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Produce a given amount of heat with 1 vs 2 heat pumps

Austin G | Posted in General Questions on

With resistance heaters, any given fixed amount of heat produced, it’s going to use (pretty much) the same amount of power whether you do it with 1 massive heater or a bunch of little ones.

With heat pumps/mini splits, what does that same fixed amount of heat do to power consumption when produced with one large vs 2 smaller heat pumps?  Let’s forget about oversizing problems for these purposes.

Can anyone help with this?

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Replies

  1. Walter Ahlgrim | | #1

    In terms of dollars cost to purchase the equipment one 4 ton unit will cost much less than two 2 ton units.

    In terms of fuel general one large machine is more likely use less fuel than 2 smaller machines doing the same work. My guess this would be a small difference 2 -9% for one 4 ton unit vs. two 2 ton units.

    In green terms one unit requires less materials to build. One unit requires less fuel to ship. One unit creates less packaging waste

    The case for twin units is won and lost bases on comfort IE zoning in that you have twice as many points in the home that are exactly at the set point. Redundancy sooner or later something will fail with one system you will have zero heat when it does fail. With twin systems you will almost certainly still have one system running.

    Walta

    1. BFW577 | | #2

      My experience has been multiple smaller heat pumps that run at partial load can be close to twice as efficient than one large one running near max.

      I use 3 12k Gree Sapphires in a 1800 sq ft split level in CT. The Grees have almost double the cop at minimum capacity compared to their max. Its way more efficient for me to split the load up between the units so they run as much as possible near their lower more efficient capacities.

      Here is a good example from my house. At 17 degrees my heat loss is around 11-13k btu/hr. I could turn on one split and cover the load but it would be running near its max with a cop of 2.38 consuming 1.85 kw. If I turn on all 3 I now have 3 units running just slightly above their minimiium capacities at a cop close to their 4.32 minimum. The 3 units would also be using considerably less electricity with each unit drawing around .19 kw or 600 watts. The single zone would be using close to 3x the electricity for the same capacity.

      https://ashp.neep.org/#!/product/25406

      1. Eric Habegger | | #4

        I’m a little confused by your explanation. Can you explain how cop goes up with turn down of power? I thought cop went up for a given ac unit when the difference between outside air temp and desired inside temperature is decreased. Are you saying that that’s wrong and the fact that you are using less power in that example is what is causing the increase in cop and in efficiency?

  2. Deleted | | #3

    Deleted

  3. Austin G | | #5

    COP is, I believe, the metric I don’t understand and what is keeping me from my answer.

    What I’m really after is, say I can heat my home with a 24k heat pump (successfully) maxed out. Now say I have TWO 24k heat pumps. Forgetting about the cost to purchase a duplicate unit - just hypothetically, will more power or less be consumed heating my house to the exact same btu output as the one running dead out/full blast.

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