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Good source for minisplit turndown ratios and turndown vs. HSPF / SEER?

keithhoffman22 | Posted in Mechanicals on

Hi,

I was going to ask this on this thread:

But realized it was a separate question.

Does anyone know of a good analysis of the energy impact of turndown ratio vs seer/hpsf for current mini split equipment? It would be interesting to see some modeling of higher hpsf/seer equipment vs broader turndown ratios? It would seem that for a lot of applications, especially divided spaces with modest loads, that turndown ratio would matter more for both efficiency and comfort. For example, in Colorado, evening temperatures (master bedroom mini for example) require cooling typically until midnight but the demand is fairly low beyond initial startup. 99% peak load will be pretty high compared to typical use, especially if the equipment is mostly off during the day. If you aren’t talking about a space with 1 ton+ load during typical operation, it seems like turndown ratio could matter a lot more for efficiency than hpsf/seer. To point, does a lower minimum load on LG (1000 btus I believe) potentially trump higher SEER on equipment with a higher minimum (i think some of the high seer mitsubishi’s only turndown to 2800 btus). Not surprisingly, a manual D/j doesn’t help much.

Maybe this was covered elsewhere?

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Replies

  1. user-626934 | | #1

    Minimum capacity of 1,000Btu/hr sounds fishy to me. In cooling mode, at lowest compressor speed and reasonably low outdoor temperatures (<85F), a good mini-split will have a COP in the ballpark of 10 (maybe higher). COP of 10 at 1,000Btu/hr = 29W total power input. I really doubt they can go that low.

    NREL's lab testing from a couple of years ago showed minimum capacity to be significantly higher than the listed minimum capacity from the manufacturers.

  2. user-626934 | | #2

    Sorry...meant to include the link to the NREL report: http://www.nrel.gov/docs/fy11osti/52175.pdf

  3. Dana1 | | #3

    Per the engineering manual specs the LG Art Cool Premier can modulate down to 1023 BTU/hr in either cooling or heating mode, but I have no direct experience with them, haven't watched them cycling at low/very-low loads, nor have I seen third party test data on them.

    http://www.lg-dfs.com/art-cool-premier.aspx/Download?filename=EM_SZ_ArtCoolPremier_ALL_12_15.pdf&id=188

    I agree that it's a bit difficult to believe that it modulates well at that very low output level, but that's the claim.

  4. keithhoffman22 | | #4

    Huh. No email notification of responses.

    John, I guess I'd discount that report based on age. 5 year old report. The tech seems to be changing quickly.

    Dana, I agree the range seems remarkable. If it is true, could it have a lot of efficency and comfort implications (isn't oversized ac cycling why many people turn the thermostat down or the fan on continuous? )? Additionally, perhaps it could create a new grid control option. Instead of a 'saver switch' which turns off the unit (resulting in comfort loss and withdrawal from the program), perhaps a switch could limit amperage etc in a way that allows some cooling but not the full demand.

    Anyways, just wondering about whether there are simulations/models out there looking at the implications of high turndown ratio or if folks thought SEER/HSPF accounted for it.

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