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reverse cycle chiller and radiant

Big Will
Big Will Member Posts: 396
I think a even dozen more than I have done. Thanks for the input. I should see if I can find a tank with the heat exchanger at the top for domestic and do like you say and run the same water through the floor and the Unico. I Intend to use a small backup tank heater for domestic. I would think in the winter it will not do a lot more than a mild pre-heat like you say. I would love to hear your control strategy for outdoor reset and when an if you need a back up heat source for the radiant. Keep in mind this is northern California and we design for 32deg. If we see 32 or lower for 45 days out of the year its a cold year.

Comments

  • Big Will
    Big Will Member Posts: 396
    Outdoor reset and domestic hot water

    My first thought is to intentionally oversize the reverse cycle chiller and use a dual coil 80 gal. indirect as a buffer. If I use the first coil as a heat transfer for the radiant and a taco pump block to provide outdoor reset for the floor. The second coil would heat the domestic hot water. If I keep the tank at 120deg and use a outdoor temp sensor to change from the reverse cycle heat pump to a boiler at what ever temp is appropriated. I need to talk to the guys at Unico about capacities at different outdoor temps. Thoughts?
  • Josh M.
    Josh M. Member Posts: 360


    Will, Unico actually publishes the capacites at different outdoor air temperatures.

    We are currently experimenting with oversizing chillers and installing without any backup. Make sure that buffer tank has allot of capacity. As a general rule of the (very general) you need 2 gallons of buffer for every 1,000BTUH. However, we always use simulation software and size for a minimum run cycle of 10 minutes, which is also the RPA standard cycle time.

    Be very careful running the chiller water through a coil. Coils are very dependent on a temperature difference between the surrounding water and the coil water temperature, so thinking that you can get that tank up to 120 degrees through a coil is probably wishful thinking. Why not run have the same water/glycol solution that runs through the chiller in the heating system? It really doesn't effect your flows that much.

    Also, I plan for 110 degree water, it's tough to get the water temp up to 120. I use a single coil buffer tank and run the domestic through the coil and then to a secondary tank that maintains 120. It basically only gets preheated, which is all you will get anyway.

    Feel free to email me for more info, I'm also okay with sharing some of our piping diagrams. After 12 Unichillers in service, we have the kinks worked out.


  • Josh, no turbomax for preheat? ;)


  • Josh M.
    Josh M. Member Posts: 360


    I'm not following. Are you speaking of a Turbomax instantaneous water heater?
  • Big Will
    Big Will Member Posts: 396
    Wow

    That is quite the heat exchanger. I have never heard of that product but I will call the vendor tomorrow. I cant imagine anything transferring heat as well as that. That is probably better than even the triangle tube.


  • Yeah, makes a good buffer with maximal preheat capabilities. Of course... it's not cheap. I have no idea if it can be cost justified in enhanced preheat.. but with an electric on demand for "boost", and a RCC not being asked to do cooling, you could get pretty close to 110 fixture temp maintaining the tank at 110.

    that's what we do with heat only geo anyway...
  • Josh M.
    Josh M. Member Posts: 360


    The cost benefit ratio has always been the hang up with pre-heating domestic hot water with an RCC or Geo for us. The extra $5-8K could be put to much better use elsewhere.


  • now that's a lot of money. that's more than just a tank upgrade, what are you talking about adding for the pre heat portion?
  • Josh M.
    Josh M. Member Posts: 360


    Well when you add in labor, valves, and piping it can get that expensive very quickly if a contractor is honest about their pricing.


  • I see. I agree that would be hard to get payback on. I'm just trying to make sure we're talking about the same thing: you aren't saying that the turbomax is that much more than a regular tank to set up; you are simply saying that using preheat is that much more than a coilless buffer tank?
  • Big Will
    Big Will Member Posts: 396


    Another wow. Just got of the phone with the distributor in Las Vegas. The shipping will cost more than my first truck. Fortunately the customer is more interested in being green than payback.
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