Iowa WF Series 7 - HWG usage and efficiency

Discussion in 'General Discussions' started by Neokane, Feb 18, 2022.

  1. Neokane

    Neokane Member

    I will be hooking up my marathon buffer tank this weekend to my WF series 7 5 ton unit.
    I am curious if it is recommended to run the HWG year round or just during the summer.
    In SD2700AN, I was surprised to find that the hot water capacity is greater in heating mode than cooling mode under both partial and full load.
    I guess maybe I misunderstood the process in which how the unit generates hot water.
    I assumed I would want to shut it off during winter months not rob Peter to pay Paul.

    Any input or explanation to why I am confused and backwards regarding this process.
  2. gsmith22

    gsmith22 Active Member Forum Leader

    I've got many past posts correcting others on this too. Hot water production is much less to nonexistent during summer months primarily based on incoming water temperature. It has to do with how heat is being sucked off of the superheat portion of the refrigeration cycle; the temperatures and pressures of the refrigeration cycle during cooling in summer months vs those conditions during heating in winter months. In short, for reasons that I can't understand, a lot of people are very mistaken about when desuperheaters produce the most hot water - its in the winter, some in the shoulder seasons, and almost none in the summer (depending on incoming water temp). All heat pumps work this way, its not just yours. I would keep the desuperheater on year round and especially during the winter if you want to produce hot water. If you shut it off during the winter and only run it in the summer, you will likely produce little to no hot water ever. In the event you have some crazy cold snap for like a month, your loop is undersized for your heating load, or some combination thereof, then sure, shut the desuperheater off during that specific cold period to give some extra loop capacity to the heat pump. But the reality is that loops respond to long cycle heat input/extraction and not daily or even weekly heat input/extraction. A two day cold snap will barely if at all affect loop temperatures.
  3. Deuce

    Deuce Member

    I have said many times that my desuper water heater provides much hotter water in the winter than it does in the summer.
  4. SShaw

    SShaw Active Member Forum Leader

    HW capacity in summer is dependent on entering water temperature. You need to get up around 70F to get good output. If your area is heating dominant and/or you have an oversized loop, then your loop will be oversized for cooling and you're not going to see high EWT in summer and wont see much hot water output.

    In winter, when the DSH is on it will reduce the heat output going into your house. People say it's about 10% of the capacity. I wouldn't worry about that though. The 7 series controller shuts off the DSH pump when the buffer tank reaches the set point, so the lowered capacity doesn't happen all the time.
    gsmith22 likes this.
  5. gsmith22

    gsmith22 Active Member Forum Leader

    SShaw points out something very important here that I think needs to be highlighted and might be the reason why perceptions of hot water production are misplaced. Since hot water output in the summer while cooling is dependent on incoming water temp, and you don't get hot water output until you get higher incoming temps (> 70s), anyone in a heating dominated climate is probably not going to produce hot water in the summer. Why? Because their loop is going to be (or should be) sized for heating load and not cooling load. so the loop will be much larger than necessary during cooling operation meaning moderate incoming water temps and no or very little hot water production. For a cooling dominated climate, the loop is sized for cooling and you will likely get higher water temps and hot water production during the summer. I don't hear of lots of geothermal systems for cooling dominated climates with air source heat pumps being so cost effective to install.

    Single stage geothermal heat pumps were originally a cooling thing with a combination of heat output+electric strip heat to account for winter conditions - even in heating dominate climates. With loops sized for cooling, you would get high incoming water temps in summer and hot water output. Dual stage and variable speed has changed all that with units better able to control humidity in the summer even if sized for heating in the winter. With a loop sized for cooling, you would get high incoming water temps in summer and hot water output. Not so for a loop sized for heating. So it probably used to be true that summer hot water production was a thing everywhere with a cooling sized loop but now its really only true in a cooling dominated climate. And with air source heat pumps being so cost effective, not many geothermal systems get installed in cooling dominated climates so there probably aren't a lot of examples of people with hot water production in the summer remaining. People repeat mantra without understanding the underlying physics leaving all of us heating dominated geo system guys/gals left wondering why anyone thinks they get hot water in the summer. At least this is my theory :)
    SShaw likes this.
  6. Neokane

    Neokane Member

    I am 100% certain that my system is sized for heat given my location. I appreciate the feedback and explanation. I always imagined the the unit "takes heat out of thr house and puts it in the hot water". But it is much more complicated than that. I will have to monitor my loop temp over the summer and see how it performs.

    Currently my loop temp is 31deg and compressor stage 4.
  7. gsmith22

    gsmith22 Active Member Forum Leader

    Yes, far more complicated. It takes heat out of the refrigeration cycle specifically at the "superheat" phase. Which is why it is called a desuperheater.
  8. Neokane

    Neokane Member

    So once I flip the switch I assume I have to wait for an aid tool to turn on the hwg?
    I use to be able to access the menu from the local ip Address but that seemed to be changed.
  9. gsmith22

    gsmith22 Active Member Forum Leader

    there is the physcial switch on the unit and I think you are correct that there is a setting using Symphony to change too. I'm not aware of any change - I was able to log in remotely with local ip last time I checked something. I do note that some of the menus take a little while to show up - sometimes even 5 minutes after logging in locally so maybe that is what is going on?
  10. Neokane

    Neokane Member

    Thanks @gsmith22 and @SShaw
    I had to put the AWL into local mode and was able to access the settings needed to turn on the DSH and changed the desired setpoint to 120 deg. The dsh circ pump is now running. Now we wait for the buffer tank to warm up.
    Thanks for all the help.
    I'm really curious on the opinions of buffer tank and primary tank configuration.
    I have a 50 gal rheem marathon (un-energized) as my buffer tank and then my primary tank is a rheem hybrid.
  11. xSpecBx

    xSpecBx Member

    You hot water setup is similar to mine. I have a 40 gallon buffer tank with an 80 gallon hybrid hot water heater. From what I have read, the buffer tank is important to protect the hot water tank from an overheating condition since DSH in some cases can get pretty hot. I’ve seen mine get into the 130 degree range when the system is really working.
  12. gsmith22

    gsmith22 Active Member Forum Leader

    I have 2 heat pumps both feeding my 50 gallon buffer tank whcih feeds my 80 gallon hybrid heat pump hot water heater. If I were to do it again, I would put in a larger buffer tank because I see in the AWL where the desuperheaters are constantly shutting off due to the buffer tank temp being satisfied regularly - essentially I am producing more hot water with the two heat pumps than I can store (due to only 50 gallon buffer) and apparently use (two kids approaching teenage years so we shall see).

    I can't recall at the moment but I may have my desuperheaters set to 130 and my hybrid heat pump hot water heater set to 120. So in effect hot water heater being fed by water above its set point which is why it never runs in the winter. Wife did laundry all day and haven't heard the heat pump hot water heater come on once.
  13. Neokane

    Neokane Member

    I may change my DSH setpoint to 130 for that reason. seems pretty logical. In addition, the marathon should be able to retain most of that heat.

    Last question.. Does the symphony app or web port display dsh temp? I haven't found it or seen it if it does..
  14. gsmith22

    gsmith22 Active Member Forum Leader

    not that I am aware of. the only thing I have seen is the "error" messages in AWL indicating the DSH reached the set point and was shutting off. In combination with my hot water heater being set to 120 and not running I think it is safe to assume that the temp gets to the 130 set point

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