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Heat pump selection

Sofiane | Posted in Mechanicals on

Hi,

I need a bit more help with and HVAC project I started planning last year in zone 6, but couldn’t yet start until this year. 

After a bit of redesign with our engineer I was about to sign the contract this year with my HVAC contractor when we hit a small snag.

Our final plan was to go with a Carrier system containing:

2x (40MBDQ18 +  38 MAQB18R)

Unfortunately, the 38 MAQB18R is discontinued and its replacement, the 38 MARBQ has lower modulation, especially in summer time when my loads will be lower:

https://ashp.neep.org/#!/product/36669/7/25000///0

I know 1:1 is usually favoured and multizones are a bit less efficient, but I keep wondering whether it would make more sense in my situation as the minimum modulation of the multizone is almost the same as that of the single zone. 

38MGRQ36D–3


https://ashp.neep.org/#!/product/30605/7/25000///0

I omitted some elements of the design for the sake of simplicy as this is the only contentious point that remains. 

Thanks for your thoughts. 

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Replies

  1. Expert Member
    Akos | | #1

    Looks like paired with a 24k indoor unit, you get a bit more heat and better turndown out of the single zone:
    https://ashp.neep.org/#!/product/62706/7/25000///0

    Also the NEEP data isn't always 100%, I would check the engineering manual for the unit.

    Generally a right sized multi split connected to large indoor units works well but there are too many unknown how exactly it will work. Since the BOM cost is about the same, I rather have the two one to ones.

  2. Sofiane | | #2

    Thanks Akos, helpful as always.

    The engineering manual for the older model was the same as the neep info whereas the neep info for the new model is a bit all over the place compared to the manual. At least the engineering manual for 38 MARBQ claims the lowest cooling is 6500 but which isn’t bad if true.

    I guess a further question would be : I had the option of going with a pair of PEAD-A15AA7 with SUZ-KA15NAHZ with the same company. The specs were rather similar and pricing was more so I didn’t think it made sense although it had a bit more leeway with static pressure.

    Would you pick the Mitsubishi over the Carrier? Or does it truly not matter as long as the install is good?

    1. Expert Member
      Akos | | #3

      Unlike the 12k unit, the Carrier/Midea 18k units have decent pressure, not quite as high as PAED but good enough. They can also be mounted in vertical orientation which might help with install.

      The better option is the Fujitsu low/mid static unit which have better turndown but don't come with a base pan heater. Generally in very cold climate or if you are in a place that sees a lot of very humid just bellow freezing days, a base pan heater is a good idea.

      At the end of the day, all of these are so close in performance that it is hard to pick between them.

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