link to emissivity explanation .
  16. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    IR thermometers do not like shinny surfaces.
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    In addition, each 10 degree F higher supply temperature will refer your system about 10-15% less efficient. So yes, it all starts to add up. You should get an outdoor reset, which lowers your supply temperature on warmer days, running the system more efficient. I would also ask your installer what his rationale was to install so many and inefficient pumps. Your system might run only on one source pump, and 2 load pumps. He might take the extra pumps out at no extra charge for you, saving you significant pumping power.
  18. geoxne

    geoxne Active Member Forum Leader

    Doc has addressed your pumping issues very well and I agree. He has touched on outdoor reset control and I also believe it is important control strategy for hydronic geothermal systems.

    Lower entering load temperatures mean a significant gain in efficiency. Every 20f drop in LoadEWT will increase COP by approximately 1. An ODR, programmed properly, will lower load temps whenever possible.

    There is alot more going on here than we know. Your Ranco does sounds like it is acting strange but without knowing how the whole system is piped and controlled currently (AC/Heat changeover manual or demand based from thermostats, single or dual buffer, location of sensors and more) any diagnosis at this point would be a shot in the dark.

    Control strategies to encourage efficiency should be in place before a system is piped, especially for a geothermal system.

    There is a lot of good info here-
    Last edited: Dec 18, 2014

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