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Community and Q&A

Sanden water heater, split CO2 heat pump

user-1137156 | Posted in Energy Efficiency and Durability on
It looks like this is the way to go for Domestic Hot Water (DHW)! There are a couple of places to buy these over the internet with the contractor support gambit of no warranty but the published pricing should, hopefully, reduce contractor greed. The 43 gallon system @ $3900 or the 83 gallon for $3950
Why would anyone choose the 43 gallon? The installation only involves water pipes so NO refrigeration skills are needed, just plumbing and electrical. Only needs 15 amp 240V circuit. There is NO resistance heater! Plumbing MUST include a “tempering” valve on the output side as the system can produce up to 175 deg f. hot water. There is an online test report of the Australian version which is a good bit different (149 deg fixed water temp & 84 gallon tank) but the tank heat loss should be close & was reported as 4 BTU/Hr deg f and COP @ 17f out door temp was 2.1 while it delivered 4KW of heat. The US versions permit adjustable peak temperature settings from 130f to 175f and some time of day cycle time options. Obviously the most efficient operation will be at the lowest temperature setting at which the owner “doesn’t run out of hot water” With 130 f tank temperature and 70 f ambient it’ll take 2.87 hours to lose 1 deg f. I couldn’t find answers to my question about set point, hysteresis and minimum heat output, it is a variable speed (inverter) system. The only partial answer to the operational details, that I found, was the compressor starts when there is 40 gallons remaining at the selected temperature. I’d sure like to know much more about operational details to avoid “short cyclic” operation. Now all I’ve got to do is build the house for it.

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  1. _matt_p | | #1

    Hi, looks promising. I am also interested in this unit, but cannot assess how concerned I should be about freezing pipes in winter. With these heatpumps, the heat exchanger is outdoors and the water travels to the tank indoors. When you loose power in winter, the freeze protection and heat cable they have stops working, then there is supposed to be a automatic three way valve that you can add which drains the water automatically when it feeezes I think, but I did not quite understand what it is doing or when it kicks in. Did you understand it? Maybe you live in want parts of the country?

  2. user-1137156 | | #2
    I found the details I was looking for. the "set point is the temperature of the water being fed into the top of the tank. The cycle begins when the mid tank temp drops below 113deg f. and ends when the water entering the outdoor unit is 122f or above So it'll NEVER short cycle! COP is 4.5 @ 47 deg f outdoor temp with a set point of 140f! WOW! this thing is way better than I'd even hoped .
    EDIT, After more studying & noting that the COP falls above 67f outside I'll use the timer to inhibit operation between 6 AM and 10 PM. Combined with a 130f set point I should be close to a COP of 5.5 all summer, simply Awesome!

  3. Expert Member
    Michael Maines | | #3

    The Sanden unit is awesome. I haven't used it on a project yet but have spec'd it as an option several times. It's expensive, but nothing approaches its efficiency, and getting the condenser outdoors solves a few problems. A company I used to work for installed what I think was the first one in the US, in Maine, so cold climates are not an issue. I would think the smaller units would be fine in parts of the world that are stingy with water use. We're very wasteful with hot water here in the US.

    1. bob_swinburne | | #25

      I have heard that you can add a small radiant loop off the Sanden. That would be excellent for those of us in the frozen north (not today) who heat with wood stoves but need a little backup now and then.

  4. Yupster | | #4

    Keep in mind that hot water is typically maintained at 140°F to prevent legionella bacteria from surviving. At 140°F legionella bacteria die within 30 minutes, well within the likely resident time of water in the tank.

  5. Jon_R | | #5

    A Chiltrix HP comes close in efficiency and is rated for significant space heating use.

    I suppose that a design that drains whenever power fails would protect either one - but antifreeze and a heat exchanger might be better.

  6. user-1137156 | | #6

    The "drainback" freeze protection is, I believe, incorrectly, shown in the second previously linked "white paper" IMHO the authors of the paper got the types of valves backwards, and what is shown REQUIRES power to all three valves to drain What is shown can only work with a "standby" power source and additional relay that powers all three valves during a power failure. The implementation with battery power to the valves would add less parasitic power consumption, during normal operation, than the simpler version with all line powered valves energized by power to the system. . FWIW I am building in central Kentucky and must expect both freezing and power outages so I will implement a drain back concept in addition to the heat tape..
    Edit After a drain back event the system may need to have air purged before restarting, if this is true the "version" using a battery could also lock out a restart thereby forcing a manual restart.

  7. user-1137156 | | #7

    Based on the following data on Wikipedia
    "Temperature affects the survival of Legionella as follows:[3]

    Above 70 °C (158 °F) – Legionella dies almost instantly
    At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)
    At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (Decimal reduction time (D) = 80–124 minutes)
    48 to 50 °C (118 to 122 °F) – can survive but do not multiply
    32 to 42 °C (90 to 108 °F) – ideal growth range
    25 to 45 °C (77 to 113 °F) – growth range
    Below 20 °C (68 °F) – can survive, even below freezing, but are dormant
    Other temperature sensitivity[29][30]

    60 to 70 °C (140 to 158 °F) to 80 °C (176 °F) – Disinfection range
    66 °C (151 °F) – Legionella dies within 2 minutes
    60 °C (140 °F) – Legionella dies within 32 minutes
    55 °C (131 °F) – Legionella dies within 5 to 6 hours

    With a turn off temperature of 122f the whole tank is heated to 122f. I rather doubt that Sanden is taking any risk in allowing the 130f setpoint.

  8. Yupster | | #8

    122°F is just at the top of the range where legionella survive. 130°F is in the range where they die in a few hours. 140°F is the recommended temperature in any literature I've seen for setting your tank to reduce the risk of legionella. You can do whatever you want, it's your water (although many building codes mandate 140°F as a minimum, so there is that). The length of time you want to permit potentially deadly bacteria to survive in your system is determined by your water temp. If you aren't killing them fast enough, there is potential for them to be transported into your water lines and hang out multiplying at the end of a seldom used run, where the water temperature is much cooler. Lots of documented cases of this occurring, mostly in health care institutes where this sort of thing is sampled.
    Here's an interesting report on it that might do you better than Wikipedia ;)
    EDIT: Here is an even better article:

  9. user-1137156 | | #9

    To be sure of eliminating

    There is an energy price for eliminating the threat which probably doesn't occur at a 140f set point but definitely happens with a 150f set point which is the Sanden recommendation.. "66 °C (151 °F) – Legionella dies within 2 minutes"

  10. calum_wilde | | #10

    I love the idea of this system, but I'm holding out for something better. These are over priced and the fact that they have water outside is a huge mistake for the target audience.

    Compared to the price of the Sanden system, I paid about an extra $900 for a high end ductless mini split last year. That system is heating half of my house. One of these HPWH with an 83 gal tank doesn't need anywhere near the heat output yet the system alone costs 80% of what the installed ductless mini split did? No, thanks.

    Also, I looked extensively into these, they require heat tape in any climate that could get freezing temperatures. That's just going to throw heat into the winter air. Hard no. Even with the price being almost double what I think this unit is worth, I was still considering it. The heat tape is what made me put my wallet back in my pocket. That's the stupidest thing I've seen in this space. It solves the need to train and equip technicians to work with CO2, but it's completely stupid from a consumer point of view and just looks like the company was too lazy to solve that issue correctly.

    In case the right person is reading this: I've got $2k CAD burning a whole in my pocket right now for the first company that comes out with a north american compliant mini split HPWH that has CO2 going to the outside unit. I'm in the Halifax area of NS. Call me if you have a product appropriate for this climate that you're charging a reasonable price for. I've been a technician in a few fields; of the related fields are refrigeration, electronics, and instrumentation. If you want a somewhat educated/knowledgeable user to monitor energy usage for a case study or just to guinea pig a new product, I'm your guy. We're a typical family of four with fairly typical water usage. I'm in the market for a monitoring system right now to get an educated estimate of our present water heaters energy consumption, I hope to have something in place in the next couple of weeks.

    1. T_Barker | | #20


  11. Jon_R | | #11

    I expect that any water heater that is pumping water through an external heater won't stratify nearly as much as a typical electric water heater. So my guess is that a Sanden at 122F would have less Legionella risk than a typical electrical water heater at 140F.

  12. lance_p | | #12


    You mention "getting the condenser outdoors solves a few problems". Which problems specifically? I'm looking into conventional HPWHs and just want to make sure I'm not overlooking something.

  13. STEPHEN SHEEHY | | #13

    Is this one of those situations where installing an ordinary resistance water heater and spending the $3,000 you save on additional pv panels is cost effective?

  14. Expert Member
    Michael Maines | | #14

    Lance Peters,
    The common complaints about "conventional" heat pump water heaters are noise, cooling the space, and using air you've already paid to heat once. With a split unit, none of these are issues.

  15. onslow | | #15

    Just want to point out that most Legionella cases seem to relate to large systems, not home showers. Not that it can't happen. Failing management or infrastructure (like Flints problems) or disasters impacting waters supplies like (name your part of the country), could deliver substandard water to your water heater.

    However, quoting the CDC site, "Outbreaks are commonly associated with buildings or structures that have complex water systems, like hotels and resorts, long-term care facilities, hospitals, and cruise ships. The most likely sources of infection include water used for showering, hot tubs, decorative fountains and cooling towers (parts of centralized air-conditioning systems for large buildings). I suspect that most of the roughly 6700 cases a year relate to non-home sources.

    It has been recommended for many years, that homeowners set their water heaters for 125F to avoid scalding risk. If the Legionella problem was that grave, one would expect to see a very different distribution of cases. The energy penalty and scald risk of holding a tank at 140F doesn't seem to be justified. Mr Liebler set out the death factors at 122F which seems to support my sense of it.

    A bit suprising to me is the lack of legionella outbreaks in the southwest region (where I am). There are many houses which use swamp coolers in place of regular AC. The whole premise of swamp coolers is to bath an absorbent mat with water and blow air through it into your house. The coolers sit on top of roofs which around here easily hit 100 to 110 which is prime incubator range. No one seems to think this a risky idea, and as far as I know they must be right as legionella doesn't get much thought around here.

    I guess the take away might be that home systems do not generate sufficient colony sizes to pose harm in most cases. The risk may change, but I would rather focus on keeping the municipal systems in good repair and management on the ball.

  16. heidner | | #16

    You can sanitize the water all you want in the hot water tanks and still have significant growth in Legionella within the building. Legionella can continue to grow in dead end stubs, sinks faucets, and pipe runs that are not frequently used. The Legionella can enter water system via the cold lines also. At 125F the Legionella may surve or die slowly... , you just don't want them multiply while in the tank. If the Legionella isn't multiplying - then the count of bacteria is likely to be the same as if you are getting the bacteria from your cold water tap.

    If you believe you have significant Legionella entering the house water system - then - think UV disinfection at the point of entry in the house... but that also consumes energy (potentially a lot) and it still may not solve the problem completely.

    Running a DHW tank at 140F, suggests (or is required by code in some locations) to tempering valves that lower the water temp to prevent scalding for children and seniors (some of whom can't sense water temps as well). But that 140F tank temp doesn't do anything for the Legionella in the cold lines, the lines after the tempering valve or at the faucets. Tempering valves can add another location for Legionella to grow.

    Running a DHW heater to sanitize instantly (160F) is a great method to consume a significant amount of energy... while incorrectly assuming you've solved a future in home Legionella problem.

    Jim Lutz had a pretty reasonable presentation last year (2017) at the ACEEE hotwater forum which shows more of the issues,

    If you are on city water, in locations that add chlorine that water treatment and combination of 125F-130F is likely to be all you need to prevent Legionella outbreaks in the tank.

    Again, the tank temperature doesn't help the Legionella growth elsewhere in the system.... and using reverse osmosis or activated charcoal filters on the incoming supply for the whole house doesn't offer long term protection... Legionella has its ways to infect a system.

    And if you are worried about chlorine in the system... use point of use filtering that you replace frequently.

  17. Expert Member
    MALCOLM TAYLOR | | #17

    What is the sweet spot? I probably keep my water heater a bit warmer than is necessary for health reasons so as to have enough hot water to fill a good sized bath. Would it make more sense to have a larger capacity tank and keep it cooler? or maybe the opposite?

  18. Yupster | | #18

    Evaporative coolers don't produce any aerosols, which is the transfer mechanism for the disease. No problems there. Same reason you don't catch the disease from stagnant natural sources. Common infection sources are showers, hot tubs, fountains, etc. Things that create a spray.

    In reference to the assumption that this is a problem for large scale systems, I'll quote the article from the Canadian Journal of Infectious Diseases article I linked to "in a case-control study of sporadic cases of community-acquired legionellosis, Straus et al (6) concluded that the residential drinking water supply was responsible for a substantial proportion of sporadic cases of Legionnaires’ disease. These findings are supported by Stout et al (7) in a study of 20 Pittsburgh patients with culture-confirmed Legionnaires’ disease." The same article also mentions reasons why the actual problem is underestimated.

    I'm certainly no expert as to the risk of Legionella but there seems to be a general consensus of risk and a consensus by many organizations including the World Health Organization that a 140°F setpoint is a simple and effective method for reducing risk. Seems wise to follow the recommendation of professionals, much like we do here at GBA when it comes to construction. Maybe the risk is low enough that you can set it lower. But I will err on the side of caution when it comes to people using my designs being exposed to infectious diseases. Scalding seems like an easier risk to manage.

  19. onslow | | #19

    I have a friend who is an epidemiologist. I will have to ask how much effort is put into monitoring the types of infections. It may well be that cases are under reported in the residential context for simple lack of looking for and identifying causal agents. One more thing to end the world with a whimper.

  20. user-2890856 | | #21

    Roger Berry . Most of the outbreaks you hear about are because they happen in large gathering places . fact is that 50% of cases are misdiagnosed as a form of pneumonia and they are isolated due to originating in households .

    1. Expert Member
      Dana Dorsett | | #22

      Richard: Good information, but you realize that Roger last posted on this thread about 6 months ago, right?

  21. Andrew_Camarata | | #23

    I know this is an old article but just wanted to share my experience. I had issues with my Sanco2 unit and tech support has been unable to diagnose the issue leaving me with an expensive paperweight. The co-owner (formerly the primary salesman) is the one providing tech support and doesn't seem to have a good understanding of how the unit operates functionally. He wanted to just throw parts at it which didn't work then he stopped responding after changing parts didn't work. For anyone purchasing this unit understand that this company may not stand behind the product or be able to help you if things go wrong. Even if they replaced the entire unit via warranty you or you're client would not have any hot water for an extended period. It would be a good idea to have a back up hot water source in conjunction with the Sanco2

    1. Trevor_Lambert | | #24

      This is sobering information. I was considering buying a used Sanco2 from a guy who installed it without any heat tape, with unsurprising results. He decided to replace the system, after having been shipped a part under warranty. Your story makes one wonder how likely this part is to return functionality to the system, and whether they'd even be able to assist in troubleshooting if it didn't.

      1. Andrew_Camarata | | #26

        Trevor, After my experience I’d say to avoid that. Why would someone not just get it fixed if they had the part on hand. It’s safer to assume it’s not repairable. Besides the lack of manufacturer tech support there’s no significant technical documentation on how the units controls operate.

        On a separate note; If it doesn’t work out...I’m hypothesizing that I need a new controller/display for mine and I’d be willing to buy just that part to experiment and maybe get lucky. I contacted all the online resellers to try and buy one but I got no response regarding that part. I think that shows more reason to beware. You can’t go to your local supply house and get a part

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