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Community and Q&A

Dual ductless heat pump

ticlaude | Posted in General Questions on

I have a New Sharp heat pump
one outside unit & 2 inside unités on heat mode m’y downstair unit set to 24c the upper unit  set to 16c but Room température raises Up to 21c 
they tell me that IT is normal because the heat from the Botton unit is transfering to the upper unit i don’t agree the publicity says that we can control the température on Each devices .Am i wrong or
they are right.Why have two units
Thanks for your advise
Thank you but my question is that the upper unit in fan mode only should not blow hot air but it does they all dual makes have the same issue I wasn’t told that 2 years ago when I bought the system they tell they do not recommend dual heat pumps no more because of this issue.
Thanks again 

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  1. Expert Member
    Dana Dorsett | | #1

    If there nothing to block air from moving between the upper and lower floors, heating the lower floor at 24C could very easily keep the upper floor at 20C+.

    Warmer air is less dense than cooler air, so the warm air will rise, and the cooler air will sink. With open doorways it will be difficult to keep the upper floor 8C cooler than the lower floor. Even with the doors closed there may need to be insulation between the floors to keep the temperature difference that large.

  2. Trevor_Lambert | | #2

    Yes, just to reiterate what Dana said, the heat is coming from downstairs. Even if you didn't have a head upstairs this would be the case. If you need the upstairs that much cooler in winter you need closed doors and insulated floors. Even then it might not be possible, since you're sharing the same ventilation and there's going to be air leakage between floors. 8C is a pretty big difference, and it's in the opposite direction that is natural. 24 upstairs and 16 downstairs would be a lot easier. The opposite is the case in the summer.

    1. ticlaude | | #3

      My question ,i know heat rise IT is not m'y question because at Nights door close upper unit off bedroom température 17c to 19c
      downstairs unit set to 24c we sleep Very well.My question why is heat comming out off m'y upper unit in fan mode only Sharp is saying that IT is normal with dual ductless regardless if the brands

      1. bfw577 | | #4

        There is always refrigerant flowing to the unit even if its off. If the other unit is in heating mode there will be hot refrigerant flowing through the coil in the other unit thats in fan mode. Thats how they operate when there is more than one unit on the same outside condenser.

  3. ticlaude | | #5

    Ok thanks IT is normal,last question
    why in there publicité they say that you can contrôle the température in each room i now IT is false impossible with one outside unit only, again heat pump distributors don't now there product . Thanks again

    1. Expert Member
      Dana Dorsett | | #7

      It is possible to control the temperature in each room reasonably well ONLY if the ductless head for each room is correctly sized for the amount of heat/cool needed. Most people seem to think "bigger is better", but with multi-zone ductless heat pumps there is definitely such a thing as "too big". A 9000 BTU/hr ductless head in a bedroom is almost always going to have 3 to 4 x the amount of capacity needed.

      When a head has three times more capacity than needed the room can over-heat (or over-cool) just on the bypass refrigerant flows when another head is active, even if the blower in the non-active head doesn't run. If the blower is set to always run the problem is worse.

      It is true that distributors (and even many professional installers) do not know very much about the product or how to make it work well.

  4. Trevor_Lambert | | #6

    There is a certain amount of control, but it has some limitations. You can deliver more heat to one area, but not zero to the other. In most cases this is not a big deal, because there's usually at least some heat demand to both zones at the same time. 8C is just too big of a difference it seems. Is there a reason you keep the lower level at 24C? That would be uncomfortably warm for most people, and I would have thought that someone comfortable sleeping at 16C would be comfortable at 20C the rest of the time.

  5. ticlaude | | #8

    Thank you very much everyone for your answers

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