what should I expect from my sesuperheater?

Discussion in 'Maintenance and Troubleshooting' started by martyg, Feb 15, 2012.

  1. martyg

    martyg New Member

    I'm using a 3-ton Climate Master 27 to heat and cool my house. I have a propane fired Rani tank-less water heater coupled with a circulating loop under the house. I decided to try the built in desuperheater so I could stop using propane but it doesn't seam to heat much water. I installed a 50 gallon electric water heater and a loop from the desuperheater to the tank with the idea of using it for a pre-heat for my hot water loop. Climate Master has two temperature settings and I have it set for 150 degrees. After a 48 hour period the water in the tank has only warmed to 98 degrees (from about 70degrees).
    My HVAC contractor tells me that the desuperheater will only raise the temperature of the water about 1 degree as it passes through the heater; at the rate it is operating there doesn't seam to be any benefit to using it.:confused:

    Comments please
  2. zfink

    zfink New Member

    The desuperheater produces hot water as a byproduct of the compressor running. It appears that your desuperheater and buffer tank is indeed piped in correctly. If you can provide a picture of the installation, we can confirm that for you.

    According to the ClimateMaster manual the 3.0 ton Tranquility 27 unit produces between 2,500 and 3,500 BTUH on low stage and 3,000 and 4,000 BTUH on high stage. The BTUH capacity of the desuperheater depends on the entering water temperature of your ground loop (or water well) and blower speed.

    I typically expect a 5-8 degree rise between the entering and exiting water temperature on the desuperheater piping. It will take a while to heat the entire tank, which is why I advise customers to go with a larger tank. You might only be using hot water for an hour or two each day giving the buffer tank 22 hours to recover when the house is not in use.

    The unit will typically produce more hot water in the summer than in the winter.

    I'm not sure what you are referring to with the 150 degree set point. Is that the high limit on the desuperheater (which I believe is fixed at 130 degrees). ClimateMaster does make a water to water unit that is capable of heating to 150 degrees, but it is the THW series.

  3. jrh

    jrh Member


    Zach is right, I would add that 98* might be as high as it gets in the winter. You still got 28* of your Load met by the COP of the machine. This is good.

    If your only getting a 1* diff. , You might restrict a some flow, on the return, partially close a ball valve?

    As for the 150 setting. Make sure you have anti scold protection you will likely need it in summer.
    Last edited: Feb 15, 2012
  4. martyg

    martyg New Member


    Zach, thanks for responding to my post. I could take a picture but you can't tell much by looking at it. The Climate Master 27 has two dip switch settings on the circuit board for the desuperheater, 1 for "on" at the default temperature of 125 and a second dip switch to increase the out put water temperature to 150 degrees. Or probably I should say those are the maximum water temps it will allow before switching off.

    The piping is very simple, the inlet and outlet connections are clearly labeled on the air handler. I have a 1" pex line running from the furnace to the cold water inlet on the water heater and a 1" pex line running from the cold water outlet on the water heater back to the furnace. The return line (hot water) has a tee in it and I have another line that feeds my house hot water loop (through an adjustable temperature valve to prevent scalding). The house hot water loop returns to the water heater and enters through the P/T opening (I removed it and installed a tee) so that the house loop water short circuits and only runs through the top of the tank.
    When the water heater is powered on the system works very well, but I was trying to get an idea of how much of that was do to resistance heating from the tank and how much was supplied by the desuperheater.
    Outdoor temperatures have been mild her in Raleigh this winter but the thermostat setting for heat changes from night to day 3:00am and runs steady for four hours (I have the stat set for 71 day time and 67 night).
    I'm just disappointed that the desuperheater isn't make more hot water.

  5. zfink

    zfink New Member


    I suspect that the desuperheater is not correctly plumbed.


    If you look at page 16, diagram 15, is your unit plumbed like that? If so, was the air bleed out of the lines? I have seen some desuperheaters that are not correctly working due to being air bound.

    When the temperature is mild outside the geothermal unit runs less, lowering your energy bills, but it also lowers the amount of heat produced by the geothermal units.

    The electric heating element on that tank should not be wired and it should be an unpowered storage tank that feeds preheated water into your instantaneous hot water heater.

  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    In heating dominated climates you will produce way more hot water in winter than summer.
    DSH is capable of more than 150F.
    Do not throttle flow from DSH to improve DT as more GPM (even with lower DT) can often deliver more BTU's.

    What should you expect from your Desuperheater?:
    A DSH is not "on demand" water heating. A DSH will give you about 10% of the BTUS you are extracting/rejecting. A DSH Will make it more expensive to heat your home but- it will save more on your hot water heating bill than it costs on your home heating bill.
  7. ================================

    Sometimes I think that manufacturers have set desuperheater expectations a little too high. Residential desuperheaters when piped and insulated correctly, raise the temperature in a water tank anywhere from 6 - 30 degrees depending on tonnage and run time. You are not normally simply getting 120 degree water.

    I will not rehash the well covered point covered in geo forums elsewhere that you should use two separate hot water tanks. You preheat tank one from the heat pump which then feeds final tank # 2. I recommended studying the hot and cold piping carefully and using brass gravity check valves at key locations to prevent heat from leaving the tank when hot water is not being used. For example I have a brass check valve on the cold water inlet of tank number one and the feed line going to my tank # 2; and one other. Why do that? Well, we are trying to keep all that heat in the tanks. We do not want to lose that heat.

    If you use one tank, it is very doubtful that you will have HOT water much of the year, unless the electric elements are also on and functioning. I know Carrier and Climate Master have specific recommendations for temperature settings of the upper and lower electric heating elements.

    So think of it this way. The water out of the ground is 58 degrees or even less. The heat pump when running, raises the temperature of water in the first tank to 74 - 97 degrees. (I see these values in my own heat pump) Your final heater starts with 97 degree water which slowly drops towards the 70's as you wash dishes or shower. You actually get excellent heat transfer here because heat transfers most readily from hot to cooler.

    Heat up time of the final tank is less, which is where savings come from.

    One other important thing. With the exception of the Marathon electric water heater, most water heaters are poorly insulated and lose 1 1/2 degrees an hour. It can be even worse if they are located in the cold outdoors. Keep that in mind.
  8. tstolze

    tstolze Member

    This is very true, the only time I see a 120 degree buffer tank are after we stay in the low 20's or teens all day, with lows in the low teens or single digits. In the summer on the hottest day's the buffer gets to 110-115 typically.

    Today after a couple of morning showers and 7 total hours of single stage run time my buffer is currently at 96.
  9. johnny1720

    johnny1720 Member

    I have a tankless hot water thank that can only handle 120 degree incoming water, anything more and it shuts down. What would the ideal setup be for me? I love the tankless hot water heater. Unlimited hot water in my house is worth the $500 per year that I pay.
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I don't know, most of our systems run the buffer tank between 120-140F all winter long, even if cycling in 1st stage. Summer is tougher, hardly break 90F.

    Temperature and Energy logging by: Web Energy Logger
    Temperature and Energy logging by: Web Energy Logger
    Temperature and Energy logging by: Web Energy Logger

    Here are more:
    Buffalo GeoThermal Heating

    Heat dominated climate helps since the DSH has higher output in heating than in cooling mode. EWT matters, too. EWT is too low in the summer to get enough desuperheat out of it.
    Last edited: Feb 17, 2012
  11. martyg

    martyg New Member


    Thanks everyone for your comments and advice. You've answered my question, I simply need to adjust my expectations.

    For Docjenson, my Rannai brand water heater has a default high water temperature of 120 but I purchased a "remote" control that allows me to increase that limit to as high as 140. 130 degrees works best for our family.

    To re-cap a bit, I had the tankless water heater (propane) and circulating loop before I installed the GSHP, and it worked just fine. But I just can't leave anything alone so I installed an electric water heater another loop from the furnace and then blended the two loops together. That works marginally well. My "problem", if you can call it a problem is that my house is very tight, the crawl space is "closed" and well insulated and the house is very well insulated. I live in a relatively mild climate and I just don't get much run time on my unit. Another consideration driving my decisions is that my back up generator is at full capacity when running the GSHP and geeting hot water by a demand gas water heater relives that presure (we seem to lose power a lot around here).
  12. Comment


    We have to be precise here: but my experience for RESIDENTIAL application suggests that summer use can produce MORE heat if you tweak water flows down.

    Why? the answer, at least for smaller tonnage is that you have TWO heat exchange coils carrying heat away, not just one. (I will leave comments for closed loop systems to those who own closed loop).

    By the way, one thing that often occurs here is that is closed loop returns at warmer temperatures, may still cool ok, economically, but tend to produce MORE hot water.

    Commercial air to air supermarket application, for example, would be an ENTIRELY different story because supermarket refrigeration produces ENORMOUS amounts of HEAT. Supermarkets remove heat differently.

    I have seen earlier supermarket desuperheaters heaters (designed to heat 150 gallon water heaters) blow up a water heater when the aquastat and safety failed and water went past 212 degrees!

    Any desuperheating in winter automatically subtracts 10% of available output heat in winter, though hot water desuperheating does not produce any negative in summer. You might increase winter heat output with higher water flows, although that comes with the cost of the higher flows (higher electric bill).

    Obviously a key factor is the temperature of the incoming water. 70 degree water is surely more economical than 58 degree water, or 36 degree water!

    The only way I see lower hot water heat production in summer is if you keep the original setting of the installers AND NEVER CHANGE IT EVER.

    In many cases temperature of incoming water changes between summer and winter, by as much as 12 degrees, or more, so in a certain sense, it is a relative adjustment.
  13. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    HVAC Tech

    I do not miss large commercial work. If I had learned how to manage heat exchange on a large big box type supermarket I might not be typing here. I would be someplace warm having a drink in shorts and a "t" shirt instead of trying to warm my feet. Alas that is not the road I took and I shall be ever thinking in geothermal radiant.

    I have learned that heat transfer is heat transfer. The laws of thermal dynamics do not change by supreme energy court thinking. The only thing that changes are the rules of engagement.

    A de-superheater is what it is. It takes some of the BTUH from the hot gas side of the refrigeration system and converts it to usable hear out put, ie, reuse before the BTUH is dispersed into the air, a cooling tower or in our case the earth. That is all it does.

    If one has a de-superheater or domestic hot water generator loop, on one's geothermal heat pump, then you are able to capture some of the heat one is generating and instead of discarding it, one directs it to production of DWH.

    Directing BTHU to DHW and harvesting the BTUH takes care in piping. It is not a be all for DWH but it can play a significant part in an over all plan to payless for what we want and need.

    Harvesting this BTUH requires proper planning, piping, plumping and patience.

    Your mileage may very. Please keep your hands and feet inside the ride at all times.

  14. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You talk a bit of a mystery here to me. First of all, yes we are talking about residential applications, not about supermarkets here. This thread started with a 3 ton CM.

    Second, if you look up the performance tables, a 3 ton CM always has a higher DSH output in heating mode versus cooling. Interestingly, in 1st stage there is a balance point where at about 90F EWT the DSH starts to produce more BTUs in cooling than in heating.

    Third, yes, you have more DSH output if you throttle the flow, but you loose overall efficiency. Not worth it.

    Fourth, yes it does steal 10% of the heat from the heatpump, but that is the purpose. Since it does produce this heat with the efficiency of the heatpump, this is pretty much the cheapest way to make your hot water, or at least part of it.

    Yes, higher flow is always more efficient, but there is a balance point where you pay too much for pumping. To go from 1.5 gpm/ton to 3.0 gp/ton will increase output of both the total capacity and the DSH by roughly 10%, but to go beyond 3 gpm/ton increases the pressure drop exponentially and is not worth the extra pumping power.

    Our loops run down to 30F in the winter and up to 65F in the summer, so our EWT varies by about 35F between summer and winter.

    Again, changing (reducing) flow for the purpose of higher DSH production does not make sense because your overall efficiency decreases.
  15. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I would say that throttling DSH raises the temperature, but that doesn't mean you are getting more heat as GPM and Delta T determine amount of BTUs delivered.
  16. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Throttling reduces delta-T between refrigerant and water, so reduces total heat transfer
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Last edited: Feb 23, 2012

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