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Old 08-12-14, 03:42 AM   #1
SDMCF
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Default Used mini split installation

I recently bought a job lot of used stuff that included 2 mini split systems. I know little about such systems and I would welcome any advice about how to install these - and indeed whether I should install them. I have read a lot on here, especially the "Mini Split install" thread which was very helpful (thanks) but I am unclear about how installing used items might differ from installing new equipment.

The units I have are Mitsubishi MUZ-FD25VABH (outside) and MSZ-FD25 (inside). I know where these came from and I am confident they were working well before removal, but I did not remove them myself and do not know how the removal was done. So I don't know if the regrigerant has been lost, or what is currently in the devices. Nor do I know how to check that. Does this mean I should remove the content of the equipment and re-charge from scratch? If so, how do I do that and what do I do with the material I remove? How do I re-charge the units?

Our climate is such that I would rarely use the devices for cooling, so I am only really concerned with the heating capability. My doubt about whether I should install the units concerns how efficient they can be compared to my existing heating, which uses a ground source heat pump. At a simplistic level I would assume that the efficiency of my GSHP is similar to these mini splits, so the main factor is the temperature of the heat source (ground or air). For most of the winter the ground will be considerably warmer than the air. Does this mean the splits would only be more efficient during short intervals at the start and end of the heating system when the air is warmer than the ground? So is it worth fitting them or would I be better off re-selling them?

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Old 08-12-14, 07:01 PM   #2
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Use a differential controller to decide whether to use air source or ground source. Since heating dominates in your use case, you could also look into adding some solar collectors to "recharge" the ground thermal mass.
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Old 08-13-14, 12:04 AM   #3
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Quote:
Originally Posted by SDMCF View Post
At a simplistic level I would assume that the efficiency of my GSHP is similar to these mini splits, so the main factor is the temperature of the heat source (ground or air). For most of the winter the ground will be considerably warmer than the air. Does this mean the splits would only be more efficient during short intervals at the start and end of the heating system when the air is warmer than the ground? So is it worth fitting them or would I be better off re-selling them?
I would guess that if your GSHP was properly installed, it is more efficient and will be far more reliable than your used mini-splits.

In other words, regarding your GSHP, you are pretty much already in heaven, you can't get much better than that.

However, if you are of such a disposition that you just crave getting in and thrashing around and making things work, simply for the joy of it, then there are many people here that can help make your life a lot more complex and interesting... but probably not more efficient.

It's your call...

Best,

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Old 08-13-14, 12:26 AM   #4
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I would guess that if your GSHP was properly installed, it is more efficient and will be far more reliable than your used mini-splits.
OK. The GSHP was professionally installed and I am happy that it works well.

If I am not going to get any tangible benefits from installing these units I will probably not bother. I have enough other projects going on without taking on even more stuff just for playing with!
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Old 08-13-14, 07:42 PM   #5
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How cold is it in the part of Finland you're in during the winter? Heat pump starts to become inefficient below around 5C as the coil needs to run below freezing point which means you'll expend energy to remove the ice through defrost cycle.

If you already have the loop for ground source, air sourced heat pump would be silly.
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Old 08-13-14, 10:25 PM   #6
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If there are enough "warm" days, using air source can conserve the ground thermal mass for the colder days. Or you can make a heat pump water heater, either if the geothermal doesn't have a desuperheater or if there are times when neither heating nor cooling is needed but hot water is.
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Old 08-14-14, 11:26 AM   #7
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ICanHas, it gets a lot colder than that here. The coldest I have known it at my home is -39C, but of course that was exceptional. It regularly goes below -20C though, and is usually below 5C for several months. This is why I thought the splits would only be of use for a short period at the start and end of the heating season, and it seems that is correct.
The GSHP is installed and has been running for a few years now, using pipe work buried under a field out the back. We installed double the amount of field loop we thought we would need so we could support a second heat pump if the first one was not enough (it was theoretically borderline) but it is fine most of the time. The splits are a new aquisition that came in a job lot of stuff I bought. They weren't the reason I bought that bunch of stuff, so I am trying to work out whether I should keep them or sell them on.

NiHaoMike, I like your thinking about using a heat pump to make a water heater, but I will pass on the idea. Solar panels plus lots of additional insulation on the hot water tank mean we use very little paid-for energy to provide hot water.

It seems clear that these units won't be much advantage to me, so I will try to move them on.

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