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Thread: Heat Pump with inground Spa

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    Join Date
    May 2016
    Loomis, CA

    Heat Pump with inground Spa

    I am in the process of building our pool and want to finalize and order the equipment. Our build is here if interested: New Owner Build Pool with Rock Blasting - Loomis, CA

    We live in Northern California (Sacramento area) and have a large PV solar system feeding our house (with excess as we built it in preparation for the pool).

    Our pool designer detailed plumbing for future solar with a Hayward CSPA XI 11 electric heater for the spa.

    I am now doubting this set up and wondering if a combo Heat Pump for the pool/spa would be better or quicker to heat the spa? Does anyone have real world experience using electric heaters or heat pumps for in ground spas? Basically I am trying to figure out what will heat the spa the quickest powered by electricity.

    We live on 5 acres and have plenty of room for solar panels so heating the pool I am less worried about.

    Spa size is 8' diameter or roughly 800 gallons.

    Pool is 20'x44' with a shelf roughly 33000 gallons.

    Thanks in advance!

  2. Back To Top    #2

    TFP Guide
    needsajet's Avatar
    Join Date
    Jan 2016
    Sydney, NSW, Australia

    Re: Heat Pump with inground Spa

    I know you want real-world, but also noticed not much iscoming in for you.

    Speed of heating is purely about how many BTU or kW you put into the water per hour.So look at the Output figures for the two options. The resistance (element)style heater is very easy; it's just a flat amount of heat no matter what, andinput energy will equal output energy.

    The heat pump will only reach it's "headline" output at the tested water andair temperature quoted in its specs. The heat pump will have a Coefficientof Performance (CoP). Let's say it's 4, whichwould mean 1 kWh of energy going in and 4 kWh getting into the water.1 kWh comes from your PV or the grid, and 3 kWh comes by absorbing heat energy from the surrounding air.It's kind of like 400% efficiency relative to electrical energy in toheating energy out.

    You can't rely on headline output for all conditions, because as air tempdrops, so does the CoP. You can dig up the performance curve for most heatpumps, or find a typical one and get a rough idea how it works. You'll findthat it's pretty flat from about 60d and up. It will drop a bit steeper down toaround 45/50d and then go pear-shaped somewhere below that. When you get verylow temperatures, the heat pump also needs to defrost itself, so energy isneeded for that as well.

    If you want year-round use, and you get temps in the 30s/40s, you might wantboth heat pump and resistance, or heat pump and a small gas heater. The heatpump running during winter could rack up a lot of hours getting the jobdone, so that's a life expectancy consideration. This is only my own opinion,but heat pumps running under 45/50 always sound like they're running hard,so I personally don't like them as it gets near freezing. At some colderpoint, it will just reach it's limit and shut down. I've heard that it'spossible to get heat pumps with a resistance element that cuts in when CoP forthe heat pump drops to 1, but I haven't been able to find one down here yet.

    I don't know about the USA, but I searched high and low for the magical latesttechnology European heat pumps with CoPs of 6 to 9. It took a while, but Ifinally learned that they're allowed to quote specs in Europe that are"compressor only". A true CoP would include power for fans,controls, etc. and be performed at conditions the equipment is designed for. Ifyou're only using it under swimming season conditions, it's fair not to includethe defrost power. Most people seem to think a CoP of 4 to 4.5 is a reasonable real world CoP toexpect for swimming season conditions.

    Better experts will correct me where I'm wrong ormisleading, and some people with real-world pool experience will see the threadbump!
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