Maryland Newbie Thread #2 - DWH in the Summer

Discussion in 'Maintenance and Troubleshooting' started by 262runner, Jun 23, 2020.

  1. 262runner

    262runner New Member

    Sorry for two posts in one day, I'm just really trying to make sure I have proper expectations for my system. I have a WaterFurnance Series 7 4 ton with the performance monitoring package. Official number NVV048A111CTL0KN. I have it plumbed to a Marathon 85 Gallon buffer tank and then connected to a Rheem Hybrid finishing tank. It was installed over this part winter.
    My questions is about the desuperheater. It seemed to work well in the winter. The circulating pipes were warm when the system was running. The energy monitoring of the hybrid tank showed little energy use during the cold days when the GEO was running a lot, indicating the buffer tank was getting nice and warm (it's hard to tell on the Rheem marathons with their super-insulation). When I was sold the system, I was told that in the summer, it would create a ton of hot water. My simple understanding of AC systems seemed to think it would make sense that it would extract heat from the system during the refrigerant compression stage. So when the warm weather hit, I was excited to see how warm the circulating pipes got. Turns out, not much.
    I have accessed AID port using the local network access through the AWL. AXB setup indicated DHW is enabled and I've tired setting the temp between 130 and 140. Under the diagnostics menu, AXB Inputs indicates Hot Water of 81.5F after about 10 hour of running the AC and little water use (no showers, tubs, pools, etc). Is that the correct place to check the DHW temp? Since the switchover to cooling, I've had around 30 "Hot Water Limit E15" faults. I know those are "normal" but at no time have the circulating pipes felt anything close to warm. Nothing even close to the winter even after a full day of AC. I've opened the unit and the circulating pump feels a little warm. I've about 95% sure water is indeed circulating. When I begin to close the circulating circuit valves sightly, I can hear the sound of water"whooshing" over the slightly closed valves. When I put my ear to the pipes with the DHW switch on and off, the sounds are distinctly different. So it seems like the pump is working.

    So here is my problem. A tech came out to look at the system and he didn't know why I was not getting more warm/hot water. He removed the sensor from the circulating pipe and said it correctly read the ambient temperature, so he didn't think that was the problem. He's convinced its the circulating pump. Although it's drawing current, he thinks the impeller is damaged and not really circulating water. Because of the different sounds I hear when it's running, I think it is. I also find it hard to believe that a pump would fail after just 7 months. I really don't want to have a tech tear into a nearly new system on a hunch, especially what feels like a bad one. I asked if he could access the system data from the WaterFurnance Dealer Portal to see historical DHW recorded temps, but he said they never use the dealer portal to troubleshoot. My tech seems averse to the monitoring systems and had me do a lot of the Symphony setup when it was first installed. Which makes the money I spent on it feel half useless if the dealer doesn't use it and I can see it either.

    In researching further on the forum and the WF install guides. I'm reading "Compressor hot gas temperature is dependent on loop temperature in cooling mode, loop temperatures may be too low to allow proper heating of water. The control will monitor water and refrigerant temperatures to determine if conditions are satisfactory for heating water." My EWT is varies between 56 and 64 degrees based on runtime. LWT is usually 8-10 degrees above that. So I'd assume that should result in refrigerant temps warm enough for DHW.

    Are my expectations for summer DHW too high? Should I let the tech replace the pump or have him get on the phone with WF first? What else can I check on my side via the AID port or other on board diags to troubleshoot.

    Id really like to see this system work for 20-25 years. A pump after 7 months scares me. HELP (and thank you!). I'm happy to pull any data.
     
  2. SShaw

    SShaw Member

    The 85 gallon buffer tank is a little larger than most recommend, but it should work fine.

    Your system is almost certainly operating normally. There is very little hot water generation capacity at your EWT in cooling mode, about 1/3 to 1/4 of the winter capacity. Before you dismantle anything else, download the WF7 submittal data document (SD2700AN.pdf) from the WF website. Look at the performance tables and you will find the hot water generation capacity listed for heating and cooling modes as a function of EWT. Capacity is less in the Summer, particularly at the early season when the EWT is lower. The capacity will increase as the summer progresses and the EWT increases.
     
  3. Stickman

    Stickman Member Forum Leader

    My heat pump ran for 12 hours total in the past 24 hours. Short on cycles don’t generate much HW. Here’s graphs of the compressor cycles and coordinating buffer tank temp (shower ran at -6 hours):

    upload_2020-6-23_22-36-33.png
    upload_2020-6-23_22-36-20.png
     

    Attached Files:

  4. gsmith22

    gsmith22 Member

    download the document SShaw is talking about to look at performance data for the unit. In cooling at entering water temps below 60 deg F, there is no hot water production. At 60 deg F entering water temp, there is like 1200 BTU/h. At 80 to 90 deg F entering water temp, there is almost 3x as much hot water production than at 60 deg F entering water temps. I would wait until August and revisit your hot water production to see if there is really a problem. In heating mode, there is hot water production at all entering water temps and at 2 to 3x what you get during cooling.

    Your other thread mentioned a 5 series split system - does that one have a desuperheater too plumbed into the same marathon buffer tank? I mention it only because if you have two units with desuperheaters plumbed into the same buffer tank, you have to have check valves on the output of the desuperheater pipes so you don't get short-cycling with one desuperheater pump pushing backwards through the other desuperheater pump.
     
  5. geoxne

    geoxne Active Member Forum Leader

    E15 is not a fault. It reports the DSH pump is disabled when High Limit temperature is reached OR control logic has determined Compresser Discharge temperature is not high enough compared to entering Hot Water temperature to support hot water generation. The DSH pump will turn on again in 15 minutes to recheck temperatures and so on. Each attempt will report an E15.

    The above posters are correct the BTUs available for hot water production while cooling are significantly less than in heating mode until source EWT approaches 90F.
     
  6. 262runner

    262runner New Member

    First of all, thank you all for the reply and the data. Very informative!

    And I have a little bit more to share after an experiment this morning with heating.

    A few answers to your questions:
    GSMITH22: Only the Series 7 has the DSH, so hopefully plumbing isn't an issue. The plumbing installer seemed to follow the WF recommendations and ones I've seen here. I see here. I could provide a diagram and/or photo is you like.

    GEOXNE: Great info on the E15 fault, "Control logic has determined Compressor Discharge temperature is not high enough compared to entering Hot Water temperature to support hot water generation". They should do a better job of documenting that.

    STICKMAN - Is that the WEL data logger? That's good data. I wish WF gave users access to similar data.

    My experiment this morning was to try HEAT mode (it's a little cooler outside today so I was able to open the windows and not overheat the house) to to try to verify that the pump was working and if I'd see heating.

    I ran the system for about 40-45 minutes. The compressor staged up to about 9 with the fan also around 9. I had the AWL in local mode to monitor the hot water temperature the system was reporting. Everything looked really good. I was seeing a slow, but consistent heating from about 90 degrees up to about 97 in about 20 minutes according to the AID tool. A touch of the OUT pipe confirmed the water was indeed warming. IN pipe was likewarm. After about 20 minutes the compressor and fan kicked into level 12. The temperature spiked...I mean really spiked, climbing about 10 degrees in one minute. The water temp as reported by the AID tool very quickly rose over 100, 110, 120, 130 and then seems to level out a bit around 131-32 for a few minutes. I checked the OUT pipe and it was indeed hot. The rest of the circulating circuit was quickly getting hot, although it didn't seem to be warming quite as fast as the output. I'm not sure what the flow rate of the circulating pump is, if it's low, it would make sense for the whole circuit to take a minute or two to warm up. The IN pipe was still just lukewarm. It ran like this for about another 2 minutes and then started to climb again. It went over the 140 setpoint at which time I expected it to level out. It didn't. It continued to climb slowly until it eventually reached 147 degree, with NO NEW E15 faults. The compressor was at 12 during the steep climbs.

    I have a old phone that only connects to the WF and has the browser preset to the IP of the AWL that I use as my AID tool. I recorded the climb and other observations on my primary phone and uploaded it to YouTube if you'd like to see what I saw in the 10 minutes of recording. I stopped the video after 10 minutes when the temp leveled out at around 142. But it did start climbing a little bit again and reached 147 before I turned everything off. I have that on another video if anyone wants to see it.


    So now I've gone from "should I expect more hot water when the AC is running" to "Is it normal to see THAT MUCH hot water suddenly when the compressor goes from 9 to 12. It that much heat being produced that the circulating pump just doesn't draw it away very quickly. Also a little concerned that the temperature continued to rise well past the 140 setpoint. This is probably why WF doesn't allow consumers access to this data. It creates too many questions.

    I'm very open to your thoughts. And thanks again.
     
  7. gsmith22

    gsmith22 Member

    as I suggested, go to www dot waterfurnace dot com/residential/products/literature, download the specification catalog and look up in the performance data what the "HWC" is for your entering water temperature and approximate heating or cooling stage (50% vs 100%). That will tell you how much heat should be being produced (kW/hr) by the desuperheater. then you have to take the approximate gallons of water storage in your tank and from those figures, you should be able to calculate how long it should take to heat up the water for a particular change in temperature (don't turn on any hotwater faucets/laundry while doing this experiment because then the volume and temperature of the stored hot water changes). By definition, it takes 1BTU to heat 1 pound of water 1 deg F and (assuming 62.4lb/cu ft density of water) there are 8.34 lbs of water in 1 gallon. apply some math and you will be able to tell if it is functioning properly, but nothing seems amiss from my vantage point.

    If the split 5 series doesn't have a desuperheater, then ignore what I wrote. it won't be plumbed into any of the domestic hot water circuit and you will only have 1 desuperheater feeding the buffer tank so no chance at short circuiting multiple parallel plumbed desuperheaters.

    I can't stress enough taking the available WF literature (specification catalog, installation catalog, etc.) and reading through it. It provides a lot of background info that will probably answer most questions or at least allow you to figure out the answer.
     
  8. 262runner

    262runner New Member


    Thanks for the reply. I did indeed look at the Submittal Data referenced . It doesn't look the the WF 7 even starts turning on hot water generation when cooling until the EWT is above 60 F. It's been fairly cool here so I've only used the AC maybe 10 days and with no long streaks, so my EWT has started in the mid to high 50's most days and then got into the low to mid 60's throughout the day (vertical wells). Even with temps in the 60's it looks like it will only produce about 1200-1400 BTUs an hour for for hot water generation at 50% load and only 2600-3000 BTUs at 100%. On my 85 gallon buffer tank, that translates to about 1.7 (50%) - 4.23 (100%) degrees F of temperature increase per hour of run time. And since I seem to be running a lot of the time in the compressor stage 4-6 range, I'm probably closer to 1-2 degrees an hour. That's much lower than I expected or what I felt I was sold. Thankfully, I also selected a hybrid hot water heater, so in the summer, it's pretty efficient, especially on heat pump only mode.

    I also feel like the tech should have known this. He's all ready to swap the pump. I think I need to request a tech that has a better grasp of this technology.

    It looks like in heating, that number is much higher. With a EWT of 40 F (what I was seeing in the early winter) , It'll make 2600 BTU's on the low end at 50% and up to 7500 BTUs on the high end at 100%. On my big 85 gallon tank, That's an increase of 3.6 degrees an hour at 50% and as much as 10.6 degrees an hour on the high end.

    So the short answer for anyone reading this in the future, don't expect really any hot water generation in the summer if your EWT is below 60. And very little after that until your EWT really starts to climb into the 80s and 90s. I need to try to better understand where its drawing the heat from, simply because I like to understand how things work. Like I said, in my mind, during the summer I would have expected more waste heat to draw from. If anyone has a link to a video or diagram, I'd be very curious to learn more.


    Lastly, with regards to the video, does anyone know if that's normal? Where the temp rises pretty slowing at compressor speed 9, but then pretty much goes through the roof at compressor speed 12? When in compressor stage 9, the DSH output temperature went up about 3 degrees at the output in about 13 minutes. At compressor stage 12, it went up 10 degrees at the output in about 40-45 seconds. Not really as linear as I would have thought it should be. Is the circulating pump variable speed? I suspect not. But it seems like it should be sized to remove heat fast enough that the output water temperature doesn't hit 147. Again, just questions for the curious side of me.

    Thanks again.
     
  9. Stickman

    Stickman Member Forum Leader

  10. geoxne

    geoxne Active Member Forum Leader

    The Hot Water sensor is located on the DSH In in close proximity to the DSH coil. The DHW pump must be running to provide a valid tank temperature. If the pump is off the temperature reading can continue to rise due to conduction through the coil as superheated refrigerant continues to flow.

    Check AXB OUTPUTS to see if the DHW Pump is OFF or ON.
     
  11. gsmith22

    gsmith22 Member

    Unfortunately, techs (in all fields) are mostly parts hangers and not investigators. Its more rare that someone has the initiative to not only investigate a problem, but understand how a system works and what might cause it not to work so they don't spend their time (and customer's money) changing stuff out until it works. Those that do this, mostly graduate to higher management levels to be replaced by those that don't do this (Peter principle). I wish this were not the case, but I see it over and over again across every field I come in contact with. So, sites like this, with owners and the cream of the crop installers interested in solving an issue, are a great resource to be able to steer an investigation toward the appropriate problem under the guise of suggestions to said parts hanger. Its what I have done. I think you will find that any tech frequenting this board falls into the category of "wants to understand how a system works and properly investigate a problem." The ones you get at your house probably don't know this site exists and wouldn't waste their time reading/learning. Its a generalization that is unfortunately more true than not.

    My wife tells me I'm a pessimist. I would like to think I am a realist that is hoping to be pleasantly surprised.
     

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