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HPHW sizing

Post in 'The Green Room' started by ajamison, Jan 29, 2014.

  1. ajamison

    ajamison New Member

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    I live in Virginia, have a 20+ year old electric HW in a semi-conditioned basement that requires dehumidification at least 1/2 the year, so I'm a good candidate for a HPHW.

    We currently have a 50 gallon tank for a family of 4, and it has been fine, but the kids are very young and we might not quite yet be done growing as a family. I've heard about the longer recovery time with HPHW and seen several recommendations to go with 80 gallon sizes for that reason.

    The 80 gallon integrated units are too tall for my basement (and pricey). So I'm trying to decide between a 60 gallon AO Smith Voltex or buying an 80 gallon electric tank and a Nyle Geyser.

    Some of the aspects I'd appreciate feedback on are:

    1) Is the higher efficiency of the Voltex and its smaller tank size a net efficiency gain over the 80 gallon/Nyle combo or

    2) would the 80 gallon/Nyle combo enable us to stay in heat pump mode longer than the 60 gallon AO Voltex thereby being the more efficient scenario (assuming a family of 4-5 is pushing the limits of the Voltex)?

    3) What is the life expectancy like on the integrated units - how big of a plus is it in the Nyle's favor to be able to separately replace the tank down the road if it fails first?

    Thanks.

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  2. semipro

    semipro Minister of Fire

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    Just a thought, not an answer to your questions.
    If you have the room you could install the HPWH in front of your existing HWH to get both increased capacity, increased efficiency, and humidification.
    The HPWH would do most of the water heating and the existing resistance HWH would only engage when you've overtasked the HPWH.
    A 20 year old electrical resistance water heater is perfectly serviceable as long as the tank is sound.
    You could do this with a less expensive and smaller HPWH like the GeoSpring.
  3. Dave A.

    Dave A. Minister of Fire

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    Ask This Old House had a recent episode where they showed the modification of an electric WH with a heat pump using a similar idea. The bottom element of the original WH was diverted to a heat pump unit and the top element was left intact to handle quick recovery needs. The episode is prolly still available to view online through the PBS site.

    Edit: also there was another thread on this site not too long ago discussing a heat pump unit that was being offered inexpensively for use with a WH.

    I'd consider doing it myself but I have a gas WH.
    Last edited: Jan 29, 2014
  4. semipro

    semipro Minister of Fire

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    That's the Nyle system the OP referred to.
  5. woodgeek

    woodgeek Minister of Fire

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    Quickly, I had similar concerns about HW quantity for my family of 4, and went with the 80 gal Voltex. My teen daughter can shower for well over an hour (with a ~2.0 gpm head) and still have hot water, in HP mode. In the end, even when we have house guests, and are trying to shower all the adults, it has never been a problem. I think I prob could have gotten by with the GE. I am in a (colder) attached garage, so the higher eff and lower min operating temps of the Voltex are a plus. So no regrets. In your app, I suspect you would be happy with either the Voltex or a GE (I don't know about the Nyles, etc.). Both combined units have long warranties on the tanks, and the compressors might be field replaceable in the future..who knows. Need plumbers with refrigerant experience? HVAC folks with plumbing experience?

    The Voltex is on the loud end for these units, if that matters to you. And the GE prob does better dehumidifcation. (the voltex moves a lot of air, making it more efficient, louder, and poorer at dehum).
  6. Dave A.

    Dave A. Minister of Fire

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    Hmm. It sure is. I don't think Nyle minded the exposure but Ask TOH would have done more service for the public with a mention of the full detailed You-tube video at rather than acting like they themselves came up with the installation.
    Last edited: Jan 29, 2014
  7. ajamison

    ajamison New Member

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    That is an interesting idea. Once the original heater did bite the dust, I could see if the GeoSpring was enough by itself, and if not, then buy a 40 gallon electric tank for a couple hundred dollars to hook up the same way.

    Does running the GeoSpring in series w/ an existing electric HW affect the efficiency in any way? How exactly would the two be hooked up?
  8. begreen

    begreen Mooderator Staff Member

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    That should be de-humidification?
  9. semipro

    semipro Minister of Fire

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    Yeah. Unless you have a leak. ;)
    Good catch.
  10. semipro

    semipro Minister of Fire

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    The only loss in efficiency I can see is from the heat losses from the old electric resistance HWH. As long as its insulated well and heat traps are installed on the outlet the losses should be minimal.
    Connection-wise: you'd just install the Geospring in series before the old HWH. The cold water would now enter the Geospring inlet and the Geospring outlet would go to the old HWH inlet. Pretty simple really.
    The big downside that I see is that another 220 Volt circuit would be needed.

    Edit:in theory, any heat lost to the room by the old tank would be used by the Geospring HPWH to heat water.
  11. woodgeek

    woodgeek Minister of Fire

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    I wouldn't go that far. Like a woodstove in a basement, a good bit of the heat emitted will get soaked up by the basement walls. And remember that pumping the heat still takes energy. So, the parasitic losses of a well insulated tank would likely have almost nil beneficial effect on the cost to run the HPWH (it would still be a loss).
    Last edited: Jan 29, 2014
  12. ajamison

    ajamison New Member

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    If the goal is to have larger storage/buffer is this really a better set up than having a Nyle Geyser hooked into an 80 gallon electric tank (aside from being able to utilize my current 50 gallon HW)? More efficient in any way as to producing hot water?
  13. semipro

    semipro Minister of Fire

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    I don't know. I was thinking of capital costs and how to meet your goals with less investment and comparable efficiency. One less thing hauled to the dump too.
    Given the same amount of insulation the single larger tank should have less heat loss but the relative efficiency differences between the hybrid setup and a larger Nyle setup may overshadow that difference.
    I don't know how the Geyser and HPWHs compare as far as efficiency. I really like the Geyser concept for a number of reasons; flexibility, ability to duct the airflow, ability to use existing tank. However, I'm not crazy about how they do the heat exchange through the drain in the tank. If I were to install one I'd plumb it in at the inlet per their instructions.
  14. semipro

    semipro Minister of Fire

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    So the basement walls are both heat sink and source depending upon temps inside the room where the HPWH is. If this is true I'd say that heat lost to the walls from the resistance HWH may later be recaptured by the HPWH. I agree that there are still pumping losses.
    This relates to my recent internal debate on where best to place for our Geospring HPWH. Obviously an ideal place would be where there is an ample source of warmer air. However, mine and many others are located in basements.
    I'd suggest that in a basement the air is only a transfer media for heat coming from basement walls or other parts of the house. There is not an abundance of warmer air in a basement. There is however, typically, a large source/sink in the basement walls and the soil surrounding them.
    I've been spending nights insulating and sealing up our basement and I've lately come to the conclusion that I should not insulate the below-grade walls in the room where the Geospring is located.
  15. Justin M

    Justin M Feeling the Heat

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    Keep it simple and just get the Geospring. Try running it in heat pump only mode. If the revovery time is too long for you then switch it to hybrid mode... done. My Geospring works fine for my family of 4 in heat pump only mode.
    Last edited: Jan 30, 2014
    woodgeek likes this.
  16. woodgeek

    woodgeek Minister of Fire

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    It comes down to whether you think the basement temp is the same as your deep soil temp, or above it due to heat from the house. You seem to be assuming the former, me the latter. But you are somehow assuming the basement is well insulated, rather than well coupled to the ground. ?? Bottom line, the 50W of heat from a tank will not budge the basement temp, so the eff of the HPWH will not be effected.

    As for Geyser/Nyle, I thought the EF was like 2.0, while for the all in ones its like 2.2-2.3 (for the first generation). So, maybe like 10-15% maybe, or $30-40/year in operating costs. Maybe.
  17. ajamison

    ajamison New Member

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    Yes, I'm probably leaning towards that. I guess worse case, I end up running in hybrid some, but still come out ahead. Considering I can get one of these for under $1000, not sure that the extra 10 gallons in an AO Smith 60 gallon is worth almost $400 more.
  18. semipro

    semipro Minister of Fire

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    I'm assuming the basement is well coupled to the ground. At least it was. I'm in the process of insulating walls and floors in some basement areas, maybe not in others.
    I agree, whether heat comes from the house or the surrounding earth would be dependent upon temperatures of sinks/sources.
    I'm not sure yet whether the walls are a source of heat in the winter or not but I'm wondering. No assumptions at this point.
    We'll have to disagree as to whether heat lost from the electrical resistance WH is recovered by the HPWH. I maintain that once the heat is out there, it will increase air or ground temps (even if not measurable),and become HPWH fodder.
    Last edited: Jan 30, 2014
  19. woodgeek

    woodgeek Minister of Fire

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    Yeah, we can't tag heat. The point is that you pay for the heat that leaves the tank. In a closed system, you would get that heat back, so recover some of the expense in principle. IF you are well coupled to a heat sink, though, the temp at the HPWH doesn't change, and so that lost heat saves you no money on the operation of the HP. So, even if you got some heat 'back', loss is still loss.
  20. ajamison

    ajamison New Member

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    Still mulling this over, but I had one more question. With a 50 gallon unit, like the new AO Smith SHPT-50, if the unit is set in hybrid mode, will its recovery rate be the same as a conventional 50 gallon electric DHW or still be slower?
  21. woodgeek

    woodgeek Minister of Fire

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    The AO Smith in engineered to make the hybrid recovery no faster than the HP, to discourage folks from running hybrid. I find the recovery is fast enough 3-4 hours on my 80 gallon. Some hot water before that time.
  22. Ehouse

    Ehouse Minister of Fire

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    How would this set up rate for efficiency? I have an upstairs closet/chase above my wood stove containing the class A chimney which sheds heat which is mostly lost to the attic. If I place a HPWH next to the pipe, I can scavange that heat before it exits the living space. In summer, I could pull heat from the Attic or just cool and distribute the ambient house air using the closet/chase for a plenum. To helk with the basement. Keep everything in the living space. There's even a south facing sloped roof 10' away if I need to supplement with solar, but it may not be necessary.
  23. ajamison

    ajamison New Member

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    So is there really a practical difference between the two modes? I guess that how/why they got such a high EF (2.75) for both modes.
  24. woodgeek

    woodgeek Minister of Fire

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    Sadly, I forget the details now, but they wanted to nudge people towards running 'eco' all the time. But I think my model has EF=2.4.
    Last edited: Feb 22, 2014
  25. woodgeek

    woodgeek Minister of Fire

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    To be honest, a lot of these ideas leave me cold. The system runs a few hours per day, tops. If its at night, the attic will be cool. How much heat will you lose through the attic duct 24/7? As for the chimney...say 20 hours of extra heat will not be 'recovered'. I think this sort of stuff is unlikely to make a noticeable difference in usage. The major point is that a HPWH uses 40-60% less than conventional. **Maybe** you'd get a 62% versus 60% reduction? Is it worth the trouble when the bill is <$20 mo?

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