Domestic Hot Water Using Indirect Tank

Discussion in 'General Discussions' started by tdoe, Mar 20, 2008.

  1. mseifert

    mseifert Member

    $940 installed.

    The real kicker here is that if I choose to go with the indirect tank instead of desup option, I am faced with the choice of either
    1) ordering the CM unit itself without the desup but (according to CM) delivery potentially taking 2 months instead of one or

    2) paying for the desup option but not using it but getting delivery in one month. I'm guessing this is about $450 extra. (I'm tired of being cold)
  2. bryanfoit

    bryanfoit New Member

    I have successfully done this on three installations. All of which have been my personal home or family member. I have used ClimateMaster GSW036 and TMW036 W-W units. Both work equally well. On the first installation I used a standard 80Gallon electric water heater and installed a plate to plate heat exchanger to separate the system. The W-W unit is also used in conjunction for radiant heat in the garage (Cold weather in Iowa). The radiant heat was the original intention but my engineering side couldn't leave that as good enough. This provides 125-130°F DHW in ample quantity to fill the whirlpool or any other high demand application. Recovery times are very quick after a shower. This is installed on my own home and I am very happy with the system. The second installation used a WeilMclain Plus 60 (46gal) indirect. It works very well and supplies 125-130°F water as well, but I wasn't very happy with the quantity of water. By the second shower it was getting cold. The third installation utilized a Plus 110 (95gal) and performance was great, could fill the whirlpool, and have sufficient hot water for anything. I have had great luck with the WeilMclain Indirect water heaters in this application because of the huge surface area they provide. It takes a little trial and error to get the T-Stat set correctly on the indirect water heaters so the W-W does not fault on high pressure. The first installation has been going for 4 years and has worked flawlessly. Highly recommend the setup for extremely cheap DHW. The setup would be costly if you purchased the W-W for the sole purpose of DHW.
  3. mseifert

    mseifert Member

    Being the OP, I thought I'd update everyone on what I worked out with the installer for hot water. We will use reverse indirect. It is a 56 gallon tank. I believe the model is a Triangle Tube Smart Tank - Model Smart 60.

    His cost installed is $2,450 for the indirect. Higher than I was hoping for.

    I'm trying to calculate how long until it pays for itself. Does anyone know what the COP will be to heat the water during the summer with the CM TMW 060? Its rated at COP 3.0.
  4. bryanfoit

    bryanfoit New Member

    Assuming 50F EWT source side and 100F EWT Load side (average of recovery EWT temp 80-120), this gives a range of COP of 3.7-4.3 depending on flowrates for source and load sides. COP drops to around 3.0 if EWT is 30F. The engineering specifications can be found on ClimateMaster's website, if you would like to look at the chart.
  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm not familiar with the CM model number, but summer COP ought to be well north of 3.0.

    In fact, extracting heat from a loop to heat domestic water is especially helpful during summer if system is in cooling mode and thus rejecting heat to loopfield
  6. mseifert

    mseifert Member

    The posted COP for this model is 3.0 and it is a water to water. I won't be cooling with it in the summer so the only use of the unit will be to produce hot water using the 60 gallon reverse indirect as a buffer tank. I presume this will mean short cycling and a reduction of COP. Will the COP go down from 3.0 to 2.0 or will I do better than that?
  7. bryanfoit

    bryanfoit New Member

    The heat pump will not short cycle. Short cycle is considered less than 5 min on/off cycle. It will tend to cycle 15-30min. Typically as you use hot water, cold water will enter into the bottom of the tank until the thermostat calls for heat. At this point the bottom of the tank will be around 80°F. This will be very close to your EWT of the heat pump load side and give you a starting COP of around 4.0. As the tank recovers, the EWT of the HP will slowly increase to 120°F which will give you a COP of around 2.5. The average COP of the recovery will be around 3.25 (4+2.5)/2, subtract out your pumping losses because they are not calculated in the COP of the heat pump and you will be very close to an average COP of around 3.0 for an indirect water heater with a Geothermal Heat pump.

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